ABSTRACT

Low-permeability coal seam gas (CSG) reservoirs are a significant worldwide, unconventional resource for the future. In low-permeability coals, a diagnostic fracture injection test (DFIT) has been identified as the most applicable method to characterise low-permeability CSG reservoir permeability based on the inherent limitations of conventional transient testing methods. Further, determining permeability anisotropy can assist development in spacing wells or evaluate completion technologies, such as fracture stimulation, horizontal wells and multistage hydraulic fracturing from horizontal wells. This paper uses representative interburden and coal reservoir properties from a Bowen Basin case to properly define an area and develop a working hydraulic fracturing model. This model can generate a series of fracture realisations, varying bulk permeability and pressure-dependent leak-off (PDL) values to provide scenarios for later multi-well interference test analyses. Previous studies have noted that a pressure-dependent permeability (PDP) capable reservoir simulator can be used to model and history-match the after-closure period and better constrain the reservoir model for forecasting PDP effects. Finally, a multi-well DFIT/interference test programme can be evaluated using techniques to back analyse the bulk permeability and anisotropy and establish the optimal well spacing between the DFIT and observation wells. This paper presents a holistic workflow and guidelines for implementing multi-well DFIT/interference testing for low-permeability CSG fields. It can also be applied to higher-permeability coals where compart-mentalisation or permeability anisotropy is not aligned with the current, localised stress regime.