二叠系火成岩地层井壁稳定性分析

Analysis on wellbore stability in Permian igneous rock formation

火成岩地层是井壁失稳的高危地层,目前针对火成岩井壁稳定性研究缺乏系统分析。基于此,考虑火成岩结构,形成了多结构面强度准则,利用准则构建火成岩地层坍塌压力预测方法,分析该类地层井壁稳定性。研究结果表明:火成岩弱结构面发育,易导致岩石沿结构面破坏,从而降低岩石强度;结构面存在时,坍塌压力分布复杂,尤其弱面数量增多,岩石强度逐渐受弱面控制,坍塌压力显著上升;同时,水化作用也会导致地层坍塌压力增加;水化与弱结构面是火成岩地层井壁失稳的主要因素,考虑两者耦合作用是建立井壁稳定技术的关键。

The igneous rock formation is the high risk formation of wellbore instability, and the systematic investigation on the wellbore stability in the igneous rock formation was lacking. Therefore, the strength criterion of multiple structural planes was formed considering the structure of igneous rock, then the prediction method of collapse pressure in the igneous rock formation was constructed by using the criterion, and the wellbore stability in this type of formation was analyzed. The results showed that the weak structural plane of igneous rock developed, which was easily to cause the rock failure along the structural plane, thus reduce the rock strength. Due to the existence of structural plane, the distribution of collapse pressure was complicated, especially, the number of weak plane increased, and the rock strength was gradually controlled by the weak plane, then the collapse pressure increased obviously. Meanwhile, the hydration effect would lead to the increase of collapse pressure in the formation. The hydration and weak structural plane were the main factors of wellbore instability in the igneous rock formation, and considering their coupling effect was the key to establish the wellbore stability technology.