Experimental investigation of reservoir characteristics of the upper Ordovician Wufeng Formation shale in middle–upper Yangtze region,China

Abstract

The main lithofacies of the upper Ordovician Wufeng Formation is black shale, which is one of the most important source rocks of shale gas reservoir in middle–upper Yangtze region, SW China. To make a convincing study on the reservoir characteristics of Wufeng Formation, four rock core samples were collected from an exploration shale gas well and their mineral composition, pore characteristics, specific surface area, organic geochemical characteristics, organic matter maturity, and methane adsorption capacity were analyzed. The results show that clay minerals and quartz are the major mineral composition of Wufeng Formation shale, and the Brittleness Index indicates a possible better efficiency during the prospective hydraulic fracture process. The pore types of Wufeng Formation shale are various, and the total pore porosity ranges between 2.19% and 2.97%, while the permeability ranges from 0.12 × 10⁻³ µm² to 0.18 × 10⁻³ µm², and the specific surface area varies between 11.52 cm²/g and 19.73 cm²/g. The total organic carbon content of Wufeng Formation shale varies between 3.22% and 4.87%, representing the great hydrocarbon generation ability, while the R_o stably ranges between 2.48% and 2.60% and presents an over-mature stage so that mass generation of hydrocarbons from shales occurred during the geological history. Compared with the existing information of some shales from different geological ages in middle–upper Yangtze region, Wufeng Formation shales possibly have a relatively preferable methane adsorption capacity. In general, despite it possesses a thinner thickness, as for as its reservoir characteristics, Wufeng Formation plays an unneglectable role in the reservoir combination system of Wufeng Formation and its overlying the Lower Silurian Longmaxi Formation.