Physical Properties of Hydrocarbon Source Reservoir in the Lucaogou Formation in Junggar Basin (China) and Its Influence on Adsorption Ability and Surface Free Energy

Abstract

A physical property of a shale gas reservoir affects shale gas content, then restricts the shale gas resource potential. In this paper, lithofacies and spatial distribution of the southern margin of the Junggar Basin in Xinjiang Province are identified and occurrence strata, gas content, and reservoir properties of shale gas are studied. Based on adsorption potential theory, adsorption and surface free energy of all the sample is discussed. The conclusions are as follows. (1) All the shale samples can be divided into five lithological phases. For example, black oil shale/shale (lithology) phase and gray-black-gray/dolomite mudstone (lithology) phase are the most developed; compared with the middle and lower sections, the vertical development continuity of the upper hydrocarbon source rock is better. Lithology of this section is mainly composed of shale mixed with marlstone and dolomite interlayer. From the horizontal view of this section, the overall trend is gradually thickening from west to east and from north to south. (2) Semi-deep lake-phase is the most developed, indicating a decreasing trend of thickness from sedimentary center to surrounding strata. (3) Sedimentary period of Lucaogou Formation is a deep water area of the lake basin; then, the TOC content is affected by the sedimentary environment. As sedimentary water depth increases, TOC content will increase, which results in the highest TOC content in the area. A specific surface area is roughly positively correlated with porosity, clay mineral content, and percentage of illite/montmorillonite interlayer ratio and negatively correlated with TOC content. (4) During the adsorption process, adsorption potential decreases with an increase in equilibrium pressure, and adsorption space increases with an increase in equilibrium pressure. Maximum adsorption space of all the sample were 0.20~0.25 cm3·g−1; then, its value is larger than the maximum adsorption space of other coal samples (0.025~0.20 cm3·g−1). In the same adsorption space, the corresponding adsorption potential of the coal sample is much larger than that of other samples. The reason is that the porosity permeability of this sample is relatively larger, leading to its better physical properties.