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Title: Fully coupled two-phase flow and poromechanics modeling of coalbed methane recovery: Impact of geomechanics on production rate

Abstract

This study presents the development and application of a fully coupled two-phase (methane and water) flow, transport, and poromechanics num erical model for the analysis of geomechanical impacts on coalbed methane (CBM) production. The model considers changes in two-phase fluid flow properties, i.e., coal porosity, permeability, water retention, and relative permeability curves through changes in cleat fractures induced by effective stress variations and desorption-induced shrinkage. The coupled simulator is first verified for poromechanics coupling, and simulation parameters of a CBM reservoir model are calibrated by history matching against one year of CBM production field data from Shanxi Province, China. Then, the verified simulator and the calibrated CBM reservoir model are used for predicting the impact of geomechanics on the production rate for twenty years of continuous CBM production. The simulation results show that desorption-induced shrinkage is the dominant process in increasing permeability in the near wellbore region. Away from the wellbore, desorption-induced shrinkage is weaker, and permeability is reduced by pressure depletion and increased effective stress. A sensitivity analysis shows that for coal with a higher sorption strain, a larger initial Young's modulus and a smaller Poisson's ratio promote the enhancement of permeability as well as an increased production rate.more » Moreover, the conceptual model of the cleat system, whether dominated by vertical cleats with permeability correlated to horizontal stress or with permeability correlated to mean stress, can have a significant impact on the predicted production rate. Overall, the study clearly demonstrates and confirms the critical importance of considering geomechanics for an accurate prediction of CBM production.« less

Authors:
ORCiD logo [1];  [2];  [2];  [3];  [4]
  1. China Univ. of Mining and Technology, Jiangsu (China); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  3. China Univ. of Mining and Technology, Jiangsu (China)
  4. Shandong Univ. of Science and Technology, Shandong (China)
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Fossil Energy (FE), Clean Coal and Carbon (FE-20)
OSTI Identifier:
1379925
Grant/Contract Number:
AC02-05CH11231
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Natural Gas Science and Engineering
Additional Journal Information:
Journal Volume: 45; Journal Issue: C; Journal ID: ISSN 1875-5100
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
03 NATURAL GAS; 58 GEOSCIENCES; CBM recovery; Two-phase flow; Poromechanics; Coupled model

Citation Formats

Ma, Tianran, Rutqvist, Jonny, Oldenburg, Curtis M., Liu, Weiqun, and Chen, Junguo. Fully coupled two-phase flow and poromechanics modeling of coalbed methane recovery: Impact of geomechanics on production rate. United States: N. p., 2017. Web. doi:10.1016/j.jngse.2017.05.024.
Ma, Tianran, Rutqvist, Jonny, Oldenburg, Curtis M., Liu, Weiqun, & Chen, Junguo. Fully coupled two-phase flow and poromechanics modeling of coalbed methane recovery: Impact of geomechanics on production rate. United States. doi:10.1016/j.jngse.2017.05.024.
Ma, Tianran, Rutqvist, Jonny, Oldenburg, Curtis M., Liu, Weiqun, and Chen, Junguo. Sat . "Fully coupled two-phase flow and poromechanics modeling of coalbed methane recovery: Impact of geomechanics on production rate". United States. doi:10.1016/j.jngse.2017.05.024.
@article{osti_1379925,
title = {Fully coupled two-phase flow and poromechanics modeling of coalbed methane recovery: Impact of geomechanics on production rate},
author = {Ma, Tianran and Rutqvist, Jonny and Oldenburg, Curtis M. and Liu, Weiqun and Chen, Junguo},
abstractNote = {This study presents the development and application of a fully coupled two-phase (methane and water) flow, transport, and poromechanics num erical model for the analysis of geomechanical impacts on coalbed methane (CBM) production. The model considers changes in two-phase fluid flow properties, i.e., coal porosity, permeability, water retention, and relative permeability curves through changes in cleat fractures induced by effective stress variations and desorption-induced shrinkage. The coupled simulator is first verified for poromechanics coupling, and simulation parameters of a CBM reservoir model are calibrated by history matching against one year of CBM production field data from Shanxi Province, China. Then, the verified simulator and the calibrated CBM reservoir model are used for predicting the impact of geomechanics on the production rate for twenty years of continuous CBM production. The simulation results show that desorption-induced shrinkage is the dominant process in increasing permeability in the near wellbore region. Away from the wellbore, desorption-induced shrinkage is weaker, and permeability is reduced by pressure depletion and increased effective stress. A sensitivity analysis shows that for coal with a higher sorption strain, a larger initial Young's modulus and a smaller Poisson's ratio promote the enhancement of permeability as well as an increased production rate. Moreover, the conceptual model of the cleat system, whether dominated by vertical cleats with permeability correlated to horizontal stress or with permeability correlated to mean stress, can have a significant impact on the predicted production rate. Overall, the study clearly demonstrates and confirms the critical importance of considering geomechanics for an accurate prediction of CBM production.},
doi = {10.1016/j.jngse.2017.05.024},
journal = {Journal of Natural Gas Science and Engineering},
number = C,
volume = 45,
place = {United States},
year = {Sat Jun 03 00:00:00 EDT 2017},
month = {Sat Jun 03 00:00:00 EDT 2017}
}

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  • Injection of CO{sub 2} into deep unminable coal seams is an option for geological storage of CO{sub 2} and may enhance the recovery of CH{sub 4} in these systems, making coal reservoirs interesting candidates for sequestration. New analytical solutions are presented for two-phase, three- and four-component flow with volume change on mixing in adsorbing systems. We analyze the simultaneous flow of water and gas containing multiple adsorbing components. The displacement problem is solved by the method of characteristics. Mixtures of N{sub 2}, CH{sub 4}, CO{sub 2}, and H{sub 2}O are used to represent enhanced coalbed-methane (ECBM) recovery processes. The displacementmore » behavior is demonstrated to be strongly dependent on the relative adsorption strength of the gas components. In ternary systems, two types of solutions result. When a gas rich in CO{sub 2} displaces a less strongly adsorbing gas (such as CH{sub 4}), a shock solution is obtained. As the injected gas propagates through the system, CO{sub 2} is removed from the mobile phase by adsorption, while desorbed gas propagates ahead of the CO{sub 2} front. The adsorption of CO{sub 2} reduces the flow velocity of the injected gas, delaying breakthrough and allowing for more CO{sub 2} to be sequestered per volume of CH{sub 4} produced. For injection gases rich in N{sub 2}, a decrease in partial pressure is required to displace the preferentially adsorbed CH{sub 4} and a rarefaction solution results. In quaternary displacements with injection-gas mixtures of CO{sub 2} and N{sub 2}, the relative adsorption strength of the components results in solutions that exhibit features of both the N{sub 2}-rich and CO{sub 2}-rich ternary displacements. Analytical solutions for ECBM recovery processes provide insight into the complex interplay of adsorption, phase behavior, and convection.« less
  • CO 2 -enhanced coalbed methane recovery, also known as CO 2 -ECBM, is a potential win-win approach for enhanced methane production while simultaneously sequestering injected anthropogenic CO 2 to decrease CO 2 emissions into the atmosphere. Here, CO 2 -ECBM is simulated using a coupled thermal–hydrological–mechanical (THM) numerical model that considers multiphase (gas and water) flow and solubility, multicomponent (CO 2 and CH 4 ) diffusion and adsorption, heat transfer and coal deformation. The coupled model is based on the TOUGH-FLAC simulator, which is applied here for the first time to model CO 2 -ECBM. The capacity of the simulatormore » for modeling methane production is verified by a code-to-code comparison with the general-purpose finite-element solver COMSOL. Then, the TOUGH-FLAC simulator is applied in an isothermal simulation to study the variations in permeability evolution during a CO 2 -ECBM operation while considering four different stress-dependent permeability models that have been implemented into the simulator. Finally, the TOUGH-FLAC simulator is applied in non-isothermal simulations to model THM responses during a CO 2 -ECBM operation.Our simulations show that the permeability evolution, mechanical stress, and deformation are all affected by changes in pressure, temperature and adsorption swelling, with adsorption swelling having the largest effect. The calculated stress changes do not induce any mechanical failure in the coal seam, except near the injection well in one case of a very unfavorable stress field.« less