Application of microfocus computed tomography in carbonate reservoir characterization: Possibilities and limitations

Normally thin-section petrography, by which observations are made in two dimensions, forms the basis of sedimentpetrological reservoir appraisal studies. In reservoir characterization however, insight in the three-dimensional mineral and porosity distribution is necessary. In this study microfocus computed tomography (μCT), which is a non-destructive technique, has been used for 3D characterization of the mineral phases (i.e. calcite, dolomite, anhydrite) and porosity in carbonate reservoir rocks. In order to obtain quantitative information on density and atomic number of the scanned reservoir samples, as well as about their rock texture, a dual-energy scanning technique has been used. Additional beam artifact correction and a segmentation algorithm, focused on differentiating calcite, dolomite and anhydrite, have been implemented. To validate the developed methodology, thin sections of scanned samples of the Khuff Formation (Oman) have also been analyzed petrographically and compared to corresponding μCT sections and to the results of the dual-energy algorithms. Despite the lower resolution when compared to thin-section analysis, the accuracy of the dual-energy technique is in the range of the standard point counting technique and estimations can be made concerning the microporosity of the samples. Since the developed dual-energy methodology provides a fast and objective determination of the percentages of the mineralogical phases, μCT becomes a very powerful tool in the evaluation of the reservoir potential and in the quantification of mineralogical changes in sedimentary systems (e.g. cycles). In addition, images are acquired visualizing and quantifying the spatial distribution of these phases in three dimensions, which is a major advantage compared to classic 2D thin-section petrography.