LDEO-BRG designed, manufactured and deployed a three-axis SWD pilot sensor which is rigidly fastened on the drill string below the top drive. The pilot sensor is capable of acquiring drill string vibration data for 60-72 hours without interferring with normal rig floor operations. Data is telemetered in real-time to the downhole measurement lab using wireless technology. The onboard accelerometer measures drill string movements up to 460 Hz although the frequencies between 0.6 Hz to 50 Hz are used for analysis. Data analyzed from two sites in the Indian Ocean has revealed possible correlations with drill string vibration signal and porosity (Myers et al., 1999). Physical properties of the drilled rock may be infered in real time, even in the absence of core and log data. The unit can be adapted to acquire high resolution drill string heave data.

Applications

Seismic-while-drilling (SWD) a.k.a. reverse VSP
There are two significant advantages.
(1) Measurements can be made without taking substantial rig time.
(2) With a suitable telemetry link and on-line processing, measurements can be made in near real-time, providing useful information to both drillers and scientists as the hole is being drilled.

Drill String Vibration Experiments
(1) The autocorrelation function of the drill pipe may be used to detect in gross-scale boundary contacts in real-time
(2) measure ship's heave

Specifications

Data Transmission	text
Freewave wireless modem	t Color
DRG0-115 spread spectrum transceiver	text
Freqency	902 - 928 MHz
Transmission rate	115 Kbaud
Output power	1W (+30 dBm)
Sampling rate	400 Hz
Accelerometer	t Color
Type 34103A precision tri-axial accelerometer	text
Sensitivity	~850 mV/g
Measurement range	+/- 2.5g
Upper cutoff frequency	460 Hz (-3 dB)
Signal Processing	t C
Number of channels	3
Frequency bandwidth	0.6 - 50Hz
Pass-band ripple	+/- 1 dB
Programmable gain amplifier	1 0 - 18 dB, 6 dB step
Programmable gain amplifier	2 0 - 60 dB, 20 dB step
AD Converter	AD976, 16 bits
ADC dynamic	Range 96 dB
ADC SNR	86 dB
Simulation signal sinewave	20 +/- 2 Hz 50 mV, controlled on/off
Physical	t C
DrillPipe diameter	8 inch
Weight	100 lbs (approx)
Height	36 inches (approx)
Diameter	20 inches (approx)
Clamp	Bronze Wedge Clamps

Data Presentation

The acceleration data acquired by the SWD pilot sensor are compared to core measurements. Note the sharp contact at the 370 meters. This indicates that the accelerration data may be useful in inferring lithologic contacts.

Deployment

The SWD pilot sensor is easily installed and removed from the drill pipe. Once installed the pilot sensor does not interfere with normal rig floor operations nor consume any additional time.