One of the few remaining geochemical properties yet to be accurately characterized by conventional wireline logging tools is the total organic carbon (TOC) content of hydrocarbon source rocks. The amount of organic carbon in a source rock is important in that it determines the productivity and economic viability of a potential formation. Currently, the most accurate methods for determining TOC involve the manipulation of formation resistivity and formation density logs. However, these methods often produce poor results because of the number of assumptions inherent in the analysis.

Using a Ge-68 source, Ortec Ge-crystal detector, and Triumph Maestro¨ software, we analyze Doppler broadening spectrum along the length of a recovered source rock in the laboratory. Using a piece of annealed NiCu plate to restrict the location of annihilations to either the core or the plate, we cover the source and place it in the center of a four-inch wide slab of source rock. Located in between the edges of the core, we conduct runs at pre-determined optimum intervals. Distance between the source and detector stays fixed at 6.75? to achieve a satisfactory counting rate. The core under study belongs to Mitchell Energy, from well T.P. Simms #2 and is from the Barnett Shale Formation under Wise County, Texas. We measured twelve feet of the core at 2? increments based on core recoverability, variance in TOC, and the presence of a drastic change in lithology in the form of a turbidity current.

Analysis of the results shows a remarkable correlation between S-parameter calculations and geochemically measured TOC values. Future studies involve an expansion of the project into different core of varying geologic locations, periods and conditions.

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