High-Resolution Ground-Penetrating Radar: An Aid to Reservoir Analog Outcrop Studies: ABSTRACT

Abstract

Outcrop analog studies are important for defining the small-scale stratigraphic architecture of producing reservoirs, but are commonly insufficient for determining 3-D geometries. Ground-penetrating radar (GPR), which generates an image similar to a seismic section, can be very useful for generating high-resolution images of reservoir analogs. GPR data from eastern Kansas show that in some areas, high-frequency (500 MHz) antennas can achieve vertical resolutions of approximately a decimeter down to depths of 5 m or more. GPR data were acquired over an outcrop of an upper estuarine sandstone facies within an incised valley fill of the Upper Pennsylvanian Tonganoxie Sandstone. The Tonganoxie is a minor reservoir in Kansas, and is an analog for valley fill sandstone reservoirs. Excellent correlation between outcrop data and two parallel GPR lines less than 6 in from the outcrop face demonstrate that features as small as individual foresets were successfully imaged. The high resolution may result partly from thin (1 mm) clay/micaceous drapes on foresets. The clay and micaceous drapes are conductive and have a dielectric constant different from adjacent sandstone. GPR data reveal a complex sandstone body architecture. Onlap and downlap relationships on GPR profiles result from trough and tabular planar cross bedding. GPR profilesmore » reveal significant lateral and vertical changes in geometry and scale of cross bedding. A decrease in cross bedset thickness upward may reflect channel filling. Future work will involve collection of minipermeameter data in order to correlate GPR responses to changes in permeability.« less