Investigating the Pore Structure Characteristics and Reservoir Capacities of Lower Jurassic Continental Shale Reservoirs in the Northeastern Sichuan Basin, China

Abstract

The Lower Jurassic shale in the northeastern Sichuan Basin is one of the main research intervals of continental shale gas. The shale pore structure is an important indicator for evaluating the reservoir capacities of shale reservoirs. We concentrate on the pore structure to indicate reservoir capacity using several testing methods, for example, N2 adsorption-high-pressure mercury pore size combined experiments, X-ray diffraction (XRD) experiments, and the total organic carbon (TOC) method. The results show that the clay mineral content of the continental shale is high. The pore type is mainly a mineral matrix pore, followed by an organic matter pore, and the microcracks are locally developed; the distribution interval of the main pore size is mesoporous, between 10 and 50 nm; the pore volumes and specific surface areas of the continental shale reservoirs are negatively correlated or unrelated to the TOC, mainly due to the failure of pore development in the organic vitrinite and fusinite and the occupation of pore volume and adsorption sites by the soluble organic matter. The larger pores are mainly formed by clay minerals; the reservoir capacities of the continental shale reservoirs were evaluated using a two-factor evaluation method of the pore volume and specific surface area. It was found that the continental shale mainly comprises free reservoirs and has a storage gas capability level of II–IV. The research results elucidate the pore structure characteristics and reservoir capacities of the continental shale reservoirs in the northeastern Sichuan Basin, having important theoretical and guiding significance for the gas-bearing evaluation and dessert target optimization of the continental shale in the study area.