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<abstract>
<title>Time-lapse seismic imaging of enhanced coalbed methane 
production: a numerical modelling study</title>
<author>Sarah E. Richardson and Don C. Lawton</author>
<p>Coalbed methane (CBM) production relies on dewatering coal seams to
allow gas flow, and the injection of carbon dioxide to maintain
effective reservoir pressure.  Injection of carbon dioxide into CBM
strata also serves as an effective method of subsurface greenhouse gas
sequestration. Both dewatering and gas injection alter the acoustic
impedance and hence reflectivity of coal strata. Physical tests and
numerical modelling suggest that time-lapse seismic imaging may be
used effectively to image the changes in a coalbed methane reservoir
that result from CBM production. Seismic responses of coal seams
change due to differences in the acoustic impedance of the coal, and
decreased velocities within coal zones results in delayed reflections
from deeper horizons. Modelling provides "proof of concept", and
provides parameters to be considered in survey design prior to a field
trial involving the Ardley coal zone in Alberta.
</p>
</abstract>
