层理性地层钻井稳定性分析模型

针对钻井工程常遇的层理性地层，以应力张量坐标转换关系和井孔应力集中方程为基础，引入弱面剪切滑动和岩体Mogi-Coulomb双强度准则，建立了分析层理性地层井壁稳定性的模型。对含层理弱面的典型油气储层中钻井的合理钻井液密度和安全钻井方向进行研究，结果表明：层理面的存在加剧了井壁围岩的破坏，且改变了围岩破坏的位置；水平井坍塌压力随着钻井方向变化而连续性变化，其在特定钻井方向取得最小坍塌压力；斜井取得最小坍塌压力的方位与层理面在空间中并不垂直，空间中关于主平面对称的斜井破裂压力相同；既可获得较大钻井液安全压力窗口又可取得较小坍塌压力的方向为优选钻井方向，在钻井液压力窗口变化大的倾向上钻井需严格控制钻井轨迹曲线。

Analysis Model of Borehole Stability in Bedding Formations

Bedding formations are often encountered in drilling operations. On the basis of the stress tensor coordinate transforming relation and the borehole stress concentration equation, both the weak-plane shear slip criterion and rock mass Mogi-Coulomb criterions are introduced to build an analysis model for borehole stability. Researches on the reasonable drilling fluid density and safe drilling direction in typical reservoirs show that the existence of bedding plane significantly aggravates the rock damage and changes the damage position on the borehole wall; the collapse pressure of horizontal well continually varies along with the changes of drilling direction, thus the minimum collapse pressure is obtained in a particular drilling direction; in the inclined borehole, the minimum collapse pressure direction acquired is not vertical to the bedding plane experimentally, while the symmetrical inclined boreholes about principal planes have the same fracture pressure in space; the optimum drilling direction is the one with both larger safe density window of drilling fluid and smaller collapse pressure, and the drilling trajectory curve should be controlled strictly in the azimuth where the density window of drilling fluid changes greatly.