Implementation of horizontal well CBM/ECBM technology and the assessment of effective CO2 storage capacity in a Scottish coalfield

In this study the theoretical and effective methane recovery and CO2 storage potential of four coal seams within a well characterised section of a CBM license in Scotland are estimated, considering different horizontal well patterns, the effect of permeability heterogeneity and the composition of the injected fluid. The study concerns the Airth area of the Clackmannan coalfield in the Scottish Midland Valley. The effort on building the static earth model and the history match results of the pre-existing vertical and newly drilled horizontal wells is briefly described. Initial simulations of the horizontal well primary methane production and CO2/flue gas enhanced recovery enabled the length, configuration and alignment of the horizontal wells to be optimised for the long-term simulations. This configuration was then used to estimate the Effective Capacity of a selected area within the Airth field for CBM, ECBM and CO2 storage. To evaluate the impact of permeability heterogeneity and uncertainty on reservoir performance and Effective Capacity for methane recovery and CO2 storage, multiple realisations of possible permeability distributions across the selected area were geostatistically generated. Initially, primary production runs were performed using 100 permeability distributions with a median value of around 1 mD. A number of realisations with different median permeabilities were then selected and used for flue gas (13% CO2/87% N2) and mixed gas (50% CO2/50% N2) enhanced CBM recovery and CO2 storage runs.