1. Design, Testing and Modeling of Axial Oscillation Tools
Emmanuel Omojuwa, P.E.

2. Presenter Introduction
Licensed Professional Engineer (P.E.) – OK State Board of Engineers
Education
BS Mechanical Engineering (University of Lagos, Nigeria) – 2007
MS Petroleum Engineering (University of Oklahoma, Norman) – 2011
Ph.D. Candidate, Petroleum Engineering (University of Oklahoma, Norman)
Professional Experience
Drilling Engineer, Sterling Oil Exploration, Lagos, Nigeria –
MWD/LWD Engineer, Schlumberger Oilfield Svcs, Youngsville, LA –
Well Placement Engineer, Schlumberger Oilfield Svcs, Midland, TX–
Drilling Analysis Engineer, Schlumberger Oilfield Svcs, Midland, TX –
Senior Product Engineer, JA Oilfield Mfg. Inc., Oklahoma City, OK – 2015-

3. Presentation Outline Introduction
Design and Operation of Axial Oscillation Tools (AOTs)
Testing of AOTs
Modeling of AOTs in Drillstrings
Model Validation and Parametric Study
Conclusions and Recommendations

4. Introduction
Slide Drilling in Mud Motor Applications: Horizontal and Extended-Reach Wells
SWOB
Flow Rate
No RPM
Inefficiencies
Poor Weight Transfer
High Stick Slip & MSE
Unstable Toolface Control
Low ROP
Increased Drilling Cost
High Frictional Force
Gravity
Hydraulic Loading
Buckling
Axial Oscillation Tool (AOT)
Breaks Static Friction

5. Introduction Axial Oscillation-Supported Drillstrings (AOSD)
One or more axial oscillation tool(s) (AOTs) in the drillstring
Friction reduction technology for high-angle and extended reach wells
Conclusions from experimental and field studies show that axial vibrations is most effective in reducing friction
70,000+ successful runs across six continents in conventional and unconventional formations
Improved drilling efficiency: 200% increase in ROP and 50% reduction in WOB
(NOV Website, 2019)

6. Design and Operation of AOTs
Pulse height
Pressure drop
Total flow are (TFA)
Rotor/Stator Configuration
Pulse frequency
Rotor speed
Rotor/Stator Configuration

7. Design and Operation of AOTs
Performance of Axial Oscillation-Supported Drillstrings
AOTs Operating Parameters: Flow rate, frequency, fluid density, valve sizing, Pressure drop, AOT spring rate, pump open area (POA), type of drilling fluid, downhole temperature
Drilling Parameters: Weight-on-bit (WOB) and RPM
Friction: Coulomb friction damps oscillations (most dominant)
Borehole Geometry: High friction in curve and lateral sections
Drillstring characteristic: Stiffness, Length/Diameter ratio

8. Design and Operation of AOTs
Methods Used to Evaluate the Effectiveness of AOTs
Weight Transfer and ROP Improvement
Stick-slip and Torsional Vibrations
Toolface Control
Mechanical Specific Energy (MSE)
Drilling Dynamics (Axial Vibrations)
Source: (Skyles et al., 2012)

9. Testing of AOTs

10. Testing of AOTs Input Data (6.5 in. AOT) 200 gpm 400 gpm
Flow Rate vs. Frequency Relationship
Soft Stack
Stiff
Stack

11. Testing of AOTs Design Optimization of the Orifice/Valves Using FEA
Stress Analysis
Velocity Profile
Pressure Profile

12. Modeling of AOTs in Drillstrings
Displacement Excitation Model
Spring Rate ~ Key Input
Coulomb Damping ~ Equivalent Viscous Damping
Omojuwa, E., Ahmed, R., Acquaye, J. Practical Approach to Functional Testing and Analytical Modeling of Axial Oscillation-Supported Drillstrings. ASME. J. Energy Resour. Technol. 2019

13. Model Validation Martinez et al., 2013 Soft Stack at 200 gpm
Tian et al., 2016
Stiff Stack at 200 gpm
Stiff Stack at 400 gpm

14. Parametric Study Well Profile Drillstring Operating Parameters
8.5 in Bit
6.75 in. Motor
6.75 in. Float Sub
6.75 in. UBHO
2 x in. NMDC
6.75 in. Flex Joint
6.75 in. Crossover Sub
81 x 5 in. Drillpipe
6.75 in. AOT
5 in. DP to Surface
Flow rate (gpm)
Frequency (Hz)
Pressure Drop (psi)
250
9.5
280
300
11.4
380
350
13.3
540

15. Parametric Study 250 gpm, 9.5 Hz and 280 psi

16. Conclusions and Recommendations
Model inputs use practical data without the use of arbitrary values (e.g. excitation force).
Flow rate is the most fundamental parameter in the operations of AOTs.
Spring rate improves the accuracy of the model.
Embedding real time dynamic pressure transducers and strain gauges on AOTs and drillstring
Effects of damping and friction can be delineated with vibrations data on AOT and drillstring
Training of stakeholders on operating parameters of AOT and optimization strategies

17. Thank You