Monitoring freshwater‐seawater interface dynamics with audiomagnetotelluric data

Falgàs, Ester; Ledo, Juanjo; Marcuello, Álex; Queralt, Pilar

doi:10.3997/1873-0604.2009038

Cited by 38 publications

(22 citation statements)

References 57 publications

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“…The second more complex test case is inspired by the experiment of Falgàs et al (2009), who monitored a seawater-freshwater mixing zone over time using AMT. The models at t = 0 and t = 1 are shown in Figs.…”

Section: Seawater Intrusion Examplementioning

confidence: 99%

“…The situation is more favorable for groundwater applications, as the targets of interest are typically located at shallower depths than hydrocarbon reservoirs. In a rare case study , Falgàs et al (2009) successfully used AMT to monitor saltwater intrusion dynamics in a coastal aquifer in Spain. However, as the repeat surveys were not taken at the same positions, a timelapse strategy could not be used and they inverted for independent models at each time.…”

Section: Introductionmentioning

confidence: 99%

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Focused time-lapse inversion of radio and audio magnetotelluric data

Rosas‐Carbajal¹,

Linde²,

Kalscheuer³

2012

Journal of Applied Geophysics

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Geoelectrical techniques are widely used to monitor groundwater processes, while surprisingly few studies have considered audio (AMT) and radio (RMT) magnetotellurics for such purposes. In this numerical investigation, we analyze to what extent inversion results based on AMT and RMT monitoring data can be improved by (1) time-lapse difference inversion; (2) incorporation of statistical information about the expected model update (i.e., the model regularization is based on a geostatistical model); (3) using alternative model norms to quantify temporal changes (i.e., approximations of l 1 and Cauchy norms using iteratively reweighted least-squares), (4) constraining model updates to predefined ranges (i.e., using Lagrange Multipliers to only allow either increases or decreases of electrical resistivity with respect to background conditions). To do so, we consider a simple illustrative model and a more realistic test case related to seawater intrusion. The results are encouraging and show significant improvements when using time-lapse difference inversion with non l 2 model norms. Artifacts that may arise when imposing compactness of regions with temporal changes can be suppressed through inequality constraints to yield models without oscillations outside the true region of temporal changes. Based on these results, we recommend approximate l 1 -norm solutions as they can resolve both sharp and smooth interfaces within the same model.

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Section: Seawater Intrusion Examplementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Focused time-lapse inversion of radio and audio magnetotelluric data

Rosas‐Carbajal¹,

Linde²,

Kalscheuer³

2012

Journal of Applied Geophysics

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“…Le Pape et al 2012;Kühn et al 2014), characterizing the geoelectrical subsurface in a large variety of regions and for both academic and commercial applications (e.g. Heinson et al 2006;Falgàs et Complementing MT profiles with T and H data 1819 Campanyà et al 2011;La Terra & Menezes 2012;Ogaya et al 2014;Piña-Varas et al 2014). However, limitations of the MT method still exist and there is ample room for improvement.…”

mentioning

confidence: 99%

The advantages of complementing MT profiles in 3-D environments with geomagnetic transfer function and interstation horizontal magnetic transfer function data: results from a synthetic case study

Campanyà¹,

Ogaya²,

Jones³

et al. 2016

Geophys. J. Int.

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: The advantages of complementing MT profiles in 3-D environments with geomagnetic transfer function and interstation horizontal magnetic transfer function data: results from a synthetic case study. -Geophysical Journal International, 207, 3, pp. 1818-1836 S U M M A R YAs a consequence of measuring time variations of the electric and the magnetic field, which are related to current flow and charge distribution, magnetotelluric (MT) data in 2-D and 3-D environments are not only sensitive to the geoelectrical structures below the measuring points but also to any lateral anomalies surrounding the acquisition site. This behaviour complicates the characterization of the electrical resistivity distribution of the subsurface, particularly in complex areas. In this manuscript we assess the main advantages of complementing the standard MT impedance tensor (Z) data with interstation horizontal magnetic tensor (H) and geomagnetic transfer function (T) data in constraining the subsurface in a 3-D environment beneath a MT profile. Our analysis was performed using synthetic responses with added normally distributed and scattered random noise. The sensitivity of each type of data to different resistivity anomalies was evaluated, showing that the degree to which each site and each period is affected by the same anomaly depends on the type of data. A dimensionality analysis, using Z, H and T data, identified the presence of the 3-D anomalies close to the profile, suggesting a 3-D approach for recovering the electrical resistivity values of the subsurface. Finally, the capacity for recovering the geoelectrical structures of the subsurface was evaluated by performing joint inversion using different data combinations, quantifying the differences between the true synthetic model and the models from inversion process. Four main improvements were observed when performing joint inversion of Z, H and T data: (1) superior precision and accuracy at characterizing the electrical resistivity values of the anomalies below and outside the profile; (2) the potential to recover high electrical resistivity anomalies that are poorly recovered using Z data alone; (3) improvement in the characterization of the bottom and lateral boundaries of the anomalies with low electrical resistivity; and (4) superior imaging of the horizontal continuity of structures with low electrical resistivity. These advantages offer new opportunities for the MT method by making the results from a MT profile in a 3-D environment more convincing, supporting the possibility of high-resolution studies in 3-D areas without expending a large amount of economical and computational resources, and also offering better resolution of targets with high electrical resistivity.

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“…Falgàs et al 2009). Here, we present such an approach while conserving the Legendre moments Figure 2.…”

Section: Resistivity-difference-based Probabilistic Time-lapse Inversionmentioning

confidence: 99%

“…More recently, Rosas Carbajal et al (2012) applied this type of inversion approach to time-lapse electromagnetic (EM) data, specifically radio magnetotelluric (RMT) and audio magnetotelluric (AMT). Inspired by the work of Falgàs et al (2009), who monitored saltwater intrusion in a coastal aquifer, Rosas Carbajal et al (2012) demonstrated significant improvements in the resulting models by incorporating information about the expected temporal changes in the subsurface and by removing systematic errors.…”

mentioning

confidence: 99%

Probabilistic 3-D time-lapse inversion of magnetotelluric data: application to an enhanced geothermal system

et al. 2015

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S U M M A R YSurface-based monitoring of mass transfer caused by injections and extractions in deep boreholes is crucial to maximize oil, gas and geothermal production. Inductive electromagnetic methods, such as magnetotellurics, are appealing for these applications due to their large penetration depths and sensitivity to changes in fluid conductivity and fracture connectivity. In this work, we propose a 3-D Markov chain Monte Carlo inversion of time-lapse magnetotelluric data to image mass transfer following a saline fluid injection. The inversion estimates the posterior probability density function of the resulting plume, and thereby quantifies model uncertainty. To decrease computation times, we base the parametrization on a reduced Legendre moment decomposition of the plume. A synthetic test shows that our methodology is effective when the electrical resistivity structure prior to the injection is well known. The centre of mass and spread of the plume are well retrieved. We then apply our inversion strategy to an injection experiment in an enhanced geothermal system at Paralana, South Australia, and compare it to a 3-D deterministic time-lapse inversion. The latter retrieves resistivity changes that are more shallow than the actual injection interval, whereas the probabilistic inversion retrieves plumes that are located at the correct depths and oriented in a preferential north-south direction. To explain the time-lapse data, the inversion requires unrealistically large resistivity changes with respect to the base model. We suggest that this is partly explained by unaccounted subsurface heterogeneities in the base model from which time-lapse changes are inferred.

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Monitoring freshwater‐seawater interface dynamics with audiomagnetotelluric data

Cited by 38 publications

References 57 publications

Focused time-lapse inversion of radio and audio magnetotelluric data

Focused time-lapse inversion of radio and audio magnetotelluric data

The advantages of complementing MT profiles in 3-D environments with geomagnetic transfer function and interstation horizontal magnetic transfer function data: results from a synthetic case study

Probabilistic 3-D time-lapse inversion of magnetotelluric data: application to an enhanced geothermal system

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