Experimental investigation of the molecular migration of C1–C6 hydrocarbons: Kinetics of hydrocarbon release from source rocks

Abstract

In a series of experiments the release of C1–C6 hydrocarbons from different source rock samples under isothermal conditions was recorded over periods of up to 14 days. The resulting release curves were interpreted in terms of four mathematical models involving molecular diffusion and first-order desorption kinetics. Significant differences were observed between the release curves obtained from different source rocks. Experiments with samples from the Lias epsilon source rock sequence in NW Germany indicate a change in the release mechanisms with increasing maturity. None of the experimental hydrocarbon release curves measured so far could be satisfactorily represented by a simple diffusion function. In some cases a combined model, including a first order desorption step preceding diffusion of hydrocarbons out of the rock sample, was found to describe the experimental curves adequately. Diffusion coefficients and first-order desorption rate constants were calculated from the experimental data. Diffusion coefficients obtained with this method show a reasonable agreement with data obtained from previous permeation experiments.