Datapages, Inc.Print this page

Abstract: Natural Fracture Characterization: A Key to Success in an Exploration Play, Converse County, Wyoming

Steven L. Parks, Melinda S. Gale, Michael C. Mueller, Van S. Mount

Numerous vertical wells drilled in the southern Powder River basin have encountered fractured, tight, overpressured Cretaceous reservoirs, Vastar Resources, Inc. is actively exploring for these reservoirs with horizontal wells targeting the Niobrara and Frontier formations. The initial exploratory test of this concept confirmed the presence of fractures, but in an orientation different than originally predicted. This led to a re-evaluation of the play concept and illustrated the importance of accurate fracture prediction The new exploration play involves drilling highly deviated wells to maximize the number of fractures intersected in the Niobrara and Frontier formations. Initially, fractures related to movement along the Hartville uplift were considered the dominant expected fracture set. However, the actual fractures encountered in the subsurface appear to be a pre-Laramide fracture system unrelated to the Hartville uplift. This was determined by integrating detailed surface outcrop studies, regional cross-sections, Landsat lineament analysis, FMS data acquired in the exploratory well, and 2D multicomponent, multisource shear wave seismic. Additionally, the influence of present day maximum horizontal stress was taken into account by incorporating borehole breakout data in the play area.

Subsequent wells in the play have confirmed the pre-Laramide fracture orientation. Although overpressure and reservoir character remain issues, the detailed understanding of the fracture system has provided an anchor for further exploration and development.

AAPG Search and Discovery Article #90959©1995 AAPG Rocky Mountain Section Meeting, Reno, Nevada