循环载荷作用下微环隙的产生及演变

Emergence and evolution of micro-annulus under cyclic loading

席岩 李军 陶谦 曾夏茂 钟文力4

北京工业大学建工学院，北京100124 中国石油大学（北京）石油工程学院，北京 102249 中国石化石油工程技术研究院，北京 100101 中石化西南石油工程有限公司固井分公司，四川 德阳 618003

College of Architecture and Civil Engineering, Beijing University of Technology, Beijing 100124, China College of Petroleum Engineering, China University of Petroleum, Beijing 102249, China Research Institute of Petroleum Engineering, SINOPEC, Beijing 100101, China Southwest Oilfield Service Corporation Cement Branch, SINOPEC, Deyang 618003, China

针对页岩气井多级压裂过程中出现的环空带压问题，运用力学实验手段以及数值分析方法，明确了导致B环空带压的主控因素，分析了循环载荷作用下直井段、斜井段、水平段Ⅰ，Ⅱ界面微环隙产生和演变的过程。实验结果表明：循环载荷作用下水泥石产生了累积塑性应变，初始塑性应变最大（0.28%），后续呈近似线性增长，20次循环后达0.65%。全尺寸水泥环密封能力评价实验表明，B环空Ⅰ界面在14个循环加卸载后监测到气体。数值模拟结果与实验结果具有较好的一致性。降低套管内压、降低弹性模量至2～4 GPa、提高泊松比至0.27以上，有利于保持水泥环密封完整性。研究成果可为压裂过程中水泥环密封完整性设计及控制提供参考，并具有重要的理论和工程意义。

Aiming at the problem of sustained casing pressure occurred during multistage fracturing in the shale gas horizontal wells, mechanical experiments and numerical analysis were carried out to analyze the process of generation and evolution of the micro-annulus at the first and second interface in the vertical, inclination and horizontal sections, in order to definite the main controlling factor in B annulus. The experimental results show that accumulated plastic deformation occurred in cement under the cyclic loading, and the initial plastic deformation was maximum(0.28%). The plastic deformation grew linearly and it could reach 0.65% after 20 cycles. The test results of full size cement sheath sealing ability evaluation device indicated that the gas was monitored at the first interface in the B annulus after 14 cycles. The numerical simulation results were in good consistency with the experimental results. Decreasing the casing inner pressure, reducing the elasticity modulus to 2￣4 GPa and increasing the poisson ratio(more than 0.27) were beneficial to protect the integrity of the cement sheath. The research results can offer the reference to the design and control of cement sheath seal integrity for fracturing, and were of theoretical and engineering significance.

10.6056/dkyqt202004024