Li Wenhui, Zhang Mingshan, Nan Yiling, Pang Wanying, Jin Zhehui
School of Mining and Petroleum Engineering, Department of Civil and Environmental Engineering, University of Alberta, Edmonton, Alberta T6G 1H9, Canada.
Langmuir. 2021 Jan 12;37(1):542-552. doi: 10.1021/acs.langmuir.0c03232. Epub 2020 Dec 21.
CO sequestration in shale reservoirs is an economically viable option to alleviate carbon emission. Kerogen, a major component in the organic matter in shale, is associated with a large number of nanopores, which might be filled with water. However, the CO storage mechanism and capacity in water-filled kerogen nanopores are poorly understood. Therefore, in this work, we use molecular dynamics simulation to study the effects of kerogen maturity and pore size on CO storage mechanism and capacity in water-filled kerogen nanopores. Type II kerogen with different degrees of maturity (II-A, II-B, II-C, and II-D) is chosen, and three pore sizes (1, 2, and 4 nm) are designed. The results show that CO storage mechanisms are different in the 1 nm pore and the larger ones. In 1 nm kerogen pores, water is completely displaced by CO due to the strong interactions between kerogen and CO as well as among CO. CO storage capacity in 1 nm pores can be up to 1.5 times its bulk phase in a given volume. On the other hand, in 2 and 4 nm pores, while CO is dissolved in the middle of the pore (away from the kerogen surface), in the vicinity of the kerogen surface, CO can form nano-sized clusters. These CO clusters would enhance the overall CO storage capacity in the nanopores, while the enhancement becomes less significant as pore size increases. Kerogen maturity has minor influences on CO storage capacity. Type II-A (immature) kerogen has the lowest storage capacity because of its high heteroatom surface density, which can form hydrogen bonds with water and reduce the available CO storage space. The other three kerogens are comparable in terms of CO storage capacity. This work should shed some light on CO storage evaluation in shale reservoirs.
页岩储层中的CO封存是缓解碳排放的一种经济可行的选择。干酪根是页岩中有机质的主要成分，与大量可能充满水的纳米孔有关。然而，人们对充满水的干酪根纳米孔中的CO储存机制和容量了解甚少。因此，在这项工作中，我们使用分子动力学模拟来研究干酪根成熟度和孔径对充满水的干酪根纳米孔中CO储存机制和容量的影响。选择了不同成熟度的II型干酪根（II-A、II-B、II-C和II-D），并设计了三种孔径（1、2和4纳米）。结果表明，1纳米孔径和较大孔径的CO储存机制不同。在1纳米的干酪根孔隙中，由于干酪根与CO之间以及CO之间的强相互作用，水被CO完全置换。在给定体积下，1纳米孔隙中的CO储存容量可达其体相的1.5倍。另一方面，在2纳米和4纳米的孔隙中，虽然CO溶解在孔隙中间（远离干酪根表面），但在干酪根表面附近，CO可以形成纳米级簇。这些CO簇将提高纳米孔中的整体CO储存容量，而随着孔径增加，这种增强作用变得不那么显著。干酪根成熟度对CO储存容量影响较小。II-A型（未成熟）干酪根的储存容量最低，因为其杂原子表面密度高，可与水形成氢键并减少可用的CO储存空间。其他三种干酪根在CO储存容量方面相当。这项工作应该为页岩储层中的CO储存评估提供一些启示。
