The formation conditions of the Upper Carboniferous near-source tuff tight oil reservoir in Santanghu Basin, Xinjiang province

The source rock of the Upper Carboniferous strata in Santanghu Basin was formed in the environment of volcanic eruption, which results in alternate occurrence of source rock and tuff with unequal thickness. The tuff tight reservoirs vary both in thickness and in physical property, and the contact relationship between tuff reservoir and source rock is complicated. Therefore, the formation of the near-source tuff tight oil reservoir requires special conditions. To investigate the accumulation conditions of the Upper Carboniferous near-source tuff tight oil reservoir in Santanghu Basin, the authors analyzed M36 which serves as a typical tight oil reservoir. The evaluation standards of the Upper Carboniferous tuff tight reservoir and source rock in Santanghu Basin were established based on the analysis of core, slice, logging, as well as well geochemical testing, and the accumulation model of nearsource tuff tight oil reservoir was also established. The results indicate that, where reservoir porosity is 5%~12% and permeability is 0.07~0.7×10^-3μm², the tuff reservoir can be called high-quality reservoir. The carbonaceous mudstone and dark mudstone whose organic carbon content is higher than 2.0%, and R_o is higher than 0.6% are effective hydrocarbon. Good reservoir, high quality source rock and interbedded source rock-reservoir collocation constitute the formation conditions of near-source tuff tight oil reservoir.