Research On Sedimentary Systems And Reservoir Characteristics Of The Yanchang Formation In Fuhuang Area Of The Ordos Basin

Based on regional geological background, the previous results and exploration date about Fuhuang exploration area of Triassic Yangchang Formation, the latest theory and methods such as sedimentology. reservoir sedimentology, petroleum geology and so on were used comprehensively., the stratigraphic characteristics, sedimentary system and characteristics of reservoir development were analyzed systematically in this paper. Meanwhile, the reservoir forming dominated factors.distribution of high-quality reservoirs and oil reservoir enrichment patterns were used as the anlysing ways in order to study reservoir forming geologic condition, accumulation model, high-quality reservoir characteristics and distribution, reservoir-forming rule and the optimization of prospective area.By the recognition of field section and the division of drilling core sedimentary facies, on the foundation of stratigraphic correlation and division, it was recognized that delta and lake sedimentary systems developed in chang 8-chang 1 oil formation, which can be divided into 2 kinds of sedimentary facies,3 kinds of sedimentary sub-facies,9 kinds of sedimentary micro-facies, and their characteristics and patial-temporal distribution rules were analyzed.Turbidite sedimentary in Fuhuang exploration area mainly developed in Chang6, Chang7 and Chang4+5 oil formation. Because of the strong subsidence of the lake basin and the injection of country rock along the depression axis in Chang7 period, turbidite sedimentary reached its peak. Since Chang6 age, the lake basin's subsidence tends to be stable. Provenance supplies sufficiently, and. The Fuxian and Huanglong deltas with multiple water system and provenances developed, which made turbidite sedimentary gradually degenerate. Viewing through spaces, turbidite sedimentary distributed both in steep slope zone and plain zone.Controlled by tectonic uplift and the multi-period of deltaic development, its distribution range, morphological characteristics, area size were different, forming unequal scale turbidite fan and turbidite sand body.According to the analysis of reservoir characteristics, the main factors which lead to low porosity and low permeability about Fuhuang exploration area of Triassic Yangchang Formation were as follows:the original mineral composition and structural characteristics were the basic conditions of forming; early diagenetic compaction and cementation were the main factors; meanwhile, in later stage diagenesis B period, calcite cement fills most residual intergranular pore and dissolution pore, which forms low porosity and low permeability reservoir, and finally led to poor reservoir property.Based on the study of reservoir's lithology, physical properties, oiliness and electrical property relationship, and according to the previous sandstone reservoir rock division standard, reservoir level classified evaluation standard were set up, combining with the sedimentary facies of study area and reservoir characteristics, sandstone reservoir of Yangchang Formation were divided intoâ… -class reservoir,â…¡-class reservoir,â…¢-class reservoir andâ…£-class reservoir. The most developed reservoir wereâ…¡andâ…¢-class reservoirs.Started with effective hydrocarbon source rock evaluation. taking reservoir physical conditions and source reservoir cap assemblage configuration as hub, using reservoir controlling factors and hydrocarbon accumulation as target, the main accumulation model of Yangchang Formation in study area were present: vertical short distance accumulation model, forming lithologic reservoir. The main controlling factors about oil reservoir formation were:â‘ Effective source rock is the material base of lithologic reservoir's enrichment.â‘¡High quality reservoir bodies of underwater distributary channel and turbidite micro facies that formed by sedimentation were the main reservoir enrichment areas.â‘¢Lacustrine-delta sedimentary system is an important factor of the formation about lithologic reservoir.Yangchang Formation has a feature of multi-layer oil-containing, but the main oil production horizons are Chang6 and Chang2, while some places of Chang7, Chang3 and Chang4+5 layers also have productivity. Analysis suggests that underwater distributary channel and turbidite facies were the geological foundation of oil reservoir formation. High quality reservoir bodies of underwater distributary channel and turbidite facies were the basic of oil reservoir development. The main sand body development area and secondary porosity development area produced by dissolution are the favorable zones of hydrocarbon accumulation.