多级压裂水泥环界面密封失效数值模拟

四川地区页岩气开发过程中环空带压现象严重,严重影响页岩气井的高效开发,因此准确了解页岩气井多级压裂过程中固井界面微环隙的产生机理具有重要意义。考虑到页岩气改造压裂级数多的特点,采用有限元方法,基于内聚力单元,构建了周期载荷作用下的水泥环界面密封性评价数值模型,研究了多级压裂过程中的水泥环界面胶结失效演变规律。研究结果表明:第一次循环结束后,后期循环加载过程中水泥环界面位移的累计增长程度较小,控制水泥环初次加载过程中的塑性变形可以提高维持水泥环密封完整性的压裂次数;降低水泥环弹性模量,适当提高水泥环的泊松比可以有效增加水泥环的长期密封能力,进而降低多级压裂过程中油气井环空带压的现象。研究成果可为页岩气井多级压裂过程中油气井环空带压的有效控制提供理论参考。

Numerical Simulation Study on Interface Seal Failure of Cement Sheath During Multistage Fracturing

During the development of shale gas in Sichuan, China, the annulus pressure phenomenon is serious, which seriously affects the efficient development of shale gas wells. Therefore, it is of great significance to accurately understand the mechanism of micro-annulus formation at cementing interface in multi-stage fracturing process of shale gas wells. Considering the characteristics of shale gas reforming and fracturing series, this paper uses the finite element method to construct a numerical model of cement ring interface sealing evaluation under cyclic loading based on Cohesive Cohesive unit, and studies the multi-stage fracturing process. The evolution law of cementation failure of cement ring interface. The results show that after the end of the first cycle, the cumulative growth of cement ring interface displacement during the late cyclic loading process is small, and controlling the plastic deformation during the initial loading of the cement ring can improve the number of fracturing to maintain the integrity of the cement ring seal; Reducing the elastic modulus of the cement ring and appropriately increasing the Poisson"s ratio of the cement ring can effectively increase the long-term sealing ability of the cement ring, thereby reducing the annulus pressure of the oil and gas well during the multi-stage fracturing process. The research results can provide a theoretical reference for the effective control of the annulus pressure of oil and gas wells in the multi-stage fracturing process of shale gas wells.