Bolivar Coastal Fields
The Bolivar Coastal Fields, also known as the Bolivar Coastal Complex, is located on the eastern margin of Lake Maracaibo, Venezuela. Bolivar Coastal Field is the largest oil field in South America with its 6,000-7,000 wells and forest of related derricks, stretches thirty-five miles along the north-east coast of Lake Maracaibo. They form the largest oil field outside of the Middle East and contain mostly heavy oil with a gravity less than 22 degrees API. Also known as the Eastern Coast Fields, Bolivar Coastal Oil Field consists of Tía Juana, Lagunillas, Bachaquero, Ceuta, Motatán, Barua and Ambrosio. The Bolivar Coast field lies in the Maracaibo dry forests ecoregion, which has been severely damaged by farming and ranching as well as oil exploitation. The oil field still plays an important role in production from the nation with approximately 2.6 million barrels of oil a day. It is important to note that the oil and gas industry refers to the Bolivar Coastal Complex as a single oilfield, in spite of the fact that the oilfield consists of many sub-fields as stated above.
Bolivar Coastal Complex is entirely owned and operated by Petróleos de Venezuela, S.A. , the Venezuelan state-owned oil
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 Company conducted the first geological investigations on the east shore of Lake Maracaibo but sold its concession to Royal Dutch Shell in 1912. Shell drilled the discovery well at Mene Grande in 1914 and the famous Los Barrosos 2 gusher at Cabimas in 1922. Another major find was the 'Zumaque 1' well in 1914, in the area of Mene Grande, Maracaibo Basin, about southeast of Cabimas. Production grew rapidly and this became Shell's most important producing property worldwide. Edward Doheny's Pan American Oil then took the unusual step of obtaining concessions in the lake itself. These concessions were purchased by Indiana Standard in 1925, but development was minimal until they were sold to Standard Oil of New Jersey in 1931. Development in Lake Maracaibo proceeded rapidly after the end of the Second World War and this became Exxon's most important producing property worldwide throughout the 1950s and 1960s.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 Occidental and Shell in 1994 marked the beginning of a new phase of international participation in the Maracaibo basin. Another block was subsequently awarded to a consortium of Tecpetrol, Nomeco, and Wascana, and Chevron has agreed in principal with Maraven, a subsidiary of Petroleos de Venezuela, on a venture that would include the giant Boscan heavy oil field and Chevron's asphalt division in the U.S. Two blocks in the basin are to be offered in the 1995 exploration round.
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 Royal Dutch Petroleum with Shell Transport and Trading.
Introduction
The Gulf Caribbean region currently contains 5% of the total ultimate recoverable reserves of hydrocarbons on Earth. 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 . 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. 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 were produced by diachronous oblique convergence between Caribbean arc terranes and the South American continental margin from Late Cretaceous to the present. 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 Paleocene and early to middle Eocene, the Caribbean plate and the northwestern margin of South America produced a complex foreland wedge filled by clastic sediments in the northeastern part of the Maracaibo Basin. The foreland basin was characterized by an approximately 5-km -thick Eocene wedge of fluvial-deltaic sedimentation, where the most prolific hydrocarbon reservoirs of the Maracaibo Basin are concentrated. Fluvial and shallow-marine sedimentation continued in the south and southwest areas of the Maracaibo Basin. The Eocene unconformity represents the main seal above Eocene reservoirs, but it is locally breached by faulting, allowing the upward ascent of hydrocarbons into Miocene reservoirs at the basin edges.
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. Only 6% of reservoirs are found within underlying Cretaceous–Paleocene carbonate rocks and basement.
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 petroleum system from Cretaceous source rock to Eocene and Miocene reservoirs. The two interpreted seismic lines show the northeast thickening of the Eocene clastic wedge, the southwest thickening of the Miocene–Holocene clastic wedge, and the main structural and stratigraphic controls of the basin inherited from the north-northeast–striking fault family.
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 considered 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. The average original total organic carbon 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 Perijá 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 normal fault, inverted faults on the flexed continental plate. Stratigraphic traps are found in heterogeneous, mixed fluvial, and tidal-dominated deltaic systems defining regressive-transgressive cycles on the Eocene Maracaibo shelf and nearshore to fluvial Miocene sandstone rocks. Major reservoir facies are stacked distributary channels and tidal bars. Hydrocarbon reservoirs can be classified in three main types:- 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
- * 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
- * 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