Australia has over two decades of successful coal seam gas (CSG, coalbed methane or CBM) developments but has failed to develop low permeability, highly compartmentalized coals. Australian research has specifically focused on defining pressure-dependent permeability (PDP) behavior and evaluating technologies to enhance the stimulated reservoir volume (SRV) in order to better appraise these highly attractive resources for future development.
This research highlights three key technology enablers to progress improved understanding and stimulation of low permeability coals. The first is improved diagnostic methods to identify and quantify PDP and enable better stimulation of such coals. History-matching diagnostic fracture injection testing (DFIT) after-closure data with reservoir simulators can derive best-fit values for fracture compressibility and aid stimulation designs. The second enabler is an improved understanding of proppant transport and screen-out behavior along with potential benefits of micro-proppant stimulation. Through better history-matching of DFIT and production data insight can be gained into the potential benefits of stimulation using micro-proppant technologies to counter negative PDP effects. Finally, vertical well stimulation in coals has been met with significant near-wellbore difficulties, particularly with respect to placement of hydraulic fractures in low permeability coals. To improve low-permeability coal drainage, multi-stage, horizontal, indirect hydraulic fracturing (IHF) wells are successfully interconnecting larger SRVs including under-performing SIS well patterns. Three, horizontal, multi-stage IHF wells have placed 54 stages to date with little to no near-wellbore pressure losses (NWBPL), abject proppant responses or screen outs, and extending the SRV into poorly producing, offset non-stimulated horizontal wells.
This paper will bring the key findings from research in these three technology areas together in a cohesive framework and provide practical workflows based on modelling and laboratory studies to implement these technologies for better productivity in low-permeability coals. These technologies specifically address several hurdles facing the Eastern Hemisphere where high-stress, low-permeability, and coexisting CSG developments with mining tenements are a key unconventional gas resource for the future.
