The role of faults and fractures in local and regional perturbation of present-day horizontal stresses - an example from the Clarence-Moreton Basin, eastern Australia

Abstract

The present-day stress field has numerous applications in both conventional and unconventional hydrocarbon reservoirs, particularly for borehole stability, reservoir drainage and flooding patterns, pore pressure and fracture gradient prediction, fluid flow in naturally-fractured reservoirs, hydraulic fracture stimulation, seal breach by fault reactivation and any geomechanical modelling. The orientation of present-day maximum horizontal stress (SHmax) in most tectonic plates, such as North America, South America and Western Europe, is primarily parallel to absolute plate motion; suggesting that the plate boundary forces that drive plate motion also control the intra-plate stress field. However, the Australian continent displays a complex pattern of stress and is not oriented parallel to its north-northeast absolute plate motion. In this study we conduct the first analysis of drilling-related present-day tectonic stress in the Clarence-Moreton Basin, which is located in the New England Orogen of eastern Australia. We analysed 11.3 km of acoustic image logs in 27 coal seam gas wells and interpreted more than 2800 drilling induced stress indicators (borehole breakouts and drilling induced tensile fractures) with a total length of 1.6 km, which suggest a mean SHmax of 068°N for the basin. However, there are significant localised perturbations of the horizontal stress orientation, both spatially and with depth due to presence of faults, fractures and lithological contrasts; suggesting that geological structures are a key control on the stress pattern in the basin.