High-potential Source Rocks Of Jurassic In Indus Basin,pakistan,and Their Significance In Hydrocarbon Accumulations

The Lower to Middle Jurassic sedimentary succession of the Indus Basin,Pakistan,represents significant siliciclastic and carbonate rock packages.In this basin,the Lower Jurassic Datta Formation is composed of thick rocks such as dark shales,which were sedimented under anoxic conditions.In the same way,the Middle Jurassic Shinawari and Chiltan formations show shale layers interbedded with carbonates sequences.This study seeks to determine the key formation for hydrocarbon generation and the factors that controlled its deposition.As well as evaluating the potential of source rock which is responsible for hydrocarbon generation and production in the basin.The geochemistry analyses adopted for the identification of these properties are the following:total organic carbon contents（TOC）,rock-eval^TM(R.E^TM),GC-MS analysis,vitrinite reflectance（Ro%）,and X-Ray diffraction（XRD）with clay mineralogy.In addition to the conventional organic geochemistry,the in-organic analyses are also performed to evaluate the sedimentary depositional scenarios.The criteria used to evaluate source rock is comprised of well-defined stratigraphic units related to dark shale having a minimum 30 m thickness,abundant of organic matter i.e.TOC≥2%,HI≥150 or 200 mg HC/g TOC,T_max≤465℃,good maturity such as 1.3–2.0 Ro%,thermal alteration index≥2,stratigraphic thickness≤100 meter and kerogen types I and II.On the other hand,the kerogen types I and II,the TOC,HI,T_max,Ro%,and stratigraphic thickness identified in the Lower to Middle Jurassic formations were estimated.The biomarker content included the cross plot of pristane/n-C₁₇ with phytane/n-C₁₈ ratio and Ph/Pr with terrigenous/aquatic ratio and Pr/Ph ratio<1,indicates mixed and marine organic matter having reducing conditions.The sterane(C₂₇-C₂₉)ternary plot represents the deposition of organic matter in terrestrial deltaic to the marine shelf setting.The low saline condition is shown by the gammacerane index in the studied strata.The regular steranes/hopanes ratio,and pristane/n-C₁₇ and phytane/n-C₁₈ ratios and polycyclic biomarker show that both oil and source rock are genetically related to having well-defined oil to oil and oil to source rock linkages.Furthermore,1 D maturity modeling is used to find out the burial history,petroleum system,thermal history,paleo-heat flow,source rock maturity,and hydrocarbon generation and expulsion.In addition to organic geochemistry and basin modeling,the controlling factors on the formation of the source rock are defined by an integrated study of carbon and oxygen isotopes(δ¹³C andδ¹⁸O),organic geochemistry,palynofacies,major and trace element investigation.The normalized trace elements ratio of Ti/Al and Cr（less than 1）indicates low clastic input with low oxygen to the more stratified and stagnant water.The V/（V+Cr）,V/（V+Ni）,V/Mo,V/Ni,V/Cr,（Cu+Mo）/Zn,Mo/Al elemental ratio,andδ13C andδ18O isotopic data of the studied source rock strata indicate anoxic conditions.In an anoxic setting,the organic matter was deposited in the proximal to distal shelf setting from the palynofaices such as DFPF A-D and SFPF A-B.The influx of organic matter is determined from the palynoafacies investigation,and abundance and correlation of Ni,Cu,Ni/Al,and Cu/Al with total organic contents.The palynoafacies indicate 57%terrestrial organic influx and 43%primary production in the dysoxic-anoxic depositional setting.