Water Saturation Evaluation of Murteree and Roseneath Shale Gas Reservoirs, Cooper Basin, Australia Using Wire-line Logs, Focused Ion Beam Milling and Scanning Electron Microscopy

Abstract

Abstract Roseneath and Murteree organic shales in Nappamerrie trough are part of most prolific unconventional gas reservoirs in Cooper Basin, South Australia. The cumulative effect of rocks, minerals, fluids and organic content in these shale gas reservoirs has been investigated and incorporated using Archie's equation and other resistivity models such as Indonesian, Siamandoux and total shale model for water saturation evaluation. In this study, wireline logs have been calibrated with QEMSCAN and FIB/SEM images. We have found that the shale content in Murteree formation is around 50% using QEMSCAN analysis. Also, it is found that using Steiber formula, the shale volume is close to 50%. Therefore, the Steiber formula is selected as the proper correlation to estimate shale content for Murteree formation. Furthermore, the free porosity of Roseneath and Murteree shale was measured to be 2% based on QEMSCAN and CT scanning. Then, Using Wyllie formula for sonic porosity with Hilchie's correction factor, the porosity was also determined close to 2%. Thus, Wyllie formula with Hilchie's correction factor was also found to be the appropriate correlation for porosity calculation in Roseneath and Murteree shale. For water saturation, both Simandoux and Indonesian correlations were shown to give reasonable results. However, it is found that if free porosity is more than 9%, both total shale and Archie models can also give acceptable results. The sensitivity of true resistivity in water saturation calculation was investigated as well. Furthermore, the evaluation of Archie's parameters (cementation exponent, m, tortuosity factor, a, and saturation exponent, n) were examined. Also, FIB/SEM images show that brine and organic matters are both attached to the clay particles which have caused a modified true resistivity for the shale.