Accumulation mode of Quaternary mudstone gas reservoir in Sanhu Depression, Qaidam Basin

The study of formation conditions and accumulation mode of biogenetic mudstone gas reservoir in Sanhu Depression is essential for understanding the accumulation mechanisms and enrichment rules of such gas reservoirs. It holds significant theoretical and practical implications for guiding the exploration and development of Quaternary mudstone gas reservoirs. This research focuses on the Quaternary mudstone in the Sanhu Depression as the main subject. To determine the reservoir formation conditions and establish the accumulation mode, various experiments were conducted, including soluble organic carbon analysis, porosity determination, and chromatography-mass spectrometry analysis. The results reveal that the presence of high levels of soluble organic carbon and herbaceous humic organic matter, along with cold and dry conditions, create favorable conditions for the generation of biogenetic mudstone gas. The Quaternary formation in Sanhu Depression has the characteristics of high porosity and low permeability with numerous micro-nano pores that provide ample space for the occurrence of biogenetic gas. Gas flow primarily occurs through Fick diffusion and slip flow. The self-sealing effect of mudstone leads to the in-situ accumulation of biogenetic gas. However, during the late Himalayan tectonic movement, the gas containment of mudstone is disrupted. As a result of buoyancy, the gas migrates upward and accumulates in high parts of the mudstone, which are adjacent to the gas-generating center, and are superimposed longitudinally with sandstone biogenetic gas reservoirs.