Note: Descriptions are shown in the official language in which they were submitted.
CA 02457307 2004-03-08
HYBRID COILED TUBING/FLUID PUMPING UNIT
Field of the Invention
The present invention relates to a coiled tubing unit for use in the servicing
of oil
and gas welis and more particularly to a unit mounted on a single mobile
platform
capable of providing both coiled tubing and pressurized fluid injection with
non-fired heat
recovery.
Background
Well bores require periodic maintenance to remove for example accumulated
sediments or for a host of other reasons well known in the industry. When
maintenance
is required, it is the usual practice to remove existing pumping equipment
from the
wellhead, and to move in a service rig to maintain control over the well
during servicing
and to inject and remove the necessary tools and eqiuipment required to
complete the
maintenance or servicing operations.
For well servicing and workovers, the use of coiled tubing is preferred.
Coiled
tubing is a single length of continuous unjointed tubing spooled onto a reel
for storage
in sufficient quantity to exceed the maximum depth of the well being serviced.
Coiled
tubing is favoured because its injection and withdrawal from the well can be
accomplished more rapidly compared to conventional jointed pipe, and it is
particularly
well suited for use in underbalanced wells. However, as with conventional
pipe, service
fluids and wire lines for downhole tools and instruments pass through the
tubing's
interior. The tubing is wound on a reel or spool mounted on a wheeled trailer
or the
flatbed of a truck for transport. The coiled tubing unit will normally also
include an
injector for insertion and removal of the tubing from the wellbore and a
guidearch which
leads the tubing into the injector.
For a typical cleanout, the tubing is injected into the well and a pressurized
fluid
is pumped through the tubing to circulate the well contents out through the
annulus
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between the tubing and the well bore. The fluid can be a liquid but is often
an inert gas
such as air, nitrogen or carbon dioxide.
As a cleanout fluid, air has the obvious advantage that it costs nothing and
it
works. reasonably well particularly in shallow wells of less than 1200 metres
in depth.
In shallow wells, the ratio of oxygen to hydrocarbons is not critical and
there is relatively
little risk of explosion: In deeper wells however, partial pressures increase,
and. the
concentration of oxygen and its reactiveness increase sharply. This creates a
real risk
of explosion and the oxygen's reactiveness can cause sever corrosion by the
oxidation
of metallic surfaces.
Another disadvantage to the use of air is that the equipment needed to
compress
and pump it adds substantially to the weight of a coiled tubing rig. A major
issue with
coiled tubing units is the amount of coil they can carry without exceeding
load limits on
both the trailer and public roadways. So called "bob tailed" coiled tubing
units
incorporate the air compressor. The compressors typically pump 300 to 650
standard
cubic feet per minute (scfm) at a maximum pressure of approximately 2000 psi.
This is
not sufficient in itself to blow sand from deeper wells. To add more lifting
capacity, soap
is added to the air stream which produces a foam. The soap is stored in a
tank, and the
tank and compressor combined weight approximately 7500 lbs. (approximately
3400 kg),
which reduces the amount of coil the unit can carry by the same amount. This
limits
deeper well applications.
These and other factors mitigate against the use of air for deep well
applications
and favour the use of nitrogen. Nitrogen is inert at all depths and creates a
safer
working environment around hydrocarbons. Its also non-corrosive. It is pumped
at a
volume of up to 1500 scfm at pressures up 5000 psi which is sufficient to blow
sediments
from the wellbore without the need for soap. .
To complete a job using nitrogen, both a coiled tubing unit and a nitrogen
unit are
required on location. The two units are rigged together at the well site and
as the coiled
tubing is run into the well, the nitrogen is pumped through the tubing to
extrude any fluids
and/or solids accumulated in the well.
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Nitrogen is normally stored and transported to the site as a liquid in a
pressurized
container forming part of the nitrogen rig, which also includes a tractor for
moving the rig
from job to job, a pumping unit and a heating unit to vaporize the nitrogen
prior to
injection through the coiled tubing and into the welibore. The heater is
normally an open
flame unit and by regulation it must therefore be kept at a predetermined safe
distance
from the wellhead.
The above described setup has numerous disadvantages. Most obviousiy,
operating costs for two rigs are high because of the eAra personnel, fuel and
equipment
required. There is the added pollution and cost resulting from the use of two
tractor units .
and an open flame heater. The mandated separation of the nitrogen and coiled
tubing
units greatly enlarges the footprint at the well site which sometimes
necessitates
enlarging the site. The high pressure tubing delivering the nitrogen gas to
the coiled
tubing unit is a hazard and setup and breakdown tiimes before and after the
job are
increased.
Summary of the Invention
The present invention seeks to overcome the above disadvantages by providing
a hybrid coiled tubing/fiuid pumping unit. The hybrid unit consists of a
coiled tubing reel
and injector, together with a nitrogen rig on a single platform. The nitrogen
rig must have
a non-fired heat recovery system between the pump and the coiled tubing to
vaporize
20. the nitrogen prior to injection. The term "single platform" can include
both a single
supporting surface such as a single trailer or flatbed, or two or more
supporting surfaces
that when in use can be situated close enough to one another that enlargement
of the
work site is unnecessary.
In operation, the hybrid coil tubing/nitrogen rig is driven to the well site
requiring
service. The unit has the capability of towing a pup trailer supporting the
liquid nitrogen
reservoir. Once at the site, the coiled tubing is deployed according to
standard
procedures known in the art; the tubing is delivered over a guide arch into
the injector,
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and the injector then inserts the tubing into the bore. If the bore is
underbalanced, a
lubricator can be used in conjunction with the injector.
The outer end of the coiled tubing can be permanently connected to the
nitrogen
rig, thus eliminating the need to connect tubing which could potentially be a
weak spot
in a high pressure line. The permanent connection also limits the amount of
high
pressure tubing exposed at the work site, making for a safer environment.
Because the
heater used to vaporize the liquid nitrogen is non-fired, it can be deployed
on the hybrid
unit imrnediately adjacent the well bore, which greatly reduces the onsite
footprint.
According to the present invention then, there is provided apparatus for the
servicing of a bore hole in the earth, comprising a first sub-assembly adapted
for the
insertion and removal of a continuous length of coiled tubing into and from
said bore
hole; and a second sub-assembly adapted for the vaporization of liquified gas
and the
pumping of the resulting gas through said coiled tubing into said bore hole
said second
sub-assembly including first heat exchanger means for vaporization of said
liquified gas,
said heat exchanger means allowing heat transfer between a heat transferring
fluid and
said liquified gas, and means for loading an internal combustion engine to
produce heat
within said means for loading, wherein at least a portion of said heat
transferring fluid is
circulated through said means for loading for the transfer of said heat to
said fluid, said
means for loading having a first inlet for said heat transferring fluid and an
outlet for the
discharge thereof; and platform means adapted to support said first and second
sub-
assemblies thereon.
According to another aspect of the present invention, there is also provided a
hybrid coiled tubing and pumping rig for servicing a well comprising a coiled
tubing spool;
coiled tubing wound about said spool; a coiled tubing injector for injecting
said
coiled tubing into said well; a guide arch for guiding said coiled tubing into
said injector;
a flameless heating unit for heating a liquified gas to produce gas, said
flameless heating
unit including a heat exchanger for vaporizing said liquified gas by heat
transfer between
a heat e:xchanging fluid and said liquified gas; a source of heat for said
heat exchanging
fluid including a water brake drivingly connected to a prime mover; a first
pump for
pumping said heat exchanging fluid through said heat exchanger and said water
brake;
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and a reservoir for said heat exchanging fluid wherein said heat exchanging
fluid is
circulated from said reservoir, through said second pump, said heat exchanger,
said
water brake and back to said reservoir; and a second pump for pumping said gas
through said coiled tubing into said well wherein said spool, injector,
flameless heating
unit and first pump are supported on a single platform for transportation and
use.
jkccording to yet another aspect of the present invention, there is also
provided
a method for the servicing of a bore hole in the earth by injecting a
pressurized gas
thereinto, comprising the steps of supporting a first sub-assembly adapted for
the
insertion and removal of a continuous length of coiled tubing into and from
said bore
hole on a platform; and supporting a second sub-assembly adapted for the
vaporization
of liquified gas and the pumping of the resulting gas through said coiled
tubing to said
bore on said same platform, said vaporization of said liquified gas comprising
the
additional steps of circulating said liquified gas through a heat exchanger in
which said
liquifiecl gas is vaporized by heat transferred from a heat transferring fluid
and heating
said heat transferring fluid by the circulation thereof through a water brake
drivingly
connected to a prime mover.
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Brief Description of the Drawings
Preferred embodiments of the present invention will now be described in
greater
detail and wiil be better understood when read in conjunction with the
following drawings,
in which:
Figure 1 is a perspective, partially schematical view of a well site set up
for
servicing using conventional nitrogen and coiled tubing units;
Figure 2 is a side elevational partially schematical view of a hybrid coil
tubing/pumping unit;
Figure 3 is a top plan view of a nitrogen rig forming part of the present
invention;
Figure 4 is a side elevational view of the nitrogen rig of Figure 3;
Figure 5 is a rear elevational view of the nitrogen rig of Figure 3;
Figure 6 is a schematic flow diagram of the nitrogen rig;
Figure 7 is a hydraulic schematic of the nitrogen rig; and
Figure 8 is a pictorial representation of a water brake forming part of the
nitrogen
rig.
Detailed Description of the Preferred Embodiments
Reference is now made to the drawings. Figure 1 shows prior art rigs and the
ways these rigs are used. In particular, Figure 1 shows a typicai setup for a
coil tubirig
unit 10 and a nitrogen rig 30.
Coil tubing unit 10 is situated adjacent to wellhead 5. The rig consists of a
mobile
tractor/trailer unit 9 fitted with a spool 12 for coiled tubing 14, a boom
mounted guide
arch 16 and a tubing injector 20 that inserts and removes the coiled tubing
from the well
bore. As will be appreciated, the tubing unit is shciwn in its working
position. For
transport and storage, the boom 18 is used to withdraw the guide arch and
injector into
a stored position on top of the trailer as best seen in Figure 2
A conventional stand-alone nitrogen rig 30 includes its own tractor trailer 31
with
the trailer supporting a tank 32 for liquid nitrogen, a flame fired heater 36
for vaporizing
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the nitrogen and a high pressure pump 44 for pumping liquid nitrogen from tank
32 into
the heater and then into and through the tubing. The pump will normally use
the tractor's
motor for power via an intervening hydraulic pump.
As seen in Figure 1, the nitrogen rig is physically separated from the coiled
tubing
unit and the wellhead by the mandated distance required by law. The two units
are
rigged together using a high pressure line 38 to deliver= pressurized gas from
the pumper
into the coiled tubing for injection down the well bore. If additional
nitrogen is needed,
rig 30 can be outfitted with a pup trailer as known in the art.
Reference is now made to Figure 2 showing the hybrid unit 50 of the present
invention which provides both tubing and pumping operations from a single
platform. In
Figure 2, like numerals have been used to identify like elements.
The hybrid unit of the present invention includes all of the components of a
conventional coiled tubing unit including spool 12, guide arch 16, injector 20
and boom
18 to deploy the arch and injector from the storage position shown in Figure 2
to the
operational position shown in Figure 1. Unlike conventional rigs, however, the
present
unit also includes its own integrated nitrogen rig or skid 40 mounted on a sub-
frame 48
that can be conveniently and securely attached to the unit's trailer in any
known fashion.
In one embodiment constructed by the applicant, rig 40 weighs approximately
2650 lbs.
(approximately 1200 kg) compared to the 7500 lb. (approximately 3400 kg)
weight of a
combined air compressor and soap tank. The nitrogen rig will be described in
greater
detail below but it generally comprises the nitrogen pump 44, a flameless heat
exchanger 46 for vaporizing the liquid nitrogen and a heat producing and
engine loading
device such as a water brake 47 used to ioad the truck's engine for increased
heat
production used to vaporize the nitrogen. Heat exchanger 46 is flameless for
safety
reasons. As aforesaid, regulations require that no flame be present within a
predetermined distance of the wellhead. By using a flameless heater, hybrid
unit 50 can
be situated immediately adjacent the well in the same manner as a conventional
coiled
tubing unit.
The nitrogen is transported to the site as a compressed liquid which must be
vaporized prior to injection into the well for clean outs. Assuming that up to
90,000 cubic
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feet of nitrogen gas will be pumped per hour, approximately 1.7 million
British thermal
units (btu) of heat per hour will be required to vaporize this amount of
nitrogen. Some
of this heat can be obtained from the truck's engine up to approximately
250,000 btu's
with the bulk of the remaining heat being obtained fr-om water brake 47, with
perhaps
some additional heat being scavenged from the hydraulic fluid used
throughout.the unit.
Power for the hybrid rig is taken from the truck's engine. As will be known in
the
art, the truck's gearbox (not shown) will have at least two auxiliary power
take-offs. One
is used to drive the coiled tubing hydraulics including the injector and the
boom. This is
a conventional hookup and therefore will not be described in further detail.
The
gearbox's other power outlet is used to supply driving force to the nitrogen
rig through
for example a belt or chain drive 2.
The nitrogen rig includes its own gearbox 4 having two outlets 5 and 6 seen
most
clearly in Figures 3 to 5. Drive 2 is connected to gearbox 4 by a shaft 8 and
coupling 9.
Gearbox 4, which can be a John Deere FunkT"" model, distributes power between
outlets
5 and 6. Water brake 47 is mounted onto outlet 6 which couples it to the
truck's engine.
A hydraulic pump 41, such as a Kawasaki, is mounted onto outlet 5. Pump 41 is
used
to drive the skid's hydraulics which include the triplex nitrogen pump 44, a
boost pump
43 (shown schematically in Figure 6) which is sometimes used to boost pressure
to
pump 44's intake and a centrifugal pump 60 (also shown schematically in figure
6) which
circulates heated fluid through the heat exchange apparatus used to vaporize
the liquid
nitrogen as will now be described below with reference to Figure 6.
Pump 44 pumps liquid nitrogen from tank 32 through high pressure supply line
45 into heat exchanger 46. A smaller boost pump 43 between tank 32 and pump 44
is
actuated as required to ensure a continuous supply of liquid nitrogen at pump
44's intake
and to boost pressure at the intake. The liquid nitrogen is vaporized in the
heat
exchanger and the resulting gas flows through conduit 49 which can be
permanently or
semi-permanently coupled to the outer end of coiled tubing 14.
Heat exchanger 46 includes an inlet 52 for hot fluid, which can be water but
more
typically will be glycol or a water/glycol mixture, and an outlet 53 for cold
fluid. To heat
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the glycol, heat is derived from two principal sources, the truck's cooling
system and
water brake 47.
To maximize the production of heat from the truck engine's cooling system,
it's
preferred that the engine be fully loaded. Some of this load will come from
the engine's
peripherals such as the alternator, water pump and so forth, and some frorn
the power
required for the coiled tubing's hydraulics. These loads are not sufficient by
themselves
however to cause the engine to produce its maximum horsepower and heat output.
The
engine is therefore mechanically coupled to water brake 47 as described above
to
produce the required added load and to generate heat of its own.
Water brakes are well known in the art and therefore will not be described in
great
detail. Generally however they comprise a sealed chamber that is normally kept
full of
fluid. A plurality of radially extending, shaft mounted blades or
rotor/stators are disposed
to rotate within the chamber against the resistance of the fluid. The shaft is
rotated by
the motor being loaded. The mechanical energy from the spinning rotors is
converted
to heat energy in the fluid which is continuously circulated through the
chamber to cool
the water brake and its bearings and seals and to produce hot glycol for
circulation
through heat exchanger 46.
The present system incorporates a pump such as centrifugal pump 60 which
circulates the glycol throughout the system. The pump is connected at its
intake end to
two sources of hot glycol. The first is supply line 56 which delivers heat
extracted from
hot engine coolant circulated through hoses 57 into an engine coolant heat
exchanger
58. The second source is supply line 64 that delivers hot glycol from glycol
tank 65.
Pump 60 forces the hot glycol through a filter 66 following which the flow is
split
up to three different ways. Part of the glycol is deviated into inlet 52 of
heat exchanger
46. Another part is divided into feed line 69 that flows into water brake 47.
Feed line 69
is typically an inch in diameter but this can vary. A smaller portion is
diverted into 1/4
inch lines 71 and 72 that connect with secondary inlets such as 1/8 inch
orifices into the
water brake that divert glycol against the water brake's seals and bearings
when the
water brake runs empty as will be described below in greater detail. Glycol
entering the
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water brake through lines 69 and 71 and 72 drains through line 75 which flows
the hot
fluid back into glycol tank 65.
The cold fluid leaving heat exchanger 46 is circulated through line 77 in
which it
can be delivered directly to engine heat exchanger 58 for recovery of waste
engine heat
prior to circulation back into pump 60. Or, if valve 80 is closed, the fluid
can be diverted
through hydraulic heat exchanger 84. This exchanger can be used to scavenge
heat
from hot hydraulic fluid from the skid's hydraulic pumps and motors circulated
through
the exchanger via inlet 85 and outlet 86.
The flow rate through heat exchanger 46 is approximately 295 gallons of glycol
per minute.
There are times when its unnecessary to operate the water brake. In
conventional systems, this requires that the gearbox be adapted to disengage
the brake
from the truck's engine. These gearboxes however are heavy and expensive. To
avoid
this, the present water brake in a preferred embodiment of the present
invention has
been adapted to run empty which otherwise would normally cause the brake and
its
seals to burn out.
In the present system, the brake's aluminum housing is hardened to 85
Rockwell,
and supply lines 71 and 72 continuously deliver a small amount of glycol to
1/8 inch
orifices which internally direct the glycol against the seals and/or bearings.
When valve
90 is closed to stop the delivery of glycol to the water brake, pressurized
air (7 to 10 psi)
from an expansion tank 94, arranged above and in fluid communication with
glycol tank
65 through a 2 inch connecting iine 97, flows through oneway check valve 98
and
through air hose 96 into line 69 to purge the fluid from the brake. Check
valve 98
prevents any reverse flow of glycol into the expansion tank when valve 90 is
open during
normal operation. Without fluid, the water brake simply spins without loading
the truck's
engine. The additional hardening of the water brake's housing and the
continuous flow
of glycol against the seals and bearings prevents burnout.
In operation, hybrid unit 50 can tow its own trailer supporting a liquid
nitrogen tank
32. At the well site, the trailer is disconnected from the iunit and
conveniently located for
connection to pump 44 and to boost pump 47 if one is needed.
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Figure 7 is a schematic of the skid's hydraulic connections. Hydraulic fluid
from
reservoir 100 is drawn through filter 102, and is then pressurized by pump 41
for delivery
to centrifugal pump 60, boost pump 43 and triplex motor 44 through supply
lines 104,
105 and 106, respectively. Flow to boost pump 43 and motor 44 is regulated by
a
HaweT"~ valve 110 having two pressure compensated spools 111 and 112 to
maximize
flow to the boost pump at five gallons per minute and to the triplex motor at
60 gallons
per minute. Pressure compensated needle valve 118, such as a ParkerTM PMS 800,
regulates the flow of hydraulic fluid through pump 60. Any leakage from the
motors is
collected in lines 121, 122, 123 and 124 for drainage back to reservoir 101.
Return line
125 for fluid from the various pumps and motors can iriclude cooling unit 130
and a filter
132.
It is contemplated that the present rig can additionally incorporate an
exhaust gas
heat exchanger to recover even more engine waste heat for vaporizing the
nitrogen.
As will be appreciated from the foregoing, the hybrid unit is largely self-
contained,
quickly set up and broken down, occupies a small footprint, requires only one
crew, one
motor and enhances on-site safety.
The above-described embodiments of the present invention are meant to be
illustrative of preferred embodiments of the present invention and are not
intended to
limit the scope of the present invention. Various modifications, which would
be readily
apparent to one skilled in the art, are intended to be within the scope of the
present
invention. The only limitations to the scope of the present invention are set
out int the
following claims.
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