Production Data Analysis of CBM Wells in Surat Basin

Abstract

Abstract The advancement in Production Data Analysis (PDA) techniques allows the determination of useful reservoir properties such as permeability, drainage radius and original gas in place (OGIP). Recent publications (Clarkson8 et al 2007; Clarkson9 et al 2008) demonstrate the modification of production type-curves and material balance methods for Coalbed Methane (CBM) reservoirs. One of Arrow Energy's projects is located in the Surat basin in Queensland. The coals intersected in the Surat Basin are members of the Walloon Coal Measures (Walloon Subgroup) which are divided into the Juandah Coal Measure and the Taroom Coal Measure. The Walloon Coal Measure architecture is an inter-bedded coal, siltstone and sandstone sequence. The coals are generally thin with permeability ranging from 5–5000 mD. The Walloon subgroup coals are classified as high volatile bituminous. The Surat Basin has been developed using vertical and deviated wells penetrating the whole sequence. The Surat Basin coal reservoirs can be undersaturated or saturated. In the undersaturated case, single phase flow of water occurs during the early dewatering period. In the saturated case, two-phase flow of gas and water occurs at initial production. Arrow Energy has produced from the Surat Basin since 2006. The large amount of production data serves as a valuable source for PDA. Results indicate that the flow regime is dominated by linear flow during the transient period followed by boundary-dominated flow. A flowing material balance method is used to validate reservoir parameters from well simulation history matching and type-curves methods. The reservoir parameters such as permeability, drainage radius and OGIP obtained from all the methods are compared and quality checked. The decline curve analysis (DCA) method is performed on wells which have entered boundary-dominated flow to obtain the estimated ultimate recovery (EUR) and recovery factor. The PDA study is carried out for approximately 250 existing production wells in the Surat Basin. The reservoir parameters obtained from the various methods agree with one another, indicating reliable results. The permeability values obtained from this study are within the range of the Drill Stem Test (DST) results in the Surat Basin.