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This paper summarizes the evaluation of the Mauddud formation reservoir, in the Raudhatain and Sabiriyah fields of Northern Kuwait, in the petrographical, reservoir quality and sedimentological perspective. It will describe the core 17 wells of which 12 were cored relatively continuously and 5 which the basal Mauddud interval was cored. The wells were integrated with data with several aims: to characterize vertical and crest-to-flank reservoir quality variations, to evaluate the characterization of detrital clays that contaminate the muddy carbonates and to evaluate the distribution of grain stones, float stones and sulphur minerals. Each of the reservoir zones will be discussed in brief.
Reservoir Zone MaJ
With an average thickness of 25.0ft lt, it comprises outer ramp to basinal clay-rich skeletal wackestones and lime mudstones intercalated with pyritic clastic mud rocks. It marks the base of the Mauddud formation with a base characterized by a transition from glauconitic sandstones to glauconitic lime stones. This zone has negligible reservoir potential because of its extensive cementation of the carbonate facies.
Reservoir zone Mal2
It has an average thickness of 12.7ft lt and it is composed of basinal classic mud rocks that have a high gamma-ray response. The mud rocks act as a barrier to fluid flow and have negligible reservoir potential.
Reservoir zone Mal1
With an average thickness of 34.4ft lt, it is composed of unstained to weakly hydrocarbon-stained shallow to deep mid-ramp, predominantly clay-bearing skeletal packstones and minor intercalation of outer ramp wackestones. It is characterized by a relatively aggradational stack of packstones, punctuated by minor flooding surfaces. The carbonate lithofacies are extensively cemented, with carbonate concretions exerting a strong control on reservoir quality.
Reservoir zone MaH
It has a thickness of 36.6ft lt and consists of flooding surfaces related glauconoti/elastic prone packstones and sandstones, outer ramp wackestones and basinal mudstones and heterolitlics overlain by weakly to intensely hydro-carbon stained, upward cleaning and coarsening sandstones. The gamma-ray log responses fall under three categories: an upper sandstone interval associated with an upward-cleaning gamma-ray response, a central clastic mudrock and heteorolithic interval with a hot gamma-ray response and a basal glauconitic carbonate interval in which gamma-ray log spikes across. Overall, MaH has poor reservoir quality in Raudhatain field but moderate reservoir quality in Sabiriyah field.
Reservoir zone MaG
It has an average 48.8ft lt thickness and is composed of weakly to moderately hydrocarbon-stained predominantly shallow mid-ramp clean skeletal packstones, to high energy inner ramp skeletal peloidal grainstones in the Raudhatain field. It is characterized by a basal upward cleaning depositional cycle. Concretionary cement are extensively developed and they exert a strong control on reservoir quality. Overall, it has moderate reservoir quality.
Reservoir zone MaF
It has an average thickness of 33.3ft ld and it comprises basinal mud rocks and outer ramp day-rich skeletal wackestones, through weakly hydrocarbon-stained deep mid-ramp packstones to transitional high-energy inner ramp skeletal poloidal grainstones. It has a basal transgressive cycle which is overlain by an upward cleaning gamma-ray log motif capped by an upper upward-dirtying gamma-ray response. Overall this zone has poor reservoir quality.
Reservoir zone MaE
It has a thickness of 41.2ft ld and its made up of weakly to strongly hydrocarbon stained, transitional high-energy inner ramp/shallow mid-ramp skeletal-peloidal grainstones and clean-skeletal packstones to deeper mid-ramp clay bearing packstones. It has aggradational to progradational depositional cycles that lack flooding surfaces and this represents an upward-cleaning gamma log motif. Overall, the zone has moderate reservoir quality.
Reservoir zone MaD
Has an average thickness of 59.8ft lt and it is made up of moderately to strongly hydrocarbon stained’ shallow to deep mid-ramp clean to clay-bearing skeletal-peloidal grainstones. The zone is characterized by aggradational deposits and muddier packstones or isolated modular cements. There is rumbling within the upper portion of the zone and these rubbled intervals are generally accompanied by a ratty resistivity log response. Overall the zone has probably the best reservoir quality within the Mauddud.
It has a thickness of 32.7ft lt and it is made up of moderately hydrocarbon-stained, protected inner ramp diffuse clay-bearing skeletal packstones, wackestones and mudstones that have a restricted microfauna. The interval is characterized by aggradational to weakly progradational package and it also has a retrogradational package. The reservoir quality is controlled by the primary depositional fabric and the rarer shallow mid-ramp packstones. Overall, this reservoir zone has moderate reservoir potential.
It has 24.4ft lt thickness and it is made up of weakly to moderately hydrocarbon-stained, predominantly mid-ramp clay bearing skeletal packstones. Its mid-ramp depositional cycles are aggradational to weakly retrogradational and are punctuates by deeper mid-ramp flooding surfaces. These cycles have weakly upward-dirtying gamma-ray log responses. The reservoir quality is controlled by the primary depositional fabric of the mid-ramp packstones which are modified by the presence of concretionary cements. Overall the reservoir zone has moderate reservoir potential.
Reservoir zone MaA
It has a thickness of 17.6ft and it consists of outer ramp clay-rich skeletal wackestones with mimor clastic mudrock incursions. Interval has a high gamma-ray response even though it has a serrate retrogradational depositional package. The depositional facies are extensively cemented and therefore the zone has negligible reservoir potential.
In conclusion, the distribution of carbonate concretion which are a major control on the reservoir quality in the Mauddud reservoir, vary within and between the zones.