FROM PETROPHYSICS TO ROCK MECHANICAL PROPERTIES: A SUPPORT TO SHALE- GAS HYDRAULIC FRACTURING PROGRAM IN COOPER BASIN, AUSTRALIA

摘要

Unconventional shale-gas reservoirs are emerging exploration targets for the petroleum industry in the Cooper Basin, South Australia. This interest derives from the recent success of the Permian Roseneath and Murteree shales that are thermally mature and contain high-organic source rocks. This paper presents a case study of mechanical rock properties for a shale-gas reservoir within the Cooper Basin. Acoustic and nuclear wireline petrophysical log data was used to determine the dynamic rock moduli that improved our understanding of the rock parameters. The rock dynamic moduli were calibrated to the static Young’s Modulus and Poisson’s Ratio from core tri-axial tests to determine mechanical properties of the targeted reservoir. Young’s Modulus and Poisson’s Ratio are also combined to predict induced fracture complexity (‘pseudo brittleness’). Lower values of Poisson’s Ratio indicate the rock will be more brittle (Rickman et al., 2008). To design a hydraulic fracturing program, an estimation of fracture closure pressure is an important requirement. This pressure is determined by the overburden pressure (a function of depth and rock density), pore pressure, Poisson’s Ratio, porosity, and tectonic stresses. To validate the calculated closure pressure, a calibration from a mini-frac diagnostic is performed. The results of this case have improved our understanding of how shale gas in the Cooper Basin should be completed and commercially produced.