Sequence Stratigraphy for Optimize Development Strategy, Ahmadi Carbonates, Case Study, South Iraq Oil Fields.

Abstract

The Early Cenomanian Ahmadi carbonates succession in selected oil-wells in south Iraqi oil fields have undergone; into sequence stratigraphic analysis as new reservoir stratigraphy optimization understanding. The sequence stratigraphy context: has applied on the mentioned carbonate reservoir in selected oil-wells from West-Qurna and Majnoon oil fields, with respect to Arabian-plate (AP) chronosequence stratigraphy and chrono-markers setting.

A meso-genetic buildup has infra-structured the studied Formation based-on; smallest-set of the genetically-related high-frequency lithofacies-cycle and cycles-set modeling. A genetic sequence (meso-sequence one MS1) is described as a well-encountered buildup between the (MFS-K120 of lower Ahmadi shale) and (MFS-K125 of upper Ahmadi shale) chrono-markers, with key-surfaces (K121 to K123a). HST-facies-buildup has distinguished by (K122 and K123a) key-surfaces, and TST-facies-buildup by (K123a and top of Ahmadi Formation). The maximum flooding surface (MFS-K125) is confirmed by this study as a local stratigraphic term terminates the sequence MS1. The lithostratigraphic member (Mc2) of the Ahmadi is well described as; carbonate-buildups of progradational-HST high-frequency-cycles, followed by retrogradational-TST high-frequency-cycles. The Ahmadi multi-carbonate reservoirs are well defined by downward shift shoals and isolated Rudistid-banks. The shoals are well-encountered between the key-surfaces (K122 and K123a) of good to very-good reservoir characteristics, whereas; the Rudistid-banks encountered between (K123a and base of MFS-K125), differently behave in reservoir characteristics owing to open marine facies effects. The reservoir facies and distribution framework of the clino /or shingled shoal-bodies, are well developed from the platform-site (western-flank) toward the basinal-site of the field (eastern-flank). For reservoir optimization strategy, it is highly advised to apply the sequence steering schedule by building the high frequency lithofacies cycles into selective-perforation/isolation plan in the well completion agenda.