Impact of gas adsorption on apparent permeability of shale fracture and shale gas recovery rate

Abstract CO2 displacement has been proposed to enhance shale gas recovery and unlock a big potential market for CO2 beneficial utilization. Theoretically, gas adsorption is inversely related to the temperature, so gas can be desorbed by elevating the temperature. This paper investigates the economic performance of enhancing shale gas recovery by injecting CO2 at high temperatures through displacement as well as desorption by rising temperatures. Influences of operation temperature and injection pressure were studied for three potential shale plays in China. Study results show that both factors exerted obvious impacts, and CO2 procurement was the largest cost component. It is found that the net revenue was not always proportional to the operation temperature, but more controlled by the injection–production ratio. This is because of the different temperature impacts to the various patterns of adsorbed CH4 and CO2 contents. Consequently, in some cases, more CO2 is needed to displace CH4 when operation temperature is raised, resulting a higher cost. The modeling results demonstrate that based on the adsorption characters of reservoirs, the productivity and profitability of CO2 enhanced gas recovery can be further improved by choosing appropriate operation temperatures.

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Study on Competitive Adsorption and Displacing Properties of CO2 Enhanced Shale Gas Recovery: Advances and Challenges

Geofluids ◽

10.1155/2020/6657995 ◽

2020 ◽

Vol 2020 ◽

pp. 1-15

Author(s):

Shuyang Liu ◽

Baojiang Sun ◽

Jianchun Xu ◽

Hangyu Li ◽

Xiaopu Wang

Keyword(s):

Shale Gas ◽

Adsorption Mechanism ◽

Competitive Adsorption ◽

Gas Adsorption ◽

Organic Matter Content ◽

Gas Production ◽

Gas Recovery ◽

Model Studies ◽

Displacement Experiments ◽

Adsorption Of Co2

CO2 enhanced shale gas recovery (CO2-ESGR) draws worldwide attentions in recent years with having significant environmental benefit of CO2 geological storage and economic benefit of shale gas production. This paper is aimed at reviewing the state of experiment and model studies on gas adsorption, competitive adsorption of CO2/CH4, and displacement of CO2-CH4 in shale in the process of CO2-ESGR and pointing out the related challenges and opportunities. Gas adsorption mechanism in shale, influencing factors (organic matter content, kerogen type, thermal maturity, inorganic compositions, moisture, and micro/nano-scale pore), and adsorption models are described in this work. The competitive adsorption mechanisms are qualitatively ascertained by analysis of unique molecular and supercritical properties of CO2 and the interaction of CO2 with shale matrix. Shale matrix shows a stronger affinity with CO2, and thus, adsorption capacity of CO2 is larger than that of CH4 even with the coexistence of CO2-CH4 mixture. Displacement experiments of CO2-CH4 in shale proved that shale gas recovery is enhanced by the competitive adsorption of CO2 to CH4. Although the competitive adsorption mechanism is preliminary revealed, some challenges still exist. Competitive adsorption behavior is not fully understood in the coexistence of CO2 and CH4 components, and more experiment and model studies on adsorption of CO2-CH4 mixtures need to be conducted under field conditions. Coupling of competitive adsorption with displacing flow is key factor for CO2-ESGR but not comprehensively studied. More displacement experiments of CO2-CH4 in shale are required for revealing the mechanism of flow and transport of gas in CO2-ESGR.

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Study on Two Component Gas Transport in Nanopores for Enhanced Shale Gas Recovery by Using Carbon Dioxide Injection

Energies ◽

10.3390/en13051101 ◽

2020 ◽

Vol 13 (5) ◽

pp. 1101

Author(s):

Chaohua Guo ◽

Rongji Li ◽

Xin Wang ◽

Hongji Liu

Keyword(s):

Carbon Dioxide ◽

High Pressure ◽

Shale Gas ◽

Molecular Diffusion ◽

Gas Transport ◽

Transport Mechanisms ◽

Apparent Permeability ◽

Gas Concentration ◽

Gas Recovery ◽

Two Component

Injecting carbon dioxide to enhance shale gas recovery (CO2-EGR) is a useful technique that has raised great research interests. Clear understanding of the two-component gas transport mechanisms in shale nanopores is the foundation for the efficient development of shale gas reservoir (SGR) and also the long-term geological storage of CO2. Although extensive studies on single-component gas transport and corresponding models in shale nanopores have been carried out in recent years, limited studies have been conducted on two-component or even multi-component gas transport models in shale nanopores. In this work, the shale nanopores were classified into inorganic and organic nanopores. The corresponding models for two-component gas transport were constructed. Mechanisms including Knudsen diffusion, slip flow, viscous flow, and molecular diffusion are considered in the inorganic pores. In the organic pores, due to existence of adsorption gas, surface diffusion is further considered besides the aforementioned mechanisms. Effects of pressure, temperature, fraction of organic nanopores, and gas concentration were analyzed. Results show that gas apparent permeability is negatively correlated with pressure, and positively correlated with temperature and organic nanopore fraction. As the concentration of CH4 decreases, the apparent permeability of CH4 increases continuously, while the apparent permeability of CO2 decreases. The permeability ratio of CH4 in the total permeability is negatively correlated with pressure and gas concentration ratio. Additionally, the contribution of transport mechanisms to the total gas apparent permeability has been analyzed. It is found that the surface diffusion contributes up to 5.68% to gas apparent permeability under high pressure. The contribution of molecular diffusion can reach up to 88.83% in mesopores under low pressure. Under high pressure and macropores, it contributes less than 1.41%. For all situations, the contribution of viscous flow is more than 46.36%, and its contribution can reach up to 86.07%. Results of this study not only can improve the understanding of two-component gas transport in nanochannels, but also can lay the foundation for more reliable reservoir simulation of CO2-EGR.

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Effect of gas adsorption-induced pore radius and effective stress on shale gas permeability in slip flow: New Insights

Open Geosciences ◽

10.1515/geo-2019-0073 ◽

2019 ◽

Vol 11 (1) ◽

pp. 948-960 ◽

Cited By ~ 3

Author(s):

Asadullah Memon ◽

Aifen Li ◽

Wencheng Han ◽

Weibing Tian

Keyword(s):

Effective Stress ◽

Shale Gas ◽

Pore Radius ◽

Gas Adsorption ◽

Gas Permeability ◽

Slip Flow ◽

Flow Regimes ◽

Gas Production ◽

Adsorption Parameters ◽

Apparent Permeability

Abstract Shale, a heterogeneous and extremely complex gas reservoir, contains low porosity and ultra-Low permeability properties at different pore scales. Its flow behaviors are more complicated due to different forms of flow regimes under laboratory conditions. Flow regimes change with respect to pore scale variation resulting in change in gas permeability. This work presents new insights regarding the change of pore radius due to gas adsorption, effective stress and impact of both on shale gas permeability measurements in flow regimes. From this study, it was revealed that the value of Klinkenberg coefficient has been affected due to gas adsorption-induced pore radius thickness impacts and resulting change in gas permeability. The gas permeability measured from new proposed equation is provides better results as compare to existing equation. Adsorption parameters are the key factors that affect radius of shale pore. Both adsorption and effective stress have an effect on the pore radius and result gas permeability change. It was found that slip effect enhances the apparent gas permeability and also changes with effective stress; therefore, combine impact of slip flow and effective stress is very important as provides understanding in evolution of apparent permeability during shale gas production.

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