The Science of Stick-Slip IADC Stick-Slip Mitigation Workshop July 15, 2010 John Macpherson Baker Hughes Inc.
1
Three Modes of Vibration
Lateral Vibration
Bending Bending Whirl Whirl
Torsional Vibration
Stick -Slip Stick-Slip
Bit Bit Bounce Bounce Axial Vibration Jarring Jarring (impact) (impact)
2
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 Torsional Oscillation Period, seconds
14 12 10 8 6
6-3/4 x 200 ft BHA 8-1/4 x 200 ft BHA
4 2 0 0
5000
10000
15000
20000
25000
30000
Drillstring Length, feet • Analytic Calculation: Bailey J.J., and Finnie I., "An Analytical Study of Drill-String Vibration",
Trans. ASME, May 1960, pp 122-128 • Empirical: period of oscillation increases by 2 seconds per 1,000m of 5” pipe (Dufeyte and Henneuse, 1991, IADC/SPE 21945)
Torsional Vibrations Smooth rotation
Torsional Oscillations
Stick-Slip
Bit Rotation Rate
Field Example, downhole rotation measurements
A
B
C
Time (secs)
• A – Increase RPM, B – Torsional Oscillations, C – Stick-Slip (period = 4.5s)
Stick -Slip: bit Stick-Slip: bit rotation rotation periodically periodically stalls stalls during during continuous continuous surface surface rotation. rotation.
Severe Stick Slip Maximum DRPM 645; Surface 70
Stick periods 24 s rotation periods 2.5s
Increase RPM
600 400 200 0 -165 RPM for 1.4s
kN.m 30 20 10 0 kN 150 100 50 200
250
300
Vertical Well (2.5 deg), about 10,300 feet, measurements 8 feet above bit.
350
Time (seconds)
400
Stick-Slip Example Roller Cone Bit
Torque, kN.m
15 10 5 0
Weight, kN
-5 400 300 200 100
RPM
0 -100 100 50 0 320
330
340
350
Elapsed Time, seconds
• Downhole Rotation Rate • Stick-slip period = 3.3 seconds
360
370
Modeling: Stick-Slip Visualization • Drillstring Simulation – Finite Element Model – Arbitrary curved and straight boreholes – String can move freely in wellbore – Wall contact penalty formulation – Friction during drillstringwall contact – Torque on bit from a coupled bit model
Downhole -slip behavior Downhole torsional torsional oscillations oscillations and and stick stick-slip behavior are are visible visible as as periodic periodic torque torque fluctuations fluctuations on on surface surface
Comparison Comparison of of measurements measurements and and simulation simulation for for the the Stribeck Stribeck type type bit bit model model
TB 5231.608 100.658 n B 49.91 n B
Torque on Bit [Nm]
properties) important • Validated with high frequency downhole measurements • “Falling friction” characteristic • Stribeck type bit-friction model
Rotational Speed [RPM]
• Bit interaction with rock (rock
Torque on Bit [Nm]
Bit and Drillstring Coupled Modeling 9000
Measurement
6000
Simulation
3000 0 0
50 100 150 Rotational Speed [RPM]
200
9000 6000 3000 0 0
5
10 T ime [s]
15
20
0
5
10 T ime [s]
15
20
200 100
0
Reckmann, Jogi, Herbig, 2007, “USING DYNAMICS MEASUREMENTS WHILE DRILLING TO DETECT LITHOLOGY CHANGES CHANGES th AND TO MODEL DRILLING DYNAMICS” DYNAMICS”, paper 29710, OMAE, 26 International Conference
Bit and Drillstring Coupled Modeling Stick-Slip Likely
Stick-Slip Unlikely
• Stick-slip likely when operating in region of “falling friction” • Increase RPM to reduce likelihood of stick-slip Reckmann, Jogi, Herbig, 2007, “USING DYNAMICS MEASUREMENTS WHILE DRILLING TO DETECT LITHOLOGY CHANGES CHANGES AND TO MODEL DRILLING DYNAMICS” DYNAMICS”, paper 29710, OMAE, 26th International Conference
Measuring Stick-Slip Downhole: Stick-Slip Index maxRPM min RPM SSI 2 avgRPM SSI
0.1
0
0.1 inc to 1.0
> 1.0
RPM
A
B
C
• A – Increase RPM, B – Torsional Oscillations, C – Stick-Slip (period = 4.5s)
SSI SSI is is encoded encoded in in aa few few bits bits and and transmitted transmitted to to surface surface
CoPilot Memory Depth Log Surf WOB klbf DH WOB klbf
Surf TRQ ftlb DH TRQ ftlb Surf RPM
Max RPM RPM Avg RPM RPM Min RPM RPM
Min, Max, Average RPM
DH and SURF Torque
DH and SURF WOB
Example Example MWD MWD Memory Memory Log Log showing showing wellbore -slip wellbore friction friction and and stick stick-slip
S Slip Severity
Bit Bounce
Whirl Severity
Tangential Vib gravity
Axial Vib gravity
Lateral Vib gravity
Stick-Slip Severity
Axial Vibration Severity
Lateral Vib Severity
Stick-Slip: Relationship to Failure •
MWD Components – –
•
2010 study, IADC/SPE 127413 Significant relationship to MWD tool failures: 1. Lateral Acceleration Peak Energy 2. Lateral Acceleration 1s RMS Energy 3. Cumulative RPM Variation (revolutions) 4. Cumulative Backward Whirl 5. Cumulative Stick-Slip Index
PDC 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 Downhole
•
Measure rotation rate of drillstring Magnetometers and/or centripetal acceleration Bit periodically stalls (MWD diagnostic transmission)
– – –
Measurement on Surface
• – –
•
Rotary torque & rotary speed Large periodic fluctuations in torque
Stick-Slip Control – Manual (follow flow charts) 1. Reduce WOB, increase RPM 2. 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
Stick-Slip and Lateral Vibrations Downhole Data Distribution for 219 MWD runs
Lateral Vibration (g)
60
40
20
0 0
2
1
Stick-Slip Index
Sliding
1 Fully Developed StickStick-Slip
Reckmann etal 2010, “MWD Failure Rates Due to Drilling Dynamics” Dynamics”, IADC/SPE 127413
Stick-Slip, Lateral Vibrations and ROP Downhole Data Distribution for 219 MWD runs
High ROP Mod Laterals Low SSI
High ROP Low Laterals Moderate SSI
lateral Vibration (g)
60
40
20
0 0
2 Stick-Slip Index
Sliding
Fully Developed StickStick-Slip
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. Reckmann etal 2010, “MWD Failure Rates Due to Drilling Dynamics” Dynamics”, IADC/SPE 127413
The Science of Stick-Slip – Conclusions – Torsional drillstring behavior includes both torsional oscillations and stickslip. 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
