Geochemical Evaluation of Paleocene Source Rocks in the Kohat Sub-Basin, Pakistan.

Area of Science:

• Geochemistry
• Petroleum Geology
• Organic Geochemistry

Background:

• The Kohat sub-basin in Pakistan is a key hydrocarbon-producing region with depleting conventional resources.
• Exploration for unconventional resources is crucial to meet energy demands.
• Geochemical techniques are vital for assessing shale gas reservoir potential.

Purpose of the Study:

• To evaluate the source rock potential of Paleocene formations (Patala, Lockhart, Hangu) in the Kohat sub-basin.
• To determine organic richness, thermal maturity, kerogen type, and depositional environment using geochemical analyses.
• To assess the potential for shale gas exploration in the region.

Main Methods:

• Analysis of well cuttings from the Tolanj-01 well.
• Total organic carbon (TOC) assessment, Rock-Eval pyrolysis, and organic petrography (vitrinite reflectance).
• Analysis of extractable organic matter (EOM) using gas chromatography (GC-FID) and gas chromatography-mass spectrometry (GC-MS).

Main Results:

• Low to fair total organic carbon (TOC) content was found in all analyzed Paleocene formations.
• Hydrogen index values indicate kerogen types II/III, with thermal maturity in the oil window for all formations.
• Biomarker analysis suggests a marine source input and deposition in a transitional, suboxic environment.

Conclusions:

• The Paleocene rocks in the Kohat sub-basin exhibit generally poor source rock potential for hydrocarbons.
• Despite low TOC, the thermal maturity indicates the presence of mature oil window, suggesting potential for residual hydrocarbons.
• Further exploration for unconventional resources should consider these geochemical characteristics.