Geochemical Characterization and Relationship of Oils and Solid Bitumens From Se Turkey

Abstract

Solid bitumens from the Seridhalivein, occurring in the Upper Cretaceous—Palaeocene Germav Formation, and five oils from different oilfields in SE Turkey, were investigated by a variety of organic geochemical methods. Based on biomarker distributions (pristane/phytane, carbon number preference (CPI), Norhopane/hopane, extended hopane distribution, pregnanes/regular steranes), a marine carbonate depositional environment is inferred for the source of these oils. The oils are “early mature‘, as indicated by their ethylcholestane 20S/20S + 20R ratios, and the 17α(H), 21β(H)‐bishomohopane 22S/22S + 22R ratios. Differences in relative abundance of some compounds typical of higher salinities in the depositional environment (docosane, pregnane) suggest different sources of facies variations within a common source. No aromatic sulfur compounds were detected in the oils. The solid bitumens were characterized by a high abundance of dibenzothiophenes, naphthalenes, phenanthrenes and their alkyl‐substituted homologues in the aromatic fractions, and an abundance of n‐alkanes in the saturate fraction. The high maturity of the solid bitumen (epi‐impsonite, R %equiv. ? 1.2) makes an interpretation on the origin of these substances difficult. An origin due to biodegradation of sulfur‐rich oil is excluded, since the alkane and aromatic fractions do not show signs of a severe microbial degradation. The absence of sulfur compounds in the oil extracts and the pyrolysis products of the asphaltene fraction show genetic differences between the oils and solid bitumens of SE Turkey. Pyrolysis of the asphaltenes from the bitumen extracts and of the unextracted bitumens produced sulfur compounds similar to those found in the aromatic fraction.

Australasian asphaltite strandings: Their origin reviewed in light of the effects of weathering and biodegradation on their biomarker and isotopic profiles

“…According to the classification scheme of Curiale (1986), pre-oil bitumens are early (immature) expulsion products of rich source rocks that migrate over short distances as viscous fluids, whilst post-oil bitumens are commonly viewed as remnants of altered oils which have been subjected to severe biodegradation and/or water washing. Other possible origins for post-oil bitumens include thermal maturation of previously generated oils, residues precipitated along oil migration pathways, and deasphalting of reservoired oils by gas (Curiale, 1986;Wilhelms and Larter 1994a, b;Mueller et al, 1995;Mossman and Nagy, 1996;Head et al, 2003). Such bitumens characteristically contain high proportions of NSO-compounds and asphaltenes relative to saturated and aromatic hydrocarbons.…”

“…Orinoco heavy oil belt, Venezuela), bituminous dykes (e.g. Neuquén Basin, Argentina; Unita Basin, Utah, USA; Seridahli vein, Turkey) and tar mats in both clastic and non-clastic petroleum reservoirs (Wilhelms and Larter 1994a, b;Mueller et al, 1995;Hwang et al, 1998;Cobbold and Rossello, 2003;Head et al, 2003;Peters et al, 2005). Tar mats, which have been described on all scales from microscopic to several tens of metres in thickness, can be defined as zones in petroleum reservoirs where asphaltenes comprise up to 20-60 wt% of an oil's C 15+ fraction (Wilhelms et al, 1994;Wilhelms and Larter, 1994a, b;Carpentier et al, 2007).…”

Role of Maturity in Controlling the Composition of Solid Bitumens in Veins and Vugs from SE Turkey as Revealed by Conventional and Advanced Geochemical Tools

“…22 Mueller et al studied solid bitumens from the Seridahli vein and five oils from different oilfields and on the basis of biomarker distributions concluded that there is no genetic relationship between the studied oils and solid bitumens. 23 A relatively recent report suggested a Middle Jurassic source rock (Yolacan Fm.) as the origin of the heavy oils and solid bitumens.…”

“…Some authors, using the same approach, confirmed that a genetic relationship exists between the oils and solid bitumens, and they suggested the Upper Jurassic/Lower Cretaceous carbonates of the Cudi Group to be a common source. , However, others have reported the hydrocarbon potential of this unit as being low . Mueller et al studied solid bitumens from the Seridahli vein and five oils from different oilfields and on the basis of biomarker distributions concluded that there is no genetic relationship between the studied oils and solid bitumens . A relatively recent report suggested a Middle Jurassic source rock (Yolaçan Fm.)…”

Organic geochemical characterization of crude oils and source rocks from Concession 6, central Sirt Basin, Libya

“…Diasteranes are also present in relatively high concentrations in the Sirt Shale as reflected in the ratio of C 27 diasterane/C 27 R sterane (0.82 to 1.31) which may indicate that the hydrocarbons are generated from source rocks containing an abundance of clays minerals. Pregnane/ C 27 αα-sterane 20R ratios in these samples range from 0.96 to 2.04, possibly indicating hypersaline conditions during deposition of the original source materials (ten Haven et al 1985;Huang et al 1994;Mueller et al 1995).…”