Date of Award:

2011

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Geology

Advisor/Chair:

Dr. James P. Evans

Abstract

The Mesaverde Group, Uinta Basin, Utah, is the source of significant natural gas production and contains several trillion cubic feet of undiscovered natural gas resources. Tight-gas sandstone reservoirs within the Mesaverde Group require hydraulic fracture treatments in order to produce economic volumes of gas. The nature of the natural fracture network is examined here using scanline sampling, image-log, well-log, core, and microstructural analyses to evaluate and model the potential connectivity of hydraulically induced fractures to natural fractures in the subsurface. Regional fracture sets include subvertical sets with dominant orientations of: N-S (006° - 015°), NE (045° - 059°), NNW (326° - 342°) and a WNW (271° - 286°). Sedimentologic and diagenetic characteristics of seven sandstone lithofacies control the fracture development and distribution in the Mesaverde Group. Key sedimentologic and diagenetic influences on fracture distribution include bed thickness, stratigraphic architecture, the degree of cementation and the type of cement. From outcrop and core analysis, discontinuous, well-cemented sandstone have a higher fracture density when compared with continuous, tabular bedded sandstone units and friable sandstone units. Based on the sedimentologic and diagenetic controls on the character of natural fractures, lithofacies can be used to predict fracture distribution within the Mesaverde Group based on environments of deposition. Sandstones deposited in braided river environments appear to have lower fracture densities than sandstones deposited in meandering fluvial environments. Northwesterly trending, discontinuous sandstone reservoirs were deposited in meandering fluvial environments, are highly fractured by a pervasive WNW-striking fracture helps to explain fairways of prolific natural gas production within the Greater Natural Buttes field.

Comments

This work made publicly available electronically on April 10, 2012.

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