MinC(%) Parameter From Rock-Eval 6 Analysis as a Reliable and Cost-Effective Measurement of Carbonate Contents in Shale

Abstract

Content of carbonates in shale source rock intervals is an important factor to consider in source rock evaluation, especially for unconventional hydrocarbon resources exploitation. Abundant carbonate content in shale can enhance production performance due to its favorable physical property for fracking. Traditionally, the quantity of carbonates in rock samples has been determined via a combination of acid digestion, acid/base titration and/or weight loss determination. These wet-chemistry based approaches are labour-intensive and produces chemical wastes, thus are not environmentally friendly methodologies. In comparison, X-ray powder diffraction (XRD) analysis as a non-destructive method is now being widely used in the analytical laboratories to quantitatively determine the mineralogical composition of rock samples including quartz, clays and carbonates, but the method is costly and time consuming. Various thermal analytical techniques have also been developed to measure the quantity of carbonates via weight loss or the detection of CO₂ released during different temperature range of heat treatment of powdered rock samples. One of the most widely accepted in the oil industry is the Rock-Eval 6 analysis that provides a parameter MinC(%) as a measurement of carbonate content. Although Rock-Eval results for characterizing the quantity and quality of organic matter in sedimentary rocks such as TOC, Tmax, S1, S2, S3 values have been extensively used by petroleum geologists and engineers for hydrocarbon resources characterization and assessment, the MINC(%) parameter has not been that well utilized as a measurement of the carbonate contents. In this study, we have collected both Rock-Eval 6 and XRD data on over one thousands of potential source rock samples from Devonian, Triassic, Cretaceous and Tertiary shale strata in the WCSB, Sverdrup Basin, Mackenzie Corridor, Beaufort-Mackenzie Basin and Upper Ordovician of Quebec. Data analysis found that the MINC(%) from Rock-Eval 6 analysis has a positive linear relationship (R2>0.9) with the sum of the calcite, dolomite and siderite from XRD analysis. As the number of Rock-Eval 6 analysis on shale and tight reservoir samples has been growing exponentially during the last decade or so due to the increased industrial activity on unconventional resources exploitation, use of the MinC(%) values is considered to be a cost-effective and quality-efficient way to determine carbonate contents in shale and tight plays.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016