Shallow seismic AVO variations related to partial water saturation during a pumping test

Sloan, Steven D.; Tsoflias, G. P.; Steeples, Don W.

doi:10.1029/2007gl031556

Cited by 5 publications

(2 citation statements)

References 13 publications

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“…The latter may be derived from the estimated geoelectrical, geomagnetic, electromagnetic, or seismic properties by petrophysical relationships, the validity and generality of which is often questionable. Geophysical surveying techniques can also be used to monitor hydraulic experiments, such as infiltration experiments [e.g., Daily et al , 1992], pumping tests [e.g., Sloan et al , 2007; Rizzo et al , 2004], and tracer tests [e.g., Binley et al , 1996], in which the geophysical signal is directly related to the hydraulic stress applied. One of these approaches consists in monitoring salt tracer experiments by electrical resistivity tomography (ERT), leading to the distribution of changes in the bulk electrical conductivity in the aquifer which may subsequently be converted to the concentration distribution [ Binley et al , 1996, 2002; Slater et al , 2000; Kemna et al , 2002; Vanderborght et al , 2005; Singha and Gorelick , 2005].…”

Section: Introductionmentioning

confidence: 99%

Fully coupled hydrogeophysical inversion of synthetic salt tracer experiments

Pollock

Cirpka

2010

Water Resources Research

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[1] We present a method for the determination of hydraulic conductivity from monitoring of salt tracer tests by electrical resistivity tomography (ERT). To ensure that the underlying principles of flow, transport, and geoelectrics are obeyed in the inversion, we perform a fully coupled hydrogeophysical analysis using temporal moments of electrical potential perturbations. In the predictive mode, we use moment-generating equations with corresponding adjoint equations for the evaluation of sensitivities. For inversion, we apply the quasi-linear geostatistical inversion approach. The method is tested in a synthetic case study mimicking a laboratory-scale quasi two-dimensional sandbox, in which 48 electrodes and 8 piezometers are used. The hydraulic conductivity field is estimated from the mean arrival times of electrical potential perturbations and hydraulic heads. The estimated hydraulic conductivity field reproduces most features with, however, a loss of variability. Even though only the temporal moments of the electrical signals are used for inversion, the transient behavior is satisfactorily recovered. Also, the spatial patterns of concentration arrival times in the true and estimated cases are in good agreement, so that the propagation of the tracer plume can be followed fairly accurately. We test the effects of large measurement errors and erroneous prior information on the performance of the inversion. While prior statistical parameters are of minor importance in detecting the major pattern of hydraulic conductivity, a large measurement error could have an important impact on the solution. Also, the choice of electrode configurations appears to be important. In particular, strictly surface-based geoelectrical surveys do not seem to be very suitable for identifying spatial patterns of hydraulic conductivity by ERT monitoring of salt tracer tests within aquifers.

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Section: Introductionmentioning

confidence: 99%

Fully coupled hydrogeophysical inversion of synthetic salt tracer experiments

Pollock

Cirpka

2010

Water Resources Research

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“…Recently, Slater [2007] presented a review on the integration of geophysical and hydrological measurements in hydrogeological contexts. Rather than using geophysical exploration techniques for the identification of the subsurface structure, they may also be used to monitor hydraulic experiments (e.g., infiltration experiments [ Daily et al , 1992], pumping tests [ Sloan et al , 2007; Rizzo et al , 2004], and tracer tests [ Binley et al , 1996]), where the geophysical signal reflects the response to the hydraulic stress applied in the experiment.…”

Section: Introductionmentioning

confidence: 99%

Temporal moments in geoelectrical monitoring of salt tracer experiments

Pollock

Cirpka

2008

Water Resources Research

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[1] Monitoring of salt tracer experiments by electrical resistivity tomography (ERT) has been shown to be a valuable tool for characterizing the hydraulics of an aquifer, but efficient approaches of determining the spatial hydraulic conductivity distribution from ERT data are still missing. Standard inversion of ERT data obtained during salt tracer tests may even lead to estimates of the concentration distribution that are in contradiction to flow and transport of conservative compounds in porous media. In order to avoid nonphysical behavior, we consider the governing equations of groundwater flow, solute transport, and geoelectrics as a coupled system. While the tracer passes through the part of the domain that is sensitive for a particular electrode configuration, the measured electrical potential differences are perturbed. We characterize these perturbations by their temporal moments and relate them to the temporal moments of concentration, which themselves depend on hydraulic conductivity. We present temporal moment-generating equations leading from the hydraulic conductivity field via heads and velocities to the temporal moments of concentration and electrical potential perturbations. The approach makes use of a linearized version of the Poisson equation. On the basis of this system of coupled steady state equations, we compute the sensitivity of electrical potential perturbations with respect to the log hydraulic conductivity distribution by the continuous adjoint state method for coupled systems. For demonstration, we simulate salt tracer experiments in a virtual quasi-two-dimensional sandbox, monitored by ERT. We show that the ratio of the first over the zeroth temporal moment of potential perturbation is less affected by the linearization of the Poisson equation than the zeroth and first moments themselves. Thus, it appears recommendable to use the ratio of first to zeroth moments also as data in inversion. We compare sensitivity patterns resulting from different electrode configurations. The methods of forward simulations and sensitivity calculations presented in this paper can be combined with any inverse kernel to develop a complete inverse model. Altogether, using temporal moments of potential perturbation appears promising for fully coupled hydrogeophysical inversion of ERT surveys during salt tracer tests.

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Influence of frequency and saturation on AVO attributes for patchy saturated rocks

Dupuy

Stovas

2014

GEOPHYSICS

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Partially saturated rocks are considered to be major sources of seismic wave velocity dispersion and attenuation in recorded real data. From the physical description of partially saturated gas-water and oil-water reservoirs, we use upscaling theories to compute an equivalent frequency-dependent porous medium. These homogenization methods are associated with mesoscale description of attenuation and dispersion coming from wave-induced flow phenomena. To compute wave propagation, we use numerical codes in the frequency domain that allow us to take into account all the frequency-dependent parameters without approximation or local time steps. In this way, the Biot slow compressional wave is well modeled and its partially diffusive, partially propagative behavior is completely considered. The attenuation and dispersion of the waves in such media are coming partly from the wave mode conversion into diffusive slow waves, not visible on seismograms. But the amplitude of propagative P- and S-waves are mainly affected by these energy losses at interfaces. Using full waveform modeling, we investigate the amplitude versus offset (AVO) attributes with respect to saturation and frequency. For a simple three-layer case, we compute poroelastic wave propagation, extract maximum amplitude with respect to angle, and, through a least-square fitting method, we obtain the AVO attributes for PP- and PS-reflected events. Due to the influence of mesoscale induced-flow phenomena and relatively to the regime of the Biot slow wave, the main results show a strong variability of the AVO attributes with the frequency and a lower variability with the saturation for reflected PP or PS events. We show that gas-water and oil-water systems have similar behaviors. Strong differences between patchy saturation and effective fluid phase theories are highlighted, especially at high frequency, for PP events and for gas-water systems. Then, we conclude that these AVO attributes carry information about the saturation that can be used to estimate the saturation variations in time-lapse studies.

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Shallow seismic AVO variations related to partial water saturation during a pumping test

Cited by 5 publications

References 13 publications

Fully coupled hydrogeophysical inversion of synthetic salt tracer experiments

Fully coupled hydrogeophysical inversion of synthetic salt tracer experiments

Temporal moments in geoelectrical monitoring of salt tracer experiments

Influence of frequency and saturation on AVO attributes for patchy saturated rocks

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