Lower Cretaceous volcanic-sedimentary successions of the continental rift basin in the Songliao Basin, northeast China: Implication in high-quality reservoir prediction and hydrocarbon potential

The high-quality reservoirs of volcanic-sedimentary successions in faulted lake basins are important enrichment sites for deep natural gas reservoirs. However, complex volcanic-sedimentary lithology and reservoir characteristics impede the efficient prediction of hydrocarbon in these successions. Therefore, we study the volcanicsedimentary succession of the Huoshiling Formation (northern Dehui depression, Songliao Basin), focusing on the volcanic-sedimentary stratigraphic cycle (VSC), facies models and the distribution of high-quality reservoirs. Based on the log, core, casting thin-section, seismic and other data, fissure-type and central-type volcanic eruptions are identified. Three VSCs (1-3) are recognised, and six volcanic-sedimentary facies are determined based on lithological characteristics: effusive, explosive, volcanic conduit, volcanic-sedimentary transition, fandelta and lacustrine. Based on the flow regimes and lithological associations, we develop three models: a fissurecentral volcanic effusive model, an intermittent volcanic activity model and a fissure-central explosive model. Three types of pores occur in the volcanic-sedimentary reservoir space: primary pores, dissolution pores and micro-fractures. Lithology and dissolution are critical factors controlling reservoir porosity and connectivity. The distribution of high-quality reservoirs of volcanic-sedimentary successions can be effectively predicted using geostatistical seismic-inversion based on porosity constraints. High-quality reservoir characteristics, source rock and structural characteristics show that crystal debris and breccia-bearing tuff in VSC3 can form structurallithologic, fault-block and self-generating and -storing hydrocarbon reservoirs. This study's results and methods of high-quality volcanic-sedimentary reservoirs can provide a reference for the efficient exploration and development of oil and gas in similar basins.