Fracture Model, Ground Displacements and Tracer Observations: Fruitland Coals, San Juan Basin, New Mexico, CO2 Pilot Test

This study incorporates observations from some of the experiments conducted on the Southwest Regional Partnership (SWP) for Carbon Sequestration’s San Juan Basin pilot test site. This enhanced coalbed methane recovery/carbon sequestration test was conducted in the thick coals of the Fruitland Formation in the high rate production fairway of the San Juan Basin. The pilot test was funded by the U.S. Department of Energy and managed by the National Energy Technology Laboratory. The SWP in collaboration with ConocoPhilips injected approximately16,700 metric tons of CO2 into the Fruitland coals from July 23 rd of 2008 through August 14 th of 2009. 3D seismic data from the site revealed that the seismic response of the Fruitland Formation is recognizable as a well defined seismic sequence and that individual coal zones in the formation are generally detectable. 3D seismic data also revealed that structures in the Fruitland Formation and overlying Kirtland Shale are more complex than anticipated. Analysis of well log data revealed that the Fruitland Formation coal zones throughout the area surrounding the site consist of two coal beds, each separated by a shale parting. This observation indicates that the coal reservoirs consist of six separate coal beds rather than three. Perfluorocarbon tracer monitoring revealed early arrival of tracer in a direction roughly orthogonal to that anticipated prior to CO2 injection. Tiltmeter derived ground surface displacements revealed subsidence across the area rather than uplift. The additional information obtained from the studies conducted at the site during its multiyear duration provide the opportunity to revise our models of the reservoir and sealing strata and to obtain new insights into observed reservoir responses to CO2 injection. A model discrete fracture network (DFN) is developed for the Fruitland coals that incorporates results from this multiyear study. Fracture sets incorporated in the model are derived from FMI log observations. Attributes derived from the 3D seismic data over the site are analyzed to obtain insights into larger scale reservoir architecture that may control flow in the vicinity of the CO2 injection well. These attributes are combined with ground displacements observed during CO2 injection to guide the distribution of fracture intensity through the reservoir. Properties of the DFN including porosity, permeability and fracture storage volume are upscaled into a gridded model of the reservoir. The aerial distribution of reservoir parameters derived in this study will improve our understanding of Fruitland coal reservoirs; help develop more effective strategies to enhance coalbed methane recovery combined with CO2 storage; and, help guide future flow simulations of Fruitland coal CO2 floods in this region of the high rate production fairway.