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Laboratory hydraulic fracture characterization using acoustic emission
Hampton, Jesse Clay
Hampton, Jesse Clay
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2012
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2012
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2013-12-01
Abstract
For many years acoustic emission (AE) testing has aided in the understanding of fracture initiation and propagation in materials ranging from high strength steel to polymers to composite and geologic materials. Acoustic emissions are the phenomenon in which a material or structure emits elastic waves caused by the sudden occurrence of fractures or frictional sliding along discontinuous surfaces and grain boundaries. Throughout this project AE monitoring has been employed during laboratory hydraulic fracturing tests for the purpose of Enhanced Geothermal Systems (EGS) reservoir creation, as well as sample and material characterization. EGS consists of inducing fracture networks in deep Earth hot, dry impermeable rock in order to extract heat energy for production. Sample material testing and characterization played a major role throughout AE monitoring and analysis, which enhanced the capabilities and understanding of fracture growth prior to laboratory hydraulic fracturing tests. Multiple large, 30 cm cubical, analog rock and granite blocks have been monitored throughout laboratory hydraulic fracturing and geothermal reservoir simulation. Unconfined and true-triaxially confined and heated boundary conditions have been utilized. AE monitoring of laboratory hydraulic fracturing experiments showed multiple phenomena including winged fracture growth from a borehole, cross-field well communication, fracture reorientation, borehole casing failure and much more. AE data analysis consisted of event source location determination, AE fracture surface identification and validation, source mechanism determination, geothermal production well location optimization, and determining the overall effectiveness of the induced fracture network. Field scale AE data obtained from the National Institute of Advanced Industrial Science and Technology, Japan, and Central Research Institute of Electric Power Industry, Japan, for two EGS fields have been compared to laboratory data in order to determine the applicability of the laboratory testing performed.
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