Acoustic emissions during hydraulic fracturing in granite

Conference · Sun Jan 01 04:00:00 EST 1984 · Ser. Rock Soil Mech.; (United States)

OSTI ID:6719382

Pearson, C; Albright, J N

Hydraulic stimulation experiments being conducted in low-permeability crystalline rocks, at the Department of Energy's Hot Dry Rock Geothermal Site, Fenton Hill, New Mexico, often produce large numbers of microearthquakes. Typically, the early stages of these experiments are aseismic. The rate of acoustic emissions increases rapidly after a critical volume of water, equal to roughly two-thirds of the total amount previously injected, is exceeded, possibly indicating the onset of fracture extension. With local magnitudes ranging between -1 and -6, these events occurring at 3-km depth are too small to detect using surface seismometers, so we monitor the activity using a downhole triaxial geophone system(s) positioned in well(s) close to the reservoir volume. The system provided enough data in early experiments to locate the events using single station seismometry. Recently it became possible to station a second geophone system in a nearby well, that provides valuable additional constraints on event locations. The second tool was also used to measure relative changes in attenuation by comparing signal frequencies for the same event recorded on the two tools. P-wave attenuation does not vary significantly with the source region of the event, however, S-wave attenuation is quite variable, with Q ranging from 170 to 40. This suggests that the attenuation may be due to open water-filled fractures. We located large numbers of acoustic events during three hydraulic stimulation experiments, two of which occurred in March 1979 and one in December 1980. During the first two, event locations clustered near a single north-by-northwest trending vertical plane. During the third experiment (after an extended period of heat extraction) the same general trend was evident, but the zone was much wider and events seemed to occur on a series of parallel planes indicating a more complex structure within the reservoir.

• Research Organization: Los Alamos National Lab., NM
• OSTI ID: 6719382
• Report Number(s): CONF-811036-
• Conference Information: Journal Name: Ser. Rock Soil Mech.; (United States)
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
150201* -- Geology & Hydrology of Geothermal Systems-- USA-- (-1989)
ACOUSTIC EMISSION TESTING
ACOUSTIC TESTING
COMMINUTION
EARTHQUAKES
ENERGY SYSTEMS
FLUID MECHANICS
FRACTURING
GEOTHERMAL SYSTEMS
GRANITES
HOT-DRY-ROCK SYSTEMS
HYDRAULIC FRACTURING
HYDRAULICS
IGNEOUS ROCKS
MATERIALS TESTING
MECHANICS
NONDESTRUCTIVE TESTING
PLUTONIC ROCKS
ROCKS
SEISMIC EVENTS
SIMULATION
TESTING