SPE 27491torque Ndrag PA

8/19/2019 SPE 27491torque Ndrag PA

1/4

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


2/4

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


3/4

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 •

JPT


4/4

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

Documents

SPE 27491torque Ndrag PA