Comprehensive Evaluation Of Tight Oil Sweet Spots In The Yanchang Formation From The Western Ordos Basin

In order to clarify the tight oil enrichment pattern and the tight oil sweet spot distribution in the Yanchang Formation of southwestern Ordos Basin,single factor geological parameter statistic is used to further analyze the tight oil accumulation condition and main-controlling factors and to predict the favorable zone of tight oil sweet spot by combining with the tight oil reservoir distribution.According to the geological sweet spot and engineering sweet spot to establish a comprehensive evaluation index of the tight oil sweet spot in the study area,and finally obtain the Chang 6 Member tight oil sweet spot.Show that the dominant indicators to evaluate the geological sweet spot in the Chang 6 Member include source rock,reservoir,sedimentary facies,fracture development level and source-reservoir combinations.The effective source rock of Chang 7 Member provides sufficient oil source for the formation of the Chang 6 Member.The favorable reservoir facies-deposited provides tight oil reservoir conditions.The developed high-angle structural fractures and horizontal bedding fractures are acted as the migration channel.They can form a typical fracture tight oil sweet spot zone.The favorable source-reservoir combinations control the Chang 6 Member tight oil.The high oil saturation,high formation pressure,low viscosity of crude,high gas oil ratio and high friability index contribute most to the engineering sweet spot of Chang 6 Member.The lower limit of porosity is 8%,the lower limit of the cumulative sand body thickness is 40 m,the fracture development index is 0.50~0.75,the lower limit of the oil saturation evaluation index is 35%,the lower limit of the brittleness index is 0.86,and the upper limit of the crude oil viscosity evaluation index is 8MPa·s,the lower limit of the formation pressure coefficient evaluation index is 0.70.In the Chang 6 Member,there are eight sweet spot targets for the exploration and development of tight oil such as Wangpanshan and Zhidan.Thetotal amount of sweet spot resources is 5.03×108t,there are also four favorable areas.The predicted sweet spots target area have a good match with the production capacity of the study area,which effectively guide the further exploration of tight oil in Ordos Basin and provide a reference for the prediction of tight oil sweet spots in other areas with similar geological conditions.