Summary
Installing sand control in long horizontal wells is difficult and
particularly challenging in offshore fields. It is, therefore, imperative to
make decisions with regard to the most optimum completion type objectively and
based on reliable assessment of the sanding potential and its severity over the
life of the well for the intended production target. This paper introduces a
predictive tool that forecasts not only the initiation of sanding, but also its
rate and severity in real time.
A series of well-documented experiments on a large-size horizontal wellbore
was simulated using a finite difference numerical model. The model accounts for
the interaction between fluid flow and mechanical deformation of the medium,
capturing various mechanisms of failure. The model allows capturing the
episodic nature of sanding and the resulting changes in the geometry and
formation consistency and behavior within the sand impacted regions. Sand
detachment is simulated by removal of the elements that are deemed to have
satisfied the criteria for sanding based on considerations of physics, material
behaviour and laws of mechanics. The proposed numerical model is designed to
account for many of the factors and mechanisms that are known to influence
sanding in the field and as such can be used as a practical tool for predicting
the frequency and severity of sand bursts and changes in operating conditions
that can be considered for mitigating or managing such problems.
The model shows reasonable agreement with the experimental results in terms
of borehole deformation and sanding rates. The model correctly predicted
initiation of shear failure from the sides of the borehole and its propagation
to the boundaries of the sample. It was further seen that the propagation of
the shear failed zone resulting from sand production agreed well with the
numerical pattern of failure growth upon removal of elements satisfying the
sanding criteria. The approach and concepts used are considered suitable for
application to field problems involving horizontal wells.
Introduction
A significant proportion of the future oil and gas production is expected to
come from sand-prone reservoirs, many of which are offshore. While these
reservoirs are highly prolific they are complex to develop and manage. Typical
cost of completing a major offshore well exceeds $100 million and these wells
are expected to remain productive for 20 years and longer. The control of
solids production in these high-rate wells over the life of the well is a
challenge and requires a good understanding of the mechanical behavior of the
formation under a variety of conditions. Various options are available, ranging
from placing active sand control, such as gravel pack and frac pack, to natural
completion, such as a cased and perforated hole. Objectivity is required in
choosing the correct completion type, which must account for the production
strategy and natural changes in the reservoir such as changes in the stress
state, permeability, and multiphase flow, including water cut. Once the
completion type is chosen, it must be operated optimally to maximize production
while maintaining efficiency and longevity. For instance, in sand-control
completions, operations must be tailored to mitigate generation and transport
of fines that can cause plugging of the gravel pack and lead to screen erosion,
whereas in natural completions, the emphasis would be in preventing formation
sand production or keeping it under the tolerance that can be handled by the
facility. Utilization of a reliable sand production prediction tool is
essential in selecting the optimum completion technique and optimization of the
operational conditions.
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
20 September 2004
- Revised manuscript received:
15 August 2007
- Manuscript approved:
16 August 2007
- Version of record:
20 December 2007
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