【摘要】 文章建立了基于相场法的微裂缝扩展模型，通过数值模拟发现井壁微裂缝的起裂、扩展和转向等现象，分析了钻井液液柱压力和天然裂缝对井壁微裂缝扩展的影响规律，预测了防止微裂缝扩展的坍塌压力。结果表明，当钻井液液柱压力较小时，井壁经历了微裂缝的萌生、扩展、分支缝产生和交叉贯通等阶段；随着钻井液液柱压力趋近坍塌压力，井壁上产生的微裂缝数量减少、缝长变短、扩展速度降低；具有天然裂缝的岩石起裂所需能量比完整岩石破坏所需能量更低，微裂缝扩展速度更大，增大了井壁的坍塌压力。此外，天然裂缝位于最小水平地应力方向、夹角45°且与井壁连通时，最容易起裂和扩展，此处的井壁坍塌失稳风险最大。基于相场法理论的模型不仅能够可视化模拟井壁微裂缝扩展及坍塌过程，且坍塌压力预测结果与实钻情况相吻合。此研究为裂缝性地层井壁坍塌机理分析及防治提供了基础理论支撑。更多还原

【Abstract】 The model of wellbore micro-fracture propagation is established based on the phase field method. The micro-fracture initiation, propagation, steering and other complex phenomena are found through numerical simulation. The influence laws of drilling fluid column pressure and natural fracture on wellbore micro-fracture propagation are analyzed. The collapse pressure preventing micro-fracture propagation is predicted. Results indicate that when the drilling fluid column pressure is low, the wellbore experiences the main stages of micro-fracture initiation, propagation, branch fracture generation and cross connection. As drilling fluid column pressure approaches collapse pressure, the number, length and propagation speed of micro-fracture on wellbore wall decrease. The energy required for initiation of natural fracture is lower than that of rock matrix, and the micro-fracture propagation speed is higher, which increases the collapse pressure of wellbore. When natural fracture connecting with wellbore is located in the azimuth of minimum horizontal stress and the angle is 45°, micro-fracture is easy to initiate and propagate and the risk of wellbore instability is great. The model based on phase field method not only visually simulates the process of micro-fracture propagation and collapse, but also its predicted collapse pressure is consistent with the actual drilling condition. The research provides basic theoretical support for mechanism analysis and prevention of wellbore collapse in fractured formation.更多还原