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Coiled Tubing Logging System
E.P.
Howell SPE, Areo Oil Gas
Co
L. .
Smith Areo Oil Gas
Co
C.G. Blount SPE, Areo Alaska Inc.
Summary.
Techniques have been developed to use coiled tubing containing a
seven-conductor wireline to facilitate logging
operations. Equipment has been designed
to
permit the connection
o
conventional logging tools to the tubing and the recording o
logs. Operating techniques have been developed and applied under
various wellbore conditions. The system allows traditional log
measurements
in
a well while wellbore conditions are controlled. Advantages
o
the system include reduced wellbore pressure
during perforation to maximize perforation performance;
lubrication during pulling or pushing a logging tool through a
borehole so
that a more uniform velocity can be maintained with a logging
sonde; continued circulation and thus borehole stability during
logging; temperature reduction for improved reliability
o
logging sonde electronics in hot holes; and more stable
positioning
o
perforation equipment. The ability
o
coiled tubing to push tools down highly deviated
or
horizontal wellbores makes logging
or
perforating feasible in these wells. Expenses can often be
reduced with coiled-tubing logging because a rig
is
unnecessary during
many operations.
Introduction
Coiled-tubing workover operations have become quite common
for
a number o problems and can be cost-effective.
1,2
However, some
o
this effectiveness is lost when additional equipment
is
required
to perform logging services. To reduce the amount
o
equipment
needed to provide logging service during coiled-tubing
workovers,
a system was developed to use the tubing
to
convey logging tools.
While this system was being developed, a number
o
new applica
tions were found that did not previously involve coiled tubing
but
that now provide improvements in the logging operation.
Coiled-tubing operations require an injector unit with the
tubing
equipment but no workover rig. Logging in a conventional
sense
then necessitates removing the injector truck, setting up a
small
rig
or
tower to support the lubrication equipment, and positioning
the logging sonde into the well. The new system (illustrated
in
Fig. 1), with a seven-conductor wireline maintained within the
tub
ing, permits the running o logs with the tubing injector and
can
reduce the number
o
trips
or
time in the hole.
Requirements. Typical requirements for logging operations
that
are normally associated with coiled-tubing workovers are fairly
rig
orous. This logging often involves some o the more
data-intensive
measurements, such
as
casing-corrosion inspection or cement-bond
evaluation. For this purpose, electrical connections have
been
designed that use conventional seven-conductor wireline cable.
Log
ging speeds
as
slow
as
300 ft/hr [90 m/h] or
as
fast
as
6,000 ft/hr
[1830 m/h] are readily attainable with the coiled-tubing
injector
equipment. This allows extended operation
o
data-intensive tools,
as well
as
tools that make imaging measurements to locate areas
o specific interest within the well. Because coiled tubing
stretches
much less than logging cable, actual depth positioning can be
de
termined very accurately.
A requirement o pressure integrity and backup
in
case o fail
ure is obviously very important in this system. Also, the
system
has been designed to ensure that continuous fluid
circulation
is
possible throughout the logging operation.
Downhole
Equipment
The design
o
this system was developed around a conventional
seven-conductor logging wireline maintained within the coiled
tub
ing. The wireline can be enclosed while the coiled tubing is
being
manufactured, or
it
can be installed in units already prepared for
operation. The field installation requires first laying out the
tubing
in
a reasonably straight line, then pumping a slick line through
the
tubing with something like swab cups and a suitable fluid, and
fi
nally drawing the seven-conductor cable into the tubing with
the
Copyright 1988 Society of Petroleum Engineers
SPE Formation Evaluation, March 1988
slick line. This process
is
rather straightforward but requires care
in minimizing curvature
o
the tubing while the slick line is pumped
through
it
and
in
applying continuous tension while the logging wire
line
is
drawn into place.
Two separate designs for the cable tubinghead have been
devel
oped and tested. A swivel head (Fig. 2) is used when logging
tools
are run that require precise centering
in
the wellbore, such
as
some
o the ultrasonic wellbore-imaging tools. Our swivel head has
a
3 lA-in. [8.26-cm] diameter. It uses a mandrel that slides over
the
tubing and wireline and
is
then connected to the tubing
in
a man
ner that permits the setting o a specific break strength. The
man
drel contains four fluid-injection ports to maintain
circulation
through the tubing. The lower portion
o
the mandrel contains a
swivel joint that relieves the cross-stress on the logging sonde
and
allows precise centralization. A weak point is then designed
into
the system below the mandrel. The failure weight can be
chosen
to match the tubing, logging tool, and wellbore conditions. In
our
units, this
is
generally designed for 3,000 Ibf [13 345 N], leaving
exposed a I-in. [2.54-cm] -diameter fishing neck (Fig.
3
for re
trieval.
A straight, 2Ys-in. [5A cm] -diameter cable tubinghead has
also
been developed. This head provides a more rigid connection
and
fits into smaller-diameter pipe or works under more adverse
well
bore conditions. Most
o
the tests with the rigid units have been
with wireline perforation guns.
With both types
o
cable tubingheads, the cable connection is
designed to ensure that
no
wireline is left in the well in case
o
the tools sticking. Because only minimal tension
is
placed on the
wireline itself, this connection requires only a few strands o
the
cable armor for support. The pressure integrity o the heads
is
main
tained with conventional cone-and-basket assemblies similar to
those
used
in
most wireline cable heads. Both cable tubingheads also have
a pressure-check valve that sets if a failure occurs in the
tubing
system above the wellhead. This prevents borehole fluids from
vent
ing up through the coiled tubing. The downhole connector
assem
bly contains a shock-absorbing section to prevent damage to
both
the logging tool and the tubing.
Surface Equipment
At the surface, a Y connection
is
installed within the coiled-tubing
reel. One side o the Y is then connected to the pump swivel
nor
mally found on this equipment and used for fluid circulation
during
the tubing operation. A high-pressure feed-through has been
designed into a connector sub that
is
then attached to the other side
o
the Y. A seven-conductor wireline section then connects to a
collector-ring assembly mounted on the tubing drum axle. The
con
nector sub
is
actually swaged onto the tubing and uses a wireline
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TU8fNG CONTAINING
WlRELIHE
LOG
RE TJIIONI S
Fig. 1 Coiled tublng logging system.
FLUID PORTS
O-RING
''''L-
WIRELINE
o
o
o
COILED
TUBING
FISHING ASSEMBLY
AND CHECK VALVE
(INTERNAL)
BALL-JOINT
SWIVEL
LOGGING SONDE
CABLEHEAD CONNECTOR
Fig. 2 Coiled tublng swivel connector assembly.
38
. . . . . - - - -1-1/4
~ - - - - - 1
' - - - - 1 - 3 / 4
Fig.
3 Flshlng
head for coiled tubing connector.
assembly similar to a wireline cable head system for the
feed
through. Conventional logging-truck electronics modules are
then
connected to the collector rings so that logs can be recorded
and
displayed in real time. A module that converts depth
information
from the tubing injector is normally used to provide depth to
the
recording system. In some cases, a second depth encoder
is
attached
to the tubing undet the injector frame.
History
and
Tests
A number of laboratory tests of this system have been run in
shallow
boreholes designed specifically for testing logging tools. These
tests
were made in both cased and open holes. Equipment was
designed
to place specific, measured stress levels on tile logging sondes
and
coiled tubing. While minimum-diameter downhole equipment was
being designed, tests were run repeatedly to ensure that
strength
and pressure criteria were met. After original specifications
were
met with the equipment, two sondes were used for testing
under
field conditions. These were an ultrasonic imaging system,
similar
to Mobil Oil
Co. s
Televiewer, 3 and a perforating gun. The
ultrasonic imaging tool requires uniform logging velocity. This
uni
form velocity can be maintained with the tubing system, which
al
lows lubrication through fluid circulation, thus minimizing
tool
sticking or pulsed movement that can occur when a wireline
stretches. The perforating gun requires accurate depth location
and
tests the overall strength of the system with strong shock
waves
when the gun is fired repeatedly.
After successful tests
in
laboratory boreholes, the equipment was
run in a number of oil wells under workover conditions. The
sys
tem has been found to operate efficiently in both vertical and
deviat
ed wells and
to
produce quality logs without major modifications
SPE Formation Evaluation. March
988
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to normal coiled-tubing procedures. During the last 2 years,
log
ging operations have been run in wells with deviations up to
92
0
[1.6
rad] from vertical. Downhole equipment has included open
hole dual-induction gamma ray sondes, perforating guns as
large
as 3 -in. [8.57-cm] OD, and a complete production logging
system.
Potential for oiled
Tubing ogging
Coiled-tubing logging provides an economic advantage when
meas
urements are needed during some workover operations. t also
will
provide improvements when logging in such difficult openhole
con
ditions as highly deviated holes, hot holes, and possibly
unstable
holes where circulation needs to continue during logging. It
also
allows control
of
well bore conditions while logging. Examples for
potential applications include the following.
1.
A
spinner survey can be run with packer equipment to con
trol flow rate systematically so that more accurate profiles can
be
measured.
2. For some time, reduced wellbore pressure
4
has been main
tained by pumping nitrogen during workover operations so that
for
mation damage caused by wellbore fluid invasion can be
avoided.
With wireline equipment, this concept can be applied to more
elaborate perforation techniques.
3. Some logging measurements, such as temperature surveys,
are
needed while a wellbore fluid is being injected, such as during
and
after stimulation operations.
SPE Formation Evaluation, March 1988
In summary, a number of improvements can be made by using
coiled tubing to run conventional wireline logs, in many cases
with
economic advantages.
References
1.
Herring, G.D. et al.: Selective Gas Shut-Off Using Sodium
Silicate
in
the Prudhoe Field, Alaska, paper SPE 12473 presented at the
1984
SPE Formation Damage Control Symposium, Bakersfield, Feb.
13-14.
2. Harrison, T.W. and Blount, C.G.: Coile d Tubing Cement
Squeeze
Techniques at Prudhoe Bay, Alaska , paper SPE 15104 presented
at
the 1986 SPE California Regional Meeting, Oakland, April
2-4.
3. Zemanek, J. et al.: The Borehole Televiewer: A New Logging
Con
cept for Fracture Location and Other Types of Borehole
Inspection,
PT
(June 1969) 762-74; Trans. AIME, 246.
4. Weeks, S.G.: Coiled Tubing, Nitrogen Cut Workover Costs,
World
Oil
(Feb.
1,
1970) 29-32.
SI Metric onversion Factor
in. x 2.54* E+OO
cm
Conversion factor is exact.
SP F
Original SPE manuscript received for review Oct. 5, 1986. Paper
accepted for publi cation
May 12, 1987. Revised manuscript received July 16, 1987. Paper
SPE 15489) first presented
at the 1986 SPE Annual Technical Conference and Exhibition held
in New Orleans, Oct.
5-8.
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