Source reservoir configuration and geological geochemical control of coal and shale

The Longtan Formation in Sichuan Basin is a new field and new strata for the exploration and development of coal measure gas, and the evaluation of geochemical and geological conditions is lacking. In this study, elemental geochemistry, mineralogy, organic geochemistry of source rocks (organic matter type, abundance, maturity), and only geophysical analysis of bulk rock (Low-temperature nitrogen adsorption, Mercury intrusion, and nuclear magnetic resonance) were performed to determine the reservoir pore structure and source-reservoir geological-geochemical controlling factors. Geochemistry and mineralogy reveal frequent shale and tuffaceous sandstone interbeds in the southern Sichuan Basin under the Emeishan igneous rock provenance supply and relatively oxic environment. The low input of terrigenous clastics, dysoxic and suboxic or anoxic environment and frequent transgression in the central Sichuan Basin have led to frequent coal-shale interbedding. The organic matter type of the source rock is type III kerogen, which is in the stage of high-over maturation, with high TOC content and excellent hydrocarbon generation potential. The coal seam in the central Sichuan Basin has good reservoir properties (porosity 9.25%, pore volume 4.74cm³/g), and the low permeability (5 × 10^-3mD) of the shale caprock has good sealing ability. Overall, the coal-shale interbeds constitute the basic source-reservoir configuration of superimposed gas reservoir, and form a favorable development interval for coal measures.