Reservoir-scale sequence stratigraphy of Mishrif carbonates and implication to water injection strategy North Rumaila field case

Abstract

The Late-Cenomanian–Early-Turronian Mishrif multi-carbonates in the North-Rumaila oil field has undergone into reservoir-scale high-resolution sequence stratigraphic investigation. Five-carbonate sequences (M4, M5, M6, M7, and M8) are established, comprised by (fifth-order high-frequency lithofacies cycles). The chrono-surfaces (CS5, CS6, and CS7) have screened a particular construction of Rudistid-bioaccumulated-bank/shoal buildups across the North Rumaila field. The CS6 marker has clarified two main evolutionary stages of the bank structure. The first case indicates the bank buildup crossed by the CS6 marker, whereas the second case signifies a stage the marker terminating the bank by well-developed lagoonal facies. The recognized single high-frequency lithofacies cycle expresses a well developed shallowing-upward progression of mud-to-grain-dominated bioclastic wackestone/packstone facies as (non/semi-TMF characters) to coated grain (bioclastic)/peloidal grainstone facies as TMF grade. Four-chronostratigraphically based reservoir units are structured: reservoir cycle sets (M8a), (M7a), (M6a) and cycle set (M5b). Two chronostratigraphic cross sections based on CS6-flattening surface represent south-north alignment of the studied wells illustrates the bank buildup pre-to-post CS6 time, defining a new approach of the vertical stacking/lateral continuity pattern of the depositional cycles. This new approach clarifies a new Mishrif reservoir architecture in the field, highly foremost, and controls the reservoir dynamics. Accordingly, four sectional Rudist bank/shoal/lagoonal buildups are introduced, covered 25 NR wells (12 representative + 13 involved). For safe production from Mishrif carbonates, a proposed sequence stratigraphic philosophy with water injection consideration is submitted.