Stress control of seismicity patterns observed during hydraulic fracturing experiments at the Fenton Hill hot dry rock geothermal energy site, New Mexico

Conference · Mon Apr 13 04:00:00 EDT 1987

OSTI ID:6545065

Fehler, M C

Seismicity accompanying hydraulic injections into granitic rock is often diffuse rather than falling along a single plane. This diffuse zone of seismicity cannot be attributed to systematic errors in locations of the events. It has often been asserted that seismicity occurs along preexisting joints in the rock that are favorably aligned with the stress field so that slip can occur along them when effective stress is reduced by increasing pore fluid pressure. A new scheme for determining orientations and locations of planes along which the microearthquakes occurred was recently developed. The basic assumption of the method, called the three point method, is that many of the events fall along well defined planes; these planes are often difficult to identify visually in the data because planes of many orientations are present. The method has been applied to four hydraulic fracturing experiments conducted at Fenton Hill as part of a hot dry rock geothermal energy project. While multiple planes are found for each experiment; one plane is common to all experiments. The ratio of shear to normal stress along planes of all orientations is calculated using a best estimate of the current stress state at Fenton Hill. The plane common to all experiments has the highest ratio of shear to normal stress acting along it, so it is the plane most likely to slip. The other planes found by the three point method all have orientations with respect to current principal stresses that are favorable for slip to occur along preexisting planes of weakness. These results are consistent with the assertion that the rock contains pre-existing joints which slip when the effective stress is reduced by the increased pore fluid pressure accompanying the hydraulic injection. Microearthquakes occur along those planes that are favorably aligned with respect to the current stress field.

• Research Organization: Los Alamos National Lab., NM (USA)
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 6545065
• Report Number(s): LA-UR-87-1223; CONF-8704111-1; ON: DE87008992
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
58 GEOSCIENCES
COMMINUTION
EARTHQUAKES
ENERGY SYSTEMS
FEDERAL REGION VI
FRACTURING
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
GEOTHERMAL SYSTEMS
Geothermal Legacy
HOT-DRY-ROCK SYSTEMS
HYDRAULIC FRACTURING
JEMEZ MOUNTAINS
MICROEARTHQUAKES
MOUNTAINS
NEW MEXICO
NORTH AMERICA
ORIENTATION
SEISMIC EFFECTS
SEISMIC EVENTS
STRAINS
STRESSES
USA