Imaging of Deepwater Channel Architectural Elements of the Jackfork Formation, Arkansas, Using Ground Penetrating Radar and Application to Reservoir Modeling
Deepwater channel sands are common targets for offshore hydrocarbon exploration. High net-to-gross systems are desirable as reservoirs but difficult to map in conventional seismic due to the lack of differentiation of their sandy lithologies from their often-silty shales. This study uses ground penetrating radar (GPR) to image outcrops and near-outcrop subcrops of the Jackfork Formation in Pulaski County, Arkansas, a middle Pennsylvanian deepwater slope and basinfloor depositional system along the margins of an oblique foreland basin in front of the encroaching Ouachita accretionary prism. In this study, GPR data are collected for the top 3–5 meters (m) of subcrops of deepwater features of the Jackfork system using a 200 megahertz (MHz) antenna. The data are processed and corrected for variations in surface topography. Where available, data are cross-checked against adjacent outcrops. At several data collection areas, GPR lines were taken in grids that range up to one square kilometer in aerial extent to visualize the internal architecture of the deposits in 3D. These GPR images capture a variety of channel architectural elements in outcrop and the adjacent subsurface including crevasse splays, sheets, and debris material. Channels extending up to approximately 50 meters wide and 5 meters deep are captured in two dimensions as well as lateral accretion beds within asymmetric channels that are a few meters deep and hundreds of meters wide. GPR data taken in grids show the spatial continuity of crevasse deposits 3–5 meters thick. With the collected data, this work aims to use associated outcrops and GPR data qualities to identify mud-rich lenses within the high net-to-gross system to provide an example of the two- and three-dimensionality of baffling facies within the channel. With the sub-meter resolution of the GPR data, this should inform fluid flow property variability within channels at a higher resolution than conventional seismic and, where grids were taken, in added dimensionality to outcrop studies. From the analysis, this work provides valuable insight into the nature of high net-to-gross deepwater channel deposits and can assist in identifying potential baffles and barriers to flow prior to full-scale, deepwater subsurface developments in similar deposits around the world.
AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015