水力压裂过程水泥环本体裂缝扩展规律研究

Study on Fracture Propagation Mechanism in Cement Ring Bodies during Hydraulic Fracturing Process

摘要: 基于多孔介质–流固耦合方程和CZM (Cohesive Zone Method)方法建立了水力压裂过程中水泥环裂缝扩展的有限元模型，研究地应力、水泥环泊松比、水泥环弹性模量对水泥环本体裂缝扩展长度和压力等参数的影响揭示裂缝扩展规律。结果显示：随着压裂的不断进行，本体裂缝扩展长度有所增加；在压裂液注入初期，水泥环本体裂缝在轴向上迅速扩展；缝口压力在数秒内会急剧上升并在之后稳定在较低水平；随着X方向地应力的增大，水泥环本体裂缝在轴向上的扩展长度呈减少趋势；水泥环泊松比越大，本体裂缝轴向扩展长度越小；随着水泥环弹模量的增大，本体裂缝的轴向扩展距离增大。

Abstract: A finite element model for cement annulus crack propagation during hydraulic fracturing was established based on the porous medium-fluid-solid coupling equations and the Cohesive Zone Method (CZM). The study investigated the effects of in-situ stress, cement annulus Poisson’s ratio, and cement annulus elastic modulus on parameters such as crack propagation length and pressure within the cement annulus body, revealing the crack propagation mechanism. Results indicate that as fracturing progresses, the propagation length of the body crack increases. During the initial stage of fracturing fluid injection, the axial crack length within the cement annulus expanded rapidly; the fracture tip pressure surged sharply within seconds before stabilizing at a lower level; as the X-direction in-situ stress increased, the axial crack length within the cement annulus exhibited a decreasing trend; a higher Poisson’s ratio of the cement annulus resulted in a smaller axial crack length; and as the elastic modulus of the cement annulus increased, the axial crack length within the annulus also increased.