An advanced neutron spectroscopy measurement combining capture and inelastic spectroscopy with state-of-the-art hardware has been used to directly determine total organic content (TOC) and to provide detailed mineralogy characterization in an organic-rich source rock in Kuwait. The advanced spectroscopy measurement provides a direct measurement of TOC, obtained from the difference between the measured total carbon and the inorganic carbon obtained from the rock mineralogy. TOC is an important component of the evaluation of an unconventional reservoir as it is a direct input into the determination of the adsorbed gas volume.
Core studies including X-ray fluorescence, dual-range infrared Fourier transform mineralogy evaluation, and coulometry for carbon were conducted to validate the measurement. The log spectroscopy results were compared with core TOC data and to core elemental and mineralogical data. Evaluation of the advanced spectroscopy tool was conducted in parallel with the previous-generation spectroscopy measurement to compare the results.
The core TOC and the direct TOC log measurements of the advanced spectroscopy tool compared well. The core-to-log elemental dry weights comparison highlighted that, compared to the previous technology, the advanced measurement provided a more accurate evaluation of several elements (including aluminum, potassium, and magnesium). The core-to-log comparison also demonstrated that the new measurement provided robust answers in a tough logging environment, with an effective correction for the carbon content of oil-base mud and for barite, despite the high barite content in the mud. A particular finding of the chemistry/mineralogy combined core analysis was that a large quantity of sulfur, larger than is typically found in unconventional reservoirs, is associated with the kerogen.
For the first time in Kuwait, the application of an advanced spectroscopy technology in a challenging carbonate environment effectively provides a detailed and accurate mineralogical description and a model-independent TOC measurement that were not previously available with conventional spectroscopy logging techniques.