NELSON, DENNIS L., University of Utah Research Institute, Salt Lake City, UT; THOMAS C. CHIDSEY, Jr., and CRAIG MORGAN, Utah Geological Survey, Salt Lake City, UT; and WENZHI ZHAO, China National Petroleum Corp., Beijing, P. R. China

ABSTRACT: Fracturing in the Duchesne Field, Utah: Importance for Horizontal Drilling

Horizontal drilling directions vary across the Duchesne field in the Uinta Basin of northeastern Utah, because fracture directions are locally controlled by the east-west Duchesne fault zone. Away from the fault zone, northwest-trending regional fracture patterns are dominant. The Duchesne field, located in the west-central part of the basin, produces oil and gas from fracture and matrix permeability in the Tertiary Green River and Wasatch Formations. Surface and subsurface fracture patterns in the field were studied as a model to improve the success of development and exploratory drilling throughout the basin using horizontal drilling techniques.

Measurements of surface fractures in and around the field show three major orientations: (1) N83-90W, the dominant direction, parallel to the Duchesne fault zone; (2) N10-15W; and (3) N65-75E. Surface fractures are open, closely spaced in shale while more widely spaced in sandstone, and dip within 15 degrees of vertical.

Subsurface fracture information was provided by Formation MicroScanner and borehole televiewer logs from 10 wells both adjacent and distal to the Duchesne fault zone. Multiple sets of east-west oriented fractures were encountered in wells closest to the fault zone. The density of the fracturing is greatest in the immediate vicinity of the main fault zone. In wells farther away from the Duchesne fault zone, the dominant fracture orientation is northwest with northeast and very minor east-west components. The northwest trend generally corresponds to the gilsonite veins exposed in the southeastern part of the basin parallel to the Uncompahgre uplift. Horizontal drilling directions must be custom tailored to local structural conditions even in relatively small areas like the Duchesne fiel .

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.