页岩层理对水平井井壁稳定的影响

中国南方海相页岩气区硬脆性页岩储层层理/裂缝发育，层理性页岩水平井钻井井壁坍塌问题已严重制约页
岩气勘探开发进程。为此，以线弹性井壁稳定力学模型和单一弱面强度理论为基础，建立了考虑页岩层理产状、层理
弱面强度、岩石强度、水平井方位、强度弱化（含水量）等因素影响的层理性页岩水平井井壁稳定模型。在此基础上定
量分析了层理产状和含水量对水平井井壁坍塌压力的影响。结果表明：坍塌压力与层理面产状、井眼方位关系密切，
地层倾角0°<θDIP<15°、75°<θDIP<90° 时有利于水平井井壁稳定；页岩层理弱化是导致井壁坍塌失稳的重要原因，无论
层理产状如何变化，随着层理含水量的增加，井壁坍塌压力迅速增加，坍塌压力增量约为4.30～22.62 MPa，含水量20%
时坍塌压力增幅可达100%。

Influence of Shale Bedding Plane on Wellbore Stability for Horizontal Wells

Brittle shale formation developed a lot of bedding plane and microfissuring in marine shale gas region of South
China. Borehole collapse problem of horizontal well in bedding plane formation has seriously hampers the development process.
Therefore based on the linear elastic mechanics model of borehole stability and the single weak-plane strength theory，the
borehole stability model for horizontal wells in bedding plane formationis is established. It considers influence of the attitude
of bedding plane，strength of weak bedding plane，rock strength，horizontal azimuth，weakening of bedding plane（water
cuts）and etc. Based on these，this paper quantitatively analyzed the effects of attitude of bedding plane and water cuts. The
results show that collapse pressure is controlled by attitude of bedding plane and horizontal azimuth，and that the borehole
stability of horizontal well is better when dip angle of bedding is 0°<θDIP<15° and 75°<θDIP<90°. Bedding weakening is one
of the important factors，which lead to borehole collapse.No matter how attitude of bedding plane change，with water cuts of
bedding increase，borehole collapse pressure increases rapidly，and the increase range of collapse pressure is about 12～18 MPa.
When the water cuts is 20%，collapse pressure increases by 37.9%.