Mineralogical and Geochemical Characterization of Deep Tight Gas in Shahezi Formation, Songliao Basin, NE China

Tight gas is a critical unconventional energy resource, yet the geological characteristics and accumulation processes of tight gas in China’s Songliao Basin remain poorly documented. This study aims to investigate the tight gas system in the Songliao Basin as a representative continental basin, with key objectives including evaluating source rock and reservoir properties via mineralogical and geochemical analyses, characterizing lithologies and pore types, determining the gas charging mechanism in tight media, and identifying the main controlling factors for accumulation. Geochemical results indicate that the Shahezi Formation contains medium to good mudstones and excellent coals. Reservoirs consist of tight sandstones and conglomerates deposited in fan delta and braided river delta systems, with pore spaces dominated by dissolution pores and microfractures, resulting in ultra-low porosity and permeability. Conventional buoyancy-driven migration is ineffective; instead, gas charging is driven by hydrocarbon generation expansion force, creating overpressure that expels pore water and forces gas into reservoirs through fault-sand conduits. Accumulation is controlled by continuous gas supply from thick, highly mature source rocks, dissolution-enhanced and fracture-dominated reservoir space, and sufficient source–reservoir pressure difference. This study elucidates tight gas characteristics and accumulation mechanisms in continental basins, providing data applicable to both continental and marine settings.