Wave-equation datuming overcomes several of the problems that seismic data recorded on rugged surface topography presents to routine image processing. The main problems are that standard, optimized migration and processing algorithms assume data are recorded on a flat surface, and that the static correction routinely applied to compensate for topography is inaccurate for waves that do not propagate vertically. Common-midpoint (CMP) velocity analysis and migration velocity analysis after static shift can be severely affected by the non-hyperbolic character of the reflections. In this chapter, I show how to alleviate these problems by applying wave-equation datuming to upward continue the data with a known velocity and process the data from a flat datum.
Some of the last petroleum prospecting frontiers are in overthrust areas where rugged topography and irregular data coverage present significant processing challenges. The rugged terrain and complex structure make drilling very expensive, and since there is often little well control or a priori velocity information, it is critical to lower risk by extracting as much information out of the seismic data and providing the best possible image. Even when good quality data are recorded in these terrains, the processing challenges that arise due to topography, the presence of high-velocity rocks near the surface, and complex subsurface velocity can impede conventional processing and subsequent interpretation.
The distorting effects of rugged topography are a serious problem in mountainous overthrust regions and wave-equation datuming provides a useful method of transforming data to a planar datum and determining the sub-surface velocity structure. The datuming eliminates the distortion caused by the topography and allows standard wave-based processing methods such as velocity analysis and migration to be applied efficiently.
The role of wave-equation datuming in land data applications has not been established; however, the new concept that I present in this chapter is my definition of where wave-equation datuming fits into the processing flow and how it can be used to improve velocity estimation and imaging. I apply wave-equation datuming to an overthrust data set from the Canadian Rockies and show how the process provides a clear improvement over conventional statics processing. I show how wave-equation datuming transforms the data to a regular grid and how velocity estimation and imaging is improved. Because the data are regrided onto a flat datum, further processing is streamlined and structural interpretations are easier to incorporate into the analysis.