Hydraulic Fracturing in Coal Seam Gas Reservoirs, Lessons and Challenges from the Surat Basin, Australia
Abstract
The paper presents a review of the specific rock mechanical challenges of hydraulic fracturing in coals with extremely high Poisson's Ratios. The efficacy and potential limitations of fracture stimulations are reviewed in context of twenty years of fracture design optimisation in context of analytical and regional geomechanical analyses and relative benefit of fracture stimulation on well performance. The approach involves numerical geomechanical modelling which analyses (a) stress transitions based on intrinsic rock mechanical parameters (YM, PR, UCS) to establish depth dependent but rock specific stress geometry transitions (normal – strike- slip reverse sensu Anderson) and (b) regional structural influences on stress distribution as reflected in stress sensitive treatment data such as ISIP closure pressures etc. The analysis and modelling in context of past well performance allow an in principal assessment of fracture stimulation behavior which inform further optimization and modifications to fracture design, execution, surface equipment and production operations. Key modification includes lower injection rates, reduced pad volumes, increased proppant concentrations, enhanced fracture containment strategies, implementation of tub bypass operations to minimize over-flushing, and the introduction of activated resin-coated sand tail-ins to mitigate proppant flowback. The impact of reservoir pressure depletion on stress contrast, fracture containment, and stimulation efficiency is also examined, highlighting both potential benefits and risks. Field experience indicates that these changes improve fracture connectivity, proppant retention, artificial lift reliability, and operational outcomes while improving production performance. The study demonstrates the importance of integrating rock mechanics, stimulation design, and production surveillance to optimize hydraulic fracturing in mechanically complex coal reservoirs.