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A practical assessment of frequency electromagnetic inversion in a near surface geological environment

Letellier, Mattias LU (2012) In Dissertations in Geology at Lund University GEOX01 20112
Department of Geology
Abstract (Swedish)
Under de senaste 15 åren har användningen av frekvenselektromagnetiska sonderingsinstrument inom geofysiska undersökningar drivit forskningen framåt för att förbättra den använda metoden. En av dessa tekniker
är inversion vilket är den process som omvandlar elektromagnetiska data till djupvärden för geologiska lager. Inversion av frekvenselektromagnetiska data har länge varit förknippat med svårigheter. Framstegen som har gjorts både inom instrument- och mjukvaruutveckling har lett till ökad användbarhet. Det finns dock fortfarande problem beträffande precision och återgivning av geologiska förhållanden. Den här studien är ett försök att förstå de problem som är förknippade med frekvenselektromagnetisk inversion i samband med geologiska... (More)
Under de senaste 15 åren har användningen av frekvenselektromagnetiska sonderingsinstrument inom geofysiska undersökningar drivit forskningen framåt för att förbättra den använda metoden. En av dessa tekniker
är inversion vilket är den process som omvandlar elektromagnetiska data till djupvärden för geologiska lager. Inversion av frekvenselektromagnetiska data har länge varit förknippat med svårigheter. Framstegen som har gjorts både inom instrument- och mjukvaruutveckling har lett till ökad användbarhet. Det finns dock fortfarande problem beträffande precision och återgivning av geologiska förhållanden. Den här studien är ett försök att förstå de problem som är förknippade med frekvenselektromagnetisk inversion i samband med geologiska undersökningar i fält.
Ett flertal mätningar utfördes på tre lokaler med ett flerfrekvensstångslingram instrument. Lokalerna valdes med avseende på deras enkla uppbyggnad i form av två distinkta lager med olika konduktivitet. De olika lokalerna skiljde sig både geologiskt och strukturellt. Resistivitetsprofiler och borrhålsloggar användes för att bestämma det undre lagrets stratigrafiska position. Den elektromagnetiska informationen behandlades sedan i dataprogrammet
EM Inverter.
De insamlade resultaten visar på en bristande korrelation mellan den geologiska verkligheten och den modell som dataprogrammet EM Inverter producerar, och den önskade detaljnivån gick inte att uppnå. Detta upplösningsproblem är inte enbart begränsat till EM Inverter, utan kan även påvisas i stora delar av den genomgångna facklitteraturen.
Detta begränsar i nuläget tillämpningen av frekvenselektromagnetism inom geofysik men metoden är trots allt användbar för inledande studier av geologiska miljöer.
Populärvetenskaplig sammanfattning (Less)
Abstract
The adoption of frequency electromagnetic (EM) sounding devices in the past 15 years for geophysical exploration has fueled research into techniques associated with the method. One of these techniques is inversion which is the process of turning the EM data into measurements of depth for different geological layers. Inversion of frequency EM data has classically been difficult and unreliable. With advancements made in both hardware and software, frequency EM inversion has become more prominent. There are still questions, however, regarding its
consistency and precision. This study is an attempt to understand the problems associated with Frequency EM inversion in a practical geological setting.
Using a frequency EM sounding device... (More)
The adoption of frequency electromagnetic (EM) sounding devices in the past 15 years for geophysical exploration has fueled research into techniques associated with the method. One of these techniques is inversion which is the process of turning the EM data into measurements of depth for different geological layers. Inversion of frequency EM data has classically been difficult and unreliable. With advancements made in both hardware and software, frequency EM inversion has become more prominent. There are still questions, however, regarding its
consistency and precision. This study is an attempt to understand the problems associated with Frequency EM inversion in a practical geological setting.
Using a frequency EM sounding device multiple surveys were undertaken on three geologically different localities. These localities were chosen due to their two layer conductivity contrasts that make up a simple geological configuration. For quality assurance the subsurface layout for the surveys were determined from a mixture of resistivity
profiles and well log measurements. The EM data were subsequently inverted using the EM Inverter program.
The results obtained show a certain lack in capability especially associated with the EM Inverter program. These include an inability to interpret detail and only give a rough estimate of the dimensions. This problem is not unique to the EM Inverter program but can be seen quite universally in the literature. The current capability of the frequency
EM method is well suited as a complimentary device used at the initial stages of a survey. To best make use of the frequency EM method a guide is provided which offers simple suggestions in producing more accurate inversion models. These are mostly associated with an understanding of the area’s stratigraphic and conductive properties. (Less)
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author
Letellier, Mattias LU
supervisor
organization
course
GEOX01 20112
year
type
M2 - Bachelor Degree
subject
keywords
frequency, electromagnetic, sounding, inversion, GEM-2 frekvens, elektromagnetiska, sondering, GEM-2
publication/series
Dissertations in Geology at Lund University
report number
299
language
English
id
2375282
date added to LUP
2012-03-27 17:23:54
date last changed
2012-05-15 11:55:50
@misc{2375282,
  abstract     = {The adoption of frequency electromagnetic (EM) sounding devices in the past 15 years for geophysical exploration has fueled research into techniques associated with the method. One of these techniques is inversion which is the process of turning the EM data into measurements of depth for different geological layers. Inversion of frequency EM data has classically been difficult and unreliable. With advancements made in both hardware and software, frequency EM inversion has become more prominent. There are still questions, however, regarding its
consistency and precision. This study is an attempt to understand the problems associated with Frequency EM inversion in a practical geological setting.
Using a frequency EM sounding device multiple surveys were undertaken on three geologically different localities. These localities were chosen due to their two layer conductivity contrasts that make up a simple geological configuration. For quality assurance the subsurface layout for the surveys were determined from a mixture of resistivity
profiles and well log measurements. The EM data were subsequently inverted using the EM Inverter program.
The results obtained show a certain lack in capability especially associated with the EM Inverter program. These include an inability to interpret detail and only give a rough estimate of the dimensions. This problem is not unique to the EM Inverter program but can be seen quite universally in the literature. The current capability of the frequency
EM method is well suited as a complimentary device used at the initial stages of a survey. To best make use of the frequency EM method a guide is provided which offers simple suggestions in producing more accurate inversion models. These are mostly associated with an understanding of the area’s stratigraphic and conductive properties.},
  author       = {Letellier, Mattias},
  keyword      = {frequency,electromagnetic,sounding,inversion,GEM-2 frekvens,elektromagnetiska,sondering,GEM-2},
  language     = {eng},
  note         = {Student Paper},
  series       = {Dissertations in Geology at Lund University},
  title        = {A practical assessment of frequency electromagnetic inversion in a near surface geological environment},
  year         = {2012},
}