The Research Of Logging Recognition Method Of Low Porosity And Low Permeability For Yan’an Formation In Huanjiang Oil Field

Huangjiang oilfield is located in the western of Ordos Basin,and the main oil-bearing bedis the Triassic yanchang formation and Jurassic yan’an formation.Yan’an resevoir is mainlylow amplitude structure-lithologic reservoir which oil and water distribution is weak,electrical differences is small primarily in logging response,and that is affected by physicalproperties,lithology,structure,formation water salinity and other complex facterstogether,resulting in the difficulties of identifying oil and water layer,and the low coincidencerate of logging interpretation,an urgent need to carry out logging second Fine interpretation ofreservoir conditions.Therefore, the research of reservoir logging recognition methods of theYan’an formation in Huangjiang oilfield is of great significance.Though the research,thepaper mainly came to conclusion as follows:(1)The constructs of research zone was a single oblique leaning East which was high inthe West and lower in the East, which developed locally7-9nose augmentation structuresneary east-west.The palaeogeomorphic form of the pre-Jurassic was reconstructed by themethod of mold. The pre-Jurassic palaeogeomorphic frame work was divided intovalley,slope,terrace land and upland.The results indicated the provenance orientation wasNW.Braid fluvial facies were developed in Fuxian and Yan10formation and main types ofsedimentary microfacies were river sand dams and flood plain.Delta plain sediments weredeveloped in Yan9-Yan4+5,mainly developed distributary channel,inter distributarybay,natural levee and crevasse splay.(2)The rocks in the reservoir are mainly detritus quartz sandstone and feldspar detritussandstone,the content of feldspar and quartz is higher,grains are lower.Interstitial mattercomponent include kaolinite,water mica,chlorite,and so on.The pore types are mainlyintergranular pores.Pore structure is mainly medium pore with medium throat.The averageporosity of Yan’an formation reservoir is12.3%, the average permeability is43.9×10-3μm2,resevoir property ia bad.(3)On the basis of the four properties’ relations and fine interpretation model of reservior parameters,the paper determined the petrophysical lower limit value of the effectivereservior:the minimum standard of reservoir porosity is10%,and that of permeability is2×10-3μm2.By studying the resistivity and porosity well logging cross-plot of oil testingwells,we can determine the lower limit of oil layer and oil-water layer resistivity is about6Ω.m,that of density-logging curve is2.42g/cm3,and that of acoustic time is224μs/m.(4)In order to better understanding of typical log response characteristics of differentfluid properties,the well logging interpretation of Yan’an formation should pay attention togeological stratification,lithology,structure,formation water salinity and well testingtechnology on the effects of logging curves and test results. By applications of logging curveshape recognition method,micro-differential analysis method,horizontal contrast method,andother logging identification methods,we made the coincidence rate of logging interpretationgreatly increase.