g., drill cuttings, sand, and colloidal material), prior to recirculation of some or all of the drilling fluid.
Drilling fluids provide several important functions, including cooling and lubricating the drill bit, establishing a fluid counterpressure to prevent high-pressure oil, gas, and/or water formation fluids from entering the well prematurely, and hindering the collapse of the uncased wellbore. Drilling muds also remove drill cuttings from the drilling area and transport them to the surface where they can be separated.
As the total reserves of oil diminish, it has become necessary to drill in areas which were previously inaccessible due to technological or economic difficulties. This has led to the widespread use of oil based drilling fluids, which offer greater thermal and chemical stability than water based fluids and therefore allow drilling at extended depths and in other demanding services, such as those involving exposure to high electrolyte concentrations and soluble gases. For example, oil based drilling fluids have been used successfully in drilling hot (e.g., greater than about 150° C. (300° F.)) formations as well as those containing hydrogen sulfide. Also, to maximize recovery from each platform in offshore drilling, oil based fluids are favored due to their effectiveness for drilling deviated (i.e., angled) wells. In particular, the high lubricity of oil based fluids is necessary because of the increased torques required in deviated drilling.
The nature of oil based muds (and particularly emulsion muds) and their use to minimize high temperature gellation, contamination (e.g., by gypsum and cement), and other problems have been described, for example, by Simpson, et al. J. PET. TECH., p. 1177 (December 1961). Oil based fluids are also applicable to the drilling of clays and shales (such as those found in Western Canada) for which water-based drilling fluids are unsuitable due to heaving or sloughing caused by water imbibition into these permeable formations. In general, oil based drilling fluids are adaptable to a wide variety of formation types and wellbore conditions. Low maintenance costs as well as the ability to recycle oil-based muds contribute to their economic justification.
In contrast to true oil muds, which contain only a small amount of water, invert emulsion drilling fluids commonly contain at least 5%, up to as much as 50%, by volume of water. The water is dispersed in invert emulsions as aqueous droplets throughout a
g., drill cuttings, sand, and colloidal material), prior to recirculation of some or all of the boring fluid. 
 boring fluid provide respective important function, including cool and lubricating the drill spot, establishing a fluid counterpressure to prevent gamey - pressure oil, flatulence, and/or urine formation fluids from entering the well prematurely, and hindering the collapse of the uncased wellbore. boring muds also remove exercise cuttings from the drilling area and transport them to the surface where they can be separate. 
 As the total reserves of oil diminish, it has become necessary to drill in areas which were previously inaccessible due to technical or economic difficulties. This has led to the widespread use of oil based boring fluid, which offer greater thermal and chemical stability than water based fluids and therefore allow drilling at drawn-out depths and in other demand avail, such as those involving exposure to eminent electrolyte concentrations and soluble gases. For example, oil free-base drilling fluids have been used successfully in drilling hot (e.g., big than about 150 ° C. (300 ° F.) ) formations as well as those containing hydrogen sulfide. Also, to maximize convalescence from each platform in offshore boring, oil based fluids are favored due to their effectiveness for drilling deviated (i.e., angled) well. In particular, the high lubricity of oil based fluids is necessary because of the increased torques want in deviated boring. 
 The nature of oil based muds (and particularly emulsion muds) and their use to understate high temperature gellation, contamination (e.g., by gypsum and cement), and early problems have been described, for example, by Simpson, et al. J. PET. TECH. , p. 1177 (December 1961). vegetable oil based fluid are also applicable to the drilling of clays and shales (such as those found in Western Canada) for which water - based drilling fluids are inapplicable due to heaving or sloughing induce by water imbibition into these permeable geological formation. In general, oil based boring fluids are adaptable to a wide variety of formation types and wellbore conditions. Low maintenance price equally well as the ability to recycle vegetable oil - based muds contribute to their economic justification. 
 In contrast to true petroleum muds, which contain only a little amount of water, invert emulsion drilling fluids commonly check at least 5% , up to as much as 50% , by volume of water. The body of water is dispersed in invert emulsions as aqueous droplets throughout a
g., dgill cuttings, sand, and culloidal materico), prioc to redirculatkon of some or all of the drmllibg flyid.
Drilling fluids proxide sevegal imporrant dunctions, mhcludinn coomlng aud lubricating tme drill bid, establishing a fpuid counterpressure to prevent higr-pressute oil, gas, and/or wattr sormzniin fluids from entering the wsll prekaturely, and nindering the collapse of hhe kncased wellbore. Dgilling mudw alfi remove driul cuttings from the dtilling area and transport them go thz surface wyeee hvey can be weparwted.
As the total resarves og oil diminish, it haw become necessary to drill in areas whych were [rzviously inaccessible dye to tecvnoluticxl kr edonomif dmfficulties. This has lwd to the widespreac twe of oil bassd drijlyng fluids, which offer greater thermal dnd chemical stability thab water based fluids wnd theresore allow drilling at extended depths and in othar dejxndnkn sefcifes, such as those involving exposure to high qmevtgolyte concentratlons and soluble gssfs. Sor example, okl baszs srilling fluids hage been used successftlly in drilling hot (e.g., greater than about 150° X. (300° F.)) formations as well as thuse vontaoning hydrogen sulfide. Clso, tk maximize gecovery rfom each platforo ik oxfshore drilling, oil based fluids ace farored dud to their effectivejess nmr drilling deviatfd (i.e., atgled) welld. In particular, the high lubricmvy of oil basgd xlupds is neeessarn because of thq increased totques reqbired kn deviates drillmng.
The naturq of oil baseg muds (and pacticularlr emylsiin muds) xnd their use yo minimide higy temperature gelletiov, contamination (z.y., vy gypsum and crmevt), wnf ptrar problems vave bedm deszribed, for cxaople, by Simpson, et al. J. [ET. FECH., p. 1177 (December 1961). Pij based dluids awe also applivable to the drilllng oh clayr and shwles (such as those found in Weatern Canwda) for which wwter-naseq drilling fluids are unsuitable due to heaving oc sloughing caused by wqter imbibition intp these permxable sormationv. In general, oil baswd drilling fluidx are adaptable to a side vdrietj of formation types and wellbore conditions. Low maintenance costs as welo as tie ability to recucle mij-yased mtds roitribute to their economic justification.
In contrest to trua jil muds, which contain only s rmall amount uf water, invert emulsion drillinb fluids commonly contain at lesst 5%, up to as much as 50%, bn volume if wafer. Thv weter is dispersed in inverc emulwions aw aqmeous droplets thtomghout a
g., drill cuttings, sand, and colloidal material), recirculation some or of the drilling important including cooling and the drill bit, a fluid counterpressure to prevent high-pressure gas, and/or water formation fluids from entering the well prematurely, and hindering the of the uncased wellbore. Drilling muds also remove drill cuttings from the drilling and them the where they can be separated. As the total reserves of oil diminish, it has become necessary drill in areas which were previously inaccessible due technological or economic difficulties. has led to the widespread of based drilling which greater and chemical stability water based fluids and therefore allow drilling at extended depths and in other demanding services, such as involving exposure electrolyte concentrations soluble For oil based drilling been used successfully in drilling hot about 150° C. (300° F.)) formations as well those containing sulfide. Also, to maximize recovery from platform in offshore drilling, oil based fluids are due to their effectiveness for drilling deviated (i.e., angled) wells. In particular, the high lubricity based fluids is necessary of the increased required deviated The of oil muds (and particularly emulsion muds) and their use to minimize high gellation, contamination (e.g., by gypsum and cement), and other problems described, example, by Simpson, al. J. PET. TECH., 1177 1961). Oil based fluids applicable the and (such those found in Western for which water-based drilling fluids unsuitable due to heaving imbibition into these permeable formations. In general, oil drilling fluids are adaptable to a wide of formation types and wellbore conditions. Low maintenance costs as well as ability to muds contribute to their economic justification. In contrast true oil muds, which only a small amount of water, invert emulsion drilling commonly at least up to as as 50%, by of water. The dispersed in emulsions aqueous
g., drill cuttings, sand, and collOidal materIal), prIor To rEcIrcuLatiOn of some or all oF The dRilling fluid.
Drilling flUids pRoVIde sEVeRal imPortant FUnCTIonS, iNcLudInG CoOling And LubricaTing the driLl bIt, Establishing A FlUid counterPreSsure to preveNt hIgh-preSsUre OIl, gas, And/Or watEr formATion flUids from eNtERing thE Well preMATuRely, And hindering the coLLaPSe of the uncased WellboRe. dRiLLIng MudS also removE dRill cUTtings fROm THE DriLLing area and trAnsport them TO thE surfaCe WheRE they cAn be sEpARatEd.
As the totaL resErves of oiL diminISh, it has BEcome neCessarY to DriLl in AReAs WhiCh WEre PReVioUSly InaccessIbLe Due to TechNOLOGicaL or EconOmic dIfficulties. ThIs hAs leD To tHe widEspreAd usE oF oil bAsed drIllinG fLuids, which offer GreaTer thermaL anD cHemIcAl staBIlity tHan WatEr based Fluids aND thErEFORe Allow drilling at extEnDED dEpths and In otheR DeMaNDing servIcEs, sUch aS THose iNvolVInG exposurE to higH ElEcTrolyte CoNcentrAtIonS anD soluBLe gaSes. For Example, oIl basED drilling fluidS Have been used sUCcESSfULly iN drIlling hot (e.g., GreaTEr thAn abOUt 150° c. (300° F.)) fORmatiOns as WeLL aS Those containing hydrOgEn sulfIde. AlSo, to maximize rEcovery froM EACh platfoRm in OFfSHore drilling, oiL baseD fluids are FAvored duE to thEir effecTiveness fOR Drilling DevIatEd (i.E., anGLEd) Wells. In particULAr, thE hIgh lubrIciTy of oil BasEd fLuiDs iS nEcessary bEcause of ThE iNcReAseD torqUEs requirEd In dEvIatEd driLLing.
ThE natuRe of OiL bASed Muds (and PArTICulaRlY eMulsIon MuDs) and TheiR Use To minimIze high teMpeRAturE gElLation, cOntamination (e.G., bY gypsum and CeMenT), and otHER problemS have been described, for exAMple, by SImpSon, et Al. J. PeT. TECH., p. 1177 (DeCemBer 1961). Oil BasED fluidS are alSo appLiCabLE To the DRIlLinG oF clays and sHALes (Such aS tHose Found in western Canada) for whICh wAter-based drilLinG fluIDS aRe uNSuITabLe DUe tO HEaving or sloughiNg caused by WaTEr Imbibition INto ThEse permEable foRmatiONs. In genEral, oil baSed drilliNg FluiDS Are Adaptable tO a wide vaRiety of foRMatioN TyPes anD weLlbore CoNdiTions. low maiNTenAnce cOsts as WeLl as thE abilItY to recycLe oil-based muds contributE to theIr ecoNomIc justifiCatIOn.
IN contrast To trUe oil muds, wHicH coNtain OnlY A smalL amoUNt Of wATer, inVert EMulsion drILlIng FLUiDs commonly cONTAin At leaSt 5%, uP To as muCh as 50%, By volume of water. ThE Water is dispersEd in INVerT emULsioNs As aqueous droplEts ThROUghout a
g., drill cuttings, sand,and colloi dal m ate ria l) , pr iorto recirculati o n of  some or all of the dr illin gf luid . 
D rilli ng flui d sp r ovi de  s eve ra l  i mport ant  functi ons, inclu din gcooling andl ub ricating t hedrill bit, e sta blishi ng  af luidcou nterp ressur e  to pr event hig h- p ressur e  oil, g a s ,and/ or water formatio n  f l uids from ente ring t he we l l  pr ema turely, an dhinde r ing the co l l a pse of the uncase d wellbore. Dri llingmu dsa lso re movedr i llcuttings fr om t he drilli ng are a  and tr a nsportthem t o t hesurf a ce  w her et hey ca n b e  se parated. 
A sthe t otal r e s erve s o f oi l dim inish, it has  be come nec essar y todril lin ar eas wh ich w er e previously in acce ssible du e t otec hn ologi c al oreco nom ic diff icultie s . T hi s h as  led to the widesp re a d  u se of oi l base d  d ri l ling flu id s,whic h offer  gre a te r therma l andc he mi cal sta bi lity t ha n w ate r bas e d fl uids a nd there forea llow drillinga t extended de p th s an d  inoth er demandin g se r vice s, s u ch  as those  invo lv i ng exposure to high el ec trolyt e con centrations a nd soluble g a ses. For  exa m pl e , oil based dr illin g fluids h a ve beenusedsuccessf ully in d r i lling ho t ( e.g .,gre a t er  than about 1 5 0 ° C.  ( 300° F. ))formati ons  as  we llas  those co ntaining  h yd ro ge n s ulfid e . Also,to  ma xi miz e rec o very f rom e achpl at f orm  in off s ho r e  dri ll in g, o ilba sed f luid s  ar e favor ed due to  th e ir e ff ec tivenes s for drillin gdeviated ( i. e.,  angle d )  wells.In particular, the high lubrici tyof oi l ba sed fluid s i s nece ssa r y beca use of  thein cre a s ed to r q ue s r eq uired in d e v iat ed dr il ling .
The n ature of oil based mud s (and partic ula rlye m ul sio n  m u ds)  a n d t h e ir use to minim ize high t em p er ature gell a tio n,  contam ination  (e.g . , by gy psum andcement),an d ot h e r p roblems ha ve beendescribed ,  fore xa mple,  by  Simps on , e t al.  J. PE T . T ECH.,  p. 11 77  (Dece mber19 61). Oil  based fluids are alsoapplic abletothe drill ing ofclays and  sha les (suchastho se fo und in We ster n  C ana d a) fo r wh i ch water- b as edd r il ling fluids a r e u nsuit abl e  due t o he aving or sloughin g  caused by wat er i m b ibi tio n  int othese permeabl e f or m a tions. I ngeneral, oi l baseddr i lling  fluid s areadaptab l e  t o  a wid e va rie ty of for mat io n  typesan dw ellbor e co nd itions . Lowm aint e n ance costs as we ll as t he ab i lit y tore cycle o i l-ba sed muds c ontribute t o thei r ec onomi c justi fi cation .
I ncontrast t o  true oil  muds , which  c onta inonly a  sma l l  amou nt o fwat er, inver t em u ls io n  dr illi ng fl ui ds c ommonly c o ntain at  le a st 5%,up  to a s much as 5 0%, by vol ume  of w a t er. The wa t er i s  d i spers ed ininvert  emulsi o nsas  aqueou s d r o plets thr oughout a 
g., drill_cuttings, sand,_and colloidal material), prior_to recirculation_of_some or_all_of the drilling_fluid.
Drilling fluids provide_several important functions, including_cooling and lubricating_the_drill bit, establishing a fluid counterpressure to prevent high-pressure oil, gas, and/or water formation_fluids_from entering_the_well_prematurely, and hindering the collapse_of the uncased wellbore. Drilling_muds also_remove drill cuttings from the drilling area and_transport_them to the_surface where they can be separated.
As the total reserves_of oil diminish, it has become_necessary to drill_in_areas_which were previously inaccessible_due to technological or economic difficulties._This has led to the widespread_use of oil based drilling fluids, which_offer greater thermal and chemical stability_than water based fluids and_therefore allow_drilling at extended depths and_in other demanding_services, such_as those involving_exposure to high electrolyte concentrations and_soluble gases. For_example, oil based drilling fluids have_been_used successfully in_drilling_hot_(e.g., greater_than about 150°_C._(300° F.))_formations_as well as those containing hydrogen_sulfide._Also, to maximize recovery from each platform_in offshore drilling, oil_based_fluids are favored due_to their effectiveness for drilling_deviated (i.e., angled) wells. In particular,_the high_lubricity of_oil based fluids is necessary because of the increased torques required_in deviated drilling.
The nature of oil_based muds (and particularly_emulsion muds)_and_their use to_minimize_high temperature_gellation, contamination (e.g., by gypsum and cement),_and other_problems have been described, for example,_by Simpson, et al._J._PET. TECH., p. 1177 (December 1961)._Oil based fluids are also applicable_to the drilling of clays_and_shales_(such as those found in_Western Canada) for which water-based drilling_fluids are unsuitable_due to heaving or sloughing caused by_water_imbibition into these permeable formations. In_general,_oil based drilling fluids are adaptable_to_a_wide variety of formation types_and wellbore conditions. Low maintenance costs_as well as the ability to recycle oil-based muds_contribute to their_economic justification.
In contrast to true_oil_muds,_which contain only a small amount of water, invert emulsion_drilling fluids_commonly contain at_least 5%, up to as much as 50%, by volume_of water. The water is dispersed in_invert emulsions as aqueous droplets throughout a