Assessing and Calibrating the ATR-FTIR and CL-EDX Approaches as Carbonate Reservoir Characterization Tools and for Diagenetic Applications

Abstract

Being able to measure the mineralogy and chemistry of rocks rapidly is of major interest for a quick assessment of diagenesis at the rig floor. Here, we tested two underused techniques for reservoir characterization that can be deployed on rigs. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) can be used for rapid identification and quantification of carbonates, calcium sulphates and silicates in unknown samples. We used over 200 powdered samples with known concentrations for the analyses of two, three, four and five phase mixtures and derived a suite of calibration curves, which can be used to quantify minerals in unknown samples. The calibration curves have an R2 that range from 0.93 – 0.99, a RMSE 1 - 5wt% and a max error of 3 - 9wt%. Results show that the FTIR compares with XRD quantifications with a RMSD of 4.5%. The second method, cathodoluminescence coupled with energy dispersive X-ray (CL-EDX) can be used to analyse specific areas of interest identified using CL and then perform an EDX analysis for identifying and semi-quantifying the concentration of elements. The elements studied are Na, S, Mg, Ca, Fe, Al, Cl, K, Mn and Si. A total of 52 EDX spot analyses were performed using the CL-EDX too test the accuracy of the tool. Absolute values follow similar trends to ICP-AES and EPMA for the same samples. The Mg/Ca and Na/Ca ratios are identical with ICP-AES results. Overall, the CL-EDX is able to successfully differentiate between different types of matrices, cements and grains rapidly and accurately. We propose that both the ATR-FTIR and CL-EDX can be successfully used for the identification and semi-quantification of minerals and elements in geological samples, at the fraction of the time and cost compared to standard techniques used in the industry (XRD for mineralogy and ICP-AES, EPMA and SEM-EDX for chemical analysis). This is achievable as no special sample preparation is required (ATR-FTIR uses powder from cores or cuttings and a polished rock surface can be used for the CL-EDX) and data collection is rapid, and the two tools can be combined with portable XRF data currently used in industry. This combination (portable XRF and CL-EDX) enables production geologists to investigate the chemistry of the rock from the core to the thin section scale, at the rig floor. We gratefully acknowledge funding from Qatar Petroleum, Shell, and Qatar Science & Technology Park

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