--> Origin, Distribution, and Reservoir Quality Implications of the Dolomite in the Late Permian Khuff-C Reservoir, Eastern Saudi Arabia

International Conference & Exhibition

Datapages, Inc.Print this page

Origin, Distribution, and Reservoir Quality Implications of the Dolomite in the Late Permian Khuff-C Reservoir, Eastern Saudi Arabia

Abstract

The Late Permian Khuff-C reservoir in Eastern Saudi Arabia is known for its lateral and vertical heterogeneity caused mainly by extensive diagenesis. The most common diagenetic process impacting reservoir quality is the partial to complete dolomitization of limestones. Detailed petrographic analysis of 600 thin sections revealed three main replacive dolomite types: (1) fabric-preserving mimetic (FPM) dolomite, (2) fabric-preserving non-mimetic (FPNM) dolomite, and (3) fabric-destructive (FD) dolomite. With the exception of saddle dolomite in a few samples, all of these fabrics are interpreted to have formed early by reflux of evaporated seawater within a marine-burial setting. Euhedral crystals in the size range of a few microns and up to 20 μm dominate all three fabrics. Carbon isotopic compositions of dolostones dominated by each fabric are similar. Average δ18O, however, gets progressively more negative from +0.4‰ for FPM dominated dolostones, to −0.3‰ for FPNM dominated dolostones, to −0.8‰ for FD dominated dolostones. The range in dolostone δ18O values is interpreted to reflect slight differences in temperature and degrees of seawater evaporation with FD dominated dolostones formed, on average, from a less evaporated (less positive) fluid than did the FPM and FPNM dominated dolostones. Hybrid dolostones, which have a mixture of the three dolomite fabrics and none of the fabrics exceeding 50% of the total, have the best covariance between porosity and permeability and are, on average, the most porous and permeable dolostone type. Controls on dolomite fabrics development and distribution include initial textures (microfacies), position within a depositional cycle, and the nature of the dolomitizing fluid.