3-D Gpr Imaging Of Complex Stratigraphy Within The Ferron Sandstone, Castle Valley, Utah

Two detailed 3-D Ground Penetrating Radar surveys were recorded on outcrops of the Ferron Sandstone in Castle<br>Valley, Utah in an effort to image internal sedimentary structures. The Ferron Sandstone is a fluvial to proximal<br>marine sandstone which is considered to be a good analogue for some Gulf Coast oil and gas reservoirs. Because of<br>its excellent exposure in Castle Valley, the stratigraphy of the Ferron has been, and continues to be very extensively<br>studied to determine the relationships of bedforms to the distribution of reservoir properties. Our goal in imaging<br>these outcrops with 3-D GPR is to interpret reservoir heterogeneities at interwell scales. Correlation of these<br>heterogeneities to known porosity and permeability distributions from outcrop studies will be used to establish three<br>dimensional scales of reservoir flow behaviour. These data will subsequently be used to improve flow simulations<br>of analogous oil and gas reservoirs. Results of this study indicate that 3D GPR is indeed suitable for this application.<br>The first 3-D survey was recorded on a 15m by 15m grid with traces recorded every 25cm in both directions.<br>Adjacent outcrop showed the near-surface sandstones to be of a tidally reworked deltaic lithofacies, overlying lower<br>coastal plain carbonaceous siltstones. More than 4m of penetration and finer than 25cm resolution were achieved<br>using a PulseEKKO IV GPR system with 200 MHz antennae.<br>The second 3-D survey was recorded about 250m away from the first, over a stacked distributary channel to<br>nearshore sandstone lithofacies. 100 MHz antennae were used over a 25m by 25m grid, with 5Ocm spacing in both<br>directions. More than 8m of penetration and finer than 50cm resolution were observed.<br>A 2-D line with 50 MHz antennae and 1 .Om trace spacing was recorded to connect the two 3-D surveys and to<br>provide a more regional picture of stratigraphy. Reflections were recovered from as deep as 20m.<br>The data were processed both at Chevron, using the Promax seismic processing system, and at UT Dallas, using<br>in-house software. Data were flattened on the air arrival, gained, spatially smoothed and then migrated using a<br>fixed-offset prestack migration. Results were visualized with VoxelGeo, a software package which allows the user<br>to selectively render the volume with transparency to see the interior of the data cube in 3-D perspective.<br>Connectivity analysis within the cubes highlights discrete reflectors, and by implication, the main flow units of the<br>facies. Work is underway to correlate the vertical and horizontal scales of heterogeneity from the GPR data, with<br>the facies’ permeability distribution from outcrop studies.