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Depositional environment and reservoir properties of Kurrachine Dolomite and Markada Formation in Central Palmyrides, Syria

Deposits of Markada and Kurrachine Dolomite Formations were studied in more detailsin the area of INA's Concession, Hayan Block in central Palmyrides, Syria. Database comprises logs, cores, cuttings and reports from the surrounding wells. Palmyrides are considered as atype example of an intracontinental transpressive mountain belt, 400 km long and 100 km wide, striking N45&ordm ; ; E from the Anti-Lebanon Mountains and the Dead Sea fault system. Markada formation, Carboniferous, predominantly consist of shale/sandstone intercalations with minor siltstone and limestone. Sandstones were grouped into four (A, B, C and D) genetic packages for correlation purposes. The depositional environment was a near shore marine setting. The major sanstone layers were deposited as small delta distributora mouth bars and/or meandering tidal channel sands that merged and pinched out laterally. Minor sandstone and siltstone were deposited as over bank depositsand crevasse-splay deposits from the main distributora channels. Intertidal clays and occasional limestone, are evidence of period of low clastic sedimentation rates (low energy) and flooding of the shallow marine platform that allowed the deposition of thin carbonate beds. Petrographic analyses indicate that sandstones southern of the study area is classified as sub arkoses, moderately sorted with angular to subangular quartz grains and K-feldspars (microcline) and plagioclase feldspars as subordinate components. Subarcose sandstones are of granite provenance, usually deposited proximal to the source area. On the other side, sandstones from the northeast are quartz arenites, containing sub rounded to sub angular grains of monocrystalline quartz and rare chert. Dandstones are fine grained and well sorted. Quartz arenite sanstones seem to more distal that subarcose sandstones from the south. Porosity=12-14%, permeability h=26-75 md, v015-46 md. It may be concluded thata the source area for clastics was from southern provinces (Arabian shield) from where was via deltaic/river system transported to the shallow shelfs and epeiric seas on Gondwana land which was to the NE during Carboniferous surrounded by the Palaeo-Tethys ocean. According to the wire line logs motives interpretation and "depositional energy modelling" it is evident that higher energy is always connected with better reservoir properties. Kurrachine Dolomite Formation, Middle-Upper Triassic, consists predominantly of various carbonate types, dolomite and limestone, evaporites, shale/claystoneand represents the major Mesozoic reservoir for gas (predominantly), condensate and oil in Palmyrides. Formation is subdivided according to its reservoir properties into subunits C2, D1, D2 (from the top to the bottom). c2-Secondary reservoir-interbedded dolomite, limestone, anhydrite, shale and claystone. The more evaporitic carbonate phases and anhydrite in the C2 are interpreted as chemical sediments of lacustrine (saline-lake) origin. These cycles were driven by cyclical variations in rainfall, aridity, influx of clay-silt fines into the basin, repeated isolation of the basin and repeated phases of evaporation of gypsum precipitation. Each of the sedimentary cycles is capped by decimetre to metre scale unit of bedde anhydrite. The plaeogeographic model for C" is a basin which many times "went lacustrine" trough repeated interludes of evaporation to gypsum precipitation, and isolation from Tethys, Average porosity 5-8. D1-Primary reservoir-it is generally shoaling-upward, cyclical carbonate sequence devoid of terrigenous sediments. Terminates upward at an irregular, sharp contac where it is overlain by a sequnce of mostly dark gray to dark greenish-gray shale. Long cycle of the D1 was accumulated an a dominantly muddy, middle/lower to inner/shallow shelf that shoaled briefly to tidal-flat conditions. D1 is divided into 3 informal subzones: Lower Dolomite: has the best reservoir properties ; represents lower partof the long marine cycle. Consists of poorly stratified, fine-to-coarse crastalline dolomite. Original grains and textures are obscured to some extend because of fabric "coarsening" by dolomitisation, but Lower Dolomite appears to have been bioclastic carbonate sand. Pore system are varied and include intercrystal, occasional, moldic and interparticle pores and a abundance of rather small, mm-cm scale vugs of irregular shapes. Middle Limestone: upper part of the long marine cycle. Represent a regime of lime-mud accumulation on a shallow shelf that ended with brief shoaling to intertidal conditions. Upper carbonate: includes Upper Dolomite interval and minor evaporites at the top. Shoaling upwared evaporite-capped cycle. Average porosity 8-9%. D2-reservoir-sequence of interbedded shale, dolomite and lime mudstone. Upper part of D2 represents a shoaling-upward succession from basinal or distal ramp/slope to lower shelf/ramp sediments. The upper D2 contains no evaporites and unlike the overlying D1 and C2shows no evidence of deposition in either shallow-marine, peritidal or non-marine environments. Average porosity 2-7%.

Depositional environment; hydrocarbon reservoirs; Carboniferous Markada formation; Middle-Upper Triassic Kuracchine formation; Syria

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