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A successful stimulation experiment has been conducted in a fluvial sandstone of the Mesaverde Formation at the Department of Energy's Multiwell Experiment site in Piceance basin of Colorado. This highly heterogeneous sandstone has submicrodarcy matrix permeability but also contains narrow natural fractures that increase the reservoir permeability to 15 microdarcies. Examination of the core showed a primary, unidirectional, natural fracture system with evidence (unlike previous zones) for second and third sets at oblique orientations. The stimulation experiment consisted of stress tests, a three-well prefrac interference test, step-rate/flow-back tests, a minifrac, a full stimulation treatment, borehole geophone diagnostics during fracturing, and a post-frac interference test. Prefrac rates of 65 MSCFD were measured and a permeability anisotropy ratio of 30:1 was inferred. Ten stress tests yielded containment barriers of 600--700 psi abutting the reservoir, lower than previous zones. Minifrac results showed that leakoff was very high during injection because of loss into the natural fractures. This leakoff was successfully controlled with 10 mesh sand during the treatment. A foam fluid with a new breaker system was used to minimize damage to the natural fractures. Borehole geophones in observation wells indicated that propped fracture length was at least 250 ft on each wing and fracture height was about 120 ft. After the stimulation, the well cleaned up readily and was flowing over 300 MSCFD within 24 hours. Flow rates after 16 days of production were 200--220 MSCFD and little damage to the natural fractures was evident. Anisotropic behavior persisted throughout a postfrac interference test. 27 refs., 14 figs., 2 tabs. (ERA citation 13:053087)