Reservoir Characterisation of Surat Basin Coal Seams using Drill Stem Tests

Abstract

Abstract Drill Stem Testing (DST) is a primary means of evaluating skin and permeability of exploration and appraisal wells. It is no exception in the case of Coal Seam Gas (CSG) reservoirs. A modified form of DST is routinely used by the CSG industry in this region (Queensland, Australia) as a low cost means of getting skin, permeability and pressure information for these land based wells which have to be mass-drilled given the nature of these coal seam reservoirs and the well productivity. In this paper we review about 450 individual DSTs with a variable permeability and skin values. Observed high skin and permeability values from many of these wells called for better understanding of these parameters in conjunction with core and log data. About 50 wells in the subject study were cored. Image logs were run in addition to routine openhole wireline log suite. Some of the abnormal (very high) skin and permeability values could be explained from detailed analysis of these logs. Examples of DST, log and core data reconciliation have been reviewed. Various studies have been conducted to understand root causes of the observed high skin values. Well interference tests have been conducted to understand horizontal permeability anisotropy and reservoir continuity. This DST, log and core assisted reservoir characterisation has opened the way for completion optimisation for more than 6000 wells to be drilled in the Surat Basin, Queensland, Australia.