Summary
The Etame oil field, offshore Gabon, West Africa, has been producing since
September 2002. The Etame oil reservoir is an oval-shaped, low-relief structure
with a moderate aquifer drive. To maximize ultimate field recovery, the ET-6H
well was drilled with a horizontal lateral positioned to traverse the reservoir
near the structural crest and to be within the Upper Gamba sandstone throughout
its length. The Gamba sandstone averages 45 ft in thickness and overlies a
significant angular unconformity. The subcropping Dentale-aged sandstones and
interbedded shales below this unconformity have dips to 12°. The oil column of
approximately 170 ft extends below this unconformity. Previous wells in the
field were completed using openhole horizontal gravel packs (OHGPs) and have
experienced excellent sand-control performance. However, OHGPs offer no
protection against early water breakthrough. The Gamba sand averages 30%
porosity with a permeability range of 1 to 3 darcies. The Dentale sands are
much more variable, with porosities of 18 to 30% and a permeability range of 50
to 1,000 md. Thus, if a portion of the lateral is situated immediately above a
high-permeability Dentale sand, the well will be at risk of early water
breakthrough and subsequent reduced recovery if it is completed with a standard
OHGP.
The operator gravel packed the ET-6H well and used a system that provides a
near-uniform inflow profile along the entire lateral length to protect against
early water breakthrough. The gravel packing of inflow-control devices (ICDs)
presented some unique challenges because of their differences from standard
sand-control screens.
This paper describes the implementation of the world’s first gravel packed
inflow-control completion, including: inflow-control device selection process,
gravel-pack design, data from the gravel-pack operation, and resulting well
performance.
Etame
The structure of the top Gamba sandstone at Etame field is shown in Fig.
1 (depths are in meters). The three previous horizontal OHGP completions
are shown in orange, and the ET-6H completion is shown in red. The discovery
well for the field (the ET-1VA well on the southeast flank) was completed with
an OHGP as a vertical well.
Fig. 2 illustrates how the Gamba sandstone is draped over the
subcropping Dentale formation at a significant unconformity surface. Pilot-hole
drilling confirmed that the Gamba and Dentale sandstones have a common
oil/water contact (OWC) in all but the southeast portion of the field (Gill and
Cameron 2002). The aquifer is obviously quite complex. Additionally, there is a
lack of seismic resolution of these Dentale sandstones. When this is coupled
with their variable distribution, it makes it difficult to avoid placing a
lateral drain over a potentially high permeability Dentale sandstone. An
inflow-control completion is, therefore, desirable.
The Gamba sandstone, which is Cretaceous in age, is remarkably
unconsolidated. Fig. 3 is a thin-section photomicrograph illustrating
the high porosity and unconsolidated nature of this fine-to medium-grained
sandstone. Minimizing fines migration is another important aspect of the
completion design.
© 2008. Society of Petroleum Engineers
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History
- Original manuscript received:
4 October 2006
- Meeting paper published:
24 September 2006
- Revised manuscript received:
14 May 2007
- Manuscript approved:
8 September 2007
- Version of record:
20 March 2008
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