Abstract
ABSTRACT
Coalbed Methane (CBM), also known as Coal Seam Gas (CSG) or Coal Seam Methane (CSM) in Australia is fast becoming a significant contributor to the country's energy needs. The potential coal seams for methane production in Australia are found in coal zones that are Jurassic to Permian in age with coal ranks ranging from sub-bituminous to low volatile bituminous coals. Many Australian coal seams contain high volumes of methane gas upto 25 m3 per tonne. Australia began producing CBM in 1988 but it was not until 1996 when the commercial CBM production started in the state of Queensland. Australia has total CBM reserves of about 300 to 500 Tcf (8.6 to 14.3 trillion m3).
With the total amount of CBM in-place reserves worldwide estimated to be between 3,500 and 95,000 Tcf (100 and 272 trillion m3), CBM is considered one of the world's largest sources of fossil fuel. In the United States, the total CBM in-place reserves are estimated at 749 Tcf (21.4 trillion m3), and CBM now represents almost 10% of its domestic natural gas production. Canada has just begun producing gas from CBM reservoirs and its estimated in-place CBM reserves are about 1,300 Tcf (37 trillion m3). In Australia, as CBM is seen as a clean and pipeline-quality energy, it is rapidly developing. Along with the large CBM resource, the main drivers for this move are the continuously reducing cost of coal seam gas production, and the depleting conventional energy resources.
A number of sophisticated CBM reservoir simulation and exploitation tools have been developed by the University of New South Wales and CSIRO to simulate the conventional CBM production as well as the CBM recovery using multi-component gases. In the field, Australia looks toward enhancing CBM recovery by injecting nitrogen and or carbon dioxide to increase CBM extraction. This paper will focus on how Australia is maximizing its CBM production.
INTRODUCTION
Coal is "the black rock that burns" (Land and Rice, 1993). It is defined as a readily combustible rock that contains more than 50% by weight and more than 70% by volume of carbonaceous material including inherent moisture formed by compaction and induration (hardening of sediment) of various altered plant remains. The type of plant materials, degree of metamorphism, and the range of impurity characterize coal (Bates and Jackson, 1980). A coal seam is a bed of coal, and the natural gas or methane produced from coal seams is referred to as coalbed methane (CBM).
CBM production began initially to keep coal mining safe from explosions. If the methane-air mixture was in the range of 5 to 15%, methane would be explosive (Cervik, 1967). However, with the global oil production decline and the coalbed methane being a clean-burning fuel compared to the conventional fossil fuels, it has become an important resource that can assist in addressing the world's growing energy needs.
In Canada, since 2000, there has been an increase in CBM exploration due to increasing natural gas prices, increased natural gas demand both domestically and internationally, development of new technologies, and the maturation of the Western Canadian Sedimentary Basin (Beaton, 2007). It is expected that CBM will contribute significantly to future natural gas supply. Currently, it is contributing nearly 10% of the U.S. gas needs.