for mineral composition, visual sign of hydrocarbons and recorded mud logs of lithology, ROP, gas detection or geological parameters. Wireline logging measure – electrical, sonic, nuclear and magnetic resonance. Potential productive zone are isolated and performed formation testing and drill stem testing. Mud helps not to disperse of cuttings and also improve cutting transport for mud loggers determine the depth of the cuttings originated. Oil-based mud, lubricants, asphalts will mask hydrocarbon indications. So mud for drilling core selected base on type of evaluation to be performed (many coring operations specify a bland mud with minimum of additives). Control corrosion (in acceptable level) Source: Drill-string and casing in continuous contact with drilling fluid may cause a form of corrosion. Dissolved gases (oxygen, carbon dioxide, hydrogen sulfide) cause serious corrosion problems; Cause rapid, catastrophic failure May be deadly to humans after a short period of time Low pH (acidic) aggravates corrosion, so use corrosion coupons to monitor corrosion type, rates and to tell correct chemical inhibitor is used in correct amount. A corrosion coupon is a small piece of metal exposed to the process so to evaluate the effect the corrosive conditions would have on other equipment of similar composition. Mud aeration, foaming and other O2 trapped conditions cause corrosion damage in short period time. When drilling in high H2S, elevated the pH fluids + sulfide scavenging chemical (zinc). Facilitate cementing and completion Source: Cementing is critical to effective zone and well completion. During casing run, mud must remain fluid and minimize pressure surges so fracture induced lost circulation does not occur. Temperature of water used for cement must be within tolerance of cementers performing task, usually 70 degrees, most notably in winter conditions. Mud should have thin, slick filter cake, with minimal solids in filter cake, wellbore with minimal cuttings, caving or bridges will prevent a good casing run to bottom. Circulate well bore until clean. To cement and completion operation properly, mud displace by flushes and cement. For effectiveness; Hole near gauges, use proper hole cleaning techniques, pumping sweeps at TD, and perform wiper trip to shoe. Mud low viscosity, mud parameters should be tolerant of formations being drilled, and drilling fluid composition, turbulent flow - low viscosity high pump rate, laminar flow - high viscosity, high pump rate. Mud non progressive gel strength Minimize impact on environment Source: Mud is, in varying degrees, toxic. It is also difficult and