An integrated sedimentological and sequence stratigraphic analysis of the mixed carbonate and clastic Albian Mauddud Formation in the Bahrah and Sabiriyah fields provides an improved understanding of this important reservoir in north Kuwait. The reservoir comprises two broad stratigraphic units: the lower Mauddud represents the culmination of a long-term transgressive retreat of the underlying Burgan delta system, whereas the overlying upper Mauddud records a low-gradient carbonate shelf or ramp system. A highly layered reservoir architecture of carbonate and clastic facies suggests a combination of high-frequency relative sea-level and/or climatic fluctuations. Sedimentological analysis and regional correlations reveal a complex mixed carbonate-clastic system in which there is a tripartite arrangement of proximal coarse-grained deltaic, distal prodeltaic, and offshore to along-strike carbonate facies. These form correlatable reservoir units bound by flooding surfaces and/or significant influxes of clastic sediment.
The distribution of clastic and carbonate facies produces a pronounced variation in reservoir properties, between the neighboring Bahrah and Sabiriyah fields of north Kuwait. Primary stratigraphic and depositional reservoir heterogeneities are controlled by carbonate facies transitions from poor quality, micritic lagoonal facies to high-quality, grain-rich shoals and localized, reworked rudistid build-ups. These carbonate facies are cyclically layered with deltaic sandstone and prodeltaic shales. In combination with secondary diagenetic (e.g., cementation and dissolution) and structural characteristics (e.g., faults and fractures), this facies variability exerts a control on reservoir quality and produces a complex mosaic of reservoir heterogeneity. Reservoir variability controls differences in production performance of the neighboring fields, and these have been accommodated by contrasting field development strategies.