Abstract

Coal and organic rich shales of the Talang Akar Formation in the deep Ardjuna Basin of Indonesia can be identified using a conventional suite of wireline logs. The method employed in this study is based on the calibration of well log data with core data from several wells in order to estimate the amount of Total Organic Carbon (TOC) along with the corresponding Hydrogen Index (HI) values. Based on the TOC and HI values, which are estimated from well logs, it is possible to indicate the presence or absence of good quality source rocks, to differentiate oil prone from gas prone shales or coals, and to calculate the respective thicknesses of each.

This technique involves a special multivariate non-linear statistical regression method developed internally using density, sonic, neutron, and resistivity log measurements versus core data. The current computer programs are written in FORTRAN as user programs that run on the PETCOM PC log analysis system but can easily be ported to other computer platforms. Coefficients of independent variables have been determined that allow the TOC and HI values to be estimated on other wells in the Ardjuna Basin.

Source rock identification in approximately 61 wells in the Ardjuna basin and the surrounding area have been obtained by using these programs. The results of this work, such as : net source rock thicknesses of shales or coals maps, oil or gas prone shale/coal maps, initial TOC, initial HI maps of each source interval, etc. can be used to better evaluate charge analyses and to improve prospect appraisals.