摘要
This study deals with a detailed geochemical characterization of three crude oils from the Upper Indus Basin,Punjab,Pakistan.The samples were obtained from three productive oil fields of the Datta Formation(Jurassic),Lochhart(Palaeocene) and the Dhak Pass zone(Palaeocene).The GC parameters for and the bulk properties of Datta Formation oils are essentially coincident with those of the oils from the Dhak Pass Formation in the Upper Indus Basin,Pakistan and the oils likely originate from a marine source rock.In contrast,the Lockhart Formation oils show different behaviors and seem to be originated from dirty carbonate rocks although all three crude oils are mature,being of non-biodegraded and somewhat mixed organic matter origin.Low Pr/Ph values and high C35 homohopane index for the Lockhart Formation oils suggest a source of anoxic environment with low Eh while oils from the Datta Formation and Dhak Pass Formation showed different trends,i.e.,lower values of C35 homohopane index indicating different depositional environment than oil from the Lockhart Formation.All three crude oils from the Upper Indus Basin are mature for the hopane ratios,i.e.,Ts/Ts+Tm,C3222S/(S+R) and C30 αβ/(αβ+βα) and sterane ratios,i.e.,C2922S/(S+R) and C29ββ/(ββ+αα) but oils from the Lockhart Formation seem to be less mature than those from the Palaeocene and Datta Formation according to plots like API° vs.homohopane Index,Pr/Ph vs.sterane.The relative composition of 5α(H),14β(H),17β(H)-24-ethylecholestanes and the C2920S/20S+20R index,indicate that all three crude oils are equally mature,which makes it unlikely with respect to the above said plots.This difference is may be due to the migratory chromatography which alters the concentrations of sterane and hoapnes and hence gives different results.These oils do not exhibit UCM and have complete n-alkane profiles indicating non-biodegradation.
This study deals with a detailed geochemical characterization of three crude oils from the Upper Indus Basin, Punjab, Pakistan. The samples were obtained from three productive oil fields of the Datta Formation （Jurassic）, Lochhart （Palaeocene） and the Dhak Pass zone （Palaeocene）. The GC parameters for arid the bulk properties of Datta Formation oils are essentially coincident with those of the oils from the Dhak Pass Formation in the Upper Indus Basin, Pakistan and the oils likely originate from a marine source rock. In contrast, the Lockhart Formation oils show different behaviors and seem to be originated from dirty carbonate rocks although all three crude oils are mature, being of non-biodegraded and somewhat mixed organic matter origin. Low Pr/Ph values and high C35 homohopane index for the Lockhart Formation oils suggest a source of anoxic environment with low Eh while oils from the Datta Formation and Dhak Pass Formation showed different trends, i.e. lower values of C35 homohopane index indicating different depositional environment than oil from the Lockhart Formation. All three crude oils from the Upper Indus Basin are mature for the hopane ratios, i.e., Ts/Ts＋Tm, C3222S/（S＋R） and C30 αβ/（αβ＋αβ） and sterane ratios, i.e., C2922S/（S＋R） and C29ββ/（β＋αα） but oils from the Lockhart Formation seem to be less mature than those from the Palaeocene and Datta Formation according to plots like API° vs. homohopane Index, Pr/Ph vs. sterane. The relative composition of 5α（H）, 14β（H）, 17β（H）-24-ethylecholestanes and the C2920S/20S＋20R index, indicate that all three crude oils are equally mature, which makes it unlikely with respect to the above said plots. This difference is may be due to the migratory chromatography which alters the concentrations of sterane and hoapnes and hence gives different results. These oils do not exhibit UCM and have complete n-alkane profiles indicating non-biodegradation.
