基于统一强度理论的水平井井壁稳定性分析

Analysis of wellbore stability for horizontal wells based on unified strength theory

贾利春 陈杨 余晟

中国石油川庆钻探工程公司钻采工程技术研究院，四川 广汉 618300

Drilling & Production Technology Research Institute, Chuanqing Drilling Engineering Company Limited, CNPC, Guanghan 618300, China

基于统一强度理论弱面准则，结合水平井井壁应力状态，分析了层理性地层弱面产状和准则中特定参数b对水平井井壁稳定性的影响规律。研究结果表明，水平井钻进方位、弱面倾角和走向均与安全钻井液密度密切相关。弱面倾角在60°~90°时，沿着特定方向钻进，井壁稳定性较好；除弱面走向为0°外，危险钻进方位均为0°和180°。随着b值升高，安全钻井液密度ρ■逐渐降低，在b为0和1.00时，ρ■分别达到最高、最低值。在不同b值时，水平井安全钻进方位虽存在略微差异但大体上相近，与b=0时的Mohr?鄄Coulomb弱面准则相比，计算结果更接近实际情况。基于统一强度理论的弱面准则更适用于层理性地层水平井井壁稳定性分析以及钻进方位和钻井液密度的设计。

Combined with stress state of horizontal well, the borehole stability under different weak planes occurrence and different values of b is analyzed based on the weak plane criterion of unified strength theory. The results show that the equivalent drilling fluid density of collapse pressure is closely related to the drilling direction of horizontal well and weak plane dip angle and trend. The borehole is much stable in certain drilling direction as the weak plane inclination is 60°￣90°. The dangerous drilling direction is 0° and 180° for all weak plane trend except for θtr=0°. The collapse pressure gradually decreases as the value of b increases, with maximum collapse pressure of b=0 and minimum collapse pressure of b=1.00, respectively. The safe drilling directions of horizontal well are slightly different but substantially similar as the values of b change. Compared with the Mohr-Coulomb weak plane criterion with b=0, the result is much close to the actual cases. The analysis indicates that the weak plane criterion of unified strength theory can be used to analyze the borehole stability of horizontal well, design optimal drilling direction and drilling fluids density.

10.6056/dkyqt201805020