Characteristics of Reservoir Spaces and the Influence of Lithology on Reservoir Development in the Basement Gas Reservoir of the Dongping Well Block, Qaidam Basin

The Dongping area has become an exploration hotspot due to the discovery of China’s first metamorphic rock-type bedrock gas reservoir. This region also serves as one of the key targets for natural gas exploration in the eastern segment of the Altun piedmont within the Qaidam Basin. However, systematic research on the characteristics and controlling factors of its bedrock reservoirs remains relatively limited at present. Based on core observations and thin-section identification, combined with whole-rock Xray diffraction analysis, scanning electron microscopy microanalysis, statistical calculations of surface porosity–fracture ratio, and analysis of conventional logging data, this study conducts an indepth investigation into the lithological characteristics, reservoir space features, and their influence on reservoir development of the bedrock gas reservoir in the Dongping area of the Qaidam Basin. The results indicate that the bedrock reservoir rocks in the Dongping area are mainly composed of ortho-metamorphic rocks, including granitic gneiss and plagioclase gneiss, as well as para-metamorphic rocks such as quartz schist, calcareous gneiss, slate, calcareous schist, and metamorphic limestone. The reservoirs are of fracturepore type, with an average porosity of about 2.5% and an average permeability of approximately 0.02 mD. Among the ortho-metamorphic rocks, granitic gneiss represents the favorable reservoir lithology, whose reservoir space is primarily derived from tectonic fractures formed in brittle minerals such as quartz and feldspar under structural stress. In para-metamorphic rocks, slate is the favorable reservoir lithology, and its reservoir quality mainly benefits from dissolution pores, vugs, and fractures developed in easily soluble carbonate minerals dominated by calcite. The findings of this research provide important guidance for further exploration of the bedrock gas reservoir in the Dongping area.