关键词: 超深层, 成藏条件两分性, 烃源灶, 储集层, 生-储-盖组合, 有效性, 勘探地位, 中国陆上

Abstract: The ultra-deep oil and gas resources are abundant in China’s superimposed basins, which are an important strategic replacement field. The exploration and research work has revealed that there is a dichotomy of accumulation conditions for ultra-deep oil and gas reservoirs; favorable accumulation conditions only exist in specific basin environments, characterized with regionality, while the unfavorable accumulation conditions are inherent attributes of ultra-deep layers, characterized with universality. The decisive factors determining whether ultra-deep layers have exploration value are the effectiveness and scale of source kitchens, the effective reservoir and its scale, as well as the spatial combination and effectiveness of source, reservoir, and cap. The basins with exploration potential in ultra-deep layers have the following characteristics: (1) there is differential subsidence evolution in cratons, which have not been deeply buried during a long geological history, and where source kitchens are developed and still in an effective hydrocarbon-generation window to this day; (2) sedimentary strata mainly composed of carbonate rocks are developed, with granular platform marginal-platform shoals and intraplatform shoals, and have undergone constructive diagenesis and modification, or have experienced groundwater dissolution and leaching during geological history, as result of which reservoirs with pores in ultra-deep layers (including fractures and caves) are developed and have been effective till today; (3) the development of clastic rock, basement, or volcanic reservoirs requires a combination of single or multiple factors, such as long-term shallow burial and later deep burial with a short burial time, the presence of structural bridges for supporting effect, less compaction, the generation of fractures by tectonism, or long-term weathering for constructive reformation of crystalline rocks; (4) the basin generally presents a medium to low geothermal field, or there is no excessive radioactive material in the environment during the development of source rock, and the large-scale hydrocarbon generation is not accelerated. The reasons for the occurrence of unfavorable accumulation conditions in ultra-deep layers include: (1) mechanical compaction and high temperature and pressure result in strong diagenesis and increased plasticity of rock particles in ultra-deep layers, which is not favorable to the preservation of reservoir pore space; (2) most source rocks in ultra-deep layers have lost their hydrocarbon-generation potential, and the effectiveness of source kitchens is limited due to deep burial and long burial history; (3) there is a low probability for forming an effective combination of source-reservoir-seal-trap, and the probability of economic resource mineralization is reduced. China has abundant oil and gas resources and great exploration potential in ultra-deep layers, but large-scale exploration faces challenges in terms of the hydrocarbon accumulation theory to be perfected and engineering technology, and it is urgent to carry out researches to achieve relevant breakthroughs.

Key words: ultra-deep layers, dichotomy of accumulation conditions, source kitchen, reservoir, source-reservoir-seal combination, effectiveness, exploration position, onshore China