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Drilling dbs vibration
- 1. Modes Of Vibration MECHANISMS MODE OF VIBRATION FREQUENCY BIT BOUNCE AXIAL 1 - 10 Hz BIT CHATTER LATERAL 50 - 350+ Hz BIT WHIRL LATERAL / TORSIONAL 5 - 100 Hz BHA WHIRL LATERAL / TORSIONAL 5 - 20 Hz SLIP STICK TORSIONAL 0 - 5 Hz MODAL COUPLING AXIAL,LATERAL,TORSIONAL 0 - 20 Hz Bit Bounce • Causes – Bit/Formation Interaction – Multilobe Pattern of RC Bits – WOB Variation • Consequences – Impact Loading of Cutters, Seals and Bearings – Drill String Can Flex Causing Lateral Shocks • Detection – Axial movement of String at Surface at Shallow Depths – Shaking of Hoisting Equipment at Shallow Depths – Use Downhole Shock Sensor mounted for Z-Axis (DDS) – Broken Teeth / Inserts and Ball Race Indention's on RC Bits – Broken Nose Cutters on PDC Bits • Corrective Actions – Decrease WOB and/or Decrease RPM – If Persists Stop, Pick up and Restart with Low RPM and WOB until Bit is bedded in. • Other Solutions (Post Run) – Less Aggressive Bit – Use Shock Sub if run with correct RPM, WOB and ROP Bit Bounce Backward Whirl n Bit or BHA Whirl – Eccentric rotation about a point other than geometric center – Caused by Bit or BHA / Wellbore gearing – Results in backward rotation of circumferential points (e.g. blade tip) Backward Whirl Potential Consequences • Bit damage • MWD / BHA Tool component failures • Localized Tooljoint / Stabilizer Wear (Flat Spots) • Connection fatigue cracks leading to washout and / or twist off • Excessive torque • Enlarged / spiral wellbore profile Bit Damage Resulting From Whirl • Impact damage on rear of blades due to backward rotation, resulting in broken blades Forward Whirl • Eccentric rotation about a point other than geometric center – May occur with bent housing motors – Results in bit ‘rolling around’ wellbore synchronously with direction of rotation – Not generally damaging Bit Whirl Bottom hole patterns obtained from roller cone bits with 3 (left) and 2 (right) cones. (Ref SPE paper 28323) Lateral Vibration • Sideways movement of BHA • Random (chaotic) forward & backward whirl • Caused by imbalance BHA components • DDS indications: – Medium to high Px & Py – Low to medium Ax & Ay • Consequences similar to whirl Bit Chatter
- 2. • High frequency resonance of Bit and BHA caused by impacts of individual cutter blades or individual cutters • Occurs with PDC bits in high compressive strength rocks • Consequences – Bit cutter damage – Failure of electronic components and solder joints Bit Chatter • Detection – DDS high peak x and y accelerations – DDS high average x and y accelerations – Burst data shows high frequency peak in x and y axes • Corrective action – Adjust RPM and WOB down away from resonant condition • Other Solutions (Post Run) – Consider a bit more suitable to drill the high compressive strength rock or stringers Slip-Stick • Torsional Vibration of the Drill String • Initiated by mechanical or frictional resistance to Rotation – Non-Uniform Rotation of the Drill String – Repeated Stalling of the Bit, Twisting and Build up of Energy in the Drill Pipe then Freeing of the Bit Causing Energy Transfer from the Drill String to the BHA. – Rotary Drive Reacts to RPM Changes by Increasing or Decreasing the Torque Causing a Self Perpetuating Cycling • Consequences – Torque Cycling Over or Under Torques Connections – Fatigue Rates are Increased Through High Amplitude Shear Stress Cycling – Extreme Levels Cause the String to Rotate Backwards at the End of the “Slip” Phase Damaging PDC cutting Structures – Extreme Levels Can Back off Connections – Lateral Shocks are Associated with the Free Spinning in the Slip Phase Stressing Collar Connections and Damaging Downhole Electronics Slip-Stick • Detection – Surface Torque and RPM Oscillations : “Slip-Stick” monitoring Systems or DrilSaver – Downhole Sensors : DDS, 4D – Surface Instrumented Subs : Adams • Corrective Actions – Increase RPM, Decrease WOB – If Vibration Persists Pick up and Restart Drilling with Higher RPM. Slip-Stick • Other Solutions – Less Aggressive PDC bit, Select Rock Bit – Good Drilling Practices to Create Smooth Well Profile Slip-Stick Slip-Stick Torsional Vibration Example ‘FLAT-TOP’ TRQ TRACE DUE TO LIMIT BEING Coupling of Vibration Mechanisms Coupling means that one vibration mechanism can induce another SLIP-STICK HIGH RPM During slip phase BIT WHIRL AXIAL BIT WHIRL D WOB & Bending • Hole Angle – Lateral Vibrations are More Likely in Vertical Wells – In Directional and High Angle Holes Gravity Damps Lateral Displacement – Deviated and High angle Holes are More Likely to Induce Torsional Vibration – High Angle, Tortuous Holes and Large Dogleg Severities Increase Frictional Torque Factors Effecting Downhole Vibration • BHA Design
- 3. – Use of a Downhole Motor Reduces Energy Interactions Between BHA and Wellbore – Packed Assemblies are less Susceptible to Vibration than Slick Assemblies – Under Gauge Stabilisers are more likely to generate Whirl – Surround MWD with Full Gauge Stabilisers to protect the Tool Factors Effecting Downhole Vibration • Drill Bits – PDC bits tend to Whirl at High RPM in Hard formations – Dull or Under Gauge PDC bits can generate “Slip-Stick” Torsional Vibrations – Too High WOB and Too Low RPM creates Torsional Vibration and “Slip-Stick” – Roller Cone bits can bounce, Axial Vibration, in Hard Formations or if too low WOB is applied Factors Effecting Downhole Vibration Factors Effecting Downhole Vibration • Lithology – Vibration Increases with Formation Strength – Vibrations are Particularly Associated with Zones of High and Low Compressive Strength • Hole Size – Over Gauge Hole leads to Lateral Shocks, BHA Whirl and Bit Whirl – Under Gauge Hole Creates Torsional Vibration • Drilling Mud – Mud Condition and type can Influence Vibration levels Vibration Mechanisms • Each Mechanism Describes the Behaviour of the Drill String During Vibration – Bit Bounce – Slip-Stick – Bit Whirl – BHA Whirl – Modal Coupling – Bit Chatter – Lateral Shock Motion Methods of Reducing Vibration Damage • Bit Design – F.A.S.T., SE3000, • Planning - BHA design – WHIRL • Real-time vibration monitoring – DDS, DrilSaver, Instrumented Bit, VSS, AcoustiCaliper, WOB/TOB • Improved Tool Reliability • Reduced Vibration Drilling systems – SlickBore, Geo-Pilot Force Balancing Penetration and Drag Cutter Forces Fvertical = WOB Mcenterline = TORQUE Fradial = 0 M M M Engagement PDC Cutter F P WOB TORQUE • Symmetric blades create a lobed bottom hole pattern in a regular periodic manner which can lead to self-regenerative whirl • Asymmetric blade layout upsets the periodic pattern thus disrupting the harmonic effects of a lobed bottom hole pattern Asymmetric Blade Layout 0 0° 248° 105° Asymmetric Symmetric 0° 120° 240° Symmetric
- 4. Predicted Lobe Generation for Symmetric & Asymmetric • Symmetric Asymmetric 120° 0° 240° 0° 105° 248° Low Torque Gauge Pads • Removal of sharp edges and aggressive wear surface reduces ability of gauge pad to bite into borehole wall. • Creates less drag between the bit and the borehole wall reducing any tendency to pivot about a gauge pad. Spiraled Blades As with asymmetry, spiraled cutter layouts and gauge pads help break up any regenerative lobed cutting patterns by: • Lessening probability of a new center of rotation occurring along a cutter blade or gauge pad. • Effectively increases resistance of the gauge pad from biting into the borehole wall. • When spiraled, the release of a blade happens in closer proximity with the contact of the next, passing the load to the next blade more smoothly. Trac-Set Cutting Structure Unlike the standard layout, the ridged pattern created by a Trac-Set cutting structure resists the bits tendency to move laterally by stabilizing on formation ridges. Standard Layout Trac-Set Restoration Forces Standard Set 13mm PDC. 50 FPH. 120 RPM No Offset Total Vertical Fv = 408 lbf = = Net Radial Force Fr = 0.0 lbf = = Outside Radial Fr1 = 38.4 lbf Fr1/Fv = 0.094 Inside Radial Fr2 = 38.4 lbf Fr2/Fv = 0.094 13 mm PDC. 50 FPH. 120 RPM < - Offset 0.025” Total Vertical Fv = 408 lbf < = = Net Radial Force Fr = 8.48 lbf < = = Outside Radial Fr1 = 35.7 lbf Fr1/Fv = 0.088 Inside Radial Fr2 = 44.1 lbf Fr2/Fv = 0.108 Restoration Forces Trac Set 13mm PDC. 50 FPH. 120 RPM No Offset Total Vertical Fv = 451 lbf = = Net Radial Force Fr = 0.0 lbf = = 13 mm PDC. 50 FPH. 120 RPM < - Offset 0.025” Total Vertical Fv = 454 lbf = = > Net Radial Force Fr = 35.8 lbf = = > Outside Radial Fr1 = 81.0 lbf Fr1/Fv = 0.180 Inside Radial Fr2 = 81.0 lbf Fr2/Fv = 0.180 Outside Radial Fr1 = 96.4 lbf Fr1/Fv = 0.212 Inside Radial
- 5. Fr2 = 60.6 lbf Fr2/Fv = 0.180 Impact Arrestors Impact Arrestors act to dampen chaotic vibrations that typically exist downhole by providing stabilization to both the axial and lateral modes of vibration. Impact Arrestor PDC Impact Arrestors Standard W / Impact Arrestors ROP Time > Axial Vibration Reduction ROP DDS Tool The DDS Sensor consists of tri-axial accelerometers mounted on the DGR gamma sensor electronics insert Records accelerations in g as Average, Peak, and Burst Vibrations DrilSaver • DrilSaver is an advanced “Slip-Stick” monitoring system – Uses Fourier analysis to breakdown the torque signal, providing a frequency domain spectrum of the of the torque oscillation – Sinusoidal oscillation in the torque signal is characteristic of torsional vibration present in the drillstring – DrilSaver provides a method of quantifying torsional vibration (KT magnitude) Whirl Program • Based on the DYNAMICS program developed by Boeing • Further developed by Dykstra at Tulsa University and Amoco • Incorporated into Sperry-Sun’s well planning software (PLANIT) • Uses Jacobi and finite element analysis to predict critical rotary speeds for excitation of fundamental lateral vibrations (resonance) of BHA in drilling fluid in a straight hole (vertical or inclined) Slickbore Bit Slickbore Bit on Geopilot Slickbore Bit • End of story