Shear-Wave Splitting Analysis for Natural Fracture Zone Identification, Rulison Field, Piceance Basin, Colorado

Elizabeth A. LaBarre
Geophysics, Colorado School of Mines, Golden, CO

Shear-wave seismic acquired at Rulison Field, Piceance Basin, Colorado by the Reservoir Characterization Project in 2003 exhibits evidence of natural fractures from shear-wave (S-wave) splitting analysis. Rulison Field is a thick unconventional natural gas reservoir producing from the fluvial tight gas sandstones of the Late Cretaceous Williams Fork Formation. Natural Fractures are known to vary throughout the reservoir and to greatly increase the permeability of the tight reservoir rock (Lorenz, 2003). S-wave splitting analysis can be used to predict these changes in fracture density. Since the reservoir interval is thick (~2500ft), S-wave splitting calculations were done using an unconventional approach on 3-D seismic volumes through the reservoir interval as opposed to the traditional horizon-based approach. This process resulted in S-wave splitting volumes that correlate to existing well data. These volumes show lateral and vertical changes in fracture intensity and some of the discontinuous fractured fluvial sandstone bodies. These volumes can ultimately be used to optimize well locations and drilling efficiency.

AAPG Search and Discovery Article #90092©2009 AAPG Rocky Mountain Section, July 9-11, 2008, Denver, Colorado