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Influence of In-Situ Stresses on Hydraulic Fracture Stimulations in Coals of the Surat Basin, Southeast Queensland – Australia


The contribution investigates the relationship between in situ stress regimes, natural fracture systems and the propagation of induced hydraulic fractures in APLNG's (Australia Pacific Liquid Natural Gas) acreage within the Jurassic to Cretaceous Surat Basin in southeast Queensland, Australia. On a regional scale the data suggest that large basement fault systems have significant influence on the lateral and vertical interplay between geomechanical components which ultimately control permeability distribution in the area. At a local scale we present case studies showing the interaction between reservoir fractures and in-situ stress regimes. Stresses are characterized using image log interpretations and geomechanical models which are constructed from wireline sonic and density data. Stress models are calibrated via rock failure analysis, rock strength data and/or monitored pressure decline analyses. Stress regimes change vertically from reverse to strike-slip geometries with significant variability in both differential horizontal stress magnitude and horizontal stress azimuth. Stress variations are reflected in the propagation characteristics of hydraulic fractures, monitored through microseismic and tiltmeters. In areas of higher differential stress linear hydraulic fracture orientations are common. In regions of lower differential stress the orientation of hydraulic fractures is less unidirectional and appears influenced by both stress and pre-existing fractures. Reverse stress regimes can result in the propagation of horizontal hydraulic fractures. The results presented highlight the benefits of geomechanical modeling for the prediction of hydraulic fracture styles in regions with complex in-situ stresses.