Conventionally trapped natural gas accumulations in the Jurassic tight sandstone reservoirs: A case study from the Center of the Western Sichuan Basin, SW China

Abstract

Tight gas accumulations, commonly characterized by low permeability, low porosity, and complicated pore structure, are widely distributed in the Sichuan Basin. Recent exploration in the Chengdu Sag, Western Sichuan Basin has proven that Jurassic tight-sandstone reservoirs attach significant gas potential. However, long distance migration between source and reservoir intervals entangles understanding of the tight-gas accumulation mechanism. It is unclear whether producible gas in Jurassic intervals is either from ''simple sweet-spots in a continuous accumulation'' or ''conventionally trapped accumulations in low-permeability reservoir rocks''. To identify the regionally active gas system and characterize the charging pattern, a geochemical study was performed by interpreting the gas molecular and carbon isotope compositions in Jurassic and conducting gas-source correlations as well as gas migration distance calculation with the relationship among d 13 C 1 vs. R o vs. H (burial depth). Research results indicate that the Jurassic tight gases in Majing-Shifang areas are coal-derived dry gases generated by the primary cracking of kerogen. Gas/source correlation and gas migration distance calculation reveal that gases are mainly sourced from the Upper Triassic humic source rocks (T 3 x 5 , the fifth member of the Xujiahe Formation). Gas accumulations in the Jurassic Penglaizhen Formation were formed with an original vertical migration of about 2-3 km and then a long-distance lateral migration within tight sand layers, which is verified by the decreasing d 13 C 1 and the general increasing iC 4 /nC 4 in the Penglaizhen Formation. The Jurassic tight-sandstone reservoirs in Majing-Shifang areas occur in low-porosity and low-permeability reservoir rocks in conventional lithological traps, which are not continuous-type gas accumulations or basin-centered gas systems. The faults in Majing area serve as dominant vertical conducting pathway and the relatively permeable

The differential diagenesis controls on the physical properties of lithofacies in sandstone reservoirs from the Jurassic Shaximiao Formation, western Sichuan depression, China

“…Figure 1 shows that the location of the eastern slope of western Sichuan depression and the stratigraphic column of the Jurassic Shaximiao Formation (Liu et al, 2018). As can be seen in Figure 1a, the western Sichuan depression is located in the western part of Sichuan Basin of China, and surrounded by the east of the Longmen Mountain Thrust Belt and the west of the middle Sichuan uplift in Sichuan Basin (Guo et al, 2018;Liu et al, 2018). The western Sichuan depression underwent multi-stage tectonic movements from the Mesozoic.…”

Characteristics of coal-measure source rock and its controlling effect on gas-water distribution of tight sandstone of He8 Member in Sulige Gas Province, Ordos Basin

“…One is that tight gas reservoir belongs to deep basin gas (Law, 2002) and has continuous accumulation type (Schmoker, 2002). The second type is considered as conventional lithologic reservoir (Guo et al, 2018), which belongs to discontinuous distribution characteristics. The third understanding is that tight gas accumulation belongs to quasi-continuous accumulation characteristics, that is, it is different from continuous hydrocarbon accumulation, and also different from conventional type, showing differences about 10 aspects (Zhao et al, 2017(Zhao et al, , 2019.…”

A reservoir quality evaluation approach for tight sandstone reservoirs based on the gray correlation algorithm: A case study of the Chang 6 layer in the W area of the as oilfield, Ordos Basin

“…With continuous progress in oil and gas exploration and development theory, domestic and international oil and gas exploration and development have gradually developed from conventional to unconventional resources (Aguilera, 2018;Guo et al, 2018;Liu et al, 2019a;Stephen et al, 2020;Wang et al, 2015). Meanwhile, the world's oil and gas exploration and development turn to deeper, more complex and more challenging unconventional oil and gas fields with more complex enhanced oil and gas recovery approaches than those applied to conventional sources (Liu et al, 2019b(Liu et al, , 2020Wei et al, 2020;Zhang et al, 2020;Zhong et al, 2020).…”

“…Tight oil exploration has made a series of new discoveries and breakthroughs in the Ordos Basin (Zhou et al, 2020), Sichuan Basin (Guo et al, 2018), Songliao Basin (Xi et al, 2018), Junggar Basin, Tarim Basin (Wei et al, 2020), etc., with rapid growth of reserves and production (Zheng et al, 2017). The Ordos Basin is one of the main production areas of tight oil and gas in China.…”