Carbon Dioxide Enhanced Coalbed Methane and Storage: Is There Promise?

Abstract

Since the early 1980s, engineers and geologists have been unlocking the secrets of coal seam gas reservoirs. With time and technology advances, such as multi-lateral horizontal drilling, these reservoirs have contributed mightily to the Nation's gas supply. Many of these prolific reservoirs are maturing and field operators now look to improve incremental recoveries from these natural gas sources. One such method is through the use of carbon dioxide enhanced coalbed methane (CO 2 -ECBM).CO 2 -ECBM is a process by which the gas is injected into a coal seam, it is preferentially adsorbed onto the coal, allowing incremental methane to desorb and be produced. This very unique characteristic of a coal allows it to serve double-duty as both a storage reservoir and the seal. As such, geologic sequestration of carbon dioxide in deep, unmineable coal seams may hold tremendous promise for long-term, secure storage of the greenhouse gases as well as providing incremental methane recovery.However, with only a handful of CO 2 injection pilots having been conducted, it seems more questions are being asked regarding the viability of the process than being answered. This paper will focus on the lessons learned from several large-scale and small-scale tests, framing these results against capacity and injectivity estimation and long-term suitability for various coal types/ranks. Enhanced Coalbed Methane (ECBM) BackgroundECBM is the process by which gas is injected into the coalbed in order to recover the remaining hydrocarbon gases from the reservoir that may otherwise be stranded. Nitrogen (N 2 ) and carbon dioxide (CO 2 ) injection has been the subject of ECBM research in recent years and has been shown to have substantially different recovery processes. These two methods are briefly described below.

Laboratory Measurements of CO2-H2O Interfacial Tension at HP/HT Conditions: Implications for CO2 Sequestration in Deep Aquifers

“…Potential subsurface CO 2 disposal and storage candidates include depleted oil and gas reservoirs (Krumhansl, et al, 2002;Le Gallo et al, 2002;Oldenburg and Benson, 2002;House, et al 2003;Seo and Mamora, 2003;Pawar, et al 2004;Sobers et al, 2004;Barrufet et al, 2010;and Oldenburg and Doughty, 2010 ); coalbed methane and shale gas reservoirs (Plug, et al, 2008;Jikich, et al, 2009;Koperna and Riestenberg, 2009;and Schepers, et al, 2009); and deep saline or brackish aquifers (Pruess et al, 2001;Kumar et al, 2005;Ozah et al, 2005;Izgec et al, 2008;Nghiem et al, 2009;Fang et al;and Han et al, 2011).…”

A Field Study on Simulation of CO2 Injection and ECBM Production and Prediction of CO2 Storage Capacity in Unmineable Coal Seam

“…At present, several geological CO 2 sequestration technologies, such as CO 2 injection into saline aquifer, CO 2 -EOR, CO 2 -ECBM, and so forth, have been studied to minimize the CO 2 release into the atmosphere, and these projects have been operating all over the world [1][2][3][4][5][6]. Studies have shown that unmineable coal seams (seams too deep or too thin to be mined economically) are pretty attractive as one of the promising options for CO 2 sequestration because of their large CO 2 sequestration capacity, long time CO 2 trapping, and extra enhanced coalbed methane (ECBM) production bene�ts [1,[7][8][9][10]. Field experience with CO 2 injection into coal seam is limited, although �eld tests are planned or are being conducted in the USA, Canada, Poland, Australia, and Japan [3].…”

Desorption and Transport Mechanisms of Gas Through Coal Matrix Pores and Gas Production Forecasting

“…It was often believed that the desorbed gas in matrix pores moved to cleats driven by concentration difference in molecular diffusion form (Cervi, 1967;Smith and Williams, 1984;King, 1985;Gray, 1987a;Gray, 1987b;Ertekin and Sung, 1989;Kolesar et al, 1990;Anbarici and Ertekin, 1990;Harpalani et al 1991;Zhou and Lin, 1992;Saulsberry et al, 1996;Kong, 1999;Reeves and Pekot, 2001;Fu et al, 2003;Shi and Durucan, 2003;Shi and Durucan, 2008;Hossein, 2006;Koperna and Riestenberg, 2009). The common diffusion models included: (1) pseudo steady-state diffusion model, in which it was assumed that the moving process of desorbed gas from matrix pores to cleats followed the Fick's first law and there was an average gas concentration in each matrix block unit.…”