PROVINCE GEOLOGY

Province Boundary and Geographic Setting

The Red Sea Basin Province includes offshore and adjacent onshore areas, from the northern Gulf of Suez (350 km by 70 km) and Gulf of Aqaba (185 km by 25 km) southeastward along the Red Sea to the Gulf of Aden in the Indian Ocean. The province is a Tertiary cratonic rift south of Egypt’s Sinai Peninsula between northeastern Africa and the Arabian Peninsula (Figure 3a). Northwest-southeast length of the province is 2300 km, with a width to 400 km. The Gulf of Suez is an abandoned rift basin with less than 100-meter water depths. The Gulf of Aqaba is a younger, rapidly subsiding wrench basin with maximum water depth of 1850 meters. The remaining Red Sea Basin Province is an active rift where sea-floor spreading has occurred for the last 5 m.y. and where water depths locally exceed 2300 meters in the axial region.

Political Entities

Within or directly bordering the Red Sea Basin Province are Egypt, Sudan, Eritrea (formerly part of Ethiopia), Djibouti, Yemen, Saudi Arabia, Jordan, and Israel. Saudi Arabia is a member of the Organization of Petroleum Exporting Countries (OPEC). Both Saudi Arabia and Egypt are members of the Organization of Arab Petroleum Exporting Countries (OAPEC). Border disputes exist between Saudi Arabia and Yemen and between Egypt and Sudan. Sudan has been chronically plagued by civil war and, in 1996, was sanctioned by the United Nations for sponsoring terrorism. A civil war in Yemen ended in 1994. Eritrea and Ethiopia have had recent conflicts.

Geologic Setting

The Red Sea Basin Province originated as an Oligocene continental rift impacted by left-lateral wrenching. Rift location and borders are defined by crustal weaknesses created more than 500 Ma – including the late Proterozoic to early Paleozoic cratonization of the Arabian-Nubian shield, its suturing to the African continent, and subsequent supercontinent breakup. Those events resulted in the juxtaposition of structurally and compositionally different basement terranes and the establishment of major fault systems. Periodic Paleozoic and Mesozoic subsidence focused around the present-day southern Mediterranean (Tethyan) margin was complemented by local and regional uplifts (e.g., late Paleozoic Hercynian orogeny, late Cretaceous to early Tertiary Tethyan closure and Syrian arc formation).

Parts of the Paleozoic and Mesozoic rock record were either eroded or not deposited, particularly in the central Red Sea area, and various structural fabrics were imparted to the region. When present and preserved, pre-rift stratigraphy is more marine in character northward through the northern part of the province, and only Cretaceous seas ever transgressed south of the Aqaba-Suez-Red Sea triple junction. Tethys shorelines to the east failed to completely transgress the Arabian Peninsula westward except in late Jurassic and earliest Cretaceous time, when marine environments covered the southern quarter of the Red Sea, south from the Farasan and Dahlak islands.

Oligocene continental rifting began with subsidence, extension and normal faulting, associated with the episodic and segmented movement of the Arabian peninsula away from Africa. Magmatic expansion resulted in igneous emplacements, and isostatic compensation caused the rift shoulders to undergo uplift and local erosion into the rapidly subsiding and tilting block-faulted basins (Figure 4). Syn-rift depositional conditions (thus, facies and lithologies) varied laterally. Later thermal re-equilibration resulted in reduction of subsidence, regional basin uplift and further rotation of faulted blocks. Post-rift evaporite deposition was extensive until Pliocene when open marine conditions were established.

Rifting was sequentially younger northward, and tens to hundreds of meters of fault-block relief were common. Total extension in the Red Sea decreased northward into the Gulf of Suez. Gulf of Suez rifting essentially ceased (early-middle Miocene, 18 - 14 Ma) (Figure 2) when continental separation became more oblique because of the dominant movement on the left-lateral transform fault that extends through the Gulf of Aqaba northeastward to the Dead Sea. Gulf of Suez fault blocks are generally smaller and more highly rotated southward, concurrent with increased basin extension. Subsidence continued at reduced rates in the southern Gulf of Suez, but Pliocene uplift in the northernmost part caused limited basin inversion. Fault blocks in the northern and southern thirds of the Gulf of Suez dip dominantly southwestward, whereas those in the center third tilt mostly northeastward.

Extensive wrench faulting resulted in the development of transtensional and transpressional areas in the Gulf of Aqaba and along the northern (northwestern Saudi Arabia) and western (Egypt and Sudan) margins of the Red Sea, trending southward toward the East African rift system. Thus, crustal profiles across the Red Sea rift are asymmetric. The steep Egyptian-Sudanese margin has a narrow shelf delineated by wrench faults and ancient suture zones, with pull-apart basins floored by oceanic crust. The eastern margin and southern area are floored by attenuated continental crust. A continuous marine connection from the Gulf of Suez to the Indian Ocean was first established 5 Ma (Pliocene) with the advent of sea-floor spreading in the southern part of the province (Figure 2). Contemporaneous local salt movement throughout the region ranged from the creation of massive domes and walls to total removal.

Exploration History

        Gulf of Suez (120+ fields or discovery wells)

Gemsa field along the southwestern Gulf of Suez coast was discovered in 1869 and first produced in 1910, followed by Hurghada field in 1913. Five more fields were discovered between the two world wars when well completion rates were several-to-ten per year. After World War II, activity spread to the eastern coast, and annual well completions increased to several dozen by 1973. During the early to mid 1980s, as many as 133 wells were completed in one year, but 1990s levels declined to an annual range of 50 to 60. The 1900+ wells in the Gulf of Suez basin define more than 120 fields, with nearly half currently listed as one-well discoveries (Petroconsultants, 1996). Thirty fields include ten or more producing wells, and fewer than ten fields are abandoned.

        Western Side of Red Sea (4 fields)

The Egyptian Red Sea south of the Gulf of Suez has 22 dry holes, six with hydrocarbon shows. One well was drilled in 1916, five in the late 1930s and 1940s, 14 between 1976 and 1985, and two in 1994. The Sudanese Halaib area with one 1982 penetration is in a disputed border zone with Egypt. Three dry holes were drilled along the central Sudanese Red Sea coast in 1962, and Sudan’s southern Tokar Delta has three unproduced, one-well gas fields resulting from 10 attempts between 1961 and 1996. (Durwara 2 was discovered in 1963, and Suakin 1 and Bashayer 1A were both discovered in 1976. Suakin has associated condensate, and the one offset (1996) is dry.) Eritrea has an offshore, one-well gas field not yet produced. Eleven wells were drilled in the salt-cored Dahlak Islands from 1938-1940. Deeper wells (one hydrocarbon show) tested eight Eritrean offshore locations from 1966-1977.

        Eastern Side of Red Sea (2 fields)

No wells have been drilled within the Gulf of Aqaba, but two fields were discovered in an adjacent Saudi Arabian transpressional basin (Midyan basin) – offshore Barqan field in 1969 and onshore Midyan field in 1992. Both fields tested gas, condensate and oil, but neither has produced. The Saudi Arabian coastal area has more than 30 penetrations (1967-1994) over the 1500-km distance from the Gulf of Aqaba to the Yemen border. Data and locations are published for nine wells, six of which are near Yemen. Seven shallow 1930s tests were drilled near oil seeps in the salt-cored Farasan Islands. Thirteen Yemeni wells – several with oil or gas shows – have tested (1961-1996) the Red Sea Basin Province.