SOURCE ROCK EVALUATION OF DATTA FORMATION AND OIL TO SOURCE CORRELATION TOOT FIELD UPPER INDUS BASIN

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.