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Title Acoustic emission associated with the formation of sets of fractures in sandstone

Authors King, M.S. Pettitt, W.S.

Publication Reference Shiraz 2009 First International Petroleum Conference and Exhibition, Shiraz, Iran.

Abstract A polyaxial (true-triaxial) stress-loading system, developed originally for determining all nine components of P- and S-wave velocities and attenuation, and fluid permeability, for 50.8mm-side cubic rock specimens tested to failure, has been modified to permit the measurement of acoustic emission (AE) events associated with the failure process. Results are reported for Crosland Hill sandstone tested to failure under loading conditions leading to the formation of sets of aligned microcracks, achieved by maintaining the minor principal stress at a low value while increasing the two other principal stresses until failure of the rock. An ultrasonic survey associated with the test has been employed to map the transversely-isotropic velocity structure created by through-going parallel fractures resulting from the sets of aligned microcracks. This velocity structure has then been employed to locate AE events recorded during the test by 4 AE sensors located in each of the six specimen loading platens. A selection of AE events associated with one of the fractures has been processed for moment tensor analysis information, in order to determine the source type and orientation of microcracking as the fracture grows. The mechanisms indicate tensile behaviour during initial fracture propagation. Shear failure, however, appears to dominate as the fracture finally approaches each of the platens at the edge of the cubic specimen.

Key Figure Key Figure
Time dependency of the located AE events, looking in the intermediate stress direction.

Link http://www.eage.org/events/index.php?eventid=108&Opendivs=s3



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