井底应力场对气体钻井井斜的影响

建立了油气井钻井过程中的井底力学模型,该力学模型考虑了井眼内压力、岩石节理、井眼深度、地应力、岩石材料特性、井眼直径等影响因素,并讨论了各个因素对井底应力场的影响,阐明了气体钻井时井底应力场分布变化对井眼井斜的影响.气体钻井时井眼内的压力远小于井眼周围的围压,井底会出现很大的拉应力,岩石容易破坏,因此,气体钻井时钻井速度远远大于钻井液钻井,但拉应力越大,井眼与岩石节理面交接处产生的应力集中越大,应力集中处岩石更容易破坏,也更易产生井斜.气体钻井时井底的应力状态对地层倾角、材料特性、井眼直径、井眼深度及初始地应力的变化较钻井液钻井时更敏感.

Effects of stress field in bottom hole on borehole deviation during gas drilling

A mechanical model of bottom hole was set up, considering affecting factors such as subsurface pressure, joints, hole depth, geostress, material behavior, diameter of borehole and so on. The effects on stress field in bottom hole of those factors on the stress ficrd of bottom bole are discussed; and the effects on borehole deviation of stress field in bottom hole while gas drilling are also expounded. The Pressure in downhole is far less than ambient pressure while gas drilling. There will be large tensile stress at bottomhole; and the rock is easy to destroy, so, drilling speed of gas drilling is far more than that of fluid drilling; but while tensile stress is larger, the stress concentration at interface between downhole and joint plane is larger. The rock at stress concentration is easy to be destroyed and deviated. The stress status of gas drilling is more sensitive to the change of dip angle, material property, diameter, depth and original stress than that of fluid drilling.