GEOCHEMICAL EVALUATION OF SOURCE ROCKS OF PALEOCENE AGE, KOHAT SUB-BASIN, PAKISTAN

Abstract

Kohat basin is present in the northwest extension of Indus basin KPK, Pakistan. It is the main hydrocarbon producing basin of the province. It has numerous petroleum plays in production and potential categories from Cambrian to Miocene. Detailed geochemical analyses of well cutting of Tolanj-01 were carried out to understand the Paleocene (Patala, Lockhart and Hangu Formation) potential in the basin. The geochemical analysis included total organic carbon (TOC), rock Eval pyrolysis (RE) and organic petrography (vitrinite reflectance). These results were used to evaluate organic richness, thermal maturity, kerogen type, hydrocarbons type and environment of deposition were determined. Well cuttings of Hangu Formations (0.08-1.8) shows poor to Good, Lockhart limestone (0.05-0.5) poor to fair and Patala Formation (0.8- 0.19) shows poor to fair TOC content. The present kerogen appears to be Type III. Thermal maturity of the extracts shows high thermal maturity and mature oil zone. GP is generally poor but some of Lockhart limestone and Hangu Formation shows Fair potential. Vitrinite reflectance of all these formations exist in oil window. Ro values are in the range of 0.82 to 0.95 %. Pr/Ph values are greater than 1 which indicates the presence of sub-oxic environment of deposition. Pr/n-C17 versus Ph/n-C18 shows that the extracts falls in the category of mixed organic matter deposited in transitional depositional settings. C19TCT/C19TCT+C23TCT ratio, C24TeCT/ C24TeCT+ C23TCT ratio indicate source as marine. Ternary diagram shows as higher plant input for Lockhart and Hangu Formation while Patala shows higher marine input. CPI, 2-MP and 3-MP show higher thermal maturity. Pr/n-C17 versus Ph/n-C18, shows higher thermal maturity. Moretane index, extracts fall in thermally mature window. Ts/Ts+Tm ratio shows more thermal maturity. Steranes value shows extracts as mature and fall in oil window.