Regional Tectonic Setting of Marine Ultra-deep Oil and Gas
Hydrocarbon source rock is the material base of hydrocarbon formation reservoirs, is also the dominated factors of hydrocarbon reservoirs, does not have the generation just not having oil gas of hydrocarbon source rock, and only has effective hydrocarbon source rock just to keep contribution to oil gas. Li et al (2021) discussed the regional tectonic background of ultra-deep oil and gas in Chinese marine facies in the article " Geological conditions, reservoir evolution and favorable exploration directions of marine ultra-deep oil and gas in China".
By analyzing the structural background, petroleum geological conditions, and typical regional (paleo) oil and gas reservoirs in marine ultra-deep oil and gas regions in China, this paper reveals the evolution process of marine ultra-deep oil and gas reservoirs and the key controlling factors of accumulation. The marine ultra-deep oil and gas resources in China at burial depth of greater than 6 000 m are mainly distributed in the Precambrian and Lower Paleozoic ancient marine strata in the Sichuan, Tarim and Ordos cratonic basins. The global breakup-convergence cycles of the supercontinent control the evolution of intracratonic rifts, cratonic marginal rifts, and intracratonic depressions. The Sichuan Basin is dominant in source rocks, followed by the Tarim Basin. The early high-energy sedimentary environment and the later dissolution and faulting control the development of high-quality carbonate reservoirs. The regional caprocks are dominated by gypsum salt rocks, shale, and tight carbonate rock. The ultra-deep oil and gas fields in China have generally experienced two stages of oil-reservoir forming, thermal (complete or partial) cracking of oil in paleo-reservoir into gas, and late accumulation of kerogen-cracked gas (high-over mature oil and gas). The oil and gas accumulation is controlled by static and dynamic geological elements jointly. Major hydrocarbon-generation center, high quality and large-scale reservoir resulted from karstification of high energy facies belt, thick gypsum rock or shale caprock, and stable trapping and preservation conditions are the key factors for accumulation of ultra-deep oil and gas. Based on petroleum geological conditions, factors affecting hydrocarbon accumulation and evolution, and the latest exploration knowledge, we propose three favorable exploration directions, i.e. the areas around intracratonic rift and intracratonic depression, and craton margin.