Modeling of Kerogen Swelling by Solvents with Flory-Rehner and Regular Solution Model

Abstract: Oil and gas production from shale reservoirs has become an indispensable component of the world energy supply. However, the oil recovery rate from shale reservoirs is still relatively low. To achieve efficient exploitation of shale reservoirs, one of the prerequisites is to have a precise capture of the phase behavior of reservoir fluids in shale reservoirs. Compared with conventional oil reservoirs, shale reservoirs contain organic matters within the rock matrix. These organic matters are mainly composed of kerogen, which is in equilibrium with generated hydrocarbons during the expulsion process. Swelling of kerogen by different solvents is a well-known technique to characterize the thermodynamic properties of kerogen and to describe the phase equilibria between different solvents and kerogen. In this thesis, experimental data of kerogen swelling tests from the literature are first collected to validate the efficacy of the Flory-Rehner and regular solution (FRRS) model in describing oil-kerogen two-phase equilibria. The FRRS algorithm can be tuned to well match the measured kerogen swelling test results. The swelling ratios of different types of kerogen are then predicted as a function of solubility parameters and molar volumes of different solvents. The effects of sulfur content and thermal maturity of kerogen on kerogen’s swelling ratio are also studied. Our calculation results show that the swelling ratio of kerogen follows a bell-shaped trend with the change of solubility parameter and molar volume of solvents. Kerogen tends to absorb more aromatics and heavy hydrocarbons than light and saturated hydrocarbons. Compared with normal alkanes, naphthenes induce higher swelling ratios of kerogen. The capacity of kerogen to retain hydrocarbons decreases with an increasing thermal maturity or sulfur content of kerogen.