Abstract

Measured outcrop sections have long been essential components of an exploration play or field development toolkit. For every outcrop analog, considerable time and effort are invested to qualitatively or semi-quantitatively evaluate how representative these analogues are to in-field reservoir facies and flow-unit connectivity. The Greater Natural Buttes area in the east-central Uinta Basin is currently undergoing extensive in-fill drilling; gas production is dominantly from upper Cretaceous Mesaverde sands beneath the initially productive Eocene Wasatch Formation.

Nearest outcrop equivalents to the fluvial, tight-gas sands of the Greater Natural Buttes area lie approximately 50 miles to the south/southwest. Well exposed “windows” of upper Mesaverde and Wasatch outcrops occur above the shoreline systems of the lower Mesaverde northeast of Green River, Utah, in Tusher and Sego canyons. These windows were selected for comprehensive study including GPS-rectified photomosaics, measured sections, and paleocurrent trends. One of the initial criteria in window selection was finding lateral outcrop dimension along canyon walls that would be equal to or greater than a 20- and/or 40-acre well spacing. Statistics on sand-body dimensions and connectivity have been generated and are being compared to Greater Natural Buttes reservoir architecture.

Paleocurrent trends from upper Mesaverde (Farrer and Tuscher formations) demonstrate a generally northeasterly channel trend toward the Greater Natural Buttes area. Wasatch sand bodies exhibit a north/northeasterly channel trend with more variability than the high net-to-gross stacked channels of the underlying Mesaverde. Definition of the between-well reservoir architecture of both the Mesaverde Group and Wasatch Formation is contributing to a better understanding of wells drilled on a 40-acre spaced grid and in predicting channel connectivity of 20-acre infills or extended lateral wellbores from the same surface location.