Summary
Although the stacked reservoirs of the Bokor field, offshore Sarawak,
Malaysia, are prone to sand production, the field-development team did not opt
a priori for gravel packs in every well. While such completions can
indeed eliminate sanding risk, the team also wanted to consider the impact of
the completion on the production rate of a well. The optimum completion not
only excludes sand, but it also maximizes hydrocarbon production.
The team carried out a geomechanics and sand-production study, using readily
available data. The paper gives an insight in the physics of sand production
and how this process can be modeled geomechanically. It shows how the model is
used to select feasible completions and quantify sand-free production rates
over the life of the reservoir.
One important outcome was that screenless completions were possible in the
deeper reservoirs by optimizing perforation orientations. Apart from other
advantages of screenless completions, this leads to significant potential
increases in sand-free production rates.
An integrated sand-management process brought together geomechanics,
petrophysics, and reservoir and completion engineering to truly optimize
completions.
Introduction
Certain questions have to be answered before completing a well in a
weak-sandstone reservoir: Will sand production be an issue now, or as the
reservoir depletes? If so, which completion options are feasible, and when do
they need to be installed? Several techniques exist to prevent sand from being
produced, from screens, gravel packs, or frac packs to optimized and oriented
perforating, each with its own merits. But the choice of completion also has a
major impact on hydrocarbon-production rates, and therefore on the lifelong
economics of a well. To truly maximize sand-free hydrocarbon production, an
integrated approach is needed. This includes reservoir knowledge from
petrophysical and geomechanical interpretations, reservoir and production
engineering, completion design, and implementation.
If it can be shown that sand production is going to be a problem, screens,
gravel packs, or frac packs can be run. The choice of sand-exclusion equipment
will likely have an impact on productivity, which needs to be considered.
The industry has become aware that oriented perforations can prevent sand
production in many cases. Oriented-perforation completions have an advantage
that they minimize the cost and complexity of the completion. More importantly,
they also generally give higher production rates than a screen or gravel pack
would give in the same well.
Clearly, there is a need to predict reliably under which circumstances the
technique of oriented perforating can prevent sand production. Geomechanical
analysis can provide the answer. While no generally accepted models exist today
that can predict rates or total amounts of sand production, we are able to
predict the onset of sand production with reasonable accuracy. In many cases,
such a prediction is enough to make an informed decision.
The Bokor field in the Baram delta, offshore Sarawak, Malaysia, has produced
oil since 1982. Its unconsolidated, stacked reservoirs are prone to sand
production and were completed traditionally with gravel packs. In 2003, a full
field-review study identified new development opportunities, including deeper,
previously untapped reservoirs.
Given new developments in geomechanics and sanding-prediction models, the
study team did not opt a priori for gravel packs in every well. While
such completions can indeed eliminate sanding risk, the team also wanted to
consider the impact of the completions on the production rates of the wells.
The optimum completion not only excludes sand but also maximizes hydrocarbon
production over the life of the well.
The team seized the opportunity to conduct a sanding-propensity study to
gain an understanding of sand-production risks and to optimize completion
designs. Geomechanical modeling played an important role in the study.
In this paper, we aim to give an insight into some aspects of the physics of
sand production and how the process can be modeled geomechanically. We explain
how geomechanical models were built from readily available data and how the
models were used to select feasible completions and compute critical drawdown
pressures (CDP) for various completion scenarios. We discuss how this helps the
Bokor-field study team quantify sand-free production rates, now and over the
life of the reservoir, and we comment on the role of geomechanical modeling in
the integrated, multidisciplinary approach that is needed to optimize
completions.
© 2008. Society of Petroleum Engineers
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History
- Original manuscript received:
6 July 2006
- Meeting paper published:
24 September 2006
- Revised manuscript received:
15 April 2008
- Manuscript approved:
10 April 2008
- Version of record:
10 December 2008
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