FRACTURE MODEL, GROUND DISPLACEMENTS AND TRACER BSERVATIONS: FRUITLAND COALS, SAN JUAN BASIN, NEW MEXICO, CO_2 PILOT TEST

摘要

This study incorporates observations from some of the experiments conducted on the Southwest Regional Partnership (SWP) forCarbon Sequestration’s San Juan Basin pilot test site. This enhanced coalbed methane recovery/carbon sequestration test wasconducted in the thick coals of the Fruitland Formation in the high rate production fairway of the San Juan Basin. The pilot test wasfunded by the U.S. Department of Energy and managed by the National Energy Technology Laboratory. The SWP in collaborationwith ConocoPhilips injected approximately16,700 metric tons of CO_2 into the Fruitland coals from July 23rd of 2008 through August14th of 2009. 3D seismic data from the site revealed that the seismic response of the Fruitland Formation is recognizable as a welldefined seismic sequence and that individual coal zones in the formation are generally detectable. 3D seismic data also revealed thatstructures in the Fruitland Formation and overlying Kirtland Shale are more complex than anticipated. Analysis of well log datarevealed that the Fruitland Formation coal zones throughout the area surrounding the site consist of two coal beds, each separated by ashale parting. This observation indicates that the coal reservoirs consist of six separate coal beds rather than three. Perfluorocarbontracer monitoring revealed early arrival of tracer in a direction roughly orthogonal to that anticipated prior to CO_2 injection. Tiltmeterderived ground surface displacements revealed subsidence across the area rather than uplift. The additional information obtained fromthe studies conducted at the site during its multiyear duration provide the opportunity to revise our models of the reservoir and sealingstrata and to obtain new insights into observed reservoir responses to CO_2 injection. A model discrete fracture network (DFN) isdeveloped for the Fruitland coals that incorporates results from this multiyear study. Fracture sets incorporated in the model arederived from FMI log observations. Attributes derived from the 3D seismic data over the site are analyzed to obtain insights intolarger scale reservoir architecture that may control flow in the vicinity of the CO_2 injection well. These attributes are combined withground displacements observed during CO_2 injection to guide the distribution of fracture intensity through the reservoir. Properties ofthe DFN including porosity, permeability and fracture storage volume are upscaled into a gridded model of the reservoir. The aerialdistribution of reservoir parameters derived in this study will improve our understanding of Fruitland coal reservoirs; help developmore effective strategies to enhance coalbed methane recovery combined with CO_2 storage; and, help guide future flow simulations ofFruitland coal CO_2 floods in this region of the high rate production fairway.