Formation And Destruction Of Bulonggoer Devonian Paleo-oil Resevoir At The Northwestern Marigin Ofjunggar Basin

Bulonggoer paleo-oil reservoir (BPR) was the first paleo-oil reservoir found inDevonian around the whole northern Xinjiang, China. The discovery and researchabout it will lead us to knowledge and revaluate the geological conditions of thehydrocarbon accumulation of Devonian in north of Xinjiang. Based on field inspectionand measured geological section, Bulonggoer paleo-oil was studied intensively,including the structural features of Bulonggoer Area, the attitudes and geochemistrycharacteristics of solid bitumens, the characteristics of source rocks, reservoirs and coprocks, the time and process of pale-oil formation and destruction, using organicgeochemisty, fluid inclusion and Zircon U-Pb age dating analysis methods.The research results are as follows:1) According to unconformities, the Middle Devonian to Neogene formation ofBulongguoer can be divided into six stockwerkes. Faults are very developed inresearch area. Compresso-shear faults are the most developed and they are large inscale and parallel to the regional stratigraphy aligement and folds axial trend. Shearfaults are also very developed assorted with compresso-shear faults. However,extension faults can only be founded in few region. The folds of the Bulongguoermainly format during Hercynian, Yenshan and Himalayan movement epoch.2) Two different types of solid bitumen occur: reservoir solid bitumen and veinedsolid bitumen remaining in the oil degradation pathway. The reservoir solid bitumensand veined solid bitumens have the different bitumen reflectance, showing that theywere occurred in different time. All solid bitumens of Bulonggoer paleo-oil, formed byoxidation, water washing and other natural processes in low thermal condition, arenon-pyrogenic solid bitumens.3) The dissolved organic matter of palo-oil reservoir solid bitumen is rich innonhydrocarbon and poor in saturated hydrocarbon, aromatic hydrocarbon andasphaltine. The content distribution style of n-alkane mainly includes ante-single-peakand two-peaks. The distribution of n-alkane and C27>C29>C28normalized relativeabundance of regular steranes suggest a mixed organic matter for the source rock ofBPR. 4) There are two different reservoir types in BPR -- clastic and andesitic. Foliatedcutinitic liptobiolite and mudstone of Hujiersite Formation were the principal sourerocks. Mudstone deposited in lake environment of Badaowan Formation were thesecondary source rocks. The proto-petroleum of Bulonggoer paleo-oil was preservedin a anticlinal trap formatted in late Early Carboniferous to Early Permian.5) The hydrocarbon accumulation model of BPR was builded up by analyzing thetime and process of paleo-oil reservior formation and destruction. There were Twohydrocarbon accumulation epoch of BPR. The first was in Middle Jurassic, then thesource rocks of Hujiersite Formation reached mature stage and massive hydrocarbonwere generated and accumulated in the anticline of Hujiersite Formation. The secondhydrocarbon accumulation epoch was in Early Crataceous. A small amount ofhydrocarbon were generated by the mudstones of Badaowan Formation and chargedinto the anticline of Hujiersite Formation.6)The hydrocarbon excaped along the destructive channel since the BPRformatting. The BPR was elevated to or near surface and destroied completely with theuplifted of Xiemisitai Mountain. Mass of reservoir solid bitumen was generated by thereservoir alteration processes of once liquid petroleum at that time.