Theory of relative homogeneity in low-permeability reservoirs

Based on the geological characteristics and development practices of low-permeability oil and gas resources in China, this study extends the conventional understanding that such reservoirs are typically tight and highly heterogeneous and proposes the theory of relative homogeneity in low-permeability reservoirs. As to this theory, its concept is systematically articulated, its connotation is clarified, and its mathematical model is constructed. Based on the successful development practices of low- and ultra-low-permeability reservoirs in the Ordos Basin, and incorporating pore-throat structure, sand body scale, seepage mechanisms, waterflooding displacement patterns, water-cut rise rate, natural decline rate, and recovery factor, the practice standards for the theory of relative homogeneity are established. Subsequently, the identification criteria for the theory of relative homogeneity are comprehensively elaborated from multiple dimensions, ranging from microscopic to macroscopic scales, from reservoirs to fluids, and from sedimentary geology to reservoir development engineering. Practical applications in development pilot areas have demonstrated that the complementarity and synergistic development of the “relative homogeneity” and “heterogeneity” concepts have effectively driven the optimization of development schemes, including drilling, fracturing, and injection-production, providing reliable theoretical support for the development of low-permeability reservoirs.