Drilling Fluids – 5.3 – The non-aqueous Drilling Fluids

The term non-aqueous refers to the fluids whose base fluid not water; hence, it is either oil or synthetic fluid. Prior to discuss this type of mud, first let’s go over the concept of emulsion. When two immiscible fluids such as water and oil mixed together, they are incapable of forming molecularly distributed mixtures to attain homogeneity; they separate into two phases with an interface between them. Thus, a chemical additive called emulsifier is used to create an emulsion. Emulsion is a dispersion of one immiscible liquid into another, by reducing the interfacial tension between them.

In WBM, dispersion of oil droplets into the aqueous/continuous/external phase is needed to form emulsion mud. In contrast with oil base mud, the continuous phase of the emulsion is oil; therefore, water droplets are dispersed into the oil external phase, which refers to as invert-emulsion or oil base mud in general.

Nonwater-based mud is a drilling fluid that is composed of oil as the continuous phase and water as the dispersed phase in conjunction with emulsifiers for emulsion, wettability, and stability. The external phase is an oil that does not allow water to contact a formation; it can be diesel, kerosene, fuel oil, crude oil, mineral oil, or synthetic fluid. ?The former four types of oil are low in cost, commonly available, and have excellent performance in drilling difficult wells; however, there has been trend to replace them in land drilling by mineral-oil muds and offshore by synthetic-fluid muds because of their associated health, safety and environmental concerns.

Non-aqueous mud in general are developed to meet difficult drilling targets such as: drilling water-sensitive shale zones that swell and disperse in water based mud, reducing drilling problem of WBM (tight hole / washout), drilling deep and high-temperature holes that dehydrate water-based mud, stabilizing?borehole formations, drilling water-soluble zones and drilling production zones. In addition, it can be used as a completion and workover fluid, a spotting fluid to relieve a stuck pipe and as a packer or casing fluid.

The term synthetic-base mud SBM is known as low-toxicity OBM (LTOMB). It describes any oil-base mud that has a synthetic fluid as external phase instead of oil. Techniques use chemicals emulsifiers to disperse green fluid environment friendly into fluid rather than diesel. It is designed to replace the traditional oil-based mud used in offshore. SBM is environmentally accepted, and has the approval of cuttings disposal into the water. That is why it is popular in most offshore drilling areas, nevertheless of its high costs.