Occurrence and composition of solid bitumens from the Bulonggoer Devonian paleo-oil reservoir, North Xinjiang, China. (June 2015)

• Record Type: Journal Article
• Authors: Song, Daofu; He, Dengfa; Qi, Xuefeng; Wang, Shurong; Li, Di
• Is Part Of: Organic geochemistry. Volume 83/84(2015)
• Page Start: 1
• Page End: 15
• Publication Date: 2015-06
• Subjects: North Xinjiang -- Bulonggoer paleo-oil reservoir -- Solid bitumens -- Geochemical characteristics -- Bitumen type; Organic geochemistry -- Periodicals; Biogeochemistry -- Periodicals; Géochimie organique -- Périodiques; 553.205
• DOI: 10.1016/j.orggeochem.2015.01.014
• Languages: English
• ISSNs: 0146-6380

Abstract

Highlights: The first report of a Devonian paleo-oil reservoir found in North Xinjiang, China. Bitumens in sandstone pores and veins are altered relics of a disrupted reservoir. Devonian mudstone source with a mixed algal and higher plant input in inferred. This siliciclastic source was deposited in a reducing hypersaline conditions. The petroleum charge was generated at peak oil window maturity. Abstract: The Bulonggoer paleo-oil reservoir (BPR) on the northwest Junggar Basin is the first Devonian paleo-oil reservoir discovered in North Xinjiang, China. Solid bitumens occur within sandstone pores and as veins filling fractures. Samples of both types were analyzed using stable carbon isotope and reflectance measurements, as well as molecular biomarker parameters. The extremely positive δ 13 C values and biomarker indicators of depositional environment/lithology, such as pristane/phytane (Pr/Ph), C29 /C30 hopane, diasteranes/regular steranes and dibenzothiophene/phenanthrene ratios, indicate a siliciclastic source for the BPR and their deposition in a highly reducing hypersaline environment. The presence of long chain n -alkanes and abundant tetracyclic diterpanes, C20 –C21 tricyclic terpanes and perylene are indicators of higher plant organic matter input. Moreover, the bimodal distribution of C27 > C28 < C29 regular steranes and abundant methyltriaromatic steroids also support a contribution of microalgae as well as higher plants organic matter. The similar molecular composition and thermal maturity parameters indicate that the reservoir and veined solid bitumens were altered from a common paleo-petroleum, which originated from peak oil window matured source rocks. All solid bitumens from the BPR are characterized by relatively low bitumen reflectance values (Rb% < 0.7), suggesting that they were generated from low temperature processes rather than oil thermal cracking. Comparatively, the Rb% values for veined bitumens are higher than reservoir bitumens, indicating that the veined bitumens occurred earlier and experienced higher thermal conditions.