Physical model for the downhole orbital vibrator (DOV) - I. Acoustic and borehole seismic radiation

Details Physical model for the downhole orbital vibrator (DOV) - I. Acoustic and borehole seismic radiation Physical model for the downhole orbital vibrator (DOV) - I. Acoustic and borehole seismic radiation

Nov 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005geoji.163..647l&link_type=abstract

Geophysical Journal International, Volume 163, Issue 2, pp. 647-662.

Physics

Geophysics

2

Borehole Geophysics, Flow Imaging, Radiation Patterns, Synthetic Waveforms, Vibroseis

Scientific paper

The downhole orbital vibrator (DOV) applies the Vibroseis principle to borehole seismic sourcing. Accelerations by an internal rotating eccentric mass excite cylindrical pressure waves converted at the wellbore to seismic waves essentially within 20°-30° of the plane normal to the borehole. DOV pressure waves in open water are quantitatively described by a rotating point force radiating acoustic waves with displacement amplitude u(r) ~ 1/2 u0γR1/r, where R1=π2ρdov/ρwatera2l/λ2~ 1 mm is the DOV effective size for DOV radius a~ 5 cm, length l~ 1 m and acoustic radiation wavelength λ~ 10 m, and u0~ 1μm and γx are, respectively, the frequency-independent DOV displacement amplitude and the direction cosine of the observer relative to the instantaneous point-force axis in the plane of the rotating point force. Crosswell seismic radiation amplitude, spectrum and angular dependence are quantitatively described by acoustic wave diffraction at a slit with DOV axial cross-section 2al, followed by conversion to seismic waves at the wellbore. Seismic wave displacement amplitudes u(r) ~u0γR2/r scale with effective radius R2~ 2al/λ~ 1 cm. The frequency dependence of R2 is observed as linear frequency enhancement of the seismic wavelet spectrum relative to the source wavelet spectrum. DOV borehole P- and S-wave production peaks strongly in the plane of DOV rotation, with converted S waves both parallel to and transverse to the borehole axis. The small effective source sizes R1~ 1 mm and R2~ 1 cm at operational frequencies 50-350 Hz imply that DOV motion in a borehole is dynamically decoupled from the borehole wall. Dynamic decoupling allows DOV borehole seismic correlation wavelets to be quantitatively modelled in terms of a stable kinematic relation between source and sensor motion. Acoustic and seismic data rule out dipole-source action associated with claims for shear traction and primary S-wave radiation from boreholes. The stable linear kinetics of DOV acoustic action in borehole fluids produces (i) useful crosswell seismic signals at offsets to 650-800 m, (ii) negligible tube waves and (iii) stable seismic wavelets suited to in situ time-lapse seismic imaging of fluid migration fronts in crustal reservoirs.

Affiliated with

Also associated with

No associations

Rating

Physical model for the downhole orbital vibrator (DOV) - I. Acoustic and borehole seismic radiation does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Physical model for the downhole orbital vibrator (DOV) - I. Acoustic and borehole seismic radiation, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Physical model for the downhole orbital vibrator (DOV) - I. Acoustic and borehole seismic radiation will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1657328