TOTAL ORGANIC CARBON (TOC) PREDICTION FROM RESISTIVITY AND POROSITY LOGS: A CASE STUDY FROM IRAQ

Abstract

     The open hole well log data (Resistivity, Sonic, and Gamma Ray) of well X in Euphrates subzone within the Mesopotamian basin are applied to detect the total organic carbon (TOC) of Zubair Formation in the south part of Iraq. The mathematical interpretation of the logs parameters helped in detecting the TOC and source rock productivity. As well, the quantitative interpretation of the logs data leads to assigning to the organic content and source rock intervals identification. The reactions of logs in relation to the increasing of TOC can be detected through logs parameters. By this way, the TOC can be predicted with an increase in gamma-ray, sonic, neutron, and resistivity, as well as a decrease in the density log. In calculating TOC content, sonic/resistivity overlay technique was used. The results detected that the upper and lower parts (3300-3460 and 3570-3700 respectively) of the formation were the principal source rock in this location. The TOC results from logs are ranged respectively from 1-6 and 1-4 wt % for the upper and lower parts from the formation. These results are compared with TOC from (58) samples of Rock -Eval Pyrolysis, which showed a close pattern of increasing and decreasing in TOC values. This comparison was made so as to enhance the results of this technique. In addition, this tool revealed the possible lithology of the studied intervals, where the logs originally would give an indication to the lithology, as such high TOC is significant to relatively low energy environments. TOC calculation showed that the upper and lower packages represent source-seal rocks, while the middle had good reservoir properties. This relation may indicate a locally stratigraphic trap, and a need for further detailed studies.