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Bolivar Coastal Complex | |
---|---|
Country | Venezuela |
Region | Bolivar |
Location | Lake Maracaibo |
Offshore/onshore | Onshore/Offshore |
Coordinates | 9.385971, -71.800428 |
Operator | PDVSA |
Field history | |
Discovery | 1914 |
Start of development | 1917 |
Start of production | 1922 |
Production | |
Current production of oil | 2,600,000 barrels per day (~1.3×10 8 t/a) |
Estimated oil in place | 44,000 million barrels (~6.0×10 9 t) |
Recoverable oil | 3,032,000 million barrels (~4.136×10 11 t) |
Producing formations | La Luna Colón |
Maracaibo Basin: Bolivar Coastal Complex
The Bolivar Coastal Fields (BCF), also known as the Bolivar Coastal Complex, is located on the eastern margin of Lake Maracaibo,
History
The large oil seeps around Lake Maracaibo were noted in the 16th century by the Spanish, who used the tar to caulk their ships and treat skin problems on livestock. The U.S. based General Asphalt Co. conducted the first geological investigations on the east shore of Lake Maracaibo but sold its concession to
Nationalism then played a role in the oil industry; no new exploration concessions were offered after 1958, and the industry was nationalized at the end of 1975. The nationalized entity, Petroleos de Venezuela SA, is now one of the world's largest integrated oil companies.
The award of marginal field reactivation blocks to
In summary, the Maracaibo basin oil fields played a major role in the growth of three of the world's largest oil companies; the Royal Dutch/Shell group, Exxon, and Petroleos de Venezuela. Much early development of the technologies of offshore production and steam injection took place there.
Sir Henri Deterding once described Shell's purchase of the General Asphalt properties around Lake Maracaibo as his best business deal. That is a strong statement from someone whose business deals included the merger of
Introduction
The Gulf Caribbean region currently contains 5% of the total ultimate recoverable reserves of hydrocarbons on Earth (Horn, 2003). Venezuela has the largest reserves of hydrocarbons of all the hydrocarbon regions of the western hemisphere, with proved oil reserves of about 70 billion bbl oil and proved gas reserves of 147 tcf (U.S. Geological Survey, 2000; Audemard and Serrano, 2001). These reserve estimates do not include the immense, unconventional reserves of the Orinoco heavy oil belt, with an estimated approximately 1200 billion bbl of heavy and extra-heavy oil in place (Fiorillo, 1987; U.S. Geological Survey, 2000). [5] The active tectonic setting of petroleum in Venezuela is complex. Several tectonic belts that include volcanic-arc, fore-arc, and back-arc basins are found offshore of the Venezuelan margin. A west-to-east lounging pattern of thrusts and lateral ramp faults and foreland basins onshore (Babb and Mann, 1999; Mann, 1999) were produced by diachronous oblique convergence between Caribbean arc terranes and the South American continental margin from Late Cretaceous (western area of Colombia) to the present (eastern area of Trinidad) . This ideal combination of tectonic and stratigraphic events yielded one of the most prolific petroleum systems in the world.
Geology
The deposition of rift-related rocks in the Late Jurassic marked the beginning of the sedimentary geological history of the Maracaibo Basin in structural lows or half grabens controlled by linear, north-northeast–striking normal faults. During the Early Cretaceous–Paleocene, a mixed clastic-carbonate platform developed across the area of present-day Maracaibo Basin. Thermal subsidence and tectonic quiescence of the passive margin led to sediment accumulation and the absence of deformation of the basin during this period. The few structures present in the Maracaibo Basin during the Cretaceous formed by tectonic uplift of the Western and Central Cordilleras of Colombia. This uplift is responsible for an increase in subsidence by the end of the Cretaceous that resulted in deposition of thick marine shale of the Colon Formation during the Maastrichtian. During the late Turonian–Campanian, the La Luna Formation was deposited in a shelf-slope setting under anoxic conditions. The La Luna Formation became the main source rock of northwestern South America.
In the late
Petroleum Systems
The figure below shows the hydrocarbon reservoirs in the Maracaibo basin. Most Eocene reservoir rocks are spatially aligned with the north-south–striking Icotea and Pueblo Viejo faults, whereas most Miocene reservoirs rocks are clustered along the eastern and northeastern margin of the present-day Lake Maracaibo.
Ninety four percent of hydrocarbon reservoirs in the Maracaibo Basin are found within Eocene–Miocene clastic rocks (Talukdar and Marcano, 1994). Only 6% of reservoirs are found within underlying Cretaceous–Paleocene carbonate rocks and basement.[5]
The figure to the right shows an east-west and a north-south interpreted seismic line in the central Maracaibo Basin, summarizing the main elements of the Maracaibo
Source Rocks
Hydrocarbon source rocks in the Maracaibo Basin are Upper Cretaceous marine carbonate rocks (calcareous shales and argillaceous limestones) that make up the La Luna Formation of
A Santonian change in depositional environment to more oxygenated and cooler waters in the La Luna Formation (Tres Esquinas Member) suggests the advent of tectonic activity (Erlich et al., 2000; Bralower and Lorente; 2003; Parra et al., 2003; Zapata et al., 2003). Late Cretaceous tectonic activity was possibly related to the reactivation of faults beneath the basin or regional plate convergence in western Colombia that caused abrupt changes in the paleotopography and paleoclimate and ended passive-margin conditions. An increase in upwelling and more oxygenation of shelf waters of northern South America may be related to (1) the migration of the South American plate toward the Cretaceous intertropical convergence zone (Villamil et al., 1999); (2) an increase in freshwater runoff produced by the emergent Central Cordillera of Colombia (Erlich et al., 2003); and (3) the establishment of wet-dry cycles and submersion of paleobathymetric barriers for ocean circulation (Erlich et al., 2003).[5]
La Luna Source Rocks and Hydrocarbon Characteristics
The La Luna formation is the most prominent formation in the Maracaibo Basin and is the source rock content for majority of Bolivar Coastal Field. This is considerded to be a great oil-prone source rock. At the figure to the right, the distribution in percentages of hydrocarbon generated by the La Luna formation source rocks is shown.
Comparison of gas-chromatographic and biomarker characteristics of oils and La Luna source rock extracts shows that the La Luna Formation is the source rock for more than 98% of the oil accumulations in the Maracaibo Basin. The La Luna source rocks contain oil-prone type II kerogen and are rich in hydrogen content, with the bulk of the organic matter derived from algae and bacteria (Perez-Infante et al., 1996). The average original total organic carbon (TOC) of La Luna source rocks in the Maracaibo Basin is 5.6%. Maximum TOC values are locally as high as 16.7% . In the southwestern area of the basin, the average TOC is 4.3% . In the Sierra de Perij area, TOC values range from 3.7 to 5.7%. In the Merida Andes, TOC values range between 1.7 and 2%. At the figure to the right, the distribution in percentages of hydrocarbon generated by the La Luna formation source rocks is shown. Comparison of gas-chromatographic and biomarker characteristics of oils and La Luna source rock extracts shows that the La Luna Formation is the source rock for more than 98% of the oil accumulations in the Maracaibo Basin.
Reservoir Rocks
They are a wide variety of reservoir rocks throughout the Maracaibo Basin, ranging from metamorphic rocks to shallow, unconsolidated, Miocence rocks. According to Harding and Tuminas, structural traps are controlled by a variety of features, including
- Sub-Eocene Reservoirs
- Cretaceous limestone and Paleocene sandstone
- Reservoirs include fractured rocks associated with the reactivation of north-south strike-slip, northwest-southeast–striking normal fault, and thrusts related to the uplift of Merida Andes
- Eocene Reservoirs
- Most prolific
- Structural traps associated with anticlines (i.e Icotea and Pueblo faults)
- Eocene unconfromity forms traps in fluvial deltaic sandstone
- Miocene Reservoirs
- Second most prolific
- Fluvial Miocene sandstone facies located in anticlines
- Stratigraphic wedges beneath Eocene unconformity (i.e Burro Negro fault)
- Oil escaped to the surface and formed seeps that outline the edges of the Maracaibo basin where no structural or stratigraphic traps were present
Migration and Trapping
Petroleum geologists summarize the petroleum system evolution of the Maracaibo Basin in four phases. The image to the right shows the four main tectonic phases controlling the petroleum system of the Maracaibo Basin.
Carbonate Platform Phase
During this phase in the Late Cretaceous to Paleocene, the La Luna Formation source rock was deposited on a shallow, passive-margin, shelf-to-slope environment. It thickness ranges from 40 to 150 m (131 to 492 ft). Carbonate thickness variations were controlled by minor basement relief of underlying pre-Cretaceous structures like the Merida arch.[5]
Foreland Phase
During the early Eocene, oblique collision between the Caribbean and South American plates formed an asymmetric wedge of fluvial-deltaic Eocene rocks that were deposited in a foreland basin (Lugo and Mann, 1995; Escalona and Mann, 2006a). Cretaceous source rocks were buried to depths of 5 km (3.1 mi) in the north-northeastern part of the Maracaibo Basin and reached the oil window. A pull-apart basin controlled by reactivated Jurassic north-northeast–striking faults formed in the central Maracaibo Basin (Icotea subbasin; Escalona and Mann, 2003b). Strike-slip faults provided vertical pathways for hydrocarbon migration from Cretaceous source rocks (La Luna Formation) to Eocene reservoir sands.[5]
Isostatic Rebound Phase
During the late Eocene to
Maracaibo Syncline Phase
During the
Future
The complex interplay of deformation, burial, and sedimentation in the Maracaibo Basin during the Cretaceous combined to make the basin one of the most effective and prolific petroleum systems on Earth. Deposition and distribution of ideal source and reservoir rocks were stratigraphically and structurally controlled by multiple tectonic events that led to hydrocarbon generation, migration, and accumulation. [6]The Maracaibo Basin has a promising hydrocarbon discovery potential in the mostly undrilled deeper structural and stratigraphic traps of the central and eastern basin (e.g., Icotea and Pueblo Viejo subbasins) . More than 14 billion bbl of medium to light oil of ultimate recoverable reserves are predicted to be produced from these areas (U.S. Geological Survey, 2000). The Maracaibo basin has a long history as a major oil producing basin, but many areas remain poorly explored. The large exploration potential combined with the enormous amount of remaining oil in place in known reservoirs guarantees that the Maracaibo basin will have a long future as a major oil producing basin.[4]
See Also
- conventional oilfieldin the world
- List of oil fields, list of most notable oilfields in the world
- Petrocaribe, oil alliance of many Caribbean states with Venezuela to purchase oil on conditions of preferential payment
- Oil reserves in Venezuela, additional quantitative data on Venezuela's reserves
- A Large Heavy Oil Reservoir in Lake Maracaibo Basin: Cyclic Steam Injection Experiences, SPE paper technical paper on steam injection in the BCF
References
- ISSN 0149-1423.
- ^ "South America: Northwestern corner of Venezuela | Ecoregions | WWF". World Wildlife Fund. Retrieved 2017-11-28.
- ^ "PDVSA". Wikipedia. 2017-09-20.
- ^ a b Stauffer, Karl (6/05/1995). "A MODERN LOOK AT THE PETROLEUM GEOLOGY OF THE MARACAIBO BASIN, VENEZUELA". www.ogj.com. Retrieved 2017-11-28.
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(help) - ^ ISSN 0149-1423.
- ^ "The List: Taking Oil Fields Offline". Foreign Policy. Retrieved 2017-11-29.