Tectonic Evolution of the Eastern Mediterranean Basin and its Significance for the Hydrocarbon Prospectivity of the Nile Delta Deepwater Area

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1 GeoArabia, Vol. 6, No. 3, 1 Gulf PetroLink, Bahrain Tectonic Evolution of the Egyptian Mediterranean Basin Tectonic Evolution of the Eastern Mediterranean Basin and its Significance for the Hydrocarbon Prospectivity of the Nile Delta Deepwater Area Ahmed Abdel Aal1, Ahmed El Barkooky, Marc Gerrits, Hans-Jürg Meyer, Marcus Schwander and Hala Zaki Shell Egypt NV ABSTRACT The deepwater area of the Nile Delta is within the eastern Mediterranean basin on the Nile Delta Cone between the Herodotus abyssal plain to the west and the Levant basin to the east. The complex evolution and interaction of the African, Eurasian and Arabian plates have shaped the Late Miocene to Recent Nile Cone and its substratum. The tectonostratigraphic framework is controlled by deep-seated basement structures with distinct gravity and magnetic expressions, and by the interaction of the NW-trending MisfaqBardawil (Temsah) and NE-trending Qattara-Eratosthenes (Rosetta) fault zones. In addition, significant salt-induced deformation of a Messinian evaporitic sequence up to, m thick has occurred, together with large-scale rotational block movement. The deformational pattern is largely the result of multiphase tectonic movements along preexisting basement faults on the continental margin of the Neo-Tethys ocean. The Nile Cone consists of late Paleogene to Late Miocene sediments that pre-date the Messinian evaporites, and Pliocene-Pleistocene sequences. In the east, the pre-salt deposits (as much as 3, m thick) are primarily deepwater sediments with local condensed sequences over syndepositional intrabasinal highs. Shale occurs westward across the Rosetta trend. The Messinian evaporitic sequence exhibits three distinct seismic facies suggesting cyclic deposition with the occurrence of interbedded anhydrite, salt and clastic sequences and pure halite deposition. During the Messinian salinity crisis, large-scale canyons were excavated that resulted in multiphase cut-and-fill clastic systems. The Pliocene-Pleistocene sequences were deposited in a slope to basin-floor setting. Exploration targets are the Pliocene-Pleistocene deepwater channel and basin-floor turbidite sands in a variety of structural settings. Water depths range from 8 to,8 m. The Upper Miocene sequence offers additional exploration objectives in the form of fluvial and/or turbidite sands. The focus of pre-salt exploration is the delineation of distal turbidities within the Serravallian to Tortonian sequence and the identification of new reservoir sequences deposited on pre-existing intrabasinal highs. Hydrocarbon charge has yet to be proven by drilling, but seismic amplitude anomalies and the occurrence of natural surface slicks suggest both gas and liquid charges from pre-salt source rocks through faults and salt-withdrawal windows. INTRODUCTION The NE Mediterranean Deepwater Block (NEMED) of 1, sq (Figure 1) was awarded to Shell Egypt (1%) in July The pre-effective letter was signed on November, 1998 allowing operations to start on February 1, 1999 with the acquisition of a 7,, -D (6 cable, 8 seconds, 1 fold) seismic survey. Key pre-1999 data were 1, of -D seismic acquired by the Egyptian General Petroleum Corporation in In December 1999, Exxon Exploration and Production Egypt Limited obtained a percent interest in the concession. Current exploration activity includes the acquisition of a 7, sq area of 3-D seismic aimed at the identification of exploration targets. The evaluation 1 Present address: Shell Houston, USA Copyright Gulf PetroLink 16. All Rights Reserved. Downloaded by munirelmahdy87@gmail.com IP:

2 Abdel Aal et al. challenge of the initial -D campaign was to identify the main plays and the target area of the 3-D survey by integrating seismic with new gravity and aeromagnetic data. The Block is exceptional for its size and its location in front of a major productive delta. The newly acquired -D seismic data has enabled mapping of the geology of the whole concession for the first time and shows that it contains four distinct geological domains, each with unique play characteristics. Of these, only the Nile Delta gas/condensate Pliocene and Miocene Platform domain has been tested. No wells have been drilled in the Deepwater Block, but direct hydrocarbon indicators on seismic attest to a high probability of charge. The nearest wells are in the Scarab and Saffron gas fields to the south in the West Delta Deep Marine concession (Figure ). Shallow boreholes of the Deep-Sea Drilling Project (DSDP) Leg 16 provide data in the area of the Erastothenes Seamount and to the west of Cyprus (Figure ). During seismic acquisition, approximately 1, of onboard gravity data was acquired and fully integrated with the available satellite gravity data. In addition, some 3,7 line- of high-resolution aeromagnetic data is available. In the central and eastern part of the block, the line spacing is x 1, increasing in the west and northwestern areas to x. Special studies focused on quantitative seismic interpretation (development of the rock property database, amplitude versus offset, and other hydrocarbon indicator studies) integrated seismic and potential field-data analysis, surface slick analysis and basin modeling. Thirty-five years of exploration activity in the Nile Delta has led to the discovery of about 3.8 billion barrels oil equivalent (BOE), primarily gas and condensate (Figure ). The newly acquired -D seismic data have substantially upgraded the prospectivity of the Block s ultra-deepwater area. Based on the results of the -D seismic data, 7, sq of 3-D data was acquired. The survey covers the prospective parts of the Platform, Diapir Salt and Rotated Fault Block play areas in water depths of less than, m. E TURKEY 36 N 36 Crete CYPRUS Mediterranean Sea 3 ne rra ite idge d Me R an 3 Eratosthenes Seamount NE Mediterranean Deepwater Block (NEMED) N Nile Cone Cairo Bathymetry (meters) Nile Delta 1 9 EGYPT 3, 3 Figure 1: Regional geographic setting of the NE Mediterranean Deepwater Block (NEMED). Copyright Gulf PetroLink 16. All Rights Reserved. Downloaded by munirelmahdy87@gmail.com IP:

3 Tectonic Evolution of the Egyptian Mediterranean Basin E 36 N TURKEY 36 N 7 E Crete CYPRUS X' Mediterranean Sea 3 3 ED 3 NE M A B C C' B' A' N 1 X 7 EGYPT 9 3 E Nile Delta Discoveries 3.8 billion BOE Mediterranean Sea m Ha'py Akhen Rosetta Baltim E. Asfour Seti Port Fuad C C' Figure 6c EGYPT 3 B B' Figure 6b Kersh / Abu Zakn / Wakar Abu Madi X X' Figure A A' Figure 6a Abu Seif El Qar'a Abu Qir W. Abu Qir Nile Delta seismic Temsah Seth Baltim S. N. Abu Qir Gas field Deep Sea Drilling Project sites Shell D seismic Scarab Baltim N. 3 Nile Delta well 1, m N Saffron Figure : NE Mediterranean Deepwater Block database: locations of Nile Delta wells and gas fields, seismic surveys, and shallow wells of the Deep Sea Drilling Project. TECTONIC FRAMEWORK AND STRUCTURAL SETTING Plate Tectonic Framework The Northeast Mediterranean Sea Deepwater Block is situated near to the northern margin of the African Plate. The plate is being actively subducted (presumably since the Late Cretaceous) along the destructive, compressional plate boundary south of Crete and Cyprus (Strabo-Pliny/Cyprus trenches; Figure 3). Seismic refraction and potential-field data (magnetic and gravity) do not yet Copyright Gulf PetroLink 16. All Rights Reserved. Downloaded by munirelmahdy87@gmail.com IP:

4 Abdel Aal et al. E N 3 TURKEY 36 TURKISH PLATE Crete CYPRUS Tre nc h 3 -B ar Figur e ED EM l N AFRICAN PLATE ta et ) 1 Er Levant Basin (Te ms Herodotus Abyssal Plain N ra ta 9 Qat 7 os (R Nile Delta ARABIAN PLATE wi da ESM at os t hen e s aq an ne rr a ite ed M e dg Ri X' isf M bo ra St 3 lin -P Cy pru s h nc re T y ah ) X EGYPT 3 Figure 3: Regional geological setting of the NE Mediterranean Deepwater Block (ESM = Eratosthenes Seamount). allow a firm statement on the nature of the crust underlying the Pliocene-Pleistocene Nile Cone. What appear to be present are a thinned crust and an elevated crust/mantle boundary at a depth of 18 to. This contrasts with the Egyptian mainland and the Eratosthenes Seamount (Figures 1 and 3), where refraction and potential-field data indicate a complete upper and lower continental crust 3 to thick (Figure ). South North X Upper Miocene Salt Cyprus Trench X' Mediterranean Sea Nile Cone Crustal velocities (/sec) Below sea-level () Eratosthenes Seamount? Continental crust Cyprus ophiolite complex? Moho Mantle 3 1 Bouguer gravity Gammas Milligals Magnetics Figure : Structural cross-section from the Nile Cone to Cyprus showing crustal seismic velocities (/sec) and gravity and magnetic profiles (modified from Hirch et al., 199). See Figures and 3 for location of XX. Copyright Gulf PetroLink 16. All Rights Reserved. Downloaded by munirelmahdy87@gmail.com IP:

5 Tectonic Evolution of the Egyptian Mediterranean Basin Various authors (Morelli, 1978; Biju-Duval et al., 1979; Dixon et al., 198; Geiss, 1987; and Hirsch et al., 199) envisage the presence of an oceanic crust, the maximum age of which, however, is disputed and not constrained by direct observations. If oceanic crust is present, it could be as old as the late Paleozoic/ Early Triassic or as young as the Late Cretaceous. The maximum age of sediments underlying the Pliocene Nile Cone (and the occurrence of the oldest possible source-rock sequences) would logically be younger than the age of creation of the oceanic crust. The present investigation indicates the presence of a very thick sedimentary sequence beneath the Upper Miocene salt section and of sediments older than Late Cretaceous. Even pre-cretaceous sedimentary rocks cannot be excluded. Structural Setting The structural pattern of the study area is the result of a complex interplay between three major fault trends (Figure 3): 1. NW-oriented Misfaq-Bardawil (Temsah) trend;. NE-oriented Qattara-Eratosthenes (Rosetta) trend (Abdel Aal, et al., 199; Argyriadis et al., 198; Neev, 197); and 3. E-trending faults delineating the Messinian salt basins. The tectonic framework and structural setting of the study area indicates the presence of five main structural domains (Figure ) separated by strands of the three major fault trends. The domains are Platform; Rotated Fault Blocks; Basin Floor; Diapiric Salt Basin; and Inverted Salt Basin. 9 E Mediterranean Sea E' Basin Floor NE M ED F' N ve rte d Sa lt Ro t ed at In s lock lt B u Fa Ba si n Platform West Safron Scarab Nile Cone F Rosetta W. Abu Qir N. Abu Qir Abu Qir Figure 8 N 9 E Baltim N. Ha'py Akhen Temsah Seth Baltim E. Seti Asfour Baltim S. Abu Seif El Qar'a Kersh / Abu Zakn / Wakar Abu Port Fuad Madi Diapiric Salt Basin Platform East EGYPT Figure : Geological domains of the Nile Cone and the NE Mediterranean Deepwater Block and locations of geological cross-sections EE' and EFF'; see Figure 8. Copyright Gulf PetroLink 16. All Rights Reserved. Downloaded by munirelmahdy87@gmail.com IP:

6 Abdel Aal et al. The fault trends are parallel to the circum-mediterranean plate boundaries, and seem to be old, inherited basement faults that have been periodically reactivated throughout the development of the area. The Temsah and Rosetta oblique-slip faults intersect in the southern part of the Block to create a faulted, regional high. The Platform area to the west of this high is an extension of the relatively unstructured Nile Delta Province to the south. The Rosetta trend shows large-scale structural relief created by transpressional movement (Figure 6a). Fault movement is of Late Cretaceous age, as indicated by the onlap of the source-rock-prone Late Cretaceous and early Tertiary deepwater sediments. By Late Miocene times, the structural high was covered by basinal sediments. DSDP data from the Eratosthenes high indicates that Upper Miocene shallow-marine carbonates may be present in atoll-like features together with Upper Miocene (Messinian) salt as much as, m thick. The dominant fault movement was pre-salt and there is little evidence of post-salt reactivation along the Rosetta trend. In contrast, the Temsah trend shows Pliocene wrench-fault activity (Figure 6b) contemporaneous with the oblique subduction of the African Plate beneath the Cyprus Trench. The tectonic activity appears to have triggered pillowing of the Messinian salt throughout the Pliocene to create a distinct Diapiric Salt Basin (see Figure ) with ponding of strata in mini-basins. Uplift of part of this basin to form the Inverted Salt Basin in the east and toward the Eratosthenes high is associated with the wrench faulting. The interaction of the two major faults within the Block has produced a variety of structural styles. In addition to brittle deformation related to fault movement, salt tectonics deformed the PliocenePleistocene sedimentary section to create diapiric structures, salt walls and sediment ponding between the salt domes. The southern margin of the Messinian salt basin appears to be fault controlled. This is indicated by the sudden change in structural styles across an east-west lineament (Figure 6c) from the stable Platform in the south to the Rotated Fault Blocks domain to the north. Although some degree of gravity gliding over the salt has been identified, the location of the Rotated Fault Blocks domain was probably controlled and triggered by deep-seated basement uplift. The domain is on the southern margin of the Messinian Salt Basin, the trend of which is parallel to the active plate margin between the African and Turkish plates that lies south of Crete and Cyprus. The Messinian Salt Basin is cut by a NW-trending pre-salt structural ridge flanked by thick salt pods, diapiric structures and associated salt. Seismic facies analysis of the evaporitic sequence indicates three distinct cycles of salt deposition. In the western part of the Deepwater Block, the northern boundary of the Platform coincides with the southern limit of the Messinian salt. Here, the northward roller-pinning of the salt forms a succession of large E-trending normal faults that are replaced northward by large, salt-induced anticlines. Gravity data show a prominent E-W anomaly coinciding with the main platform-bounding fault, and it is likely that this fault, at least, has a deep-seated origin. Northeast of the Platform-bounding fault, the NE Mediterranean Deepwater block is characterized by Pliocene mini-basins and widespread diapiric salt. The mini-basins were filled by rapid sediment influx from channels in the Platform area. Salt movement continued until recent times, and much of the succession is steeply dipping and truncated at the sea floor. The northern part of the block is characterized by thick, shallow salt deposits and by widespread thrust faults. The thrusts are offshoots of the Temsah strike-slip faults. The integration of the newly acquired gravity and magnetic data has confirmed the variety of structural domains that highlight basement highs and lows (Figure 7) and the location of major basement faults. Geological models developed using seismic data have been tested against the observed gravity and magnetic measurements. The -D and 3-D gravity models indicate a sedimentary thickness of to 1 (Figure 7) that, in addition to Pliocene and Miocene sediments, consists of a largely uncalibrated pre-salt succession. This thickness of sediments could contain all the main source rock intervals observed in the surrounding areas. Copyright Gulf PetroLink 16. All Rights Reserved. Downloaded by munirelmahdy87@gmail.com IP:

7 Tectonic Evolution of the Egyptian Mediterranean Basin Northwest 1 Southeast A A' Figure 6: Seismic profiles of the NE Mediterranean Deepwater Block. See Figure for locations of profiles. Rosetta Trend Two-way Time (sec) 3 Pliocene Upper Miocene Messinian Salt Carbonate build-up Tertiary Base Messinian Unconformity 6 (a) Profile AA' across the Rosetta Fault and the Upper Miocene (Messinian) Salt Basin. 7 Cretaceous and older 1 8 Southwest 1 Northeast B B' Temsah Trend Two-way Time (sec) 3 Pliocene Salt Tertiary 6 Cretaceous and older (b) Profile BB' across the Temsah Fault and the Upper Miocene (Messinian) Salt Basin. 7 1 Northwest Southeast C C' Rotational Block Faulting Pliocene Two-way Time (sec) 3 Canyon Salt 6 Mobile Shales 7 Early Tertiary 1 Rosetta Trend (c) Profile CC' across the E W normal faults and rotated fault blocks. Copyright Gulf PetroLink 16. All Rights Reserved. Downloaded by munirelmahdy87@gmail.com IP:

8 Abdel Aal et al. Gammas Northwest Southeast 3 Magnetic 1 1 Milligals Calculated Observed Gravity Post-Salt Tertiary Salt Depth () Pre-Salt Tertiary Pre-Tertiary 1 Basement 1 Figure 7: A -D potential field model derived from observed and calculated magnetic and gravity data to illustrate depth-to-basement in the NE Mediterranean Deepwater Block. STRATIGRAPHY AND RESERVOIR PREDICTION Three major stratigraphic levels have been investigated and all have attractive hydrocarbon potential; they are: 1. Pliocene turbidite system;. Miocene shallow-marine system grading laterally into the Messinian salt province, and; 3. Pre-salt system; Hydrocarbon discoveries have been made within equivalent petroleum systems in shallow-water areas of the Nile Delta proper. The Pliocene deposits consist of slope and basin-floor turbidites in the form of channel/channel-levees and sheet sands (Figure 8). Late Miocene submarine canyons that were formed due to the lowering of sea levels during the Messinian salinity crisis may contain shallowmarine and turbidite systems. The pre-salt section could contain several types of reservoirs, such as Miocene reefal-limestones overlying seamounts (see Figure 6a) and Miocene turbidite sands in large, wrench-faulted structures. Tectonic activity throughout the late Mesozoic and later periods resulted in a variety of structural styles. These styles influenced the pattern of sediment transport into the Mediterranean basins (Ross et al., 1977; Vail et al., 1977; Rizzini et al., 1978; Posamentier et al., 1988; May, 199; Abu El Ella, 199; El Heiny et al., 1996). The Pliocene and Upper Miocene sections are thought to contain the principal reservoir targets in the Block. Copyright Gulf PetroLink 16. All Rights Reserved. Downloaded by munirelmahdy87@gmail.com IP:

9 Tectonic Evolution of the Egyptian Mediterranean Basin South North E Nile Cone E' NE Mediterranean Deepwater Block Pliocene-Pleistocene Depth () Miocene Canyon Miocene Paleogene Cretaceous 6 Salt 1 8 South Northeast F E F' Pliocene-Pleistocene Depth () Salt Paleogene Miocene Cretaceous 6 Eratosthenes Seamount 1 8 Figure 8: Geological cross-sections through the Nile Cone and the NE Mediterranean Deepwater Block to illustrate the Upper Miocene (Messinian) canyon and Pliocene-Pleistocene turbidite depositional sequences. See Figure for locations of EE' and EFF'. Pliocene Reservoirs Well calibration and seismic facies mapping in the Nile Delta area indicate that throughout much of the Pliocene, the area of the eastern Mediterranean was a deepwater environment, transitional between slope and basin floor (Figure 9). Overall, the Pliocene section shows a basinward progradation through time. Seismic facies analysis allows the subdivision of the Pliocene into six major depositional cycles that together form the Pliocene Nile Delta system. These cycles contain an overall prograding shelf to slope system and a basin-floor setting where the occurrence of sheet sands is likely. Throughout the Pliocene succesion the southern area of the Deepwater Block was characterized by N-trending linear turbidite channels as much as wide that can be mapped for distances of up to 1 (Figure 9). The channels are typically aggradational, with seismic facies and compaction features indicating gross reservoir thickness of over 1 m. Channel thicknesses typically decrease outboard to between 3 and m. In the west of the Block, the fault bounding the Platform marks a transition from channels to channeled sand sheets. Overall, the net/gross ratio is low, but sands are concentrated in discrete stratigraphic intervals. This pattern continues outboard, with gradually diminishing sand content and a general thinning of the section. In the east, syn-depositional uplift on the Temsah trend seems to have diverted platform channels toward the northwest. Channels recognized within the mini-basin sequences probably originated from the Temsah fault trend to the southeast. Copyright Gulf PetroLink 16. All Rights Reserved. Downloaded by munirelmahdy87@gmail.com IP:

10 Abdel Aal et al. 9 E Sheet Sands Mediterranean Sea Slope Channels Prograding Shelf NE N E re 11 F ig u NEMED Safron Fig ur e1 W Scarab Rosetta Nile Cone N Baltim N. SW Ha'py Akhen Temsah Seth Baltim E. Seti Asfour Baltim S. Abu Seif El Qar'a Kersh / Abu Zakn / Wakar Abu Port Fuad Madi 9 EGYPT Figure 9: Pliocene-Pleistocene depositional systems of the Nile Cone and the NE Mediterranean Deepwater Block, and the location of the SW NE Sequence Stratigraphic Depositional Model (Figure 1) and W E Regional Seismic profile (Figure 11). Local and worldwide analogs suggest that the Pliocene sands are likely to be unconsolidated and of excellent reservoir quality with porosity values of between and 36 percent. Net sand content over the discrete sand-prone intervals is expected to range between 3 and 9 percent. High-resolution stratigraphic prediction has been carried out with the aid of -D stratigraphic forward modeling. The model (Figure 1) is constrained by subsidence calculated from seismic and well data, global sea level curves, fault movements, sediment input rates and depositional gradients. The model allows the identification of higher-order cycles, the nature and geometry of important sequencestratigraphic boundaries, the prediction of depositional environments and, importantly, the prediction of turbidite-prone intervals. Confined and Unconfined Settings Selective reactivation of old faults and/or salt diapirism has resulted in a confined channeled-slope setting in the eastern part of the Block, whereas the western slope setting is relatively unconfined (Figure 11). Seismic identification of channels appears to be straightforward, but prediction of basinal sheet-sand deposits is more difficult due to the absence of any local calibration. The occurrence of distinct onlapping patterns at the base of the slope/basin-floor setting indicates gravity-flow deposits. Channels in Rotated Fault Blocks Pliocene-Pleistocene isopach maps show that the main axis of Pliocene sedimentation trends southeastward across the Rotated Fault Block domain. The sediment channels that provide an attractive exploration target are cut by large, salt-induced faults. Outboard, seismic interpretations indicate the presence of large, unfaulted anticlines. Copyright Gulf PetroLink 16. All Rights Reserved. Downloaded by munirelmahdy87@gmail.com IP:

11 Depth () Depositional gradients Sediment input rates Global sea level curve Subsidence from seismic and well data MODEL INPUT Ma Nile Cone Ma 1 Ma Ma Age of stratigraphic horizon Turbidites Deep-Marine sediments Shallow-Marine sediments Deepwater Block Northeast Figure 1: Pliocene-Pleistocene Sequence Stratigraphic Depositional Model illustrating the relationships of Shallow Marine, Deep Marine and Turbidite sedimentation in the Nile Cone and the NE Mediterranean Deepwater Block. See Figure 9 for location of profile. 3 1 Southwest Tectonic Evolution of the Egyptian Mediterranean Basin Copyright Gulf PetroLink 16. All Rights Reserved. Downloaded by munirelmahdy87@gmail.com IP:

12 Abdel Aal et al. Intersecting multiseismic line West East Unconfined Confined Two-way Time (sec) 3 6 Slope Channels Sheet Sands Figure 11: E W Regional Seismic Profile illustrating the unconfined Pliocene slope and base of slope depositional setting (slope channel sequences) and the confined salt basin (sheet sand sequences) of the NE Mediterranean Deepwater Block. See Figure 9 for location of profile. Basin Floor Sheet Sands Structural closures are observed in the basin floor setting where onlap patterns suggest ponding of sheet sands. Upper Miocene Reservoirs The primary Upper Miocene reservoir sequence in the Platform area is of late Messinian age (Abu Madi Formation equivalent). It was deposited in a complex deltaic/shallow-marine setting in, and basinward of, major fluviatile canyons (Figure 1). The late Messinian deposits overlie anhydrites (Rosetta Anhydrite equivalent) and/or an age-equivalent unconformity surface (Intra-Messinian unconformity). These, in turn, overlie the lower Messinian (Upper Qawasim Formation equivalent) sequence of immature sediments in a canyon setting (Figure 13) that forms a secondary exploration objective. The Upper Qawasim Formation was deposited during rapid downcutting resulting from the pronounced Messinian sea-level falls. Outside the canyon area, the Upper Qawasim sequence changes to parallel-bedded sheet sands, as represented by reservoirs in the Abu Qir field (Figure ). The Rosetta Anhydrite is widespread in the Nile Delta but is absent from the fluvial- to shallow-marine upper Messinian Abu Madi Formation. There, the canyon-fill is inferred from seismic data to be chaotic, sand-prone and up to 3 m thick. Copyright Gulf PetroLink 16. All Rights Reserved. Downloaded by munirelmahdy87@gmail.com IP:

13 Tectonic Evolution of the Egyptian Mediterranean Basin 9 E Salt diapirs Mediterranean Sea Salt basin Canyon system N NEMED Safron Scarab Rosetta Nile Cone N N. Abu Qir Baltimi N. Ha'py Akhen Seth Baltimi E. Asfour Baltimi S. El Qar'a Seti Abu Seif Kersh / Abu Zaku / Wakar Port Fuad Abu Madi Abu Qir Temsah W. Abu Qir 9 EGYPT Figure 1: Upper Miocene (Messinian) depositional system of the Nile Cone and the NE Mediterranean Deepwater Block. The Platform-bounding fault is thought to mark the transition between the canyon system and deeper marine reservoir facies. In the western part of the NE Mediterranean Deepwater Block, mapping of the Miocene package immediately above the Messinian salt indicates that turbidite sheet sands onlap the developing salt ridges (Figure 1). Seismic data show a basement high oriented toward the northwestern corner of the Block and having a thin salt cover. It appears to have funneled the turbidities to the outboard area. In the eastern part of the concession, a platform ridge related to the Temsah fault may have hindered the development of canyons and there is no evidence of time-equivalent sheet sands deeper in the basin. Reservoir quality is likely to vary according to the depositional environment. Canyon fill will tend to be of lower quality (porosities 8%), whereas sheet sands are likely to be of excellent quality and have porosity values as high as 3 percent. HYDROCARBON PLAY TYPES Platform: Pliocene Channel Play The Pliocene Channel Play consists of slope/basin-floor turbidites in channel, channel-levee and sheet sand systems in subtle structural closures on the Platform and on large fault blocks and salt-induced anticlines, and around diapiric structures. Traps are formed by channels crossing -way closures or structural noses. Evidence from seismic surveys shows the widespread presence of amplitude anomalies at various, stacked levels throughout the Pliocene section (Figure 1). The prospectivity of the Pliocene channel play (Figure 9) has been demonstrated by successful wells south of the Block (Seth, Ha py, Osiris, Seti, Rosetta, Scarab and Saffron discoveries). Copyright Gulf PetroLink 16. All Rights Reserved. Downloaded by munirelmahdy87@gmail.com IP:

14 Abdel Aal et al. South North Inner Shelf Nile Cone NE Mediterranean Deepwater Block Slope Miocene Canyon Plio cen e-p Depth () Miocene leis Basin Plain toc ene Paleogene Salt Cretaceous Coastal Plain N Shore Face Inner Shelf Outer Shelf Slope Abyssal Plain Scree Sea Terrace Salt lagoon Eoc turbidites ene Cretaceo us Oli go cen e Upper Miocene Low er an d Mid dle M ioce ne Figure 13: N S geologic cross-section and schematic block diagram illustrating the Upper Miocene (Messinian) canyon, canyon front, and turbidite depositional settings of the Nile Cone and NE Mediterranean Deepwater Block (modified from Abdel Aal et al., 199). Platform: Upper Miocene Canyon Play The Upper Miocene depositional system offers attractive exploration opportunities. It may prove to be the prime target in the deepwater area due to the variety of depositional environments (fluvial, shallow marine reservoirs and/or deepwater turbidite sands) the sequence may contain. During the Late Miocene Messinian salinity crisis, large, deep canyons were cut along the margin of the salt basin, while salt deposition (cyclic in nature and associated with the repeated cut-and-fill sequences), occurred in the basin. The canyon system has a northwesterly trend (Figures 1 and 13). They are filled updip by proven fluvio-marine systems, but downdip toward the transition into the salt basin a turbidite system is Copyright Gulf PetroLink 16. All Rights Reserved. Downloaded by munirelmahdy87@gmail.com IP:

15 Tectonic Evolution of the Egyptian Mediterranean Basin Shelf margin facies Turbidite sands Turbidite facies Anhydrite facies Layered sandstone facies Salt Chaotic facies Two-way Time (sec) Shale Base Messinian Figure 1: Upper Miocene (Messinian) sequence depositional model illustrating shallow-marine shelf-margin to turbidite deposits of the Nile Cone and the NE Mediterranean Deepwater Block. Salt Salt a 1 d 1 b 1 e 1 c 1 f 1 Figure 1: Selected magnified seismic expressions of the slope and channels levee systems of the Pliocene Channel Play. Copyright Gulf PetroLink 16. All Rights Reserved. Downloaded by munirelmahdy87@gmail.com IP:

16 Abdel Aal et al. more likely to be present. The play is well established in the Platform area, where several structures south of the Block (Abu Madi, El Qar a and Baltim fields) contain gas accumulations in the 1 trillion cubic feet (TCF) to 3 TCF range. Prospects consist of subtle structural traps within a large Messinian canyon system (Figure 16). Rotated Fault Block Play The southern limit of the Messinian Salt Basin is marked by major E W-oriented, rotated fault blocks. They were formed by the northward displacement of salt by Pliocene sedimentation. The upthrown fault blocks form large structural closures that are important exploration targets (Figure 17), and amplitude support indicates the likely presence of gas and/or oil charge in thin, more distal and channeled sheet-sand reservoirs. Diapiric Salt Basin Play The Diapiric Salt Basin Play covers the eastern half of the Block where it is characterized by major intersecting strike-slip zones. This area has the thickest Pliocene section because of deposition in mini-basins created by salt withdrawal. Slicks attest to the presence of an oil charge that has migrated along strike-slip faults and through salt windows. Reservoirs consist of sheet sands correlated with channels mapped in the Platform area, as well as channel-levees formed alongside channels that originated to the southeast. Seismic profiles indicate a high degree of deformation that has provided a large variety of trap configurations. Subtle structural closures in shallow-marine sands were recognized, and turbidite-sand pinch outs or over-salt anticlines represent attractive exploration targets. Basin Floor Fan Play The northern bounding fault to the Platform marks the approximate northern limit of the Messinian Canyon Play. Sheet sands (Figure 18), interpreted as alluvial fans distal from the Messinian canyons are an attractive reservoir objective in the northwest of the Block. The sands are confined to a relatively narrow, NW-oriented corridor north of the Platform that is thought to coincide with an area of thin Northwest Southeast 3. Subtle structural traps Two-way Time (sec)... Upper Miocene "cut and fill" sequences Base Messinian incised valley. Figure 16: Seismic expressions of subtle structural traps in Upper Miocene (Messinian) Canyon Play. Copyright Gulf PetroLink 16. All Rights Reserved. Downloaded by munirelmahdy87@gmail.com IP:

17 Tectonic Evolution of the Egyptian Mediterranean Basin Southeast Northwest Channeled sheet sands in rotated fault blocks 3 Potential for sheet sands Two-way Time (sec) magnified interval Figure 17: Seismic section illustrating Pliocene channeled sheet sands in the Rotated Fault Blocks Play. salt, and hence to have better potential to receive charge. To date, only a very coarse seismic grid is available in this ultra-deepwater area, which nevertheless indicates attractive hydrocarbon-trapping possibilities. Pre-Salt Play Very little is known about the pre-salt section in the northern part of the Block. Gravity data indicate a 1--thick section below the salt that may contain potentially prospective Miocene, Oligocene, Cretaceous and Jurassic sediments. Elsewhere, these sediments are reservoir and source rocks. For example, sands of Middle Miocene (Tortonian-Serravallian) and Oligocene age are the main reservoir units for the Temsah, Abu Zakn, Wakar, Kersh, Port Fouad Marine and Tineh fields in the eastern part of the Nile Delta. Seismic profiles show that the section below the Messinian Salt Basin is well defined in the eastern part of the Block but that mappable stratigraphic units are more difficult to identify farther west. Large potential reservoir structures mapped at the base of the salt are attractively located with respect to availability of charge. In addition, the Miocene geological setting was favorable for shallow-marine carbonate growth on intrabasinal highs (or seamounts), as proven on the nearby Eratosthenes Seamount. A possible carbonate build-up is interpreted in the northern part of the Block overlying a condensed pre-miocene section (see Figure 6a). The pre-salt section could contain several types of reservoirs, such as Miocene reefal-limestones overlying seamounts and Miocene turbidite sands in large, wrenchfaulted structures (see Figure 6a). The Pre-Salt Play has all the ingredients of an attractive oil play with potentially large trap capacities but it is challenging because it underlies a considerable thickness of salt. Although the potential is enormous, risks are high and the play is presently considered less attractive than shallower options. Copyright Gulf PetroLink 16. All Rights Reserved. Downloaded by munirelmahdy87@gmail.com IP:

18 Abdel Aal et al. Northwest Southeast Two-way Time (sec) 6 Potential sheet sands 7 Figure 18: Seismic section illustrating Pliocene sheet sands in the Basin Floor Fan Play. Source Rocks and Hydrocarbon Prediction The absence of well data from the NE Mediterranean Deepwater Block means that much of the charge modeling in the northern part of the Block is speculative. Gravity data can be modeled to show the presence of a pre-salt section as much as 1 thick (see Figure 7) that may contain Miocene, Oligocene, Cretaceous and Jurassic sediments. Source rocks of equivalent ages occur in the Nile Delta area and it is probable that at least the Upper Cretaceous black shales contain good-quality source rocks with a high content of Total Organic Carbon (TOC) (Figure 19). Given the significance of the Platform-bounding fault, the presence of Oligocene-Miocene rocks (considered the main source of Nile Delta gas/ condensates), is also likely. In addition, Pliocene sapropels with exceptionally high TOC values are present in deep, untested marine source rocks across the fault. Maturity models for the outboard area are uncalibrated. Although heat-flow measurements have been made in the shallow part of the Nile Delta (Morgan et al., 1977) and in Cyprus, these are probably not representative of the Deepwater Block. Because of the heightened tectonic activity and the presence of salt, it is likely that much of the Block has a heat flow that is higher than in the Delta. Data from the Block confirm very warm (13.8ºC) sea-bottom conditions at depths of, m. The presence of hydrates in a restricted water-depth interval narrows the likely heat-flow range considerably. For the purposes of modeling, a heat flow of to Heat Flow Units was assumed. Proven gas accumulations suggest that the southern part of the Block is likely to be gas-prone. Farther north, maturity modeling indicates mixed oil and gas charges from various source rocks. The transition is thought to occur in the area of the main Platform-bounding fault. High-quality oil slicks along major strike-slip faults (Figures 19 and a) indicate the presence of a liquid charge. In addition, direct indicators of hydrocarbons can be interpreted from the seismic data (Figure b). Given that the basal Pliocene section is only marginally mature at best, it is likely that the charge would be mainly pre-salt in origin. However, access to oil charge in particular could be difficult within the salt basin, although the slicks confirm that the movement of charge is possible through the salt. In addition, salt displacement in much of the area immediately north of the platformcopyright Gulf PetroLink 16. All Rights Reserved. Downloaded by munirelmahdy87@gmail.com IP:

19 Tectonic Evolution of the Egyptian Mediterranean Basin Southwest Northeast HC Messinian inverted canyon HC Pliocene Salt Potential source rock levels 6 7 Source rock maturity profile Two-way Time (sec) 3 Oil Miocene Gas Oligocene Upper Cretaceous 1 Figure 19: Seismic section illustrating source rock maturity and the location of hydrocarbon slicks (HC) in relation to deep-seated faults in the NE Mediterranean Deepwater Block. bounding fault means that the Pliocene section is grounded, so providing ample salt windows for charge access. The discovered hydrocarbon resources in the Nile Delta are gas/condensate-dominated in the central part of the delta whereas oil discoveries have been made at the western and eastern margins of the Delta (Figure a). The difference in charge is interpreted as being due to differences in the depth of burial of the source rocks. Thermal and subsidence modeling indicate that whilst the main source rocks in the central parts of the Delta are gas-mature or overcooked, they occur within the oil-generating window at the margins and toward the Block. CONCLUSIONS The NE Mediterranean Deepwater Block is an area of 1, sq located north of the main gas/ condensate-producing Nile Delta. It is characterized by: 1. Several distinct structural domains, namely: Platform; Rotated Fault Blocks; Basin Floor; Diapiric Salt Basin; and Inverted Salt Basin. The structural pattern is the result of a complex interplay between the major fault trends of Rosetta (NE-trending) and Temsah (NW-trending). Along the Rosetta trend, Late Cretaceous to early Tertiary transpressional structures are onlapped and covered by a pre-salt sequence as much as 3, m thick. These sequences are interpreted as being late Paleogene to Late Miocene age. They consist predominantly of deepwater sediments with local condensed equivalent sequences on syndepositional intrabasinal highs. The Late Miocene pre-salt sequence appears to shale-out westward across the Rosetta trend to become strongly deformed by mud diapirism and gravitational faulting. Complex deformation took place along the Temsah trend, with the dominant fault movement being in late Tertiary to Recent times. This was associated with large-scale north-verging uplift, the inversion of part of the Messinian Salt Basin, and recent strike-slip faulting that is most intense in the Levant area. Copyright Gulf PetroLink 16. All Rights Reserved. Downloaded by munirelmahdy87@gmail.com IP:

20 Abdel Aal et al. (a) Direct Hydrocarbon Indicators Gas Chimney Slicks Slick 6 (6%) Slick 7 (6%) NEMED Safron Scarab Nile Cone Ha'py Akhen Seth Asfour Rosetta Baltim E. N. Abu Qir Discoveries W. Abu Qir Baltim S. El Qar'a Abu Qir Abu Madi Temsah Seti Abu Seif Kersh / Abu Zakn / Wakar Port Fuad Mango Marakia Gas/Condensate N EGYPT Oil (b) Amplitude versus Offset Near Stack 3 Gradient Stack Two-way Time (sec) Far Stack Flat spot 3 Figure : Hydrocarbon prediction (a) Evidence of hydrocarbon charge; (b) Direct hydrocarbon indicators. Two-way Time (sec) Flat spot Copyright Gulf PetroLink 16. All Rights Reserved. Downloaded by munirelmahdy87@gmail.com IP:

21 Tectonic Evolution of the Egyptian Mediterranean Basin. Turbidite and shallow-water depositional systems. Basin-fill models calibrated by detailed stratigraphic analysis in the explored part of the Nile Delta predict a variety of turbidite environments affected by syndepositional fault movement and by mobile salt. These settings coexist along strike with a graded slope on which unconfined turbidite deposition occurred in slope channels with the potential for sheet sands in fault-induced depressions. 3. Three major stratigraphic levels the Pliocene turbidite system, the Miocene shallow-marine system grading laterally into the Messinian salt province, and the pre-salt system have attractive hydrocarbon potentials. Hydrocarbon play types are Pliocene Channel, Upper Miocene Canyon, Rotated Fault Block, Diapiric Salt Basin, Basin Floor Fan, and Pre-Salt.. Possibilities for discovering gas, gas/condensate and oil are good. The prospectivity of the Pliocene Channel Play has been demonstrated by discoveries in the Seth, Ha py, Osiris, Seti, Rosetta, Scarab and Saffron gas fields. The Upper Miocene Canyon Play has proved successful in the Abu Madi, El Qar a and Baltim gas fields. Upthrown fault blocks of the Rotated Fault Block Play form large structural closures that make important exploration targets. Attractive exploration targets exist in the salt basin domain and in the sheet sands of the Basin Floor Fan Play. The Pre-Salt Play is challenging because of its location beneath a considerable thickness of salt. The potential of the Pre-Salt Play is enormous but the risks are high and at present it is considered less attractive than shallower options. ACKNOWLEDGMENTS The authors thank the management of Shell Egypt for allowing them to publish this paper. We are indebted to the members of the Shell Deepwater SEPTAR and SDS for their constructive comments and discussions. We appreciate the geochemical interpretation by Magda Nour El Din, the seismic AVO interpretation support of Ahmed Awad and Ahmed Helmi, and the assistance of Shell Egypt draftsman Mohamed Hindy. The design and drafting of the final graphics was by Gulf PetroLink. REFERENCES Abdel Aal, A., R.J. Price, J.D. Vaitl and J.A. Sharallow 199. Tectonic evolution of the Nile Delta, its impact on sedimentation and hydrocarbon potential. Egyptian General Petroleum Corporation 1th Exploration and Production Conference, v. 1, p Abu El Ella, R The Neogene-Quaternary section in the Nile Delta, Egypt; geology and hydrocarbon potential. Journal of Petroleum Geology, v. 13, no. 3, p Argyriadis, I., P.C. Graciansky, J. Marcoux and L.E. Ricou 198. The opening of the Mesozoic Tethys between Eurasia and Arabia-Africa. French Bureau de Recherches Géologiques et Minières, Memoir 11, p Biju-Duval, B., J. Letouzey and L. Mondart Variety of margins and deep basins in the Mediterranean. American Association of Petroleum Geologists Memoir 9, p Dixon, J.E. and A.H.F. Robertson 198. The geological evolution of the eastern Mediterranean. Blackwell, Oxford. El Heiny, I. and N. Enani Regional stratigraphic interpretation pattern of Neogene sediments, Northern Nile Delta, Egypt. Egyptian General Petroleum Corporation 13th Exploration and Production Conference. Geiss, E A new compilation of crustal thickness data for the Mediterranean area. Annals Geophysica, v. B, no. 6, p Hirsch, F., A. Flexer, A. Rosenfield and A. Yellin-Dror 199. Palinspastic and crustal setting of the eastern Mediterranean. Journal of Geology, v. 18, no., p May, P.R The eastern Mediterranean Mesozoic basin; evolution and oil habitat. American Association of Petroleum Geologists Bulletin, v. 7, no. 7, p Morelli, C Eastern Mediterranean geophysical results and implications: Tectonophysics, no. 6, p Morgan P., D.P. Blackwell, J.C. Farris, F.K. Boulous and G. Salib Preliminary geothermal gradient and heat flow values for northern Egypt and Gulf of Suez from oil well data. Proceedings of the Copyright Gulf PetroLink 16. All Rights Reserved. Downloaded by munirelmahdy87@gmail.com IP:

22 Abdel Aal et al. International Congress on Thermal Waters, Geothermal Energy and Volcanism of the Mediterranean Area (1976). Natural Technology Athens, p. 38. Neev, D Tectonic evolution of the Middle East and the Levantine basin (easternmost Mediterranean). Geology, no. 3, p Posamentier, H.W., M.T. Jervey and P.R. Vail Eustatic controls on clastic deposition I conceptual framework. In, C.K. Wilgus et al., (Eds.) Sea-level changes: an integrated approach. Society of Economic Paleontologists and Mineralogists, Special Publication no., p Rizzini, A., F. Vezzani, V. Cococcetta and G. Milad Stratigraphy and sedimentation of a NeogeneQuaternary section in the Nile Delta area. Marine Geology, v. 7, p Ross, D.A. and E. Uchupi Structure and sedimentary history of southern Mediterranean Sea Nile Cone area. American Association of Petroleum Geologists Bulletin, v. 61, no. 6, p Vail, P.R., P.M. Mitchum and S. Thomson Seismic stratigraphy and global changes in sea level. American Association of Petroleum Geologists Memoir 8, p ABOUT THE AUTHORS Ahmed Abdel Aal joined Shell in 1997 having spent the previous 16 years in GUPCO (Amoco Egypt joint venture Company). Ahmed worked in the NEMED Deepwater Team and is currently with the Regional Deepwater Team in Houston, Texas. Hans-Jürg Meyer joined Shell in 198 and has worked as a Geophysicist/Seismic Interpreter in Libya, Gabon, The Netherlands and Pakistan. In 1997, he moved to Shell Egypt and is currently working in the NEMED Deepwater Team. Ahmed El Barkooky joined Shell Egypt in 199 as a Senior Stratigrapher. He is currently working on the regional stratigraphy and depositional systems of the Nile Delta in relation to the Mediterranean Ultra Deepwater Area. Ahmed has a PhD from Cairo University. Marcus Schwander joined Shell in 198 at the E&P Research Laboratory in The Netherlands and has subsequently worked in Norske Shell and in New Business Development in The Hague. Marcus moved to Shell Egypt in 1997 and is Project Manager for Shell s Deepwater Exploration Acreage. He has a PhD from the University of Basel. Marc Gerrits joined Shell in 1986 and has had postings in Australia, UK and Angola. He joined the NEMED Deepwater Team in Hala Zaki joined Shell in 199 after several years working for Deminex Oil Company, Egypt. In 1998 she returned to Shell Egypt after secondment to PDO. Hala is a Seismic Interpreter in the NEMED Deepwater Team. This paper is based on a presentation made at the Mediterranean Offshore Conference held in Alexandria, Egypt, April 18,. Manuscript Received June 17, Revised August, Accepted August 8, Copyright Gulf PetroLink 16. All Rights Reserved. Downloaded by munirelmahdy87@gmail.com IP: