Friday, November 14, 2008

SEG 2008

Just returned from the 2008 SEG meeting in Las Vegas. I gave two talks. In the regular sessions on Tuesday afternoon it was "The Wolf ramp: Early work on reflectivity dispersion." The session was poorly attended, maybe 25 total. On Thursday afternoon in the Best of the Development and Production (D&P) Forum, my talk was "The physical basis of reflectivity dispersion" and it was much better attendance, perhaps 60 people in the room.

The basic idea of both is careful analysis of the seismic reflection process and what can lead to frequency dependent reflectivity. My list of candidates, in likely order of importance, is:
  1. Interference effects due to closely spaced reflection coefficients
  2. Processing errors (residual normal moveout, etc.)
  3. Geological or pore fluid transition zone (Wolf ramp)
  4. Rough surface scattering
  5. Porous-Porous reflection physics (Biot contact)

Tuesday, November 4, 2008

Thin Bed?

Hi Professor,

What would be a the thickness of thin beds roughly, in terms of travletime in ms or seconds, if you have an idea. Even a nudge in the right direction, in terms of references would be useful as well.

Thank you



The vertical resolution limit defines the thickness of a thin bed

h = L/4 = v / (4*f) = v*T/4 = v*t/2

L = wavelength, v = thin bed interval velocity, f = dominant
frequency, T = dominant period = 1 / f, and t = 2-way travel time
through the thin bed. Solving for the time thickness, t, gives

t = 2*h/v = L/2 = 1/(2*f) = T/2

So it looks like a bed is "thin" in a time sense when it is less than
or equal to the one-half of the period (for a monohromatic wave) or
one-half of the dominant period (for a broadband wave).

For example, if a wavelet has dominant frequency of about 30 Hz, a thin bed is one that has less than 15 ms time thickness.