交变热载荷下水泥环缺陷对储气库井储层段套管的影响

Impact of cement sheath defects on casing in the reservoir section of gas storage well under alternating thermal load

敬俊 单鸿斌 祝效华 孙汉文 许尔跃

西南石油大学机电工程学院，四川 成都 610500 中海油服墨西哥公司，墨西哥 坎佩切州卡门 66550

College of Mechanical and Electronic Engineering, Southwest Petroleum University, Chengdu 610500, China COSL Mexico S.A. DE C.V., Carmen 66550, Mexico)

水泥环缺陷可能诱导储气库井储层段套管在循环注采条件下发生失效。为了揭示水泥环缺陷对储气库井储层段套管完整性的影响，基于弹性力学理论，在储气库井极限压力条件下，考虑循环注采引起的井筒交变热载荷，建立了“套管￣含缺陷水泥环￣地层”有限元模型。结合中国北部某储气库井作业工况，分别研究在注气（压力50 MPa、温度30 ℃）和采气（压力28 MPa、温度160 ℃）条件下，水泥环缺陷形态及其几何参数对储气库井套管应力分布状态的影响规律。结果表明：水泥环点蚀缺陷的环向开度、轴向长度及纵向裂纹的环向开度对套管安全性影响明显；横向剪切错断和微环隙导致套管安全性明显降低，在高温采气生产时套管最大应力接近P110的屈服强度；储气库井注采周期中，下限压力因温度和围压的影响对储层段套管安全性影响更明显，危及储气库井注采过程的安全运行。研究结果可为由生产井改建、新建储气库井储层段套管的完整性提供判断依据。

 Under the condition of continuous "injection-production" cycle, the casing in the reservoir section of gas storage well may be induced to failure by cement sheath defects. In order to reveal the influence of cement sheath defects on the integrity of casing in reservoir section of gas storage wells, based on the theory of elastic mechanics and considering the wellbore alternating thermal load caused by injection-production cycle, the finite element models of "casing-cement sheath with defects-formation" under the limit pressure in gas storage wells are established. Combined with the operating conditions of a gas storage well in northern China, the influence law of cement sheath defects morphology and geometric parameters on casing stress distribution in gas storage wells is studied under the conditions of gas injection pressure of 50 MPa with temperature of 30 ℃ and gas production pressure of 28 MPa with temperature of 160 ℃. The results show that circumferential opening angle and axial length of cement sheath′s corrosion defects and the circumferential opening angle of longitudinal crack have an obvious impact on the casing safety. Transverse shear and micro-cracks lead to a significant reduction in casing safety. It is close to the P110 yield strength in high temperature gas production. And in the injection-production cycle of gas storage well, the effect of lower limit pressure on the casing safety of the reservoir section is more obvious due to the influence of temperature and confining pressure, which endangers the safe operation of the gas storage well during the injection-production process. The research results can provide a judgment basis for the integrity of casing in reservoir section of gas storage wells reconstructed from production wells or newly built.

10.6056/dkyqt202304022