Undergraduate Course: Controlled Source Electro-Magnetic (CSEM) Methods (EASC11003)
|School||School of Geosciences
||College||College of Science and Engineering
|Credit level (Normal year taken)||SCQF Level 11 (Year 4 Undergraduate)
||Availability||Available to all students
|Summary||This course teaches the theory and application of controlled source electromagnetic (CSEM) exploration for the determination of resistivity variations in the Earth. Resistivity variations are linked to the fluid content of the rocks; salt water, or brine, is electrically conductive, while fresh water and hydrocarbons are more resistive. The course is based on practical industry experience of the application of CSEM methods to petroleum exploration onshore and offshore.
Ohm's law and resistivity; resistivity of rocks; resistivity anisotropy; effect of hydrocarbon saturation on resistivity; Archie's law; example well logs; seismic and EM propagation compared; extraction of resistivities from CSEM data: the problem of inversion.
Overview of CSEM methods. Sources; receivers; source-receiver configurations; source time functions; land CSEM; marine CSEM; sources of EM noise.
Maxwell's equations; constitutive relations; electromagnetic wave equations; transformation of wave equations to the frequency domain; plane wave solutions of the electromagnetic wave equations; skin depth; electromagnetic propagation in air and free space; electromagnetic propagation in conducting media: diffusion equation; boundary conditions; introduction of sources and Helmholtz decomposition; point current source and current dipole source.
The convolutional model in CSEM; source control and the source time function; pseudo-random binary sequence (PRBS); response to a transient input signal; square-wave function; signature deconvolution; frequency response functions.
Marine CSEM with continuous source signal and receiver nodes. Electrical conductivity of sea water; effect of water layer on marine CSEM data; the deep-towed EM dipole source; EM ocean-bottom receiver node; inline and broadside responses; acquisition geometries; positioning; timing, clocks and clock drift; source normalization; determination of receiver rotation angle; source tilt and yaw; ExxonMobil example.
Land CSEM with a transient source signal: the MTEM method. Data acquisition; data processing: deconvolution; impulse response and time to peak; impulse response in dimensionless time; frequency domain response; variation of response with time and offset; bandwidth of recording; signal-to-noise ratio of MTEM data; maximising signal; attenuation of cultural noise; apparent resistivities from travel-time data; data example from underground gas storage site.
Marine CSEM with a transient source signal. Data acquisition using ocean-bottom cable (OBC); optimisation of source signal parameters; marine MTEM data; spatially-correlated noise removal; example of marine time-lapse MTEM data over North Sea Harding field; towed streamer marine transient CSEM data; combined marine seismic and EM data acquisition.
Forward modelling of CSEM data. Electric dipole source in a horizontally-stratified Earth; electric dipole response in a three-dimensional Earth.
Recovery of resistivities from CSEM data. Inversion as repeated forward modelling; 1-D inversion of 1-D data; 1-D inversion of 3-D data; 3-D inversion; quantification of misfit: data and model weighting; the starting model: incorporation of information from seismic and well data; resistivities from seismic velocities: example from the Harding Field; implications for survey planning.
Information for Visiting Students
|High Demand Course?
Course Delivery Information
|Not being delivered|
On completion of this course, the student will be able to:
- Appreciation of the value of knowledge of subsurface resistivity variations for exploration purposes.
- Appreciation of electromagnetic diffusive propagation and wave propagation characteristics in conducting and non-conducting media.
- Appreciation of the effect of conductivity variations on CSEM data.
- Familiarity with different industry approaches to the acquisition, processing and interpretation of CSEM data.
|Introduction to Electrodynamics by David J. Griffiths, Pearson.|
Course notes are provided online.
|Graduate Attributes and Skills
|Keywords||CSEM,Controlled Source Electro Magnetic-(CSEM) Methods
|Course organiser||Prof Anton Ziolkowski
Tel: (0131 6)50 8511
|Course secretary||Miss Sarah Thomas
Tel: (0131 6)50 8510