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FeedsHome: Issue 7 2009 › Lead Story › What lies beneath
What lies beneath
01/07/2009 | Channel: Exploration & Production, Equipment, Technology
Exploration efficiency can be vastly improved if we understand what lies beneath the surface, as Leon Walker and Chris Berridge of Global Marine Systems Ltd. explain
As existing reserves of oil and gas become increasingly scarce, and alternative forms of energy are still a nascent market, finding and estimating oil and gas reserves in the most cost-effective manner is a priority. Ultimately, to know if there is oil or gas down there, one has to drill, but a method that can detect subsurface hydrocarbons from the surface effectively and efficiently will become profitable and reduce potentially environmentally-hostile drilling. Quite simply, any success in the oil and gas exploration industry relies on finding and estimating reserves before any exploration takes place.
For years, seismic surveys led the way in the offshore oil and gas business. Known as reflection seismology, seismic surveys have, for some time, been the most popular way in which to map the subsurface structure of rock formations, and in turn to translate this data to find potential hydrocarbon reserves. The technology, which can be used to explore hydrocarbon reserves on land, under the sea and in the interface between the sea and land, has developed dramatically over the last 20 years, but essentially involves the same basic principles.
Sound energy waves are sent into the earth, where the different layers reflect the energy back. These reflected signals are stored in various data recorders and can be analysed to give information about the various layers of the earth, and any possible natural resources that may be present.
However, as resources become increasingly difficult to find and the industry develops at a rapid pace, new techniques for reading information stored in the earth have been in continuous development. Even before seismic techniques became widespread, scientists had already started to use electromagnetic methods.
At the most basic level, the passage of electrical energy through any material is affected by its resistivity. In the earth, sedimentary rocks have pore space which is filled with either saltwater or hydrocarbons, the latter of which are relatively poor conductors of electricity. Electromagnetic (EM) surveys therefore measure the response of the earth to an electric or magnetic input, and the analysis of that response gives the resistivity structure of the earth from which the hydrocarbon content may be inferred. This method is becoming increasingly popular with exploration companies, and is already yielding successful results.
Case study
Petroleum Geo-Services (PGS) and Global Marine Energy, a division of marine engineering company Global Marine Systems Ltd., recently completed three successful deployments of its innovative Multi-Transient ElectroMagnetics (MTEM) survey technique to detect the presence of hydrocarbons beneath the ocean floor, helping to pinpoint the location of oil and gas deposits. The success of these projects proves the viability and value of the technique at a time when reserves are becoming increasingly expensive to access. Since, the system has been deployed offshore to improve drilling success rates while reducing the environmental impact of drilling unsuccessful and expensive dry holes.
Traditionally, EM methods have been low resolution and unable to see deep enough. Hydrocarbon reserves are often as deep as five kilometres below the surface or seabed, and MTEM applies the methodology of seismic to electromagnetic surveying to overcome this challenge. The fundamentals of the method, which produces resistivity profiles over potential reservoirs, were conceived and developed during the 1990s by a consortium of universities and companies with a European Union grant. The project was led by the world-renowned seismic expert Professor Anton Ziolkowski, of the University of Edinburgh, who worked with Dr Bruce Hobbs, a leading expert in EM and also a senior lecturer at the University of Edinburgh. It was the unique combination of seismic and EM minds that led to the development of MTEM.
During the mid-1990s Ziolkowski and his team designed and conducted surveys over a gas storage reservoir in the Paris basin that had more in common with 2D seismic than with standard EM methods. The equipment was laid out in a straight line configuration, with the sources and receivers arranged to test all types of electromagnetic inputs and outputs, such as cross line electric field inputs into horizontal magnetic field receivers. After an initial hiccup with the data analysis thanks to unsynchronised receiver boxes, the data produced the expected results and the theory was proven correct. In late 2001 the team applied for a patent and the MTEM method was licensed into the company MTEM Limited which began trading in 2004. Over the course of two and half years the company successfully executed onshore surveys in many parts of the world, and the first marine survey in the North Sea. The company was sold to Norwegian geophysical company, PGS, in June 2007.
One of the benefits of the MTEM method is that it can be used both onshore and in any depth of water. More traditional methods suffer from airborne noise, which limits their application to very deep water where the source is placed near the bottom and this noise absorbed by the water. MTEM has been successfully used on reservoirs at two and a half kilometres deep, and R&D is underway to develop a bigger source in order to reach five kilometres in depth. The role of specialised ships in a successful MTEM survey is central, as the method relies on two vessels – a ‘master’ receiver vessel and ‘slave’ source vessel to transmit and record the signals. Global Marine Systems Ltd. has worked in close conjunction with MTEM to develop a strict set of operational procedures for deployment of the technique offshore. First a length of receiver cable, with up to 30 receivers embedded along it at regular intervals, is carefully deployed by the master vessel. The slave vessel then deploys a cable with specially designed source electrodes allowing a current of up to 800A (producing good signal to noise for deep or thin targets) that send a signal down through the seabed. The reflected transients are sampled by the receiver cable and the data recorded onboard the master ship. The source cable is then lifted and moved by 200 metres and the process is repeated until subsea oil or gas reservoirs are located. The final stage of the process involves sending the data ashore for processing and detailed study.
The first commercial deployment of MTEM took place in the North Sea in 2007, using Global Marine’s cable ship ‘CS Sovereign’ which laid receiver cable on the seafloor at depths of 80-100 metres. The cables accurately collected recordings, which were transmitted to the Sovereign’s onboard laboratories for evaluation. During 2009 two further offshore MTEM projects have been successfully completed, both using specialist cable-laying and receiver ships provided by Global Marine Energy. By demonstrating the effectiveness of the technique, PGS and Global Marine are opening up new possibilities for the exploration of oil and gas deposits around the globe in a way that is more accurate, cost-effective, and environmentally viable than ever before. MTEM, and similar systems throughout the industry are certain to have a positive effect on the future of oil and gas exploration.
Global Marine Systems Ltd
Leon Walker, president, PGS EM and Chris Berridge, project manager, work at Global Marine Systems Ltd., one of the world’s leading marine technology and engineering company’s. Specialising in submarine telecom cables, the company serves the oil and gas, defence, telecoms and renewables industries.
For further information please visit: www.globalmarinesystems.com
For years, seismic surveys led the way in the offshore oil and gas business. Known as reflection seismology, seismic surveys have, for some time, been the most popular way in which to map the subsurface structure of rock formations, and in turn to translate this data to find potential hydrocarbon reserves. The technology, which can be used to explore hydrocarbon reserves on land, under the sea and in the interface between the sea and land, has developed dramatically over the last 20 years, but essentially involves the same basic principles.
Sound energy waves are sent into the earth, where the different layers reflect the energy back. These reflected signals are stored in various data recorders and can be analysed to give information about the various layers of the earth, and any possible natural resources that may be present.
However, as resources become increasingly difficult to find and the industry develops at a rapid pace, new techniques for reading information stored in the earth have been in continuous development. Even before seismic techniques became widespread, scientists had already started to use electromagnetic methods.
At the most basic level, the passage of electrical energy through any material is affected by its resistivity. In the earth, sedimentary rocks have pore space which is filled with either saltwater or hydrocarbons, the latter of which are relatively poor conductors of electricity. Electromagnetic (EM) surveys therefore measure the response of the earth to an electric or magnetic input, and the analysis of that response gives the resistivity structure of the earth from which the hydrocarbon content may be inferred. This method is becoming increasingly popular with exploration companies, and is already yielding successful results.
Case study
Petroleum Geo-Services (PGS) and Global Marine Energy, a division of marine engineering company Global Marine Systems Ltd., recently completed three successful deployments of its innovative Multi-Transient ElectroMagnetics (MTEM) survey technique to detect the presence of hydrocarbons beneath the ocean floor, helping to pinpoint the location of oil and gas deposits. The success of these projects proves the viability and value of the technique at a time when reserves are becoming increasingly expensive to access. Since, the system has been deployed offshore to improve drilling success rates while reducing the environmental impact of drilling unsuccessful and expensive dry holes.
Traditionally, EM methods have been low resolution and unable to see deep enough. Hydrocarbon reserves are often as deep as five kilometres below the surface or seabed, and MTEM applies the methodology of seismic to electromagnetic surveying to overcome this challenge. The fundamentals of the method, which produces resistivity profiles over potential reservoirs, were conceived and developed during the 1990s by a consortium of universities and companies with a European Union grant. The project was led by the world-renowned seismic expert Professor Anton Ziolkowski, of the University of Edinburgh, who worked with Dr Bruce Hobbs, a leading expert in EM and also a senior lecturer at the University of Edinburgh. It was the unique combination of seismic and EM minds that led to the development of MTEM.
During the mid-1990s Ziolkowski and his team designed and conducted surveys over a gas storage reservoir in the Paris basin that had more in common with 2D seismic than with standard EM methods. The equipment was laid out in a straight line configuration, with the sources and receivers arranged to test all types of electromagnetic inputs and outputs, such as cross line electric field inputs into horizontal magnetic field receivers. After an initial hiccup with the data analysis thanks to unsynchronised receiver boxes, the data produced the expected results and the theory was proven correct. In late 2001 the team applied for a patent and the MTEM method was licensed into the company MTEM Limited which began trading in 2004. Over the course of two and half years the company successfully executed onshore surveys in many parts of the world, and the first marine survey in the North Sea. The company was sold to Norwegian geophysical company, PGS, in June 2007.
One of the benefits of the MTEM method is that it can be used both onshore and in any depth of water. More traditional methods suffer from airborne noise, which limits their application to very deep water where the source is placed near the bottom and this noise absorbed by the water. MTEM has been successfully used on reservoirs at two and a half kilometres deep, and R&D is underway to develop a bigger source in order to reach five kilometres in depth. The role of specialised ships in a successful MTEM survey is central, as the method relies on two vessels – a ‘master’ receiver vessel and ‘slave’ source vessel to transmit and record the signals. Global Marine Systems Ltd. has worked in close conjunction with MTEM to develop a strict set of operational procedures for deployment of the technique offshore. First a length of receiver cable, with up to 30 receivers embedded along it at regular intervals, is carefully deployed by the master vessel. The slave vessel then deploys a cable with specially designed source electrodes allowing a current of up to 800A (producing good signal to noise for deep or thin targets) that send a signal down through the seabed. The reflected transients are sampled by the receiver cable and the data recorded onboard the master ship. The source cable is then lifted and moved by 200 metres and the process is repeated until subsea oil or gas reservoirs are located. The final stage of the process involves sending the data ashore for processing and detailed study.
The first commercial deployment of MTEM took place in the North Sea in 2007, using Global Marine’s cable ship ‘CS Sovereign’ which laid receiver cable on the seafloor at depths of 80-100 metres. The cables accurately collected recordings, which were transmitted to the Sovereign’s onboard laboratories for evaluation. During 2009 two further offshore MTEM projects have been successfully completed, both using specialist cable-laying and receiver ships provided by Global Marine Energy. By demonstrating the effectiveness of the technique, PGS and Global Marine are opening up new possibilities for the exploration of oil and gas deposits around the globe in a way that is more accurate, cost-effective, and environmentally viable than ever before. MTEM, and similar systems throughout the industry are certain to have a positive effect on the future of oil and gas exploration.
Global Marine Systems Ltd
Leon Walker, president, PGS EM and Chris Berridge, project manager, work at Global Marine Systems Ltd., one of the world’s leading marine technology and engineering company’s. Specialising in submarine telecom cables, the company serves the oil and gas, defence, telecoms and renewables industries.
For further information please visit: www.globalmarinesystems.com
