Ma Ming, Emami-Meybodi Hamid
John and Willie Leone Family Department of Energy and Mineral Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, United States.
Langmuir. 2024 Aug 16. doi: 10.1021/acs.langmuir.4c01305.
Dynamics of fluid transport in ultratight reservoirs such as organic-rich shales differ from those in high-permeable reservoirs due to the complex nature of fluid transport and fluid-solid interaction in nanopores. We present a multiphase multicomponent transport model for primary production and gas injection in shale, considering the dual-scale porosity and intricate fluid-solid interactions. The pore space in the shale matrix is divided into macropores and nanopores based on pore size distribution. We employ density functional theory (DFT) to account for fluid-solid interactions and to compute the inhomogeneous fluid density distribution and phase behavior within a dual-scale matrix. The calculated fluid thermodynamic properties and transmissibility values are then integrated into the multiphase multicomponent transport model grounded in Maxwell-Stefan theory to simulate primary oil production from and gas injection into organic-rich shales. Our findings highlight DFT's adeptness in detailing the complex fluid inhomogeneities within nanopores─a critical concept that a cubic equation of state does not capture. Fluids within pores are categorized into confined and bulk states, restricted by a threshold pore width of 30 nm. Different compositions of fluid mixtures are observed in macropores and nanopores: heavier hydrocarbon components preferentially accumulate in nanopores due to their strong fluid-solid interactions. We utilize the developed model to simulate hydrocarbon production from an organic-rich shale matrix as well as CO injection into the matrix. During primary hydrocarbon production, strong fluid-solid interactions in nanopores impede the mobility of heavy components in the near-wall region, leading to their confinement. Consequently, heavy components mostly remain within the nanopores in the shale matrix during primary hydrocarbon production. During the CO injection process, the injected CO alters fluid composition within macropores and nanopores, promoting fluid redistribution. Injected CO engages in competitive fluid-solid interactions against intermediate hydrocarbons, successfully displacing a considerable number of these hydrocarbons from the nanopores.
由于纳米孔隙中流体传输和流固相互作用的复杂性，诸如富含有机质页岩等超致密储层中的流体传输动力学与高渗透储层不同。我们提出了一个用于页岩初次开采和注气的多相多组分传输模型，该模型考虑了双尺度孔隙度和复杂的流固相互作用。基于孔径分布，将页岩基质中的孔隙空间划分为大孔隙和纳米孔隙。我们采用密度泛函理论（DFT）来考虑流固相互作用，并计算双尺度基质内非均匀流体密度分布和相行为。然后，将计算得到的流体热力学性质和渗透率值整合到基于麦克斯韦 - 斯蒂芬理论的多相多组分传输模型中，以模拟富含有机质页岩的原油初次开采和注气过程。我们的研究结果突出了DFT在详细描述纳米孔隙内复杂流体非均匀性方面的能力，而这是状态方程所无法捕捉的关键概念。孔隙内的流体分为受限态和本体态，由30纳米的临界孔隙宽度限制。在大孔隙和纳米孔隙中观察到流体混合物的不同组成：较重的烃类组分由于其强烈的流固相互作用而优先在纳米孔隙中积累。我们利用所开发的模型来模拟富含有机质页岩基质中的烃类生产以及向基质中注入CO₂的过程。在初次烃类生产期间，纳米孔隙中强烈的流固相互作用阻碍了重质组分在近壁区域的流动性，导致它们被限制。因此，在初次烃类生产期间，重质组分大多保留在页岩基质的纳米孔隙内。在注入CO₂过程中，注入的CO₂改变了大孔隙和纳米孔隙内的流体组成，促进了流体重新分布。注入的CO₂与中间烃类进行竞争性流固相互作用，成功地将大量这些烃类从纳米孔隙中驱替出来。
