Preliminary Assessment of the Coalbed Methane Potential of the Mukahbalingian Coal Field, Sarawak

Worldwide increase in coalbed methane development began in approximately 1988, prior to this coalbed methane was considered a safety hazard and was intentionally vented to the atmosphere to prevent mine gas explosions. In 2007, the United States has produced more than 50 billion cubic meter of pipeline quality coalbed methane (EIA, 2007). To date no effort has been made to explore the coalbed methane potential in the Malaysia’s coal basins. Early coalbed methane exploration targeted thermally mature high rank coals, but the study carried out by Bustin and Clarkson (1998) on a series of Australian, Canadian and United States coals have indicated that there is no or little correlation between coal rank and methane adsorption capacity as commonly assumed.<br>With the successful development of coalbed methane in the Powder River Basin, San Juan Basin and the Greater Green River Basin of the United State of America (SanFilipo, 2000, Nuccio, 2001, Breland, 2004), low rank coals have also become exploration target. Basically, at the current state of knowledge on coalbed methane, the study of coalbed methane is an empirical process (SanFilipo, 2000). Coalbed methane is believed to be generated during three distinct stages of the parent coal's maturation history: Stage 1, early biogenic gas due to bacterial activity during the conversion of peat to coal, Stage 2, thermogenic gas due to volatilization of coals constituents as rank increases, and Stage 3, late biogenic gas due to bacterial activity after the coal has been<br>uplifted to near surface (Rice, 1993). The Mukah-Balingian Coal Field consists of Mukah Coal Basin hosting the Miocene Balingian Formation and Balingian Coal Basin hosting the Pliocene Liang Formation (figure 1). These coals are of low rank whereby the vitrinite reflectance of the exposed Mukah- Balingian coal ranges from 0.34%-0.54% (Chai and Wan Hasiah, 2004) indicating the Mukah-Balingian coals are at the early thermogenic methane generation stage (figure 2), which usually unable to generate enough<br>methane for development. However, the possibility of the coals also accumulating migrated thermogenic and late biogenic methane, which will enhance the development potential of the methane, especially for the Mukah Coal Basin, cannot be discarded. The deeper coals at Mukah Coal Basin may have already reached the peak of wet gas generation (Mazlan and Abolins, 1999), where the thermogenic methane generated has migrated up along the coal seams or faults, together with the late biogenic methane produced at near surface by the bacterial activity after the coal has been uplifted could have enhanced the coalbed methane development potential of the coal basin. The distribution and orientation of cleats in coal will serve as permeability pathways for migration and accumulation of thermogenic methane generated during coalification. Coal seams at Mukah-Balingian Coal Field have a well-developed cleats network (figure 3); with the face cleats trending NNW to NNE and the butt cleats approximately perpendicular to it. The coal resources of the Mukah and Balingian Coal Basins have been estimated to be of 550 million tonnes (Sia and Dorani, 2000) and 200 million tonnes (Hussein and Dorani, 2000) respectively. At a pessimistic gas storage capacity of 2 m3/tonne and an optimistic gas storage capacity of 10 m3/tonne, as of the biogenic gas in Soma lignites, Turkey (Inan, 2008), have translated the coalbed methane in place from 1,100 million m3 to 5,500 million m3 for the Mukah Coal Basin and from 400 million m3 to 2,000 million m3 for the Balingian Coal Basin, respectively.