Dec. 6, 2012


"Pore pressure prediction advantages (and disadvantages) of P-wave velocities, S-wave velocities, C-wave velocities, and registration-based Vp/Vs ratios from surface and borehole seismic surveys"

Velocity fields are a necessary consequence of seismic data processing, but rarely a key deliverable. The use of velocities to predict pore pressure in the subsurface generally represents an opportunistic leveraging of what is essentially a QC product, to be used in a process for which the product was not specifically intended. Some velocities are picked (or re-picked) specifically for pressure prediction, but this is the exceptional case.
Because the vast majority of seismic data are collected for P-wave imaging, the great majority of pressure predictions from seismic velocities will be performed on P-wave velocity cubes. P-wave velocities are less sensitive to pore pressure variations than are S-wave velocities, C-wave (mode converted P-wave) velocities, or interval Vp/Vs ratios. P-wave interval velocities (derived from P-wave moveout curves), as a saving grace, generally have much less pronounced anisotropic traveltime effects than SV or SH-wave interval velocities derived from SV- or SH-wave moveout curves.
3D/4C surveys are often acquired with an eye to utilizing C-wave images to augment co-located P-wave images in image-challenged portions of the survey area. As with 3D P-wave surveys, which require the production of a 3D P-wave velocity cube for seismic processing, a 3D/4C survey will require the production of a C-wave velocity cube. This C-wave velocity cube will have higher pore pressure sensitivity than the co-located P-wave velocity cube, but will also have higher VTI anisotropic moveout effects.
Land shear vibrators can be used to acquire pure mode S-wave data, whose velocities will have the highest pore pressure sensitivity. However, the production of true S-wave data is extremely limited. To the best of the speaker’s knowledge, only one commercial enterprise and a handful of academic consortia are currently collecting S-wave reflection data in North America. So the higher sensitivity of S-wave velocities to pore pressure and the greater magnitude of S-wave VTI anisotropy (SH or SV) is not a pressing issue at this time.
For custom (bespoke) pore pressure prediction problems, lookahead VSPs can offer the opportunity to derive interval Vp/Vs ratio ahead of the bit by registering near-vertical P-wave and C-wave (P-down, S-up) events. The interval Vp/Vs ratio can be converted to a pore pressure either by Eaton’s method (with suitable choice of exponent) or by application of a direct vertical method. As with a velocity based approach, a Vp/Vs pore pressure prediction requires establishment of a normal compaction trend.
Possibly the most interesting application of enhanced S-wave velocity sensitivity to pore pressure lies in the arena of well logging.  Dipole logging returns both P-wave and S-wave velocities over a given interval. The S-wave velocity has the dual benefit of not being sensitive to fluid velocities, yet being more sensitive to changes in pore pressure. On the debit side, the S-wave velocities are generally more sensitive to hole deviation than are the P-wave velocities.
References for these applications can be found in a December 2006 TLE review article “Subsalt pressure prediction from multicomponent seismics (and more!)”, or by dropping an email to the speaker at

Featured Speakers

Speaker Dan Ebrom

Date and Time

Thu, Dec. 6, 2012

5 p.m. - 5:30 p.m.
(GMT-0600) America/Chicago

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WesternGeco, Schlumberger

Richmond Avenue
Houston, Texas 77042

Houston Advanced Geophysical Training Center 10001 

Group(s): General Meeting