Brian J. Black¹, Thomas H. Morris¹, Alan L. Mayo¹
(1) Brigham Young University, Provo, UT

Abstract: Fluid flow characterization of the Castlegate Sandstone: Interpretation of reservoir partitioning through permeability and porosity analysis; Southern Wasatch Plateau, Utah

The Castlegate Sandstone is a water-bearing formation within the Wasatch Plateau in east-central Utah. The depositional system of the Castlegate is that of a high gradient braided fluvial system. Although the formation as a whole is laterally continuous over long distances, local variations in permeability and porosity of the sandstone are present.

Measured sections show that the sandstone is dominated by high- and low-angle trough cross-stratification. Convolute bedding and minor amounts of planar-laminated beds are also present. Grain size ranges from very fine sand to pebbles. The moderately sorted sandstone contains mostly upper medium- to lower coarse-grained sand. Stream channel geometry varies throughout the sandstone but is generally around 20-30 meters wide and 2-3 meters deep.

Permeability and porosity values from core-plugs show that some bedforms and second- and third-order bounding surfaces can act has barriers and baffles to fluid flow and can compartmentalize the reservoir. Permeability readings ranged from less than 1.00 millidarcy to more than 5,000 millidarcies and porosity ranged from 6% up to 27%. Geophysical well logs show that the Castlegate has mud-rich zones within the sandstone that can partition both vertical and lateral fluid flow through the rock. Bounding surfaces as well as low permeability layers may stop vertical recharge of surface water to subsurface coal mining depths.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana