川南龙马溪页岩地层井壁失稳实验研究

川南地区页岩气开采是我国页岩气发展的重点工程,然而其主要产气层龙马溪页岩地层的井壁失稳问题十分严重,影响了该地区页岩气藏勘探开发的进程。基于室内试验的方法对页岩矿物组成、微观结构和理化性质进行了归纳分析;并对流体作用下,页岩力学性质变化进行了研究,分析了页岩的稳定性。实验结果表明:龙马溪页岩属于典型的硬脆性页岩,以伊利石为主,具有弱膨胀性。微裂缝发育明显,为流体侵入的主要通道。流体侵入后,导致微裂缝扩展延伸,页岩岩石整体强度减弱,从而影响井壁稳定。

Table1 Mineral composition of Longmaxi shale

The shale gas in south Sichuan is the priority project in the development of shale in China. But the major gas reservoir in Longmaxi formation has serious wellbore instability problems that have negative influence on gas exploration in this area. Based on the laboratory experiment, we conclude the mineral composition of shale, micro instruction and physical-chemical property, do the research on the change of shale mechanics under the influence of fluid and analysis the shale stability. The consequence indicates: the shale in Longmaxi is typical hard brittle rock, is mainly composed by illite and have weak dilatability. The micro fracture exists prosperously and is major access for fluid. The fluid invades rock and makes micro fracture expand, causing the decrease of rock strengthen and wellbore instability.