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The Science of Stick-Slip

IADC Stick-Slip Mitigation WorkshopJuly 15, 2010

John MacphersonBaker Hughes Inc.

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BendingBendingBending

WhirlWhirlWhirlLateral Vibration

Stick-SlipStickStick--SlipSlipTorsional Vibration

Bit BounceBit BounceBit BounceAxial Vibration

Jarring (impact)Jarring (impact)Jarring (impact)

Three Modes of Vibration

Torsional Vibrations

•Drillstring is a Spring-Mass System (Torsional Pendulum)

• Torsional Oscillation frequency is the first natural torsional frequency for the drillstring System

• Frequency is very low, usually less than 1/2 Hz, for a drillstring of any length.

Torsional Oscillation Period

• Analytic Calculation: Bailey J.J., and Finnie I., "An Analytical Study of Drill-String Vibration", Trans. ASME, May 1960, pp 122-128

•• Empirical:Empirical: period of oscillation increases by 2 seconds per 1,000m of 5” pipe (Dufeyte and Henneuse, 1991, IADC/SPE 21945)

0

2

4

6

8

10

12

14

0 5000 10000 15000 20000 25000 30000

6-3/4 x 200 ft BHA8-1/4 x 200 ft BHA

Drillstring Length, feetDrillstring Length, feet

Tors

iona

l Osc

illatio

n P

erio

d, s

econ

dsTo

rsio

nal O

scilla

tion

Per

iod,

sec

onds

Torsional VibrationsB

it R

otat

ion

Rat

e

A B C

• A – Increase RPM, B – Torsional Oscillations, C – Stick-Slip (period = 4.5s)

Smooth rotation Torsional Oscillations Stick-Slip

Stick-Slip: bit rotation periodically stalls during continuous surface rotation.StickStick--Slip: bit rotation periodically stalls during continuous surfaceSlip: bit rotation periodically stalls during continuous surface rotation.rotation.

Time (secs)

Field Example, downhole rotation measurements

Severe Stick Slip

200 250 300 350 400

600

400

200

0

Time (seconds)

0

10

20

30

50

100

150

kN.m

kN

Stick periods 24 s rotation periods 2.5s

Maximum DRPM 645; Surface 70

-165 RPM for 1.4s

Increase RPM

Vertical Well (2.5 deg), about 10,300 feet, measurements 8 feet above bit.

Stick-Slip Example Roller Cone Bit

15

10

0

5

-5400300

200

100

0

-100100

50

0

320 330 340 350 360 370

Wei

ght,

kNTo

rque

, kN

.mR

PM

Elapsed Time, seconds

• Downhole Rotation Rate• Stick-slip period = 3.3 seconds

Modeling: Stick-Slip Visualization

Downhole torsional oscillations and stick-slip behavior are visible as periodic torque fluctuations on surface

Downhole torsional oscillations and stickDownhole torsional oscillations and stick--slip behavior are visible slip behavior are visible as periodic torque fluctuations on surfaceas periodic torque fluctuations on surface

•• Drillstring SimulationDrillstring Simulation– Finite Element Model– Arbitrary curved and

straight boreholes– String can move freely in

wellbore– Wall contact penalty

formulation– Friction during drillstring-

wall contact – Torque on bit from a

coupled bit model

Bit and Drillstring Coupled Modeling

• Bit interaction with rock (rock properties) important

• Validated with high frequency downhole measurements

• “Falling friction” characteristic• Stribeck type bit-friction model

0 50 100 150 2000

3000

6000

9000

Rotational Speed [RPM]

Torq

ue o

n Bi

t [N

m]

0 5 10 15 200

3000

6000

9000

Torq

ue o

n Bi

t [N

m]

T ime [s]

0 5 10 15 200

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Time [s]

Rota

tiona

l Spe

ed [R

PM]

MeasurementSimulation

BBB nnT 91.49658.100608.5231

Reckmann, Jogi, Herbig, 2007, Reckmann, Jogi, Herbig, 2007, ““USING DYNAMICS MEASUREMENTS WHILE DRILLING TO DETECT LITHOLOGY CUSING DYNAMICS MEASUREMENTS WHILE DRILLING TO DETECT LITHOLOGY CHANGES HANGES AND TO MODEL DRILLING DYNAMICSAND TO MODEL DRILLING DYNAMICS””, paper 29710, OMAE, 26, paper 29710, OMAE, 26thth International ConferenceInternational Conference

Comparison of measurements and simulation for the Stribeck type bit

model

Comparison of measurements and Comparison of measurements and simulation for the Stribeck type bit simulation for the Stribeck type bit

model model

• Stick-slip likely when operating in region of “falling friction”• Increase RPM to reduce likelihood of stick-slip

Bit and Drillstring Coupled Modeling

Stick-Slip Likely Stick-Slip Unlikely

Reckmann, Jogi, Herbig, 2007, Reckmann, Jogi, Herbig, 2007, ““USING DYNAMICS MEASUREMENTS WHILE DRILLING TO DETECT LITHOLOGY CUSING DYNAMICS MEASUREMENTS WHILE DRILLING TO DETECT LITHOLOGY CHANGES HANGES AND TO MODEL DRILLING DYNAMICSAND TO MODEL DRILLING DYNAMICS””, paper 29710, OMAE, 26, paper 29710, OMAE, 26thth International ConferenceInternational Conference

Measuring Stick-Slip Downhole: Stick-Slip Index

RPM

RPMRPMSSIavg2

minmax

RPM

A B C

SSI 0 0.1 0.1 inc to 1.0 > 1.0

• A – Increase RPM, B – Torsional Oscillations, C – Stick-Slip (period = 4.5s)

SSI is encoded in a few bits and transmitted to surfaceSSI is encoded in a few bits and transmitted to surfaceSSI is encoded in a few bits and transmitted to surface

CoPilot Memory Depth LogCoPilot Memory Depth Log

Surf WOBSurf WOBklbfklbf

DH WOBDH WOBklbfklbf

Surf TRQSurf TRQftlbftlb

DH TRQDH TRQftlbftlb

Surf RPMSurf RPM

Max RPMMax RPMRPMRPM

Avg RPMAvg RPMRPMRPM

Min RPMMin RPMRPMRPM

S Slip SeverityS Slip Severity

Tangential VibTangential Vibgravitygravity

Bit BounceBit Bounce

Axial VibAxial Vibgravitygravity

Whirl SeverityWhirl Severity

Lateral VibLateral Vibgravitygravity

Stick-Slip SeverityMin, Max,

Average RPM

DH and SURF Torque

DH and SURF WOB

Axial Vibration Severity

Lateral Vib Severity

Example MWD Memory Log showing wellbore friction and stick-slip

Example MWD Memory Log showing Example MWD Memory Log showing wellbore friction and stickwellbore friction and stick--slipslip

Stick-Slip: Relationship to Failure

•• MWD ComponentsMWD Components– 2010 study, IADC/SPE 127413– Significant relationship to MWD tool failures:

1. Lateral Acceleration Peak Energy2. Lateral Acceleration 1s RMS Energy3. Cumulative RPM Variation (revolutions)4. Cumulative Backward Whirl5. Cumulative Stick-Slip Index

•• PDC BitsPDC Bits– May be damaged during stick-slip– Center of rotation off the center of the bit– Cutters on some part of the bit move

backwards for some portion of a revolution– Chipped and damaged cutters

Stick-Slip: Recognition and Control•• Measurement DownholeMeasurement Downhole

– Measure rotation rate of drillstring– Magnetometers and/or centripetal acceleration– Bit periodically stalls (MWD diagnostic transmission)

•• Measurement on SurfaceMeasurement on Surface– Rotary torque & rotary speed– Large periodic fluctuations in torque

•• StickStick--Slip ControlSlip Control– Manual (follow flow charts)

1. Reduce WOB, increase RPM2. Stop drilling, restart with decreased WOB, increased RPM

– Automatic• Soft-torque stick-slip control systems• Modifies drive speed control to reduce torsional fluctuations

– Downhole / Autonomous• Torque control Subs

0 2Stick-Slip Index

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20

40

60

Late

ral V

ibra

tion

(g)

1

Downhole Data Distribution for 219 MWD runsDownhole Data Distribution for 219 MWD runs

Fully Developed StickFully Developed Stick--SlipSlip

1

SlidingSliding

Reckmann etal 2010, Reckmann etal 2010, ““MWD Failure Rates Due to Drilling DynamicsMWD Failure Rates Due to Drilling Dynamics””, IADC/SPE 127413, IADC/SPE 127413

Stick-Slip and Lateral Vibrations

Contours showing data sets with average ROP in excess of 45 ft/hr, overlaid on colored surface defined by Stick-Slip Index and Maximum Lateral Acceleration.

0 2Stick-Slip Index

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20

40

60la

tera

l Vib

ratio

n (g

)

SlidingSliding Fully Developed StickFully Developed Stick--SlipSlip

High ROPLow LateralsModerate SSI

High ROPMod LateralsLow SSI

Downhole Data Distribution for 219 MWD runsDownhole Data Distribution for 219 MWD runs

Stick-Slip, Lateral Vibrations and ROP

Reckmann etal 2010, Reckmann etal 2010, ““MWD Failure Rates Due to Drilling DynamicsMWD Failure Rates Due to Drilling Dynamics””, IADC/SPE 127413, IADC/SPE 127413

The Science of Stick-Slip – Conclusions

– Torsional drillstring behavior includes both torsional oscillations and stick- slip. In stick-slip the bit periodically stalls in rotation

– Stick-slip is detrimental to drill bits, and sustained stick-slip can be damaging to MWD components

– Stick-slip behavior is relatively well understood, can be modeled, and can be recognized both downhole and on surface while drilling

– Stick-slip behavior can be mitigated manually, automatically, and using downhole subs

– Removing torsional oscillations from the system will result in the BHA being susceptible to high lateral vibrations, which could result in rapid MWD failure