Pore structure characterization and its effect on methane adsorption in shale kerogen
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ORIGINAL PAPER
Pore structure characterization and its effect on methane adsorption in shale kerogen Tian‑Yu Wang1,2 · Shou‑Ceng Tian1,2 · Qing‑Ling Liu3 · Gen‑Sheng Li1 · Mao Sheng1,2 · Wen‑Xi Ren1,4 · Pan‑Pan Zhang1,2 Received: 3 February 2020 / Accepted: 22 October 2020 © The Author(s) 2020
Abstract Pore structure characterization and its effect on methane adsorption on shale kerogen are crucial to understanding the fundamental mechanisms of gas storage, transport, and reserves evaluation. In this study, we use 3D scanning confocal microscopy, scanning electron microscopy (SEM), X-ray nano-computed tomography (nano-CT), and low-pressure N2 adsorption analysis to analyze the pore structures of the shale. Additionally, the adsorption behavior of methane on shales with different pore structures is investigated by molecular simulations. The results show that the SEM image of the shale sample obviously displays four different pore shapes, including slit pore, square pore, triangle pore, and circle pore. The average coordination number is 4.21 and the distribution of coordination numbers demonstrates that pores in the shale have high connectivity. Compared with the adsorption capacity of methane on triangle pores, the adsorption capacity on slit pore, square pore, and circle pore are reduced by 9.86%, 8.55%, and 6.12%, respectively. With increasing pressure, these acute wedges fill in a manner different from the right or obtuse angles in the other pores. This study offers a quantitative understanding of the effect of pore structure on methane adsorption in the shale and provides better insight into the evaluation of gas storage in geologic shale reservoirs. Keywords Shale · Methane adsorption · Pore structure · Kerogen · Molecular simulation
1 Introduction
Edited by Yan-Hua Sun Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12182-020-00528-9) contains supplementary material, which is available to authorized users. * Shou‑Ceng Tian [email protected] 1
State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum (Beijing), Beijing 102249, China
2
Harvard SEAS-CUPB Joint Laboratory on Petroleum Science, 29 Oxford Street, Cambridge, MA 02138, USA
3
China National Oil and Gas Exploration and Development Company Ltd, Beijing 100034, China
4
State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, China
The extraction of gas from shale is regarded as an energy game-changer (Hughes 2013). As a transition fuel, shale gas offsets reducing of conventional gas production (Vidic et al. 2013). Horizontal drilling coupled with multi-stage hydraulic fracturing makes it possible to extract hydrocarbons from shale reservoirs (Ren et al. 2016; Shi et al. 2019). Gas in shale reservoirs mainly exists in three forms: free gas, adsorbed gas, and dissolved gas. Particularly, about 20%‒85% of the total gas-in-place is adsorbed gas (Curtis 2002). In shale gas production, the desor
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