Best Practices in Static Modelling of a Coalbed Methane Field: An Example from the Bowen Basin in Australia

Abstract

Development of a coalbed methane (CBM) field in its early stage is often plagued by the lack of well control and scarcity of geological data over a large geographical area. Therefore, constructing a representative static model to estimate the in-place-volume presents a formidable challenge. In this paper we proposed a workflow to overcome this challenge and applied it to a CBM field in the northern Bowen Basin of Australia.This workflow may be considered as a best practice for the following reasons. First, it makes use of data from various sources including cores, well logs, seismic interpretation, and topography. Second, it performs rigorous quality control on these data, such as depth shift and log normalization. Third, coal ply division and correlation and subsequent structural modeling are based on three types of correlation: well-to-well, well-to-seismic and, well-seismic-Graphic Information System. Fourth, it establishes the low, base and high trends for the most important reservoir properties. Fifth, it constructs a base case static model by combining the aforementioned structural and reservoir property models. Sixth, it uses sensitivity analysis, which varies one reservoir parameter at one time, to rank the impact of reservoir parameters on in-place-volume. Seventh, it uses uncertainty analysis which varies all reservoir parameters simultaneously to arrive at the P10, P50 and P90 in-place-volumes and their corresponding static models which can then be used for reservoir simulations to estimate the recoverable volumes.

An investigation of numerical facies models for coal seam gas reservoirs; Walloon Subgroup, Surat Basin

“…The industry standard approach for CSG reservoir modelling (e.g. Zhang et al 2014) is impeded in the WSG by the reliance upon subjective lithostratigraphic correlations, resulting in uncertain deterministic frameworks for most WSG reservoir models. Although recognized as problematic, this workflow has remained largely unchanged over the past two decades.…”

“…Since the proliferation of geological computer modelling in the 1990's, a standard methodology followed by most industry practitioners when constructing CSG reservoir models has emerged and is well documented (Zhang et al 2014). …”

“…In the typical workflow, a structural framework is constructed first, following which properties are populated inside this container (Zhang et al 2014). In some CSG reservoir models, coal layers are deterministically populated using well-to-well correlations of coal plies and other stratigraphic markers .…”

“…Deterministic approaches are commonly applied to CSG reservoir models and involve the manual correlation of facies between neighboring wells (Zhang et al 2014). In this approach, environment of deposition facies are delineated in well bores based on core calibrated wireline log motifs.…”

“…, Zhang et al 2014. These earlier studies highlight the challenges in reproducing the complex stratigraphic architecture inherent to coal bearing alluvial successions in numerical facies models.…”