Summary
Choosing the most economic sand-control system from the available options is
a central component in field development planning. The choice of sand-control
system depends on a number of factors such as production and sand-control
performance, reserves recovery, reliability, ease of installation, and
life-cycle economics. Logistical and health, safety, and environment (HSE)
issues are also important, especially in areas with limited support
infrastructure.
A key input to the process of sand-control-system selection is data on how
the various systems compare in a given environment. Ideally, this comparison
should be made over time to compare properly long-term performance and
reliability. These data can be obtained only by analyzing existing
installations fairly and objectively.
The Mokoko-Abana field is situated offshore Cameroon. It is a mature
heavy-oil field with unconsolidated formations that require sand control from
the onset of production. A wide variety of sand-control solutions have been
used in this field, with varying levels of success and performance. Cased-hole
internal gravel packs (IGPs), milled-casing openhole underreamed gravel packs
(MCGPs), and cased-hole frac packs (CHFPs) have been used in vertical wells.
Prepacked standalone screens (PPSASs), openhole gravel packs (OHGPs), and
openhole expandable sand screens (OHESSs) have been used in horizontal and
highly deviated wells.
Each of the completion options now has several years of production history.
This allows their initial performance and their performance over time to be
modeled and compared. The wells chosen for study were in the same sand body
with an installation as close to perfect as possible. The MCGP had relatively
good performance, as did the CHFP; unfortunately, however, the CHFP fractured
into a water-bearing leg and only added water cut. The PPSAS had initially low
mechanical skins, but its performance declined quickly. The OHGP had higher
initial skins, but the rate of production decline was much slower. The OHESS
had a very low initial skin with no impairment over the 5-year production
period.
Mason et al. (2005) provide background information on the Mokoko-Abana field
and look at the productivity performance of the PPSAS, OHGP, and OHESS
techniques on initial completion and after 2 years of production. This paper
follows on from that work and examines the operational, productivity,
reliability, and economical aspects of the completion techniques over 5 years
or more of production.
Introduction
A comparison of the performance of sand-control completions in the
Mokoko-Abana field was carried out in 2004 and 2005. This study compared three
wells completed on the same oil sand with essentially the same hole size,
similar drilled trajectories, similar drilling mud, the same rig, and largely
the same personnel. All were successfully executed and can be considered as
objects of a fair and reasonable comparison. Each well at that time had at
least a 2-year production history. Differences in reservoir properties and in
artificial lift method and minor differences in fluid characteristics were
modeled and compensated for. The end result was a derived mechanical-skin value
for each completion system. The derived skin after 2 years’ production for the
PPSAS was +29.5, for the OHGP was +10.8, and for the OHESS was approximately
zero.
The Mokoko-Abana OHESS deployment was one of the earliest
expandable-sand-screen (ESSO) installations (number 26 out of 400 to date from
various vendors), and it is now possible to look at the completion performance
of this technology over several years.
The best sand-control completion is the one that is technically suited for
the particular application and then provides the user with the best value over
the life cycle of the well. Installation cost, productivity, and reliability
(both installation and production risk) are all important factors in achieving
this. Meaningful comparisons are usually available only in mature fields, where
different sand-control completions have been attempted over different time
periods. Skin data over time have not been studied in detail to date; most
studies report skin data within a short time period following completion
installation. This paper seeks to begin to address this issue and to provide
operators with a balanced and objective comparison among the systems carrying
on from the original Mason et al. (2005) study.
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
6 February 2006
- Revised manuscript received:
10 January 2007
- Manuscript approved:
22 January 2007
- Version of record:
20 June 2007
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