Summary
Extended-reach, naturally perforated, water-injection, frac-pack producing
completions and frac-pack producing selective completion interventions were
successfully implemented in the deepwater Gulf of Mexico Petronius field,
setting both Gulf of Mexico and world records. Success was achieved through
careful planning of procedures and specification of equipment. This paper
describes the planning for these challenging extended-reach completion and
intervention operations, along with the lessons learned while implementing
these case-history jobs.
Introduction
Chevron and Marathon each have a 50% working interest in the Petronius
project, which is operated by Chevron. The field is located in the Gulf of
Mexico, 150 miles south of Mobile, Alabama. The project was sanctioned in
August of 1996 after both compliant-tower and subsea-development options were
evaluated. The compliant-tower alternative was selected because of its greater
well-intervention capability, less-complex seawater-injection-system design,
lower investment requirements, and future hub potential. The 2,001-ft-tall
Petronius compliant tower is set in 1,754 ft of water and is the world’s
tallest free-standing structure.
The Petronius project originally targeted two main reservoirs which were
delineated by seven preplatform-well penetrations. Once these two original pay
sands were developed, the operators set their sights on developing suspected
pay zones much farther from the platform in deeper water. The development of
these distant zones required mechanical success in implementing difficult
world-record extended-reach processes and, of course, success in finding
economic quantities of pay.
For the past 3 years, a successful program of just such world-record
extended-reach development has been ongoing. The program has seven wells to
date, with horizontal displacements ranging from 14,000 to more than 25,000 ft.
These horizontal-displacement values far exceed the »11,000-ft true vertical
depth (TVD) of these wells. Fig. 1 summarizes the directional data for
the Petronius extended-reach program in chronological order of well
development, and Fig. 2 illustrates the complexity of the directional
profile of the most challenging of these wells.
This extended-reach program is quite an accomplishment considering the
unconsolidated deepwater environment. To date, the program includes two
water-injection wells and five frac-pack producing wells. Three of the five
producing wells include stacked-frac-pack completions. Future well plans
include an additional extended-reach frac-pack producing completion and a
sidetrack of an extended-reach water-injection well.
Workstring Design and Execution
Proper workstring design is essential for extended-reach completions. In
addition to typical drillpipe design criteria, torque, drag, pipe stretch,
buckling, and casing wear caused by high metal-to-metal friction should be
considered. In a worst-case scenario, a completion plan without workstring
rotation should be ready to implement. Additionally, hydraulic friction for
pumping various fluids throughout the completion processes of cleanout,
displacement, perforating, washout, and frac packing should be evaluated for
deep wells. Both hydraulic and metal-to-metal friction should be modeled in
advance with one of the many available industry software packages.
The Petronius program consists of wells with ever-challenging directional
profiles that provided opportunities for continuous learning using pre- and
post-well torque, drag, and hydraulic models. Despite this methodical learning
process, excessive and greater-than-expected drag was observed during the
tubing-conveyed perforation (TCP) of Well #7. Fig. 3 illustrates the
pickup weights observed while going into the hole and just before entering the
7-in.-outer-diameter production liner. The next attempt to obtain a
pickup-weight reading was »1,000 ft into the liner, when the drillpipe was
pulled to its maximum safe pickup value of »625,000 lbm (without the block
weight). This pickup weight was equivalent to a friction factor greater than
0.40. The workstring was inspected to 95% wall thickness and was designed to
accommodate a pickup friction factor of 0.30 using a 90% safety factor for
tension. This design friction factor of 0.30 was based on observations from
previous extended-reach wells with similar casing and workstring profiles.
To reduce the observed metal-to-metal friction, an environmentally friendly
liquid friction-reducing product was added to the 9.7-lbm/gal CaCl2
brine in the well at 0.6 vol%. This additive passed local oil and grease
concentration regulations before its use (according to laboratory data) and
also when evaluating brine samples from wellbore returns. The product reduced
the pickup weight by more than 125,000 lbm, which ultimately prevented a
drillpipe failure. Because the pickup friction factor was reduced from
>0.40 to approximately 0.30, the TCP string was run to total depth (TD) and
the TCP job was a success. The slackoff friction factor was calculated to be
slightly lower than the pickup friction factor, which is consistent with values
reported in previous publications (Johancsik et al. 1983). The brine additive
reduced the slackoff friction factor from 0.32 to 0.23. Following this
near-catastrophic event, the top 4,500 ft of drillpipe was replaced with a
landing string that safely allowed 150,000 lbm of additional pickup weight
compared to the original workstring design. Running the gravel-pack assembly
with this new workstring, the observed values of friction factor ranged from
0.25 to 0.30. Because of hurricane platform damage, the completion was
suspended for 6 months. When work resumed, the brine required filtering because
of iron precipitation; however, the good news is that it retained its 0.30
friction factor and low oil and grease content.
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
12 December 2005
- Revised manuscript received:
17 January 2007
- Manuscript approved:
23 February 2007
- Version of record:
20 June 2007
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