ORIGINAL PAPER Reservoir-scale sequence stratigraphy of Mishrif carbonates and implication to water injection strategy North Rumaila field case Awadees M. R. Awadeesian & Sameer Noori Ali Al-Jawed & Afrah Hasan Saleh Received: 18 April 2014 /Accepted: 22 September 2014 # Saudi Society for Geosciences 2014 Abstract The Late-Cenomanian–Early-Turronian Mishrif multi-carbonates in the North-Rumaila oil field has undergone into reservoir-scale high-resolution sequence stratigraphic in- vestigation. 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 evolu- tionary 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 res- ervoir 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 build- up 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. Keywords Reservoir . Sequence stratigraphy . Mishrif carbonates . North Rumaila field Introduction Definition The Mishrif formation was initially defined by Rabanit (1952, Rock units of Basrah area, unpublished) as a Late- Cenomanian–Turronian carbonate succession between the drilled depths (2,195–2,371 m) at Zubair well number 3 in the Zubair oil field (25 km) southwest of Basra city, Fig. 1. General perspective The study area is located in the Basra subzone of the Meso- potamian foredeep of the tectono-sedimentary framework of Iraq. The studied succession is well encountered in the giant North Rumaila and West Qurna oil fields, (75–85 km) west of Basra city, Fig. 1. The both fields are almost of one south-north asymmetrical anticlinal structure, with geometry around 85 km length and 12–18 km width at the top of Mishrif formation, with 110 to 200 m varying thickness. Previous studies submitted by Owen and Nasr (1958), van Bellen (1959), Al-Naqib (1967) pointed out that the succes- sion is particularly made up by open marine facies progressed to reefal and lagoonal facies buildups. Al-Siddiki (1975, Regional geology of Southern Iraq, unpublished), Al-Khayat and Razoian (1978, Geologic A. M. R. Awadeesian : S. N. A. Al-Jawed (*) Ministry of Oil, Baghdad, Iraq e-mail: d.samir@yahoo.com A. H. Saleh College of Science, University of Baghdad, Baghdad, Iraq Arab J Geosci DOI 10.1007/s12517-014-1650-1