关键词: 水敏性, 油基钻井液, 井壁失稳, 井眼清洁, 旋转导向, 高效PDC钻头

Abstract: Reservoirs in well block Fudong5 are typical of highly water-sensitive channel sand bodies. The target Toutunhe Formation has a structure of sand-in-mud. With a clay mineral content as high as 27%～31% and a montmorillonite content as high as 56%～82%，the formation is highly water sensitive. Due to the strong water sensitivity，there is a high requirement for wellbore stability during drilling. Because of the high montmorillonite content，the rocks are very likely to become hydrated and swell，causing wellbore sloughing or collapse. The formation is likely to absorb water and swell，which changes the overall strength of mudstone，and causes wellbore instability. In the early stage of drilling，water-based drilling fluid was used，mudstone was very likely to swell，collapse，which caused sticking，backfilling，sidetracking and other drilling troubles many times. In this paper，the technical problem that has restricted the horizontal well drilling in the highly water-sensitive channel sand bodies in well block Fudong5 is solved by using such technogies as oil-based mud，borehole cleaning，real-time optimization and analysis of drilling parameters，and safe running of drillstring，which is of certain reference significance for accelerating the high-efficiency evaluation and massive development of water-sensitive channel. 

Key words: water-sensitivity; oil-based drilling fluid, wellbore instability, borehole cleaning, rotary steering, high-efficiency PDC bit