Fracture and 3D seismic interpretations of the Fruitland Formation and cover strata: Implications for CO2 retention and tracer movement, San Juan Basin Pilot test

This study presents data on faults and fractures in the Fruitland Formation and its cover strata at a carbon sequestration pilot site in the high-rate Fruitland coal fairway in the northeastern San Juan Basin. The study incorporates satellite imagery, fracture detection and shear wave anisotropy logs and 3D seismic to identify potential issues that could impact long term reservoir integrity, CO2 flow and retention. The properties of fracture networks within the reservoir and sealing strata are important to understand in carbon sequestration and enhanced recovery efforts. Fracture networks exert significant control on the ability of a reservoir to retain CO2 for long (thousand year) time frames with minimal leakage.Local structural complexity at the pilot site resulted in tracer migration patterns that differed from predictions based on regional descriptions of fracture and cleat orientations measured in areas several miles from the site. Perfluorocarbon (PFC) tracer breakthrough in the production stream of nearby producing wells, for example, occurred first in a well to the east, in a direction close to the presumed butt cleat trend rather than in a well at equal distance along what had been assumed to be the more permeable face cleat trend. The study reveals local tectonic complexity not suggested by well log derived structure maps of the area and suggests that fractures and faults disrupt the local Fruitland coal reservoir and the overlying Kirtland Shale primary seal.

► PFC tracer first-arrival appears along unexpected trend. ► Open fractures are observed in the primary seal of this CO2 sequestration reservoir. ► 3D seismic attribute unveils structural complexity in reservoir and seal. ► Differential compaction and detachment may influence reservoir permeability trends. ► Structural complexity increases potential for minor CO2 leakage.