Processing for time-lapse seismic
As illustrated by the foregoing material, data from two or more time-lapse surveys are quite likely to have repeatability problems. One question that therefore arises is: how successfully or justifiably can we "force" a match between them? After all, 99% of the earth volume covered by the survey will not have changed perceptibly between the two surveys. In this section we investigate a few guiding examples of attempts to do this.
Fig. 5.1 shows a dip line from two co-positioned 3D data volumes from 1985 and 1995 surveys–a typical "legacy" data situation. The oil-water contact is initially at 1.9 s on the 1985 data, and the column has moved about 50 m upwards during the 10-year interval. It also shows the difference section, first that obtained with just a single "global" amplitude matching scalar, and without any trace "matching" of any kind, although the two data sets have been processed with time-lapse intentions. Clearly, the subtraction has not been especially successful, although there is a strong event in the region of the oil-water contact.
Figures & Tables
“This book, prepared for use with the first SEG / EAGE Distinguished Instructor Short Course, discusses Â"time-lapse seismicÂ" and enables geoscientists to assess the value and risk of this new technology. It covers the rationale and driving forces behind time-lapse seismic by examining the limitations of existing methods of tracking fluid flow between wells. It examines those reservoir properties that change with time and what can be observed on seismic data over elapsed time. The repeatability of seismic data and the use of Â"legacyÂ" data sets are discussed, along with a review of the seismic data acquisition schemes and data processing requirements for time-lapse analysis. The rock-physics foundation for data analysis and interpretation options also are described. A selection of industry case histories illustrates many of these points. The reader will gain an understanding of key success factors, key calibration requirements, and key uncertainties of time-lapse seismic in reservoir management.”