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Fracture Interpretation from Image Logs: Skinner Ridge, Piceance, CO

Vincent Heesakkers, Meghan Playton, and Li-Fan Yue

Production from tight reservoirs often depends on the presence of open natural fractures and/or stimulation of the reservoirs in order to become economic. The distribution and orientation of natural fractures and the local in-situ stress fields are often poorly understood in such reservoirs, despite their significant impact on the stimulated rock volume. The tight gas sandstone reservoirs of Skinner Ridge Field in Piceance Basin, Colorado are an example of reservoirs for which stimulation by hydraulic fracturing is needed. This study presents the findings from a natural fracture interpretation study on this reservoir, with emphasis on the integration of results with the regional structure, a micro-seismic study, and a 2009 Statistical Curvature Analysis Technique (SCAT) analysis. A total of eight image logs were analyzed, most of which comprise 4,000 – 5,000 ft of images through the Wasatch, Ohio Creek, Upper and Lower Williams Fork, Cameo Coal, Rollins, and Cozzette Formations (in order from stratigraphic top down). We analyzed fractures, faults, and primary and secondary bedding structures and determined the in-situ stress direction (SHmax) from wellbore failures. Two dominant open fracture (joint) trends are observed, with the most dominant set (i.e. most abundant) trending NE to ENE, dipping 79 deg. The second set trends SSE, dipping 55 deg towards both dip directions. Fracture density varies from well to well, with enhanced density in the Ohio Creek and Lower Williams Fork to Cameo Coal Formations. Several regional and small scale faults are observed, dominantly trending parallel to the NW strike of the Crystal Creek Anticline. Borehole breakouts occur dominantly within shale intervals, while drilling induced tensile fractures occur within the sandstones, suggesting a strong mechanical stratigraphy throughout the reservoir. The SHmax direction trends NE to ENE, parallel to fracture set 1, with local rotations of SHmax near observed faults. Our predicted orientation for hydraulic stimulation fractures (NE to ENE) is supported by results of a recent micro-seismic study. Our observations are compared to results from a 2009 SCAT study, supporting several of the proposed potential fault locations. In addition, integration with the regional structure suggests a significant break in the trend of fracture set 1 and SHmax near the synclinal axis of the Crystal Creek Syncline, potentially related to underlying regional faults parallel to the synclinal axis.

 

AAPG Search and Discovery Article #90156©2012 AAPG Rocky Mountain Section Meeting, Grand Junction, Colorado, 9-12 September 2012