Heterogeneity of porous carbonate reservoir and its influence on water injection development—a case study from the Mishrif Formation in Y Oilfield, Middle East

This study addresses production challenges in the Mishrif Formation reservoirs of Y oilfield, including uneven water injection efficiency, and unclear water flooding characteristics. Combining geological, logging, and production data, we examine the macro-scale heterogeneity of these reservoirs and their impact on water injection. Results show that the inter-layer coefficient of permeability variation ( V K ), permeability rush coefficient ( T k ), and permeability contrast ( J k ) are high, indicating strong heterogeneity. Barriers in the formation fall into three main categories: lagoonal, incised valley, and swamp facies. These barriers affect water flooding, with high-permeability zones flooding more readily, while residual oil accumulates at the base of barriers and in facies transition zones. The intra-layer rhythmicity is mainly positive rhythm (70.2%), with the intra-barrier lithology primarily consisting of argillaceous limestone (0.5–2.5 m thick). Water flooding concentrates along high-permeability layers, leaving more residual oil at the top of these layers. In areas with homogeneous or reverse rhythmicity, water flooding is more uniform, yielding better development results. Horizontal heterogeneity is characterized by strip-like tidal channels and sheet-like bioclast shoals. The tidal channels exhibit directional distribution, while the bioclast shoals are more uniform. The variation in physical properties is controlled by sedimentary microfacies, resulting in significant horizontal heterogeneity. Water flooding efficiency is influenced by the distribution of these microfacies and the optimization of the injection-production well pattern, which determines the remaining oil distribution across the plane.