Sequence Stratigraphic Analysis of the Mid‐cretaceous Mishrif Formation, Southern Mesopotamian Basin, Iraq

Abstract

The middle Cenomanian -early Turonian Mishrif Formation, a major carbonate reservoir unit in southern Iraq, was studied using cuttings and core samples and wireline logs (gamma-ray, density and sonic) from 66 wells at 15 oilfields. Depositional facies ranging from deep marine to tidal flat were recorded. Microfacies interpretations together with wireline log interpretations show that the formation is composed of transgressive and regressive hemicycles. The regressive hemicycles are interpreted to indicate the progradation of rudist lithosomes (highstand systems tract deposits) towards distal basinal locations such as the Kumait, Luhais and Abu Amood oilfield areas. Transgressive hemicycles (transgressive systems tract deposits) represent flooding of the shallow carbonate platform and are recorded in oilfields such as Amara, Halfaya and Zubair.A sequence stratigraphic framework has been constructed for the Mishrif Formation based on correlation of the transgressive and regressive hemicycles which are separated by maximum flooding surfaces. Three third-order sequences are identified which show lateral and vertical facies variations depending on relative sea-level changes. Sequence boundaries are characterized by karstic, exposure and drowning features. Middle Cenomanian -Turonian eustatic sea-level changes together with regional-scale tectonic deformation of the Arabian Plate controlled the availability of accommodation space and therefore the depositional profile during development of each sequence. Both of these factors controlled the maximum flooding surfaces and sequence boundaries which have been identified.The sequence stratigraphic key surfaces presented in this study represent typical candidate horizons or datum surfaces for future seismic or resevoir modelling studies. Also, lateral facies variations in each transgressive-regressive sequence and associated carbonate bodies (i.e. prograding shelf margin, forced regressive wedge) may form important stratigraphic traps in the Mesopotamian Basin.

Characterization of flow units, rock and pore types for Mishrif Reservoir in West Qurna oilfield, Southern Iraq by using lithofacies data

“…The laboratory measurements (RCA) were conducted. (Mahdi and Aqrawi, 2014) The second step in this study was to insulate the plugs stated according to the layers depending on the upper and lower limit of each unit and also on the specified depth that each core has been taken from a certain well. The data have been analyzed and tabulated for each unit of Mishrif Formation Figs.…”

Identification of facies‐controlled eogenetic karstification in the Upper Cretaceous of the Halfaya oilfield and its impact on reservoir capacity

“…The Upper Cretaceous Senomanian–Turonian cycle started with transgressive Ahmadi Formation marl (Ehrenberg, Aqrawi, & Nadeau, ), overlain by the Rumaila Formation shelf chalk‐bearing carbonate deposits (Alsharhan & Nairn, , ), then followed by regressive Mishrif Formation carbonate deposits with rudist bivalves (Mahdi & Aqrawi, ; Sadooni, ), and then open platform facies carbonate deposits of the Khasib and Tanuma Formations (Al‐Qayim, ; Figure ). The Mishrif Formation is about 350–400 m thick on average and thins to 150 m in the southwestern basin.…”

Microfacies Patterns and Depositional Environments of the Sarvak Formation in the Abadan Plain, Southwest of Zagros, Iran

“…This mud-supported facies comprised of small rudist, echinoderm and bivalve debris and small foraminifers (Figure 4(i)). The mud-supported nature, a low abundance of benthic fauna and the absence of wave and current patterns show low energy calm environments of the outer ramp (off-shoal) depositional setting [8] [14].…”