AHLGREN, STEPHEN G., and GEORGE H. DAVIS
The University of Arizona, Tucson, AZ

Abstract: Visualizing Reservoir-Scale Compartmentalization through Three-Dimensional Digital Modeling of Mapped Systems of Deformation Band Shear Zones

Deformation band shear zones (DBSZs) are sub-seismic scale structures found primarily in porous sandstones. They are exquisitely exposed in the Navajo Sandstone of southern Utah along the eastern fringe of both the East Kaibab monocline and the Waterpocket Fold, and typically range from a few centimeters to hundreds of meters in length and a few millimeters to tens of centimeters in thickness. DBSZs are marked by negligible across-strike permeability due to elimination of porosity by cataclasis of the host sandstone. As a result, families of DBSZs may effectively compartmentalize an otherwise ideal reservoir rock.

To best visualize and interpret these complex structures, we combined 1:600 field maps and digital topography into three-dimensional structural models using 3DMove. The models provide, a unique virtual journey through three-dimensional DBSZ networks, and may also be used to evaluate the interconnectivity of DBSZs and the shapes of resulting compartments.

The structural models facilitate determining the net effect of DBSZs on fluid flow in deformed sandstone using three-dimensional fluid flow modeling. The fluid flow models will incorporate flow properties from deformed and undeformed rock to compute both a bulk-rock permeability tensor and the tortuousity of fluid flow. We stress the importance of transfer zones between major DBSZs as they represent the primary potential spill points between adjacent compartments. Fractures in DBSZs also offer potential opportunities for communication between adjacent compartments. Models of this type may give insight into the challenges of recovery in currently producing fields and may be applied as predictive tools in similarly deformed reservoirs.

AAPG Search and Discovery Article #90919©1999 AAPG Rocky Mountain Section Meeting, Bozeman, Montana