Stimulation Design Improvements for Optimized Well Performance in Shallow Coal Bed Methane Wells

Abstract The wells completed in shallow coal seam gas reservoirs of Surat basin, eastern Australia, have been fracture stimulated for more than a decade with ever evolving treatment designs. In a recent fracturing campaign, critical design changes led to improvements in well performance and in mitigating issues related to proppant flow back and fines production. The paper discusses the improvements in treatment designs that helped achieve these favorable results. The Jurassic age Walloons coal measures present in Surat basin were formed as a part of an extensive intra-continental sag basin where the non-pay interburden is mainly composed of water sensitive layers of mudstones, siltstones and reactive clays that often disintegrate when exposed to non-native water. The wells are completed in multiple stages using coiled-tubing based pin-point stimulation that targets various coal seams with small average thickness of 0.4 m (1.31 ft). The treatment designs are intentionally varied to account for varying stress regimes from normal to reverse stress regime as a function of depth. The fracture treatment deign improvements were aimed at accelerating dewatering, improving the well performance, and mitigating proppant flowback while remaining constrained on total proppant volumes earmarked for the treatments. The major changes included reduction of pad volume, lowering gel viscosity, increasing maximum proppant concentration, re-arrangement of proppant stages and volumes in pumping schedules, introduction of rate-ramp to contain vertical fracture growth, packing the proppant to generate enough net pressure for consolidation, and dewater/flowback using new guidelines. The new treatment designs aimed at improving performance successfully demonstrated the need for constant evolution of treatment parameters to counter the challenges observed in the field development process. Often, the solutions to typically occurring problems can be found by altering the approach and testing engineering limits of designs. The approach adopted in this study can be readily implemented on similar completions worldwide.