A Review of Pre-Stack Depth Migration (PreSDM) Process Flow Development in the Gulf of Mexico

By

Jock M. Drummond¹, David Walraven¹

(1) Anadarko Petroleum Corporation, The Woodlands, TX

 The past decade has been a period during which rapid advances have taken place in the application of imaging technology and in particular in Pre-Stack Depth Migration (PreSDM). Improvements in the application of PreSDM have been brought about by the need in the industry to resolve increasingly more difficult imaging problems, to understand the fundamentals of complex regional geology, to provide a cost effective PreSDM solution and ultimately to continually strive for the most accurate geological model.

PreSDM can be considered the ultimate link between Geophysics and Geology. In order to obtain the most accurate depth image the pre-stack seismic data must be imaged with a velocity model that is based on the geology and derived through the seismic data. Generating the full velocity model is an iterative process requiring close interaction between seismic processing geophysicists, interpretive geophysicists and regional or structural geologists. PreSDM the ultimate link, is also a catalyst to improved communication between geoscientists in the exploration and development teams.

In the past two years new approaches to PreSDM, other than Kirchhoff, have been implemented. These include for example full wavefield acoustic based shot domain wave equation migration (WEM), plane wave imaging solutions, and grid based tomographic solutions to velocity model building. As well as the inherent advantages of WEM new challenges are also introduced for the processing/interpretation teams. Through massive clusters, recent NEC Earth Simulator has 35,600 Gigaflop capability, PreSDM products include WEM image results both in stack and gather mode, velocity and geological models, and illumination models.

In future Geoscientists will use all of these products and more in a fully integrated environment to enhance their understanding of the geology and to reduce cycle time. Other challenges, including for example anisotropic model building and WEM elastic solutions, in PreSDM remain to be solved in a regular commercial basis.