Ground-penetrating radar facies characterization of deepwater turbidite outcrops

Abstract

High-resolution outcrop studies are becoming an increasingly important tool in building reservoir architectural models (Slatt, 2000). By providing attributes of strata in both the lateral and vertical directions, outcrop studies can help constrain reservoir characterization models (e.g., identify seals or barriers to fluid flow). Outcrop exposures, at best, are limited in their extent. Boreholes, even when they are spaced tightly together, may yield an inaccurate picture of sedimentary features. Because the type and scale of information important to hydrocarbon production can be beneath the resolution of 3D seismic data, there is a need for a geophysical method that yields a high-resolution, continuous image of the subsurface. Ground-penetrating radar (GPR) is one of the more recent geophysical technologies used in examining outcrops (Slatt, 2000;Young et al., 2001). GPR is an electromagnetic imaging procedure that generates reflections from boundaries between layers and can use modified seismic processing to create images (Young et al., 1995). The short wavelengths of GPR signal provide data, which is subseismic scale in resolution. The resulting profiles are good for interpreting small-scale sedimentary features of bed continuity, stratification patterns, and facies boundaries. This paper presents the results from a GPR study of the Lewis Shale turbidite outcrops in Wyoming. The objective of the project is to collect subseismic scale resolution data to aid in determining small-scale sedimentary features. The interpretations, in turn, could be used to provide a better understanding of fluid flow and reservoir production modeling. The Lewis Shale, a Cretaceous age turbidite deposit, is an active gas exploration target and analog for the lower Cretaceous sequences in South Africa and tertiary deposits in the Gulf of Mexico. The formation crops out along the western edge of the Rawlins-Sierra Madre uplift within southeast Wyoming. The geology of three areas along the Lewis Shale outcrop has been studied. …