Summary
This article presents the development of a computational tool to guide
horizontal gravel-pack design for long horizontal offshore wells. Mechanistic
model hypotheses, experimentation at a large-scale flow loop, and software
development are detailed. The computer simulation results are then compared
with field data collected in the Campos basin operations, offshore Brazil. A
discussion on design alternatives for a long horizontal well at low
fracture-gradient formations is presented. This discussion includes a
sensibility analysis on screen eccentricity, open and closed blowout-preventer
(BOP) configurations, and alpha (alone) vs. alpha plus beta wave displacement
options.
Introduction
Gravel packing is, today, the most frequently applied sand-control technique
in the Campos basin. Because of the critical conditions, such as the deep and
ultradeep water and low fracture gradients, a lot of precision is required to
ensure gravel-packing success. Most models available in the industry for
horizontal gravel-pack design are essentially empirical, resulting in imprecise
predictions for extrapolated conditions.
The new scenario for offshore development in Brazil includes heavy-oil
fields in deep waters in which 2000-m horizontal sections are required. Because
of the nonconsolidated formations found, sand-control options are a major
issue, and gravel packing is a strong candidate for sand control, if
pressure-loss issues can be overcome.
These aspects were the main motivators for a research project that included
theoretical and experimental developments. A mechanistic model to describe the
whole operation, including sand injection and alpha/beta waves propagation,
fluid leakage, multizonal isolation, and beta wave pressure-reduction
optimization, was developed. The main core of the model—aiming the
definition of alpha wave height—is based on a two-layer model approach.
Initially developed for hydrotransport applications, this kind of model has
been adapted by several authors for drilled-cuttings transport analysis. There
is a consensus among design and operation engineers that physically based
software is a necessary rigsite tool for determining operational parameters,
especially when last-minute data have to be considered.
Several authors present experimental results of horizontal gravel packing
performed in test facilities.1–3 In the present study, 15 runs on a
full-scale displacement loop in which the effects of pipe eccentricity,
particle diameter, particle shape, fluid flow rate, and return flow rate could
be quantified. The results enabled the adjustment of fundamental coefficients
in the mechanistic model.
Theoretical Model
The proposed model consists of the following steps: pressure propagation
during string injection, alpha wave height prediction, and pressure propagation
during alpha/beta wave deposition. A brief description of the physics involved
in each step follows, while the formulation and more details are highlighted in
Martins et al.4
© 2005. Society of Petroleum Engineers
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History
- Original manuscript received:
10 May 2004
- Revised manuscript received:
31 January 2005
- Manuscript approved:
26 April 2005
- Version of record:
15 June 2005
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