HR: 0800h
AN: H41F-0476    [Abstracts]
TI: Self Potential Observations During Hydraulic Fracturing in the Laboratory
AU: * Moore, J R
EM: moore@decf.berkeley.edu
AF: University of California, Berkeley, Department of Civil and Environmental Engineering 760 Davis Hall, Berkeley, CA 94720 United States
AU: Glaser, S D
EM: glaser@ce.berkeley.edu
AF: University of California, Berkeley, Department of Civil and Environmental Engineering 760 Davis Hall, Berkeley, CA 94720 United States
AB: The self potential (SP) response during hydraulic fracturing of intact Westerly granite specimens was investigated in the laboratory. A strong electrokinetic SP was observed prior to fracture for 'heat-treated' specimens due to injectate infiltration into dilatant micro-porosity under increasing pore pressure. This result is in contrast to 'fresh' specimens where no fluid infiltration was noted before fracturing, and is supported by a decrease in the specimen resistivity for 'heat-treated' specimens prior to hydraulic fracture initiation. Spatial SP measurements are shown to exhibit a directional variation indicating the location of fracture initiation and the direction of fracture propagation. Similarly, anomalous spatial SP variation, related to varying amounts of fluid infiltration, may be able to forecast the geometry of the impending hydraulic fracture. Precursory SP anomalies were observed between 5 - 10 s prior to fracture initiation and were able to predict the direction of fracture propagation as well as the location of fracture initiation. Results reveal that the SP response during hydraulic fracturing is created primarily by electrokinetic coupling. At the time of fracture initiation, however, a large SP spike is observed that may be created by other mechanisms such as separation electrification, fracto-emissions, or co-seismic electrokinetics. The SP spike during fracture may be characteristic of brittle failure of earth materials and may enable the time and location of fracture initiation to be resolved directly from raw SP data. This testing demonstrates the unique ability of the SP method to respond to hydraulic fracture events and may aid in monitoring of fracture networks in the field.
DE: 1835 Hydrogeophysics
DE: 1859 Rocks: physical properties
DE: 1895 Instruments and techniques: monitoring
DE: 3914 Electrical properties
DE: 5104 Fracture and flow
SC: Hydrology [H]
MN: Fall Meeting 2005