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Title: Nanostructural control of methane release in kerogen and its implications to wellbore production decline

Abstract

In spite of the massive success of shale gas production in the US in the last few decades there are still major concerns with the steep decline in wellbore production and the large uncertainty in a long-term projection of decline curves. A reliable projection must rely on a mechanistic understanding of methane release in shale matrix–a limiting step in shale gas extraction. Here we show that methane release in nanoporous kerogen matrix is characterized by fast release of pressurized free gas (accounting for ~30–47% recovery) followed by slow release of adsorbed gas as the gas pressure decreases, and we use molecular simulations to demonstrate it. The first stage is driven by the gas pressure gradient while the second stage is controlled by gas desorption and diffusion. We further show that diffusion of all methane in nanoporous kerogen behaves differently from the bulk phase, with much smaller diffusion coefficients. The MD simulations also indicate that a significant fraction (3–35%) of methane deposited in kerogen can potentially become trapped in isolated nanopores and thus not recoverable. Finally, our results shed a new light on mechanistic understanding gas release and production decline in unconventional reservoirs. The long-term production decline appears controlled by themore » second stage of gas release.« less

Authors:
 [1];  [1];  [1]
  1. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Publication Date:
Research Org.:
Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1257808
Alternate Identifier(s):
OSTI ID: 1257813
Report Number(s):
SAND2016-1324J; SAND2016-3375J
Journal ID: ISSN 2045-2322; 619327
Grant/Contract Number:  
AC04-94AL85000
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Scientific Reports
Additional Journal Information:
Journal Volume: 6; Journal ID: ISSN 2045-2322
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English
Subject:
03 NATURAL GAS; 97 MATHEMATICS AND COMPUTING; 58 GEOSCIENCES

Citation Formats

Ho, Tuan Anh, Criscenti, Louise J., and Wang, Yifeng. Nanostructural control of methane release in kerogen and its implications to wellbore production decline. United States: N. p., 2016. Web. doi:10.1038/srep28053.
Ho, Tuan Anh, Criscenti, Louise J., & Wang, Yifeng. Nanostructural control of methane release in kerogen and its implications to wellbore production decline. United States. doi:10.1038/srep28053.
Ho, Tuan Anh, Criscenti, Louise J., and Wang, Yifeng. Thu . "Nanostructural control of methane release in kerogen and its implications to wellbore production decline". United States. doi:10.1038/srep28053. https://www.osti.gov/servlets/purl/1257808.
@article{osti_1257808,
title = {Nanostructural control of methane release in kerogen and its implications to wellbore production decline},
author = {Ho, Tuan Anh and Criscenti, Louise J. and Wang, Yifeng},
abstractNote = {In spite of the massive success of shale gas production in the US in the last few decades there are still major concerns with the steep decline in wellbore production and the large uncertainty in a long-term projection of decline curves. A reliable projection must rely on a mechanistic understanding of methane release in shale matrix–a limiting step in shale gas extraction. Here we show that methane release in nanoporous kerogen matrix is characterized by fast release of pressurized free gas (accounting for ~30–47% recovery) followed by slow release of adsorbed gas as the gas pressure decreases, and we use molecular simulations to demonstrate it. The first stage is driven by the gas pressure gradient while the second stage is controlled by gas desorption and diffusion. We further show that diffusion of all methane in nanoporous kerogen behaves differently from the bulk phase, with much smaller diffusion coefficients. The MD simulations also indicate that a significant fraction (3–35%) of methane deposited in kerogen can potentially become trapped in isolated nanopores and thus not recoverable. Finally, our results shed a new light on mechanistic understanding gas release and production decline in unconventional reservoirs. The long-term production decline appears controlled by the second stage of gas release.},
doi = {10.1038/srep28053},
journal = {Scientific Reports},
number = ,
volume = 6,
place = {United States},
year = {Thu Jun 16 00:00:00 EDT 2016},
month = {Thu Jun 16 00:00:00 EDT 2016}
}

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Cited by: 11 works
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