Evaluation Of Source Rock Potential Of Data Formation Nashpa Field, Kohat Sub-Basin, Pakistan

Abstract

The Kohat Basin is northwest extension of the Indus Basin in Khyber Pakhtunkhwa It is the one of the main hydrocarbons producing basin of the country. More than 10 hydrocarbon fields have been discovered in the Kohat basin. Datta sandstone acts as reservoir. It is also reported that Datta Formation is producing Type-II and Type III kerogen, but we know very little about the source potential of shale of Datta Formation. The potential to generate hydrocarbons is based on many parameters. Well cuttings of Nahpa-2 were analyzed for geochemical parameters to understand the source of organic matter, environment of deposition, thermal maturity, and possible type of hydrocarbon generation of the area under study. The geochemical study of Datta shale using well cuttings indicates variation in organic richness (TOC) in vertical section. Datta Formation encountered at depth of 4220m, total thickness of Formation is 90m well cuttings are acquired at intervals of 20m. The study of well cuttings of Datta shale reveals that this shale can be categorized in the category of fair to good source rock. Datta shale mainly comprises marine organic matter with some terrestrial input. Rock Eval shows maturity of the sample in oil generation phase. Calculated vitrinite Reflectance values are also very low. Datta shale well cuttings show higher abundance of saturated hydrocarbons, being >36% as compare with aromatics while NSO compounds have high abundance more than 40%. OEP and CРІ values are close to one, indicating maturity. Pr/Ph ratio indicating suboxic environment of deposition with mixed shale and carbonate lithology. Isoprenoid/n- alkane ratio indicates the mixed organic matter predominated by marine organic matter. Well cuttings show higher bacterial source contribution than algal as terpenes biomarkers fingerprint is dominated by hopanes with low relative abundance of tricyclic terpenes. The sterane maturity parameter, S/S+R for isomers and values of these parameters shows maturity. BB/BB+aa values also indicate moderate maturity. Unresolved complex mixture (UCM) presents, missing of small chain n-alkanes and shift in baseline indicates biodegradation of organic matter.