(227b) Adsorption and Transport Properties of Alkanes in Kerogen-Containing Shale-Rocks

Oil and natural gas from deep shale formations are expected to greatly impact the entire world economy as these are spread out everywhere around the globe. The abundance of shale gas resources worldwide --and the fact that burning natural gas emits less CO₂ than other fossil fuels-- has created the expectation of a golden age of natural gas in a global energy system. This revolution relies on the large-scale deployment of new technologies allowing the production of hydrocarbons (oil, and especially natural gas), from source rock formations that were considered unproductive until very recently. The modeling of the hydrocarbons flow in nanoporous rocks such as shale has become an important new area of fluid mechanics. Gas/oil shale are sedimentary rocks with ultralow permeability. Estimates of long-term production and technically recoverable resources remain highly uncertain. The fundamental mechanisms controlling shale gas extraction remain poorly understood, and the classic theories and simulation techniques used by the oil and gas industry have proven inadequate for shale source rocks. Flow through shale poses a distinctive challenge that is new to the oil and gas industry: a large part of pores in shale have typical widths in the order of a few angstroëms, and are within an organic porous material (kerogen) containing adsorbed hydrocarbons. At these scales, the pore size is on the order of the mean free path of the hydrocarbon molecules, and the Navier-Stokes equations with no-slip boundary condition cannot adequately represent the flow. In the present talk, a generic model describing the flow in a multi-scale porous medium (such as shale) and fully taking into account the thermodynamics of confined fluids in nano and sub-nanopores, (including adsorption processes) is proposed without postulating any transport or diffusion mechanism. The model assumes that the rock pore void consist of different types of domains with different of pore sizes starting at the sub-nanometer level with a realistic atomistic description of the kerogen porosity (close to that of common porous carbons). This is a key improvement compared to current attempts to model flow (and production) in shale which all assume that the flow has to comply to Darcy's equation.