INTEGRATION OF WELL LOGS WITH GEOCHEMICAL DATA TO EVALUATE SOURCE ROCK: A CASE STUDY FROM THE TALHAR SHALE, SOUTHERN INDUS BASIN, PAKISTAN

Abstract

Determination of total organic carbon (TOC) by using well logs has been a challenging task in the process of formation evaluation of shale gas. This research is conducted for the formation evaluation of shale-gas potential of Talhar Shale, a member of Lower Goru in Southern Indus Basin, Pakistan. In this research total organic carbon (TOC) is estimated through well logs by different methods and is then correlated with core data to standardize the best method for estimation of TOC especially when core data is not available. Two wells Dangi-01 and Chak7A-01 located in the Sanghar-south district Sindh Pakistan were selected for the intended purpose. The well cuttings of above-mentioned wells were collected and analyzed from Oil and Gas Development Company Limited (OGDCL) Islamabad, Pakistan. The geochemical analysis is carried out in OGDCL to determine the quality, quantity and thermal maturity of the Talhar Shale. According to geochemical data finding Talhar Shale of Dangi-01 well is good to very good and Chak7A-01 is fair to good organic rich source rock. In the case of generation potential, Talhar Shale of Dangi-01 well is good to very good petroleum potential source rock, whereas, Talhar Shale of Chak7A-01 well is fair to good petroleum potential source rock. According to Ven Krevalen cross plot Chak7A-01 well has type II/III kerogen, it can produce both oil and gas. Whereas Dangi-01 well has type III kerogen, it can only produce gas. The geochemical analysis results suggest that the Talhar Shale is thermally mature. Talhar Shale is mature enough to generate mainly gas with some oil. Based on Tmax and production index (PI) Talhar Shale of Chak7A-01 well is present in the oil window while in Dangi-01 well Talhar Shale produces wet gas. Suits of well logs were loaded in Geographix software and TOC is estimated by us using different methods i.e. Schmoker method and Multivariate fitting method. This estimated TOC is then correlated with core data. Finally, the Multivariate fitting method is selected as a standard method for the estimation of TOC if the core TOC is not available. The correlation of this method with well cuttings TOC data shows strong correlation i.e. 90% to 93%. Unfortunately, resistivity logs are not run in the zone of interest of my research, so Passey method (ΔlogR method) of TOC estimation is not applicable. KEYWORDS: Talhar Shale, total organic carbon, kerogen type, organic richness, thermal maturity, logging data, Schmoker method, Multivariate fitting method.