Experimental characterization and molecular modeling of kerogen in Silurian deep gas shale from southern Sichuan Basin, China

Abstract

A representative molecular model of kerogen is the prerequisite to the study on molecular interaction of fluid molecules with organic nanopores of shale. The molecular kerogen model in Silurian deep gas shale from southern China remains to be developed. In this work, the chemical structure of the targeted deep shale kerogen is characterized by organic geochemical measurements. The derived structural parameters are utilized to build the molecular structure of the kerogen unit. The kerogen unit shows a good representation of realistic kerogen structure in shale reservoir in terms of carbon skeleton, heteroatomic compositions and groups. The kerogen matrix and a extended kerogen slit model are constructed based on the kerogen unit, which match well with the experimental results in matrix density and kerogen porosity, respectively. The kerogen matrix is overall disordered with gentle stacking of polyaromatic fragments, due to the bendable aliphatic linkages and large-size aromatic units. The kerogen nanopores are not saturated with methane at deep shale reservoir conditions. At high pressure, the absolute adsorption tends to reach a maximum, while the excess adsorption shows a decreasing trend. The effect of pressure on the dissolved gas density is not pronounced. The generated kerogen model can serve as a starting point for further theoretical investigations on fluid storage and transport in organic nanopores of deep shale reservoir at microscopic scale.