基于震源机制的页岩气压裂井套管变形机理

Research on casing deformation for shale gas wells based on focal mechanism

郭雪利 李军 柳贡慧 陈朝伟 任凯 来东风4

中国石油大学（北京）石油工程学院，北京 102249 北京工业大学，北京 100124 中国石油集团钻井工程技术研究院，北京 102206 中国石油冀东油田分公司勘探开发建设项目部，河北 唐山 063200

College of Petroleum Engineering, China University of Petroleum, Beijing 102249, China Beijing University of Technology, Beijing 100124, China CNPC Drilling Research Institute, Beijing 102206, China Exploration and Construction Project Department, Jidong Oilfield Company, PetroChina, Tangshan 063200, China

在页岩气多级压裂过程中，断层滑动是导致套管变形的重要因素。震源机制可以较为准确地刻画断层参数，高应力降、高矩震级和低剪切模量会增加断层滑动距离。文中分析了断层力学状态，明确了断层滑动的力学机理，基于震源机制原理，利用现场微地震数据反演了断层滑动距离。在此基础上利用分步有限元建模方法建立组合体模型，对断层夹角、断层滑动距离、水泥环弹性模量、水泥环和套管厚度进行了敏感性分析。模型计算结果与现场套管变形量较吻合。研究表明：断层与井眼夹角为45°时，套管应力和变形量达到最大值；滑动距离为50 mm时，套管最大变形量可达35 mm；若断层发生滑动，则水泥环弹性模量、厚度以及套管壁厚等参数的调整都很难保证套管安全。因此，压裂施工之前，必须对页岩储层的断层分布有清晰认识，避免在断层发育部位施工，以保证套管安全。

During the multi-stage fracturing process of a shale gas well, fault slippage is an important factor causing casing deformation. Fault parameters can be accurately described by the focal mechanism. High stress drop, high moment magnitude and low shear modulus increase the sliding distance. In this paper, the fault mechanics condition and the fault slip mechanism were analyzed. Based on the principle of focal mechanism and the micro-magnitude data of the shale gas play, the fault slip distance was calculated. Considering temperature-pressure coupling, the assembly model was established by using the stage finite element procedure. Sensitivity analysis was carried out considering the angle of fault, the fault slippage distance, the elastic modulus of cement sheath, and the thickness of cement sheath and casing. The casing deformation was in good agreement with the actual casing deformation. The results show that when the angle between the fault and wellbore is 45°, the stress and deformation of casing reach the maximum. When the slippage distance is 50 mm, the maximum deformation of the casing could reach up to 35 mm. Under the condition of fault slippage, changing parameters cement such as sheath modulus, cement sheath thickness, and casing thickness cannot ensure the safety of casing. Before fracturing, it is necessary to have a clear understanding of the fault distribution in a shale reservoir and to avoid construction near the place with large fault to ensure the casing safety.

10.6056/dkyqt201805026