中文摘要：

油气田在开发中后期会发生储层压力衰竭，压力衰竭将导致储层地应力发生变化，进而影响钻井中的井壁稳定性。从压力衰竭对储层地应力的影响入手，结合压力衰竭地层的井周应力分布规律对安全钻井液密度窗口随压力衰竭程度的变化规律进行了研究。结果表明，在压力衰竭储层钻定向井时存在一个中性角，当井斜角小于中性角时，压力衰竭使安全钻井液密度窗口变宽；当井斜角大于中性角时，压力衰竭使安全钻井液密度窗口变窄；中性角的大小与地层压力衰竭程度无关，与钻井方位有关，保持井斜角小于中性角并远离水平最大地应力方向有利于压力衰竭地层的钻井安全。研究结果可以为油气田在不同压力衰竭时期的钻井设计提供参考。

英文摘要：

In the late development periods of many oil and gas fields, reservoir pressure decreased to depletion, and the pressure coefficient would be reduced less than 0.4. Formation pressure reduction would result in in-situ stress changes and cause the influence on wellbore stability in drilling. Based on the influence of pressure depletion on reservoir in-situ stress and stress distribution around the wellbore in depleted reservoir, this paper analyses the effect of pressure depleted on wellbore stability of directional wells. Calculation results shows that there is a neutral angle in depleted reservoir drilling, when inclination angle is smaller than the neutral angle, the safety window of drilling fluid density will become wider, and when inclination angle is larger than the neutral angle, the safety window of drill- ing fluid density will become narrower. The neutral angle has no relationship with the level of pressure depleted, but has relationship with azimuth angle, and keep inclination angle below the neutral angle and away from the azimuth of maximum horizontal principle stress is beneficial to drilling safety. It provides a reference for drilling designing in depleted reservoirs of different periods.