South Gharib Research Articles

Structural assessment and petrophysical evaluation of the pre-Cenomanian Nubian sandstone in the October Oil Field, central Gulf of Suez, Egypt

The low quality of the seismic resolution of the studied Cambrian Pre-Cenomanian formations, which rest directly on the basement in the October Field in the Gulf of Suez, requires study, and the structure pattern controlling these formations is uncertain. The poor quality of the seismic data resolution in the Gulf of Suez is due to the presence of thick sequences of evaporites represented by the South Gharib and Zeit formations. Therefore, the current study used seismic reflection data integrated with well-log data to define the structural-stratigraphic setting of the pre-Cretaceous Nubian reservoir sequence. The study aims at locating and delineating zones having excellent reservoir potential within the Nubian sequence horizons (Nubian Transition, main Nubian, Nubian marker-1, and Nubia marker-2, referred to as NT, MN, M1 and M2, respectively) through the integration of the 3D static modelling and the petrophysical parameters deduced from the well-log data processing. A detailed petrophysical analysis, based on the wireline logs of some wells, was performed to determine the lithological units using two types of cross plots (Neutron-Density and M-N plots), and the different petrophysical parameters that characterize the various Nubian horizons were also computed. 3D modelling was used to visualise the lateral and vertical changes of the reservoir characteristics. The seismic mapping reveals that the Nubian structure is controlled by an NW-SE trending (Clysmic trend) of an NE-plunging asymmetrical anticlinal feature unconformably resting on a basement horst. The main structure is affected by two major normal faults, which trend NW, andis cut by two smaller sub-parallel faults that disturb the core of the structure, which is unaffected by the easterly oriented faults of the Aqaba trend. The petrophysical analyses indicate that the Nubian sandstones have intervals of good reservoir quality, with a total net-pay thickness of about 500 m, net sand ratios (60–90 %), effective porosity (10–25 %), and hydrocarbon saturation (85%), which may encourage further drilling, especially in the southeast portion. The result of this study can be extended to the other Nubia sandstones resting on the basement complex in the Gulf of Suez.

Petrophysical analysis of well logs and core samples for reservoir evaluation: a case study of southern Issaran Field, Gulf of Suez province, Egypt

Understanding basic petrophysical properties may enhance the recovery of residual oil saturation and help in reservoir management. Reservoir oil saturation is the fraction of the porosity of a zone occupied by oil. The trapping may increase with the increase of porosity. Oil reservoirs represent a significant fraction of the reservoirs in the world-wide. We try to make a reservoir evaluation using petrophysical analysis of well logs and core samples at Issaran Field, South Gharib Formation, West of the Gulf of Suez, southeast Egypt. This area was heavily influenced by the structural setting of the Gulf of Suez’s central province, which is characterized by major SW dipping faults with a regional stratigraphic dip toward the NE. The high structural blocks are located in the center of the research area, and the low structural region is located in the southwest. South Gharib Formation is primarily composed of carbonates with few sulfates that grade upwards into sulfate-rich beds in the upper part. Laminated dolomitic limestone, with evaporites grades, changes downward into laminated dolomitic limestone and marly limestone, in the lower part. The anhydrite and dolomite units near the bottom have spotty oil stains. The structural setup is continued by the spread and deposition of this formation. We try to make analytical examination, of some reservoirs, accomplished by analyzing both well log data and core rock samples, vertically and laterally. According to the study of the horizontal permeability to vertical permeability ratio (Permeability anisotropy; lambda_{k}), the reservoir is laminated rock (lambda_{k} = 1.1 - 5), with a few data samples nearly isotropic (lambda_{k} = {1 mathord{left/ {vphantom {1 {1.1}}} right. kern-nulldelimiterspace} {1.1}}–1.1) and fractured (lambda_{k} = {1 mathord{left/ {vphantom {1 {2.5}}} right. kern-nulldelimiterspace} {2.5}}–1/1.1). Reservoir data histograms show that the most typical values of the data are 20–30% oil saturation and 7–10% porosity. The net-pay zone varies from four to 71 feet at different depths (897–1414 feet). Due to low shale content, water saturation, high effective porosity values, hydrocarbon saturation, may show higher net-pay thickness. These results may help to enhance the oil recovery. The area in the middle of the research area is suggested for future hydrocarbon development and using more petrophysical analysis.

Electrical properties of sedimentary microfacies and depositional environment deduced from core analysis of the syn-rift sediments, Northwestern shore of Gulf of Suez, Egypt

The present work is based mainly on core rock samples investigation of CSS-38 well, northwest of Gulf of Suez, Egypt. The cores cover the whole the South Gharib Formation (upper Miocene). The stratigraphic succession of the Gulf of Suez includes three mega units, recorded from old to young as pre-rift, syn-rift, and post-rift sediments. The syn-rift sediments from old to young are Nukhul, Rudies, Kareem, Belayim Equivalent, South Gharib, and Zeit. The core samples reveal that South Gharib Formation is not a good reservoir. It consists of sulphate-rich beds with few carbonates intercalation, laminated dolomitic limestone and marly limestone. Patchy oil staining is detected in the thin streaks and basal laminated dolomitic limestone. The microfacies are found to be evaporites, carbonates, calcareous marl, and calcareous claystone. Evaporites microfacies are considered the most frequent microfacies. Gypsum and anhydrite are generally represented by nearly equal distribution with parallel variation in content. The core samples differentiated South Gharib Formation into seven zones of depositional environment; they are arranged from base to top as shallow sub-tidal, shallow lagoonal, intertidal, shallow lagoonal, intertidal, shallow lagoonal, and supra-tidal Sabkha cycles. Some samples from South Gharib Formation were measured electrically. We will try to highlight interrelations between electrical (conductivity, permittivity, and impedance) and petrophysical properties with petrography and mineral composition. Electrical properties were measured with a frequency range from 10 Hz to 100 kHz. The dielectric constant decreases with increasing frequency and increases with increasing conductor content (up to percolation threshold). The conductivity increases with the increase in conductor content and with increasing frequency. Many parameters can combine to affect electrical properties. The present research is a trial to relate the surface to subsurface measurements.

Improvement of Gulf of Suez subsurface image under the salt layers through re-processing of seismic data- a case study

ABSTRACT Advanced technology in processing the old seismic data in the Gulf of Suez (G.O.S) has been used and applied using new parameters to emphasise the optimisation of geological structures and stratigraphic units as much as possible. The primary reflections in Gulf of Suez have low frequency while multiple reflections have higher frequency where there is a high reflection contrast in the shallow section represented by Zeit Formation due to alternation of shale and anhydrite that generates a lot of multiple reflections. The deeper formations will be affected by low-frequency reflections resulted from the incident energy itself with the common attenuation parameters such as transmission loss, adsorption, and spherical spreading of waves. Otherwise, the data in the Gulf of Suez suffer from a lot of loss mechanism from the salt of South Gharib Formation and anhydrite of Zeit Formation. In this study, new software are adapted to apply new technology in processing and analysis of seismic data such as VISTA 11 software from GEDCO company. After a lot of iterations of all seismic data parameters, seismic flows and parameters have been chosen to retain the primary frequency contents and relative amplitude while suppressing multiples energy. The reprocessing produced seismic sections with the increased temporal and spatial seismic resolution, facilitating more accurate interpretation of the data. Enhanced imaging of both the salt structures and the sub-salt sequence has been achieved, which in turn leads to a more and better understanding of salt deformation and improve the mapping of structural subdivisions within the study area.

Structural setup of Gara Marine area as deduced from 3D seismic interpretation and gravity-magnetic modelling, Gulf of Suez, Egypt

ABSTRACT An integrated interpretation utilising seismic data and inverse modelling is executed to more-reveal the subsurface complexity in Gara Marine area. The shallow features are identified by doing the seismic analyses on tops of Miocene formations. The deeper structures are deduced through constructing two gravity-magnetic models constrained by seismic and well data. The seismic results indicate that upper-Miocene rocks are characterised by a thick salt section (~2Km), which rarely cut by faults. South Gharib exhibits a structural closure at the centre due to a salt dome with dipping limbs towards the east and west. Belayim and Kareem are thinner in thickness, uniform distribution and steeply dipping to the southwest. Rudeis seems thicker westward, deposited in the downthrown side of a master block-fault. The uncertainty in seismic interpretation due to Miocene salts is estimated on tops of different horizons (±70 m static). The models indicate that Pre-Miocene sediments were deposited on a rough basement surface, with southwest regional dip-regime. The basement is deformed by the cross-faults (NW and NE) which vanish within Miocene section, with no evidences support presence of magmatic materials. The dip-reversal along flanks of Miocene salt structure, and limbs of pre-Miocene uplift, are the most potential traps.

Geopressure evaluation using integrated basin modelling, well-logging and reservoir data analysis in the northern part of the Badri oil field, Gulf of Suez, Egypt

The evaluation of pore and fracture pressures represents the gist of well planning and execution in drilling operation and exploration, where accurate pore and fracture pressures modelling enables the oil and gas companies to drill targets safely. The scope of this paper is to evaluate pore and fracture pressures in the northern part of the Badri Field, in the Gulf of Suez, Egypt to determine the convenient pore pressure fracture gradient model (PPFG) and to define the pore pressure regime in the subsurface within the Zeit, South Gharib, Belayim and Kareem formations from the top downwards.The pore pressure and fracture gradient model has been assessed using integrated data that include: burial history, well logs (sonic, resistivity and density), offset wells drilling problems, and reservoir pressure. The Amoco overburden equation and Eaton's sonic and resistivity methods were used to estimate the overburden stress and the pore pressure values respectively, while fracture pressure was calculated using the Eaton method. Results show that the maximum pore pressures is in the South Gharib Formation and the lowest pore pressure is within the reservoir sections. Six abnormal pressure zones were detected, these includes four overpressure zones and two sub-normal pressure zones, where the maximum estimated pore pressure was up to 10.5 pound per gallon (ppg) equivalent gradient, which was recorded in the South Gharib Formation. While the minimum measured pore pressure value was recorded at 4.7 (ppg) in the Kareem sandstone reservoir. The fracture gradient ranged between 11.5 and 13.1 (ppg) equivalent density for both the Belayim (Hammam Faraun Member) and Kareem sandstone reservoirs.The main conclusions of this study are, 1) the pore pressure profile is normal, sub-normal and over-pressurized in the study area, 2) the integration of basin modelling, well-logging, drilling problems and direct measurements allow us to evaluate the geopressures in the subsurface horizons, 3) the use of low mud density while drilling into the depleted reservoir zones is the best solution for fluid losses mitigation, 4) the modified surface, intermediate and production casing seats is adequate for the future planned wells profile. 5) providing insights on downhole pressure behavior across stratigraphy in the area of study, to achieve optimum drilling mud designing and adequate casing seats as well as safe and successful operational planning.

Structures and sequence stratigraphy of the Miocene successions, southwestern Gulf of Suez, Egypt

The subsurface structural evolution, facies changes and sequence stratigraphic interpretations of the Miocene successions of the southwestern part of the Gulf of Suez, Egypt, were studied by seismic reflection data of Twenty seven 3D seismic sections supported by the composite, velocity and vertical seismic profiles (VSP) logs of eight wells. Among them five sections and two geoseismic cross sections were selected to reveal the structural framework and depositional history of the study area. The analysis of depth-structure contour maps revealed that the Miocene strata are dissected by two major faults trends: The NW–SE trending faults (Clysmic trend) and the NE–SW trending cross faults running nearly perpendicular to the Clysmic faults. The facies changes of the syn-depositional Miocene units are controlled by the structural framework of the southern part of the Gulf of Suez being evolving diapiric structure of South Gharib Formation. The Miocene units are subdivided into two major 3rd order depositional sequences: S1 and S2.

Hydrocarbon potential, structural setting and depositional environments of Hammam Faraun Member of the Belayim Formation, Southern Gulf of Suez, Egypt

The Middle Miocene Belayim Formation is one of the most prolific formations in the Southern Gulf of Suez. It consists of four members; two members are evaporitic (Baba and Feiran) and the other two members are prospective, mostly clastics (Hammam Faraun and Sidri). The hydrocarbon potential and depositional environment of Hammam Faraun Member, the target of the present study, have been studied in 11 wells distributed in the southern province of the Gulf of Suez. The traditional well log data, as well as the Spectral Gamma-Ray logs ‘SGR’ and dipmeter data were used to evaluate the petrophysical properties and distribution of the Hammam Faraun Member in the Southern Gulf of Suez. It varies greatly in thickness with the greatest thicknesses in GS 365 (372 ft) and GS 373 (430 ft) fields in the central parts and the thinnest at the basin margins of the studied area at GH376 (65 ft) and Ras El Bahar (67.5 ft) fields. It is composed of clastic rocks, mainly shales and sometimes reef carbonates. The very good petrophysical properties of the studied sequence indicate a good reservoir in some fields with good to very good porosity (13.5 ≤ ∅ ≤ 25.0%). The shale volume of this reservoir sequence is less than 33% and the water saturation is less than 42.3%, while the net-pay thickness is up to 58 ft.The SGR and Pe logs indicate that, the studied rocks were deposited mostly in lagoonal to shallow marine environments, with illite and montmorillonite as dominant clay minerals.The dipmeter data obtained in some wells indicate slightly tilted beds, mostly less than 20° with an overall dip direction towards the SW, which represents the regional dip in the Southern Gulf of Suez. Based on dipmeter data, two major angular unconformities can be detected; one at the top of the sequence, separating it from the overlying South Gharib evaporates, and another one at the base of the sequence, separating it from the underlying Feiran Member.

The Nature of Pre-Miocene and Miocene Sediments in the Offshore Northern Part of the Gulf of Suez, Egypt

The present study deals with subsurface geology pre-Miocene and Miocene rock units penetrated in the extremely northern offshore Gulf of Suez area. Throughout the pre-Miocene and Miocene, changes in the tectonic pattern, depositional environment, and sediment types indicate different magnitudes and tectonic instability. Based on the available seven dry subsurface composite well logs (GS 9-1, Darag 17-1, GS 24-1, X 80-1, GS 56-1, Fina Z 80-1A, and GS78-1 wells) besides dipmeter logs, 39 stratigraphic maps (isopach and facies maps) are constructed to show thickness variations, facies changes, and paleogeology of Jurassic (Massajid Formation), Lower Cretaceous (Nubia Formation), Upper Cretaceous (Raha, Abu Qada, Wata, Matulla, and Sudr formations), Lower Miocene (Nukhul, Rudeis, and Kareem formations), and Middle Miocene (Belayim, South Gharib, and Zeit formations) times. Moreover, two cross sections are constructed to show thickness and lateral variations in facies changes and tectonics affecting the area at that time. Despite this, the study area has suitable conditions for hydrocarbon generation and accumulation, the seven wells drilled in the study area are considered to be dry or nonproductive. They are considered to be dry or not productive due to tilting of strata to the SW direction, absence of cap rocks (evaporites and salts) and shale in most parts of the study area (especially in the extremely northern parts), and affecting the area by a large numbers of normal faults due to active and continuous tectonic events on the Gulf of Suez area. These reasons may be aided to the migration of hydrocarbons from the area to outside and to the adjacent oil fields.

The improvements of three-dimensional seismic interpretation in comparison with the two-dimensional seismic interpretation in Al-Amal oil field, Gulf of Suez, Egypt

Thirteen 2D seismic lines were interpreted with the help of well velocity and time-depth trace conversion to construct the structure-tectonic maps. This is to characterize the different stratigraphic tops of Al-Amal area, as well as to confirm the validity of the proposed structural model. Most of the available seismic data in Al-Amal area were investigated and reviewed to select the best quality set.In order to study the detailed structural elements based on the 3D seismic lines; six depth structure contour maps were constructed on the tops of Zeit, South Gharib, Belayim, Kareem, Nukhul and Matulla formations from top downward. Interpretation was aided by the missing sections detected from the available well tops and dip-meter data as well. These maps indicate that, both of Miocene and Pre-Miocene formations in Al-Amal field were affected by elongated tilted graben blocks trending in the NW–SE directions and bounded by two sets of faults, which are down throwing toward the west and eastern directions.

Exploring subtle exploration plays in the Gulf of Suez

Abstract The Gulf of Suez Basin is a classic extensional rift basin of Miocene age, with a number of syn- and pre-rift hydrocarbon plays. Exploration started in 1886, targeting areas around documented oil seeps, and was highly successful. During the boom in offshore exploration in the 1950s and 1960s, a combination of diligent geology and serendipity resulted in the discovery of a number of giant fields whose reserves form a major part of some 10 billion barrels discovered to date. However, the pursuit of smaller fields, both structural and stratigraphic, has been hampered by the poor quality seismic data characteristic of the basin. The poor quality of the seismic data is due to the interbedded shales and evaporites of shallow post-rift Zeit and South Gharib formations that create massive reverberation and severe attenuation of the seismic signal. Incremental progress in imaging the deeper horizons, including the key pre-rift Nubia Sandstone reservoir, has been achieved through low frequency enhancement and 3D seismic data acquisition. However it is still common for exploration and development wells to miss the Nubia objective due to the poor imaging and consequent misinterpretation of the seismic data. Exploration is now directed towards the smaller targets and subtle plays of the Gulf of Suez. To improve seismic imaging the focus has been on improved acquisition, with 3D ocean-bottom cable seismic data. This has the advantages of reduced multiple energy, higher fold and a broader bandwidth over streamer 3D data. Combined with detailed models of the tectonically controlled sedimentation that characterizes the syn-rift section, this has allowed the development of a re-invigorated exploration programme.

Petroleum geology and potential hydrocarbon plays in the Gulf of Suez rift basin, Egypt

The Gulf of Suez in Egypt has a north-northwest–south-southeast orientation and is located at the junction of the African and Arabian plates where it separates the northeast African continent from the Sinai Peninsula. It has excellent hydrocarbon potential, with the prospective sedimentary basin area measuring approximately 19,000 km 2 , and it is considered as the most prolific oil province rift basin in Africa and the Middle East. This basin contains more than 80 oil fields, with reserves ranging from 1350 to less than 1 million bbl, in reservoirs of Precambrian to Quaternary age. The lithostratigraphic units in the Gulf of Suez can be subdivided into three megasequences: a prerift succession (pre-Miocene or Paleozoic–Eocene), a synrift succession (Oligocene–Miocene), and a postrift succession (post-Miocene or Pliocene–Holocene). These units vary in lithology, thickness, areal distribution, depositional environment, and hydrocarbon importance. Geological and geophysical data show that the northern and central Gulf of Suez consist of several narrow, elongated depositional troughs, whereas the southern part is dominated by a tilt-block terrane, containing numerous offset linear highs. Major prerift and synrift source rocks have potential to yield oil and/or gas and are mature enough in the deep kitchens to generate hydrocarbons. Geochemical parameters, sterane distribution, and biomarker correlations are consistent with oils generated from marine source rocks. Oils in the Gulf of Suez were sourced from potential source rock intervals in the prerift succession that are typically oil prone (type I), and in places oil and gas prone (type II), or are composites of more than one type (multiple types I, II, or III for oil prone, oil and gas prone, or gas prone, respectively). The reservoirs can be classified into prerift reservoirs, such as the Precambrian granitic rocks, Paleozoic–Cretaceous Nubian sandstones, Upper Cretaceous Nezzazat sandstones and the fractured Eocene Thebes limestone; and synrift reservoirs, such the Miocene sandstones and carbonates of the Nukhul, Rudeis, Kareem, and Belayim formations and the sandstones of South Gharib, Zeit, and

Aridity and humidity: two aspects of the late Miocene climate of North Africa and the Mediterranean

The physiography of North Africa is not greatly changed from that of the Messinian. With the drawdown of the Mediterranean in the late Messinian the then existing river systems were incised into the landscape and emptied into Lake Cyrenaica, which occupied the substantially drained Eastern Mediterranean Basin. The record of incision provides a record of the magnitude of the Messinian river systems. An analysis of these river systems demonstrates that Messinian rainfall, a consequence of the Zeit Wet Phase, was greatest in east and south-central North Africa, in keeping with the derivation of the water mainly from the Indian Ocean. In central North Africa the Eosahabi River flowed from Messinian Lake Chad eroding the East Tibesti Valley and cutting a channel which is especially well preserved near the coast of the Gulf of Sirt. The penetrated sediments of Lake Cyrenaica and the marginal basins of the Messinian transgression are known as the Upper Evaporites and are generally fine clastics, gypsarenites and gypsum/anhydrite. They were rapidly deposited. Underlying them is the halite of the Lower Evaporites. This sequence of Upper and Lower Evaporites is much like the lower halite of the Tortonian South Gharib Formation and the overlying clastics and anhydrite of the Messinian Zeit Formation in the Gulf of Suez/Red Sea area. This type of sequence is termed an evaporitic couplet and, as has been demonstrated for the Gulf of Suez/Red Sea, is a consequence of a transition from a dry to a more humid climate in a restricted or semirestricted basin. This transition occurred at about 7.5 Ma in the Gulf of Suez/Red Sea and at about 5.8 Ma in the Mediterranean. The Zeit Wet Phase manifest in the above events developed in association with the initiation and development of the Asian monsoon and the drying of the Mediterranean. It can be understood in terms of the development of an evolving monsoon/desert system. The Asian monsoon was initiated 8–7 Ma in association with the uplift of Tibet; at this time the North African desert zone was displaced northwards to be over the Mediterranean and central and eastern North Africa became seasonally humid. A concept is advanced in which the early stage of the development of the Asian monsoon is seen as having two phases alternating at the precessional ca 21 ka cycle. One phase transferred moisture from the Indian Ocean mainly to southern Asia, the other phase transferred moisture mainly to North Africa. With the drawdown of the Mediterranean at about 5.8 Ma the Zeit Wet Phase intensified. A further northward movement of the humid and desert zones occurred at the time of drawdown. With the Messinian and early Pliocene transgressions the wet phase ameliorated but a substantial river system still crossed central North Africa. At about 4.6 Ma North Africa became drier probably in response to the developing dominance of the features of the monsoon that transferred moisture mainly to southern Asia, features of the monsoon that are well recognised today.

Subsalt Depth Imaging Using 3-D VSP Technique in the Ras El Ush Field, Gulf of Suez, Egypt

ABSTRACT In 1995 oil was discovered in the pre-Miocene Matulla and Nubia Sandstones in the Ras El Ush field, Gulf of Suez, Egypt. The discovery was based on an aeromagnetic anomaly from a basement high. After drilling several delineation wells, based on a geological model, it became evident that the field is very complex as it is broken into tilted and rotated compartmental blocks by two perpendicular fault systems. Also the 2-D seismic data were of poor quality beneath the thick Miocene South Gharib Evaporite. Since part of the field lies below shallow-water, 3-D seismic was considered to be too costly. When a delineation well did not encounter the reservoir, due to an unanticipated fault, a 2-D walkaway Vertical Seismic Profile (VSP) was acquired. It clearly revealed the presence of a cross fault. The success of the 2-D VSP in imaging the fault led to the acquisition of the first Middle East 3-D VSP survey in the following well. A downhole, tri-axial, five geophone array tool was used to acquire the 3-D VSP. The 3-D volume of the final migrated VSP data provided the means for the reliable mapping of horizons beneath the South Gharib Evaporite. These maps improved the definition of the field and helped detect previously unrecognized prospective blocks. Four further successful delineation wells confirmed the 3-D VSP interpretation.

The late Miocene climate of northeastern Africa: unravelling the signals in the sedimentary succession

Examination of the depositional profile of the Miocene/Plio-Pleistocene succession at two locations in the Gulf of Suez and seven locations in the Red Sea leads to the conclusion that the Messinian (Zeit Formation and equivalent) sedimentary rocks were deposited at a rate greater than other units of the Miocene/Plio-Pleistocene in these areas. The Zeit Formation contains a significantly higher clastic content than the underlying South Gharib Formation. These two aspects of the stratigraphy are taken to indicate that the Messinian was a time of high rainfall and high sediment yield rates. This period, named the Zeit Wet Phase, stands in marked contrast to the arid conditions of the preceding Tortonian Stage. The latter stage is represented in the Gulf of Suez and Red Sea area by the halite-bearing South Gharib Formation and its equivalents. Physical evidence for a humid Messinian is provided by five lines of evidence involving four sites around the Red Sea and two sites offshore. It is suggested that the Zeit Wet Phase was marked by high monsoonal activity as demonstrated by drilling sites of the Ocean Drilling Program. It is probable that the wet phase peaked in the late Messinian at the time of the low-stand of the Mediterranean during the Messinian Salinity Crisis.

THE RED SEA — GULF OF ADEN: BIOSTRATIGRAPHY, LITHOSTRATIGRAPHY AND PALAEOENVIRONMENTS

Sediments of Palaeozoic, Mesozoic and early Palaeogene ages experienced a similar geological history in Ethiopia, Yemen and Somalia. During the late Eocene, however, uplift and differential erosion took place, prior to rift development in the middle Oligocene, when the proto‐Gulf of Aden became established. To a certain extent, a similar sequence of events had also taken place in those regions of Egypt, Sudan, Ethiopia, Yemen and Saudi Arabia which border the Red Sea, but post‐Eocene subsidence is now believed to have commenced during the late Oligocene in the southern Red Sea and progressed later, during the early Miocene, in the northern Red Sea and Gulf of Suez. Timing of this progressive development of the Gulf of Aden rift complex through the Red Sea and Gulf of Suez is well constrained by biostratigraphy, and provides a new approach to the understanding of lithological variations within the region.These lithological variations have, until now, only been considered on a country‐specific basis, thus hindering establishment of a regional history of sedimentation. The well‐understood and well‐documented lithostratigraphic nomenclature of the Miocene succession of the Gulf of Suez has been used as a reference, or type, with which the lateral facies variations within the Red Sea have been compared. By this method only has it been possible to produce palaeoenvironmental maps for the entire study region, and for each formation and member. Lateral equivalents of the Gulf of Suez Nukhul, Rudeis, Kareem, Belayim, South Gharib. Zeit, Wardan and Shagara Formations have been identified within the Red Sea syn‐rift and post‐rift episodes.

Miocene Salt Structures as Exploration Indicators in the Offshore B-Trend, Gulf of Suez, Egypt

The B-Trend is a structural horst block extending in a northwest-southeast direction for about 40 km in the southern offshore area of the Gulf of Suez. It contains six individual sub-structures (six oil fields) oriented along strike and dipping toward the southwest. Subsurface geologic data from 60 wells together with the available seismic data in the area were integrated to explain the development of salt structures along this belt and their influence on oil exploration. These salt structures are restricted to the Belayim and South Gharib formations of middle and upper Miocene age, respectively. Moreover, they are arranged as linear features along the trend. Thickening in the Belayim salt is due in some cases to injection and in others to deposition. The apexes of the Belayim injected salt bodies are located down-dip from the crest of the underlying structures and are shifted westward from the apexes of the overlying larger South Gharib salt bulges. The highset corner of the pre-Miocene structures is located to the east of the injected Belayim salt pillows. Thick Belayim salt of depositional origin usually exists on the downthrown side of the leading edge fault to the east. The thickness ratios between the different members ofmore » the Belayim Formation help to differentiate between the injected and deposited salt bodies. These ratios can be used to orient well tracks to the optimum structural target while drilling.« less

THE PHYSIOGRAPHIC FEATURES OF THE MIOCENE RAS MALAAB GROUP BASIN, SOUTH BAKR OILFIELD, GULF OF SUEZ, EGYPT

The lithostratigraphy and petrography of the Ras Malaab Group were investigated in order to define the physiography and structure of the depositional basin. The Ras Malaab Group consists, from the top, of the Zeit, South Gharib and Belayim Formations.The basal Belayim Formation consists of carbonate barrier (reefal, lagoonal and marine tidal‐flat carbonates, located from east to west respectively in the basin. Thus. reefal limestones and evaporites are associated within the succession of the Belayim Formation.The overlying South Gharib Formation is composed of thick evaporite sediments that were deposited in a restricted, subsiding salina basin. Intense subsidence in the western part of the basin is related to faulting.The Zeit Formation consists of evaporites and fine clastics derived from surrounding land‐masses. The Zeit sequence indicates relatively deeper, semi‐restricted, lagoonal conditions.

Early depositional history of a rift basin: Miocene in Western Sinai

The Cenozoic stratigraphic record in the Gulf of Suez provides a model of six events for the early sedimentologic history of a rifted basin. Classic exposures on the east coast of the Suez in the Western Sinai yield a composite section of the Miocene succession. 1. (1) Oligocene?—Early Miocene (Nukul Formation) terrigenous clastics in fluvial, fandelta and littoral environments filled local valleys. 2. (2) During Early Miocene transgression (Lower Rudies Member), nearshore and shelf sediments accumulated at a rate no less than 4 cm/1000 yrs. Rates of accumulation increased dramatically at the beginning of the Middle Miocene. 3. (3) During the early part of the Middle Miocene basinal muds and evaporites (Upper Rudeis Member, Kareem Formation and part of Belayim Formation) accumulated at a rate of 106–146 cm/1000 yrs. 4. (4) Rates slowed during short-term shoaling periods when shelf carbonates (Hammam Faraun Member) were deposited. 5. (5) A fifth event is represented by more than 2 km of Late Miocene evaporites (Zeit— South Gharib Formations), which accumulated at a minimum rate of 32 cm/1000 yrs. 6. (6) The post-evaporite event of alluvial and shallow—deep marine sedimentation began in the Pliocene and is continuing today. Local carbonate buildups developed upon fault blocks during the second and fourth stages. Evaporite deposition can be a very rapid process in the filling of rifted basins.