Carbon isotope fractionation during shale gas transport: Mechanism, characterization and significance

Li, Wenbiao; Lu, Shuangfang; Li, Junqian; Zhang, Pengfei; Wang, Siyuan; Feng, Weijia; Wei, Yongbo

doi:10.1007/s11430-019-9553-5

Cited by 38 publications

(32 citation statements)

References 38 publications

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“…Canister desorption experimental study about the Longmaxi shale samples at reservoir temperatures showed a rapid enrichment of 13 C up to 13.7‰-16.2‰ in methane as desorption proceeds (Ma et al, 2020). Li et al (2020) proposed to divide the gas transport process during a complete production into four stages and demonstrated that methane became depleted in 13 C during the transition stage (stage II) and became enriched in 13 C during the adsorbed gas desorption stage (stage III), while became depleted in 13 C again during the diffusion stage (stage IV). Carbon isotopic enrichment of methane due to adsorption/desorption during stage IV might contribute to the heavy carbon isotope of methane in Taiyang and Jiaoshiba shale gas fields.…”

Section: Diffusion and Adsorption/desorptionmentioning

confidence: 97%

Geochemical Characteristics and Origin of Shale Gases From Sichuan Basin, China

Dong

Yao

et al. 2022

Front. Earth Sci.

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Natural gases from the Taiyang (shallow), Jiaoshiba (middle), and Weirong (deep) shale gas fields in the southern Sichuan Basin were analyzed for molecular and stable carbon isotopic compositions to investigate the geochemical characteristics and gas origins. All the gases belong to shale gas from the Upper Ordovician–Lower Silurian shale and are dominated by methane with gas wetness generally less than 0.83%. The δ13C1 values are −28.5‰, −30.3‰, and −35.2‰ in Taiyang, Jiaoshiba, and Weirong shale gas fields, respectively. The extremely high thermal maturity is the controlling factor for the enrichment of 13C in methane, with a minor contribution from the heavy carbon isotope of the organic matter in the Ordovician Wufeng Formation. Fischer–Tropsch-type synthesis of hydrocarbon gas from CO2 and H2 contributes to the increase of wet gas, which results in the offset from the δ13C1∼wetness linear trend in the Taiyang and Jiaoshiba gas fields. Methane, ethane, and propane in the Taiyang shale gas field have increasing δ13C values with increasing burial depth, which is mainly caused by diffusive migration. All gases are characterized by a complete carbon isotopic reversal trend (δ13C1 > δ13C2 > δ13C3), and it is mainly caused by the reversible free-radical reactions with the conversion from alkane to alkyl groups, with some contribution from the Fischer–Tropsch-type synthesis. The results of this study will improve our understanding of the geochemical characteristics of shale gases from different burial depths and have important implications for future shale gas exploration in the deep and shallow layers.

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Section: Diffusion and Adsorption/desorptionmentioning

confidence: 97%

Geochemical Characteristics and Origin of Shale Gases From Sichuan Basin, China

Dong

Yao

et al. 2022

Front. Earth Sci.

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“…CFSR is strongly affected by the sediment source and sedimentary environments [29,30]. Consequently, CFSR is highly heterogeneous, which is primarily manifested in the mineral types, rock compositions, structural characteristics, pore space, organic matter (OM) characteristics, and hydrocarbon mobility [31][32][33][34][35][36]. Some scholars have studied this issue.…”

Section: Introductionmentioning

confidence: 99%

Coupling Relationship between Lithofacies and Brittleness of the Shale Oil Reservoir: A Case Study of the Shahejie Formation in the Raoyang Sag

Song

et al. 2022

Geofluids

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Analyzing the characteristics of rock brittleness in low-permeability mudstone and shale (MS) formations is imperative for efficient hydraulic fracturing stimulation. Rock brittleness depends on the mineral composition, organic matter abundance, and bedding structure. Based on the MS from Shahejie Formation mineral composition (clay mineral, felsic mineral, and calcareous mineral contents), total organic content, and bedding structure (laminated, laminar, and massive), six types of lithofacies were identified: clay-rich MS, felsic-rich MS, calcareous-rich MS, clay MS, felsic MS, and calcareous MS. The quartz, feldspar, calcite, and dolomite of the Shahejie Formation are brittle minerals. Consequently, lithofacies with high felsic and calcareous mineral contents are more brittle. In addition, laminated and laminar MS are also conducive to hydraulic fracturing. Therefore, laminated, organic-rich, and calcareous-rich MS are the dominant lithofacies for hydraulic fracturing in the Shahejie Formation. The lithofacies and brittleness index were predicted by the response characteristics between mineral compositions and logging curves. The 3521–3552 m section of well B11x is dominated by calcareous-rich MS with developed laminae, representing a favorable section for hydraulic fracturing. Fragile minerals and oil are widely developed in the lower part of the lower 1st member of the Shahejie Formation (Es1L) in the southwestern part of Zhaohuangzhuang-Suning, where hydraulic fracturing can be used to increase shale oil production.

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“…4−6 Compared with other direct and indirect methods for the evaluation of gas content, the isotopic composition of methane can provide a more precise calculation method for the gas-in-place content in shale reservoirs and reflect the stage characteristics of gas production. 4,5 In addition, carbon isotopic compositions are also important agents in identifying the origin of shale gas, gas migration patterns, and maturity of shale. 7,8 Isotope fractionation is the phenomenon of differences in chemical or physical behavior of isotopic molecules.…”

Section: Introductionmentioning

confidence: 99%

“…18 This phenomenon is more evident in shale formations with strong gas storage capacity. 4 Moreover, isotope fractionation may also result from the dissolution of methane isotope gas into an aqueous phase due to higher solubility for 13 CH 4 compared to that of 12 CH 4 , but the contribution of dissolution to fractionation can be ignored in shale gas production. 6,11 In addition to adsorption/desorption and dissolution, the discrepancy between transport capacity of isotopic gases during transport through shale pores also results in isotope fractionation.…”

Section: Introductionmentioning

confidence: 99%

“…26 The mean free path of methane isotopes is small (i.e., intermolecular collision is dominant), and the isotope fractionation is not obvious. 4 The mean free path of methane isotopes increases during the pressure depletion process, and Knudsen diffusion dominates when the pressure in shale nanopores is low. 27 Methane isotopes prefer to exchange energy and momentum with pore walls instead of colliding with each other.…”

Section: Introductionmentioning

confidence: 99%

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Carbon Isotope Fractionation during Shale Gas Transport through Organic and Inorganic Nanopores from Molecular Simulations

Wang

Zhao

et al. 2021

Energy Fuels

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Carbon isotope fractionation is a promising method to predict gas-in-place content and evaluate the shale gas production stage. In this study, molecular simulations are conducted to investigate fractionation characteristics of 12CH4 and 13CH4 in high-Kn (Knudsen number) flows (Kn > 0.1) within organic and inorganic pores under shale reservoir conditions (353 K, 5–25 MPa). The results show that isotope fractionation is more obvious (i.e., the difference in transport capacities between 12CH4 and 13CH4 is larger) in organic pores than in inorganic pores. Methane adsorption capacity and surface roughness of pore walls are two major reasons. High-coverage adsorption in organic pores reduces the effective pore size, and the Knudsen diffusion becomes significant. Moreover, the specular reflection of molecules occurs frequently on the smooth surfaces of organic pores, which enlarges the difference in isotope diffusion capacity. Indeed, the difference in energy (specific enthalpy) transport of methane isotopes in organic and inorganic pores is the intrinsic reason for fractionation. Furthermore, the fractionation level is positively correlated with Kn due to the enhanced contribution of Knudsen diffusion and surface diffusion in high-Kn flows. In addition, the isotope fractionation level decreases as pore size increases because Kn and the contribution of the adsorbed phase to the total molar flux reduce in a large pore. Our findings and related analyses may help us to understand isotope fractionation in different pore types and sizes from the atomic level and assist future applications in engineering.

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Carbon isotope fractionation during shale gas transport: Mechanism, characterization and significance

Cited by 38 publications

References 38 publications

Geochemical Characteristics and Origin of Shale Gases From Sichuan Basin, China

Geochemical Characteristics and Origin of Shale Gases From Sichuan Basin, China

Coupling Relationship between Lithofacies and Brittleness of the Shale Oil Reservoir: A Case Study of the Shahejie Formation in the Raoyang Sag

Carbon Isotope Fractionation during Shale Gas Transport through Organic and Inorganic Nanopores from Molecular Simulations

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