High Speed Orbital Vibrator Development Status: March 2003

1. High Speed Orbital VibratorDevelopment Status: March 2003 Tom Daley Ernie Majer, Ray Solbau (all at LBNL) Engineering Design: Jack Cole (Independent, Univ. of Arkansas) Assistance: Ramsey Haught, Don Lippert, Cecil Hoffpauir (LBNL)

2. Why use an orbital vibrator? • O.V. generates P- and S-waves from separate orthogonal components of motion • S-wave is separated from P-wave coda • O.V. can obtain S-wave single-well data • Borehole seismic source choices are limited, e.g.: • Piezoelectric • Air Gun * • Clamped mechanical vibrator* *Difficult to maintain and operate

3. Example Crosswell O.V. Data Cross-Line source minimizes P-wave coda Cross-Line Source (Y) In-Line Source (X) Time (ms) 0 100 200 300 P-Wave S-wave S-wave Source at 2864 ft; Sensors 2048 – 3648 ft. at 8 ft intervals Well Spacing ~ 250 ft. Data from Bayou Choctaw, La

4. Example Single-Well Shear-Wave Data4-component data measures S-wave Splitting Receiver Component Y X Shear Wave Depth Depth Time X Source Component Time Y Data from Lost Hills, Ca

5. O.V. Operating Principle

6. O.V. Frequency vs TimePrevious Max Frequency ~380 Hz Frequency (Hz) 0 100 200 300 400 500 600 700 800 900 1000 0.0 2.0 Time (s) 4.0 6.0 8.0

7. Needs for High Speed O.V. • Need Higher frequency (1000 Hz) • Better resolution, more power • Need Smaller diameter (< 4”) • Well Access – especially for environmental applications • Need Crosswell and Single-well

8. First: Get a high speed motor • 1100 Hz • Diameter < 2.5'' • Three phase AC, 460 V, 4 amp, 4 H.P. Second: Design the source around the motor

9. The “guts” of the source Motor 3.85'' Stator 2.37'' Shaft 1'' Weights Rotor Weights

10. All Major Internal Parts Accelerometer Housing Bearings Bearings Ceramic bearings rated to 700 Hz Seals (now removed)

11. The Eccentric Weights Tungsten Rods 1''

12. Initial Shop Test: 6 Weights Frequency (Hz) 0 200 400 600 800 1000 1200 1400 1600 1800 2000 0.0 5.0 10.0 Time (s) 15.0 20.0 Sweep designed for 1000 Hz, only reached ~850 Hz

13. Test sweeps 800 Hz 900 Hz 1000 Hz No Weights 2 Weights 800 Hz 4 weights

14. Radial Force of Spinning Eccentric Weight F = m r w2 me = 0.027 kg for 2 weights re = 0.0086 m For f = 900 Hz, w = 5655 radian/s Fe = 7426 N = 1670 lbs

15. High Speed O.V. Force and Acceleration Force on tool (Ft) = Force of mass (Fe) Ft = mt at = me ae at = me ae / mt Tool Mass (as tested without outer shell) = 3.6 kg at = 2046 m/s2 (predicted at 900 Hz) at = 1991 m/s2 (measured at 900 Hz) = 200 G Ft = 7227 N (1634 lb) measured Displacement at 900 Hz = 6 x 10-5 m (measured)

16. O.V. Acceleration For 2 rods at 900 Hz: at predicted: 2046 m/s2 at measured: 1991 m/s2 (200 g) For 2 rods at 1000 Hz: at predicted: 2525 m/s2 at measured: 2197 m/s2 (224 g) For 6 rods at 850 Hz: at predicted: 5271 m/s2 at measured: 2350 m/s2 (240 g)

17. Fully Assembled Cable Head Outer Shell 3.5 inch O.D. Approximate Location Of Motor Shell

18. First In Well Test: March 11, 2003Bldg 64 Test Wells 0 200 400 600 800 1000 1200 1400 1600 1800 2000 0 10 20 30 Time (s)

19. Raw Data Clipped (Too Much Energy !)

20. Clipped Sensor Data 0 200 400 600 800 1000 1200 1400 1600 1800 2000 0 10 20 25 Time (s)

21. First Borehole TestDeconvolved, Decomposed(P-wave despite clipped raw data!) X Source Component Y 0 3 6 9 12 14 P-wave Time (ms) ~ 3 m Between Wells

22. First In-Well Test Results • P-wave Data obtained despite clipping sensors • Deconvolution fairly robust • 3 m well spacing too close! • 1000 Hz data obtained in shallow soils • Post survey inspection of source showed motor housing slipped inside of outer shell.

23. Status • Source needs to be modified to keep motor housing from slipping inside outer shell. • Source control needs to be automated • Different cable needed: too much noise on accelerometer • Next test probably at R.F.S. where wells are farther apart