The detailed analysis of cross well seismic data for a gas reservoir in
Texas revealed two newly detected seismic wave effects, recorded
approximately 2000 feet above the reservoir. A tube-wave (150) is
initiated in a source well (110) by a source (111), travels in the source
well (110), is coupled to a geological feature (140), propagates (151)
through the geological feature (140), is coupled back to a tube-wave
(152) at a receiver well (120), and is and received by receiver(s) (121)
in either the same (110) or a different receiving well (120). The
tube-wave has been shown to be extremely sensitive to changes in
reservoir characteristics. Tube-waves appear to couple most effectively
to reservoirs where the well casing is perforated, allowing direct fluid
contact from the interior of a well case to the reservoir.