Quantitative analysis of tight sandstone reservoir heterogeneity based on rescaled range analysis and empirical mode decomposition: A case study of the Chang 7 reservoir in the Dingbian oilfield

Of the characteristics of tight sandstone reservoirs, heterogeneity is one of the most difficult characteristics to analyze. Heterogeneity is mainly manifested in three properties: lithology, porosity and electricity. The Chang 7 reservoir in the Dingbian oilfield is a tight sandstone reservoir controlled by delta front deposits. In this sedimentary environment, the underwater distributary channel oscillates frequently, resulting in considerable heterogeneity of the Chang 7 formation in the study area. The rescaled range method can calculate the fractal dimension D of logging curves, thus quantitatively characterizing reservoir heterogeneity. After analyzing the relationship between average wave number and IMF number by EMD method, the reservoir heterogeneity can be quantitatively characterized by ρ value. By comparing D value, ρ value and F value of different heterogeneous types, it is found that F value can distinguish different heterogeneous types. The order of F value also satisfies the actual situation of formation heterogeneity. The new heterogeneity coefficient is used to study the heterogeneity of Chang 7 reservoir, it is found that the relationship between the lithological heterogeneity represented by the natural gamma (GR) log and oil production is a quadratic function that initially increases and then decreases, that the relationship between the pore heterogeneity represented by the interval transit time (AC) log and oil production is linear, and that the relationship between the reservoir electrical heterogeneity represented by the deep induction log (LLD) and oil production is linear too.