Agbami Field
The Agbami Field, Blocks OPL 216 and 217, Niger Delta
G. O. AYENI (200202549)
M. Sc Exploration Geophysics, University of Leeds
Management Summary
The Agbami field with recoverable crude potential in excess of 1 billion barrels is
among the largest single finds to date in deepwater West Africa and Nigeria’s
largest oilfield. The vastness of the oil field called for participation from a
consortium of oil companies and the Nigerian government. With an estimated
production rate of 250,000 BOPD and 450,000 (Mcf/D) gas expected to
commence in 2007, major facilities including an FPSO and 40 tree subsea
system are currently being installed.
Introduction
Agbami Field is located between latitude 30 30’N and 30 50’N and longitude
latitude 40 45’E and 40 58’E, 220 miles south-east of Lagos and 70 miles offshore
Nigeria, in the central Niger Delta (Figure 1). The field discovered in late 1998 is
about 150Km west of Akpo field and 200Km SE of Bonga field straddling
concession blocks OPL216 and 217 in approximately 4500 meters of water in the
Gulf of Guinea (See Figure 2). Agbami field is Nigeria’s largest field and one of
the 10 largest discoveries of the 1990s with peak production estimated at
250,000 barrels of oil a day by 2007 and capital investments projected at $3.5 to
$4 billion (Appelbaum, 2000).
The Agbami structure is a 30Km long northwest/southeast trending doubly
plunging thrust-faulted, detachment-fold anticline covering an area of 45,000
acres (Appelbaum, 2002 and ChevronTexaco, 2003a). The field is in a lower
slope environment outboard of the modern shelf slope break (Figure 1) in a
Miocene-to-recent depobelt where structure is dominated by detachment folds,
shale ridges and toe thrust anticlines induced by upslope extensional growth
faulting on the outer shelf margin (Shirley, 2002). According to Grimes et al
(2004), the pay intervals consist of two principal zones namely; primary
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reservoirs -17 million year (MY) old sands - and shallower productive secondary
reservoirs -13MY/14MY/16MY sands.
Figure 1. Map of the Niger Delta showing location of the Agbami Field. (Adapted
from the Korea Engineering consultancy (KEC) website)
History
Licensing
Famfa Oil Limited was awarded the leasehold rights to OPL 216 in August 1993
and signed a farm-in agreement with Star Deepwater Petroleum Limited (a
wholly owned ChevronTexaco subsidiary) in 1996 wherein Star was designated
as technical advisor for the block. In 1998, 20% of Star’s interest in the block was
assigned to Petroleo Brasileiro Nigeria Limited (ChevronTexaco, 2001). In March
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2000, the Nigerian Government acquired an interest in OPL 216, obtaining a
portion of Famfa’s interest. The OPL 217 contractor working interest partners are
Statoil (54%) and Texaco Nigeria Outer Shelf (46%) pursuant to a Production
Sharing Contract (PSC) with the Nigeria National Petroleum Company
(ChevronTexaco, 2001, 2003 & 2005). Other concessions and production fields
around the Agbami field are shown in Figure 2.
Figure 2. Map showing major production fields in offshore Niger Delta. Agbami Field
highlighted (pink). (Adapted from the Nigeria Sao Tome Joint Development Zone (JDZ)
website)
To minimize cycle time to first oil, preliminary facility design/engineering was
carried out concurrently during the field appraisal phase. The project gained
sanction approvals in late 2003 and early 2004, and major facility construction
contracts (including the construction of a $1.1 billion FPSO to Daewoo Shipping
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and Marine Engineering) in 2004 and 2005 with first production expected in 2007
(ChevronTexaco, 2001 & 2005).
Exploration
An insight into the tectono-stratigraphic evolution of Agbami field (and the deepwater Niger Delta as a whole) is well illustrated in a regional 2D multi-client
seismic section shown in Figure 3.
3D seismic data was acquired over the 617,000-acre OPL Block 216 after
exploration right was granted in late 1996. Acquisition, processing and
interpretation of the seismic data were done using Texaco's 3D visualization
technology (Appelbaum, 2002). The seismic reflections from the shallower,
secondary reservoirs occur above the water bottom multiple and are of relatively
good quality whereas the seismic data from the deeper, main pay intervals in the
17MY interval suffer from significant multiple energy contamination (Grimes et al,
2004).
Figure 3. 2D Multi-client seismic section around the Agbami field showing typical structural
traps. (Adapted from the Nigeria Sao Tome Joint Development Zone (JDZ) website)
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The discovery well Agbami-1, completed in January 2000, encountered 420 net
feet of pay, in multiple oil zones from 8,200ft to the total depth of 12,400ft
(Appelbaum, 2002). The well penetrated stacked reservoir sands saturated with
oil, ranging in overall column thickness from 400 to over 1,000ft. The quality of
the oil from these zones is 35-45 degree API gravity, with very low sulphur
content and preliminary data indicates the reservoirs contain several hundred
million barrels of recoverable oil (Appelbaum, 2002 and SPG, 2006).
Drilling and Appraisal
The Agbami-2 appraisal well drilled in 2000 encountered 534ft of pay in five
separate oil-bearing zones, one of which flowed at a maximum rate of
10,000bopd and wellhead pressure of 2,200psi with surface equipment
limitations prevented the achievement of a higher flow rate (Appelbaum, 2002).
The well proved that the structure had recoverable reserves of about one billion
barrels of oil equivalent (SPG, 2006). Statoil drilled the Ekoli 1 well into the same
structure in adjacent Block OPL217 around the same time (Grimes et al, 2004).
Before development plans were considered, a four-well appraisal program was
conducted in 2001 to confirm earlier reserve figures, define the productive limits
of the field and establish reservoir continuity (ChevronTexaco, 2001). The results
formed the basis of a development plan incorporating conceptual facilities
design, reserves, production rates and optimization of development drilling
(Appelbaum, 2002).
Field Stratigraphy
The stratigraphy of the Niger Delta is divided into three diachronous units of
Eocene to Recent age that form a major regressive cycle (Figure 4). The
reservoir section penetrated by the Agbami Field appraisal wells comprises four
distinct stratigraphic units that range from Lower Miocene (Burdigalian) to Middle
Miocene (Serravalian) and falls entirely within the marine, sand and shale
lithostratigraphic unit of the Akata Formation (Short and Stauble 1967 and
Avbovbo 1978).
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Agbami Field
Figure 4. General stratigraphic section of the Niger Delta showing the major stratigraphic
units in the area. (Adapted from the Nigeria Sao Tome Joint Development Zone (JDZ)
website)
Oligocene and earliest Miocene sediments deposited over the Akata shale
Formation are middle to lower bathyal shales and basin floor fans with broad
areal distribution. According to Shirley (2002) the biostratigraphy and facies
analyses of the Agbami 1 and 2 wells have confirmed bathyal environments
within the middle Miocene slope channel, slope fan and basin floor fan facies. As
the shelf prograded outward, depositional loading induced structural folding,
beginning about 12.5 million years ago. This has resulted in bathymetric features
that channelized subsequent sedimentation, leading to channel-levee type
deposition (Shirley, 2002). The regional depositional and structural environment
of Agbami field is shown in Figure 5.
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Agbami
Figure 5. Structural and depositional subdivisions of deepwater Niger Delta. (Adapted from
the Nigeria Sao Tome Joint Development Zone (JDZ) website)
Geophysics
The seismic reflections from the shallower, secondary reservoirs occur above the
water bottom multiple and are of relatively good quality whereas the seismic data
from the deeper, main pay intervals in the 17MY reservoir suffer from significant
multiple energy contamination (Grimes et al, 2004). Also due to the limited
frequency content of the seismic data, stratigraphic information from seismic was
restricted to the identification of thick, sandstone-prone fairways that were
mapped throughout the field. Although on-going reprocessing may eliminate the
multiples, to better image the reflectors from the inboard limb of the fold at the
northwest end of the structure, seismic data may be re-acquired parallel to the
thrust front (Grimes et al, 2004).
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Trap
The trap (Figures 3 and 6) is an Anticline characterized by crestal extensional
faulting of the Pleistocene to upper Miocene sequences over middle Miocene to
Paleocene strata that were thrust-faulted and later uplifted by a shale-cored
detachment fold (Shirley, 2002).
Figure 6. Reservoir Model Framework of the Agbami Field showing different reservoir
horizons. (Adapted from Grimes et al, 2004)
Reservoir
The pay intervals consist of two principal zones namely; primary reservoirs (17
million year old sands containing about 80% of the reserves) made up of slope
channel, slope fan, and basin floor fan facies and shallower productive
secondary reservoirs (13MY/14MY/16MY sands containing 20% of the reserves)
comprised of channel and levee-overbank facies (Grimes et al, 2004).
Grimes et al (2004) give a detailed overview of potential range of depositional
systems and associated in-place volumes and connectivities caused by variable
net-to-gross and reservoir architecture.
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Source
Although source rock potential exists in lacustrine deposits of the pre-delta rift
sequences, the Akata shale is considered the principal source rock in the Agbami
field and indeed for most of the other fields in the Niger Delta (JDZ, 2004).
Additional thermal modeling indicates that sediments in the area are within the
maturity window.
Hydrocarbon reserves/Resources
The five wells drilled so far in the Agbami field penetrated an average of 107m of
oil with production test results suggesting a recoverable reserve potential of 1.0
billion stock tank bbl (STB) of sweet crude (ChevronTexaco, 2001, 2003, 2005
and Famfa, 2005).
According to Narahara et al (2005), the facility design capacity for the field
includes:
- 250,000 stock-tank bbl per day (STB/D) oil.
- 450,000 thousand cubic ft per day (Mcf/D) gas production.
- 250,000 STB/D water production.
- 450,000 STB/D liquid production.
- 450,000 STB/D water injection.
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References
Appelbaum, B., 2002. A premier for Global Success: Science, Alliance Yields
Agbami. American Association of Petroleum Geologists February 2002 Explorer
magazine. (Online at http://www.aapg.org/explorer/2002/02feb/agbami.cfm).
Date visited: 10th March 2006.
Avbovbo, A., 1978. Tertiary lithostratigraphy of Niger Delta. Association of
Petroleum Geologists Bulletin, v. 62, no. 2, p. 295-300.
ChevronTexaco, 2001. Texaco Press Release Archive. (Online at
http://www.chevron.com/news/archive/texaco_press/2001/pr8_9.asp).
Date
visited: 10th March 2006.
ChevronTexaco,
2003.
Online
Press
Reports.
(Available
at:
http://www.chevron.com/news/press/2003/2003-07-14.asp ). Date visited: 10th
March 2006.
Chevron, 2005. Online Press Reports. (Available at (http://www.chevron.com/
news/press/2005/2005-02-22.asp). Date visited: 10th March 2006.
Famfa, 2005. Famfa Oil Limited website. (Online at: http://www.famfa.com/).
Date visited: 11th March 2006.
Grimes, D., Ginger, E. and Spokes, J., 2004. Agbami Field, Nigeria–Addressing
Challenges and Uncertainty. Houston Geological Society International Group
Meeting June 21, 2004. (online at: http://www.hgs.org/en/articles/printview
.asp?209). Date visited: 10th March 2006.
JDZ, 2004. Nigeria Sao Tome Joint Development Zone: Guide to 2004 licensing
round (online at: http://www.nigeriasaotomejda.com/PDFs/JDZ%20Brochure.pdf).
Date visited: 10th March 2006.
KEC, 2005. Korean Engineering Consultancy Company website. (Online at:
http://www.hkecc.co.kr/images_index/agbami%20location.jpg)
Narahara, G.M.; Spokes, J.J.; Brennan, D.D.; Maxwell, G.; Bast, M., 2005.
Incorporating Uncertainties in Well-Count Optimization with Experimental Design
for the Deepwater Agbami Field. Reservoir Evaluation & Engineering Journal
Issue, Volume 8, Number 6, pp. 548-560. (Online at: http://www.spe.org/
elibinfo/eJournal_Papers/spe/2005/EREE/12/SPE-91012-PA/SPE-91012-PA.htm
Shirley, K., 2002. Agbami: a 20-Mile Long Thrust-Faulted Anticline. American
Association of Petroleum Geologists February 2002 Explorer magazine. (Online
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at http://www.aapg.org/explorer/2002/02feb/agbami_geology.cfm). Date visited:
10th March 2006.
Short, K. C. and Stauble A. J., 1967. Outline of geology of Niger delta.American
Association of Petroleum Geologists Bulletin, v. 51, no. 5, p. 761-799.
SPG, 2006. SPG Media Limited website: Agbami Discovery Well, Niger Delta,
Nigeria. (Online at http://www.offshore-technology.com/projects/agbami/
index.html #agbami2
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