The present invention relates to dual curing silicone compositions which are capable of cross-linking when subjected to ultraviolet (xe2x80x9cUVxe2x80x9d) or visible (xe2x80x9cVISxe2x80x9d) light and/or by a moisture condensation method. When cured, these compositions have excellent adhesion to a variety of substrates. These are particularly useful in potting and coating applications.

The present invention relates to dual curing silicone compositions which are capable of cross-linking when subjected to radiation in the ultraviolet (xe2x80x9cUVxe2x80x9d) or visible (xe2x80x9cVISxe2x80x9d) regions of the electromagnetic spectrum, and/or by a moisture condensation method. When cured, these compositions have excellent adhesion to a variety of substrates. They are particularly useful in potting and coating applications.
Silicone rubber and liquid compositions exist in various forms and their characteristics may be modified to impart specific characteristics such as cure chemistry, viscosity, polymer type and purity. They can be formulated into one-part or two-part systems and a particular silicone composition can be engineered to be cured by more than one mechanism. Moisture-curing mechanisms, heat-curing mechanisms, and photoinitiated curing mechanisms are among those mechanisms used to initiate cure, i.e., cross-linking of reactive silicones. These mechanisms are based on either condensation reactions, whereby moisture hydrolyzes certain groups on the silicone backbone, or addition reactions which can be initiated by a form of energy, such as electromagnetic radiation or heat. For example, reactive polyorganosiloxanes can be cured by heat in the presence of a peroxide, or they can be cured by heat in the presence of a silicon hydride-containing (SiH) compound and a metallic hydrosilylation catalyst, such as an organo-platinum catalyst.
Typically, moisture curable materials are manufactured by endcapping xcex1,xcfx89-silanol terminated silicones with various crosslinkers such as alkoxysilanes, oximinosilanes, acetoxysilanes, aminosilanes, and other silanes with hydrolyzable groups attached to the silicon atom(s) thereof. The resulting silicone materials are stored in moisture impermeable containers.
During application to a respective substrate, the materials are extruded or otherwise applied and exposed to ambient conditions for curing. The moisture in the air then will hydrolyze the hydrolyzable groups (such as alkoxy, oximino, acetoxy, and amino) on the silicon atom(s) to form silanol, either with or without inclusion of a catalyst. The resulting silanol can then further react with remaining unhydrolyzed groups in a condensation reaction, to form a siloxane linkage resulting in the cure of the silicone material.
Although these materials when cured are very reliable and possess superior properties as coatings, the moisture cure tends to be slow. Cure times of 24 hours or more may often be needed before a full cure can be achieved. Such cure times limit through-put in the manufacture of coated components, since full cure of the coated components is needed before the components can be used in the next step of the manufacture process.
As a result, a third curing mode, ultraviolet light curing, has gained wide acceptance in recent years. The curing is relatively fast, with the cured elastomer showing good adhesion to the substrates. In situations where portions of the coated material are shaded during the UV cure, a secondary cure mode, usually moisture cure can be further incorporated.
Typically, UV cure of silicone compositions can be achieved by either a thiol-ene cure or by an acrylate cure. In the thiol-ene cure, a thiol functional silicone is reacted with a vinyl functional silicone. The cure is fast and the surface dry to the touch upon the completion of the cure. However, it has been reported that in commercial applications the cured product does not heat age well, and the uncured composition tends to lack long-term storage stability.
On the other hand, acrylate functional silicone is usually storage stable and the cured products exhibit excellent high temperature resistance. However, with an acrylate cure in the presence of atmospheric oxygen, the surface cure tends to be incomplete and the cured product often times tends to be tacky.
Dual-curing silicone compositions using UV light and moisture curing mechanisms are disclosed in U.S. Pat. No. 4,528,081 (Lien) and U.S. Pat. No. 4,699,802 (Nakos). These patents disclose compositions particularly useful for conformal coatings in electronic applications where the substrate has shadow areas which are not readily accessible to direct UV light and require moisture cure for cross-linking of those areas. Ordinarily, in addition to the photoinitiator present for radiation polymerization, a moisture curing catalyst such as an organotitanate or organotin is present. Without the moisture curing catalyst, moisture cure does not ordinarily take place with any degree of certainty or in any predictable time frame. Thus, as a practical matter, without the moisture curing catalyst, the moisture curing aspect of these compositions would not be practical for commercial use.
U.S. Pat. No. 4,587,173 (Eckberg) discloses dual curing silicone compositions using heat and UV light as separate cross-linking mechanisms. This patent discloses a reactive polyorganosiloxane which requires direct silicon-bonded hydrogen atoms and direct silicon-bonded alkenyl radicals on the same or different polysiloxane chains. These compositions also contain a photoinitiator and a precious metal/hydrosilation catalyst. The presence of the photoinitiator allows cross-linking of the silicon-bonded hydrogen atoms and silicon-bonded alkenyl radicals. These compositions are said to be able to cross-link at room temperature or at elevated temperatures by the precious metal catalysis of the silicon-bonded hydrogen atoms and silicon-bonded alkenyl radicals. Platinum is among the catalysts used for the thermal hydrosilation cure reaction. Moreover, this patent requires a peroxide, which can decompose over time even at room temperature and thereby limit shelf-life.
U.S. Pat. No. 4,603,168 (Sasaki) discloses a method of curing organopolysiloxane compositions, which requires the use of heat in combination with ultraviolet radiation. These compositions contain an organopolysiloxane having per molecule at least two alkenyl groups bonded directly to the silicone atom. Other organic groups may also be present, such as alkyl groups, halogenated alkyl groups, aryl groups, aralkyl groups, and alkaryl groups on the organopolysiloxane backbone. In addition, an organohydrogenpolysiloxane containing at least two organohydrogensiloxane or hydrogensiloxane units per molecule, a platinum catalyst, an addition-reaction retarder and a photoinitiator are also disclosed. The alkenyl groups must be bonded directly to the silicone atom without an organo group therebetween. Both the ""173 and ""168 patents are also limited to very thin coatings.
Dual-curing compositions employing UV- and moisture-cure mechanisms have a basic disadvantage in that once exposed to ambient moisture, they begin to cure. In many cases, this results in premature curing and shortened shelf life, as well as pot life in use. The advantage of the moisture cure mechanism is that it provides a means to cure shadow areas blocked from UV light. This is particularly important when high temperature curing is not an acceptable commercial option due, for instance, to the heat sensitivity of the substrate to which the reactive silicone is applied. For example, in conformal coatings where the substrate is an electronic circuit board, high temperature curing systems such as those which use peroxides, are not practical. Conventionally, moisture, UV, heat or combinations thereof have been employed as curing mechanisms for such applications.
More recently, as disclosed in the ""173 and ""68 patents discussed above, heat and UV curing mechanisms have been combined. While these patents disclose compositions which may be useful for heat sensitive substrates due to the combination of UV and low temperature heat cure, each requires a specific type of organopolysiloxane. In the ""173 patent, the polyorganosiloxane backbone contains both a hydrogen atom bonded to a silicon atom in the backbone, as well as an olefinic group bonded to a silicon atom. In the ""168 patent, the polyorganosiloxane contains an alkenyl group bonded directly to a silicone atom.
U.S. Pat. No. 5,179,134 (Chu) and U.S. Pat. No. 5,212,211 (Welch, II) describe acryloxy functional capped silicones. The silicones of the ""134 patent cure only through a photoinitiated mechanism, whereas the silicones of the ""211 patent cure through such a mechanism, as well as through a second mechanism, such as moisture or heat, by virtue of additional functional groups attached to the siloxane backbone.
U.S. Pat. No. 5,498,642 (Chu) discloses a dual curing silicone composition, which uses a vinyl dialkoxysilyl-terminated polydimethylsiloxane polymer to provide both UV and moisture curing. This polymer provides better surface skinning during UV exposure, largely due to the presence of the vinyl group, which serves to help eliminate tackiness. Further curing of the composition beneath the UV-formed skin occurs over time through a moisture curing mechanism.
U.S. Pat. No. 5,516,812 (Chu) also discloses a radiation and moisture-curable silicone composition. This composition also employs a silicone endcapped with vinyl functionality in combination with a second silicone fluid having radiation and moisture curable groups present. This composition is specifically designed for conformal coating compositions having improved surface tack.
Notwithstanding the state-of-the-art, it would be desirable to provide a dual UV-curable, moisture-curable silicone composition where cure of the composition by UV results in a coating that is dry to the touch without the common tacky surface often associated with an acrylate cure. It would also be desirable to provide such compositions having at least two different siloxanes, one of which has the ability to photocure and the other of which has the ability to both photocure and cure through exposure to moisture.
The present invention provides compositions which cure through a photo-initiated mechanism and a dual photo-initiated moisture-curing mechanism. That is, at least two different functionally-terminated polyorganosiloxanes are present in the inventive composition. In a particularly desirable aspect of the present invention, three of such different functionally terminated polyorganosiloxanes are present. These compositions are specifically designed to be curable by exposure to actinic radiation and/or moisture.
In one aspect, the invention provides a radiation and moisture-curable silicone composition that includes:
(A) a silicone fluid comprised of a monovalent ethylenically unsaturated functional group capped silicone capable of UV and moisture curing:
(B) a (meth)acryloxy-functional capped silicone fluid capable of UV curing, wherein the (meth)acryloxy-functional capped silicone fluid is formed as a reaction product of: (i) a silyl di(meth)acrylate compound of the formula:
wherein R1, R2, R3, R4, R5, R6, R7, R8, R9 and R10 are independently selected from the group consisting of hydrogen, halo, and organo radicals; and n is an integer having a value of from 1 to 4; and (ii) a silicone having at least one functionality which is reactive with a (meth)acryloxy functionality of said silyl di(meth)acrylate compound to yield said (meth)acryloxy-functional capped silicone;
(C) a photoinitiator effective for radiation curing of the silicone composition; and
(D) a moisture curing catalyst.
The capped silicone of (A) is the product of a reaction between a silanol-terminated silicone and a silane having a monovalent ethylenically unsaturated functional group and at least 2 hydrolyzable groups. The (meth)acryloxy-functional capped silicone of (B) is the product of a reaction between a silanol-terminated silicone and a silane having a (meth)acrylate and at least 2 hydrolyzable groups.
In the particularly desirable aspect noted above, the present invention provides compositions that include the silicones of (A) and (B), as well as a third silicone (E), which includes at least one (meth)acryloxydimethoxyalkyl-terminated polyorganosiloxane.
In another aspect, the present invention provides compositions that include:
(i) a first silicone which is capped with vinyl functionality and is the reaction product of a silanol-terminated silicone having at least 60 mole percent Sixe2x80x94OH terminated groups, and has a viscosity at room temperature of greater than 1,000 cps, desirably 1,500-10,000 cps, and a silane having at least one vinyl group and at least two hydrolyzable functional groups [such as the silane having a monovalent ethylenically unsaturated functional group and at least 2 hydrolyzable groups described for silicone (A)];
(ii) a second silicone fluid having radiation-curable (meth)acryl functional groups as described above; and
(iii) an effective amount of a photoinitiator.
These compositions may also include a moisture cure catalyst.
The inventive compositions are particularly advantageous when used in potting applications, or as coatings for electronic applications, particularly those which are temperature sensitive.
The present invention provides an improvement over known dual cure silicone compositions, which depend primarily on siloxanes having the UV and moisture cure capabilities on the same polyorganosiloxane for cure, by providing compositions that include separate polyorganosiloxanes, a first of which depends primarily on vinyl groups for photocure and moisture, and a second of which depends on both (meth)acrylate photocuring groups for photocure. By providing separate polyorganosiloxanes in this manner, the composition can be tailored for specific desired characteristics by balancing the proportions of one polyorganosiloxane with respect to the other polyorganosiloxane. The present invention allows for enhanced UV cure capability, particularly at the surface, in a relatively short time frame, as well as completeness of curexe2x80x94or cure through volumexe2x80x94by virtue of the moisture cure mechanism and/or the UV cure mechanism.
The inventive compositions once cured provide cured elastomers having improved adhesion to a variety of substrates and by-products which are non-corrosive.
Moreover, the present invention does not suffer from the limitation of being for use as thin coatings, as described by the ""173 and ""168 patents previously discussed, and either cure mechanism can be used to cure a range of thicknesses, for example, up to 50 mm or more. Certain of the benefits and advantages of the present invention are believed to be attributed to the specific combination of siloxanes and photoinitiators and moisture cure catalysts, which will become more readily apparent from a reading of the sections entitled xe2x80x9cDetailed Description of the Inventionxe2x80x9d and xe2x80x9cExamplesxe2x80x9d, which follow.
The ethylenically unsaturated functional group capped silicone (A) used in the inventive compositions is formed as the reaction product of a silanol terminated silicone and a silane having a monovalent ethylenically unsaturated functional group and at least two hydrolyzable groups. These silicones are disclosed in U.S. Pat. No. 5,498,642 (Chu), the disclosure of which is hereby expressly incorporated herein by reference.
The silanol terminated silicone used to make silicone (A) should include a linear polydiorganosiloxane having a viscosity as measured on a Brooksfield viscometer at ambient temperature (about 25xc2x0 C.) of more than 1,000 centipoise (xe2x80x9ccpsxe2x80x9d), desirably between 2,000 and 10,000 cps, such as between 2,000 and 5,000 cps.
This silicone is ordinarily a predominantly linear structure in character, having the silanol (xe2x80x94SiOH) functionality located at the terminus of a polysiloxy [xe2x80x94(SiO)xxe2x80x94] moiety in the silicone molecule.
The silane which reacts with the silanol capped silicone may be described with reference to the formula: RaSiXb, where each R is independently selected from monovalent ethylenically unsaturated radicals, hydrogen, C1-8 alkyl, C6-12 aryl, C7-18 arylalkyl, C7-18 alkylaryl, and X; X is a monovalent functionality imparting moisture curability to the reaction product of the silanol-functionalized silicone and silane crosslinker; a has a value of 1 or 2; b has a value of 2 or 3; and a+b=4, provided that when a is 1, R is a monovalent ethylenically unsaturated radical, and that when a is 2, at least one R is a monovalent ethylenically unsaturated radical.
Thus, R may be a monovalent ethylenically unsaturated radical for example, selected from the group consisting of vinyl, propenyl, butenyl, pentenyl, hexenyl, octenyl, allyl, alkenyloxy, alkenylamino, allyloxy, allylamino, furanyl, phenyl and benzyl groups. Examples include vinyltrimethoxysilane, vinyltriminosilane, vinyltriisopropenyloxysilane and vinyltriacetoxysilane.
The monovalent ethylenically unsaturated functional group capped silicone (A) may be present in amounts of about 5 to about 60% by weight, desirably in amounts of about 15 to about 40% and more desirably about 20 to about 35% by weight. This component provides UV surface curing and moisture curing throughout the thickness of the inventive composition.
The (meth)acryloxy-functional capped silicones (B) of the present invention are formed as a reaction product of a silanol terminated silicone and a silane having a (meth)acrylate and at least two hydrolyzable groups. These (meth)acryloxy-functional capped silicones are set forth in detail in U.S. Pat. No. 5,212,211 (Welch, II), the disclosure of which is hereby expressly incorporated herein by reference.
The acryloxy-functional capped silicone fluid (B) is formed as a reaction product of:
(i) a silyl di(meth)acrylate compound of the formula:
xe2x80x83wherein R1, R2, R3, R4, R5, R6, R7, R8, R9 and R10 are independently selected from the group consisting of hydrogen, halo, and organo radicals; and n is an integer having a value of from 1 to 4; and
(ii) a silicone having at least one functionality which is reactive with a (meth)acryloxy functionality of said silyl di(meth)acrylate compound to yield said (meth)acryloxy-functional capped silicone. This silicone reactive with the silyl di(meth)acrylate may impart a curing mechanism other than photocuring. Desirably, this silicone imparts moisture curing due to the presence of one or more of the following moieties which can undergo hydrolysis and which are selected from the group consisting of hydroxyl, enoloxy, amino, alkoxy, aryloxy, oxime, N,N-dialkylamino, N, N-dialkylaminoxy, N-alkylamido, Oxe2x80x94C(CH3)xe2x95x90CH2,xe2x80x94Sxe2x80x94C3H6Si(OCH3)3,xe2x80x94Oxe2x80x94NHxe2x80x94Cxe2x80x94(O)xe2x80x94H and combinations thereof.
The (meth)acryloxy-functional capped silicone (B) may be present in amounts of about 5 to about 90% by weight, desirably about 30 to about 70% and more desirably about 40 to about 60% by weight. This component provides UV curing throughout the thickness of the inventive composition.
The (meth)acryloxyalkyldialkoxy-terminated polyorganosiloxanes (E) that may be included in certain aspects of the present invention include at least one terminal alkoxy group, and desirably two reactive functional groups. Such a material is a product of the reaction of an organopolysiloxane, having at least one end (and desirably both ends) terminated with a silanol group, with a silane containing at least two (and desirably three) alkoxy groups. The number and type of functional group(s) present can be varied according to the desired properties of the final silicone composition. Due to the presence of these functional groups on (E) and the presence of silicones (A) and (B) referred to above, these compositions can be initially cured on a surface by exposure to actinic radiation through a photoinitiated mechanism to thicknesses considerably greater than compositions known heretofore, and more fully cured at ambient temperature in the presence of moisture.
For purposes of this invention, the term xe2x80x9cactinic radiationxe2x80x9d is meant to include particle or wave electromagnetic radiation and photochemical radiation.
The ability to cure tack free through a photo-induced mechanism through a variety of thicknesses, for example, from about 0.1 mm up to about 50 mm, allows for a variety of potting and/or coating applications heretofore not permitted by other potting compositions using UV curing mechanisms. For example, the ""178 patent either does not cure or only partially cures at thicknesses of 8 mm. (See Table 1, col. 10.) Moreover, the ""168 patent uses one gram per square meter of this composition as a coating, presumably due to the inability to or difficulties in cure at greater thicknesses. Thus, the advantages obtained by the specific functional groups on the polyorganosiloxane backbone of the present invention are readily apparent. In addition, as noted herein, the use of moisture cure catalysts, such as titanates, which do not absorb appreciable amounts of actinic radiation provide the ability to cure to greater thicknesses as the moisture cure catalyst used in the present invention does not compromise the ability of the composition to cure under exposure to such radiation.
The (meth)acryloxyalkyl-terminated polyorganosiloxane (E) desirably should be in accordance with formula I below:
wherein R1, R2, R3 and R4 may be the same or different and are monovalent hydrocarbon radicals having up to 10 carbon atoms (C1-10) or halo or cyano substituted hydrocarbon radicals; R3 may also be a monovalent heterohydrocarbon radical having up to 10 carbon atoms (C1-10) where the hereto atoms are selected from halo atoms, O, N, and S; R5 is alkyl (C1-10), such as methyl, ethyl or isopropyl; provided that at least one R3 or a terminal end is a (meth) acryloxyalkyl group; R5 may also include an ether linkage, such as CH2CH2OCH3; n is an integer; a is 0, 1 or 2; b is 0, 1 or 2; and a+b is 1 or 2.
The number of repeating units in the reactive polyorganosiloxanes can be varied to achieve specific molecular weights, viscosities and other chemical or physical properties. Generally n is an integer such that the viscosity is from about 25 cps to about 2,500,000 cps at 25xc2x0 C., such as when n is from 1 to 1,200 and desirably from 10 to 1,000.
Component (E) may be present in amounts sufficient to provide enhanced UV and moisture curing capability. Desirably (E) is included in amounts of about 5 to about 70% by weight and more desirably about 5 to 25% by weight.
A particularly desirable silicone fluid for (E) has the following formula II where R3 on formula I is a methacrylate-propyl group, CH2C(CH3)xe2x80x94COOC3H6, R4 and R5 on formula I are methyl, and R1 and R2 are as described in formula I above to give:
where MA is the methacryloxypropyl group, n is from 1 to 1,200, a is 1 and c is 0 or 1.
The functional terminated polyorganosiloxanes of the present invention may be present in combined amounts of about 5 to about 95%, such as about 30 to about 70% by weight, desirably about 40 to about 60% by weight.
Due to the presence of both alkoxy and vinyl groups, and desirably alkoxy, vinyl and acrylate groups, these compositions are capable of curing by both moisture and photo curing mechanisms. Thus, for example, the inventive compositions can be subjected to UV light in the presence of a photoinitiator to partially cure or gel the material, which can then be allowed to cure further by moisture in ambient conditions.
The number of repeating units in the polyorganosiloxanes can be varied to achieve specific molecular weights, viscosities and other chemical or physical properties. Generally, n is an integer such that the viscosity is from about 25 cps to about 2,500,000 cps at 25xc2x0 C., such as when n is from 1 to 1,200 and desirably from 10 to 1,000.
The photoinitiators useful in the present invention may be selected from any known free radical type photoinitiator effective for promoting crosslinking reactions. For example, suitable photoinitiators include UV initiators such as benzophenone and substituted benzophenones, acetophenone and substituted acetophenones, benzoin and its alkylesters, xanthone and substituted xanthones. Desirable photoinitiators include diethoxyacetophenone (DEAP), benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, diethoxyxanthone, chloro-thioxanthone, azo-bisisobutyronitrile, N-methyl diethanolaminebenzophenone, and combinations thereof.
Visible light photoinitiators include camphoquinone peroxyester initiators, non-fluorene carboxylic acid peroxyester initiators and alkyl thioxanthones, such as isopropyl thioxanthone.
While the photoinitiator may be present in any effective amount, desirable ranges include about 1 to about 10% by weight, such as about 2 to about 6% by weight. A particularly desirable photoinitiator is DEAP.
The compositions also include moisture curing catalysts to enhance the rate at which the hydrolyzable groups on the polyorganosiloxane react with moisture to cure. Such hydrolyzable groups include amino, oxime, acetoxy, alkoxy, aryloxy, alkaryloxy, aryalkoxy and the like. Where the hydrolyzable groups are amino, oxime or acetoxy, however, moisture cure may occur fast enough such that a moisture catalyst may not be necessary.
The moisture curing catalysts include organo-metal catalysts including titanates such as tetraisopropylorthotitanate and tetrabutoxyorthotitanate, as w ell a s metal carboxylates such as dibutyltin dilaurate, dibutyltin dioctoate and the like.
The moisture cure catalyst should be used in an amount sufficient to effectuate moisture cure, which desirably is in the range of about 0.1 to about 5% by weight.
Useful UV radiation sources include conventional mercury-vapor lamps designed to emit ultraviolet energy in various ultraviolet wavelength bands. For example, useful radiation wavelength ranges include 220 to 400 nm.
It should be understood that while the photoinitiator is generally used as a separate component, the formulations used in the inventive composition are intended to include those in which photoinitiating groups are included in the backbone of the same organopolysiloxane polymer which includes the photocuring groups.
The inventive compositions may also contain other additives so long as they do not interfere with the curing mechanisms. For example, conventional additives such as fillers, adhesion promoters, pigments, moisture scavengers, inhibitors and the like may be included.
Fillers such as fumed silica or quartz are contemplated , as are moisture scavengers such as methyltrimethoxysilane and vinyl trimethoxysilane. Fillers may be present in amounts up to about 30% by weight, such as about 4 to about 20% by weight.
Inhibitors may be present up to about 10% by weight, desirably about 0.5 to about 1% by weight. The particular amount of inhibitor should be balanced in a given composition to produce or improve stability of the composition.
Adhesion promoters may be present in amounts of up to about 5%, such as about 2% by weight.
UV cure is generally effected in the range of 40 milliwatts/cm2 (xe2x80x9cmW/cm2xe2x80x9d) to about 300 mW/cm2, such as in the range of about 70 mW/cm2 to about 150 mW/cm2.
As an alternative aspect of the invention, heat curing may be used to cure the compositions, provided a heat cure catalyst, such as platinum, is used, and at least one of the polyorganosiloxanes includes a hydride terminal group available for condensation with the ethyleneically unsaturated group on another of the polyorganosiloxanes. For example, room temperature cure is contemplated, as well as temperatures up to about 150xc2x0 C., such as in the range of from about 65xc2x0 C. to about 125xc2x0 C. and desirably in the range of from about 85xc2x0 C. to about 100xc2x0 C. Although heat curing can be effected at higher temperatures than these given, the recited temperatures allow for use of the compositions in applications, such as potting applications and coatings for electronic applications, which are temperature sensitive.
The compositions of the present invention may be prepared by mixing together the respective components to obtain a substantially homogenous or uniformly blended material and stored in containers which are non-transmissive to UV light and moisture. Generally, a single package system is employed, but two-part package systems may be used if desired. Whereas single package products are ready-for-use upon being dispersed, two-part systems require mixing of the dispersed parts prior to use.
The inventive compositions may be used as noted above in potting applications and coatings for a variety of substrates including electronic parts and other heat-sensitive materials.


An improved side saddle riding skirt is disclosed. The improved side saddle riding skirt includes a knee loop coupled to a knee dart of the skirt, and a strap coupled to the hem of the skirt. This strap is removably coupled through the knee loop to prevent the skirt from flying up. The side saddle riding habit further includes mechanisms for adjusting the skirt to a range of different sizes.

The present invention is related to side saddle riding habits. More particularly, the present invention relates to a side saddle riding apron which is flexible and convenient for modem riders and can be adjusted for use by riders of a number of different sizes.
Although women have been riding side saddle for centuries, clothing appropriate for use with the side saddle has always been problematic. Riding habits for side saddle riding must be capable of preventing a long skirt from flying up as the horse is in motion, while allowing the rider sufficient flexibility to control the horse and to dismount quickly in the event of an accident. To meet these needs, a number of different types of riding habits have been developed over the years.
One type of riding habit is disclosed in U.S. Pat. No. 445,203 to Rossberg. Rossberg discloses a riding habit that includes two flaps that button around the right leg and two elastic stirrups, one for each foot. The flaps maintain the skirt against the right leg, while the stirrups provide support for the feet while riding. Other prior art riding habits include various means for maintaining the skirt in proper order while seated on the horse. For example, in some cases buttons are sewn on internal breeches which can be buttoned to the inner facing of the skirt. In other cases, straps including button holes can fasten the edge of the skirt to internal buttons. In one particular case, for example, a Y-shaped elastic piece was used to fastened to the knee dart in the skirt to internal buttons located at the hem of the skirt. This configuration prevented the skirt from xe2x80x9criding upxe2x80x9d. In more recent times, many skirts have been fitted with a long elastic strap that was wound through a buttonhole in the edge of the skirt, and then around the leg and foot of the rider.
While all of these prior art devices serve their intended purpose, to prevent the skirt from riding up or flying open while riding the horse, they suffer from a number of disadvantages. Internal buttons, for example, can be difficult to fasten and unfasten. Therefore, a significant amount of time and effort is required in preparing to mount the horse, and in reconfiguring the habit once the ride is over. Furthermore, because the rider""s leg is closely fastened to an often heavy, inflexible outer skirt, it can be difficult for the rider to maneuver appropriately in the event of a fall or accident, or even to dismount. Similarly, an elastic band wound around a leg can be difficult to remove and can even become entangled in the saddle, in the reins, or with other pieces of the rider""s clothing. Often, the devices used to secure the skirt can be torn off or easily ripped from the clothing. Additionally, because of the need to provide straps, stirrups and other fastening devices in the skirt, the skirt must often be sized very specifically to the individual. Therefore, prior art devices must generally be custom-made or produced in a large number of sizes to fit a variety of riders. Furthermore, although riding side saddle is increasingly popular both in historic reenactments and for general riding, women today are less inclined to submit to restrictive and complicated clothing than in the past.
Therefore, there remains a need for a side saddle riding habit which allows the rider to ride side saddle in comfort. The riding skirt would preferably be easy to put on and take off. The riding skirt would also be flexible, to allow the rider to respond appropriately in the event of an accident, and to dismount easily. The skirt would be sturdy in construction, and would not tear easily. Preferably, the skirt would easily adjust to walking after the horse has been dismounted. The skirt would preferably also be adjustable, and therefore easily fitted to riders in a variety of size categories.
The present invention is a side saddle riding apron constructed, in part, to provide increased flexibility and freedom of movement for the rider. A loop of material (the xe2x80x9cknee loopxe2x80x9d) is coupled to or near a knee dart on the inside of the skirt. A strap coupled to an end of the skirt section of the apron can be removably attached around the leg of the rider and through the knee loop to retain the flap of the skirt against the right leg of the rider while riding, thereby preventing the skirt from xe2x80x9cflying up.xe2x80x9d Because the leg is inhibited only by a small flexible strap, rather than buttoned to the side of the skirt or to internal breeches, the rider can move relatively freely during the ride. When the rider dismounts, the strap can be looped through a belt of the skirt, so that the rider can also walk comfortably. The knee loop and strap are preferably constructed of elastic, rubber, or other stretchable materials, thereby maximizing flexibility of movement. However, the loop and strap can also be constructed of cloth materials, string, rope, or other suitable substitutes.
In another aspect of the invention, the riding apron can be adjusted to fit riders in a variety of size categories. The knee dart described above, for example, can be varied in length, and the knee loop repositioned as appropriate to fit the height of the rider.
The riding apron can also include one or more size adjusters, such as belt buckles or slide fasteners, to adjust the waist of the skirt to fit riders of different sizes. One or more size adjusters are preferably located in the sides of the skirt, where they cannot be easily seen, and where they do not interfere with xe2x80x9ccenteringxe2x80x9d the long skirt section on the rider. If multiple size adjusters are used, they are preferably located at diametrically opposed positions on the skirt waist band to assure that the adjustment can be achieved without offsetting the center of the skirt. In one embodiment of the invention, for example, the first size adjuster is a belt buckle located on the right side of the skirt, and the second size adjuster is a slide fastener at the left side of the skirt. Although belt buckles and slide fasteners have been described, it will be apparent that the size adjusters can also be hook and loop fasteners, hook and eye fasteners, snaps, buttons, or other known types of fasteners.
To further adjust the size, the skirt can also include a fold-over section of material. The fold-over section can be folded under to reduce the waist of the skirt, or folded out to increase the waist of the skirt. The combination of the fold-over section and the size adjusters allows the waist of the skirt to be adjusted to a number of different sizes.


Pumpable multiple phase compositions for carrying agents and components downhole and controllably releasing them by breaking the suspensions are described. The multiple phase composition may have an external or third phase, which in turn has a first pumpable emulsion internally. The first pumpable emulsion has a second phase containing a first phase which bears the agent to be controllably released. The entire pumpable multiple phase composition may thus be an oil phase-in-aqueous phase-in-oil phase emulsion, or an aqueous phase-in-oil phase-in-aqueous phase emulsion. The agent may be released by one or more of a variety of mechanisms. For example, a water-soluble shale stabilizer could be delivered downhole in an aqueous phase-in-oil phase-in-aqueous phase multiple phase emulsion by injecting the multiple phase composition into a water-based drilling fluid, and then the suspension broken by rotary bit nozzles under high shear stress to release the shale stabilizer at the drilling zone. The multiple phase emulsion compositions of this invention may also be used to deliver agents to remote locations along a conduit.

The present invention relates to methods and compositions for the controlled release of agents and components downhole in an oil recovery operation, and more particularly relates, in one embodiment, to emulsions for the controlled release of agents and components downhole.
Drilling fluids used in the drilling of subterranean oil and gas wells as well as other drilling fluid applications and drilling procedures are known. In rotary drilling there are a variety of functions and characteristics that are expected of drilling fluids, also known as drilling muds, or simply xe2x80x9cmudsxe2x80x9d. The drilling fluid is expected to carry cuttings up from beneath the bit, transport them up the annulus, and allow their separation at the surface while at the same time the rotary bit is cooled and cleaned. A drilling mud is also intended to reduce friction between the drill string and the sides of the hole while maintaining the stability of uncased sections of the borehole. The drilling fluid is formulated to prevent unwanted influxes of formation fluids from permeable rocks penetrated and also often to form a thin, low permeability filter cake which temporarily seals pores, other openings and formations penetrated by the bit. The drilling fluid may also be used to collect and interpret information available from drill cuttings, cores and electrical logs. It will be appreciated that within the scope of the claimed invention herein, the term xe2x80x9cdrilling fluidxe2x80x9d also encompasses xe2x80x9cdrill-in fluidsxe2x80x9d.
Drilling fluids are typically classified according to their base material. In water-based muds, solid particles are suspended in water or brine. Oil can be emulsified in the water. Nonetheless, the water is the continuous phase. Oil-based muds are the opposite. Solid particles are suspended in oil and water or brine is emulsified in the oil and therefore the oil is the continuous phase. Oil-based muds which are water-in-oil emulsions are also called invert emulsions.
It is apparent to those selecting or using a drilling fluid for oil and/or gas exploration that an essential component of a selected fluid is that it be properly balanced to achieve the necessary characteristics for the specific end application. Because the drilling fluids are called upon to do a number of tasks simultaneously, this desirable balance is not always easy to achieve.
It would be desirable if compositions and methods could be devised to aid and improve the ability of drilling fluids to accomplish these tasks by delivering agents and components downhole, which could be released controllably to accomplish one or more jobs.
Accordingly, it is an object of the present invention to provide a method and composition for delivering an agent downhole in a hydrocarbon recovery operation, particularly during a drilling and/or completion operation.
It is another object of the present invention to provide a method and composition for delivering an agent downhole where the agent is released at a controlled time and place.
In carrying out these and other objects of the invention, there is provided, in one form, a pumpable multiple phase composition, also called a multiple phase emulsion drilling or completion fluid, for carrying an agent having a first phase, a second phase, and a third phase. The first phase is suspended in the second phase to form a first pumpable emulsion, and next the first pumpable emulsion is dispersed in the third phase to form the final pumpable multiple phase composition. The pumpable multiple phase composition may be an oil phase-in-aqueous phase-in-oil phase emulsion, or an aqueous phase-in-oil phase-in-aqueous phase emulsion. The agent is present in the first phase.
Additionally, there is provided in one form, a method for releasing an agent downhole beginning by forming a first pumpable emulsion for carrying an agent. The first pumpable emulsion has a first phase containing the agent, and a second phase. The first phase is suspended in the second phase to form a first pumpable emulsion. The first pumpable emulsion may be an oil phase-in-aqueous phase emulsion, or an aqueous phase-in-oil phase emulsion, where the agent is present in the first phase or is the first phase. Next, the first pumpable emulsion is injected into a fluid which may be either a drilling fluid or a completion fluid, such that the external phase of the drilling or completion fluid is immiscible with the second phase of the first pumpable emulsion thereby forming a pumpable multiple phase composition (multiple emulsion). Finally, the pumpable multiple phase composition is broken downhole to release the agent. The pumpable multiple phase composition may be broken by shear, for example, by pumping through drill bit nozzles.
Pumpable multiple phase compositions (emulsions) are anticipated as being useful to organize a liquid phase to isolate one miscible phase from another. An oil-in-water emulsion could be used in an invert emulsion, hydrocarbon-based or ester-based or other water immiscible, non-aqueous-based system (forming an oil-in-water-in-oil system), while a water-in-oil emulsion could be used in an aqueous system (forming a water-in-oil-in-water system). In short, the multiple emulsion compositions of this invention and methods for their use may be applied to any two immiscible phases that form stable emulsions. The phases need not be xe2x80x9coilxe2x80x9d and xe2x80x9cwaterxe2x80x9d, although such phases are likely to be the most common implementation. One non-limiting example is the combination of a water soluble, relatively high molecular weight glycol that forms an emulsion with brine.
One important application of this kind of organization would be the controlled release of the internal phase contents, such as an agent within the innermost (first) phase. A non-limiting example of such an application would be the emulsion of, for instance, a polyglycol, potassium salt, aluminum salt, calcium salt, a silicate salt, chelate or other shale stabilizer, or an aqueous solution thereof, as a first, internal phase in a hydrocarbon or hydrophobic carrier (second phase) optionally containing an emulsifier and/or stabilizer, and then adding the emulsion to a water-based drilling fluid. The polyglycol, potassium salt, aluminum salt, etc. or other shale stabilizer, alone if liquid, or in solution, e.g., is isolated from the water in the external phase of a water-based drilling fluid. Dilution is prevented, suppressed, or delayed until the emulsion is broken intentionally. A likely area for breakage of the emulsion is the high shear environment of and below the drilling bit, where the shale stabilizer is released to the borehole and cuttings in concentrated form on a localized basis. While the invention does not contemplate, as a preferred embodiment, making the multiple emulsion so stable that it is not broken in a drilling fluid or completion fluid application, such stable multiple emulsions are anticipated and may find utility.
Of course, emulsifiers, viscosifiers, or other structural stabilizers may also be added to increase the mechanical stability of the first pumpable emulsion in some cases to delay release of the contents (agent).
In more detail, the agent to be delivered as the contents of the internal phase or the first phase, may be any conventional agent, including, but not necessarily limited to, a shale stabilizer, as noted above, a filtration control additive, viscosifier, suspending agent, dispersant, thinner, an anti-balling additive, a lubricant (particularly in the oil-in-water-in-oil multiple phase compositions), a wetting agent, a seepage control additive, a lost circulation additive, drilling enhancer, penetration rate enhancer, corrosion inhibitor, acid, base, buffer, scavenger, gelling agent, cross-linker, catalyst, and the like, and mixtures thereof. Specific useful shale stabilizers include, but are not necessarily limited to, polyglycols, potassium salts, aluminum salts, calcium salts, silicate salts, chelates, amines, alkanolamines, alkanolamides, amphoteric compounds, alone if liquid or in aqueous solutions, and mixtures thereof. Some other specific agents include, but are not limited to amines (failing quartz bonds in certain sands, corrosion inhibitors in clay based systems, shale stabilizers) and metal halides, e.g. aluminum and thorium halides. The term xe2x80x9cacidsxe2x80x9d in this context includes organic acids and inorganic acids. Such acids can be used to treat cement contamination. If appropriate or desirable, the agent may be in aqueous or hydrocarbon solution.
This first or internal phase should match that of the ultimate fluid in which the first pumpable emulsion is to be injected or added. That is, if the first pumpable emulsion is to be injected into an aqueous fluid, the first, internal phase should be aqueous; if the fluid is hydrophobic, the first, internal phase should be hydrophobic.
Of course, the second phase, which together with the first or internal phase forms the first pumpable emulsion, should be of the opposite type. It may be necessary or desirable to add emulsifiers, viscosifiers, stabilizers, and mixtures thereof as structural stabilizers to increase the mechanical stability of this first emulsion to aid in delaying release or breaking. In the context of this invention, emulsifiers should be understood to include, but are not limited to, surfactants and the like, and viscosifiers are understood to include, but are not limited to, gelling agents and the like. The emulsifiers and viscosifiers may be in liquid or solid (e.g. powder) form. Suitable emulsifiers include, but are not necessarily limited to, sorbitan fatty acid esters including sorbitan monooleate and sorbitan trioleate, glycerol fatty acid esters including mono- and/or dioleates, polyglycerol fatty acid esters, polyglycols, alkanolamines and alkanolamides such as ethoxylated amines, ethoxylated amides, ethoxylated alkanolamides, including non-ethoxylated ethanolamides and diethanolamides, and the like. Viscosifiers and gelling agents include, but are not necessarily limited to, polymers of ethylene, propylene, butylene, butadiene, styrene, vinyltoluene and various copolymers and terpolymers thereof, organophilic clays, aluminum soaps and alkoxides and other aluminum salts, alkaline earth soaps, lithium soaps, fumed silica and alumina and the like and mixtures thereof. Other suitable stabilizers include, but are not necessarily limited to, cholesterol and long chain oil soluble waxy alcohols, and the like. These structural stabilizers would usually be added directly to the second phase although they may be added to the third phase, if that is more convenient. In one non-limiting embodiment of the invention, the proportion of structural stabilizer based on the second phase ranges from about 0.1 to about 90 vol. %, preferably from about 1 to about 50 vol. %.
However, the pumpable multiple phase compositions of the invention (emulsions) are designed to be broken in a preferred embodiment. Indeed, they are desirably and rather controllably broken within a certain area of the borehole at a designated and relatively controlled time.
The preparation of the first pumpable emulsion would typically involve the mixing of the first phase with the second phase, where any emulsifier or structural stabilizer is preferably present in the second phase. The speed of stirring or mixing of the two phases would depend upon the size of the emulsified internal phase droplets desired, and the particular system used. It is expected that the size of the first phase droplets would range from about 0.01 to about 1000 microns or less, preferably from about 1 to about 100 microns or less, as non-limiting examples. In one embodiment of the invention, the first phase droplets would be as large as is practical. The proportion of first, internal phase to the overall first pumpable composition may range from about 90 to about 5 vol. % or less, preferably from about 60 to about 40 vol. % or less, and most preferably, 50 vol. % or less, as non-limiting examples. A lower threshold of 5 vol. % may be appropriate in some embodiments of the invention.
The formation of the first pumpable emulsion could be accomplished within an injection pump itself. This technique would be similar to in-line mixing the first, internal phase xe2x80x9con the flyxe2x80x9d with the second phase forming the first emulsion before it exits into the third phase finally forming the multiple emulsion in the mud system.
The first pumpable emulsion is then, in turn, suspended in the drilling and/or completion fluid which is the third phase. This third phase is generally to be miscible with the first phase and may contain an emulsifier to help disperse the first pumpable emulsion into suitable sized droplets. Conventional drilling and/or completion fluids may be used as the third phase. If the third phase is oil-based or a hydrocarbon, in a preferred embodiment, the hydrocarbon is a synthetic material, and, for instance, may include, but is not necessarily limited to, esters, iso-olefins, alpha-olefins, polyolefins, poly-alpha-olefins, paraffins, Fischer-Tropsch reaction products, and the like. The oil phase may be a mixture or blend of petroleum distillates and synthetic hydrocarbons. Suitable petroleum distillates include, but are not limited to, diesel oil, kerosene, mineral oils, food grade mineral oils, paraffinic oils, cycloparaffinic oils, aromatic oils, or n-paraffins, isoparaffins and similar hydrocarbons. Crude oil could be used in some cases. In the case where the second phase is an oil-based phase, it is anticipated that any of these hydrocarbons may be used.
In the case where the multiple phase composition is water-in-oil-in-water multiple emulsion, the aqueous phase may be brine. Careful adjustment of the internal phase salinity of brine multiple emulsions may be required (osmotic pressure gradient adjustment). Too much salt or too low an activity in a first aqueous phase may make the droplets unstable. However, this mechanism may be intentionally used to cause failure or rupture of the first pumpable emulsion droplets or capsules downhole. For example, the droplets could be designed to grow on the journey downhole and break at or near the desired zone.
It is expected that the size of the droplets of the first pumpable emulsion (first phase in second phase) in the third phase would range from about 10,000 to about 1 micron or less, preferably from about 5 to about 1,000 microns or less, as non-limiting examples. In one embodiment of the invention, the pumpable emulsion droplets would be as large as possible. The larger the first phase droplets in the first emulsion droplets, all things being equal, the easier it would be to break the multiple phase composition to release the agent from the first emulsion.
The proportion of the first pumpable emulsion to drilling and/or completion fluid (third phase) may range from about 0.5 to about 90 vol. %, alternatively from about 0.5 to about 40 vol. %, preferably from about 1 to about 10 vol. %, in another embodiment from about 1 to about 5 vol. %, and most preferably from about 2 to about 6 vol. %, as non-limiting examples, to make the overall pumpable multiple phase composition.
Conventional drilling and/or completion fluid additives may, of course, be employed, including, but not necessarily limited to, wetting agents, viscosifiers, suspending agents, weighting agents, shale stabilizers, filtration control additives, anti-balling additives, lubricants, seepage control additives, lost circulation additives, corrosion inhibitors, alkalinity control additives, thinners, dispersants, and the like. Indeed, the agents to be delivered by the multiple emulsion compositions and methods herein may also be present in the third phase.
The method of this invention may find particular usefulness in increasing the local concentration of an agent downhole after rupture of the first pumpable emulsion droplets while keeping the overall concentration of the agent in the drilling mud (including the entire multiple phase composition) low. For example, styrene-butadiene rubber (SBR), useful as a viscosifier and/or filtration control additive, could be the agent in the first phase of the first pumpable emulsion and be in relatively low concentrations overall. However, once the first pumpable emulsion droplets are broken or failed, the local concentration of SBR at the droplet failure zone would be relatively increased.
Using the pumpable emulsion composition of the invention is straightforward and requires no special equipment. The first pumpable emulsion is injected into a fluid that is pumped downhole. The fluid may be a drilling fluid, drill-in fluid, a completion fluid, or the like. In a preferred embodiment of the invention, the fluid is a drilling fluid or drill-in fluid. A number of mechanisms could be used to break the pumpable multiple phase composition at a particular time, including, but not limited to, input of energy, including but not limited to, an increase in temperature, increase in pressure, increase in shear stress or shear rate, mechanical action (such as a rotating drill bit or drill string), change in pH, change in electrical potential, solvent thinning, presence of a chemical agent, presence of a catalyst, change in magnetic flux, and the like. A non-limiting, but preferred method is breaking the multiple phase composition by subjecting it to a high shear environment, in particular the fluid stream exiting a nozzle impinging on the borehole such as below a bit or opposite a reamer or hole opener. In a preferred method of the invention, the multiple phase emulsion is broken within a required period of time, and within a required physical volume. In one embodiment, if the agent being delivered was a shale stabilizer, the shale stabilizer could be delivered essentially instantaneously to the borehole and cuttings in a concentrated form on a localized basis.
It will also be understood that more than one agent may be delivered downhole, and that the two or more agents may interact or react with each other to provide a beneficial effect. For example, crosslinkers could be transported in first water-in-oil emulsion in the same aqueous third phase as a second water-in-oil emulsion containing the agent to be cross-linked. Alternatively, two separate internal phases which react on contact could be delivered in the same first emulsion added to the third phase such as an aqueous cross-linker and aqueous polymer solution could both be transported in the same first emulsion and added to a water-based mud. Indeed, one reactant could be present in the third phase and another reactant could be present in the first phase and the reaction could occur when the boundary of the second phase (first pumpable emulsion) is broken.
The agent may also be a polymer serving any of the stated functions, or a monomer to be polymerized or in the course of being polymerized to such a polymer.
Further, the multiple phase compositions of this invention are not limited to utility in downhole applications, but could be used to deliver and transport agents along a pipeline or other conduit, such as agents to prevent blockages (e.g. asphaltenes, hydrates, etc.) in a subsea pipeline or the like, or other agents. Any of the agents previously mentioned may be used in this way, and suitable agents may additionally include, but are not limited to, hydrate inhibitors, asphaltene inhibitors, scale inhibitors, etc.

Pumpable multiple phase compositions for controlled release applications downhole


A method for treating an underground reservoir, which method comprises introducing into the reservoir a treatment fluid comprising, dissolved or dispersed in water, an ester and a polymer breaker, such that the ester hydrolyses to produce an organic acid to dissolve acid soluble material present within the reservoir and the polymer breaker degrades polymeric material present within the reservoir.

The method of the present invention is generally applicable to the production of oil, gas or water from wells drilled into underground reservoirs.
During drilling, workover and production operations there are numerous situations where the production rate of an oil, gas or water well following these operations is limited due to the presence of formation damage. Types of damage include, but are not limited to, the presence of polymer-containing filter cakes, fluids (including hydraulic fracturing fluids) filtrates or residues including polysaccharide-containing filter cakes, fluids, filtrates or residues, particulate materials such as fluid loss control agents and rock fines, biofilms, scales and asphaltenes.
Damage can be near wellbore, for example the presence of filter cake, or damage may be present deeper into the formation, for example in natural or induced fractures or in the rock matrix.
The effective removal of damage, especially near wellbore damage such as filter cake, can significantly increase the production rate of hydrocarbon or water producing wells penetrating underground formations. The effective removal of damage can also increase the injectivity of injection wells.
Conventional acids have been used for many years to treat damage in underground formations and stimulate the rate of oil or gas production. However, conventional acids have several drawbacks. They react rapidly with acid soluble materials which can result in poor zonal coverage and they are hazardous in use. To improve zonal coverage the use of high pressure, high rate injection is often attempted, which increases the hazards associated with their use. Due to the high corrosivity of conventional acids the use of corrosion inhibitors is also generally required. There is a greater need for corrosion inhibitors in higher temperature formations and corrosion inhibitors are generally toxic.
Damage is often caused by a combination of several components. For example, certain drilling muds or drill-in fluids contain calcium carbonate or dolomite in combination with a polymer or polymers which provides suitable rheological properties. Both the carbonate and the polymer contribute to the formation of a filter cake. Carbonate fines generated during drilling of carbonate rocks may also be present in the filter cakes.
Filter cakes generally contain high densities of polysaccharide. U.S. Pat. No. 5,247,995 cites SPE Paper 21497 which states that they can contain up to about 48% polysaccharide versus about 4% in fracturing fluids.
Filter cakes which do not contain carbonate may be susceptible to treatment with acid if they are present on wellbore surfaces in carbonate formations, as acid may attack the underlying carbonate and cause disruption of the filter cake.
It is an object of the present invention to provide a simple and effective method for treating formation damage within an underground reservoir.
It is a particular object of the present invention to provide simple and effective methods for the effective removal of filter cakes over long horizontal intervals.
Another object of the present invention is to provide single stage treatment methods which can remove damage and provide further stimulation of production or injection rate by increasing the matrix permeability of adjacent undamaged regions of the formation.
It is a further object of the present invention to provide methods which are environmentally acceptable by utilising components which are of low environmental impact.
Accordingly, the present invention provides a method for treating an underground reservoir, which method comprises introducing into the reservoir a treatment fluid comprising, dissolved or dispersed in water, an ester and a polymer breaker, such that the ester hydrolyses to produce an organic acid to dissolve acid soluble material present within the reservoir and the polymer breaker degrades polymeric material present within the reservoir.
The reservoir may be a hydrocarbon, such as gas or oil, reservoir. Alternatively the reservoir may be a water reservoir.
Sufficient ester or esters is present in the treatment fluid to produce sufficient acid, when the ester is hydrolysed, to have a substantive effect on filter cakes or other types of damage. By substantive effect it is meant that sufficient acid is produced on the hydrolysis of the ester to give sufficient dissolution of acid soluble material, present in or adjacent to the filter cake or other damage, to assist in the removal of damage. For example the dissolution of carbonate present in a filter cake, the dissolution of carbonate rock adjacent to a filter cake or the dissolution of carbonate rock adjacent to a biofilm. To obtain sufficient dissolution, it is necessary that a minimum of several percent w/v of acid is produced. The concentration of ester incorporated into the treatment fluid of the present invention will typically be at least 1% w/v but may be up to 20% w/v or higher. In general it has been found that 5% to 10% w/v ester when used in combination with a suitable polymer breaker or breakers is sufficient to give good removal of damage caused by filter cake. Preferably 5% to 20% ester will be used.
It is also intended that sufficient polymer breaker is present in the treatment fluid to have a substantive effect on the polymeric material present. The concentration of polymer breaker incorporated into the treatment fluid will vary according to the type of breaker employed but will be of the order of 0.005 to 60 kg/m3, preferably 0.2 to 10 kg/m3.
In general it is desirable to use a concentration of breaker which results in the breaking of the polymer over a period of several hours to allow the effective placement of the fluid. For example, too rapid a degradation of a filter cakes or biofilm may lead to localised fluid leak off, adversely affecting placement of the treatment fluid. This is analogous to the situation experienced in treatments using conventional acids, where the fast reaction rate can result in rapid breakthrough and wormholing and uneven fluid leak off. This can prevent the even placement of fluid over long horizontal intervals or into fractures or the rock matrix. It is a feature of the treatment fluids of the present invention that use of an ester rather than a reactive acid avoids wormholing and improves the placement of the fluid. In order to maintain this advantage in certain applications such as the treatment of long horizontal intervals, too rapid a degradation of polymers in for example filter cakes or biofilms should in general be avoided. Ideally, breakthrough of filter cakes or biofilms will be achieved after a period longer than that amount of time needed to place the treatment fluid. A delay in producing a substantive amount of acid and in breaking polymer allows even treatment of the target zone and excellent zonal coverage.
Use of an ester gives the advantages of effective placement of the fluid and avoidance of the use of corrosion inhibitors. Where suitable esters are selected, in particular where low toxicity, high flash point esters are used, there are also health and safety and environmental advantages. The initially neutral or slightly acidic pH of the fluid permits the incorporation of polymer breakers such as enzymes and oxidative breakers into the fluid without the compatibility problems encountered when such breakers are incorporated into highly acidic formulations based on mineral or organic acids.
It is preferable to use polymer breakers which are activated by, or whose activity is enhanced by, the change in conditions as the ester hydrolyses to produce acid. For example, peroxides which are activated by the development of acidic conditions or enzymes which have their activity enhanced by the development of acidic conditions.
An example of the former is the decomposition of calcium peroxide . This decomposes under acidic conditions to generate hydrogen peroxide.
Enzymes useful as polysaccharide breakers generally have a pH optimum in the range ph 3 to ph 7. Such enzymes will therefore have their activity enhanced by the generation of the moderately acidic conditions arising from hydrolysis of an ester. The generation of acidic conditions by the hydrolysis of esters in the presence of acid soluble material such as calcium or magnesium carbonates results in the formation of a self-regenerating buffer. For example, the production of acetic acid will produce an acetic acid-acetate buffer or production of formic acid a formic acid-formate buffer. If the produced acid reacts with acid soluble material it is replenished by more acid produced from the hydrolysis of remaining ester precursor ensuring maintenance of the buffer. This can provide ideal conditions for polysaccharide degrading enzymes causing less of the enzyme or enzymes to be needed to give the same degree of polymer breaking compared to the same enzymes working under sub-optimal pH conditions. The continual production of acid and maintenance of a buffer system in the method of the present invention even when the produced acid reacts with acid soluble material, ensures favourable pH conditions for enzyme breaker activity are maintained over a prolonged period. This contrasts with standard buffer fluids which contain a low concentration of acid or formulations which produce low concentrations of acid from precursors. In both these cases the acid will react with acid soluble material and will not be replenished. Any enzyme breakers present in this fluid will only operate at a favourable pH for a short period of time before the acid is spent and the pH becomes more alkaline.
Preferred esters for incorporation into the treatment fluid to be used in the present invention are carboxylic acid esters with low toxicity, high flash point and high environmental acceptability. Esters of ethanoic and methanoic acid (acetic and formic acid) are particularly suitable. The calcium and magnesium salts of these acids have good solubility in water.
The ester should be at least slightly water soluble. Preferably the ester should be soluble to at least 1% w/v in water and most preferably soluble to at least 5% in water.
The acid produced according to the method of the present invention is an organic acid, generally an aliphatic carboxylic acid. Preferably the acid is of formula RCO2H wherein R is hydrogen, an alkyl group having from 1 to 6 carbon atoms or xe2x80x94Rxe2x80x2xe2x80x94CO2H where Rxe2x80x2 is a bond or an alkylene group having from 1 to 6 carbon atoms, the said alkyl or alkylene group being unsubstituted or substituted by halogen or hydroxy. Examples include 1,2,3,-propanetriol triacetate, 1,2,3,-propanetriol diacetate, ethylene glycol diacetate, diethylene glycol diacetate or triethylene glycol diacetate.
Where the acid has a hydroxy substituent, the ester may be a cyclic ester such as a lactone.
The alcohol portion of the ester may be monohydric or polyhydric as long as the esters are sufficiently water soluble at formation temperatures. Partial esters of the polyhydric alcohols can be used in which case the unesterified hydroxyl groups serve to increase the water solubility of the ester.
Most preferably the esters are acetic esters of 1,2,3-propanetriol (glycerol) and 1,2-ethanediol (ethylene glycol). The alcohol which is produced when the ester hydrolyses can act as a mutual solvent. The presence of a mutual solvent is generally considered to be beneficial in treatments of hydrocarbon bearing formations.
The treatment fluid needs to be shut in for a period long enough for the desired amount of acid to be produced. Ester hydrolysis proceeds slowly at low temperatures. For example at 10-40xc2x0 C. the hydrolysis may take several weeks. This may be acceptable for some applications such as filter cake removal from a well which has been drilled but which is shut in for an extended time (of at least several weeks) before being put on production.
However, in general to obtain more useful rates of ester hydrolysis at temperatures below about 120xc2x0 C. it is desirable to incorporate an enzyme into the treatment fluid. This is done by conventional means, for instance as described in U.S. Pat. No. 5,678,632. Lipases, esterases and proteases are the preferred enzymes for increasing the rate of ester hydrolysis in the method of the present invention.
At temperatures greater than about 120xc2x0 C. thermal hydrolysis may proceed at a sufficient rate to be useable without the need for the addition of ester hydrolysing enzyme or enzymes.
In addition to the preferred esters which would normally comprise the majority of the esters present in the formulations of the current invention, it may also be beneficial in some damage removal applications to include in the formulation esters of chelating compounds such as malonic acid, oxalic acid or succinic acid (U.S. Pat. No. 5,082,056) ethylenediaminetetraacetic acid (EDTA) nitriloacetic (NTA) citric acid or hydroxyacetic acid (U.S. Pat. No. 5,223,159) which hydrolyse to produce efficient chelating compounds. Such compounds may be particularly useful to assist in the breaking of cross-linked polymers in combination with other polymer breakers. Some of the acids produced from the hydrolysis of the ester may be able to dissolve certain types of oilfield scale. For example hydroxyacetic acid can dissolve calcium sulphate.
Preferred polymer breakers of the present invention are oxidative breakers (oxidants) and enzyme breakers.
Oxidative breakers used in the present invention may be any one of those oxidative breakers known in the art to be useful to react with polysaccharides to reduce the viscosity of polysaccharide thickened compositions or to disrupt filter cakes.
The oxidative breaker is introduced into the treatment fluid containing the ester component. The oxidative breaker may be present in solution or as a dispersion. Suitable compounds include peroxides, persulphates, perborates, percarbonates, perphosphates, hypochlorites, persilicates and hydrogen peroxide adducts such as urea hydrogen peroxide and magnesium peroxide.
Preferred oxidative breakers for incorporation into treatment fluids to be used in the present invention are peroxides which can decompose to generate hydrogen peroxide. Of the oxidative breakers most preferred are percarbonates and perborates, most especially sodium percarbonate and sodium perborate.
Preferred enzyme breakers for use in the method of the present invention include those polysaccharide degrading enzymes known in the art to be useful to hydrolyse polysaccharides and thereby to reduce the viscosity of polysaccharide thickened compositions or to disrupt filter cakes. The enzyme breakers will be selected on the basis of their known ability to hydrolyse the polysaccharide components known or believed to be contributing to the damage. Examples of suitable enzymes which may be used to break polymers include enzymes which can hydrolyse starch, xanthan, cellulose, guar, scleroglucan, succinoglycan or derivatives of these polymers,
Oxidative or enzyme breakers may also be used to hydrolyse other, non-polysaccharide polymers which may be incorporated into fluids for drilling workover or production operations.
In some embodiments of the present invention the effectiveness of the incorporated oxidant breakers can be enhanced by producing more reactive oxidants. Under certain conditions, for instance when a peroxide is included in the treatment fluid, the production of hydrogen peroxide in the presence of organic acid can result in the formation of a peracid which is a more effective oxidant than the hydrogen peroxide.
The efficiency of production of peracid can be enhanced by incorporating into the formulations certain hydrolytic enzymes which can produce a peracid from the ester and certain hydrogen peroxide yielding peroxygen compounds added as oxidants.
Esters are known to be hydrolysed by hydrolases (EC 3) such as a lipase (EC 188.8.131.52), an esterase (EC 126.96.36.199) or a protease (EC 3.4) in the presence of hydrogen peroxide or other peroxides to form a peracid (U.S. Pat. Nos. 3,974,082; 5,108,457; 5,296,161; 5,338,474; 5,352,594; 5,364,554). Peracids produced in-situ by such enzymes have been used for bleaching applications. Peracids are more effective oxidants than peroxides, particularly in the temperature range 25 to 80xc2x0 C.
However, peracids are relatively unstable and cannot be used as such but may be formed in-situ from a peroxygen compound and a suitable peracid precursor. Where esters are already present in a formulation, the use of lipase, esterase or protease enzymes to produce the peracid from an ester and a peroxygen compound is preferable to the use of chemically perhydrolysable peracid precursors such as tetraacetylethylenediamine which are generally more expensive (for background see U.S. Pat. No. 5,364,554).
If a diacyl peroxide substrate is used, a peracid can be produced directly by an esterase without a requirement for hydrogen peroxide (U.S. Pat. No. 5,364,554).
Other reactions which can produce a bleaching compound direct are the action of sulfatase (EC 3.1.6) on peroxydisulfate to form peroxymonosulfate (U.S. Pat. No. 5,183,473) and the action of phosphatase (EC 3.1.4) on peroxydiphosphate to produce peroxymonophosphate (U.S. Pat. No. 3,666,399).
The use of enzymes for in-situ peracid production for the treatment of underground formations has not been taught in any of the prior art.
Enzymes with esterase activity, including lipases, esterases and proteases, may be used in the acidising method of U.S. Pat. No. 5,678,632 and No. 5,813,466 but their use to produce peracids in underground formations has not been described. Useable rates of ester hydrolysis at temperatures below about 120xc2x0 C. are generally only obtained by the use of hydrolytic enzymes such as esterases, lipases or proteases. The incorporation of a peroxide into the treatment fluid used in the present invention, containing such enzymes, can therefore result in the formation of both organic acid and peracids giving formulations which are effective for both acidising and polymer breaking.
The ester and other chemicals required for the process of the present invention will normally be technical grade to reduce the cost of the process.
Where an enzyme is used, it is necessary to select an enzyme which remains active under reservoir conditions and in the treatment fluid for at least as long as the catalytic activity is needed.
Two types of enzymes may be used in the method of the present invention. Firstly, enzymes able to degrade polysaccharide polymers (xe2x80x9cenzyme breakersxe2x80x9d) and secondly enzymes with esterase activity, such as esterases, lipases and proteases, which can produce peracids in the presence of hydrogen peroxide. Both types of enzyme are generally water soluble enzymes. It is generally advantageous for the enzymes to be readily water soluble although the enzymes may also be active and be used in low water activity environments or two-phase systems such as emulsions or dispersions. In particular, lipases may be more active in emulsions. Many lipases exhibit their highest activity at interfaces.
Typically, isolated enzymes are used. Enzymes may be isolated from plant, animal, bacterial or fungal sources. The enzymes may be produced from wild-type, conventionally bred, mutated or genetically engineered organisms. The enzymes may, optionally, be chemically modified, as long as they retain or possess the desired catalytic ability. Preferably, the enzymes will be industrial enzymes available in bulk from commercial sources.
The treatment fluid is formulated to reflect the type of damage expected and the conditions of the reservoir, in particular the temperature.
For example, to remove damage caused by a filter cake comprising calcium carbonate, starch and xanthan in a reservoir at 60xc2x0 C. a treatment fluid comprising an acetic acid ester, an esterase and enzymes capable of degrading starch and xanthan may be formulated. The esterase enzyme is added to increase the rate at which ester hydrolysis takes place according to the method of U.S. Pat. No. 5,678,632.
To remove damage caused by a filter cake comprising-calcium carbonate, starch and xanthan in a reservoir at 110xc2x0 C. a treatment fluid comprising an acetic acid ester and an enzyme capable of degrading starch may be formulated. The rate of hydrolysis of the ester is generally sufficient to be useable at 110xc2x0 C. without addition of an esterase enzyme.
To remove damage caused by a biofilm in a carbonate formation at 50xc2x0 C. a treatment fluid comprising an acetic acid ester, an esterase and a mixture of enzymes capable of degrading the polysaccharides present in typical biofilms may be formulated.
To remove damage caused by a biofilm in a carbonate formation at 80xc2x0 C. a treatment fluid comprising an acetic acid ester, an esterase and a percarbonate may be formulated.
It is desirable that all of the components of a particular treatment fluid are compatible or if not fully compatible that they are sufficiently compatible to allow the desired amount of acid production and polymer breaking to occur over the duration of the treatment. For example it may be desirable to use a protease to enhance peracid production but the protease may adversely affect any other enzyme which is present if such enzyme is susceptible to attack by the protease. Similarly, any enzymes present will need to be tolerant to any oxidant used in the same formulation. Possible problems such as these will be evident to those skilled in the art and will generally be resolved before such formulations are used in the field.
The treatment fluid is normally prepared by dissolving or dispersing the ester and polymer breaker, optionally with an enzyme that can hydrolyse the ester and optionally with a peroxide, in suitable water. Examples include city (drinking) water, produced water or sea water although in some situations it may be desirable to inject undiluted ester or a blend of ester with a hydrocarbon such as diesel. Typically an ester solution is prepared batchwise in tanks or other suitable vessels by adding the ester to the water with agitation and achieving thorough mixing by recirculating the ester solution through a blender such as a paddle blender for a suitable period of time. In some circumstances, use of an emulsion of the ester may be desirable. The other components of the treatment fluid are then added and recirculation continued. If batch wise preparation is not possible or desirable (for example if a dispersion is used which is difficult to keep evenly dispersed in a large holding vessel), or if it is preferred, the treatment fluid may be prepared by adding the individual components to water on a continuous, preferably carefully controlled. and monitored basis as the fluid is injected into the underground reservoir. Other methods of preparing the chosen treatment fluid will be well known to those skilled in the art.
The concentrations of ester and the material present in the treatment fluid will depend on the required amounts of acid production and breaker.
This will depend on the specific formulation of the treatment fluid but will typically be of the order of 10 to 200 grams per liter of ester and 0.2 to 10 grams per liter of other components, although higher or lower concentrations may be appropriate in some situations. The concentration of any enzyme breaker will be selected such that the polymer/gel will be degraded within the desired period of time. Typical enzyme concentrations will be 0.05% to 5% v/v of commercial liquid enzyme preparations or about 0.005 to 0.5% v/v of dried enzyme preparation. Preferably liquid preparations of enzymes will be used for ease of handling.
More than one ester may be incorporated into the formulation depending on the nature of the formation damage and the type of treatment. Similarly more than one type of polymer breaker may be incorporated into the formulation. Where an enzyme preparation is included in the formulation to produce a peracid in the presence of an ester and hydrogen peroxide, more than one enzyme preparation may be incorporated. A single solution or dispersion containing all of the components is preferably used.
In some embodiments of the present invention, it may be desirable to incorporate more than one type of polymer breaker, for example an oxidant might be used in combination with an enzyme breaker in the case where two polysaccharides are present but only one is amenable to attack by an enzyme.
Oxidants and enzymes may if desired also be used in the form of delayed release preparations, such as will be well known by those skilled in the art.
The treatment fluid comprising, in water, the ester, polymer breaker and, if desired, enzyme capable of hydrolyzing the ester, is conveniently introduced into the underground formation via injection or production wells. If being introduced into a newly drilled well, particularly if being used to remove damage caused during drilling, such as filter cakes, the fluid may conveniently be introduced through the drill string using the mud pumps. The low corrosivity of the fluid will permit introduction into wells or the drill string without the need to add corrosion inhibitors. The fluid will normally be introduced at below fracture pressure but may if desired be injected at above fracture pressure.
The treatment fluid may contain further chemical additives such as are commonly used in the oil industry, such as surfactants, foaming and chelating agents if their inclusion is deemed to be beneficial and if they are compatible with the other components of the treatment fluid.
For near wellbore treatments, the volume of treatment fluid introduced into the reservoir will typically be at least equal to the wellbore volume plus an allowance for some leak off into the formation. A fluid volume of between 120% and 200% of the wellbore volume will normally be used although if a high rate of fluid loss is expected a volume up to 300% or higher of the well bore volume may be selected. For treatments where the target is damage deeper into the formation such as in natural or induced fractures or fracture networks a volume will be selected appropriate to the requirements of the treatment.
In one embodiment of the present invention, a volume of the treatment fluid, containing both ester and polymer breaker, which is sufficient to allow the fluid to penetrate one to several meters into a carbonate formation around a wellbore or behind a fracture face may be used. This can result in an increase in the matrix permeability of a carbonate formation to a depth of one to several meters in addition to and at the same time as removing damage from the near wellbore region or the fracture faces. In such cases a negative skin can result further increasing the productivity of the well beyond that which can be achieved with even complete near wellbore damage removal. The volume of fluid needed for such treatments will depend on the porosity of the formation, desired depth of penetration and dimensions of the wellbore, fracture or fracture network. Such an approach may also be effective for treating carbonate scaled sandstone reservoirs which also suffer from near wellbore damage, again using a single stage treatment.
The well will normally be shut in after introduction of the treatment fluid for a period, typically between 2 hours and a week, preferably 6-48 hours, to allow production of acid and breaking of the polymer. The well is then put on or returned to production, or in the case of injection wells, put on injection.
The present invention has the following particular advantages over the prior art:
The method provides a simple, effective and convenient way to treat damage caused by combinations of both acid soluble material and polymers using a single fluid. In particular the method provides a single stage treatment capable of completely removing filter cake damage caused by those drilling fluids containing carbonate as a fluid loss material and polymers. Previous treatment methods have been designed to treat only the acid soluble material or only the polymer component of such damage.
The method also allows the successful incorporation of oxidant or enzyme polymer breakers into a treatment fluid able to deliver a high concentration of acid. Because the acid is present in a non-acidic precursor form, the breakers are not inactivated, as many would be by contact with conventional acids, and the activity of certain breakers is subsequently enhanced by the onset of moderate acidic conditions. This takes place after placement of the fluid, ensuring that both the acid and the breaker are delivered where they are needed.
As well as near wellbore or fracture face damage removal the treatment fluid can also be used to achieve deep matrix stimulation during the same treatment. Because the fluid is essentially non-reactive when placed, excellent zonal coverage can be achieved.
Also the method is generally a very low hazard method compared to previous methods involving a substantive degree of acidising. The method uses high flash point esters and liquid preparations of enzymes. There is generally no need for high pressure, high rate injection.
The components of the system are generally environmentally acceptable. The esters and enzymes and certain oxidant components such as the percarbonates are of low environmental impact. Also, the fluids are not highly corrosive, meaning that the use of corrosion inhibitors is generally not required which gives additional environmental benefits.

Method for treatment of underground reservoirs


A fuel injector-spark plug combination includes a fuel injector for the direct injection of fuel into a combustion chamber of an internal combustion engine, and a spark plug for igniting the fuel injected into the combustion chamber, and has a spark-plug insulator including a first electrode, and includes a second electrode. The fuel injector and the spark-plug insulator of the spark plug are each disposed in a recess of a cylinder head of the internal combustion engine. The fuel injector and the spark-plug insulator of the spark plug are fixedly held in place in a shared connecting member arranged outside of the cylinder head.

The present invention is based on a fuel injector-spark plug combination.
A fuel injector including an integrated spark plug is described in European Published Patent Application No. 0 661 446. The fuel injector with the integrated spark plug is used for the direct injection of fuel into the combustion chamber of an internal combustion engine and for igniting the fuel injected into the combustion chamber. By the compact integration of a fuel injector with a spark plug, it is possible to save installation space at the cylinder head of the internal combustion engine. The conventional fuel injector with integrated spark plug includes a valve body which, together with a valve-closure member able to be actuated by manner of a valve needle, forms a sealing seat, adjacent to which is a spray-discharge orifice, which discharges at an end face of the valve body facing the combustion chamber. A ceramic insulation element insulates the valve body from a housing body in a high-voltage proof manner, the housing body being able to be screwed into the cylinder head of the internal combustion engine. Located on the housing body is a ground electrode in order to form an opposite potential to the valve body acted upon by high voltage. In response to a sufficiently high voltage being applied to the valve body, a spark arc-over occurs between the valve body and the ground electrode connected to the housing body.
This conventional fuel injector with the integrated spark plug provides that the position of the spark arc-over is not defined with respect to the fuel jet spray-discharged from the spray-discharge orifice, since the spark arc-over may occur at just about any location in the lateral region of a valve-body projection. With this configuration, a reliable ignition of the so-called jet root of the fuel jet spray-discharged from the spray-discharge orifice is not possible with the necessary reliability. However, a reliable and temporally precisely defined ignition of the fuel jet is absolutely required for reduced emissions. Furthermore, the exit orifice of the fuel jet may be subject to continually worsening carbon fouling or coking, which affects the form of the spray-discharged jet. The ceramic extrusion coat is relatively cost-intensive.
The fuel injector-spark plug combination according to an example embodiment of the present invention may provide that, by positioning the fuel injector and the spark-plug insulator of the spark plug in a shared connecting member, which may be arranged at an end face of the cylinder head of the internal combustion engine, the components may be optimally arranged relative to each other, resulting in a system that is easy to install and requires little space.
The spark-plug insulator may be secured in the housing by a threaded sleeve, the spark-plug insulator being screwed into the mounting support.
Tilting of the longitudinal axis of the spark-plug insulator relative to the longitudinal axis of the fuel injector may prevent the spark plug from being directly exposed to the fuel jet spray-discharged from the fuel injector.
Moreover, the spark plug and the ground electrode of the spark plug may each be exchangeable independently of the fuel injector.
The housing may be made of plastic and may be produced in an inexpensive manner.
An example embodiment of the present invention is represented in the drawing in schematic form and explained in greater detail in the following description.