Identifying the sources of non-repeatability.
The only way to improve repeatability is to assess all causes that impede it and determine ways to eliminate them. Likely causes include acquisition footprint problems such as the use of different equipment, inconsistent or incorrect positioning, and source/receiver variability; environmental conditions such as tides, temperatures for marine and weathered zones for land; and noise, coherent and random.
Removing the sources of non-repeatability, deterministically and/or statistically.
In an effort to follow a strict deterministic approach, tailored solutions remove whatever degrades repeatability. Solutions include tidal statics using oceanographic tide charts, 4D-friendly SNR enhancement techniques, such as SNIP™, or our Acquisition Dependent Amplitude (ADA) compensation and Kirchhoff-migration scheme, which corrects for acquisition discrepancies between surveys.
For residual differences still present in the data, or to resolve spatially misaligned surveys, Geotrace has designed several cross-equalization techniques. These statistical solutions always come after deterministic steps, since it is always preferable to tackle identified problems first. This spatial matching step equalizes amplitude, phase and frequency content between the different surveys by analyzing signal in sub-cubes located away from the reservoir area, excluding over-, under- and side-burden areas if they are expected to show 4D effects associated to depletion. The result: a global or local (trace-by-trace) solution.
Case Study: Enhanced 4D processing and quantitative analysis on Troll West using multiple vintages of legacy data.
Acquisition Dependent Amplitude Correction for Imaging (ADA)