Sidian Chen, Jiamin Jiang1, and Bo Guo
Flow and transport of multiple fluid phases and components in porous materials are challenging to model, especially when thermodynamic phase change behaviors are involved. Porous materials with nanoscale pore spaces can further complicate the problem. The phase behavior of a multicomponent mixture in nanoscale pore spaces can significantly deviate from its bulk state, leading to very different triggering pressure and temperature for evaporation and condensation. This ‘shifted’ phase change behavior due to nanoconfinement—commonly observed during oil and gas recovery from shale formations—has posed significant challenges for accurate prediction of hydrocarbon production. Current theories either underrepresent the complex multiscale pore structures by using molecular simulations within a single pore, or oversimplify the nanoconfined flow mechanisms by using Darcy-scale continuum models, causing inconsistent predictions with experimental and field observations. To bridge the gap, we develop a novel pore-network model to examine how complex nanopore networks control phase change and compositional flow dynamics. The model allows us to derive new constitutive relationships for Darcy-scale continuum models by considering the interactions between phase change behaviors, two-phase compositional flow dynamics, and the multiscale nanopore structures, which can then be used for quantitative predictions of field-scale hydrocarbon production from complex shale formations.
1Stanford University, Stanford, CA