DEWEY, JOHN A., JR., and THOMAS H. MORRIS, Brigham Young University, Provo, UT

ABSTRACT: The Extent of Reservoir Homogeneity and Continuity of Mouth-Bar Sandstones: Colton Formation, Uinta Basin, Utah

The Paleocene-Eocene Colton Formation of east-central Utah has been interpreted as a fluvial-dominated lacustrine deltaic system. Suspended-load, mixed-load, bed-load fluvial sandstones and distributary mouth-bar sandstone bodies have been identified within the Colton Formation.

The distributary mouth-bar (DMB) sandstones are ledge formers at the base of the Roan Cliffs. They are composed of three separate units: a basal layer of mudstone rip-ups; a low-angle, trough, cross-stratified sandstone with rip-up lags; and a thick massive sandstone, The massive sandstone measures up to 9 m thick and appears to be laterally continuous. It is a medium-grained, slightly friable sandstone. Sedimentary structures that include convolute bedding, climbing ripple lamination, and dish and pillar fluid escape structures indicate rapid deposition. The entire unit overlies prodelta mudstones and shales. The DMB has been interpreted to be a system of middle-ground bars deposited during deposition of a major deltaic lobe.

Initial tests show that the DMB unit has approximately 20% porosity and permeability on the order of 200 md. Reservoir characteristics, sand body size, and geometry suggest that it would serve as an excellent reservoir. Subsurface identification criteria include unique porosity and permeability homogeneity, stratigraphic position, sandstone thickness, grain size, and sandstone percentage in the total section. The DMB sandstone bodies would make excellent subsurface targets for exploration in the Uinta basin or other analogous basins.

AAPG Search and Discovery Article #90993©1993 AAPG Rocky Mountain Section Meeting, Salt Lake City, Utah, September 12-15, 1993.