Seismoelectric interface response: Experimental results and forward model

Abstract

Understanding the seismoelectric interface response is important for developing seismoelectric field methods for oil exploration and environmental/engineering geophysics. The existing seismoelectric theory has never been validated systematically by controlled experiments. We have designed and developed an experimental setup in which acoustic-toelectromagnetic wave conversions at interfaces are measured. An acoustic source emits a pressure wave that impinges upon a porous sample. The reflected electric-wave potential is recorded by a wire electrode. We have also developed a full-waveform electrokinetic theoretical model based on the Sommerfeld approach and have compared it with measurements at positions perpendicular and parallel to the fluid/porous-medium interface.We performed experiments at several salinities. For 10 -3 and 10 -2 M sodium chloride (NaCl) solutions, both waveforms and amplitudes agree. For 10 -4 M NaCl, however, amplitude deviations occur. We found that a single amplitude field scaling factor describes these discrepancies. We also checked the repeatability of experiments. The amplitudes are constant for the duration of an experiment (1-4 hours) but decrease on longer time scales $24 hours ð Þ . However, the waveforms and spatial amplitude pattern of the electric wavefield are preserved over time. Our results validate electrokinetic theory for the seismic-to-electromagnetic-wave conversion at interfaces for subsurface exploration purposes.

Seismoelectric Fluid/Porous-Medium Interface Response Model and Measurements

“…Schakel et al (2011a) develop a full-waveform seismoelectric model based on the seismoelectric theory as derived by Pride (1994) and Pride and Haartsen (1996) and show that the model properly predicts laboratory measurements of coseismic and interface response fields in terms of travel time, waveform, polarity, amplitude, and spatial amplitude decay. In a similar way, Schakel et al (2011b) compare full-waveform fluid/porous-medium interface response predictions as a function of salinity and distance to the interface. They find agreement in waveform and spatial amplitude pattern at all conductivities.…”

A review on electrokinetically induced seismo-electrics, electro-seismics, and seismo-magnetics for Earth sciences

“…Measurements are performed on sand and glass microspheres and compared to the theory which predicts that the magnitude of SE potentials increases as the conductivity is lowered (from Block and Harris, 2006). tric double layer at the interface requires typically a duration of several hours. Schakel et al (2011) detected an interfacial response between water and a glass porous sample inside a water tank. They measured the waveform and the amplitude of the IR parallel and perpendicular to the interface.…”

“…If the equilibrium is not attained, the electric measurement can not be constant. Moreover measurements performed at different salinities could be difficult to compare (Schakel et al, 2011.…”

Frequency-Dependent Streaming Potentials: A Review

“…To brine bath or syringe pump To brine bath The absolute magnitude of the normalized streaming potential coefficient calculated by Packard [59] using (19) where Y a = a ωρ f /η, equivalent to (2) (modified from [59]). …”

“…Moreover fractured zones can be detected and permeability can be measured using seismoelectrics in borehole [15][16][17][18]. This method is especially appealing to hydrogeophysics for the detection of subsurface interfaces induced by contrasts in permeability, in porosity, or in electrical properties (salinity and water content) [19][20][21].…”