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.

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Five wells were drilled in North West onshore Kuwait, targeting the Jurassic Najmah/Sargelu formations. Three major depositional-units are interpreted within these formations viz; basal limestone, overlain by Kerogen and clean limestone with argillaceous intercalations towards the top and base.

Najmah Formation is an unconventional reservoir consisting of kerogen rich mudstone. It serves as an excellent source as well as reservoir and seal rock. It has low porosity and matrix permeability with sustained commercial production only in regions of high natural fracturing. Petrophysical evaluation of Najmah Formation poses many challenges and there is always a degree of uncertainty. The objective of this paper is to deliberate the methodology adopted in order to minimize the uncertainty. In the wells under study, a complete suite of logs were recorded including elemental log and nuclear magnetic resonance. Petrophysical evaluation was conducted using a mineral solver. Calcite, quartz, pyrite, illite, chlorite and kerogen were the minerals solved. The fluid volumes were obtained using Simandoux equation. Porosity was computed from sum of the fluid volumes, hence, intrinsically corrected for the presence of kerogen. TOC was computed based on the conversion of kerogen volume to TOC as proposed by Tissot and Welte (1978). The Langmuir isotherm methodology was used to determine the amount of adsorbed gas. The mineral volumes, porosity and TOC show good correlation with the core data. The computed adsorbed and total gas volumes confirm the economic potential of this unconventional reservoir. mineral dry weight fractions from neutron spectroscopy, compared with total gamma ray (red curve) and core clay dry weight fraction.