Using a New Spectroscopy Tool to Quantify Elemental Concentrations and TOC in an Unconventional Shale Gas Reservoir: Case Studies from Saudi Arabia

AbstractThe increasing complexity of today's reservoirs requires a good understanding of a formation's mineralogy to make an accurate petrophysical analysis. This is particularly true in the case of unconventional reservoirs, for which the quantification of both mineralogy and organic carbon content is critical to confidently appraise and develop new prospects.A new spectroscopy tool is being applied to evaluate challenging shale gas reservoirs. The new measurements quantify key mineral-forming elements with higher precision and accuracy than previously possible. The new technology provides a direct determination of total organic carbon (TOC), which is an important parameter in the evaluation of kerogen-rich unconventional reservoirs.Accurate lithology and kerogen volumes ultimately affect the estimation of porosity and free and adsorbed gas saturations, which are critical for evaluating resources and planning for further field development. Mineralogy can also be used in geomechanical models to determine completion quality, design stimulation operations, and specify intervals for perforation.The results obtained show excellent agreement with core data for TOC, elemental concentrations, and mineral abundances. One of the main advantages of computing TOC directly from carbon is that it does not require calibration to core data as do empirical methods based on local correlations that use more indirect measurements such as bulk density, sonic-resistivity overlay, or uranium concentration. The robustness of the proposed direct carbon approach is illustrated by comparing it with core and well-established methods for estimating TOC, such as the Schmoker technique.