Horizontal drilling is an effective way to increase the capacity of shale formations. However, in the horizontal shale drilling, the major difficulties are the problems of the wellbore stability and the well collapse prevention. In this paper, a jointed-material model is adopted to simulate the strength anisotropy and the permeability anisotropy of the bedding shale. The model is used to obtain the distribution of the plastic regions in the vicinity of the well under the condition that the stress state matches the failure criterion. The shale permeability anisotropy also contributes to the nonuniform propagation of pressure in the formation. The model is applied to study the wellbore stability law of a shale gas well in the Longmaxi formation in Sichuan Basin, China. It is shown that the drilling fluid preferably invades in the bedding plane, resulting in a higher pore pressure in the bedding plane than that in the adjusting layers. The lower strength of the bedding shale weak planes could create four plastic shear failure locations around the wellbore. This tendency is different from the normal dog-ear-shaped breakout. The study also shows that the sealing performance of the drilling fluid plays an important role in maintaining the wellbore stability. If the wellbore wall is perfectly penetrated, the increased mud weight will enlarge the plastic zone area around the well and increase the drilling risks.

水平钻井是提高页岩地层产能的有效途径。然而，在页岩水平钻井中，主要困难是井筒稳定性和防塌问题。本文采用节理材料模型模拟层理页岩的强度各向异性和渗透率各向异性。该模型用于在应力状态与破坏准则相匹配的条件下，获得井附近塑性区域的分布情况。页岩渗透率各向异性也有助于地层中压力的不均匀传播。该模型应用于四川盆地龙马溪组页岩气井井筒稳定性规律研究。表明钻井液优选侵入层理面，导致层理面的孔隙压力高于调整层的孔隙压力。层理页岩薄弱面的较低强度可能在井筒周围产生四个塑性剪切破坏位置。这种趋势不同于正常的狗耳形突破。研究还表明，钻井液的密封性能对维持井筒稳定性具有重要作用。如果井壁完全穿透，增加的泥浆重量会扩大井周围的塑性区面积，增加钻井风险。研究还表明，钻井液的密封性能对维持井筒稳定性具有重要作用。如果井壁完全穿透，增加的泥浆重量会扩大井周围的塑性区面积，增加钻井风险。研究还表明，钻井液的密封性能对维持井筒稳定性具有重要作用。如果井壁完全穿透，增加的泥浆重量会扩大井周围的塑性区面积，增加钻井风险。