Abstract:

 On the basis of quantitative characterization of development effect and geological features of extra-low permeability reservoirs, the main controlling geology factors of development effect are analyzed. And the grey correlation analysis is used to classify and evaluate the extra-low permeability reservoirs in Jiyang Depression comprehensively and quantitatively together with geological multivariate analysis. Finally, it forms a comprehensively quantitative classification and evaluation method based on geological multivariate analysis for extra-low permeability reservoir. The key technologies of this method are the use of development effect to characterize comprehensive feature of extra-low permeability reservoir, the application of grey correlation analysis, and research transiting from single well to blocks. The result shows that sedimentary facies of extra-low permeability reservoirs in Jiyang Depression are mainly beach-bar sands, turbidites and sandy conglomerates. And extra-low permeability reservoirs have the geological characteristics of great burial depth, fine and uniform size,slim pore throat, single-layer thin thickness and scattered distribution, low ratio reserve abundance and poor fluidity. The item of cumulative production deviation is defined to characterize development effect, and it is used to reflect comprehensive features of extra-low permeability reservoirs, and it’s main controlling geological factors are thickness layer ratio of oil layer, thickness layer ratio of sandstone, mean grain size, reservoir middle-depth, permeability, porosity and ratio reserve abundance. Extra-low permeability reservoirs in Jiyang Depression can be generally divided into 3 different types based on comprehensively quantitative reservoir classification and evaluation. As for typeⅠ, the comprehensive evaluation score is greater than 0.6 and cumulative production deviation is greater than 4,500, and it has the best development effect. The comprehensive evaluation score of typeⅡ ranges from 0.4 to 0.6 and cumulative production deviation varies between -2,500 and 4,500, and it has medium development effect. The comprehensive evaluation score of type Ⅲ is less than 0.4 and cumulative production deviation is less than -2,500, and its development effect is worse. By making full use of development data in the study area to test the result, it is found that classification and evaluation result is in accordance with actual production. TypeⅠ and typeⅡ of extra-low permeability reservoirs should be the preferential object for development and production of vertical well and horizon well at present.

Key words: extra-low permeability reservoir, geological feature, development effect, main controlling factor, grey correlation analysis, classification and evaluation, Jiyang Depression