页岩自封闭性与页岩气保存的微观机理研究

Study on the micro mechanism of shale self-sealing and shale gas preservation

郭旭升 胡东风 俞凌杰 卢龙飞 何陈诚 刘伟新 陆现彩

GUO Xusheng HU Dongfeng YU Lingjie LU Longfei HE Chencheng LIU Weixin LU Xiancai

中国石化 石油勘探开发研究院, 北京 102206 页岩油气富集机理与高效开发全国重点实验室, 北京 102206 中国石化 勘探分公司, 成都 610041 中国石化 油气成藏重点实验室, 江苏 无锡 214126 南京大学 地球科学与工程学院, 南京 210046

SINOPEC Petroleum Exploration and Production Research Institute, Beijing 102206, China State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Efficient Development, Beijing 102206, China SINOPEC Exploration Company, Chengdu, Sichuan 610041, China SINOPEC Key Laboratory of Petroleum Accumulation Mechanisms, Wuxi, Jiangsu 214126, China School of Earth Science and Engineering, Nanjing University, Nanjing, Jiangsu 210046, China

为加快页岩气的勘探开发，围绕页岩自封闭性阐述了页岩气保存的微观机理。页岩层系的自封闭能力主要与其纳米喉道为主的低连通性、束缚水赋存引起的低速扩散和毛细管力封闭、埋藏条件下沿层方向的突破压力有关。基于页岩孔隙形态以及连通性分析表明，页岩有机孔以纳米喉道为主，连通性差且具有明显的滞留效应，同时顶、底板及页岩层系内部多套相对致密的封隔层叠置，有利于形成纵向自封闭。结合束缚水对基质孔隙流动能力及突破压力的实验和分子动力学模拟分析，揭示束缚水赋存使得页岩基质孔隙有效扩散能力显著下降，并可形成高的毛细管力，从而对储集于有机孔隙中的气体形成有效封闭。研究中构建了渗透率—突破压力演化关系，揭示深埋条件下页岩沿层方向层理缝有效闭合可形成高的突破压力封闭，抬升阶段相对弱的挤压环境沿层方向仍可以保持较高的封闭能力，有利于页岩气保存；而强挤压改造导致层理缝开启并沟通开启性断裂面，导致保存能力失效并使得页岩气发生较大规模的散失。该研究利用实验和分子动力学模拟等手段获取的认识，进一步阐述了页岩气保存的微观机理，可为复杂构造区海相页岩气勘探提供指导。

In order to accelerate the exploration and development of shale gas, this paper elaborates on the micro mechanism of shale gas preservation based on shale self-sealing. The self-sealing capacity of shale formations is mainly related to the low connectivity of nano-throats, low speed diffusion caused by bound water occurrence, capillary force sealing, and breakthrough pressure along the layer direction under burial conditions. Results of analysis based on shale pore morphology and connectivity show that the organic pores in shale are mainly composed of nano-throats with poor connectivity and significant retention effects. At the same time, the stacking of multiple relatively dense sealing layers within the top, bottom, and shale layers is conducive to self-sealing in longitudinal direction. Based on experimental and molecular dynamics simulation analysis of the influence of bound water on the diffusion and breakthrough pressure of the shale matrix, it is revealed that the bound water occurrence significantly reduces the effective diffusion capacity of shale matrix pores and could cause high capillary forces, leading to effective sealing of the gas stored in organic pores. In the study, the permeability-breakthrough pressure evolution relationship was constructed, revealing that under deep burial conditions, the effective closure of shale bedding fractures along the layer direction can form high breakthrough pressure sealing. During the uplift stage, under relatively weak tectonic compression, the shale could still maintain a high sealing capacity along the layer direction, which is conducive to shale gas preservation. However, under strong tectonic compression, the shale bedding fractures open and communicate with open fault surface, causing the failure of preservation capacity and large-scale loss of shale gas. This study elucidates the microscopic mechanism of shale gas preservation through experiments and molecular dynamics simulations, which could provide useful guidance for marine shale gas exploration in complex structural areas.

国家自然科学基金企业创新发展联合基金 U19B6003-03-06;国家自然科学基金企业创新发展联合基金 U19B6003-03-03

https://doi.org/10.11781/sysydz202305821