spe 27491torque ndrag pa
TRANSCRIPT
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8/19/2019 SPE 27491torque Ndrag PA
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Torque and Drag Two Factors in
Extended-Reach rilling
Thor Viggo Aarrestad SPE
and
Harald Blikra
SPE
Statoil A/S
Summary
This paper addresses the various aspects
of
torque and drag prob
lems encountered in drilling extended-reach wells. It discusses how
to use torque and drag calculations and measurements to plan long
reach well profiles, to execute drilling operations that minimize
torque and drag effects, to monitor hole cleaning, and to plan jarring
operations.
Introduction
In extended-reach drilling, a limitation on the horizontal displace
ment occurs because
of
frictional forces between the drillstring and
the borehole wall. Drag is measured as the difference between the
static weight
of
the drill string and the tripping weight. Similarly, a
difference between the torque applied at the rig floor and the torque
available at the bit occurs owing to friction. Torque and drag prob
lems are often associated with each other and may be profound in
extended-reach and horizontal wells.
As Sheppard
et
al. I stated, a variety
of
sources
of
drag and torque
loss exist: differential sticking, key seating, hole instabilities, poor
hole cleaning, and the general frictional interaction associated with
side forces along the drillstring. Therefore, drag and torque mea
surements may be used to monitor operations to optimize perfor
mance. In extended-reach drilling at Statoil, torque and drag prob
lems have initiated use
of
more sophisticated well profiles
2
-4
and
use
of
torque as an indicator
of
hole-cleaning problems. Under
standing
of
torque and drag problems has been applied to the well
planning process. As a result, problems are often not found in wells
with horizontal displacements up to 5000 m.
5
Another interesting
implementation
of
drag knowledge in operational procedures is
described in a paper on the influence
of
drag on hydraulic jar
efficiency.6
In this paper, we discuss torque and drag problems in extended
reach wells, how knowledge
of
torque and drag is used in operation
al procedures, and to what extent the planning phase can help avoid
operational problems. Although always referring to extended reach,
the same principles are valid for horizontal,
s
-shaped, and design
er wells ?
Well
Profiles
Optimizing well profiles to minimize torque and drag problems has
been discussed in many publications (e.g., Refs. 1 4 and 8 through
10). Sheppard et al
I
thoroughly discussed the catenary curve prin
ciple for well drilling. Alfsen et al
4
discussed a modified catenary
principle; Banks
et al
9
included the concept
of
tortuousity and
reached the important conclusion that making a smooth well path
is
key for successfully drilling extremely long-reach wells.
To reduce friction in any well, a good mud program design is im
portant. Friction factors down to 0.16 simulations have proved to
give a best fit with measurements.
4
The torque and drag program
used in the work described here has been used extensively at Statoil
together with measurements
of
actual data. Confidence in the cal
culations has been achieved, and they have been used to monitor and
improve operational practice. Minimizing dogleg severity and even
making changes in dogleg severity have been implemented in our
procedures.
Several papers have been published on long-reach well drilling
from the Statfjord C platform.
2
-4 After a 6000-m horizontal dis-
Copyright 1994 Society of Petroleum Engineers
Original SPE manuscript,
Torque and
Drag-Two Factors In Extended-Reach
Drilling
reo
ceived for review Feb. 15, 1994. Revised manuscript received June 27, 1994. Paper ac·
cepted for publication July 5, 1994. Paper (SPE 27491) first presented althe 1994 IADC/SPE
Drilling Conference held in Dallas, Feb. 15-18.
800
placement was reached in Well 33/09-C03, it was recognized that
the well profile would need to be optimized to reach the planned
depth for Well C02-7200-m horizontal displacement. The catenary
curve, proposed
as
a possible solution to the torque and drag prob
lems, is the solution to the following problem. 12
A cable with weight per length, W has a horizontal force at left
Point A,
FH
and a tangential force at right Point
P x,y), FT.
The hori
zontal component
of
the force at Point P is in the opposite direction
of
the force at Point A.
The solution to the above problem is given in the
x-y
plane as
y = a
o s h ~ ) ,
H
where a
=
W
An interesting feature
of
the catenary curve is the zero contact
force between the drill string and the borehole wall. Consequently,
the catenary curve could theoretically give zero friction between the
borehole wall and the drillstring.
Several difficulties exist in using this approach for drilling a well.
First, the effective force at the bottom
of
the well results in drill string
compression as opposed to the tension given in the theoretical
curve. Furthermore, the catenary curve will lead to a much longer
well path than more traditional well profiles. Thus, a slight modifi
cation
of
the catenary curve must be made.
An important feature
of
the catenary curve was kept in the well
plans for Wells 33/09-C24 and 33/09-C02 in the Statfjord field: the
very slow build rate in the shallow part of the well with a slowly in
creasing build rate as well depth increases. The sailing angle
of
80
to 84° is therefore much higher than the traditional 60°.
Figs. nd 2 describe the well-path planning process with the re
sulting torque calculations.
4
The catenary curve is compared with
traditional constant-build curves with 1.5°/30- and 2.5°/30-m build
rates. A much lower sailing angle is achieved with the traditional
curve design. As a result, as Fig. 2 shows, the measured depth (MD)
of
the actual well path is longer than with traditional shapes. The
friction along the drillstring is lower, however, and a higher torque
at the bit is a welcome result.
The success
of
reducing wall contact and thereby the total friction
was reported in Ref. 4 and is shown in the simulations
of
comparison
of wall contact force in Fig. 3. Well 33/09-C03 has a standard pro
file; Well
33/09-C02 has a modified catenary profile. Note the dif
ference in scale in the two parts
of
Fig. 3. The very high normal force
in Well 33/09-C03 compared with the 33/09-C02 profile will give
similar marked higher friction and thus higher torque loss.
The well profile used in Statfjord Wells C24 and C2 may lead to
enhanced problems with formation stability and differential stick
ing owing to the high sailing angle. However, wherever these prob
lems can be handled, the modified catenary curve will give a lower
friction than traditional well profiles.
Monitoring
Hole Cleaning
The confidence in torque and drag simulation programs may give
unexpected benefits. When long-reach wells are drilled, the torque
and drag simulation curves may be used to monitor hole cleaning.
Deviations from properly modeled torque and drag simulations may
indicate hole-cleaning problems.
Fig. 4 shows torque simulations in Well 33/09-C02 and actual
measured torque in the l2V4-in. section. The three smooth curves are
the acceptable, planned, and actual torque simulations, respectively.
The marked change in simulation curves at about 2600 m was
caused by a bit change. An aggressive bit must be simulated with a
higher torque on bit than a less aggressive bit.
September 1994 •
JPl
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8/19/2019 SPE 27491torque Ndrag PA
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mTD
2
840
2.S130m
1.5130m
14
196
2520
3080
o 56 1120
1680
2240
2800
3360
3920
4480
5040
5600
Fig. 1-Well profi le planning, Well 33/09-C24.
4 5 ~ r ~ _ .
...-
...
/
. / - / ' ~ -
.....
4 1 ~
4 3 ~
/ .
/
......
,
; ;
3 7 ~ - /
::2 .........
D' . ...
..
-
o
3 5 ~
. '-
I-
3 1 ~
C2 4 PROP
•__ _1.5130
~ ~ ~
5000 5250 5500 5750
6 ~
6250 6500 6750 7000
Depth (mMD)
Fig. 2-Torque simulations for Well 33/09-C24 profiles.
Statfjord
C 33 9 C 3
65 m
Statfjord C
3319 C 2 74 m
1
4
6 12
lOOO
1
2
2
3
3
4
4
5
5
6
7
Fig. 3-lnfluence
of
profiles on wall forces.
JPI • September
1994
Torque,Nm
44000
41500
39000
36500
34000
31500
29000
26500
24000
21500
19000
16500
14000
11500
9000
6500
4000
2100 2600
3100 3600 4100 4600 5100 5600 6100 6600 7100
Depth
(m
MD)
Fig. 4-Torque simulations and measurements, 12V.-in. sec
tion, Well 33/09-C02
The acceptable hole-cleaning curve is the maximum allowable
torque to be measured before any attempt to clean the hole. The
marked drop in measured torque at 6300-m MD) was caused by a
trip with backreaming and a lower rate of penetration. The back
reaming provided a significantly cleaner hole and therefore a lower
torque.
Using the acceptable limit for maximum torque during drilling
operations provides the basis for deciding to begin hole-cleaning
operations
Planning and Running Casing and Liners
The ability to run and cement casings and liners depends heavily on
torque and drag in the well. Simulations of up- and down weights
and torque caused by rotation
of
the liners during cementing are
therefore performed in the planning phase
of
the well.
As described elsewhere.
2
4 such simulations have proved to be
in line with the measurements taken during operations. Thus. the
simulated curves for weights and torque are helpful to the driller
when running and cementing casing and liners because deviations
from the simulations may give early warnings
of
hole problems.
However. not all effects have been explained by simulation. One
example is the up- and downweights
of
the 7-in. liner in Well
33/9-C02. A thorough planning of the 7-in. liner included the fol
lowing observations from the up- and down weight simulation
curves.
From the planned curves Fig. 5). we can see that adding drill col
lars at the surface when the liner shoe is at about nOO m MD in
creases both the up- and down weight considerably because
of
weight added in the vertical part
of
the well. Changing from 5- to
51h-in. drillpipe can be seen on the slope of the upweight.
The second change in slope
of
the upweight. around 8000-m MD.
results from a minor drop in the well profile at this location. The
change in well profile also is reflected in the down weight. although
in a slightly different manner. The down weight drops as the liner en
ters the well profile change because of added friction when the liner
bends. As more liner elements enter the dropping section. the weight
2000 3000 4000 WOO
MMJl
SIOO 7000 OIO
Fig. 5-Simulation and measurements, 7-in. liner.
801
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8/19/2019 SPE 27491torque Ndrag PA
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starts to increase slightly again because of added mass in the drop
ping section. However, owing to the additional weight beneath the
change in well slope, the wall contact force increases again and
additional friction counteracts the added mass. For the rest of the
well, the weight settles more
or
less
on
the same level as before the
liner entered the dropping section.
When liner is run, one step in the operation procedure is to mea
sure the up- and downweightsof the liner. Fig. 5 shows the measured
results and the simulated curves. The similarity between the up
weight simulations and measurements is striking. However, the dis
crepancy in the down weight of the liner is also evident. The top
drive weight is approximately
40
000 kg, giving a total friction
along the borehole similar to the weight
of
the string from about
37oo-m MD.
The marked unexpected drop in downweight at 3700 to 3900 m
has not been fully explained
but
may be caused by measur ing at too
high a run-in velocity. Another possibility was that special centraliz
ers were used, although the upweight should have had similar ef
fects.
The discrepancy in the deepest part
of
the well may stem from
formation or hole-cleaning problems because it is reflected in both
up- and downweight plots. Nondestructive drillpipe buckling could
also explain this special feature.
Jarring
in
Long Reach
Wells
The influence of drag on the force available at the jar was discussed
in an earlier publication.
6
The effect on the impact force can be quite
substantial; therefore, the drag effect should be considered when an
extended-reach well is planned.
Use of a torque and drag simulator will enable calculations of
hook load for a given tension or compression on the jar. With such
calculations, it is possible to estimate the force available at the jar
if he string should stick. Therefore, the driller can use these calcula
tions to set and fire the jar in the most efficient way on the first signs
of
stuck pipe.
Another application is to plan the setting of the mechanical jar. It
is obvious that too high a setting will make the jar useless because
the available compression or tension over the jar may not be high
enough to fire it. However, with proper use of a torque and drag cal
culation program in the planning phase, the correct setting can be
used in the operations.
When deciding whether to use a mechanical or a hydraulic jar, the
available compression
or
tension at the
jar
is an important criterion.
A hydraulic jar will always fire if set and then put into tension or
compression. However, with a very low compression or tension in
the loading phase of the
jar
operations, a hydraulic
jar
may have a
loading time of several minutes. Consequently, the jarring opera
tions will not be effective. By doing the proper calculations in the
planning phase, we can avoid such ineffective jarring.
Fig. 6 gives an example of the drag influence on hook load as a
function of
jar
overpull force. The three curves are no drag, 10%
added mass to incorporate drag, and drag simulations. The addition
of 10% mass was the recommended practice but did not apply well
to extended-reach wells. It has been shown that in extended-reach
2500
. ~ ~ ~ ~
2000
+ - - - - - - - - - - ~ - _ j c - - - - - I -
......
...,
,
-- 1500
+ - - - - - - - - - _ j ~ ~ - I - - _ _ 1
Q
e
o
I
1000 +--- ---_j ___ - - - 1 - - - + - - _ _ j
H
500
+ - - - r - - ~ - - - - - 1 - - - + - - ~
250 500 750 1000
1250
Ja r
overpull
(kN)
- .. Max
with
drag
..
- •
Kax
+ 10% weight
-
Max
-
Simula ted ilnpact
Fig. 6 Drag influence on jar impact.
802
wells more than 1000-kN additional impact force at the stuck point
can be achieved by proper jar operations.
6
In such cases, thorough
knowledge of the drag effect on the available jar overpull force is
needed.
Casing Shoe Wear
During drilling of the extremely long 12Y4-in. section in Well
33/09-C02, some peculiar behavior of the torque was observed. In
Fig. 7, the predicted and measured torques are presented as func
tions of depth. Instead of increasing smoothly as predicted, the
torque seems to oscillate. Quite a lot
of
discussions have focused on
the possible source
of
these oscillations.
With a sailing angle of 82 to 84° and an extremly long 12Y4-in.
section, the possibility
of
casing wear will be present. The normal
force around the
13
3
/s-in. casing shoe will be directed upward;
therefore, the drill pipe may put a high stress on the casing shoe.
As shown, especially in the interval between 5800 and 5900 m,
there are 10 cycles of torque. The best explanation for the cycles
seems to be a groove in the casing shoe caused when the drill pipe
wore down the casing shoe. The spikes then result from the extended
diameter of the pipe around the tool joints. The observation that the
spikes were spaced about the length
of
the drill pipes was confirmed
when the string was pulled because similar torque cycles occurred
during backreaming.
When the 13
3
/s-in. casing is set at a given depth and angle, noth
ing can be done to prevent this wear. Because this well had an ex
tremely long 12Y4-in. section, this effect was more pronounced than
in standard wells. However, when future well profiles are planned,
we will select a better setting angle and thereby diminish casing
shoe wear.
mMD
P
r
~
l>
i
5700
. . -P
I
.$
...
~ ~
'
----
=
i
I
h .
1 .
~ - - - - - - l ~
- --
1-- - - ,
§:
7=
,
~
5900
1---- --------
- - - -
--
~ .
"=:.
-----
I
i S
~
g; .
_i:
r
h..
6000
~
"""'C
::::-
:::::=-
I
5-
:;;:
i
1 =
;S
6100
c=_
---_
.
o
8 16
24
32
40
Torque kNm
Fig. 7 Measured and simulated torque.
September 1994 •
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Operational
Procedures
Most North Sea fields have been planned with a rather shallow kick
off point, a build rate of3 to 4°/30 m and a sailing angle of about 60°.
In most situations, the drilling of such wells was straightforward. In
one field, however, drilling of some
of
these wells seemed difficult.
Analysis ofthese wells showed that the operations personnel continu
ously tried to get back on the planned well path whenever any devi
ations were detected in the buildup sections. Consequently, the dog
leg severity changed a lot between 0 and 4 to 5°/30 m. The wall
contact forces were therefore quite high in the shallow part of the
wells, which led to problems when trying to reach the final depth
goals in the deeper sections. It was recognized that one of the wells
that did not reach final depth probably could have achieved the
planned depth if the buildup section had been drilled more smoothly.
As a result
of
these studies, operational procedures were changed
to minimize dogleg severity in the shallow sections. Also, more
thorough planning of well paths was implemented for long-reach
wells. The success of implementing this knowledge into operational
procedures is confirmed in that torque and drag problems are not as
critical in drilling medium-reach wells.
s
In extremely extended-reach wells, one requirement for success
is incorporating teamwork into the planning and drilling of the
wells. When trying to achieve the mega-reach wells, everyone
must understand the background for the different operations.
Incorporating the torque and drag understanding of persons with
in the company into procedures for drilling is an important part of
the planning phase. The modified catenary curve demands a strict
adherence to low dogleg severity in the shallow part
of
the well and
a slow increase in build rate as depth increases.
I f
he importance
of
this plan is not understood, the final long-reach goal will not be
achieved. In Statfjord Wells 33/09-C24 and 33/09-C02, such team
work worked well, and the planned well path was followed within
acceptable deviations.
4
Conclusions
1.
Torque and drag are key factors in the planning and drilling of
extended-reach and horizontal wells.
2. Torque and drag calculations, together with measurements
of
torque and hookload, can be used to monitor hole-cleaning require
ments during drilling.
3. Torque and drag calcu lations should be used to optimize well
profiles.
4. Torque and drag calculations should be used to plan for opti
mized jarring operations in extended-reach and horizontal wells.
5. Torque and drag calculations, together with measurements,
may be used to detect drilling problems like casing-shoe wear.
6. Use of torque and drag calculations, together with measure
ments, can prevent stuck casings and liners.
cknowledgments
We thank Den Norske Stats Oljeselskap AlS (Statoil) for permission
to publish this paper. Special acknowledgment is given to the opera
tions people who planned and drilled the wells discussed in this pa
per.
References
I. Sheppard, M.C., Wick, C., and Burgess,
T.:
Designing Well Paths To
Reduce Drag and Torque,
SPE E
(Dec. 1987) 344.
JPl • September
1994
2.
Rasmussen, B. et al.: World Record in Extended-Reach Drilling, Well
33/9-CI0, Statfjord Field,
Norway, paper SPE 21984 presented at the
1991 IADC/SPE Drilling Conference, Amsterdam, March 11-14.
3.
Njrerheim,
A.
and
T j ~ t t a
H.: New World Record in Extended-Rea-::h
Drilling from Platform Statfjord C paper SPE 23849 presented lit the
1992 IADC/SPE Drilling Conference, New Orleans, Jan 18 -21.
4. Alfsen, T.E. et
at :
Pushing the Limits for Extended-Reach Drilling,
New World Record Well From Platform Statfjord C; Well C2, paper
SPE 26350 presented at the 1993 SPE Annual Technical Conference and
Exhibition, Houston, Oct.
3-6.
5. Eck-Olsen, J. et
at :
North Sea Advances in Extended-Reach Drilling,
paper SPE 25750 presented at the 1993 IADC/SPE Drilling Conference,
Amsterdam, March 11-14.
6. Aarrestad,
T.Y.:
Drag Calculations Improve Efficiency of Hydraulic
Jars,
Oil Gas
1. (March 29, 1993).
7. Eck-Olsen,
J. et at :
Designer Directional Drilling To Increase Total
Recovery and Production Rates, paper SPE 27461 presented at the
1994 IADC/SPE Drilling Conference, Dallas, Feb. 15-18.
8. Wilson, T.P. and Yalcin, 0.: Two Double-Azimuth Double-
S
-Shaped
Wells Planned and Drilled Using Torque and Drag Modelling, paper
SPE 23848 presented at the 1992 IADC/SPE Drilling Conference, New
Orleans, Jan 18-21.
9. Banks, S.M., Hogg, T.W., and Thorogood, J.L.: Increasing Extended
Reach Capabilities Through Wellbore Profile Optimisation, paper SPE
23850 presented at the 1992 IADC/SPE Drilling Conference, New Or
leans, Jan. 18-21.
10. Guo, B., Lee, R.L., and Miska, S.: Constant-Curvature Equations Im
prove Design
of
3-D Well Trajectory, Oil Gas 1. (April 1993).
11.
Aarrestad,
T.V.:
Effect
of
Steerable BHA on Drag and Torque in
Wells, paper SPE 20929 presented at the 1990 SPE European Petro
leum Conference, The Hague, Oct. 21-24.
12.
Thomas, G.B. Jr.: Calculus
and
Analytic Geometry, fourth edition, Ad
dison-Wesley Publishing Co., Reading, MA (1974).
51
Metric
Conversion
Factors
ft
x
3.048*
in. x2.54
Ibf
x
4.448 222
Ibm x 4.535 924
·Conversion factor is
exact
E-Ol =m
E+OO=cm
E+OO=N
E Ol
=kg
Thor
Viggo arrestad is an adviser for the Drilling Analysis, Drilling,
and Well Technology Dept. at Statoil in Stavanger. His expertise
is in high-pressure, high-temperature drilling
development,
dril
ling
technology
R D,
data
analysis methods,
and
arring
opera-
tion optimization. A member of the 1993 Forum Series in Europe
Committee,
Aarrestad holds
MS
and PhD degrees
in applied
mathematics from
the
U. of Bergen.
Harald
Blikra is a staff engi
neer for
the
Directional Drilling, Drilling,
and
Well Technology
Dept. at Statoil. Since joining Statoii, he has worked in direction
al drilling, directional surveying,and offshore drilling. He holds BS
and MS degrees in petroleum technology from Rogaland Dis-
triktschogskole.
arrestad Blikra
803