Meandering Channel Facies Architecture Using Ground Penetrating Radar, Ferron Sandstone (Upper Cretaceous) Emery Co., Utah

Oluwasegun Abatan, Dennis Kerr, and Kumar Ramachandran

Detailed investigations of meandering channel belts in the Ferron Sandstone was made using ground penetrating radar (GPR) with the aim of characterizing riffle facies elements. Riffles facies architecture elements are developed along channel thalweg reaches between two successive pools and flanked by lateral accretion bar facies architecture elements. Riffle elements have received little attention, despite their potential importance to pore-fluid flow within meandering channel reservoirs. This study describes the geometry and facies architecture of meandering channel fill using 2-D GPR imaging data. GPR data acquisition was guided by outcrop exposures of a meandering channel belt segment, indicating the presence of a channel thalweg between successive pools. 2-D GPR data were acquired in three 100m X 100m grids and five smaller dimension grids for a total area of 44,300 sq. meters. GPR data were processed and corrected for direct wave influences, topography and background noise. Using an average velocity of 0.15m/ns, estimated depth to the base of the channel-fill deposit is a maximum of 4m below the surface which corresponds to a basal, laterally continuous strong reflector.

Ground penetrating radar reflector geometries (inclination, continuity and termination configurations) and amplitude characteristics are used to define five GPR facies. In addition, reflectors are compared to facies architecture boundary surface hierarchy established from outcrop studies. Geometry of outcrop exposures of lateral accretion bars projected into the subsurface can be observed in the GPR data as less continuous reflectors down-lapping against the basal reflector. A pseudo 3-D GPR data volume constructed from 2-D GPR data is used to identify a riffle element as having continuous horizontal reflectors with relatively low variable density (VD) contrast amplitude values when compared to other meandering channel GPR facies, which might be due to a high level of textural sorting in riffle sandstones. Other GPR facies include the channel floodplain, characterized by chaotic reflectors; the levee deposits characterized by gently dipping oblique reflectors divergent from an up-dip termination; and the abandonment-fill characterized by a structureless, reflection free zone in radar data. Channel evolution was determined using strike and dip information from the internal reflector of lateral accretion deposits.

AAPG Search and Discovery Article #90181©2013 AAPG/SEG Rocky Mountain Rendezvous, University of Wyoming, Laramie, Wyoming, September 27-30, 2013