Abstract: Crosswell Seismic Imaging at the McElroy CO[2] Pilot
LANGAN, ROBERT T., JERRY M. HARRIS, SPYROS K. LAZARATOS, ZHIJING WANG, and KARLA A. TUCKER
We have imaged both
fluid pressure changes and CO[2]-saturation effects in a Grayburg Formation
carbonate reservoir in the McElroy oil field in west Texas using time-lapse,
high resolution
crosswell seismology. These images have a
vertical
resolution
on the order of 10 to 15 ft (3 to 5 m). We use pre-CO[2] data collected
during a water flood to compute baseline images, and then we monitor changes
in the reservoir due to CO[2] displacing the oil-water mix by collecting
data during the CO[2] flood. We obtain two types of interwell images from
the crosswell data, P- and S-wave velocity images ("tomograms"), and P-wave
reflection images with frequencies exceeding 1000 Hz. In combination these
images are very powerful tools for determining reservoir architecture and
observing flow patterns within the reservoir.
Near an injector, the bulk
of flow (as defined by the velocity changes) is confined to a 40 ft (12
m) thick interval within the upper half of the 100 ft (30 m) thick reservoir.
The flow travels along relatively flat-lying strata (as defined by both
the reflection images and the velocity changes) for about 300 ft (90 m),
appears to "jump" upwards to a 20 ft (6 m) thick interval at the top of
the reservoir, and continues horizontally to a producing well. There are
disruptions in the reflection events at the "jump" that may be an indication
of a fracture that is allowing vertical
communication between flow units.
The time-lapse changes in the reflection amplitudes clearly support this
interpretation.
Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California