Research On Sedimentary System Of Chang9-10 Oil-bearing Formations In North-west Ordos Basin

As a new exploration eara, there is no further research on the reservoir-forming rule of oil and gas and the sedimentary system of Chang9-10 oil-bearing formations in the northwest of Ordos Basin. Based on plenty of field outcrops, drilling, logging, seismic and various laboratory analysis data, an investigation about Chang9-10 oil-bearing formations in northwest Ordos Basin on the sedimentay systems and the prediction of favorable targets in the chronostatigraphic sequence framework, under the guidance of Sedimentology, Sequence Stratigraphy, Petroleum Geology and Geophysics, has been finished with several progresses as followed:The research divides the interval Chang9 to Chang10 oil-bearing formations into two long-term base level cycles (SQ1 and SQ2),which in turn are further divided into five medium-term base level cycles, all of which are stacked in base level rise asymmetrical patterns.In Chang9-10 Period, the study area mainly developed three source systems in direction of northwest, northeast and southweat. The northwest one is the primary source system, southwest source system is the minor one, the northeast source system's impact on this eara decreased because of the expansion of the lake and the uplift of this formation.The types of developed sedimentary facies in this area include braided stream facies, delta deposits facies of braided stream and meandering river, coastal shallow-lake facies. Controlled by papaeoclmate, palaeotectono-geomorphic feature, base level cycling and so no, meandering delta systems in northeast, braided delta systems in southwest, braided stream-braided delta in northwest of this eara have been developed. The evolution of the sedimentary systems presents basin-filling characters of gradually fining from the margin to the center as well as vertically deepening upward.The hydrocarbon accumulation distributes in the high location of structural in this area, which in mainly lithologically ruled, with the fourth-order sequnence boundaries, sedimentary facies and quality reservoirs controlling hydrocarbon enrichment. Based on the study on the depositional systems and hydrocarbon accumulation, the paper finally proposed five favorable targets in this eara. Chang91 (SQ2-MC2 cycle) and Chang92 (SQ2-MC1 cycle) are the main target groups, Chang101 is the minor one.