Ultrasonic Data Testing of Time-Lapse Tomography
This paper is a validation study of a time-lapse tomographic method using ultrasonic broadband waveform data recorded in a crosswell tomographic laboratory experiment. Two data sets have been obtained from two almost identical physical models simulating pre-flood and post-flood stages during an enhanced oil recovery. We have applied a time-lapse method based on ray theory and wave scattering theory to estimate velocity differences thereby induced. Our objective is to develop a 4D crosswell tomography and to validate it with ultrasonic data. The variations of the time-lapse tomographic method, i.e., how the observed travel times shifts are estimated and which type of inversion (ray of wave theory based) is used, produce four different time lapse velocity tomograms. Lastly, applications of our 4D method on real field data sets, and on a new ultrasonic experiment simulating CO2 injection in the subsurface, are discussed.