Gong Fengming, Hou Dali, Tang Ruiqian, Lei Zhiqiang, Zhong Chuanrong
College of Energy (College of Modern Shale Gas Industry), Chengdu University of Technology, Chengdu, Sichuan 610059, China.
State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation (Chengdu University of Technology), Chengdu, Sichuan 610059, China.
Langmuir. 2024 Aug 20;40(33):17601-17612. doi: 10.1021/acs.langmuir.4c01916. Epub 2024 Aug 8.
The CH storage and seepage capacity of shale kerogen are the main controlling factors of the natural gas production rate, and the porosity and permeability of kerogen are greatly affected by kerogen deformation. Therefore, the study of the deformation rule and CH adsorption characteristics of kerogen at different maturities and skeleton moisture contents has an important impact on the proper understanding of the development potential of shale gas reservoirs. In this paper, kerogen maturity (II-A, II-B, II-C, and II-D) and skeleton moisture content (0.0, 0.6, 1.2, 1.8, and 2.4 wt %) were considered. The deformation of kerogen, the adsorption of CH after deformation, and the quadratic deformation induced by CH were studied by using Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD). The results show that the kerogen volume strain increases with increasing skeleton moisture content, following the order II-A < II-B < II-C < II-D for the same moisture content. The density of the kerogen matrix decreases, and porosity increases with rising moisture content. The void fraction of immature kerogen decreases with increasing water content, while the opposite is true for postmature kerogen. The presence of skeleton moisture decreases the CH adsorption capacity of immature kerogen and increases the CH adsorption capacity of postmature kerogen. The chemical structure of immature kerogen is relatively soft, making its volume more affected by CH adsorption compared with postmature kerogen. In the same water environment, postmature kerogen has greater CH storage, diffusion, and seepage capacity compared to those of immature kerogen, suggesting that reservoirs with high organic matter maturity should be prioritized for development.
页岩干酪根的CH储存和渗流能力是天然气产率的主要控制因素，且干酪根的孔隙度和渗透率受干酪根变形的影响很大。因此，研究不同成熟度和骨架含水量下干酪根的变形规律及CH吸附特性，对于正确认识页岩气藏的开发潜力具有重要意义。本文考虑了干酪根成熟度（II-A、II-B、II-C和II-D）和骨架含水量（0.0、0.6、1.2、1.8和2.4 wt%）。采用巨正则蒙特卡罗（GCMC）和分子动力学（MD）方法研究了干酪根的变形、变形后CH的吸附以及CH引起的二次变形。结果表明，干酪根体积应变随骨架含水量的增加而增大，相同含水量下，顺序为II-A < II-B < II-C < II-D。干酪根基质密度降低，孔隙度随含水量增加而增大。未成熟干酪根的孔隙率随含水量增加而减小，而过成熟干酪根则相反。骨架水的存在降低了未成熟干酪根的CH吸附能力，增加了过成熟干酪根的CH吸附能力。未成熟干酪根的化学结构相对较软，与过成熟干酪根相比，其体积受CH吸附的影响更大。在相同水环境下，过成熟干酪根比未成熟干酪根具有更大的CH储存、扩散和渗流能力，表明应优先开发有机质成熟度高的气藏。
