Hydraulic fracturing of jointed formations

Conference · Wed Jan 01 04:00:00 EST 1986

OSTI ID:6002163

Murphy, H D; Fehler, M C

Measured by volume, North America's largest hydraulic fracturing operations have been conducted at Fenton Hill, New Mexico to create geothermal energy reservoirs. In the largest operation 21,000 m/sup 3/ of water were injected into jointed granitic rock at a depth of 3.5 km. Microearthquakes induced by this injection were measured with geophones placed in five wells drilled into, or very close, to the reservoir, as well as 11 surface seismometers. The large volume of rock over which the microearthquakes were distributed indicates a mechanism of hydraulic stimulation which is at odds with conventional fracturing theory, which predicts failure along a plane which is perpendicular to the least compressive earth stress. A coupled rock mechanics/fluid flow model provides much of the explanation. Shear slippage along pre-existing joints in the rock is more easily induced than conventional tensile failure, particularly when the difference between minimum and maximum earth stresses is large and the joints are oriented at angles between 30 and 60 degrees to the principal earth stresses, and a low viscosity fluid like water is injected. Shear slippage results in local redistribution of stresses, which allows a branching, or dendritic, stimulation pattern to evolve, in agreement with the patterns of microearthquake locations. These results are qualitatively similar to the controversial process known as ''Kiel'' fracturing, in which sequential injections and shut-ins are repeated to create dendritic fractures for enhanced oil and gas recovery. However, we believe that the explanation is shear slippage of pre-existing joints and stress redistribution, not proppant bridging and fluid blocking as suggested by Kiel. 15 refs., 10 figs.

• Research Organization: Los Alamos National Lab., NM (USA)
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 6002163
• Report Number(s): LA-UR-85-3701; CONF-860325-1; ON: DE86002406
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
COMMINUTION
ENERGY SYSTEMS
FEDERAL REGION VI
FRACTURING
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
GEOTHERMAL SYSTEMS
GRANITES
Geothermal Legacy
HOT-DRY-ROCK SYSTEMS
HYDRAULIC FRACTURING
IGNEOUS ROCKS
MATHEMATICAL MODELS
MECHANICAL PROPERTIES
NEW MEXICO
NORTH AMERICA
PLUTONIC ROCKS
ROCKS
SHEAR PROPERTIES
STIMULATION
USA