CO2 Sequestration and Coalbed-Methane Potential of Lower Mannville Group (Lower Cretaceous) Coals, Southern Saskatchewan – Preliminary Investigations S.L. Bend 1 and M.C. Frank 1 Bend, S.L. and Frank, M.C. (2004): CO2 sequestration and coalbed-methane potential of lower Mannville Group (Lower Cretaceous) coals, southern Saskatchewan – preliminary investigations; in Summary of Investigations 2004, Volume 1, Saskatchewan Geological Survey, Sask. Industry Resources, Misc. Rep. 2004-4.1, CD-ROM, Paper A-12, 17p. Abstract The long-term storage of CO2 within deep non-mineable coal seams is widely considered to be a viable means of reducing greenhouse gas emissions. Recent studies have also shown that injection of CO2 into coal seams can enhance the production of coalbed methane (CBM), a more environmentally friendly fuel than oil. The Lower Cretaceous Mannville Group (Aptian-Albian) of southern Saskatchewan contains coals of sub- bituminous rank occurring within the Cantuar Formation. Because of their low economic importance, these coals have received only minimal attention in the past, and little is known of their distribution and character. A major project was recently initiated to assess the CO2 sequestration and CBM potential of the Mannville coals. Analysis of geophysical well logs, core, and drill cuttings was performed along with coal petrography in order to identify areas of the thickest, most extensive coal deposits, and to determine their petrographic characteristics. This report presents some preliminary data on coals of the lower Mannville Group interval (Dina to General Petroleums members). To date, regions of thick (up to 5.5 m), laterally continuous (up to 65 km) coal in the lower Mannville Group have been identified in four principal areas: Winter-Senlac, Kerrobert Paleovalley, Unity-Kindersley embayments, and the Empress Basin. These areas generally coincide with the position of paleovalleys and their embayments occurring along the margins of the Unity, Kindersley, and Swift Current paleouplands. This paleotopography reflects erosion of the pre-Cantuar surface, on which the paleovalleys acted as sites for peat formation and accumulation in early Cantuar times. The most significant coals in these areas are those of the Cummings and Lloydminster members, in the lower part of the stratigraphic interval. The Cummings and Lloydminster coals generally range from 1 to 3 m thick in the principal coal areas, and are >5 m thick in the central part of the Kindersley Embayment, and the eastern part of the Kerrobert Paleovalley. The Cummings coal is generally restricted to isolated occurrences within paleovalleys. The Lloydminster coal is also best developed within paleovalleys, but may onlap paleoupland margins to a greater extent than the older Cummings coal, and provides a link across the Unity Paleoupland terrace between the Kerrobert Paleovalley and Winter-Senlac coal areas. Thick coals are also developed within the Dina (up to 3.3 m), Rex (up to 4.5 m), and General Petroleums (up to 1.5 m) members, but these occurrences are more localized than those of the Cummings and Lloydminster members. The coals of the lower Mannville show a great deal of vertical variation in that they appear dominated by dull and shaly coal lithotypes with subordinate intervals of vitrinite-rich bright and banded coal. In general, petrographic analysis supports the lithotype analysis, except in cases where stored coal is highly oxidized and erroneously appears dull. In such cases the vitrinite content is highly underestimated. Using data presented here, and from what is currently known elsewhere, the volume of CO2 that could potentially be sequestered in the Kindersley Embayment is estimated at 2.16 x 1016 cm3, which equates to a mass of 42.7 x 106 tonnes of CO2. Keywords: Lower Cretaceous, Aptian-Albian, Mannville Group, Cantuar Formation, Cummings Member, Lloydminster Member, Saskatchewan, Kerrobert Paleovalley, Kindersley Paleovalley, coalbed methane, CO2 sequestration, coal petrography. 1 Department of Geology, University of Regina, 3737 Wascana Parkway, Regina, SK S4S 0A2. Saskatchewan Geological Survey 1 Summary of Investigations 2004, Volume 1 1. Introduction Geological sequestration of carbon dioxide (CO2) may be an environmentally acceptable method of reducing atmospheric greenhouse gas emissions (U.S. Department of Energy, 1999) in compliance with the Kyoto Accord on Climate Change. Among the methods which have been proposed, sequestration in deep, non-mineable coal seams is perhaps the most attractive for several reasons (Stanton et al., 2001): 1) coal can trap CO2 for long periods of time; 2) CO2 is primarily held within coal by adsorption onto the surface of coal micro- and meso-pores, rather than merely infilling pore voids; coal is, therefore, far superior as a gas reservoir than more conventional lithologies such as sandstone; 3) CO2 injection can enhance the production of coalbed methane (CBM); and 4) globally, major coal basins with sequestration potential occur near many CO2-emitting sources. As well as having a large CO2-storage potential, coals have the ability to generate large quantities of gas. The thermal maturation of coal results in the evolution of various gases, which are dominated by methane (typically >95%), and may also contain lesser amounts of other gases such as ethane, CO2, N2, and O2. The thermogenic gas- generation potential of a coal seam is dependent on its thermal maturity (coal rank) and petrographic composition. Peak gas generation occurs at medium- to low-volatile bituminous rank (e.g., Taylor et al., 1998), with vitrinite-rich (bright) coals being more gas-prone than inertinite-rich (dull) coals. Coal seams typically act as both source rock and reservoir, with up to half of the methane generated remaining within the coal, chemically adsorbed to the coal surface. In addition to thermogenically sourced methane, coals may also act as a source for biogenic methane. The combined methane-production and gas-storage abilities of coal have led to the development of the CO2 Sequestration-Enhanced Coalbed-Methane (CO2-ECBM) concept. The CO2-ECBM concept is a synergistic approach that has CO2-sequestration potential, by adsorbing CO2 onto the coal, coupled to the enhanced co-production of sorbed methane from deep, non-mineable coal seams. Non- enhanced CBM recoveries are typically around 50%, while enhanced CBM recoveries of 70% have been reported (Reeves, 2001). The conventional production of coalbed methane requires an initial dewatering phase, which opens the cleats (naturally occurring fractures) and reduces formation pressure, thereby promoting the desorption of methane. The factors controlling CBM production include porosity, permeability, formation pressure, and hydrogeological regime of the coal (Scott, 2002). Coals below depths of ~2000 m are usually not considered as having economic CBM potential, due to high burial pressures which reduce permeability. The gas-sorption properties of coal are primarily dependent on petrographic composition, moisture content, and formation pressure. Bench-top tests have shown that CO2 is roughly twice as adsorbing on coal as methane (CH4) at an approximate ratio of 2:1 (Gasem et al., 2002; Tamon et al., 2003). Also, the density of the adsorbent CO2 is high, approaching that of a liquid. Other studies (Reeves, 2001) testing impure mixtures of CO2 and N2 (i.e., typical of flue gas) have demonstrated that CO2-adsorption is enhanced in the presence of N2, yielding approximate ratios of 4:2:1 (CO2:N2:CH4). This enhancement is due to the creation of partial-pressure disequilibria within the gaseous phase, resulting in the ‘pull’ (N2 interaction) and ‘push’ (CO2 interaction) of CH4 within cleats and micropores of the coal (Reeves, 2001). Current projects that highlight the attraction of CO2-ECBM as a means of using coal in an environmentally acceptable manner and utilizing the adsorptive properties of coal to reduce greenhouse gas emissions include: 1) U.S. Department of Energy Carbon Sequestration Program – Cretaceous coals of the San Juan Basin in Colorado/New Mexico; 2) Alberta Research Council/International Energy Agency (IEA) Greenhouse Gas Research and Development Program – Cretaceous and Tertiary sub-economic and non-mineable coals in Alberta; 3) European Union RECOPOL Project – Carboniferous coals of the Upper Silesian Basin in Poland; and 4) Japanese Government CO2-ECBM Project – Tertiary coals of the Ishikari Basin, Hokkaido, Northern Japan. Coal-bearing sediments in Saskatchewan occur in the Lower Cretaceous Mannville Group, the Upper Cretaceous Belly River Group, and the Tertiary Ravenscrag Formation. In 2003, a research project to assess the CO2- sequestration and coalbed-methane potential of coals within Saskatchewan was initiated. This report is a summary of preliminary investigations concerning coals of the Dina to General Petroleums (GP) members of the Lower Cretaceous Mannville Group (Figure 1). Preliminary investigative work on the Sparky Coal (Mannville Group) is described elsewhere (Bend et al., 2003). Saskatchewan Geological Survey 2 Summary of Investigations 2004, Volume 1 O 2. Coal Petrography D WESTGATE P A U R O O R VIKING L S S G The petrographic composition of O U U C JOLI FOU C SPINNEY HILL I O a coal exerts a direct control on R O ALBIAN COLONY E E PENSE E McCLAREN E its ability to both generate and C O L WASECA C W L A I SPARKY store gas (Lamberson and Bustin, A O T V Z GENERAL PETROLEUMS T L N E 1993; Clarkson and Bustin, 1996; CANTUAR REX E