Use Oil Based Drilling Fluid to Stabilize Borehole Wall and Prevent and Control Mud Losses in Fuxing Area

In shale gas drilling in the Fuxing area, downhole troubles, such as mud losses in the Lianggaoshan formation, coexistence of well kick and mud losses in the Dongyuemiao member of the Ziliujing formation as well as borehole wall collapse which resulted in frequent pump and top drive halt, have frequently been encountered. To solve these problems, rock samples of the Lianggaoshan formation taken from the well Xingye-L2HF and the well Xingye-1002HF as well as rock samples from the Dongyuemiao member of the Ziliujing formation are analyzed with XRD diffraction for their mineral composition. Using SEM, the micromorphology of these rock samples is analyzed. By studying the field operational data, the mechanisms of borehole wall collapse and mud losses are summarized. The oil-based drilling fluid previously used is improved based on the studies for its emulsion stability, friction reduction and plugging capacity. The new oil-based drilling fluid for the drilling operation in the Fuxing area has plugging PPA of less than 2 mL and invasion depth into the sand tube of less than 2 cm. Based on the sand blocking effect in fracturing job, a mud loss control slurry formulated with compound lost circulation material, inducing agent and suspending agent was developed. The pressure bearing capacity of the mud cakes formed by this mud loss control slurry is 7 MPa, making it suitable for controlling mud losses into formations with multiple fractures. Compared with the high density diesel oil-based drilling fluid used in drilling a well in the Fuxing area previously, this new oil-based drilling fluid has lower viscosity, lower gel strengths and higher lubricity, and the occurrence of the complex situations, such as mud losses and borehole wall instability, has significantly been reduced.