Drilling Challenges and Drilling Fluid Technologies for Shale Gas Drilling in Changning Area

Challenges encountered in shale gas drilling in Changning area from the Jialingjiang Formation to Hanjiadian Formation are as follows:bit balling in drilling long section of mudstones, mechanical collapse of formation with developed beddings, borehole wall collapse in drilling the top section of well causing pipe sticking, developed fractures with good connectivity resulting in mud losses, borehole enlargement resulted from formation creep, and contamination to drilling fluid by mudstones. Challenges encountered in drilling fluid maintenance and the solution were also provided in this paper. Based on the analyses of drilling problems encountered from Jialingjiang Formation and Hanjiadian Formation, the drilling fluid formulation to be used was optimized accordingly. The optimized drilling fluid was used in 10 times in different wells in Changning area, greatly reduced the occurrence of downhole problems. With the optimized drilling fluid, the Jialingjiang gypsum formation was penetrated with no troubles, the Feixianguan mudstone formation was drilled with success, and cave-in of the Changxing-Longtan formations was avoided. Any downhole complicationsrelated with drilling fluid were all avoided. Lithology variance in the Changning area is remarkable. An in-depth understanding of the formations in this area, and specific suggestions and measures presented in drilling fluids design help minimize the occurrence of downhole complications, providing technical support to quality, efficient and cost-effective drilling of shale gas.