Geochemical characteristics and implications of shale gas from the Longmaxi Formation, Sichuan Basin, China

Cao, Chunwei; Lv, Zonggang; Li, Liwu; Du, Lidong

doi:10.1016/j.jnggs.2016.05.001

Cited by 37 publications

(35 citation statements)

References 30 publications

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“…Longmaxi shale formation is comprised of dark gray to black graptolite shale, carbonaceous shale, siliceous shale, silty shale, and argillaceous siltstone24. The organic content of shale is larger than 0.5%, with a mean TOC of 2.54%.…”

Section: Methodsmentioning

confidence: 99%

“…In this study, shale samples were recovered from the Lower Silurian Longmaxi (LM) shale formation located in Qianjiang, southeast of Chongqing. Longmaxi shale formation is comprised of dark gray to black graptolite shale, carbonaceous shale, siliceous shale, silty shale, and argillaceous siltstone 24 . The organic content of shale is larger than 0.5%, with a mean TOC of 2.54%.…”

Section: Methodsmentioning

confidence: 99%

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Experimental investigation on the coupled effect of effective stress and gas slippage on the permeability of shale

Yang

Wang

Chen

et al. 2017

Sci Rep

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Permeability is one of the most important parameters to evaluate gas production in shale reservoirs. Because shale permeability is extremely low, gas is often used in the laboratory to measure permeability. However, the measured apparent gas permeability is higher than the intrinsic permeability due to the gas slippage effect, which could be even more dominant for materials with nanopores. Increasing gas pressure during tests reduces gas slippage effect, but it also decreases the effective stress which in turn influences the permeability. The coupled effect of gas slippage and effective stress on shale permeability remains unclear. Here we perform laboratory experiments on Longmaxi shale specimens to explore the coupled effect. We use the pressure transient method to measure permeability under different stress and pressure conditions. Our results reveal that the apparent measured permeability is controlled by these two competing effects. With increasing gas pressure, there exists a pressure threshold at which the dominant effect on permeability switches from gas slippage to effective stress. Based on the Klinkenberg model, we propose a new conceptual model that incorporates both competing effects. Combining microstructure analysis, we further discuss the roles of stress, gas pressure and water contents on gas permeability of shale.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Experimental investigation on the coupled effect of effective stress and gas slippage on the permeability of shale

Yang

Wang

Chen

et al. 2017

Sci Rep

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“…As per the studies on the origin of heavy methane carbon isotopes which may cause partial reversal of δ 13 C 1 >δ 13 C 2 in a shale system at high maturity (Cao et al., 2015; Dai et al., 2016b; Liu, 2015; Wei et al., 2016; Wu et al., 2015), some conclusions were reached. First, diffusion may cause 13 C enrichment in methane gas and consequently heavy carbon isotopes.…”

Section: Discussionmentioning

confidence: 95%

“…Organic matter is of type I-II 1 and TOC content is high (4.0% on the average) (Dong et al, 2014;Gao, 2015). The content of brittle minerals is high and pore space is composed of matrix pores and some fractures; the permeability is 0.3 Â 10 À3 lm 2 (Cao et al, 2015;Zou et al, 2015).…”

Section: Geologic Settingmentioning

confidence: 99%

“…Organic matter is of type I–II 1 and TOC content is high (4.0% on the average) (Dong et al., 2014; Gao, 2015). The content of brittle minerals is high and pore space is composed of matrix pores and some fractures; the permeability is 0.3 × 10 −3 μm 2 (Cao et al., 2015; Zou et al., 2015).

Figure 1.General maps of Changning (a) and (b) the map of Fuling gas field (modified after Guo and Zhang 2014; Guo, 2016) in the Sichuan Basin and locations of sampling wells. …”

Section: Geologic Settingmentioning

confidence: 99%

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Longmaxi shale gas geochemistry in Changning and Fuling gas fields, the Sichuan Basin

Feng

Huang

et al. 2017

Energy Exploration & Exploitation

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This paper focuses on Longmaxi shale gas geochemistry and carbon isotopic reversal in Changning and Fuling gas fields through comparative study of shale gas composition and carbon and hydrogen isotopes in North America and Changning and Fuling gas fields. Longmaxi shale gas in Changning and Fuling gas fields exhibits the features of dry gas. Specifically, the average methane (CH 4) content is 98.72 and 98.17%, respectively. The humidity is less than 0.5%. Nonhydrocarbon gases include a small amount of CO 2 and N 2. Extremely heavy d 13 C 1 value, average d 13 C 2 value of À33.3 and À34.6% for Changning and Fuling, and sapropelic organic matter indicate the properties of petroliferous dry gas. Carbon isotopic reversal, i.e. d 13 C 1 >d 13 C 2 >d 13 C 3 , may be caused by combined secondary effects at high maturity and high geotemperature. The reversal may also be related to ethane Rayleigh fractionation and late methane generation by water and transition metals reaction. Geologic setting in these two gas fields may have an impact on carbon isotopes distribution.

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Carbon isotope composition characteristics of light hydrocarbon gas from typical kerogen cracking and its application for gas source identification: A case study of the Sichuan Basin

Cao

et al. 2023

Geological Journal

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The natural gas resources in the Sichuan Basin are abundant and exhibit various phenomena, for example, mixed sources, mixed maturities and overlapping combinations, resulting in great difficulties in identifying natural gas sources. In this study, several groups of thermal simulation experiments were conducted on various types of kerogens using closed and/or semi‐open systems to investigate the characteristics of the carbon isotope compositions of light hydrocarbon gases derived from different typical kerogens. The results showed that the carbon isotope compositions and variation trends of methane and ethane are controlled by the kerogen type, thermal simulation system and thermal evolution degree. The carbon isotope compositions of light hydrocarbon gases derived from different types of kerogens exhibit some differences with increased thermal evolution degree. When the thermal simulation temperature increases from 320 to 550°C, the methane carbon isotope of typically marine source rocks, mainly type I and type II1 kerogens, is slightly higher than or equivalent to that of ethane. However, the ethane carbon isotope of terrestrial source rocks, primarily types II2 and III kerogens, is significantly heavier than methane. By comparison, the evolution trend of carbon isotope compositions of actual natural gas is well consistent with that of light hydrocarbon gases cracked from thermal simulation experiments with increased thermal evolution degree. These findings are of great importance to identify the source rock of actual natural gas with high thermal maturities, as well as to determine the sources of deep shale gas in the southern Sichuan Basin, the Yuanba gas field and the Puguang gas field. Finally, a fitting method of carbon isotope values of methane and ethane of light hydrocarbon gases can be used to more finely differentiate the sources of natural gas in complex areas with mixed sources, mixed maturities and overlapping combinations.

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Geochemical characteristics and implications of shale gas from the Longmaxi Formation, Sichuan Basin, China

Cited by 37 publications

References 30 publications

Experimental investigation on the coupled effect of effective stress and gas slippage on the permeability of shale

Experimental investigation on the coupled effect of effective stress and gas slippage on the permeability of shale

Longmaxi shale gas geochemistry in Changning and Fuling gas fields, the Sichuan Basin

Carbon isotope composition characteristics of light hydrocarbon gas from typical kerogen cracking and its application for gas source identification: A case study of the Sichuan Basin

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