页岩气地层纳微米孔隙结构特征及封堵实验评价

目前水平井段井壁失稳是制约页岩气资源钻探开发进程的主要技术难题之一。针对上述技术难题,采用低压氮气吸附与高压压汞实验,分析了硬脆性页岩的微纳米孔隙结构特征,探讨了微纳米孔隙结构特征对页岩气地层井壁稳定性的影响。利用压力传递实验,开展了页岩微纳米尺度裂缝封堵评价实验。研究表明,页岩气地层的井壁失稳与其自身的微纳米孔隙结构特征具有密切关系,微纳米尺度裂缝发育是导致页岩气地层井壁失稳的内在主要因素;在此基础上,提出了页岩气协同稳定井壁钻井液技术对策,其中强化封堵页岩微纳米尺度裂缝是解决页岩气地层井壁失稳的关键技术措施。进一步优选了新型微纳米封堵剂,其粒径在80~200 nm之间呈"单峰"分布,能够有效封堵页岩微纳米尺度裂缝,阻缓压力传递与滤液侵入,增强裂缝性页岩井壁稳定性。

The characteristic analysis of micro-nano pore structure in shale gas formation and its sealing evaluation

Wellbore instability in the horizontal drilling process significantly restricted exploration and development of shale gas. In order to solve these technical problems, the low-pressure nitrogen adsorption and high-pressure mercury intrusion techniques were adopted for micro-nano pore structure characterization and effect of micro-nano pore structure characteristic on gas shale stability was investigated. The micro-nano scale fracture plugging tests were also conducted using pore pressure transmission experiment. It was found that wellbore instability of gas shale is closely related to its micro-nano pore structure characteristics, and micro-nano scale fractures are the main controlling factors. Wellbore strengthening principles for gas shale wellbore stability were put forward, and enhancing sealing performance of drilling fluids to plug micro-nano scale fractures is key point to solve wellbore instability problems during gas shale horizontal drilling. Based on the principle above, micro-nano plugging agent as physical shale stabilizer was optimized, and it could be deformable to internally bridge and seal micro-nano scale fractures, thus reducing fluid pressure penetration into shale matrix to impart superior shale stability.