PORE-NETWORK MODELING OF THE COMPOSITIONAL FLOW AND PHASE BEHAVIOR OF HYDROCARBONS IN LIQUID-RICH SHALE FORMATIONS

Hydrocarbon recovery from unconventional shale formations has reshaped the US and worldwide energy landscapes. Despite liquid-rich shale gas formations are economically attractive, the gas-condensate flow dynamics are not well understood due to complex fluid phase behaviors resulted from effects of multiscale nanopore structures in tight shale formations. The lack of fundamental understanding on pore-scale mechanisms of the interaction between nanoconfined phase behavior and gas-condensate flow poses challenges when attempting to predict and enhance hydrocarbon production at the field scale. Limited by computational costs, prior pore-scale models, such as molecular dynamics, grand canonical Monte Carlo, and density-functional theory, have often considered a single pore with a slit or circular geometry that underrepresents the complex pore structures. To our knowledge, none of these models has the capability of modeling gas-condensate flow with nanoconfined phase behavior within a complex multiscale nanopore structure. In the present work, we develop a novel pore-network model to examine how connected nanopore structures control the compositional flow dynamics and therefore phase behavior of hydrocarbon mixtures. The modeling framework comprises: 1) A phase-equilibrium model for hydrocarbon mixtures in a single pore with different geometries; the model incorporates the effects of multicomponent sorption and strong capillary pressure.2) A dynamic pore-network model coupling the individual-pore phase-equilibrium model with the two-phase compositional flow through a multiscale pore-network extracted from 3D digital shale images. The new framework allows us to investigate the interactions between phase behaviors, two-phase compositional flow dynamics, and the complex nanoscale pore structures, as well as how they collectively influence the rate and composition of hydrocarbon production.