Comparison of Change in Nanopore Structure of Oil Shale after Anhydrous and Sub/Supercritical Water Pyrolysis

Abstract

Oil shale is an important part of unconventional resources, which is considered as an important replacement for traditional oil resources. At present, the underground in-situ conversion method of oil shale is mainly aimed at shallow reservoirs, and it is difficult to apply to in-situ exploitation of oil shale with a depth of more than 1000m. In view of the portability, fracturing and extraction characteristics of high-pressure sub/supercritical water, it has become the research direction of in-situ mining of deep oil shale. The evolution of pore structure of oil shale is the basis for exploring the production mechanism of sub/supercritical water pyrolysis of oil and gas, which has important theoretical and scientific significance for improving the development and utilization of in-situ injection of sub/supercritical water in deep oil shale. Therefore, in this paper, the oil shale of Jijuntun Formation of Paleogene in Fushun Basin is taken as the research object. The pyrolysis experiments of oil shale in three ways, namely, water-free (electric heating), subcritical water and supercritical water, are carried out by means of high temperature and high-pressure source rock pyrolysis simulation device. The evolution characteristics of nano-pore structure under different pyrolysis methods are studied by XRD and low temperature nitrogen adsorption technology. The results show that, compared with anhydrous pyrolysis at the same temperature, the pore size of 3-30 nm of oil shale increases significantly after sub/supercritical water pyrolysis. The phenomenon of kaolinite illite fossilization increases, and the overall weak acidic environment is more conducive to the transformation of illite into Illite and montmorillonite mixed layer minerals, easier to increase the pore space in oil shale, and conducive to the migration and accumulation of produced oil and gas.