Favorable Areas Selection and Reservoir Parameter Characterization of a Coal Seam Gas Block in Surat Basin, Australia

Abstract

AbstractThe low-rank CBM in Block S, located in the east margin of the Surat Basin in Australia, is currently the only CBM resource that has not been developed on a large scale. The research area has a large coal-measure (CM) strata thickness (350–400 m), and many thin single coal seams, but the coal reservoir parameters and cumulative thickness vary greatly in space, and how to develop sweet spot areas with high quality is the key to realizing scale economic development. In this paper, based on lots of logging data, core experiment data, well test data and development performance and production data, many thin coal seams in the ultra-thick CM strata were finely depicted, and the spatial distribution change law of parameters such as coal reservoir thickness, gas content, permeability, etc. was quantitatively characterized. On the basis of geological analysis, the coal seam thickness, gas content and permeability were optimized to establish a recoverable abundance index as an evaluation index for the optimization of sweet spot areas; the distribution map of the recoverable index of CBM was created using the 3D geological model; according to the developed CBM distribution areas, the standard for sweet spot areas was determined using the geological analogy method, i.e. the recoverable abundance index was determined to be more than 90. According to the optimization and evaluation result, the optimized favorable areas account for 42% of the total area of the block, the reservoir conditions in the favorable areas have been greatly improved, the thickness of the coal reservoirs is more than about 17 m, the dry ash-free base gas content is more than about 3.8 m3/t, and the overall average permeability of the coal seams is over 30 mD. The optimization of favorable areas has greatly improved the quality of produced coal reservoirs, and has provided a good technical guarantee for the preparation of the optimization scheme. KeywordsCoal reservoirLow coal rankSweet spot areaEvaluation indexRecoverable abundance index