Nano-scale multicomponent hydrocarbon thermodynamic transport mechanisms in shale oil reservoir

Abstract

Hydrocarbon mass transport in nanoporous media notably differs from that in traditional micro-scale porous media due to strong solid-fluid interaction in nanoscale confined pore space. Accurate prediction of hydrocarbon thermodynamic transport in nanoporous shale must consider the bound water distribution pattern, fluid occurrence in dual-wet pores (organic and inorganic), thermodynamic phase equilibrium, boundary slippage and rheological property. So far, there is no such a model that incorporates the above mentioned factors into assessing the multicomponent hydrocarbon mass transport in nanoporous shale. In this work, we propose a pore network based multicomponent hydrocarbon mass transport model considering above mentioned factors and the multicomponent hydrocarbon thermodynamic transport mechanisms are elucidated in detail. The bound water film stability and induced capillary condensation are first analyzed according to Kelvin equation and the extended DLVO theory. A thermodynamic phase equilibrium-fluid occurrence coupling model is further developed considering the oil-gas capillary pressure change with oil saturation on pore network model (PNM). The multicomponent hydrocarbon single pore transport model is derived considering boundary slippage, adsorption layer thickness and fluid rheology and is extended to PNM transport simulation. The multicomponent hydrocarbon permeability variations at different pressure, pore size, relative humidity and total organic carbon (TOC) are analyzed in detail. The predicted hydrocarbon flux change with pressure gradient matches well with the previous observed trend in the laboratory experiments. Study results reveal that the multicomponent hydrocarbon exhibits non-linear transport behavior determined by the fluid rheology and the threshold pressure gradient for hydrocarbon starting to flow is mutually controlled by the yield stress and pore size.