Download PhD Project - School of GeoSciences

PhD Project
Title: Application of electromagnetic methods for hydrocarbon exploration and
monitoring CO2 sequestration
Supervisors: Prof. Anton Ziolkowski & Dr. David Wright, University of Edinburgh
Background
For decades geophysical exploration for hydrocarbons has been dominated by seismic methods, which provide
excellent definition of sub-surface geological structure, but are not good at defining the fluid content of the
rocks. In the past few years new developments in controlled-source electromagnetic (CSEM) methods have
enabled geoscientists to identify the nature of the fluids in subsurface rocks by determining the resistivity of the
rocks. Normally the rocks are saturated with salt water, which is ionised and is therefore electrically
conductive. When hydrocarbons replace the salt water in the pore space, the rock becomes more resistive. The
resistivity can increase by two or three orders of magnitude, depending on the porosity of the rock and the ratio
of salt water to hydrocarbons in the pore space. Electromagnetic methods therefore complement seismic
methods for hydrocarbon exploration, providing vital information that reduces the risk of drilling ‘dry’ wells.
When carbon dioxide is injected into saline aquifers, or into reservoirs that previously contained hydrocarbons,
it behaves electrically just like hydrocarbon gas, for example methane. The effect on the seismic response is a
dramatic decrease in acoustic impedance with the early injection of a small amount of gas, as shown in the
figure. Thereafter the seismic response is essentially unchanged. The resistivity of the reservoir rock is affected
only slightly by early CO2 injection, but as the quantity of CO2 increases, the rock resistivity increases
exponentially, as shown in the figure. Electromagnetic methods therefore have the potential to monitor the
quantity of CO2 stored in a reservoir.
PGS, the sponsor of this PhD project, is a geophysical exploration company with marine operations all over the
world. It has pioneered transient electromagnetic exploration both onshore and offshore and is developing a
number of existing methods including towed streamer marine EM exploration and fibre optic seismic and EM
monitoring of existing fields. PGS recognizes the potential of this technology for hydrocarbon exploration,
monitoring hydrocarbon production, and monitoring CO2 sequestration.
This project will focus on the acquisition and processing of CSEM data to obtain maximum resolution of
resistive targets in the depth range of hundreds of metres to a few kilometres.
Methods and Investigations
Understanding the propagation of the electromagnetic signal will develop through a study of the theory,
computer modelling, and analysis of transient electromagnetic data sets provided by PGS. One aspect of this
project, founded on internal PGS documents and PGS patent applications, is to increase the signal-to-noise ratio
by reducing the noise. Most of the noise is not random: it is organized and may be removed if the method of its
organization can be understood and exploited. Noise that has already been identified and falls into this category
includes the marine air wave, magnetotelluric noise, and induction noise. Ways of enhancing the signal should
also be investigated, including different source-receiver geometries and use of additional electromagnetic
components at the source and receiver. The goal is to obtain data that would enable better resolution of the
internal properties of the resistive subsurface to be derived, including anisotropy and finer resolution of
individual resistive or conductive bodies.
Training
Training will be provided in time series analysis and processing of EM exploration data as well as
computational modelling of EM fields. This will include programming in C, C++, FORTRAN and Matlab.
Training in presentation skills will be available as well as the opportunity to present results at international
geophysical conferences.
Industry Links
PGS has strong links with the School of GeoSciences through a strategic alliance. PGS has its electromagnetics
research base in Edinburgh and the project offers the potential to spend time carrying out research there.
Qualifications required:
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First or upper-second class Bachelor degree in Applied Mathematics, Geophysics, Physics or related
field
Experience, skills and knowledge required:
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Good knowledge of theoretical geophysical principles
A thorough understanding of signal processing
Experience of numerical methods
Good computer skills
Good communication skills
Good skills in writing technical English
Related Literature
Constable, S., and Srnka, L., 2007 An introduction to marine controlled-source electromagnetic methods for
hydrocarbon exploration, Geophysics, 72, no2, WA3-WA12.
Wright, D., Ziolkowski, A., and Hobbs, B., 2002, Hydrocarbon detection and monitoring with a multichannel
transient electromagnetic (MTEM) survey, The Leading Edge, 21, 852-864.
Ziolkowski, A., Hobbs, B., and Wright, D., 2007, Multitransient electromagnetic demonstration survey in
France: Geophysics, 72, no 4, F197-F209.
Ziolkowski, A., Parr, R., Wright, D., Nockles, V., and Limond, C. 2009, Multi-transient EM repeatability
experiment over North Sea Harding field: Expanded Abstracts, 79 th SEG Annual Meeting, EM3.4, p 754758.
Mattsson, J.M., Lund, L.L., Lima, J.L., Engelmark, F.E., and McKay, A.M., 2010, Case study – a towed EM test
at the Peon discovery in the North Sea, Extended Abstracts, 72 nd EAGE meeting, C019.