Favorable factors for the formation of oil and gas reservoirs in deep basins

Abstract

This paper mainly describes three factors that form deep oil and gas reservoirs: Type I kerogen has a certain hydrocarbon generation potential at the high maturity stage; the maturation of carbonate source rocks is slower than that of mudstone source rocks, the conversion of crystal organic matter and the release of hydrocarbons are at the high maturity stage, the lower limit of oil generation of carbonate source rocks is below 1.5%, and the depth of the liquid window is 500-1000m greater than that of mudstone; higher pressure is another important factor in the formation of deep oil reservoirs. The high-pressure hydrocarbon generation simulation experiment of source rocks reveals that high pressure can delay the oil generation period and increase the oil production rate. In the Tarim and Junggar basins with low geothermal gradients, the lower limit of oil generation can reach 7000m due to high pressure. In the rapidly subsiding Cenozoic basins, due to the rapid oil generation and difficulty in discharge of mudstone, local abnormal high-pressure zones are formed. The depth of oil generation in the abnormally high-pressure zone can extend downward to more than 1,000 meters. The high-pressure zone below the seal layer is a vast place for the formation of large-scale oil and gas reservoirs in the deep.