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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 processes of the marine ultra-deep oil and gas reservoirs and the key controlling factors of accumulation. The marine ultra-deep oil and gas resources in China are buried at depth of greater than 6000 m, and are mainly distributed in the Precambrian and Lower Paleozoic strata in the Sichuan, Tarim and Ordos cratonic basins. The development of marine ultra-deep source rocks in China is controlled by cratonic rifts and cratonic depressions with the background of global supercontinent breakup-convergence cycles. The source rocks in Sichuan Basin have the most developed strata, followed by Tarim Basin, and the development strata and scale of Ordos Basin needs to be further confirmed. The marine ultra-deep reservoir in China is dominated by carbonate rocks, and the reservoir performance is controlled by high-energy sedimentary environment in the early stage, superimposed corrosion and fracture in the later stage. 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, cracking (or partial cracking) of paleo-oil reservoirs, and late finalization of cracked gas (or highly mature to 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. We propose three favorable exploration directions, i.e. the areas around intracratonic rift and intracratonic depression, and craton margin.

Based on the three dimensional seismic data and drilling data in Gaoshiti–Moxi area, the structural characteristics and evolution process of strike-slip faults in the study area and their significance for gas accumulation were examined using the method of fault structure analysis. The results show that: (1) Transtensional strike-slip faults are developed in the Paleozoic in study area. On the profile, there are three types of structural styles: steep and erect, flower structures, “Y” and reversed “Y” type faults. On the plane, strike-slip faults developed in the Cambrian extending linearly and along the nearly EW, NW and NE direction. The faults are composed of multiple secondary faults in en-echelon arrangement; faults in the Permian are mainly along nearly EW and NW direction, and the Permian faults are distributed in the middle east part of the study area and they are more in the north than in the south. (2) The nearly EW and NW trending faults are dextral strike-slip faults, and the NE trending faults are sinistral strike-slip faults. The strike-slip strength of the nearly EW trending faults are the strongest and the maximum horizontal displacement is 550 m, while the strike-slip strength of the NE trending faults is the weakest. The Cambrian faults had stronger activities than the Permian faults. (3) The transtensional strike-slip faults were active in two periods, the early Caledonian period and the late Hercynian period, and were the products of oblique extension of pre-existing weak zones in Xingkai and Emei taphrogenesis, with certain inheritance in the main faults. (4) The strike-slip faults and surrounding fractures enhance the porosity and permeability of the reservoir in Cambrian Longwangmiao Formation and control the distribution of karst reservoirs in the Permian Qixia Formation–Maokou Formation, bringing about the situation of multiple gases bearing series in this area. Key words: Sichuan Basin, Gaoshiti–Moxi area, Cambrian, Permian, strike-slip fault, structural characteristics, gas accumulation

Through new 3-D seismic data, we present relationship between maximum throw and fault length and fault segment length in fault zones, and relationship among length, width, throw and separation in overlap and tip zones of a conjugate strike-slip fault system in the intracratonic Tarim Basin, NW China. The results show that: (1) the major fault zones are in range of 23–76 km in length, and compose of 3–8 segments with low maximum throw less than 140 m; (2) a good power–law-scaling relationship of throw-segment length but not of throw-fault length; (3) more mature in NNW trending faults than in NNE trending faults; (4) the hard-linked overlap zones concentrate most deformation and exceptional high throws, with better linear correlation between throw and overlap zone length rather than soft-linked segments; (5) length/width, length/throw and separation/throw ratios from the transpressional overlap zones varies in a range of 4.6–11.2, 59–130 and 6.1–12.3, which are quite larger than those from extensional settings. Our study suggest that: (1) the fault growth depends on the stages of segment linkage (maturity); (2) the linear trends of scaling relationship between fault elements are mainly controlled by mechanical properties, while the scattered distribution of data is related to the stage of fault linkage and overlapping; (3) the deformation and displacement are localized in the overlap zones after hard-linkage following fault segments interaction; (4) fault elements could be useful to understanding fault growth and evolution stages in the deep subsurface. These results provide new insight into a better understanding of fault linkage and interaction from the subsurface seismic data in strike-slip fault zones.