Study on Wellbore Instability of Bedded Shale Gas Horizontal Wells under Chemo-Mechanical Coupling
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摘要:
针对现有页岩气水平井井壁稳定力化耦合分析大都仅考虑水化作用对岩石强度的影响，鲜有考虑水化应力应变影响的情况，以弹性力学和岩石力学等理论为基础，同时考虑水化作用对岩石力学参数的弱化效应和附加水化应力，建立了力化耦合作用下层理性页岩气水平井井壁坍塌压力预测模型，研究了层理性页岩气水平井井壁失稳机理，分析了影响井壁稳定的因素及影响规律。研究结果表明：存在层理面时，会使坍塌压力大幅升高；沿层理面方位钻进，井壁稳定性最好；当水化时间一定时，坍塌压力随距井壁径向距离增加而降低，水化时间越长，近井壁处易坍塌区域越大；考虑水化应力影响后坍塌压力会大幅升高，在设计钻井液密度时，不能忽略水化应力的影响。研究成果丰富了页岩气水平井井壁失稳理论，对层理性页岩气水平井钻井设计具有指导作用。
Abstract:In view of the fact that most of the existing chemo-mechanical coupling analysis of the wellbore stability in shale gas horizontal wellsonly considered the influence of hydration on rock strength, but rarely considered the influence of hydration strain and stress, this paper, based on the theories of elasticity and rock mechanics, and by considering the weakening effect of hydration on rock mechanical parameters and the additional hydration stress, established the prediction model of wellbore collapse pressure of bedded shale gas horizontal wells under chemo-mechanical coupling, studied the mechanism of wellbore instability of bedded shale gas horizontal wells, and analyzed the factors affecting wellbore stability and their influencing laws. The results showed that when there was a bedding plane, the collapse pressure would increase greatly; the wellbore stability was the best when drilling along the bedding plane; when the hydration time was fixed, the collapse pressure would decrease with the increase of the radial distance from the wellbore, and the longer the hydration time was, the larger the area near the wellbore that was prone to collapse would be; and after considering the influence of the hydration stress, the collapse pressure increased greatly, sothe influence of hydration stress could not be ignored when designing the drilling fluid density. The research results enriched the wellbore instability theories of shale gas horizontal wells, and played a guiding role in the drilling design of bedded shale gas horizontal wells.
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Key words:
- shale gas /
- horizontalwell /
- hydration /
- bedding plane /
- hole stabilization /
- collapse pressure
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图 3 考虑与不考虑水化应变时的坍塌压力当量密度（iw=45°，αw=45°）
Figure 3. Equivalent density of collapse pressure with and without considering hydration strain (iw=45°，αw=45°)
图 4 不同条件下的坍塌压力当量密度
Figure 4. Equivalent density of collapse pressure under different conditions
图 5 不同地应力机制下坍塌压力当量密度随井斜角和方位角的变化规律
Figure 5. Variation of equivalent density of collapse pressure with deviation angle and azimuth under different crustal stress mechanisms
图 6 不同井斜角和方位角下层理面产状对坍塌压力当量密度的影响
Figure 6. Effect of bedding occurrence on equivalent density of collapse pressure under different deviation angle and azimuth
图 7 不同含水量下坍塌压力当量密度随井斜角和方位角的变化规律
Figure 7. Variation of equivalent density of collapse pressure with deviation angel and azimuth under different water cut
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