【摘要】 储气库注采井的注气与采气、环空带压与泄压等情况使井筒反复承受加载卸载,水泥环因此受到不同程度的损害,严重时导致地层气体窜入环空。为了研究注采井水泥环的破坏机理,针对某储气库B环空上部水泥环的工况条件,开展了水泥环承受8.1 MPa和13.6 MPa循环内压的实验模拟,并对水泥环进行了密封性、渗透率、SEM电镜扫描、微CT扫描分析,探究水泥环微裂缝和孔隙的变化情况。实验表明,8.1 MPa的内压循环30次未造成水泥环气窜,13.6 MPa的内压循环23次则导致气窜,与某储气库出现浅层气窜入B环空的情况相符;循环载荷可导致水泥环产生微裂缝,随着循环载荷压力值的增加,取样渗透率逐渐小幅度增加,微裂缝产生越多,裂缝扩展越大,甚至出现贯穿缝;微环隙由水泥环微观结构破坏持续累积造成,对于固井质量良好的环空,水泥环发生微观结构破坏是气窜的本质原因;水泥环微观结构破坏和界面产生微环隙均可直接引起气窜,主导者受多种因素影响而变化。实验结果揭示了循环载荷下注采井水泥环的破坏机理以及与气窜的关联性,对储气库运行优化和新建储气库的井筒质量控制具有指导意义。更多还原

【Abstract】 Gas injection and gas production from a gas storage well and pressure accumulation and unloading of the annular space of the well result in repeated loading and unloading of the wellbore, leading to the failure of the cement sheath, or even gas invasion from formation into the well. To study the failure mechanisms of the cement sheath of a gas injector(also acted as a gas producer), a laboratory experiment was conducted in which the cement sheath was subjected to the action of internal circulation pressure of 8.1 MPa and 13.6 MPa, according to the work conditions of the cement sheath in the upper part of the annular space B of a gas storage. The cement sheath was studied for the change of micro fractures and pores in it by analyzing its sealing property and permeability as well as SEM and CT analyses. In the experiment, there was no gas channeling through the cement sheath after 30 times of circulation at 8.1 MPa; when the circulation pressure was increased to 13.6 MPa, 23 times of gas channeling were found in 30 times of circulation. This experimental result is in accordance with the situation of shallow gas channeling into the annular space B. Cyclic loading may result in micro fractures in the cement sheath, and with the increase in the amplitude of the cyclic load, the permeability of the sheath sample increased at a small amplitude. The more the number of the micro fractures in the cement sheath, the wider and longer the micro fractures extended, and some micro fractures even ran through the whole sheath. Micro-annulus path around the cement sheath were resulted from the accumulation of failures of the micro structure of the cement sheath. For a well with high quality cementing job, the failure of the microstructure of the cement sheath is essentially the cause of gas channeling. Microstructure failure in a cement sheath and micro-annulus path around the cement sheath both can directly result in gas channeling, though the dominant cause of the gas channeling is affected by many factors. The experimental results have revealed the mechanisms of failure of the cement sheath under cyclic loading in a gas injection and producing well and the relevance between the cyclic loading and gas channeling, and are of instructive significance on the optimization of gas storage operation and quality control of the wellbore of a new gas storage.更多还原