Quantifying pore structure heterogeneity of shale samples after solvent extraction following anhydrous and hydrous pyrolysis

Abstract

Heterogeneity is an important pore structure characteristic of shale formations that can impact reservoir transport properties. To better understand the heterogeneity intrinsic to the shale pore structure, gas adsorption and multifractal theory were combined to analyze data from artificially matured shale samples under both anhydrous and hydrous pyrolysis conditions. We compared two sets of samples: one that was kept intact (not treated with organic solvent), and the other set that was treated with an organic solvent to remove any liquid petroleum that was produced during the pyrolysis process. The results revealed differences in the pore structure parameters of the aliquots under these two pyrolysis conditions as well as treated vs. intact. Furthermore, at the same pyrolysis temperature, the disparity in surface area and pore volume before and after extraction of petroleum was found to be greater with anhydrous compared to hydrous pyrolysis conditions. Regardless of the pyrolysis conditions, when the pyrolysis temperature is under 400 °C, pore structural heterogeneity following extraction of petroleum is often small compared to the situation when yield is still present in the pores. As a result, the movable oil under both maturity routes can increase pore structure heterogeneity. Considering the results, when analyzing shale adsorption data for pore structure heterogeneity, experimental design would have an impact on the final outcome and data interpretation. This is the first study that investigates the effect of the movable oil and solvent extraction process on pore structure heterogeneity in relation to the thermal evolution of shale in the presence and absence of water.