Outcrop and Core Studies of the Lower Miocene Dhiban Formation, Syria By Al Ja’aidi Omar, Homewood Peter, Droste Henk, Jamal Al Jundi, Mohammed Abou Shaker, & Jürgen Grötsch. IAS 2005 Muscat Palmyra/Tadmur Talk Outline The Objectives Introduction to the Study area Outcrop Description Core Description Proposed Stratigraphic and Depositional models for the Dhiban Fm Reservoir implications Conclusions The Objectives Carry out an integrated core and outcrop study on the Miocene carbonate reservoirs in Eastern Syria. In order: to provide a depositional model of the Jeribe, Dhiban and Euphrates Formations. to assess the lateral extent of reservoir and sealing units of the above formations, in support of 3-D static reservoir modeling. Syria Carbonate Reservoirs Stratigraphy Post-Rift Syn-Rift Lower Fars (TZCA) Seal Jeribe, Dhiban, Euphrates SR/(Seal) Upper Shiranish Lower Shiranish Res. Erek Seal Res. Rmah Judea G Triassic F Res. Mulussa CDE E D Intra-Carboniferous Dolomite C Perm. B Ord. Sil. Dev. Carbonif. BKU Seal BKL Mulussa Gr. MUC Carbonate Reservoirs Pre-Rift Late Fars Jeribe Dhiban Euphrates Chilou Jaddala Aaliji Shiranish Fm Erek Fm R’mah Derro Post-Judea Sands Judea Rutbah Jurassic RU Early SHL Cretaceous Tertiary ic kers Upper Doubayat Fm I.C.D. Lower Abba Fm Khabour Fm SR Outcrop Location AL FURAT RIVER AR’RAQQAH DEIR-EZ-ZOR PALMYRA Damascus  200 km SW LOCATIONS VISITED Outcrop and Core - Wadi Rattla Oil fields Outcrops visited Wadi Al Jir - Wadi Shijiri Bishri Block Wadi - Dufina Euphrates Graben Thayyem Al Nishan Flds Outcrops Strat Unit Thickness Age Lithology Sub-Strata equivalent ‘Tortonian’ Upper Part > 500 m Tortonian based on forams Greenish gray marls and, in the upper part, quartz sandstones and limestones interbedded with evaporites Fars ‘Tortonian’ Lower part 100 to 110 m in Wadi Aj-Jir Tortonian based on forams Alternation of gypsum and limestones intervals. Limestone intervals 0.5 to a few meters thick, gypsum a few meters in the lower part to > 10 m in the upper part of the sequence. Fars ‘Helvetian’ 25 m in the Shjiri area Helvetian based on forams Light bedded occasionally arenaceous limestones overlain by gray compact arenaceous limestones in the Shijiri area limestone coquinas with gypsum and dolomite predominate Jeribe ‘Lower Miocene’ 12 –13 m in the Shjiri area according to geological map (we estimate at least 80 m) Early Miocene assumed from its stratigraphic position Barren sand series above Oligocene strata poorly defined on geological map Euphrates and Dhiban Formations Depos Facies similar Dhiban Tertiary Outcrops (Bishri High) Subsurface Fars Jeribe Dhiban Euphrates Chilou Jaddala Aaliji Stratigraphic equivalent Lower Tortonian Helvetian Lower Miocene Lower Miocene Depositional setting similarity Dhiban Wadi Aljir Helvitian limestone Stromatolites Brecciated Horizon Sand dominated with white/yellow/reddish sands with chert pebbles High energy beach/shoreface facies Wadi Aljir Stromatolites Anhydrites Core 250m Well Cores Length (m) Scale Interval A 1-4 41 1:100 Euphrates Dhiban B 1-4 33 1:100 Euphrates Dhiban C 1-3 54 1:50 D 1-2 29 1:100 Euphrates Dhiban Jeribe Euphrates Dhiban E 1-2 15 1:100 Euphrates Dhiban F 1 18 1:100 Euphrates Dhiban G 1-5 54 1:100 Euphrates Dhiban Core 831. 5 m 5 cm 5 cm 815.65 m Collapse Breccia 837. 78 m Intraformational conglomerate 5 cm 804.75 m Mollusc grainstone 845.75 m Mollusc grainstone with stromatolites Evaporite cgl overlain by elongated anhydrite capped by dissolution surface 5 cm 5 cm 5 cm 806.2 m Heterolith Euphrates Fm. Large-scale fining and coarsening upward unit. 928 m 924.8 m Bioturbated rhodolith float to grainstones overlain by laminated mudstones. fine Gst Rhodoliths laminated mudst vuggy heterolith 5 cm 5 cm The grainstones are porous throughout the formation but towards the top more vuggy porosity occurs due to leaching of mollusk fragments. 5 cm Upper part dominated by fine to coarse mollusk (bivalves and gastropods) bioturbated mud to pack/grainstones (THM-B) 845.75 m Dhiban Mollusc Grainstone The upper part of the Dhiban consists of m-scale intervals of fine bioclastic marls/muds with wavy to low angle cross bedding, in places burrowed. THM-B 831.5 Zoom in Stacked packages of anhydrite occur, beds separated by dissolution surfaces, clay layers or thin lags with cross bedding. Bioturbated molluskc pack/grainstones interbedded with dm thick algal laminated to stromatolitic beds. Algal intervals are cm to m thick and consist of laminated to stromatolitic mudstones. 5 cm Anhydrite beds are dm to m thick, bedded at the base to more massive nodular at the top. Mouldic pores after leaching of shell fragments Algal and Stromatolitic Grainstones 5 cm Dhiban Fm. THY-C 819.5 m Tortonian Wadi Shijri area Algal and Stromatolitic Grainstones 5 cm 5 cm THM-D 820.15 m THM-E 820.6 m Karst breccia 5 cm THM-B, 811 m Wadi Ajir ‘Helvetian carbonate’ Dhiban Seals Nodular anhydrite Stromatolites Lagoonal clays Playa muds Evaporite Seals Wadi Sijiri ‘Helvetian carbonate’ Summary Core Lithofacies Lithofacies Description Interpretation Evaporites Scattered nodules, Chicken wire fabric, massive/grading from nodular to massive. Result of authigenic growth of eveaporites within the sediment from hypersaline groundwater in a very arid climate Chaotic intervals of up to 2m with dispersed intraclasts and sediment filled cavities The association with evaporites may suggest collapse breccias Chaotic mix of algal (thrombolitic texture), finger corals, large bivalves,rhodoliths and gastropid fragments These beds are probably related to exposure surfaces related to karst Breccias Chaoitic rubble Algal laminated Algal intervals are cm to m and thick and consist of stromatolites laminated to stromatolitic mudstones. Algal mats may suggest an intertidal zone possibly extending into the subtidal zone Core Photo Summary Core Lithofacies Lithofacies Mollusk grainstones Laminated mud and marls Biouturbated mud and marls Dark laminated mudstones Description Interpretation Fine to coarse mollusk (bivalves and gastropods) bioturbated mud to pack/grainstones that are organized in m-scale coarsening upward packages. Some shells are covered with algal encrustations. The grainstones are porous throughout the formation but towards the top more vuggy porosity occurs due to leaching of mollusk fragments. This facies is characterized by fine bioclastic marls/muds with wavy to low angle cross bedding, mud drapes, mud cracks and only some rare burrows. The lack of bioturbation in this facies suggest deposition in a highly restricted, probably hypersaline environment. These may have been restricted lagoon/ponds (coastal salina) behind the barrier complex These consist of strongly bioturbated marls/lime mud - packstones with common bivalve fragments These form intervals of 1 to 2 m thick and are associated with the mollusk sands. These sediments were deposited in a low energy, subtidal non-restricted environment. The close association with the mollusk sands and the evaporites suggest a lagoonal environment between the semi protective shoal complex and the tidal flats These dark laminated mudstones occur between and grade into bioturbated grain to packstones. They are associated with high gamma reading values suggesting a high organic matter content This facies represent deeper marine deposits deposited under anoxic bottom water conditions. Core Photo Euphrates Dhiban Jeribe Stratigraphic Model ng30 15 Ma Top Dhiban Karst Sabkha/Playa Salina clay influx Mod/low energy lagoonal Base Dhiban Lower energy open marine ng20 Euphrates Graben ?18 Ma Bishri Block Euphrates Dhiban Jeribe Depositional models Dhiban • regressive scenario ng30 15 Ma Sabkha/Playa Salina clay influx Lower energy open marine ng20 Euphrates Graben ?18 Ma – – – – salina (salt ponds) playas stromatolites supratidal sabkha • transgressive scenario – lagoonal moderate energy grainstones – littoral deposits – supratidal sabkha Reservoir Implications Lower Dhiban Transgressive Systems Tract •Flat time correlation lines on a field scale •Very high lateral continuity of flow units •Evaporites will form horizontal baffles but will have limited lateral extend Transgressive lags may form High permeability streaks Upper Dhiban Highstand Systems tract •Flat time correlation lines on a field scale •More frequent intercalated baffles (evaporates and mud/marls) which are laterally more continuous, reducing vertical permeability •Possible incisions (channeling) near top •Stronger early diagenetic overprint than in lower Dhiban, impact of early freshwater diagenesis on rock fabric related to karst at top Dhiban Conclusions • Reservoirs consist of mollusc grainstones and stromatolitic limestones, porosity is result of secondary leaching. • Seal risk of Dhiban anhydrites – nodular, not full evaporite cycles potentially limited lateral extend (e.g. 5 m thick full rising and falling water table) – Correlation risk of Dhiban anhydrites • The Dhiban formation consist of a transgressive regressive cycle. As the transgressive and regressive parts are characterized by different facies associations, at least two depositional models may be required to describe the formation. • Each depositional model had also different implications for the lateral continuity and stacking trends of the reservoir and sealing intervals.