Apparent horizontal displacements in time‐lapse seismic images

Abstract

In addition to vertical time shifts commonly observed in time-lapse seismic images, horizontal displacements are apparent as well. These apparent horizontal displacements may be small relatively to seismic wavelengths, perhaps only 5 m at depths of 5 km, but they consistently suggest an outward lateral expansion of images away from a compacting reservoir. It is well known that apparent vertical displacements are caused mostly by a decrease in seismic wave velocities above compacting reservoirs. Those same velocity changes contribute to horizontal displacements. This contribution can be computed from the velocity changes that, in turn, can be estimated from measured vertical displacements. Horizontal displacements computed in this way are similar to those measured, and this similarity suggests that horizontal as well as vertical displacements may be largely due to velocity changes.

Practical Applications of Time-lapse Seismic Data

“…Figure 11 shows two sets of velocity-pressure curves, one for an oil with low solution GOR (a "dead oil") and one for the same oil but with high solution GOR (a "live oil"). After Han and Batzle (2000a). For both dead oil and live oil, velocity increases with increasing pressure and decreases with increasing temperature.…”

“…All the values have been corrected for fluid content. After Han and Batzle (2000a Figure 15. Oil density as a function of pressure for each solution GOR.…”

Mapping and time-lapse analysis of South Arne Chalk fault network using new developments in seismic dip computation

“…Several mechanisms seem to govern them. Hale et al (2008) demonstrated that magnitude and direction of the lateral shifts can be explained by 4D velocity changes, which in turn induce changes in both ray paths and travel times. In the same year, Aarre (2008) showed that, for prestack time-migrated seismic datasets, the velocity-induced time shifts appear to move normally to the layering (Fig.…”

A method for estimating apparent displacement vectors from time-lapse seismic images

“…If not accounted for in seismic migration ͑as it was not here͒, such a change in seismic velocity could explain these apparent crossline displacements. This explanation is analyzed and tested by Hale et al ͑2008͒.…”