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Title: Oil exploration in nonmarine rift basins of interior Sudan

Abstract

In early 1975 Chevron Overseas Petroleum Inc. commenced a major petroleum exploration effort in previously unexplored interior Sudan. With the complete cooperation of the Sudanese Government, Chevron has acquired a vast amount of geologic and geophysical data during the past 9 years. These data include extensive aeromagnetic and gravity surveys, 25,000 mi (40,200 km) of seismic data, and the results of 66 wells. This information has defined several large rift basins which are now recognized as a major part of the Central African rift system. The sedimentary basins of interior Sudan are characterized by thick Cretaceous and Tertiary nonmarine clastic sequences. Over 35,000 ft (10,600 m) of sediment have been deposited in the deepest trough, and extensive basinal areas are underlain by more than 20,000 ft (6100 m) of sediment. The depositional sequence includes thick lacustrine shales and claystones, flood plain claystones, and lacustrine, fluvial, and alluvial sandstones and conglomerates. Those lacustrine claystones which were deposited in an anoxic environment provide oil-prone source rocks. Reservoir sandstones have been found in a wide variety of nonmarine sandstone facies. The extensional tectonism which formed these basins began in the Early Cretaceous. Movement along major fault trends continued intermittently into the Miocene. Thismore » deformation resulted in a complex structural history which led to the formation of several deep fault-bounded troughs, major interbasin high trends, and complex basin flanks. This tectonism has created a wide variety of structures, many of which have become effective hydrocarbon traps.« less

Authors:
Publication Date:
Research Org.:
Chevron USA Inc., Concord, CA
OSTI Identifier:
6185385
Alternate Identifier(s):
OSTI ID: 6185385
Report Number(s):
CONF-8405216-
Journal ID: CODEN: AAPGB
Resource Type:
Conference
Resource Relation:
Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States); Journal Volume: 68:4; Conference: AAPG annual convention, San Antonio, TX, USA, 20 May 1984
Country of Publication:
United States
Language:
English
Subject:
02 PETROLEUM; PETROLEUM DEPOSITS; EXPLORATION; SUDAN; CRETACEOUS PERIOD; PETROLEUM GEOLOGY; RESERVOIR ROCK; SOURCE ROCKS; TECTONICS; TERTIARY PERIOD; AFRICA; CENOZOIC ERA; DEVELOPING COUNTRIES; GEOLOGIC AGES; GEOLOGIC DEPOSITS; GEOLOGY; MESOZOIC ERA; MINERAL RESOURCES; RESOURCES 020200* -- Petroleum-- Reserves, Geology, & Exploration

Citation Formats

Schull, T.J. Oil exploration in nonmarine rift basins of interior Sudan. United States: N. p., 1984. Web.
Schull, T.J. Oil exploration in nonmarine rift basins of interior Sudan. United States.
Schull, T.J. Sun . "Oil exploration in nonmarine rift basins of interior Sudan". United States. doi:.
@article{osti_6185385,
title = {Oil exploration in nonmarine rift basins of interior Sudan},
author = {Schull, T.J.},
abstractNote = {In early 1975 Chevron Overseas Petroleum Inc. commenced a major petroleum exploration effort in previously unexplored interior Sudan. With the complete cooperation of the Sudanese Government, Chevron has acquired a vast amount of geologic and geophysical data during the past 9 years. These data include extensive aeromagnetic and gravity surveys, 25,000 mi (40,200 km) of seismic data, and the results of 66 wells. This information has defined several large rift basins which are now recognized as a major part of the Central African rift system. The sedimentary basins of interior Sudan are characterized by thick Cretaceous and Tertiary nonmarine clastic sequences. Over 35,000 ft (10,600 m) of sediment have been deposited in the deepest trough, and extensive basinal areas are underlain by more than 20,000 ft (6100 m) of sediment. The depositional sequence includes thick lacustrine shales and claystones, flood plain claystones, and lacustrine, fluvial, and alluvial sandstones and conglomerates. Those lacustrine claystones which were deposited in an anoxic environment provide oil-prone source rocks. Reservoir sandstones have been found in a wide variety of nonmarine sandstone facies. The extensional tectonism which formed these basins began in the Early Cretaceous. Movement along major fault trends continued intermittently into the Miocene. This deformation resulted in a complex structural history which led to the formation of several deep fault-bounded troughs, major interbasin high trends, and complex basin flanks. This tectonism has created a wide variety of structures, many of which have become effective hydrocarbon traps.},
doi = {},
journal = {Am. Assoc. Pet. Geol., Bull.; (United States)},
number = ,
volume = 68:4,
place = {United States},
year = {Sun Apr 01 00:00:00 EST 1984},
month = {Sun Apr 01 00:00:00 EST 1984}
}

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  • In early 1975 Chevron Overseas Petroleum Inc. commenced a major petroleum exploration effort in previously unexplored interior Sudan. With the complete cooperation of the Sudanese Government, Chevron has acquired a vast amount of geologic and geophysical data during the past 9 years. These data include extensive aeromagnetic and gravity surveys, 25,000 mi (40,200 km) of seismic data, and the results of 66 wells. This information has defined several large rift basins which are now recognized as a major part of the Central African rift system. The sedimentary basins of interior Sudan are characterized by thick Cretaceous and Tertiary nonmarine clasticmore » sequences. Over 35,000 ft (10,600 m) of sediment have been deposited in the deepest trough, and extensive basinal areas are underlain by more than 20,000 ft (6100 m) of sediment. The depositional sequence includes thick lacustrine shales and claystones, flood plain claystones, and lacustrine, fluvial, and alluvial sandstones and conglomerates. Those lacustrine claystones which were deposited in an anoxic environment provide oil-prone source rocks. Reservoir sandstones have been found in a wide variety of nonmarine sandstone facies. The extensional tectonism which formed these basins began in the Early Cretaceous. Movement along major fault trends continued intermittently into the Miocene. This deformation resulted in a complex structural history which led to the formation of several deep fault-bounded troughs, major interbasin high trends, and complex basin flanks. This tectonism has created a wide variety of structures, many of which have become effective hydrocarbon traps.« less
  • The sedimentary basins of interior Sudan are characterized by thick nonmarine clastic sequences of Jurassic(.)-Cretaceous and Tertiary age. Over 45,000 ft (13,716 m) of sediment was deposited in the deepest trough and extensive basinal areas are underlain by more than 20,000 ft (6096 m) of sedimentary rocks. The depositional sequences include thick lacustrine shales and claystones, flood plain claystones, and lacustrine, fluvial, and alluvial sandstones and conglomerates. Those lacustrine claystones deposited in a suboxic environment provide good oil-prone source rocks. Reservoir sandstones have been found in a wide variety of nonmarine sandstone facies. The extensional tectonism that formed these basinsmore » began in the Jurassic(.)-Early Cretaceous. Movement along major fault trends continued intermittently into the Miocene. This deformation resulted in a complex structural history that led to the formation of several deep fault-bounded troughs, major interbasinal highs, and complex basin flanks. This tectonism has created a wide variety of structures, many of which have become effective hydrocarbon traps. During the past eight years, several important oil discoveries have been made. Significant accumulations have been delineated in the Heglig and Unity areas, where estimated recoverable reserves are 250-300 million bbl of oil. 14 figures.« less
  • Rift basins are a primary target of exploration in east, central, and west Africa. These intracratonic rift basins range in age from the Triassic to the Neogene and are filled with lagoonal-lacustrine sand-shale sequences. Several rift basins may be present in the Western Desert of Egypt. In the northeastern African platform, the Mesozoic Tethyan strand lines were previously interpreted to have limited southern extension onto the continent. This concept, based upon a relatively limited amount of subsurface data, has directed and focused the exploration for oil and gas to the northernmost 120 km of the Western Desert of Egypt. Recentmore » well and geophysical data indicate a southerly extension of mesozoic rift basins several hundred kilometers inland from the Mediterranean Sea. Shushan/Faghur and Abu Gharadig/Bahrein basins may represent subparallel Mesozoic basins, trending northeast-southwest. Marine Oxfordian-Kimmeridgian sediments were recently reported from wells drilled approximately 500 km south of the present-day Mediterranean shoreline. The link of these basins with the Sirte basin to the southwest in Libya is not well understood. Exploration is needed to evaluate the hydrocarbon potential of such basins.« less
  • Structural highs and syntectonic depositional sites in Central Sumatra rift basins are controlled by three-dimensional normal fault geometries and lateral fault slip distributions. The rift basins formed due to crustal extension accommodated by normal faults that flatten with depth, causing collapse of the hanging wall and formation of inclined rollover panels. The authors model this deformation by coulomb shear of the hanging wall localized along active fold hinges (axial surfaces) that are pinned at depth to fault bends. Three-dimensional fault geometries are predicted and mapped based on the shapes of rollover panels and fault segments imaged in seismic reflection (depth)more » profiles. Rollover panels widen during progressive fault slip and are bound by anticlinal and synclinal axial surfaces. Rollover panels also narrow upward into syntectonic strata, which record the kinematics and timing of basin formation. They map axial surfaces to define the positions of fault bends and widths of rollover panels, which are related to slip on underlying fault segments. Structural highs form where fault segments decrease in dip along strike and/or in regions of minimum fault slip. These areas are defined on fault maps by shallow slopes or fault segments and on axial surface maps by narrow rollover limb widths. Structural highs formed during rifting and later tectonic inversion can be defined on these maps prior to detailed contouring, which is often difficult in frontier areas and in lacustrine sequences. They present examples of producing hydrocarbon fields defined by axial surface maps from the Central Sumatra basin.« less
  • During the early 1980s, ARCO Alaska, Inc., conducted an extensive hydrocarbon exploration program in the Alaskan Interior. The study focused on several basinal areas: Middle Tanana, Minchumina, Holitna, Yukon Flats, and Kandik. Other basinal areas (Upper Tanana, Lowre Tanana, and Yukon-Koyukuk) have been reported in the literature to have lower hydrocarbon potential and were not as extensively studied. Several geological and geophysical techniques, including gravity, aeromagnetic, and CDP seismic surveys, were used to establish sediment thickness, basin volume, morphology, and structural style. Analytical data were collected for hydrocarbon source, reservoir potential, and thermal history. Specialized structural and biostratigraphic studies weremore » conducted in some areas. The Middle Tanana and Kandik basins have the highest hydrocarbon potential. A 6-mi wide by 26-mi long half-graben within the Middle Tanana basin contains 20,000 ft of section. The 1984 ARCO Totek Hills 1 well penetrated 3,015 ft of Tertiary (Pliocene to Eocene) section unconformably overlying metamorphic basement. Because it was drilled on the basin flank, the well tested only the uppermost section within the half-graben. Sandstones averaged 17% porosity and 11 md permeability. Claystones containing type II kerogen showed good oil-generating potential (pyrolysis S1 + S2 values average 17 mg/g). The Kandik basin contains excellent source rocks in the Triassic Glen Shale (S2 averaging 16 mg/g). Hydrocarbon thermal maturation changes from immature to postmature in a stepwise fashion across thrust faults from southeast to northwest. Solid residue of migrated hydrocarbons occurs in formations of Devonian, Pennsylvanian, Permian, and Triasic age.« less