Study On The Comprehensive Reservoir Evaluation Of Chang6 Oil Set Yanchang Formation In Yuanlongsi Area Of Ganguyi Oil Field

The Yuanlongsi region of Ganguyi oil field is located in Baota district of Yanan city which blongs to the Northern Slopes in the Ordos Basin, the Chang6 reservoir of Yanchang Formation is the main producing reservoir,and the exploration work is difficult because of a few scattered oil reservoirs distribute in this area.Based on constant-speed mercury intrusion and NMR, the paper researches on the chang6 reservoir characteristics,and reveales the main control factors of relatively favorable reservoirst to provide geological theory for exploration.The Chang6 reservoir group is divided into four sub-groups, 61, 62, 63, 64, in which the 61, 62sub-group is the main producing reservoir. The main type of the sandstone is fine-grained feldspathic sandstones, compositional maturity of the reservoir is low while textural maturity of the reservoir is high. The physical property of the reservoir is totally low porosity and low permeability,the average porosity is 7.65% and average permeability is 0.45×10-3μm2. The reservoir pore structure can be divided into four categories, and the dominant pore structure is low displacement pressure and small pore-throat type. The pore radius is 1.22μm, and the throat radius is 142.92μm,so it belongs to large scale pore and fine throat. The distribution of throat is the main control factors of the permeability change. The saturation of movable fluid and the saturation of bound water in the Chang 6 reservoir of reseach area is 36.81% and 32.28%. The reservoir permeability,characteristic parameters related to throat have a positive correlation with the saturation of movable fluid.The types of the diagenesis of Chang 6 reservoir in research area is rich and complex,it mainly includes compaction,carbonate cementation and dissolution.Diagenetic evolution is generally up to stage A of the middle diagenetic stage.Quantitative calculation of visual compaction ratio is 0.41 on average, while visualcementation ratio is 0.51, the intensity of compaction and carbonate cementation is medium to strong. Average visual dissolution ratio is 0.33, the intensity of dissolution is medium. Compaction, quartz cementation,feldspar cementation and calcite cementation have made more serious damage to the physical properties.Chlorite cementation,the dissolution of laumontite and feldspar and fracture improves reservoir performance.The dominated factors of reservoirs are deposition, diagenesis and tectonic fractures. Favorable reservoirs were generated in under water distributary channal or mouth bar,and tectonic fractures is the migration channel for oil and gas.On the basis of traditional reservoir evaluation, the paper seclected new parameters which reflected the pore structure features of tight sandstone reservoirs, such as displacement pressure pore texture types and throat radius.The reservoir is divided into three types, in whichⅠReservoirs are favorable reservoirs, Ⅱ Reservoirs are medium reservoirs,and Ⅲ Reservoirs are poor reservoirs. Favorable reservoirs are mainly distributed the area from T193 well to T145 well.The result of reservoir evaluation can guide the following exploration and development.