Repeatability requirements of seismic data
This section expands on some of the items listed in Section 2C. It is intended to impart a healthy suspicion of the effects of data processing parameters. These effects can be much reduced by well matching/wavelet extraction methods, but this should not be assumed. In differencing operations noise becomes much more of an issue!
Time-zero corrections and statics applications: The data must be repeatable in time. Just a millisecond of time shift allows root mean square (rms) amplitude differences of around 18% in a simple test. Fig. 4.A.1 shows a "final" processed migrated section from a 3D data volume. In the lower panel of the figure is a subtraction produced from the same section, time shifted from itself by 1 ms.
To show a more extreme example, consider the 4-ms shift shown in Fig. 4.A. 2. This produced a subtractive rms amplitude of 71% of the original data. We can conclude that time matching of seismic data is critical before its use as time-lapse data. Since many of our "final" sections exist at a sample interval of 4 ms, we have to ensure that any software used to compare several 3D data cubes has an interpolated time shift capability. Acquisition equipment and data processing time delays may easily impart a fraction of the final sampling interval
Mute applications: An early step in a processing sequence is often a first-break mute. This will be picked empirically from trial parameter tests and examination of the data. The effect of a small change
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.”