HIGH-RESOLUTION CROSSWELL IMAGING OF A WEST TEXAS CARBONATE RESERVOIR.5. CORE ANALYSIS

We conducted a core analysis program to provide supporting data to a s eries of crosswell field experiments being carried out in McElroy Fiel d by Stanford University's Seismic Tomography Project. The objective o f these experiments is to demonstrate the use of crosswell seismic pro filing for reservoir characterization and for monitoring CO2 flooding. For these west Texas carbonates, we estimate that CO2 saturation caus es P-wave velocity to change by -1.9% (pooled average, range = -6.3 to +0.1%), S-wave velocity by +0.6% (range = 0 to 2.7%), and the P-to-S velocity ratio by -2.4% (range = -6.4 to -0.3%). When we compare these results to the precisions we can expect from traveltime tomography (a bout +/-1% for P- and S-wave velocity and about +/-2% for the P-to-S v elocity ratio), we conclude that time-lapse traveltime tomography is s ensitive enough to resolve changes in the P-wave velocity, S-wave velo city, and P-to-S velocity ratio that result from CO2 saturation. We co ncentrated here on the potential for CO2 saturation to affect seismic velocities. The potential for CO2 saturation to affect other seismic p roperties, not discussed here, may prove to be more significant (e.g., P-wave and S-wave impedance).