考虑有效膜压力的坍塌压力计算模型

发布时间：2019-05-19 21:42

【摘要】：川渝气区风险探井欠平衡井段的井眼扩径率普遍较高,井眼扩径率介于20%~30%,最高可达140%,增加了风险探井的钻探风险,而且欠平衡钻井井壁稳定的问题也尚未得到有效解决。为此,针对欠平衡井段井壁失稳机理开展了研究,提出了计算欠平衡钻井井壁坍塌压力的方法:通过引入有效膜压力系数,结合达西定律、地层流体状态方程、连续性方程,求解出井周压力分布解析解;依据叠加原理得到了井周应力分布模型,并采用Mohr-Coulomb准则推导出维持井壁稳定的最低钻井液密度计算模型;研究了欠平衡、过平衡、欠平衡转过平衡3种典型工况下的井周压力演化规律,并总结了欠平衡钻井井壁失稳的规律。结论认为:该模型反映了泥饼对井壁稳定的影响,由其计算得到的坍塌压力比常规模型计算所得的结果要高,说明有效膜压力系数对井壁坍塌的影响显著,而岩石强度(内聚力、内摩擦角)、地应力、岩石孔隙度等参数对井壁坍塌的影响则相对较小,采用该模型计算的结果更加符合现场实际。
[Abstract]:The hole expansion rate of the underbalanced well section of risk exploration wells in Sichuan and Chongqing gas area is generally high, the hole expansion rate is between 20% and 30%, and the highest can reach 140%, which increases the drilling risk of risk exploration wells. Moreover, the problem of shaft wall stability in underbalanced drilling has not yet been effectively solved. In this paper, the mechanism of wellbore instability in underbalanced well section is studied, and a method for calculating wellbore collapse pressure in underbalanced drilling is put forward: by introducing effective membrane pressure coefficient, combining Darcy's law, formation fluid equation of state and continuity equation, The analytical solution of pressure distribution around the well is solved. According to the superposition principle, the stress distribution model around the well is obtained, and the minimum drilling fluid density calculation model for maintaining wellbore stability is derived by using Mohr-Coulomb criterion. The evolution law of wellbore pressure under three typical working conditions of underbalanced, overbalanced and underbalanced is studied, and the law of wellbore instability in underbalanced drilling is summarized. It is concluded that the model reflects the effect of mud cake on wellbore stability, and the collapse pressure calculated by the model is higher than that calculated by the conventional model, which indicates that the effective membrane pressure coefficient has a significant effect on the wellbore collapse. However, the influence of rock strength (cohesion, internal friction angle), ground stress, rock porosity and other parameters on wellbore collapse is relatively small, and the results calculated by this model are more in line with the field reality.
【作者单位】：中国石油西南油气田公司勘探事业部;中国石油西南油气田公司输气管理处;"油气藏地质及开发工程"国家重点实验室·西南石油大学;中国石油川庆钻探工程公司钻采工程技术研究院;
【基金】：国家重点基础研究发展计划(973计划)项目“页岩气水平井钻完井关键基础研究”(编号:2013CB228003) 四川省科技创新苗子工程培育项目[编号:XNSIIJS(2014)51] 四川省国际科技合作与交流研究计划项目(编号:2016HH0001)
【分类号】：TE24

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