Класс Месторождения: Крупное
Тип Месторождения: Нефтегазовое
Местоположение:
Местность:
Стадия разработки: Добыча
Год открытия: 1999
Источник информации:
Метод открытия:
Площадь: 30.39 км²
Ceiba Field
Ceiba Field, offshore Equatorial Guinea approximately 75 km southwest of the port of Bata and 275 km south of the city of Malabo, was discovered with the drilling of Ceiba-1 in September 1999. The first appraisal well, Ceiba-2, was drilled in November 1999 approximately 1.6 km southwest of Ceiba-1. Both wells were based on interpretation of 2D seismic data acquired between 1984 and 1999. Open-hole logs, cores, pressure data, and a drill stem test of Ceiba-1 (maximum flow rate of 12 400 b/d) indicated that both wells contained Cretaceous sands of very high quality, capable of high rates of oil production.
Despite being between two prolific hydrocarbon provinces—Niger delta to the north and the Gabon coastal basin to the south (Figure 1)—Rio Muni Basin was essentially overlooked by the industry until the late 1990s. Six wells were drilled between 1968 and 1991 in the shelfal and onshore areas of the basin. These focused on Albian and Aptian aged objectives and, although they proved the presence of a viable source rock, the early wells did not result in the discovery of any oil accumulations.
Figure 1. Ceiba Field is offshore Equatorial Guinea approximately 75 km southwest of the port of Bata and 275 km south of the city of Malabo.
In 1997, following a review of the West African margin, Triton Energy identified a number of aspects of Rio Muni Basin that suggested an unexplored deepwater play. These included an immature oil-prone source in shelfal wells, which had the potential to be more deeply buried in the outboard part of the basin, and evidence for base of slope structuring on the margins of the shelf in the 2D data. The presence of shelfal canyons suggested that bypassed clastics could potentially be deposited in deepwater. The presence, in the Sergipe-Alagoas Basin of Brazil, of a similar Albian-Aptian stratigraphy which has generated a large volume of hydrocarbons, provided a direct analog to Rio Muni Basin which sits in a conjugate position on the opposite side of the Atlantic Ocean. In addition, the Late Cretaceous Batanga play in northern Gabon, in which a number of commercial hydrocarbon discoveries have been made, provided further support for the Rio Muni deepwater play concepts. On this basis, Triton Energy (later acquired by Amerada Hess) licensed blocks F and G (5270 km2 in area) covering both the shelfal and deepwater areas in the central part of the basin.
Figure 2. Stratigraphy of the Rio Muni area. Ceiba reservoirs are Santonian and Campanian in age. These are correlative to Mungo Formation in Douala Basin of Cameroon and Batanga Formation in North Gabon.
Seismic data used to define Ceiba. The Ceiba prospect was mapped on the 2D seismic vintages acquired from 1984 to 1998. The conventional 2D seismic data formed a regular but sparse grid of about 2 * 2 km. This was infilled during 1999 by a 2D high resolution short offset data set acquired during the site survey prior to the drilling of Ceiba-1 resulting in a final seismic coverage of approximately 200 * 370 m.
Following development of the regional structural and stratigraphic model, the key play fairway risks were interpreted to be working charge and reservoir presence. The location of Ceiba-1 was chosen to test a prospect in a structurally robust part of the slope area to assess these key fairway risks. High amplitude seismic events with class III AVO were present at this location according to the 2D data. Figures 5 and 6 are near- and far-angle stack sections illustrating the hydrocarbon-fill AVO effects over Ceiba prospect. These contrast with the amplitude effects of salt, which has a strong near- and far-angle stack amplitude of the opposite polarity.
Figure 3. This regional 2D seismic line is a northwest-southeast line across block G showing the main features of basin evolution. The line runs from the western flank of the southernmost Aptian inversion feature associated with the Ascension fault zone, and across the deepwater extension of the Bata anticline. It demonstrates the development of base of slope deformation, rafting, and ponding within associated lows—all of which has occurred in association with displacement on detachment surfaces at both base Albian and base Aptian salt.
Data quality of the 2D seismic acquired in 1984-1998 is good-to-excellent, although the quality of the 1999 high-resolution 2D data varies. The short-offset 1999 data are greatly affected by several canyons in the shallow stratigraphy and, because it is a higher frequency data set, the noise level is increased.
The Ceiba-1 exploration well was drilled in September 1999 and encountered a gross column of 226 m that contained 90 m of pay (Figure 4) in Campanian aged sandstone reservoirs. Porosity averaged 26%, oil saturation averaged 63%, and the permeability was up to several darcies. The well tested oil at a maximum flow rate of 12 400 b/d. The Ceiba 1 reservoir fluid was identified as an undersaturated 31° API crude with a gas-oil ratio of 575 standard ft3 per stock tank barrel (scf/stb). The bubble point pressure was determined to be 2875 psia with an initial formation volume factor of 1.35 reservoir barrels per stock tank barrel (rt/stb).
Figure 4. Ceiba 1 summary log. The Ceiba-1 discovery well was drillstem tested in October 1999 in a single perforated interval from 2281- 2330 m subsea. The main flow period generated the following rates-a low rate of 2300 b/d, a medium rate of about 4300 b/d, and a peak rate of 12 400 b/d. The Ceiba 1 reservoir fluid was identified as an undersaturated 31° API crude with a gas-oil ratio of 575 standard ft3 per stock tank barrel (scf/stb). The bubble point pressure was determined to be 2875 psia with an initial formation volume factor of 1.35 reservoir barrels per stock tank barrel (rt/stb).
The field is on the present-day continental slope in approximately 700 m of water. Depth to the crest of the structure at top Campanian level is approximately 2125 m true vertical depth subsea with the gross-oil column height in excess of 350 m. The underlying structure is interpreted to have formed by gravity sliding on the basal Albian detachment which was subsequently modified by salt movement and development of a westward verging “toe thrust” structure. This forms part of a base of slope compressional zone.
The oil column exceeds the structural spill point by 100 m, suggesting that a stratigraphic trap component is present in addition to the structural culmination (Figure 5). Subsequent appraisal and development drilling have confirmed this. The field is interpreted to be composed of a central anticline across which a Campanian deepwater channel complex developed. This channel complex is truncated to the north and south by mudstone-filled Tertiary canyons, which form the stratigraphic component of the trap. This trap geometry has isolated the aquifer on the western flank of the field from that on the eastern flank, resulting in two separate aquifers but a single continuous oil column.
Figure 5. Ceiba Field trap configuration. The Ceiba reservoirs are trapped between two later Tertiary channels. This figure shows the seismic amplitude and stratigraphic components of the field. The anticlinal structure of the field is shown by black contours.
Data source: Exploration and development of Ceiba Field, Rio Muni Basin, Southern Equatorial Guinea PAUL DAILLY, PHIL LOWRY, KENNY GOH, and GENE MONSON, Amerada Hess, Dallas, Texas,2002
Следующее Месторождение: Damrane 2