SEISMIC MONITORING OF THE GROWTH OF A HYDRAULIC FRACTURE-ZONE AT FENTON-HILL, NEW-MEXICO

The hydraulic fracturing technique is an important method for enhancin g hydrocarbon recovery, geothermal energy extraction, and solid waste disposal, Determination of the geometry and growth process of a hydrau lic fracture zone is important for monitoring and assessing subsurface fractures. A relative-source-location approach, based on a waveform c orrelation and a grid search method, has been developed to estimate re lative hypocenter locations for a cluster of 157 microearthquakes indu ced by hydraulic fracturing at the Los Alamos Hot Dry Rock (HDR) geoth ermal site. Among the 157 events, 147 microearthquakes occurred in a t ight cluster with a dimension of 40 m, roughly defining a vertical hyd raulic fracture zone with an orientation of N40 degrees W. The length, height, and width of the hydraulic fracture zone are estimated to be 40, 35, and 5 m. respectively Analysis of the spatial-temporal pattern of the induced microearthquakes reveals that the fracture zone grew s ignificantly, averaging 0.2 m/minute in a two-hour period toward the n orthwest along the fracture zone strike.