Time-lapse 3D, or 4D, seismic technology is the use of 3D seismic surveys acquired at different times in the productive life of a reservoir. The term 4D encompasses a broad workflow from feasibility and design, to acquisition and processing, to inversion and interpretation, and finally to integration with reservoir management, although a 4D project may span only a subset of the workflow.
4D with zero time-lapse, meaning no production-induced subsurface change, is a repeatability study. The time-lapse interval for production monitoring is reservoir- and process-dependent, and may vary considerably, from as short as two weeks to monitor the pressure change due to first oil, to many years in a large, Middle East carbonate reservoir. There is no general optimal time-lapse interval, so prediction of time-lapse changes at different times in the future is an important part of 4D feasibility studies, making use of flow simulation and rock physics models.
For optimal results, 4D requires time-lapse logs, special core analysis, VSPs, pressure, and other data sources such as multicomponent, geomechanical, gravimetric, and electromagnetic data, when available. These data serve to constrain the inversion and interpretation of 4D surveys, just as they do for 3D surveys. It is possible to generate a 4D result without this constraint, but that result will be more qualitative and rely more on model-based assumptions that can degrade confidence in the result.