Source Rock Evaluation Using Geochemical Information from Wireline Logs and Cores

Susan Herron, Louis Letendre, Marc Dufour

Recent advances in geochemical logging technology and interpretation have greatly enhanced our ability to quantitatively evaluate potential source rocks from wireline logs. Use of the carbon-oxygen ratio in conjunction with inorganic elemental data obtained from gamma-ray spectroscopy tools makes it possible to first determine the total carbon content (TOC) of the formation and then correct for inorganic carbon to ultimately obtain a log of total organic carbon (TOC). The TOC results can then be combined with other logs such as uranium and sulfur to make some inferences regarding the depositional environment.

These techniques have been applied to a 20-m interval from a well in France. The depth interval was cored and logged with a Gamma-Ray Spectrometry tool as well as conventional wireline tools. The core was analyzed for both organic and inorganic geochemistry, and the logs were examined for source rock information. Preliminary results of the log interpretation indicate TOC contents as high as 5-6% with as much as additional 4-5% inorganic carbon. These results are compared with a more conventional approach of using a combination of gamma-ray, sonic, resistivity, neutron, and density logs to identify organic matter.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.