A study on coalbed methane enrichment laws and exploration strategies in the Bowen Basin, Australia – the case of the Moranbah coal measures in the Bowen block

doi:10.3969/j.issn.1672-7703.2020.04.007

Abstract

Abstract: The Bowen Basin in Australia is a typical back-arc foreland coal-accumulation basin. The Bowen block, which lies in the basin, has complex geological conditions. A considerable amount of coalbed methane (CBM) exploration work has been carried out in the block but the CBM enrichment laws remain unclear due to many controlling geological factors. In this paper, the following CBM enrichment and high-production laws are proposed: “coal development is controlled by sedimentary facies, gas-bearing properties are controlled by structure, gas accumulation is controlled by hydrology, CBM plays are controlled by stress, and the enrichment and high-production zones are the local-high positions and the marginal slope”. For the purposes of the study, the Moranbah coal measures are taken as a representative example. Analysis was carried out on a combination of coal seam development characteristics, structural characteristics, hydrogeological characteristics, and stress characteristics, as well as other geological characteristics of coal seams in the Bowen Basin such as gas-bearing properties and permeability. Sedimentary facies control the coal seam distribution and the physical properties of reservoirs. Coal seams in river alluvial plain and upper delta plain are thicker than those in the lower delta plain. Structures control gas content and enrichment zones. Syncline structures are conducive to CBM enrichment and high production. CBM enrichment and high production zones are situated at local high positions of synclines. Hydrogeological conditions control CBM accumulation, which are generally good in weak runoff-confined areas. CBM accumulation conditions are favorable when the direction of surface runoff is consistent with that of formation dip. Stress fields control the high permeability zones of coal seams. With increasing burial depth, effective stress increases and coal seam cleats and fractures are closed, resulting in a decrease in permeability. Based on the proposed CBM enrichment laws, a three-factor evaluation index system for favorable areas is determined: CBM resource scale, gas-controlling factors, and recoverability. ‘Sweet spot’ areas, favorable areas, and unfavorable areas are delineated. Based on current CBM block management policies in Australia, different exploration strategies are proposed. For the ‘sweet spot’ areas, CBM development permissions should be applied for, and pilot production and development evaluation should be given priority. In favorable areas, exploration work should be carried out to retain potential commercial areas. In unfavorable areas, blocks should be relinquished.

CLC Number:

Li Ming, Kong Xiangwen, Xia Zhaohui, Xia Mingjun, Wang Lin, Cui Zehong, Liu Lingli. A study on coalbed methane enrichment laws and exploration strategies in the Bowen Basin, Australia – the case of the Moranbah coal measures in the Bowen block[J]. China Petroleum Exploration, 2020, 25(4): 65-74.

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