AAPG Middle East Region Geoscience Technology Workshop

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Quantification of Heterogeneity for Static Model Realizations Using Borehole Image and Dual Energy CT Scan

Abstract

Porosity derived from dual energy CT (DECT) scanning of a core from the Oman Miqrat conventional tight gas formation calibrates a workflow that uses heterogeneity indications from borehole images (BHI) to create a tuning parameter to adjust static model grid cell petrophysical properties. The Miqrat Formation is a Cambrian age siliciclastic interval consisting of several hundreds of meters of vertically amalgamated alluvial sheet sandstones, bedded at the centimeter scale and variably affected by syndepositional evaporite formation (haloturbation). Present day the Miqrat is buried to depths exceeding 4km and temperatures over 140°C, giving rise to a strong but heterogeneous diagenetic overprint. DECT scanning produces a core bulk density log of very high resolution that is used to evaluate CT slice porosity, and thereby captures low and high porosity features that are not resolved by standard resolution bulk density open hole well logs. Comparison to BHI log statistics curves calibrates an index that indicates the degree of heterogeneity within each meter of depth. Adjustment of the up-scaled grid cell properties is demonstrated and a comparison of standard log based upscaled grid cells and heterogeneity adjusted grid cells is presented. Calibrating an index that represents the degree of heterogeneity that exists below standard log resolution is accomplished with DECT slice porosity, and effectively bridges the gap of scales between CT voxel slice dimension (300 microns), BHI resolution (0.5cm), standard open hole log resolution (30cm), and up-scaled static model grid cell thickness (meters). Generating the BHI heterogeneity index for non-cored wells extracts additional value from legacy BHI logs already available within the company database.