Seismic visibility of fractures

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1988

OSTI ID:6720988

Pyrak, L J

A displacement- and velocity-discontinuity theory of wave propagation across a fracture is presented, as well as experimental data that validates use of this theory for wave propagation across fractures. The boundary conditions that describe the displacement discontinuity are: (1) the stress across the boundary is continuous; (2) the displacements are discontinuous. The ratio between the seismic stress and the discontinuity in particle displacement is the specific stiffness of the fracture. The corresponding boundary conditions for the velocity-discontinuity are: (1) the stress across the boundary is continuous; (2) the velocity is discontinuous across the boundary. The ratio between the seismic stress and the discontinuity in particle velocity is the specific viscosity of the fluid in the fracture. To validate this theory, laboratory measurements of the transmission of compressional and shear waves across both intact and naturally fractured samples of granite were made. As stiffness of the fracture increases, increasingly higher frequencies are allowed to pass across the fracture. Saturating the fracture with water results in an increase in the stiffness of the fracture. Both compressional and shear wave amplitudes are found to increase upon saturation of the fracture with water. To analyze the effect of fluids on shear wave transmission, the displacement- and velocity-discontinuity theory were combined. In this theory, in addition to the discontinuity in displacement, the discontinuity in velocity is taken into account using both a specific stiffness and a specific viscosity. This combined displacement-velocity discontinuity theory is found to agree with experimental amplitudes of shear waves transmitted across fluid-filled fractures.

• Research Organization: California Univ., Berkeley, CA (USA)
• OSTI ID: 6720988
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AMPLITUDES
BENCH-SCALE EXPERIMENTS
BOUNDARY CONDITIONS
COMPRESSION
DETECTION
FLUIDS
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
GRANITES
IGNEOUS ROCKS
MATHEMATICAL MODELS
PLUTONIC ROCKS
RESERVOIR FLUIDS
ROCKS
SATURATION
SEISMIC DETECTION
SEISMIC WAVES
SHEAR
STRESSES
VISCOSITY
WATER SATURATION
WAVE PROPAGATION