Rock Property
Data Volumes from Well Logs
Denham, Leslie Richard1, H.
Roice Nelson2 (1) II&T,
Geology is sampled densely by wells
vertically, but sparsely and irregularly horizontally. A modern seismic survey
has sparse samples vertically, but close and uniform sampling horizontally.
Seismic data is more useful for regional trends, but does not convey
petrophysics, and is difficult to relate to wells. Inverting seismic data to
resemble well data is almost impossible. Can we make well data resemble seismic
data, not just a single-trace, but a complete volume?
We reduced well vertical sample interval
to 60 m, computing numerous petrophysical properties. Then we computed vertical
arrays of values for each property on a regular grid, using the samples
computed at each well location. Wells within a specified radius were used,
weighted inversely with distance, and well samples
over a limited depth range, weighted inversely with depth difference from the sample
depth. The computed three-dimensional array was written to disk in SEG Y
format, and loaded into a seismic interpretation system.
In the initial project we generated data
volumes for shale and sand P-wave velocities and densities, sand percentage, and
pressure (mud weight), for most of the
Petrophysical data volumes generated from
well information allow the geologist to integrate information from thousands of
wells using standard interpretation systems. So far, the technique seems to be
more suited to regional analysis rather than to prospect development.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California