Origins of natural gases from marine strata in Northeastern Sichuan Basin (China) from carbon molecular moieties and isotopic data

Wang, Yunpeng; Zhao, Chunhong; Wang, Hongjun; Wang, Zhaoyun; Wang, Zecheng

doi:10.1016/j.jseaes.2012.09.015

Cited by 8 publications

(2 citation statements)

References 14 publications

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“…1). Tectonically, the Sichuan Basin can be divided into East, South (including South and Southwest), West and Central Sichuan gas-oil accumulation zones, separated by the Longquanshan fault in the west and the Huayingshan fault in the east (Ma et al, 2008;Wang et al, 2013;Ni et al, 2014).…”

Section: Geological Background Of Sichuan Basinmentioning

confidence: 99%

“…More than 20 commercial oil and gas fields have been discovered in the Sichuan Basin over 60 years, with an estimated annual gas production of 10 billion m 3 (Wei et al, 2008). Geological studies regarding hydrocarbon systems such as source rocks, reservoirs and tectonic activities in the Sichuan Basin have been well documented in many studies (Wei et al, 2008;Dai et al, 2012;Wang et al, 2013;. However, the role of groundwater in gas generation, migration and accumulation processes remains unclear.…”

Section: Introductionmentioning

confidence: 99%

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Tracing interaction between hydrocarbon and groundwater systems with isotope signatures preserved in the Anyue gas field, central Sichuan Basin, China

Qin

Wang

et al. 2020

Geochimica et Cosmochimica Acta

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Anyue gas field is a large gas field located in the central Sichuan Basin, China. Although many studies have been carried out previously, the formation mechanism of this field is unclear and currently under debate. To better understand the accumulation history, the role that groundwater plays in transporting hydrocarbons within sedimentary basins and water-gas interactions, stable and noble gas isotopes were measured in thirteen free gas samples from the Anyue gas field. In addition, nine formation water samples and five reservoir bitumen samples were analyzed for stable carbon isotopes. δ 13 C(CH4) values in the gas samples range from-35.0 to-32.6‰, showing evidence of thermogenic origin. δ 13 C values among three different types of samples (free gases, water-dissolved gases and reservoir bitumen) show a pattern that cannot be explained by oil cracking followed by free gas accumulation. It suggests the occurrence of gas-groundwater interaction in the Anyue field. Free gas samples can be divided into 2 distinct groups by their geographical locations and stratigraphical source formations. 3 He/ 4 He ratios (R/Ra) in group 1 and group 2 samples range from 0.0118 to 0.0132 and 0.0115 to 0.0256, respectively, indicating He is mainly derived from the crust. 20 Ne/ 22 Ne and 21 Ne/ 22 Ne ratios suggest a mixing between the air and crust sources. 40 Ar/ 36 Ar ratios ranging from 1658 to 2019 and 2168 to 5973 in group 1 and group 2 samples, respectively, are significantly higher than the air value of 298.6. In comparison, heavier noble gas (Kr and Xe) isotopic compositions are predominantly air-like. The relative enrichment of 4 He and 21 Ne* in group 1 samples can be possibly explained by preferential release of light noble gases in a low temperature environment. Samples in group 2 show a good fit to the solubility-controlled Rayleigh fractionation model, suggesting the presence of an open system degassing of gases from the groundwater. The excess heavy noble gases in natural gas samples can be attributed to the addition of sedimentary components from the source rocks during geological evolution. 4 He groundwater ages considering in-situ production and external flux indicate the addition of 3 young groundwater into the Anyue gas field. Low gas-groundwater ratios and high CH4/ 36 Ar ratios suggest that only a small portion of the gases in the current Longwangmiao reservoir of Anyue gas field has been in contact with the relatively young groundwater. Based on the noble gas and stable carbon isotope results in all samples, we propose a two-stage gas and groundwater interaction process during the gas preservation and accumulation history in the Anyue gas field in China.

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Section: Geological Background Of Sichuan Basinmentioning

confidence: 99%