Summary
The use of multiple wells connected at a subsea manifold provides the
opportunity to reduce the number of risers and capital expense. The
problem is the proper modeling of the reservoir well flow coupled with the
combined flow into the facility network (i.e., manifolds, flowlines, and
risers), which is necessary to prevent underdesign, resulting in flow-rate
bottlenecks, or overdesign, resulting in extra expenditures. This paper
presents a tool and methodology for better modeling of the well-to-riser flow
and the optimization of riser count and configuration.
Although reservoir models coupled with facility networks is not new,
software enhancements provided the capability of including operation logic that
could duplicate operations in the field. The reservoir model coupled with
the facility network provided more reasonable and accurate modeling of
multiphase rates and pressures as wells were combined into a single
riser.
To optimize the riser count, operation logic was applied to maximize rate in
the riser at all times against the erosional-velocity limit. This in turn
prevented overdesigning by placing more risers than needed to obtain the
field-facility capacities.
The use of the coupled model and operation logic allowed the optimization of
the riser count for any particular reservoir model. The optimum riser
count was then determined for 3 earth (geologic) models.
Introduction
The Agbami structure is a northwest/southeast-trending four-way-closure
anticline and is located on the Niger delta front approximately 65 miles
offshore Nigeria in the Gulf of Guinea (see map in Fig. 1). The structure spans
an area of 45,000 acres at spill point and is located in 4,800 ft of water. The
Agbami No. 1 discovery well was drilled in late 1998. The appraisal program was
completed in 2001 and included five wells and one sidetrack drilled on the
structure, with each encountering oil pay. These five wells and a sidetrack
penetrated an average of approximately 350 ft of oil.
One of the key outcomes of the previous work phase (Phase 2) was the
selection of the facilities design. The Agbami team adopted an all-subsea
field-development scheme. This scheme involved modeling all field-production
and injection-fluid flow through numerous subsea
manifolds.
One of the important objectives in the current phase (Phase 3) of
development was to determine the optimum number and locations of the production
risers. The problem was determining how to properly model the reservoir
and facility design such that the impact of riser count can be properly
quantified. The determination of this impact was necessary to make a
quality decision on the riser count and configuration.
© 2006. Society of Petroleum Engineers
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History
- Original manuscript received:
11 June 2004
- Revised manuscript received:
20 December 2005
- Manuscript approved:
23 December 2005
- Version of record:
20 August 2006
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