Study on the mechanism and main control factors of lost circulation in deep brittle shale in Changning block

Abstract

Sichuan Changning block is rich in shale gas resources reservoirs, but the lost circulation problem is prominent during the horizontal drilling process of deep shale gas wells, which seriously restricts the exploration and development of deep shale gas resources in the Changning Block. Aiming at the problem of lost circulation in the drilling process of deep shale gas in Changning well area, the difference of the vertical and horizontal distribution of lost circulation is clarified by comparing the information of deep shale lost circulation in this block. Based on single well logging data and 3D seismic interpretation, the 3D distribution model of shale gas formation fracture, in-situ stress and formation pressure was established. The response relationships among fracture development, in-situ stress distribution, formation pressure and lost circulation in shale formations were studied, and the lost circulation mechanism and main influencing factors of deep shale gas formations in the Changning well area were clarified. The results of the study show that deep shale lost circulations in the Changning well block is prominent and widely distributed longitudinally and horizontally with unclear regularity, and that regional fracture development, in situ stress field and formation pressure have obvious effects on well leaks. The distribution of fractures, in-situ stress field and formation pressure in Changning block have a significant and highly responsive effect on lost circulation. The results of this paper reveal the complex mechanism of deep shale lost circulation in the Changning block and the main influencing factors, and provide a certain scientific basis for prevention and treatment of deep shale reservoir leakage in Changning block.