Stochastic multimineral log analysis is a powerful tool for quantifying rock properties such as mineralogy, porosity, and water saturation in complex carbonate, siliclastic and shale sedimentary basins.
To characterise the potential host rock and confining units for nuclear waste disposal for our client, NAGRA (the Swiss National Cooperative for the Disposal of Radioactive Waste), Ad Terra Energy has successfully used the MultiminTM analysis for the deep borehole exploration project in NW Switzerland. Using in-house expertise, the full workflow cycle was managed from the planning and rig-site supervision of petrophysical log acquisition to advanced log QC, composite log generation, and core-calibrated MultiminTM analysis. The input logs included the Spectral Gamma-Ray, Bulk Density, Photo Electric Factor, Neutron Hydrogen Index, Sigma, and Elemental Spectroscopy for determining the elemental composition (Si, Ca, Mg, Fe, S, Al, Ti, etc). Core measurements, including porosity, grain density and XRD mineralogy, were subsequently used for log analysis and calibration. The large input dataset allowed for accurate determination of porosity and many mineral volumes such as clays (kaolinite and smectite, illite, chlorites), silicates (quartz, potassic feldspars, micas), carbonates (calcite, dolomite, siderite), and evaporites (halite, anhydrite). The uncertainties in the log interpretation were evaluated using a Monte Carlo approach.