Application of induced gamma-ray spectroscopy measurements: characterization of a North Sea reservoir

Implementation of a correct mineral transform model and strategy on elemental chemistry, derived from gamma-ray spectroscopy logging tools, can provide a continuous accurate measurement of mineralogy through a complete reservoir section. Such mineralogy logs are potentially valuable on their own, especially for the identification of clay minerals in petroleum exploration; however, they can also be used for the determination of other important parameters, such as grain density, porosity, and cation exchange capacity (CEC). In exploration wells where core recovery is poor, such knowledge from nuclear logging can help to extend formation evaluation across these poorly defined zones, maximizing reservoir characterization. A set of reservoir cores from the North Sea (Brent Group) is used to evaluate various models developed for transforming elemental data into geologically meaningful mineralogy. Emphasis is placed on evaluating transform techniques using well constrained laboratory data before applying the models to elemental data derived from nuclear logging tools. This evaluation procedure aims to determine the most suitable transform model, as well as quantifying some of the inherent problems with mineral inversion. Strategies for overcoming such problems are also addressed