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.
