Annulus Pressure Analysis of a Shale Gas Well under Varied Temperatures and Pressures
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摘要: 为解决页岩气井环空带压的问题，进行了压裂及生产过程中温度和压力变化对页岩气井环空带压影响的力学分析。以弹性力学为基础，建立了页岩气井直井段双层套管系统的力学模型，基于界面上应力相等及位移连续条件，推导了各界面的径向应力计算方程，并讨论了套管内压、温度、地应力等因素对水泥环封隔能力的影响规律。研究结果表明：温度升高、内压及地应力增大、水泥环弹性模量增大均有利于提高水泥环的封隔能力，减小套管壁厚有利于增加界面的径向应力；随着井深的增加，界面径向应力变大，水泥环封隔能力增强，提高直井段下部水泥环的封隔能力是降低井口环空带压风险的关键；第一界面和第二界面是固井失效的危险点，提高第一、第二界面的固井质量，有利于降低形成环空带压的风险。Abstract: With consideration of the severe problems related to annulus pressure in shale gas wells,mechanical analysis were performed to clarify the impact of changes in temperatures and pressures during fracturing and production on the annulus pressure in shale gas wells.According to elastic mechanical theories,a mechanical model of a double casing system was established.The formula in calculating the stress of each contact surface was derived based on a displacement continuity condition.In addition,the impact of casing internal pressures,temperatures and in-situ stresses on the sealing ability of a cement sheath were reviewed.Research results suggest that the increase in temperatures,internal pressures,in-situ stresses,and elastic modulus of cement are beneficial and may improve the sealing ability of the cement sheath.On the other hand,decreasing casing thicknesses can be damaging because it increases the radial stress on the interfaces.Radial stresses on interfaces may increase with well depths,so the key to relieving the annulus pressure in the wellhead is to improve the sealing ability of the cement in the lower section of the vertical well.The first and second interfaces are the dangerous positions and they are where there is maximum risk of cementing failure.Improving the cementing quality of the first and second interfaces is helpful in reducing the risk of annulus pressure generation.
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Keywords:
- temperature /
- pressure /
- shale gas well /
- annulus pressure /
- double layer casing /
- cement sheath /
- radial stress
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