体积压裂过程中固井界面微环隙扩展的数值模拟

射孔完井作业中射孔会对水泥环完整性造成破坏,尤其是固井界面微环隙的产生,导致后续压裂过程中出现环空带压与环空窜流的问题。针对此问题,建立压裂过程中水泥环界面微环隙扩展三维模型,通过Cohesive单元损伤模型模拟固井界面在体积压裂过程中微环隙的扩展,对界面微环隙的扩展长度进行分析计算,研究不同参数对压裂过程中固井界面失封长度的影响。结果表明:适当降低水泥环弹性模量,提高水泥石与套管、地层的胶结强度有利于减小水泥环界面微环隙扩展长度,保证水泥环有效封固;研究结果能够对体积压裂条件下的水泥环封固性能进行评价和预测。

Numerical simulation on micro-annulus propagation of cementing interface during hydraulic fracturing

During well completion,perforation can cause damage to the integrity of cement sheath,especially the debonding of cement interface and the micro-annulus induced can lead to problems of crack propagation and annulus turbulence in sequential hydraulic fracturing process.In this study,a three-dimensional model was established in order to simulate the crack propagation of cement interface during volume fracturing process based on a Cohesive element damage model.The interface debonding length was analyzed and calculated and its influencing factors during the fracturing process were investigated.The simulation results show that it is beneficial to reduce the crack propagation length of the cement sheath interface by decreasing the elastic modulus of cement and increasing the cohesive strength of casing-cement and cement-formation interfaces,thus ensuring an effective sealing of the cement sheath.The model can be used to evaluate and predict the sealing performance of the cement sheath under volume fracturing conditions,and also can provide guidance for the design of the fracturing scheme.