Micro-computed X-ray tomography (micro-CT) allows visualization and quantification of pore space, minerals, and the calculation of rock properties at micron-scale. The technology is particularly useful in complex reservoirs where subtle changes in the fabric lead to variations in pore connectivity and fluid flow. Internal rock fabric and physical properties can be calculated with a relatively short turnaround time compared to conventional laboratory techniques.

In 2015, Saudi Aramco established a micro-CT laboratory within its Exploration Core Facility to test the feasibility of moving micro-CT analysis from "R&D" to "routine" operational support for exploration and development drilling programs. After the successful completion of this trial, Saudi Aramco is deploying into full production a digital rock physics laboratory utilizing state-of-the-art micro-CT equipment. The objective of this paper is to describe the establishment of the micro-CT lab, a workflow and its application for enhancement of well log data interpretation.

Digital rock physics is a multidisciplinary field that requires expertise in 3D imaging, image processing, numerical modeling, computational physics, and petrophysics. A typical workflow integrates micro-CT images, thin sections, mercury injection capillary pressure data, backscattered electron scanning electronic microscopy - energy dispersive spectroscopy results used for digital image analysis to characterize heterogeneities, pore classes, porosity types, mineralogy, and rock properties. Micro-CT images are acquired, processed, and analyzed with resolutions up to 2.5 microns.

The following study is focused on the characterization of isolated porosity in carbonates, where the fluids are isolated in moldic pores and may not be contacted by electrical currents of resistivity logging tools, making it difficult to consistently identify saturation. This can lead to erroneous hydrocarbon saturation estimates from wireline logs. Micro-CT analysis of the conductivity, cementation exponent, and formation resistivity factor provided constraints for the petrophysical input parameters of hydrocarbon saturation analysis. The micro-CT analysis of ten carbonate core plug samples resulted in an improved conductivity model that took into account electrical properties of the rock with isolated porosity. This provided a better match between oil saturation calculations from wireline logs and well tests/production data. Comparison of existing standard log analysis results with modified log-derived saturations from micro-CT analysis gave a more reliable estimate of hydrocarbon saturation.

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