EPA Grant Number: X83242801
Title: Improved Modeling of Coalbed Methane Production and CO₂ Sequestration

Investigators: K. A. M. Gasem (gasem@okstate.edu) and R. L. Robinson, Jr.

Institutions: School of Chemical Engineering, Oklahoma State University

EPA Project Officer: Bala Krishnan
Project Period: TBA
Project Amount: $70,000
Research Category: Experiments and Modeling

Abstract

The energy security of the U.S. is predicated on a reliable supply of energy. Therefore, one of the primary goals of the National Energy Policy is to diversify the sources of our energy supply. Among the energy alternatives, natural gas has been slated to meet power generation demands in the U.S., based on its safety and environmental benefits. Increased imports of natural gas (beyond the projected domestic production rate of 29 Tcf by 2020) are being contemplated. We assert that enhancing domestic coalbed methane (CBM) production should be a key energy strategy, since the security benefits of a domestic gas supply outweigh the convenience of foreign imports. However, at present, the state of scientific and engineering knowledge regarding coalbed methane production is inadequate to provide optimum effective strategies for its recovery.

Beyond the energy supply potential of coalbed methane, sequestration of carbon dioxide (CO₂) in coalbeds is a technology that could contribute significantly to the continued use of fossil fuels with reduced CO₂ emissions. Current national plans for carbon mitigation -- developed by researchers from universities, industry, and government agencies -- call for aggressively developing the scientific and technical knowledge to stabilize atmospheric CO₂ levels at 550 ppm. A primary challenge facing a successful carbon mitigation program is the development of low-cost carbon sequestration technologies.

Computer simulations of field operations for (a) primary CBM production, (b) production enhanced by CO₂/nitrogen injection (ECBM), and (c) for CO₂ sequestration in coalbeds, all require accurate mathematical models to describe the adsorption behavior on the coal of interest. Our recent research indicates that effective modeling of high-pressure gas adsorption is possible using two-dimensional equations of state (EOS)[3, 4], simplified local density model (SLD) [5, 6], and the Ono-Kondo lattice model [7]. The models appear both precise and amenable to coal-structure-based generalization, where the generalized predictions are based solely on readily-measured characteristics of the coal of interest. However, to realize the full benefit of these models we must address a serious deficiency in our current modeling capability. Specifically, we need to account rigorously for effects of water on gas adsorption behavior, particularly when dealing with mixtures. This must be accomplished before we can properly develop accurate structure-based coal characterizations and alleviate some of the technical uncertainties currently impeding the growth of CBM operations.

Under current support from the Coal Seq Consortium (co-sponsored by the U.S. Department of Energy and industry), we are conducting research to develop reliable coal-structure-based generalized equilibrium models that account rigorously for the effects of water in CBM production and CO₂ sequestration. Such models will be capable of describing both pure and mixed-gas adsorption isotherms. The funding requested herein will supplement and expand our current Coal Seq Consortium project. The funds will permit us to enhance our adsorption facilities with vibrating-tube density meters. This added capability will allow us to measure in-situ the density of CBM gas mixtures, which will significantly improve the quality of the data acquired.

Successful completion of this project will help accomplish the stated mission of Integrated Consortium for Energy and the Environment (ICEE).

Key Words: coalbed methane, CO₂ sequestration, adsorption measurements, adsorption modeling, moisture effects, algorithms