基于流-固耦合法的砂泥岩储层压裂裂缝延伸规律研究

Research on Fracturing Fracture Propagation Law in Sand-mud Thin Interbed Formation Based on Fluid-solid Coupling

基于多孔介质流-固耦合的基本方程,建立起砂泥岩储层压裂裂缝扩展的三维有限元模型,利用cohesive黏结单元模拟压裂过程中裂缝起裂、扩展造成的损伤,定量描述裂缝延伸规律。模型计算结果显示,砂泥岩储层裂缝缝宽剖面呈“S”型,泥岩夹层裂缝宽度较砂岩缝宽小20%~35%,施工排量与砂泥岩层应力差对裂缝宽度影响较大,建议砂泥岩储层施工排量范围为3.5-4.0m3/min。在应力差高于4 MPa的砂泥岩储层,考虑夹层厚度的条件下优先实施分层压裂。

A three-dimensional finite element model of the fracturing fracture propagation in sand-mud interbed reservoir is establishedbased on the basic equations of fluid-solid coupling. The damage caused by the initiation and propagation of the crack in fracturingprocess is simulated by using cohesive bonding unit to quantitatively describe the extension of the crack. The simulation result showsthat, the width of the fracturing crack in the sand-shale interbed reservoir is ＂S＂-shaped, and the crack width in mudstone layers is less20% -35% than that in sandstone layers ,which reveals the sand blocking mechanism of sand-shale reservoir in fracturing process. Theanalysis of the influencing factors of fracturing crack morphology shows that the flow rate in fracturing construction and the stress differ-ence in the sand-shale interbed reservoir have a great influence on the crack width, it is suggested that the fracturing flow rate in thesand-shale interbed reservoir is 3.5 -4.0 m3/min. For the sand-shale reservoir in which the stress difference is higher than 4 MPa, thelayered fracturing technology is preferred considering the condition of interlayer thickness.