Advanced

The use of positivity constraints in 4-D ERT inversion

Loke, M. H.; Wilkinson, P. B.; Dahlin, T. LU ; Chambers, J. E.; Uhlemann, S. and Dijkstra, T. (2018) EAGE-HAGI 1st Asia Pacific Meeting on Near Surface Geoscience and Engineering
Abstract

Time-lapse resistivity surveys are used to monitor changes in the subsurface. In some situations, it is expected the resistivity will only decrease (or vice versa) with time. The 4-D ERT inversion technique includes a temporal smoothness constraint to ensure that the resistivity changes in a smooth manner with time. However, it does not directly constrain the direction of the temporal changes in the resistivity. In some cases, the time-lapse models might show an increase in the resistivity with time in parts of the inverse model where it is expected to only decrease based on other information. We modify the 4-D ERT inversion method to remove this artefact. We first use the standard 4-D ERT inversion algorithm to generate an initial... (More)

Time-lapse resistivity surveys are used to monitor changes in the subsurface. In some situations, it is expected the resistivity will only decrease (or vice versa) with time. The 4-D ERT inversion technique includes a temporal smoothness constraint to ensure that the resistivity changes in a smooth manner with time. However, it does not directly constrain the direction of the temporal changes in the resistivity. In some cases, the time-lapse models might show an increase in the resistivity with time in parts of the inverse model where it is expected to only decrease based on other information. We modify the 4-D ERT inversion method to remove this artefact. We first use the standard 4-D ERT inversion algorithm to generate an initial model. If the resistivity is expected to decrease with time, for the model cells that show a resistivity increase a truncation procedure is used where the resistivities of the different time models are reset to the mean value. The method of transformations is then used to ensure that the resistivities of the later time models are always less than the first model. The constraints can be applied to selected regions in the model in cases where additional information is available.

(Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to conference
publication status
published
subject
conference name
EAGE-HAGI 1st Asia Pacific Meeting on Near Surface Geoscience and Engineering
conference location
Yogyakarta, Indonesia
conference dates
2018-04-09 - 2018-04-13
external identifiers
  • scopus:85050265387
DOI
10.3997/2214-4609.201800427
language
English
LU publication?
yes
id
194be94f-acec-447f-ba7b-de6356e9602e
date added to LUP
2018-10-01 10:53:09
date last changed
2019-02-20 11:28:32
@misc{194be94f-acec-447f-ba7b-de6356e9602e,
  abstract     = {<p>Time-lapse resistivity surveys are used to monitor changes in the subsurface. In some situations, it is expected the resistivity will only decrease (or vice versa) with time. The 4-D ERT inversion technique includes a temporal smoothness constraint to ensure that the resistivity changes in a smooth manner with time. However, it does not directly constrain the direction of the temporal changes in the resistivity. In some cases, the time-lapse models might show an increase in the resistivity with time in parts of the inverse model where it is expected to only decrease based on other information. We modify the 4-D ERT inversion method to remove this artefact. We first use the standard 4-D ERT inversion algorithm to generate an initial model. If the resistivity is expected to decrease with time, for the model cells that show a resistivity increase a truncation procedure is used where the resistivities of the different time models are reset to the mean value. The method of transformations is then used to ensure that the resistivities of the later time models are always less than the first model. The constraints can be applied to selected regions in the model in cases where additional information is available.</p>},
  author       = {Loke, M. H. and Wilkinson, P. B. and Dahlin, T. and Chambers, J. E. and Uhlemann, S. and Dijkstra, T.},
  language     = {eng},
  location     = {Yogyakarta, Indonesia},
  title        = {The use of positivity constraints in 4-D ERT inversion},
  url          = {http://dx.doi.org/10.3997/2214-4609.201800427},
  year         = {2018},
}