Suez Rift Research Articles

Geometry and architecture of faults in a syn-rift normal fault array: The Nukhul half-graben, Suez rift, Egypt

The geometry and architecture of a well exposed syn-rift normal fault array in the Suez rift is examined. At pre-rift level, the Nukhul fault consists of a single zone of intense deformation up to 10 m wide, with a significant monocline in the hanging wall and much more limited folding in the footwall. At syn-rift level, the fault zone is characterised by a single discrete fault zone less than 2 m wide, with damage zone faults up to approximately 200 m into the hanging wall, and with no significant monocline developed. The evolution of the fault from a buried structure with associated fault-propagation folding, to a surface-breaking structure with associated surface faulting, has led to enhanced bedding-parallel slip at lower levels that is absent at higher levels. Strain is enhanced at breached relay ramps and bends inherited from pre-existing structures that were reactivated during rifting. Damage zone faults observed within the pre-rift show ramp-flat geometries associated with contrast in competency of the layers cut and commonly contain zones of scaly shale or clay smear. Damage zone faults within the syn-rift are commonly very straight, and may be discrete fault planes with no visible fault rock at the scale of observation, or contain relatively thin and simple zones of scaly shale or gouge. The geometric and architectural evolution of the fault array is interpreted to be the result of (i) the evolution from distributed trishear deformation during upward propagation of buried fault tips to surface faulting after faults breach the surface; (ii) differences in deformation response between lithified pre-rift units that display high competence contrasts during deformation, and unlithified syn-rift units that display low competence contrasts during deformation, and; (iii) the history of segmentation, growth and linkage of the faults that make up the fault array. This has important implications for fluid flow in fault zones.

Update to Late Triassic – Jurassic stratigraphy of Saudi Arabia for the Middle East Geologic Time Scale

ABSTRACT This Note presents a formal update to the Middle East Geologic Time Scale 2008 (ME GTS) for the Late Triassic and Jurassic rock units of Saudi Arabia. It reviews their lithostratigraphic nomenclature, ranks and stage assignments, and proposes names for third-order chrono-sequences as compiled and/or interpreted from the published literature. The review starts with the Late Triassic (Late Norian – Rhaetian) Minjur Sandstone of the Buraydah Group, with the Triassic – Jurassic (TrJ) boundary positioned at its top. The Minjur Sandstone consists of two units, here ranked as members, which are interpreted as the Late Norian – ?Early Rhaetian Lower Minjur Sequence (Lower Minjur Member) and ?Late Norian – Rhaetian Upper Minjur Sequence (Upper Minjur Member). The Early Jurassic Unconformity - Hiatus (Hettangian, Sinemurian and Pliensbachian stages) separates the Minjur Sandstone from the Toarcian Marrat Formation of the Jurassic Shaqra’ Group. The Shaqra’ Group consists of seven formations, from base-up: (1) Marrat Formation consisting of the Lower, Middle and Upper units, here ranked as members. (2) Dhruma Formation consisting of eight units (D1–D5, Wadi ad Dawasir “delta”, D6 and D7). The Dhruma units have been named in the literature as Balum Member (D1 and lower part of D2 units), Dhibi Limestone Member (upper part of D2 unit), Uwaynid Member (D3), Barrah Member (D4), Mishraq Member (D5), ‘Atash and Hisyan members (D7); the D6 and Wadi ad Dawasir “delta” units are not formally named as members. (3) Tuwaiq Mountain Limestone consisting of the Baladiyah (T1 unit), Mysiyah (T2 unit) and Daddiyah (T3 unit) members. (4) Hanifa Formation consisting of the Hawtah and Ulayyah members. (5) Jubaila Limestone with J1 and J2 units. (6) Arab Formation consisting of D to A members. (7) Hith Anhydrite consisting of Main Hith Anhydrite Member and Manifa Reservoir/Member. The seven formations of the Jurassic Shaqra’ Group are interpreted as 11 third-order chrono-sequences: (1) Early Toarcian Marrat Sequence B (Lower and Middle Marrat members) and Mid- to ?Late Toarcian Marrat Sequence A (Upper Marrat Member), the latter containing Arabian Plate maximum flooding surface MFS J10. (2) Bajocian Lower Dhruma Sequence (Balum Member and Dhibi Limestone), formed by the Balum and Dhibi subsequences, the former containing MFS J20. (3) Late Bajocian – Mid-Bathonian Dhruma Sequence B (Uwaynid, Barrah, Mishraq members, and Wadi ad Dawasir “delta” unit), with the Mishraq containing MFS J30. (4) Late Bathonian – early Mid-Callovian Dhruma Sequence A (unit D6, ‘Atash and Hisyan members), with the Hisyan containing MFS J40. (5) Mid- to Late Callovian Tuwaiq Sequence (Tuwaiq Mountain Limestone) containing an undesignated MFS at the base the Daddiyah Member (T3 unit). (6) Early and Mid-Oxfordian Hawtah Sequence (Hawtah Member of Hanifa Formation) containing MFS J50. (7) Late Oxfordian – ?Early Kimmeridgian Ulayyah Sequence (Ulayyah Member of Hanifa Formation) containing MFS J60. (8) Kimmeridgian Jubaila Sequence (Jubaila Limestone) containing MFS J70. (9) Arab-D Sequence (Arab-D Member inclusive of the Arab-D Anhydrite) containing an undesignated MFS in the Arab-D carbonate. (10) ?Kimmeridgian – ?Tithonian Arab-C and B Sequence (Arab C and B members) containing fourth-order MFS J80 and J90 in the lower carbonates of the members; and (11) ?Kimmeridgian – Tithonian Arab-A - Main Hith Sequence (Arab-A Member and Main Hith Anhydrite below the Manifa Reservoir/Member) containing fourth-order MFS J100 in the Arab-A Member. The Tithonian Manifa Member (upper part of the Hith Anhydrite Formation) is interpreted as heralding a transgression (fourth-order MFS J110), which deposited the Late Jurassic – Early Cretaceous Sulaiy Formation of the Thamama Group. The Jurassic – Cretaceous (JK) boundary is placed in the Sulaiy Formation by stratigraphic position. Based on the Geologic Time Scale GTS 2004 and Arabian Orbital Stratigraphy (AROS), the ages in million years before present of the sequence boundaries and maximum flooding surfaces are estimated for these chrono-sequences.

Late Neoproterozoic alkaline magmatism in the Arabian–Nubian Shield: the postcollisional A-type granite of Sahara–Umm Adawi pluton, Sinai, Egypt

The Sahara–Umm Adawi pluton is a Late Neoproterozoic postcollisional A-type granitoid pluton in Sinai segment of the Arabian–Nubian Shield that was emplaced within voluminous calc-alkaline I-type granite host rocks during the waning stages of the Pan-African orogeny and termination of a tectonomagmatic compressive cycle. The western part of the pluton is downthrown by clysmic faults and buried beneath the Suez rift valley sedimentary fill, while the exposed part is dissected by later Tertiary basaltic dykes and crosscut along with its host rocks by a series of NNE-trending faults. This A-type granite pluton is made up wholly of hypersolvus alkali feldspar granite and is composed of perthite, quartz, alkali amphibole, plagioclase, Fe-rich red biotite, accessory zircon, apatite, and allanite. The pluton rocks are highly evolved ferroan, alkaline, and peralkaline to mildly peraluminous A-type granites, displaying the typical geochemical characteristics of A-type granites with high SiO2, Na2O + K2O, FeO*/MgO, Ga/Al, Zr, Nb, Ga, Y, Ce, and rare earth elements (REE) and low CaO, MgO, Ba, and Sr. Their trace and REE characteristics along with the use of various discrimination schemes revealed their correspondence to magmas derived from crustal sources that has gone through a continent–continent collision (postorogenic or postcollisional), with minor contribution from mantle source similar to ocean island basalt. The assumption of crustal source derivation and postcollisional setting is substantiated by highly evolved nature of this pluton and the absence of any syenitic or more primitive coeval mafic rocks in association with it. The slight mantle signature in the source material of these A-type granites is owed to the juvenile Pan-African Arabian–Nubian Shield (ANS) crust (I-type calc-alkaline) which was acted as a source by partial melting of its rocks and which itself of presumably large mantle source. The extremely high Rb/Sr ratios combined with the obvious Sr, Ba, P, Ti, and Eu depletions clearly indicate that these A-type granites were highly evolved and require advanced fractional crystallization in upper crustal conditions. Crystallization temperature values inferred average around 929°C which is in consistency with the presumably high temperatures of A-type magmas, whereas the estimated depth of emplacement ranges between 20 and 30 km (upper-middle crustal levels within the 40 km relatively thick ANS crust). The geochronologically preceding Pan-African calc-alkaline I-type continental arc granitoids (the Egyptian old and younger granites) associated with these rocks are thought to be the crustal source of f this A-type granite pluton and others in the Arabian–Nubian Shield by partial melting caused by crustal thickening due to continental collision at termination of the compressive orogeny in the Arabian–Nubian Shield.

زلزالية شبه جزيرة سيناء - مصر

The Sinai Peninsula has a triangular shape between the African and Arabian Plates and is bounded from the western and eastern borders by the Gulf of Suez and Gulf of Aqaba–Dead Sea rift systems, respectively. It is affected by strong and destructive earthquakes (e.g., March 31, 1969 and November 22, 1995) and moderate earthquakes (mb > 5) throughout its history. After the installation of the Egyptian National Seismic Network (ENSN), a great number of earthquakes has been recorded within and around Sinai. Consequently, the seismogenic source zones and seismotectonic behavior can be clearly identified. Available data, including both historical and instrumental (1900–1997), have been collected from national and international data centers. While the data from 1998 till December 2007 are gathered from ENSN bulletins. The seismogenic source zones that might affect Sinai Peninsula are defined more precisely in this work depending on the distribution of earthquakes, seismicity rate (a value), b value, and fault plane solution of the major earthquakes. In addition, the type of faults prevailed and characterized these zones. It is concluded that the Gulf of Aqaba zone–Dead Sea transform zone, Gulf of Suez rift zone, Cairo–Suez District zone, and Eastern Mediterranean dislocation zone represent the major effective zones for Sinai. Furthermore, there are two local seismic zones passing through Sinai contributing to the earthquake activities of Sinai, these are the Negev shear zone and Central Sinai fault (Themed fault) zone. The source parameters, a and b values, and the maximum expected moment magnitude have been determined for each of these zones. These results will contribute to a great extent in the seismic hazard assessment and risk mitigation studies for Sinai Peninsula to protect the developmental projects.

Structural geology and 4D evolution of a half-graben: New digital outcrop modelling techniques applied to the Nukhul half-graben, Suez rift, Egypt

LIDAR-based digital outcrop mapping, in conjunction with a new surface modelling approach specifically designed to deal with outcrop datasets, is used to examine the evolution of a half-graben scale normal fault array in the Suez rift. Syn-rift deposition in the Nukhul half-graben was controlled by the graben-bounding Nukhul fault. The fault can be divided into four segments based on the strike of the fault, the morphology of hangingwall strata, and the variation in throw along strike. The segments of the fault became geometrically linked within the first 2.5 m.y. of rifting, as evidenced by the presence of early syn-rift Abu Zenima Formation strata at the segment linkage points. Fault-perpendicular folds in the hangingwall related to along-strike variations in throw associated with precursor fault segments persist for a further 1.8 m.y. after linkage of the segments, suggesting that the fault remains kinematically segmented. We suggest this occurs because of sudden changes in fault strike at the segment linkage points that inhibit earthquake rupture propagation, or because displacement is geometrically inhibited at fault linkage points where the orientation of the intersection line of the segments is significantly different from the orientation of the slip vector on the fault system. Length/throw plots and throw contour patterns for minor faults show that some faults initiated in pre-rift strata, whereas late east-striking faults initiated in the syn-rift basin fill. The late initiating faults are spatially associated with the east-striking Baba–Markha fault, which was active throughout the rift history, but developed as a transfer fault between major block-bounding fault systems around 6–7 Ma after rift initiation.

Slipped deformation bands: A new type of cataclastic deformation bands in Western Sinai, Suez rift, Egypt

A type of cataclastic deformation band that features a central discrete slip surface within separate, individual bands is described. Slip surface development is normally constrained to the eventual brittle failure of a deformation band cluster zone due to strain hardening and sequential growth of deformation bands. The deformation bands described herein deviate from this model and, in comparison with classical cataclastic deformation bands previously described in the literature, feature more intense cataclasis, higher offsets, lower permeability but higher porosity. We present evidence suggesting that the bands of this study strain soften during their evolution. Thus, they can accumulate higher strains than classical cataclastic bands and are prone to be reactivated during progressive deformation. The bands appear to have formed under simple shear with minor compaction, following an evolution of (1) band nucleation by grain fracturing and crushing, (2) progressive cataclasis, (3) nucleation of a central fracture, and (4) slippage along the fracture – the end result is referred to as a ‘slipped deformation band’. Widespread background, intragranular fracturing of the host rock and relatively high porosity in the bands are suggested as the most probable causes of deviation from traditional models for tectonic deformation in high porosity sandstones.

Late Tertiary faulting along the coastal plain of Israel

This study documents a 70‐km long and 200–400 m high step at the base of the Pliocene section in the Israeli coastal plain. Depositional explanations for this lineament, such as a buried shelf edge or reef front, are very unlikely; whereas a fault scarp explanation is supported by seismic profiles and geological cross sections. The eastern elevated side of the fault was eroded before its burial, though a quantitive distinction between this erosion, earlier truncations, and original hiatuses, is not possible at this stage. Sediments covering the fault scarp constrain its age to Late Miocene and/or Early Pliocene. The presence of such a fault along the Israeli coastal plain may also shed light on numerous post‐Mid‐Cretaceous faults previously documented along the coastal plain, but never explained. In a wider perspective, the fault described here along with other documented processes indicate that in the Late Tertiary tectonism along the Levant continental margin resumed after a long passive history. This renewed activity is coeval with the Africa‐Arabian breakup and the Red Sea‐ Suez rifting. In particular, the fault described here is coeval with plate reorganization and vertical motions along the Dead Sea transform and possibly along the Cypriot Arc during the Late Miocene‐Early Pliocene.

Seismological and GPS constraints on Sinai sub-plate motion along the Suez rift

This work presents new seismological and Global Positioning System (GPS) results aimed at understanding the nature and rate of strain associated with the opening of the Suez rift that separates the Sinai sub-plate from the African plate. The Sinai sub-plate has played a significant role in the tectonic evolution of the northern Red Sea and the Eastern Mediterranean region. Most small, moderate and large earthquakes occur within belts associated with the geologically documented borders of this sub-plate including the Dead Sea fault (DSF) system in the east, the Cyprian arc (CA) in the north, and the Suez rift (SR) to the southwest. The DSF and CA are well defined; however, the SR is only partially defined. Earthquake foci distribution supports the idea that the SR is seismically active, and this earthquake activity cannot be ignored throughout the kinematics evaluation of northern Red Sea region. The earthquake activity is relatively higher in the southern part of the SR and gradually decreases northward. The high seismicity is mainly attributed to the presence of the Sinai triple junction. Earthquake focal mechanisms in the SR are dominated by oblique normal faulting with left-lateral strike-slip components on NW trending fault planes consistent with regional kinematics. The extensional semi-principal stress axes derived from fault plane solutions are oriented NNE-SSW in good agreement with the current stress field obtained from borehole breakouts along the SR as well as results from GPS surveying. Recent survey-mode GPS observations provide evidence for coherent northerly motion of the Sinai sub-plate that varies between 2 and 5 mm/yr. Moreover, strain analysis indicates that the southern SR is dominated by extension while its northern segment is characterized by constriction, inconsistent with earthquake focal mechanisms and regional tectonic models. The overall northward motion of the Sinai sub-plate indicates that slab-pull rather than ridge-push is the dominant force controlling regional kinematics. Based on the low rate of extension and lack of oceanic crust, the SR can be considered an incipient plate boundary between the Sinai sub-plate and the Nubian plate.

The October 11, 1999 and November 08, 2006 Beni Suef Earthquakes

Two felt moderate-sized earthquakes with local magnitudes of 4.9 on October 11, 1999 and 4.3 on November 08, 2006 occurred southeast of Beni Suef and Cairo cities. Being well recorded by the digital Egyptian National Seismic Network (ENSN) and some regional broadband stations, they provided us with a unique opportunity to study the tectonic process and present-day stress field acting on the northern part of the Eastern Desert of Egypt. In this study, we analyze the main shocks of these earthquakes and present 15 well recorded aftershocks (0.9 ≤ ML ≤ 3.3) which have small errors on both horizontal and vertical axes. The relocation analysis using the double difference algorithm clearly reveals a NW trending fault for the 1999 earthquake. The spatial distribution of its aftershocks indicates a propagation of rupture from the SW towards the NW along a fault length ~5 km dipping nearly ~40°SW. We also determined the focal mechanisms of the two main shocks by two methods (polarities and amplitudes ratios of P, SV and SH and regional waveform inversion). Our results indicate a normal faulting mechanism with a slight shear component for the first event, while pure normal faulting for the second one. The spatial distribution of the 1999 aftershocks sequence along with the retrieved focal mechanism confirmed the NW plane as the true fault plane. While for the 2006 event, the few aftershocks do not reveal any fault geometry; its focal mechanism indicated a pure normal fault nearly trending WNW-ESE that corresponds more likely to the extension of the 1999 earthquake fault. The seismicity distribution between the two earthquake sequences reveals a noticeable gap that may be a site of a future event. The NNE-SSW extensional stress indicated by the mechanisms of these events is in agreement with the regional stress field and the rifting of the northern Red Sea in its northern branches (Gulf of Suez and Gulf of Aqaba). The source parameters (seismic moment, moment magnitude, fault radius, stress drop and displacement across the fault) were also estimated and compared based on both the regional waveform inversion and the displacement spectra and interpreted in the context of the tectonic setting. The obtained results imply a reactivation of the pre-exiting NW-SE faults as a result of extensional deformation from the northern Red Sea-Gulf of Suez rifts.

Sedimentology and significance of an early syn-rift paleovalley, Wadi Tayiba, Suez Rift, Egypt

Wadi Tayiba is located along the western margin of the Hammam Faraun fault block, western Sinai, Egypt and is generally thought to contain exposures of the ‘type-section’ for late pre-rift to early syn-rift stratigraphy associated with the Oligo-Miocene Suez Rift. Previous studies have suggested a complex vertical succession of sedimentary facies characterise the late pre-rift to early syn-rift and imply major and abrupt variations in relative sea-level during this time. Detailed sedimentological and stratigraphic analysis of the Wadi Tayiba type-section presented in this study identifies not only a far simpler vertical facies succession than previously suggested but also the development of a major paleovalley system at the base of the early syn-rift succession. It is suggested that this subtle but significant feature is the cause of the complex vertical facies succession previously interpreted. It is concluded that continuous marine sedimentation and only moderate amplitude variations in relative sea-level occurred during the Eocene to Early Oligocene within at least this part of the Suez Rift. A major relative sea-level fall occurred during the middle Oligocene and a regionally developed erosional surface associated with this event marks the contact between late pre-rift and early syn-rift strata. The results of this study have major implications for sub-regional correlations of late pre-rift to early syn-rift stratigraphic units and resultant palaeogeographic reconstructions of the late pre-rift to early syn-rift period.

Reactivation of the Levant passive margin during the late Tertiary and formation of the Jaffa Basin offshore central Israel

Re-examination of the stratigraphic record in the continental margin of Israel indicates that the Levant passive margin was reactivated in the late Tertiary. Subsidence and, presumably, sedimentation rates increased after prolonged gradual decay; the shelf-slope facies transition zone was revived; faulting and magmatism resumed and the Judea Hills began to rise. Two parallel fault systems with large vertical displacements were formed (or reactivated) between the Levant Basin and the continent. In the Levant Basin a new 4 km thick section accumulated and at a middle level between the two faults a local basin was formed and filled with a 2500 m thick section. That basin, termed here the Jaffa Basin, provides good age control. It was initiated in the Mid–Late Oligocene, was mainly active in the Miocene and was completely buried by sediments in the Plio-Pleistocene. We suggest that at the early stage of the Arabia–Africa breakup, in conjunction with the Suez rifting, the Jaffa Basin was formed between two segments of a left-lateral fault that allowed Arabia to slip northward relative to the Mediterranean lithosphere. When this fault failed to transform the motion, both the Suez Rift and the Jaffa Basin were abandoned and the plate motion jumped inland to the Dead Sea Transform.

Evaporite accumulation during the Messinian Salinity Crisis: The Suez Rift case

The Mediterranean Basin may have not always been connected to the Atlantic Ocean. During the Messinian Salinity Crisis (5.96–5.33 Myr), the Mediterranean Sea reduced progressively its connection with the global Ocean by a complex combination of tectonic and glacio‐eustatic processes. During this period, deep erosion occurred on the margin and on the continent. Furthermore, a large quantity of evaporites was deposited in the basins (>1500 m). The way by which the evaporites accumulated in the various sub‐basins has not been precisely determined. Here we demonstrate by quantitative analysis that a combination of several Mediterranean sea‐level drawdown events associated with limited Atlantic sea inflow and continuous river discharge can explain the quantity of evaporites in the Mediterranean Basins and the observation of an intermediate lowstand at ∼500 m. Using a paleogeographical reconstruction and a numerical model, we show that the evaporites of the Gulf of Suez (GoS) are a consequence of the threshold which disconnected the GoS/Red Sea from the Eastern Mediterranean at the end of the Miocene.

Fifty Years of Wettability Measurements in the Arab-D Carbonate Reservoir

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 105114, "Fifty Years of Wettability Measurements in the Arab-D Carbonate Reservoir," by T.M. Okasha, SPE, J.J. Funk, SPE, and H.N. Al-Rashidi, SPE, Saudi Aramco, prepared for the 2007 SPE Middle East Oil & Gas Show and Conference, Bahrain, 11–14 March. The Ghawar field in eastern Saudi Arabia contains carbonate reservoirs. Most wells in the field produce from the Arab-D reservoir, an Upper Jurassic limestone sealed by anhydrite. Oil production from the field started approximately 55 years ago. Water injection started in the 1970s. A current evaluation of Arab-D wettability takes into account a long historical record of wettability measurements and production. The results of the original measurements have changed slightly, but they show a strong consistency 50 years later. Local variations in wettability indicating mixed wettability and oil-wet tendencies were observed when tar was present in a significant amount and in areas high on structure. Introduction The wetting properties of carbonate reservoirs are fundamental to the understanding of fluid flow in all aspects of oil production and can affect the production characteristics greatly during waterflooding. Therefore, knowledge of the preferential wettability of reservoir rock is of utmost importance. Carbonate reservoirs are heterogeneous in nature because of the wide spectrum of environments in which carbonates are deposited and the subsequent diagenetic alteration of the original rock fabric. These heterogeneities and the effects of wettability on residual-oil saturation, capillary pressure, electrical properties, relative permeability, and oil recovery encouraged research to characterize and evaluate wettability of carbonate reservoirs. In the past, many engineers assumed that most reservoir rocks were water-wet. Recent work showed many carbonate reservoirs are oil-wet. Other studies have shown that the wettability of carbonate rocks is oil-wet, neutral, or mixed. This paper summarizes a study of wettability for the Arab-D carbonate reservoir (Upper Jurassic) in Saudi Arabia. Arab-D Reservoir The Arab-D reservoir was discovered in 1948. Five additional areas were identified as parts of the Ghawar oil field. From north to south, they are Ain Dar, Shedgum, Uthmaniyah, Hawiyah, and Haradh. At the Arab-D level, the field is a north-northeast-trending composite anticline 230 km long by 30 km wide. The largest oil accumulations occur in the lowest grainstone cycle of the Arab formation, the Arab-D reservoir. The vertical oil column has a maximum thickness of 1,300 ft. The oil-saturated interval extends approximately 250 ft below the anhydrite that separates the Arab-D reservoir from overlying Arab-C carbonate beds. X-ray-diffraction and X-ray-fluorescence analyses revealed that the most predominant mineral in the Arab D reservoir is calcite (80–100 wt%), while dolomite constitutes a second minor mineral (0–26 wt%), along with trace amounts (<5 wt%) of quartz, pyrite, ankerite, and halite.

A comparison of Khuff and Arab reservoir potential throughout the Middle East

A compilation of average porosity and permeability data for petroleum reservoirs in the Permian–Triassic Khuff Formation and the Jurassic Arab Formation shows that most Khuff reservoirs have an average porosity of less than 12%, whereas most Arab reservoirs have an average porosity of 12–26%. Higher porosity correlates with shallower depth, suggesting that burial diagenesis is the main cause of the overall porosity difference between these units. Deeper burial of Khuff reservoirs is inferred to have resulted in greater porosity loss by chemical compaction and associated cementation. A broad correlation also exists between average porosity and average permeability, suggesting that deeper burial and the resulting porosity decrease are also a primary cause of the lower permeabilities of the Khuff reservoirs. In addition to greater burial depth, however, a combination of depositional and early diagenetic factors is also reflected in the lower average porosity and permeability values of the Khuff reservoirs. Khuff strata were deposited on an extensive, poorly circulated, very low-relief shelf and consist in large part of interbedded mudstones and grainstones having relatively fine grain size, with major amounts of depositional calcium sulfate present. Arab reservoirs were deposited under better circulated conditions near platform margins facing deep, intracratonic basins and, thus, have coarser, more grain-dominated fabrics and lesser overall content of chemically precipitated grains, calcium sulfate, and dolomite. Khuff deposits were likely composed of less stable mineralogy than Arab sediments because the Late Permian was a time of aragonite seas, whereas the Late Jurassic was a time of calcite seas. The combined result of these factors is that Arab reservoirs are characterized by greater preservation of primary depositional pore types, more coarsely crystalline dolomite fabrics, and lesser plugging by anhydrite. Finally, a possible factor affecting the average porosity and permeability values is petroleum composition, which is gas in most Khuff reservoirs and oil in Arab reservoirs. Lower economic cutoff values for gas production would favor inclusion of low-permeability zones in Khuff reservoirs, thus reducing average reservoir values. Two main aspects of these results are innovative. This is the first time that porosity and permeability values for either Khuff or Arab reservoirs have been examined regionally. Second, the conclusion that thermal exposure is the primary control on average porosity and permeability in these units is consistent with previous work from other carbonates, but is new for the Middle East.

Tropical northeast Africa in the middle–late Eocene: Paleomagnetism of the marine-mammals sites and basalts in the Fayum province, Egypt

The mid-late Eocene “Valley of Whales” in the Fayum province of Egypt contains hundreds of marine-mammals’ skeletons. Given its paleontological importance, we carried out a paleomagnetic study of the fossil-bearing formations. A sequence of basalts directly overlying the upper Eocene rocks in three distant clusters within a 25 km-long NW–SE graben in the southwestern part of the area was also studied. Thermal demagnetization of three-axis IRM was used to identify and eliminate sites dominated by hematite and/or goethite as potential remanence carriers. Progressive thermal demagnetization of the NRM isolated a characteristic NNE–SSW dual-polarity direction with a shallow inclination that passes both tilt and reversal tests. The mean tilt-corrected direction of the sedimentary formations is D/ I = 16°/30° ( k = 50, α 95 = 3°) yielding a paleomagnetic pole at 70°N/159°E. The anisotropy of magnetic susceptibility (AMS) indicated that the observed inclinations were free from inclination shallowing, as did the nearly identical characteristic remanence of the overlying basalt flows (with a tilt-corrected reversed-polarity direction of D/ I = 198°/−28° ( k = 38, α 95 = 7°) and a pole at 68°N/158°E). The new paleopoles place the Fayum province at a lower paleolatitude (15–17°N) than today (29.5°N), and point to the possible prevalence of tropical climate in northeast Africa during mid-late Eocene times. This tropical position is nearly identical to the paleolatitudes extrapolated from the mean of 36 coeval poles rotated from the other major cratons and from Africa itself. The declinations show a minor easterly deviation from those predicted by extrapolation from other continents. This is interpreted as due to a small clockwise rotation internal to NE Africa, possibly related to Red Sea/Gulf of Suez rifting after the late Eocene. The alternative explanation that the geomagnetic field had a non-zonal non-dipole field contribution is not favored.

Technology Update: Haradh III: A Milestone for Smart Fields

The Haradh III project came on stream in February 2006, adding 300,000 B/D of Arabian light crude production capacity to Ghawar, the world's largest oil field. The project's main significance, however, derives from the fact that it sets a milestone for smart technologies at a scale and complexity unprecedented for Saudi Aramco and, arguably, for the industry. Haradh III might be regarded as the entry point to a new era in upstream projects and specifically into the domain of real-time reservoir management. The project spanned a period of 21 months. It entailed construction of a grassroots surface-facility network, integrated with a complex subsurface development program. Maximum-reservoir-contact (MRC) wells, smart completions, geosteering, and i-field features provided the four main technology components. Their efficient integration was the key to the project's success. Background Haradh constitutes the southernmost portion of the Ghawar complex and covers an area 75 km long and 26 km wide at its widest section (Fig. 1). The field consists of three subsegments of approximately equivalent reserves, with an aggregate oil initially in place of 38 billion STB. Initial production from Haradh I occurred in May 1996, followed up by Haradh II and Haradh III in April 2003 and February 2006, respectively. The field developments, occurring over a span of a decade, offer a unique opportunity in gauging the impact of technologies, the main thrust of this article. Haradh I was developed exclusively with vertical wells, whereas horizontal completions provided the primary configuration for producers/injectors in Haradh II. Haradh III, the main focus here, was developed by relying mainly on smart MRC completions within an i-field framework (Fig. 2). The total Haradh production capacity is 900,000 B/D, with equal contributions from the three respective subsegments I, II, and III. Arab-D, the producing horizon, belongs to the lower member of the Arab formation of the Jurassic period. It is characterized by a complex sequence of anhydrite and limestone events, with varying degrees of "'dolomitization'." Faults, fractures, and fracture swarms were known to be part of the regional geology and attracted considerable attention in the project planning, given their propensity for creating water-encroachment problems. Project Statistics Table 1 presents the key project statistics for Haradh III. It entailed a production target of 300,000 B/D, using 32 multilateral wells. A peripheral water-injection program (with an ultimate capacity of 560,000 BWPD) preceded the crude production by 4 months as part of the planned pressure-maintenance program.

Source Rock Depositional Environment and Maturation Assessment Dependent C7 Light Hydrocarbons from Crude Oils in the Gulf of Suez, Egypt

A collection of 14 crude oil samples representing 13 giant oil fields from the prerift and synrift reservoirs of the Gulf of Suez province were analyzed for C7 light hydrocarbons. The light hydrocarbon parameters C7 star plot diagrams in conjunction with the biomarker characteristics differences were used to distinguish the Gulf of Suez into two oil groups, the prerift and synrift oils, which are predominantly source related and maturity dependent. The biomarker properties indicate that the prerift oils exhibit oleanane index 23%, while the synrift oils are characterized by relatively higher oleanane index around 30% and low gammacerane index values <10%. The prerift oils are correlated with the Upper Cretaceous Brown Limestone and Sudr chalk formations, which are possibly representative of the carbonate-rich marine source rocks of type II kerogen. The synrift oils are correlated with Lower Miocene Rudeis siliciclastic source rocks of mixed types II-III kerogen. The prerift and synrift source rocks entered the oil generation window at vitrinite reflectance between 0.7 to 0.9 Ro%, equivalent to formation temperature at 110°C and 125°C, which permits the expulsion of mature crude oils to reservoir rocks according to their stratigraphic and structural relations. The higher sterane maturity parameters, i.e., diasterane index, C 29 ααα20S/(S + R), and C 29 αββ/(αββ + aaa), of the prerift oils imply a generation from carbonate rich marine source rocks at a very high maturity level in comparison with the relatively mature siliciclastic source rocks that generated the synrift oils in the Gulf of Suez rift basin.

Oligocene–Miocene formation of the Haifa basin: Qishon–Sirhan rifting coeval with the Red Sea–Suez rift system

During mid-Oligocene to early-Miocene times the northeastern Afro-Arabian plate underwent changes, from continental breakup along the Red Sea in the south, to continental collision with Eurasia in the north and formation of the N–S trending Dead Sea fault plate boundary. Concurrent uplift and erosion of the entire Levant area led to an incomplete sedimentary record, obscuring reconstructions of the transition between the two tectonic regimes. New well data, obtained on the continental shelf of the central Levant margin (Qishon Yam 1), revealed a uniquely undisturbed sedimentary sequence which covers this time period. Evaporitic facies found in this well have only one comparable location in the entire eastern Mediterranean area (onland and offshore) over the same time frame — the Red Sea–Suez rift system. Analysis of 4150 km of multi and single-channel seismic profiles, offshore central Levant, shows that the sequence was deposited in a narrow basin, restricted to the continental shelf. This basin (the Haifa Basin) evolved as a half graben along the NW trending Carmel fault, which at present is one of the main branches of the Dead Sea fault. Re-evaluation of geological data onland, in view of the new findings offshore, indicates that the Haifa basin is the northwestern-most of a larger series of basins, comprising a failed rift along the Qishon–Sirhan NW–SE trend. This failed rift evolved spatially parallel to the Red Sea–Suez rift system, and at the same time frame. The Carmel fault would therefore seem to be related to processes occurring several million years earlier than previously thought, before the formation of the Dead Sea fault. The development of a series of basins in conjunction with a young spreading center is a known phenomenon in other regions worldwide; however this is the only known example from across the Arabian plate.

Sedimentology of rift climax deep water systems; Lower Rudeis Formation, Hammam Faraun Fault Block, Suez Rift, Egypt

In most marine rift basins, subsidence outpaces sedimentation during rift climax times. Typically this results in sediment-starved hangingwall depocentres dominated by deep-marine mudstones, with subordinate local development of coarser clastics in the immediate hangingwall derived from restricted catchments on the immediate footwall scarp. To highlight the spatial variability of rift climax facies and the controls upon them, we have investigated the detailed three-dimensional geometry and facies relationships of the extremely well exposed Miocene, rift climax Lower Rudeis Formation in the immediate hangingwall to the Thal Fault Zone, Suez Rift, Egypt. Detailed sedimentological analyses allows the Lower Rudeis Formation to be divided into two contemporaneous depositional systems, (1) a laterally continuous slope system comprising, hangingwall restricted (< 250 m wide) slope apron, slope slumps, fault scarp degradation complex and laterally extensive lower slope-to-basinal siltstones, and (2) a localized submarine fan complex up to 1 km wide and extending at least 2 km basinward of the fault zone. Interpretation of individual facies, facies relationships and their spatial variability indicate that deposition in the immediate hangingwall to the Thal Fault occurred via a range of submarine concentrated density flows, surge-like turbidity flows, mass wasting and hemipelagic processes. Major controls on the spatial variability and stratigraphic architecture of the depositional systems identified reflect the influence of the steep footwall physiography, accommodation and drainage evolution associated with the growth of the Thal Fault. The under-filled nature of the hangingwall depocentre combined with the steep footwall gradient result in a steep fault-controlled basin margin characterised by either slope bypass or erosion, with limited coastal plain or shelf area. Sediment supply to the slope apron deposits is controlled in part by the evolution and size of small footwall drainage catchments. In contrast, the localized submarine fan is interpreted to have been fed by a larger, antecedent drainage network. The structural style of the immediate footwall is also believed to exert a control on facies development and stratigraphic evolution. In particular, fault scarp degradation is enhanced by fault propagation folding which creates basinward-dipping bedding planes in the pre-rift footwall strata that large pre-rift blocks slide on.

The Cambrian Araba Formation in northeastern Egypt: Facies and depositional environments

The Cambrian Araba Formation exposed in Gabal El Zeit and in the Sinai Peninsula unconformably overlies Precambrian basement rocks, and is in turn overlain unconformably by the Ordovician Naqus formation. The Araba Formation has been subdivided into three informal lithologic units: lower, middle and upper, from field observations. Seven sedimentary facies assignable to three facies associations (fluvial, tidal and coastal to open marine) are recognized within the Araba Formation. The lower unit comprises two main facies: matrix-supported conglomerate (facies-A) in the south (Gabal Araba and Wadi Feiran) and interbeds of granulestone and sandstone (facies-B) in the north (Gabal Dhalal and Taba) deposited in fluvial conditions. The middle unit includes four facies: cross-bedded sandstone (facies-C), thin laminated sandstone (facies-D), burrowed-massive sandstone (facies-E) and rhythmically bedded sandstone–mudstone (facies-F) deposited mainly under tidal conditions in the coastal zone. The upper unit consists mainly of interbeds of burrowed mudstone-siltstone, with Skolithos, probably deposited in open marine environment. The sequence records the southward transgression of the Tethys Ocean over a horst and graben system developed in the late Precambrian on the northern margin of the Arabo-Nubian continent.