循环载荷对水泥环密封性影响试验与数值研究

为准确量化循环载荷对井筒水泥环密封性的影响,基于页岩气井多级压裂过程中套管内压多次升高和降低的实际情况,开展了高温三轴循环载荷作用下水泥石岩心应力-应变试验,建立了套管-水泥环-地层组合体数值模型,基于Mohr-Coulomb准则和损伤理论,计算了多级压裂过程中循环载荷作用下水泥环内边界处等效塑性应变量.分析结果表明:...

Experimental Study and Numerical Analysis of the Influence of Cyclic Loading on the Cement Sheath Sealing Performance

In order to accurately quantify the influence of cyclic loading on the cementing performance of cement sheath,core stress-strain test of set cement under the action of high-temperature triaxial cyclic loading is carried out based on the actual situation that the internal casing pressure goes up and down many times in the process of multi-stage fracturing in shale gas wells.The numerical model of casing-cement sheath-formation combination is established.And the equivalent plastic strain magnitude at the inner boundary of cement sheath under the action of cyclic loading in the process of multi-stage fracturing is calculated according to Mohr-Coulomb criterion and damage theory.The results show that the accumulated plastic strain on the set cement is significant and the initial plastic strain magnitude is the greatest and then increases linearly.In the process of multi-stage fracturing,accumulated plastic strain is likely to occur at the cementing interface of cement sheath and casing and the initial plastic strain magnitude is the greatest and then increases linearly,which is better accordant with the test results.It is favorable to reduce the accumulated plastic strain magnitude and ensure the sealing integrity of cement sheath by decreasing Young’s modulus and increasing Poisson’s ratio,cohesive stress and internal frictional angle of the set cement.