Laboratory Study of an Environmentally Friendly Non-toxic High Performance Water Base Drilling Fluid

Oil base drilling fluids, because of its high operation cost and pollution to the environment, are more and more replaced by water base drilling fluids. Based on the requirements for the performance of drilling fluids imposed by shale drilling, drilling fluid additives have been optimized to formulate an environmentally friendly non-toxic high performance water base drilling fluid. In selecting the additives, the environmental rules of "chloride-free, heavy metal ion-free and no black material" were followed. Amine based polyalcohol and polymers synthesized through emulsion polymerization were selected as the main shale encapsulators, whose inhibitive capacity was enhanced with potassium formate. A highly effective plugging agent was selected to improve the ability of the drilling fluid to plug the nanometer and millimeter micro-fractures. Laboratory evaluation indicated that in a density range of 1.22-2.18 g/cm³, the drilling fluid had excellent rheology and filtration property. After standing for 24 hours, the density difference between the top and the bottom of the mud sample was 0.03-0.06 g/cm³, and the settling index was less than 0.508, indicating good suspending stability and high thixotropy. The friction coefficient of the mud cakes formed by the sample drilling fluid on an API filter press was as low as 0.0262, meaning that the drilling fluid had very good lubricity. Laboratory experiments also showed that this drilling fluid had strong inhibitive capacity and tolerance to drilled cutting contamination. After contamination with 5.0% and 8.0% British evaluation clay or drilled cuttings from the well VDW** (Cuba), changes in PV, YP and gel strengths of the drilling fluid were controlled within about 25%. The evaluation results also proved that this drilling fluid satisfied the needs for drilling shales of varied formation pressures.