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The University of Southampton
Ocean and Earth Science, National Oceanography Centre Southampton

Evaluating sub-sea bed hydrocarbon reservoirs by marine electromagnetic geophysical surveying

Accurately surveying the rocks beneath the seabed can tell us if they hold oil or gas reserves. Anomalies in electrical resistivity, which may suggest the presence of hydrocarbons, can be located and measured using controlled source electromagnetic (CSEM) techniques.

The University of Southampton played a pivotal role in the first full-scale marine CSEM survey over a potential oilfield in late 2000. This survey and subsequent work spawned one of the greatest technological advances in this field since the development of 3D seismic techniques with over 600 commercial CSEM surveys completed by end of 2012. The University continues with this work through consultancy and industry-funded research projects.

Research challenge

In the past, discovering oil and gas reserves was easy. In the 19th and early 20th centuries, oil seeping from the ground in countries such as the USA gave geologists a good idea of where to sink their wells. Now those areas have been largely exhausted, it is far more difficult to find viable oil and gas fields which can produce enough supplies to satisfy world demand; oil companies are spending billions of pounds searching for potential alternatives. Specialist explorationists already use several sophisticated techniques to locate hydrocarbons beneath the ground or under the sea bed but rising costs make it more important than ever to be as accurate as possible.

Professor Martin Sinha, and his colleagues at the University of Southampton Dr Lucy MacGregor and Jenny Rust, came up with the idea of using controlled source electromagnetic surveying (CSEM) as an extra tool for oil company explorationists. Offshore Field trials from 2000 onwards using research ships proved the validity of the approach.

Context

Finding new sources of oil and gas is a high risk and expensive business. Many of the world’s easily exploitable reserves are running dry, forcing companies to explore different regions of the world, and to look for more subtle petroleum traps. However, as drilling a new rig in deep water can cost more than £150 million, geologists need as much information as they can about the likelihood of success before starting work. Exploration techniques that substantially reduce risk, and boost success rates for drilling are particularly important.

Our solution

Electromagnetic surveying can determine directly whether a potential hydrocarbon reservoir identified in seismic data has high or low electrical resistivity. This is important, as the resistivity of sedimentary rocks whose pore spaces are saturated with saline, aqueous fluids is low – just a few times that of seawater – while the resistivity of those whose pore spaces are predominantly filled with oil or natural gas is greatly increased.

Southampton academics have led the world in CSEM for more than a decade. Their contributions have included the development of survey geometries that provide a diagnostic indicator of hydrocarbons’ presence; a deep-towed transmitter strong enough to overcome the signal attenuation caused by seawater; and receivers of unprecedented sensitivity.

The first full-scale demonstration of this technology took place in late 2000. Professor Martin Sinha was the scientific lead of a project conducted with Norwegian oil and gas company Statoil and UCSD’s Scripps Institution of Oceanography. Southampton provided the bulk of the equipment and crucial elements of the survey design for the study, which was carried out on the RS Charles Darwin, offshore Angola.

Our impact

The development of CSEM has given birth to an entirely new and commercially viable industry which flourishes today.

Two spinout companies were formed in the wake of the first large-scale demonstration of the technology. The first of them, OHM, went on to acquire Rock Solid Images and is now known by that name. It currently employs 45 staff and provides services to clients including major oil companies and small independents. The second, EMGS, was formed in 2002 as a spin out from Statoil. It employs more than 250 people and declared annual revenues of US$172m, in 2011.

In 2008, the Geological Society of London presented Professor Sinha with the William Smith Medal, which is awarded annually for outstanding research in applied or economic geology. In 2011, Dr MacGregor was appointed the Society of Exploration Geophysicists’ Honorary Lecturer for Europe.

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DASI being deployed for surveying
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