Self‐potential observations during hydraulic fracturing

Abstract

[1] The self-potential (SP) response during hydraulic fracturing of intact Sierra granite was investigated in the laboratory. Excellent correlation of pressure drop and SP suggests that the SP response is created primarily by electrokinetic coupling. For low pressures, the variation of SP with pressure drop is linear, indicating a constant coupling coefficient (Cc) of À200 mV/MPa. However, for pressure drops >2 MPa, the magnitude of the Cc increases by 80% in an exponential trend. This increasing Cc is related to increasing permeability at high pore pressures caused by dilatancy of microcracks and is explained by a decrease in the hydraulic tortuosity. Resistivity measurements reveal a decrease of 2% prior to hydraulic fracturing and a decrease of $35% after fracturing. An asymmetric spatial SP response created by injectate diffusion into dilatant zones is observed prior to hydraulic fracturing, and in most cases this SP variation revealed the impending crack geometry seconds before failure. At rupture, injectate rushes into the new fracture area where the zeta potential is different than in the rock porosity, and an anomalous SP spike is observed. After fracturing, the spatial SP distribution reveals the direction of fracture propagation. Finally, during tensile cracking in a point load device with no water flow, a SP spike is observed that is caused by contact electrification. However, the time constant of this event is much less than that for transients observed during hydraulic fracturing, suggesting that SP created solely from material fracture does not contribute to the SP response during hydraulic fracturing.

Monitoring the mechanical stress of rocks through the electromagnetic emission produced by fracturing

“…Yoshida et al [5], based on observed EMEs on wet and dry granite, suggest the mechanism of piezoelectricity and compensation charges. Freund et al [6], from laboratory experiments, highlight as a generation mechanism the role of phole charges carried in the generation of pre-earthquake signals and earthquakes lights; for these phenomena, see also [8][9][10][11].…”

Electrokinetic Techniques for the Determination of Hydraulic Conductivity

“…Laboratory experiments on hydraulic fracturing on granite samples showed that the streaming potential varies linearly with the injection pressure (Moore & Glaser, 2007). However the SPC increases in an exponential trend when approaching the breakdown pressure.…”

“…The results show that the energy is focused in the vicinity of the advancing fracture's tip, however a tail can also be distinguished as the source behind the tip does not vanish instantaneously. Cuevas et al (2009) could model the streaming electrical spike recorded by Moore & Glaser (2007) during hydraulic fracturing by modeling the propagation of two cracks and adjusting the propagation velocity, the direction of propagation and the initial fracture volume. The authors concluded that direct information of the hydraulic fracture propagation can be provided by measuring the electrical field at distant.…”

Detection and characterization of hydraulically active fractures in a carbonate aquifer: results from self-potential, temperature and fluid electrical conductivity logging in the Combioula hydrothermal system in the southwestern Swiss Alps

“…where ɛ f is the dielectric permittivity of the fluid in F m , η f the fluid viscosity in Pa s, and ζ the so-called zeta potential of the double layer in V. Although the above expression for the electrokinetic coupling coefficient is strictly valid only for laminar capillary flow, there is increasing evidence to suggest that, for practical intents and purposes, it provides a good approximation for laminar groundwater flow regimes in general, including laminar flow in fractured media (e.g., Beamish and Peart 1998;Gorelik 2004;Moore and Glaser 2007).…”

“…Byrdina et al 2003) have been reported to date. Despite this remarkably broad range of applications, however, only very few systematic studies regarding the relationship between electrokinetic selfpotential signals and the hydraulic activity of fractures exist Ogilvy 1972, 1973;Wishart et al 2006;Moore and Glaser 2007) and corresponding applications to borehole studies are in even shorter supply (Hunt and Worthington 2000;Ishido and Pritchett 2003).…”