Formation mechanism of in-situ volcanic reservoirs in eastern China: A case study from Xushen gasfield in Songliao Basin

A large number of in-situ volcanic reservoirs have been discovered from the Meso-Cenozoic rift basin group in eastern China. Based on drilling results in combination with geological and geophysical analysis, a case study from the Early Cretaceous Xujiaweizi fault-depression shows that the formation mechanism of in-situ volcanic reservoirs is characterized by "fault-controlled body, body-controlled facies, facies-controlled reservoir, and reservoir-controlled accumulation". In other words, deep faults control the volcanic eruption type, volcanic body, and gas reservoir distribution; the volcanic body determines the spatial distribution of volcanic facies and volcanic gas reservoir size; the volcanic facies control reservoir physical properties and effective thickness of gas formation; the volcanic reservoir properties control gas reservoir type and gas productivity. The result is useful to guiding the discovery of in-situ volcanic gas reservoirs in faulted basins in both theory and practice.