Quantitative characterization of reservoir oil heterogeneity based on data envelopment analysis and its application: a case study of J ₁ s ₂ ² in Moxizhuang, Junggar Basin, China

To address the problems of high reservoir heterogeneity, notable differences in oil-bearing properties, and the limitations of traditional heterogeneity evaluation parameters for the second sand group of the second member of the Sangonghe Formation J1s22 in the Moxizhuang area, Junggar Basin, in this study, reservoir oil heterogeneity and its controlling effect on hydrocarbon accumulation were systematically and quantitatively evaluated. On the basis of core observations, cast thin sections, scanning electron microscopy, mercury intrusion, and physical property analysis, six parameters, namely, permeability, natural gamma ray, resistivity, acoustic time difference, density, and compensated neutron log, were selected. The data envelopment analysis (DEA) method was innovatively introduced to establish a reservoir heterogeneity evaluation model, quantitatively calculate the heterogeneity index I, and comprehensively characterize reservoir oil heterogeneity. The results revealed that the J1s22 reservoir in the Moxizhuang area is dominated by fine-grained lithologies such as fine and medium sandstone, with muddy interlayers. The reservoir space comprises mainly secondary dissolved pores, yielding a low-porosity and low-permeability reservoir with high heterogeneity. The DEA heterogeneity index I values vary largely between 0.4 and 0.95. The lower the index value is, the higher the heterogeneity and the poorer the oil-bearing properties. Reservoir oil heterogeneity significantly affects hydrocarbon accumulation. Oil and gas are enriched mainly in reservoirs with low reservoir oil heterogeneity, whereas reservoirs with high heterogeneity contain low oil saturation or no hydrocarbon accumulation. Combining reservoir sweet spots with accumulation, favorable hydrocarbon enrichment zones can be effectively delineated, and exploration targets can be optimized. These research achievements have important theoretical and practical guiding significance for subsequent oil and gas exploration and development in the study area.