Advanced Rock Characterization by Dual-Energy CT Imaging: A Novel Method for Complex Reservoir Evaluation

A quantitative model of the spatial distribution of reservoir properties is key to understanding reservoir heterogeneity. Special Core Analysis (SCAL) data is essential input for static and dynamic modeling of heterogenous reservoirs. To provide high-quality reliable data, the SCAL program should use the right samples from the core. Conventionally, integrated geological and petrophysical approaches are applied to select samples but they generally lack consistency and seldom incorporate upscaling options. This paper presents a novel methodology for core characterization and SCAL sample selection. SCAL data is used as input for spatial distribution of reservoir properties in a static reservoir model. The analysis is performed in siliciclastics and carbonate reservoirs from wells in the Bahrah Oil Field. An integrated X-ray, CT scanning, geological, and conventional core analysis approach is applied for understanding the reservoirs. We demonstrate the efficiency of dual-energy CT imaging in producing continuous whole core scans at 0.5 mm (500 micron) spacing and in deriving bulk density (BD) and effective atomic number (Zeff) logs along the core intervals. The high resolution 3D CT images improved the sedimentological descriptions of the core and the X-ray CT-derived numerical data (BD and Zeff) are used to derive porosity and mineralogy along the whole core sections. This information is then converted into lithology logs which predicted the cross-well correlation and enhanced the previously established correlation from conventional core descriptions. BD and Zeff cross plots suggested four lithotypes in the core intervals and the corresponding lithology log helped in deriving the percentage of each type: 1. Low BD (high pososity) carbonate formed around 20% of the whole cores. 2. High BD (low porosity) carbonate formed around 36% of the whole cores. 3. Low BD (high porosity) sandstone formed around 28% of the whole cores. 4. High BD (low porosity) sandstone formed around 16% of the whole cores. The data provided a unique capability for ensuring that the plugs adequately and correctly represented the lithotype variations along the core. The overall procedure helped minimize uncertainties in defining the rock types and effectively assign those rock types to the selected samples and core intervals.