DETERMINATION FROM WELL LOGS OF THE TOTAL ORGANIC CARBON CONTENT IN POTENTIAL SOURCE ROCKS

Abstract

This paper discusses, in some detail, the log responses to total organic carbon (TOC) in the Upper and Middle Velkerri Formation in an area of the McArthur Basin, Northern Territory, Australia. The Formation Density log was found to be superior to other standard well logs in assessing values of TOC in the area studied. A theoretical model was used to estimate TOC from the Formation Density log. The model was established and its applicability was verified by comparison with other models. Based on geochemical properties the Upper and Middle Velkerri Formation is classified into three categories: nonsource rocks, mature source rocks and immature source rock. They show significant differences in the well log responses, and different models had to be established for the three categories to determine the TOC content from well logs. Comparison of the results of using a different model for each category instead of a single model to cover the three categories shows that the former approach gives more meaningful answers.