Modeling on the Cheap: Creating a 3D Seismic
Velocity Model with Common
Software and Free
Data
John B. Hickman, Kentucky Geological Survey, University of Kentucky, Lexington, KY 40506-0107
Geoscientists use reflection seismic
data
to determine the
geometry of the geology of the subsurface. Unfortunately, a
seismic
section
displays in what is essentially an "apples and oranges" set of dimensions. The
horizontal (X, Y) dimensions are in distance units (meters, miles, etc.), while
depth (Z) units are in time (seconds). To make it even more complicated, the
correlation between these terrestrial and temporal units changes depending on
lithology, porosity, depth, etc. This not only changes the depth to subsurface
targets, but also can change their geometry (dips of anticline limbs, fault
planes, etc). This is not a problem for larger, well-funded petroleum
exploration companies since the calculations involved in this time-to-depth
correlation are included in all high-end
seismic
interpretation
software
packages. This software is often financially out of reach for researchers in
academia or for smaller independent exploration companies, however.
The computations and data
that make up
seismic
velocity
models are relatively simple. With the online availability of scanned images of
geophysical well logs in many areas, most geoscientists have all the software
they need already on their desktop computer. KGS researchers were able to create
a procedure using common spreadsheet and GIS software packages to manipulate
stratigraphic well tops and sonic log
data
into a 3D
seismic
velocity model. An
added advantage of this procedure is that it can be used in reverse, generating
expected depths in time of target horizons from nearby well
data
, even if no
sonic log was recorded from that particular well.
AAPG Search and Discovery Article #90059©2006 AAPG Eastern Section Meeting, Buffalo, New York