Integrated Core-Scale Volumetric Analysis: a Precambrian Carbonates Case Study

Quantifying and classifying pore systems in carbonates is notoriously challenging, particularly in rocks associated with complex diagenetic histories. Here we report novel computed tomography (CT) core and thin section image analyses through key reservoir intervals in the Buah Formation and Khufai Formation, both part of the Precambrian (Ediacaran) Nafun Group, from two wells located onshore Oman. Our primary objective is to constrain the volume, shape, connectivity, and distribution of vugs down-core in two and three dimensions — this is a key control on reservoir quality. We combine classic sedimentological core descriptions with image analysis on a range of data types. In this paper we focus on the analysis of core CT scan data, but we also introduce a high-level analysis of thin section images from discrete samples from the same boreholes, where available (sidewall core plugs, ditch cuttings and conventional cores). Finally, we integrated the results to (1) provide a holistic understanding of pore systems in the Buah and Khufai Formations; (2) identify the key uncertainties and weaknesses in our approach, and (3) plan for further reservoir assessment.