Abstract:
Potwar Sub-Basin is an active fore-land fold and thrust belt of Himalayas in
the Upper Indus basin of northern Pakistan. There are several formations in the basin
which are important for exploration of oil and gas in the region and it is one of the
most productive hydrocarbons bearing sedimentary basin in Pakistan. Datta formation
acts as reservoir and source both, there is little known about source potential of Datta
shale in Potwar Sub-Basin.Toot-16 well cuttings were analyzed to find out organic
richness, environment of deposition, thermal maturity and type of hydrocarbon
generation. These parameters were than correlated to establish Toot-16 crude oil
correlation with Datta shale. According to TOC values obtained Datta shale falls in
fair to good source rock category. Rock eval pyrolysis data for Datta shale indicates
organic matter input is mainly sourced from marine with some terrestrial input having
Type-II kerogen capable of generating oil and gas. Rock eval pyrolysis data and
vitrinite reflectance data indicates Datta shale as mature, peak oil generation phase.
Datta shale extract and crude oil sample show higher abundance of saturated
hydrocarbons than aromatic and NSO fraction and show negative correlation. OEP
and CPI values are close to one, for both samples indicating maturity. Pr/Ph ratio
indicating negative correlation with sub oxic environment of deposition with mixed
shale and carbonate lithology for crude oil and anoxic environment for Datta shale.
Isoprenoid/n-alkane ratio indicates the mixed organic matter for crude oil and
predominance of marine organic matter in Datta shale. Datta shale extract and crude
oil show higher bacterial source contribution than algal as terpane biomarkers
fingerprint is dominated by hopanes with low relative abundance of tricyclic terpanes.
Sterane maturity parameter, S/S+R and ββ/ββ+αα isomers indicates it has attained
equilibrium and values of these parameters shows maturity for both samples and has
acquired peak oil generation phase. Oleanane in Datta shale samples confirms its age,
which is different for the crude oil on the basis of C28/C29 sterane ratio.
