Lithofacies Prediction and Reservoir Quality Evaluation Using Laboratory-Measured Physical Properties in the Pennsylvanian Mixed System of the Paradox Basin, SE Utah

Christophe D. Nussbaumer, Eric Davaud, Gregor P. Eberli, G. Michael Grammer, and Marie-Claire Bernet-Rollande

The various lithofacies of Pennsylvanian siliciclastic/carbonate cycles on the Paradox shelf and basin display characteristic petrophysical signatures. Utilization of these petrophysical facies in combination with vertical stacking patterns observed in the cycles provides a powerful tool to enhance the predictability of lithofacies and reservoir characteristics from log data.

Ultrasonic velocities (P- and S-waves), permeability, porosity and density values of 356 plugs were used to define the petrophysical facies of nine lithofacies. Despite a large scatter in the data due to multiple subtle facies variations, each lithofacies yielded a characteristic petrophysical signature. The most significant distinction is seen between siliciclastics, i.e., quartz sandstones (low grain density, low porosity, low P- and high S-wave velocity), and carbonates (higher grain density, variable porosity, high P- and relatively low 5-wave velocity). The petrophysical properties (porosity, pore-type, permeability and velocities) also allow for the distinction between the two carbonate reservoirs, phylloid algal facies and ooid grainstones, and between the reservoirs and surrou ding nonreservoir carbonates.

This calibration of petrophysical facies to lithofacies provides a powerful tool to better interpret log data. For example, the admixture of quartz in the bottom of the depositional cycle is recorded in the sonic logs by a decreased velocity which helps distinguish individual cycles. In addition, acoustic response within the carbonate portions of the cycles indicates variations in porosity and, thus, reservoir heterogeneities. Furthermore, the measured rock properties combined with outcrop geometries can be used as a foundation for seismic and fluid flow modeling.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California