Research On Reservoir Characteristics Of Chang6of Upper Triassic In The Northwest Of Ansai, Ordos Basin

Ansai area is in the south eastern of Shanbei Slope of the Ordos Basin, but the explorationof new area is still in a low level. Basing on the existing research data and combining with thetheory of the sedimentology, petroleum geology, reservoir sedimentology, etc, the paper isbased on the cores desribing, annlysis test data and oil testing data, etc, and analyzes strataclassification and correlation, sandbody distribution character, diagenesis, reservoir propertycharacteristics, and so on. On above basis, favorable areas of the Chang6oil-bearing ofYanchang Formation is choosed.According to main and auxiliary marker bed, cyclical control and depth referencemethods，this paper divided Chang6oil-bearing layers into Chang6~1, Chang6~2, Chang6~3,Chang6~4. According to outcrop section, cores desribing, logging response characteristics,sedimentary characteristics, etc, the paper belives that the Chang6oil-bearing layers ofstudying area is delta front subfacies. The distributary channel deposits is the main sands.Based on cores desribing, cast slice observing, mercury intrusion, SEM, X-ray analysis ofclay minerals, cathodoluminescence, grain size analysis,etc, the paper has indicated that theChang6oil-bearing layers of studying regin sandstone oil reservoir type is chiefly fine grainedfeldspar sandstone.The cement content is mainly made up of chlorite, laumontite, and calcite.Pore types of Chang6reservoir are mainly remnant intergranular porosity, secondly feldspardissolved porosity and laumontite dissolved porosity. Chang6reservoir is mainly ultra low toextreme low porosity and ultra low to extreme low permeability reservoir. Pore structure ofChang6reservoir mainly includes small pore and micro throat type. Chang6reservoirexperienced a series of complex diagenetic processes, including those destructive diageneticsuch as compaction, cementation, replacement,and corrosion which causes increasing ofporosity, which is now mainly in the term A of middle diagenetic stage. Reservoir property ismainly controlled by sedimentation and diagenesis.Considering all these effects, the paper researchs comprehensive reservoir evaluation andfavorable areas prediction for Chang6oil-bearing layers. The reservoirs are divided into fourcategories, and the reservoirs of Chang6mainly belong to class Ⅱand Ⅲ. The paper predictlots of favorable exploration zones, including Ⅱ advantageous area of six, Ⅲ advantageous area of three,which provides further substantial geological basis for the exploration anddevelopment work of the study area.