Fine classification of ultra-low permeability reservoirs around the Placanticline of Daqing oilfield (PR of China)

Under SY/T 6285-2011 classification standard in China, reservoirs of which permeability ranging from 1 × 10⁻³μm² to 10 × 10⁻³μm² are divided into ultra-low permeability reservoir. While development practice of ultra-low permeability reservoirs around the Placanticline of Daqing shows that, water-breakthrough time and development effect of different reservoir types are greatly different. Besides the permeability values, reservoir fracture development is another important factor affecting development effect of ultra-low permeability reservoirs. Therefore, based on geologic characteristics of 63 blocks in ultra-low permeability reservoirs around the Placanticline of Daqing oilfield, using fracture parameters as primary classification index, matrix permeability, average throat radius, pore-throat ratio, movable fluid saturation and fluid mobility as main classification indexes, the method combined with grey correlation analysis, multi-parameter cluster analysis, dynamic-static consistency check and comprehensive evaluation is established. The classification evaluation criteria for two groups and four sub-groups has been determined, and the classification results of each block are verified. The results show that this method solves the problem of classification difficulty caused by classification parameters of individual blocks falling in different classification areas and realizes the goal of rational classification of 63 developed ultra-low permeability blocks. At the same time, it has the characteristics of simple calculation and high accuracy, which provides a powerful basis for the efficient and fine classification of ultra-low permeability blocks with similar geological characteristics.