Abstract: Formation Microimager, Microscanner and Core Characterization of Natural Fractures in a Horizontal Tight Gas Wellbore

Lesley W. Evans, David Thorn

In 1993 Amoco Production Company cooperated with GRI to drill and complete the Champlin 254B #2H, the first horizontal well in the Upper Almond Formation, Greater Green River Basin, to test the productivity of natural fractures.

Formation Microimages and oriented core were obtained in the slanted pilot hole to determine presence and orientation of natural fractures. Six natural fractures are present in the core, which is interpreted to have penetrated a fracture swarm. On-site description of the fractures indicates that closed fractures are cemented by amorphous calcite, whereas quartz dreuse and patchy calcite line open fractures. Electromagnetic goniometry was used onsite to determine fracture orientation. Fracture spacing varies from two inches to four feet. Core analyses are consistent with Formation Microimages in location and orientation of fractures. An additional 14 fractures are imaged outside the cored interval. The total fracture population strikes N50-70E, and dips nearly vertical. Dual Induction esistivities are used to calibrate Formation Microimages for fracture aperture, since open fractures tend to break when brought to the surface.

Formation Microscanner logs and three cores were obtained in the horizontal leg. Formation Microscanner images tie consistently with the orientation and location of cored fractures. Fracture strike and dip is identical to the pilot hole. One hundred and forty-two high quality fractures and one hundred and twenty-one lesser quality fractures were interpreted over 1700 feet of reservoir, although the total fracture population is probably greater. Reporting average fracture spacing is misleading since the spacing is non-uniform. The greatest distance between fracture images is seventy feet, whereas there are several fractures swarms where spacing is two feet or less.

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