Prism waves for imaging steep geologic features and sediment terminations against salt flanks: Examples from the Gulf of Mexico

Abstract

Subsalt imaging in the Gulf of Mexico often suffers from illumination problems where various steep geologic features are not captured with conventional imaging techniques due to the lack of a direct wave path from the source to the steep reflector and back to the receiver. The exact geometry of these invisible salt flanks or salt welds is of great interest to interpreters during salt model building and prospect mapping. This paper discusses a suite of technologies that uses prism waves for imaging geologic interfaces with reverse time migration (RTM). Prism wave RTM imaging represents an example of imaging with multiples, Due to its specific geometric setup, it is often complementary to traditional RTMs. Specifically, the prism wave reflections can illuminate steep features that are invisible otherwise. Furthermore, by utilizing prism wave RTM in “reverse,” one can specify the steep event as the input prism wave generator (often a well-constrained salt boundary) and obtain an alternative (and perhaps cleaner) image of the sediment geometries next to this input event. In the industry, a lot of resources are spent on trying to improve illumination for the geologic features of interest by acquiring additional seismic surveys. With prism wave imaging, one can instead leverage the seismic signal that has already been recorded. We believe that even with moderate prism wave illumination uplift, the interpretive value gained can be quite large. To give the reader a glimpse of what is possible, we present several real data examples highlighting the utility of prism waves in interpretation.