Leakage prevention and control in fractured formations
ZENG Yijin1，LI Daqi1，YANG Chunhe2
(1. State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development，Sinopec Research Institute of Petroleum Engineering，Beijing 100101，China；2. State Key Laboratory of Geomechanics and Geotechnical Engineering，Institute of Rock and Soil Mechanics，Chinese Academy of Sciences，Wuhan，Hubei 430071，China)
Abstract：Leakge is a big problem for the safety and efficiency of drilling. The fracture aperture，circumferential stress and stress intensity factor of fracture tip were studied in the case of bridging or sealing in different fracture locations with the numerical method. The results show that，when the wellbore pressure is constant，the longer the fracture，the larger the stress intensity factor and the fracture aperture. The bridging location in the fracture opening has the best effect，with the circumferential effective stress enhanced the most and the stress intensity factor the lowest. The lower the fracture pressure，the more enhanced the circumferential effective stress and the smaller the stress intensity factor. Suitable particle size should be chosen in accordance with the fracture aperture while drilling. Sealing micro-fractures quickly and efficiently by constantly adding LCMs and using high-performance LCMs can prevent the occurrence of pernicious mud loss effectively，and improve the pressure bearing capacity of the formation.