Reservoir characteristics of coal–shale sedimentary sequence in coal-bearing strata and their implications for the accumulation of unconventional gas

Wang, Yang; Zhu, Yanming; Chen, Shangbin

doi:10.1088/1742-2140/aa9a10

Cited by 11 publications

(9 citation statements)

References 38 publications

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“…The extent of permeability variation by swelling strain is assumed to be negligible, due to lower organic content of shale (compared to coal). 51 However, in organic-rich shale a small swelling strain may change the stress-induced pore dilation during gas injection. The total strain in organic-rich shale can be obtained by superposition of swelling-induced volumetric strain and the poromechanical strains obtained from Equations (1)-(5).…”

Section: Discussionmentioning

confidence: 99%

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A model for stress‐dependence of apparent permeability in nanopores of shale gas reservoirs

2020

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Predicting long‐term production from gas shale reservoirs is a challenging task due to changes in effective stress and permeability during gas production. Unlike coal, the variation of sorbing gas permeability with pore pressure in shale does not always feature a biphasic trend under a constant confining pressure. The present contribution demonstrates that the biphasic dependence of permeability on pore pressure depends on a number of physical and geometrical factors, each with a distinct impact on gas permeability. This includes pore size, adsorption isotherm, and the variation of gas viscosity with pore pressure. A single‐capillary model is proposed for the apparent permeability of real gas in shale. Results indicate that the biphasic relation between apparent permeability and pore pressure is prevalent when the sorbing gas flows in sufficiently small pores. In addition, the effects of sorption isotherm and internal resistance of nonideal gas to flow cannot be ignored.

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Section: Discussionmentioning

confidence: 99%

“…The proposed model can be generalized along several directions. The extent of permeability variation by swelling strain is assumed to be negligible, due to lower organic content of shale (compared to coal) 51 . However, in organic‐rich shale a small swelling strain may change the stress‐induced pore dilation during gas injection.…”

Section: Discussionmentioning

confidence: 99%

A model for stress‐dependence of apparent permeability in nanopores of shale gas reservoirs

2020

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“…The study of sedimentary facies is important for the in-depth understanding of the peat-forming environment, peat accumulation regularity and unconventional gas in coal measures during the formation and evolution of a coal-bearing basin [1][2][3][4][5][6]. Previous studies have shown that the Carboniferous-Permian coal-bearing series in the Yangquan mining area of the Qinshui Basin was formed in the marine-continental transitional environment, and the main coal-bearing strata, the Taiyuan Formation and Shanxi Formation, underwent sedimentary evolution from barrier coast systems to deltaic systems [7][8][9].…”

Section: Introductionmentioning

confidence: 99%

Seismic-Geological Integrated Study on Sedimentary Evolution and Peat Accumulation Regularity of the Shanxi Formation in Xinjing Mining Area, Qinshui Basin

et al. 2022

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Accurate identification of the lithofacies and sedimentary facies of coal-bearing series is significant in the study of peat accumulation, coal thickness variation and coal-measured unconventional gas. This research integrated core, logging and 3D seismic data to conduct a comprehensive seismic–geological study on the sedimentary evolution characteristics and peat accumulation regularity of the Shanxi Formation in the Xinjing mining area of the Qinshui Basin. Firstly, the high-resolution sequence interface was identified, and the isochronous stratigraphic framework of the coal-bearing series was constructed. Then, the temporal and spatial evolution of sedimentary filling and sedimentary facies was dynamically analyzed using waveform clustering, phase rotation, stratal slice and frequency–division amplitude fusion methods. The results show that the Shanxi Formation in the study area can be divided into one third-order sequence and two fourth-order sequences. It developed a river-dominated deltaic system, mainly with delta plain deposits, and underwent a constructive–abandoned–constructive development stage. The locally distributed No. 6 coal seam was formed in a backswamp environment with distribution constrained by the distributary channels. The delta was abandoned at the later stage of the SS1 sequence, and the peat accumulation rate was balanced with the growth rate of the accommodation, forming a large-area distributed No. 3 thick coal seam. During the formation of the SS2 sequence, the No. 3 coal seam was locally thinned by epigenetic erosion of the river, and the thin coal belt caused by erosion is controlled by the location of the distributary channels and their extension direction. This study can provide a reference for the research on the distribution of thin sand bodies, sedimentary evolution and peat accumulation regularity in the coal-bearing series under the marine–continental transitional environment.

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“…Coalbed gas (also named coalbed methane) and shale gas, storing at the coal and shale reservoirs with low porosity and low permeability in the coal measures, belong to the gas types of unconventional natural gas (Li et al., 2019a; Tan et al., 2019; Wang et al., 2018). Both gases can be commingled and produced from a well by perforating the reservoirs at different depth.…”

Section: Introductionmentioning

confidence: 99%

“…Both gases can be commingled and produced from a well by perforating the reservoirs at different depth. Gas commingling can improve the profitability of exploration and exploitation; it can also enhance the drainage efficiency and gas production output of a single well (Li et al., 2019b; Wang et al., 2018). The investigation of the pore structure characteristics of a mixed coal and shale reservoirs is one of the vital research areas in better evaluating the reservoir characteristics and gas content, to inform on the potential for commingling of both gases at the coal measures.…”

Section: Introductionmentioning

confidence: 99%

Influence of reservoir properties on the methane adsorption capacity and fractal features of coal and shale in the upper Permian coal measures of the South Sichuan coalfield, China

Bao

Yin

et al. 2019

Energy Exploration & Exploitation

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Pore structure plays an essential role in the reservoir heterogeneity and methane adsorption capacity. Significant progress has been made in the pore structure classification of porous materials (such as coal and shale). Considering the pore structure characterization of the coal measures and the measuring range of high-pressure mercury intrusion porosimetry and low-pressure N2/CO2 gas adsorption, an integrated classification for coal and shale is provided. They are micropore (<2 nm), mesopore (2–100 nm), macropore A (100 nm–1 µm), macropore B (1–10 µm), and micro-fracture (>10 µm). For coal and shale samples from Guxu mining area, the micropores and mesopores largely control the gas adsorption while micro-fractures and macropore B are significant for the storage and flow of free gas. The fractal dimensions calculated from limited N2 adsorption data are not suitable for the coal samples which are not developed in mesopore and macropore A; these samples are precisely corresponding to the N2 adsorption/desorption isotherms of group B (reversible isotherm). Furthermore, the main factors influencing the methane adsorption capacity of coal and shale in the coal measures are micropore frequency, micro-fracture width, clay mineral composition, and total organic carbon content.

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Reservoir characteristics of coal–shale sedimentary sequence in coal-bearing strata and their implications for the accumulation of unconventional gas

Cited by 11 publications

References 38 publications

A model for stress‐dependence of apparent permeability in nanopores of shale gas reservoirs

A model for stress‐dependence of apparent permeability in nanopores of shale gas reservoirs

Seismic-Geological Integrated Study on Sedimentary Evolution and Peat Accumulation Regularity of the Shanxi Formation in Xinjing Mining Area, Qinshui Basin

Influence of reservoir properties on the methane adsorption capacity and fractal features of coal and shale in the upper Permian coal measures of the South Sichuan coalfield, China

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