Summary
The Na Kika offtake guidelines were developed jointly by Shell and BP using
a blending of recent sand control operational methodologies from each
company. This paper focuses on the use of the BpfluxTM
guidelines, which give maximum safe operating rates for sand-control
completions and allow wells with excellent completion quality to produce at
twice the rate of wells with lower completion quality.
Before the Na Kika field started up, completion quality was estimated by
reviewing 20 different elements of completion design and operations.
These estimates were used to set the initial offtake limits for each
zone. As the wells started producing, pressure buildups were used to
measure the actual completion quality (skin), and the maximum operating rates
were adjusted accordingly.
By use of this methodology early in the field life, the field could be
brought up to targeted production rates without unnecessarily compromising
long-term sand control reliability. As the field matures, opportunities
will be identified to extend the production plateau, which will provide an
incremental production impact. Finally, later in the field life, the
number of workovers required is expected to be reduced, which will provide an
additional cost saving from using these guidelines.
Introduction
The Na Kika development is in the deepwater Gulf of Mexico (Fig. 1),
with 12 subsea wells that tie back to a host facility with a production
capacity of 130,000 barrels of oil per day (MBOPD) and 500 million cubic feet
per day (MMCFD) of gas. There are six separate fields that tie back to
the host, which makes this development unique because there is no large field
that justified the host on a standalone basis. With the exception of the
Coulomb field, which was developed after the scope of work in this study, Shell
and BP are equal partners in the Na Kika development. All the wells have
sand control completions, two are openhole horizontal wells with gravel packs,
and the remaining eight wells are cased holes with frac packs. As with
any deepwater and subsea development, long-term reliability of each well is
critical to project success.
Over the past few years, well operating guidelines for sand control have
moved away from drawdown-based limits and are now based on velocities at
various locations in the completion. In particular, two recent studies
both offer powerful new methods for safely operating sand control completions.
Wong et al. (2003) discuss two velocity limits: one is the perforation velocity
at the casing inside diameter, which, if too high, leads to destabilization of
the annular pack. The second is the velocity at the surface of the
screen, which if too high, causes screen erosion failure. They also present a
surveillance-tool methodology to monitor well cleanup during the startup
portion of a well’s life.
Tiffin et al. (2003) present the results of a large database used to develop
empirical guidelines for safe operation of sand-control completions. They
introduce a flux-based c-factor, which is directly proportional to the
perforation velocity and allow wells with excellent completion quality to
produce at twice the rate of wells with unknown or poor completion
quality. The focus of this paper is on the application of these
BpfluxTM guidelines to the Na Kika development.
This paper begins with a brief overview of the BpfluxTM
guidelines, highlighting the importance of a high-quality completion. It
proceeds to discuss how these guidelines were incorporated into the Na Kika
offtake guidelines. Two planned pressure buildups performed early in the well
life to document the skin for each well are discussed and analyzed. The
paper continues with examples of the use of pressure buildup (PBU) results and
actual well drawdown data to increase the rates of wells using the
guidelines. Use of these guidelines during the life of the field,
particularly for wells with increasing skin, is also discussed. The paper
concludes with a review of the actual Na Kika completion quality, examining
which elements of the completion design and execution correlate with the
measured skins.
BpfluxTM Overview
The BpfluxTM guidelines were developed by (Tiffin et al. 2003)
using an extensive database of cased-hole and openhole sand control
completions, primarily from the Gulf of Mexico and Trinidad. The
rationale for developing these guidelines is made clear in Fig. 2, which
shows the fate of 160 wells in the database. The vertical axis is the
total drawdown, and each vertical colored bar represents a well. Green-colored
wells had no sand production, yellow wells produced some sand, and red wells
were erosion failures. Only wells with confirmed good-quality completions were
included in the database; early-life failures caused by poor sand-control
placement were excluded. First, Fig. 2 shows that there is no correlation
between drawdown and well failures. Several wells with drawdown over 1,500 psi
operate with no sand production, while one well with only 250 psi drawdown
failed. Even the average values show no correlation, as the average drawdown of
wells that failed is approximately 50 psi lower than the average
for wells that produced sand-free.
These observations led to the development of the BpfluxTM
guidelines for cased-hole sand control completions, which are illustrated in
Fig. 3.
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
12 July 2005
- Manuscript approved:
19 June 2006
- Version of record:
20 March 2007
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