Anisotropy and fracture zones about a geothermal well from P‐wave velocity profiles

Abstract

The feasibility of locating fracture zones and estimating their crack parameters was examined using an “areal well shoot” method centered on Utah State Geothermal Well 9‐1, Beaver County, Utah. High‐resolution traveltime measurements were made between a borehole sensor and an array of shotpoints distributed radially and azimuthally about the well. The directional dependence of velocity in the vicinity of the well was investigated by comparing traveltimes from different azimuths. Velocity anisotropy was detected; this condition is consistent with, but not required by, the existence of fractures in the basement rock having orientations subparallel to the latest episode of local faulting. The interpretation is complicated by a variable thickness of overburden around the well. Traveltime delays also suggest the presence of a low‐angle fracture zone intersecting the well at a depth of ∼1 500 ft.