High Performance Water Base Drilling Fluid CQH-M2 and Its Application on Well Wei204H11-4

The Longmaxi shale in Chuanyu area is brittle, and is full of micro-fractures and vugs. Challenges encountered during drilling operations are borehole instability and pipe sticking resulted from borehole sloughing. In this paper, the technical difficulties in using the high performance water base drilling fluid CQH-M2 is analyzed and measures dealing with the difficulties are presented based on the geological characteristics of the Longmaxi shale. Additives, such as shale inhibitors, filter loss reducers, lubricants and plugging agents for CQH-M2 have been optimized through laboratory experiments. Laboratory experiments on the evaluation of these additives showed that the inhibitive capacity of CQH-M2 is better than that of another high performance drilling fluid CQH-M1, almost equivalent to oil base drilling fluid in inhibiting the hydration and dispersion of shale. CQH-M2 has good instant and long lasting plugging effect. Mud cakes of CQH-M2 are thin and tough, sealing off porous formations in a satisfactory manner. CQH-M2 is also resistant to the contamination caused by 9% cuttings. In field application, CQH-M2 high performance drilling fluid has satisfied the technical requirements for drilling the well Wei204H11-4. The drilling fluid performed very well during drilling and no downhole troubles have ever been encountered.