A Method to Improve Recovery in Mature Coal Seam Gas Developments Through Implementation of Indirect Hydraulic Fracturing

Abstract

This study evaluates the effectiveness of Indirect Hydraulic Fracturing (IHF) as an infill development strategy to improve recovery from low-permeability coal seams in mature Coal Seam Gas (CSG) fields without the problems associated with in-seam infill drilling. As an example, the Moranbah Gas Project (MGP) has implemented extensive legacy Surface to In-Seam (SIS) wells and expanded some areas with branch drilling. Where branch drilling has not increased incremental recovery, IHF is proposed for ‘chevron-style’ drilled pattern SIS well developments. Certainly, the IHF techniques are applicable for other Permian-aged CSG projects with other pre-existing SIS well configurations. A numerical reservoir simulation model was constructed from field-specific reservoir data and benchmarked against publicly available historical production for PL 191 from the Goonyella Middle (GM) seam within the MGP area. Two development scenarios were analysed: continued production without stimulation and infill redevelopment using IHF. To minimise drilling difficulties, the IHF fractures are initiated from underneath the seam and multiple fractures staged to interconnect adjacent underproducing SIS wells. A probabilistic framework was applied to capture uncertainty in coal permeability, gas-in-place distribution, and inter-well connectivity, enabling assessment of long-term recovery across P10–P90 outcomes. The technique and workflows are based on successful case implementation in analogue mining areas for CMM pre-drainage. P50 results indicate that a typical chevron-style well block within MGP would have produced 0.88 Bscf over 20 years, corresponding to a recovery factor of approximately 24%. Deployment of IHF within the same chevron block increases methane production by approximately 1.9 Bscf, an additional 51% in total recovery in 20 years. Probabilistic results demonstrate that IHF performance is strongly dependent on coal permeability and the volume of previously unconnected gas. IHF implementation results in a 23%–59% incremental recovery with the largest gains observed in low-permeability areas not effectively drained by the initial SIS well pattern. The study demonstrates that IHF is a technically viable and scalable infill redevelopment option for mature CSG fields where extensive SIS well networks already exist, but recovery factors remain low. Past implementations documented in highly depleted CMM pre-drainage areas indicate no drilling difficulties and expansive stimulated reservoir volume (SRV) developments post IHF implementations within existing SIS patterns. The technique and workflows can be applied to other mature Australian or Eastern Hemisphere CSG developments, which are compatible with overlapping mining tenements and have demonstrated improved production and recovery factors without potential problems likely with other infill technologies.