深层页岩孔隙结构及游离气传输特征——以四川盆地龙马溪组页岩为例

Pore structure and free gas transport characteristics of deep shale: taking Longmaxi Formation shale in Sichuan Basin as an example

万成祥 郭旭升 申宝剑 常佳琦 薛子鑫 杜伟

WAN Chengxiang GUO Xusheng SHEN Baojian CHANG Jiaqi XUE Zixin DU Wei

1. 页岩油气富集机理与高效开发全国重点实验室, 北京 102206; 2. 中国石化 页岩油气勘探开发重点实验室, 北京 102206; 3. 中国石化 石油勘探开发研究院, 北京 102206; 4. 中国石化集团 国际石油勘探开发有限公司, 北京 100029

1. State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Efficient Development, Beijing 102206, China; 2. Key Laboratory of Shale Oil and Gas Exploration & Production, SINOPEC, Beijing 102206, China; 3. SINOPEC Petroleum Exploration and Production Research Institute, Beijing 102206, China; 4. SINOPEC International Petroleum Exploration and Production Corporation, Beijing 100029, China

深层页岩气是四川盆地龙马溪组页岩气增储上产的重要攻关方向，但与中浅层页岩气在储层特征和渗流特征方面存在差异，一定程度上限制了深层页岩气的勘探开发进展。为了明确深层页岩气的储层孔隙结构特征及页岩游离气传输特征，以川南深层龙马溪组优质页岩为例，开展了页岩储层孔隙结构观察和定量表征实验，并基于体相气体传输机理，探讨了页岩游离气的传输特征、临界条件及动态演化规律。① 深层页岩储层孔隙形态特征与中浅层差别不大，但中孔的孔隙结构特征更加明显，孔体积占比为62.5%～69.7%；② 深层页岩游离气传输方式分为过渡流、滑脱流和达西流三类，永川地区页岩游离气划分3种传输方式的临界孔径分别为4.2 nm和420 nm，在此基础上建立了全盆地页岩游离气传输图版；③ 从浅层到深层，页岩游离气不同传输方式对应的临界孔径随之变小，游离气传输方式从以过渡流为主(最高占比达63.0%)转变为以滑脱流为主(最高占比达67.3%)，达西流占比不超过2%；页岩游离气传输能力从浅层到中层随埋深增加快速下降，中深层页岩游离气传输能力随埋深增加基本保持稳定。通过分析和对比深浅层页岩储层孔隙结构特征及游离气传输特征，研究成果可有力支撑深层页岩气乃至浅层页岩气下一步高效勘探开发方案的部署工作。

Deep shale gas is an important research direction for increasing shale gas storage and production in the Longmaxi Formation of Sichuan Basin. But there are differences in reservoir and seepage characteristics between shallow and medium-buried shale gas, which to some extent limits the progress of exploration and development of deep shale gas. In order to clarify the pore structure characteristics of deep shale gas reservoirs and the transport characteristics of shale free gas, this paper takes the high-quality shale of Longmaxi Formation in southern Sichuan as an example to carry out experiments on observing and quantitatively characterizing the pore structure of shale reservoirs. In addition, based on the transport mechanism of bulk gas, the transport characteristics, critical conditions, and dynamic evolution laws of shale free gas were explored. The experimental and computational results indicate that: (1) The pore morphology characteristics of deep shale reservoirs are not significantly different from those of shallow and medium-buried shale, but the pore structure characteristics of medium pores are more obvious, with pore volume accounting for 62.5%-69.7%; (2) The transport modes of deep shale free gas are divided into three types: transitional flow, slippage flow, and Darcy flow. The critical pore sizes of the three modes in the Yongchuan area are 4.2 nm and 420 nm, respectively. On this basis, a transport chart for free gas in the entire basin has been established; (3) From shallow to deep shale, the critical pore size corresponding to different transport modes of free gas decreases accordingly. The main transport mode of free gas changes from the transitional flow (up to 63.0%) to the slippage flow (up to 67.3%) and the Darcy flow accounts for no more than 2%. The transport capacity of free gas rapidly decreases from shallow to medium-buried shale, while the transport capacity of medium to deep shale free gas remains basically stable with increasing burial depth. By analyzing and comparing the pore structure characteristics and free gas transport characteristics of deep and shallow shale reservoirs, this study can effectively support the deployment of efficient exploration and development plans for deep shale gas and even shallow shale gas in the next step.

中国石化科技部项目“四川盆地志留系致密储层潜力评价”(P21042-3)资助。

https://doi.org/10.11781/sysydz2023061204