Application of new rock physics method to estimate petrophysical properties

Abstract

A new method for estimating petrophysical properties from elastic well log or seismic data is evaluated on data from the Carnarvon Basin, Northwest Australia. The study has utilized well and seismic inversion data covering part of the Triassic-aged fluvio-deltaic Mungaroo Formation on the Exmouth Plateau. The method applied is based on several recently published papers to use acoustic impedance, velocity ratio V_p/V_s and estimated constants to calculate clay volume (V_CL), effective porosity and water saturation (S_W). The case study showed exceptional results on well data. A strong match is observed between petrophysically derived V_CL, effective porosity and S_W and the estimates derived from elastic logs. When applied to seismic inversion volumes, pay in the wells is predicted from seismic, and porosity of the sands can be estimated with confidence. Petrophysical properties for nearby direct hydrocarbon indicator–supported prospects could also be evaluated, although an imprint of the direct hydrocarbon indicator was observed on the V_CL prediction, and overall predictions are less than expected based on regional well results. Using these results, a minor modification is proposed to the equations used, and a workflow is derived to enable easy application to other projects. The modified approach was validated on the well data from the original publication. The results also indicate that the approach can be used to help identify erroneous synthetic V_s estimates in limited data settings.