Petoleum geology features and accumulation controls for ultra-deep oil and gas reservoirs

According to previous studies and specific geological settings of different regions, ultra-deep reservoirs have been defined as being 6 km. Petroleum geology studies of ultra-deep reservoirs have been made, including considerations of source rock, reservoir, cap rock and trap. Compared to conventional source rocks, the source rocks in ultra-deep reservoirs entered the mature stage later and have a higher maturity. Hydrocarbon generation was controlled by temperature, time and pressure. Overpressure strongly restricted the thermal evolution of orga-nic matter and hydrocarbon generation. Secondary pores with an older age worked as the main reservoir space. Carbonate rocks account for 33% of reservoir. Cap rocks are dominated by evaporites and mudrocks. The major traps are structural, lithological, reef and combination traps. The formation of ultra-deep reservoirs was controlled by abnormal pressure and temperature. It is suggested that ultra-deep oil and gas exploration in China should focus on the areas with lower geothermal gradients, stratigraphic intervals with secondary porosity and well-developed overpressures, deeply-buried carbonate rocks, sub-salt sequences and East China's deep offshore areas.