Evaluation method of sandy conglomerate reservoir heterogeneity based on the combined weighted TOPSIS model

Abstract

At present, single parameters for characterizing reservoir heterogeneity are commonly used in oilfield exploration and development, such as the permeability coefficient of variation, permeability inrush coefficient, and extreme difference, which have problems such as characterization blind spots. The heterogeneity of thick-bedded sand and conglomerate reservoirs is affected by various factors due to their thick layer characteristics, and it is difficult to effectively evaluate the heterogeneity of thick-bedded sand and conglomerate reservoirs with a single parameter. According to the characteristics of the thick sandy conglomerate reservoir, a comprehensive index calculation method of heterogeneity based on the combination weighting TOPSIS evaluation model is developed to comprehensively evaluate the heterogeneity of the sandy conglomerate reservoir by synthesizing the parameters affecting the heterogeneity of the reservoir, such as porosity, permeability, thickness of the sand layer, effective thickness coefficient, permeability variation coefficient, permeability rush coefficient, permeability contrast, and mudstone content. This approach is conducive to the normalized evaluation of complex reservoirs, and the quantitative characterization is more accurate and comprehensive. Based on the former classification scheme and the geologic characteristics of the study area, the evaluation criteria of the heterogeneity of the sandstone conglomerate reservoir are determined according to the comprehensive heterogeneity index. The research indicates that the objective weights of each indicator parameter of reservoir heterogeneity can be reasonably calculated by improving the criteria importance though intercrieria correlation weighting method, and the combined weights reflecting the importance of the indicators can be obtained by modifying the objective weights through the analytic hierarchy process. The calculated heterogeneous comprehensive index can be used to quantitatively characterize the heterogeneity of sand conglomerate reservoirs and solve the problems existing in conventional single parameters. The heterogeneous synthetic index has a good correlation with conventional parameters and has a good positive correlation with productivity. The weaker the heterogeneity is, the higher the productivity.