The study of a naturally fractured gas reservoir using seismic techniques

The upper Green River Formation at the Bluebell-Altamont field, Utah (Figur e 1) is a tight gas sand reservoir where economic production can be sustain ed only in regions of high natural fracturing. In 1994, a demonstration sei smic project was conducted at the field to show how exploration for, and th e characterization of, naturally fractured gas reservoirs can be more effec tive through the integrated use of seismic techniques. Study of field expos ures, well logs, and regional stress indicators prior to the seismic survey indicated a high degree of preferential orientation to the dominant fractu re trend at the field. The seismic survey consisted of two crossing, nine-c omponent surface seismic lines and a nine-component vertical seismic profil e. The compression, and shear-wave surface seismic both recorded anisotropi es that were related to the presence and azimuth of the natural fracturing. The surface seismic results were supported by results from the nine-compon ent vertical seismic profile. This program demonstrates the potential offer ed by the use of integrated seismic and geological techniques for the analy sis of both land and marine naturally fractured reservoirs; furthermore, it demonstrates the possibilities of reviewing existing databases containing compression-wave surface seismic data for fracture information.