What is the smallest change caused by geothermal fluids at depth that can be seen from magnetotelluric monitoring?
Abstract
Magnetotelluric (MT) is a passive electromagnetic technique classically used in geophysical exploration for imaging electrical conductivity structures; it is recently being developed as a monitoring technique on active volcanoes and geothermal systems. We consider the case of fluid injections and/or stimulation experiments of Enhanced Geothermal Systems where MT is used in addition to microseismic observations as a tool to provide critical information to geothermal fluid flows because the electrical conductivity is related with temperature, porosity, water content and minerals of rocks. Some experiments have shown that such MT signals might be difficult to observe, especially when they occur within the so-called MT dead-band at periods of 1-10 s. We consider the sensitivity of MT monitoring by forward modeling using ModEM open source code: it is used to build a 3-dimensional model with topography and sedimentary layers and simulate different conductivity changes that could be caused by brine and/or acid injection within fractures at depth. From these models, it seems that MT monitoring in a sedimentary environment at 20 W.m could be sensitive to an increase of conductivity in a fault area at geothermal depths of 2-3 km if the size of the disturbed domain reaches about 10x0.3x2 km3.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMGP51B1386S
- Keywords:
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- 0599 General or miscellaneous;
- COMPUTATIONAL GEOPHYSICSDE: 0699 General or miscellaneous;
- ELECTROMAGNETICSDE: 0999 General or miscellaneous;
- EXPLORATION GEOPHYSICSDE: 8010 Fractures and faults;
- STRUCTURAL GEOLOGY