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Title: Magnetotelluric Detection Thresholds as a Function of Leakage Plume Depth, TDS and Volume

Abstract

We conducted a synthetic magnetotelluric (MT) data analysis to establish a set of specific thresholds of plume depth, TDS concentration and volume for detection of brine and CO 2 leakage from legacy wells into shallow aquifers in support of Strategic Monitoring Subtask 4.1 of the US DOE National Risk Assessment Partnership (NRAP Phase II), which is to develop geophysical forward modeling tools. 900 synthetic MT data sets span 9 plume depths, 10 TDS concentrations and 10 plume volumes. The monitoring protocol consisted of 10 MT stations in a 2×5 grid laid out along the flow direction. We model the MT response in the audio frequency range of 1 Hz to 10 kHz with a 50 Ωm baseline resistivity and the maximum depth up to 2000 m. Scatter plots show the MT detection thresholds for a trio of plume depth, TDS concentration and volume. Plumes with a large volume and high TDS located at a shallow depth produce a strong MT signal. We demonstrate that the MT method with surface based sensors can detect a brine and CO 2 plume so long as the plume depth, TDS concentration and volume are above the thresholds. However, it is unlikely to detect amore » plume at a depth larger than 1000 m with the change of TDS concentration smaller than 10%. Simulated aquifer impact data based on the Kimberlina site provides a more realistic view of the leakage plume distribution than rectangular synthetic plumes in this sensitivity study, and it will be used to estimate MT responses over simulated brine and CO 2 plumes and to evaluate the leakage detectability. Integration of the simulated aquifer impact data and the MT method into the NRAP DREAM tool may provide an optimized MT survey configuration for MT data collection. This study presents a viable approach for sensitivity study of geophysical monitoring methods for leakage detection. The results come in handy for rapid assessment of leakage detectability.« less

Authors:
 [1];  [1];  [1];  [1]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1357405
Report Number(s):
LLNL-TR-729937
DOE Contract Number:
AC52-07NA27344
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES

Citation Formats

Yang, X., Buscheck, T. A., Mansoor, K., and Carroll, S. A.. Magnetotelluric Detection Thresholds as a Function of Leakage Plume Depth, TDS and Volume. United States: N. p., 2017. Web. doi:10.2172/1357405.
Yang, X., Buscheck, T. A., Mansoor, K., & Carroll, S. A.. Magnetotelluric Detection Thresholds as a Function of Leakage Plume Depth, TDS and Volume. United States. doi:10.2172/1357405.
Yang, X., Buscheck, T. A., Mansoor, K., and Carroll, S. A.. Fri . "Magnetotelluric Detection Thresholds as a Function of Leakage Plume Depth, TDS and Volume". United States. doi:10.2172/1357405. https://www.osti.gov/servlets/purl/1357405.
@article{osti_1357405,
title = {Magnetotelluric Detection Thresholds as a Function of Leakage Plume Depth, TDS and Volume},
author = {Yang, X. and Buscheck, T. A. and Mansoor, K. and Carroll, S. A.},
abstractNote = {We conducted a synthetic magnetotelluric (MT) data analysis to establish a set of specific thresholds of plume depth, TDS concentration and volume for detection of brine and CO2 leakage from legacy wells into shallow aquifers in support of Strategic Monitoring Subtask 4.1 of the US DOE National Risk Assessment Partnership (NRAP Phase II), which is to develop geophysical forward modeling tools. 900 synthetic MT data sets span 9 plume depths, 10 TDS concentrations and 10 plume volumes. The monitoring protocol consisted of 10 MT stations in a 2×5 grid laid out along the flow direction. We model the MT response in the audio frequency range of 1 Hz to 10 kHz with a 50 Ωm baseline resistivity and the maximum depth up to 2000 m. Scatter plots show the MT detection thresholds for a trio of plume depth, TDS concentration and volume. Plumes with a large volume and high TDS located at a shallow depth produce a strong MT signal. We demonstrate that the MT method with surface based sensors can detect a brine and CO2 plume so long as the plume depth, TDS concentration and volume are above the thresholds. However, it is unlikely to detect a plume at a depth larger than 1000 m with the change of TDS concentration smaller than 10%. Simulated aquifer impact data based on the Kimberlina site provides a more realistic view of the leakage plume distribution than rectangular synthetic plumes in this sensitivity study, and it will be used to estimate MT responses over simulated brine and CO2 plumes and to evaluate the leakage detectability. Integration of the simulated aquifer impact data and the MT method into the NRAP DREAM tool may provide an optimized MT survey configuration for MT data collection. This study presents a viable approach for sensitivity study of geophysical monitoring methods for leakage detection. The results come in handy for rapid assessment of leakage detectability.},
doi = {10.2172/1357405},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Apr 21 00:00:00 EDT 2017},
month = {Fri Apr 21 00:00:00 EDT 2017}
}

Technical Report:

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  • The work described in this volume was conducted by Pacific Northwest Laboratory to provide preliminary recommendations on data quality objectives (DQOs) to support the Waste Characterization Plan (WCP) and closure decisions for the Hanford Site single-shell tanks (SSTs). The WCP describes the first of a two-phase characterization program that will obtain information to assess and implement disposal options for SSTs. This work was performed for the Westinghouse Hanford Company (WHC), the current operating contractor on the Hanford Site. The preliminary DQOs contained in this volume deal with the analysis of SST wastes in support of the WCP and final closuremore » decisions. These DQOs include information on significant contributors and detection limit goals (DLGs) for SST analytes based on public health risk.« less
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  • This manuscript considers some of the factors that determine the detectability of three-dimensional (3-d) silicic magma bodies using the magnetotelluric (MT) method. Model simulations show that MT detection of magma depends strongly on its one-dimensional (1-d) host. Very subdued (3-d) responses of a juvenile magma body were observed for a theoretical Great Basin 1-D host. The attenuation of 3-D responses is caused by current channeling in layered media. Two factors are responsible for this. First, the scattering currents induced by the body are short circuited into the deep, less resistive crust, below 15 km. Second, the conductive overburden in themore » top 2 km of the earth's crust further reduces the scattered electric fields that do reach the earth's surface. However, intermediate and mature magmatic systems may be detectable with the MT method. Diapiric uprise of magma may continue to the point where magma is no longer in contact with the lower less resistive crust. Further, the ascent and release of volatiles may lead to sufficient fracturing above the magma body so as to establish electrical contact with the shallow conductive crust. Thus a substantial MT response due to current channeling in the shallow crust may occur.« less
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