Summary
Uncontrolled heat transfer from production tubing to outer
annulus—especially in deepwater riser sections—can cause the deposition of
sludge, paraffin, and asphaltene materials; contribute to the formation of gas
hydrates; and limit shut-in time for unplanned downtime or remedial operations.
Generally, deepwater risers can be insulated externally or insulated by placing
nitrogen gas into the riser annulus. In recent years, a new water-based
thermal-insulating fluid system has been developed and used in field
applications. This new system reduces convection and provides a rheological
profile to facilitate fluid placement into the riser annulus. This system
has been successfully used in deepwater risers in the Gulf of Mexico (GOM).
Laboratory-scale equipment and a full-scale test well were constructed to
evaluate the thermal-insulation properties of fluids. This paper details the
testing procedures and methods. Steady-state heat-transfer- and cool-down-test
results on the new insulation fluid were determined and compared to
conventional fluids. These superinsulating fluids were found to be vastly
superior to brine and measurably better than conventional water-based
insulating fluids. Surprisingly, when compared to nitrogen (air) or argon,
the superinsulating fluids provided enhanced protection during cool down.
Field cases in the GOM are summarized to demonstrate the effectiveness of this
fluid system.
Introduction
Understanding and controlling the thermal environment of oilfield operations
has been a concern since the 1960s. Early attention was focused on hot
water and steam-injection operations (Penberthy and Bayless 1974; Eisenhawer et
al. 1981; Aeschliman et al. 1983) and applications in which insulation was
provided by filling the packer annulus with inert gas (Aeschliman et al. 1983;
Galate and Mitchell 1985; Aeschliman 1985; Willhite and Griston
1987). Even with gas-filled annuluses, heat losses were observed to be
higher than expected.
Liquid-filled annuli were also examined using oil, which has a relatively
low thermal conductivity [0.08 Btu/(hr•ft•°F)]. Heat losses were again
observed to be higher than expected. In this instance, the heat loss from
nonviscosified oil was associated with significant convection within the
annulus (Willhite et al. 1967; Willhite 1967). However, thixotropic
oil-based fluids that have a relative thermal conductivity approximately 13%
that of water have been reported (Son et al. 1983; Yousif et al. 1994; Ashford
et al. 1990; Suarez et al. 1995). While these fluids can be weighted to
higher densities, they potentially suffer from solids settling, emulsion
destabilization, incompatibility with elastomer elements, and future
environmental restrictions. Water-based silicate foams with low thermal
conductivity [0.18 to .27 Btu/(hr•ft•°F)] were evaluated by Son et al. (1983),
but the system was found difficult to control downhole, and the pipe was
vulnerable to the development of hot spots (Penberthy and Bayless 1974;
Willhite et al. 1967; Willhite 1967). Dry foam silicate (Penberthy and
Bayless 1974) and silica aerogel (Kuperus et al. 2001) systems were
reported to be 10 times more effective than liquid brine. Purdy and others
evaluated vacuum-insulated tubing (VIT) (Purdy and Cheyne 1991; Davalath and
Barker 1995; Feeney 1997), and as expected, its application was found
successful but expensive. Nonetheless, heat loss through couplings,
valves, gauges, centralizers, and damaged or scrapped coatings can dramatically
increase heat loss from a VIT system. A unique system to mitigate heat
loss uses a pipe-in-pipe arrangement coupled with electrical current to
generate heat and prevent gas-hydrate plugs in pipelines (Von Flatern
2001).
A recent paper (Dzialowski et al. 2003) described the evaluation of
oil-based and glycol-based insulating fluids designed for use in aluminum riser
applications and in the measurement of thermal conductivity based on the
nonsteady-state hot-wire method. A nonweighted oil-based system was
selected for further testing.
An overview of various applications for insulating packer fluids, including
deepwater completions, has been presented (Pearcy and Johnson 2000; Moe and
Erpelding 2000). Recent articles by Javora et al. (2002) and Wang et al.
(2005) detail the advances made in formulation and use of water-based
insulating fluids.
To control the total heat loss from produced fluids to the surrounding
wellbore, internal annuli, and riser environments, specialized water-based
insulating fluids were developed. Fluid composition is controlled to provide
inherently low thermal conductivity, effective viscosity, and favorable
environmental characteristics. These water-based fluids are oil
free. Fluid density is controlled by the amount of dissolved salt and can
be varied to provide positive wellbore-pressure control without the risk of
solids settling.
© 2006. Society of Petroleum Engineers
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History
- Original manuscript received:
13 March 2005
- Revised manuscript received:
18 August 2005
- Manuscript approved:
26 August 2005
- Version of record:
20 March 2006
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