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Seminare

   

     

    Electromagnetics

    Short Version

Electromagnetic techniques are important for hydrocarbon E&P because they can distinguish between oil and water saturated rock. Because their sensitivity decreases exponentially with depth, they are often applied when other techniques (such as seismics) fail. However, their real strength lies in their complementary use, along with seismic, to either improve the seismic velocity interpretation or to provide additional information such as inferred porosities. In the course we will introduce two techniques: Magnetotellurics (MT) and LOTEM (Long Offset Transient ElectroMagnetics); one uses the natural electromagnetic field and the other uses an artificial source. Both techniques are commercially available.
After reviewing the history of the methods we will define the framework of the techniques in an exploration and production environment. Overviews of data acquisition, data processing and interpretation will lead to system description, survey design and case histories from many places around the world.
Courses can be provided at 3 levels:
· 1 day; for Managers and Supervisors, to provide an overview of technology and its availability
· 3 days; for Practitioners and Interpreters
· 5 days; advanced course for Interpreters and Researchers (with hands-on examples)


      Long Version
       

Electromagnetic techniques are important for hydrocarbon E&P because they can distinguish between oil and water saturated rock. Because their sensitivity decreases exponentially with depth, they are often applied when other techniques (such as seismics) fail. However, their real strength lies in the complementary use, along with seismic, either to improve the seismic velocity interpretation or to provide additional information such as inferred porosities. We will introduce two techniques: Magnetotellurics (MT) and LOTEM (Long Offset Transient ElectroMagnetics). MT uses the Earth’s electromagnetic field and tensorial measurements to obtain information about the resistivity structure. LOTEM uses its own transmitter and magnetic and electric field component measurements, also to obtain information about the resistivity structure. Each technique has an optimum depth range, which depends on the resistivity environment, with some overlap between the methods.

Magnetotellurics was developed in the fifties; today numerous manufacturers offer 24 bit array systems. Marine and environmental systems are emerging. LOTEM was first developed in the former Soviet Union and subsequently several digital systems were developed in the West for R&D. For commercial applications, the first multi-channel system was developed in the late 80s. The physics of MT is based on calculating the ratios between random natural magnetic and electric field components so that the method can use the unknown source field. This ratio is an impedance tensor.It can be transformed to numerous apparent physical parameters to aid the interpretation and also further processed to improve signal-to-noise. In the LOTEM case the source generates a downward diffusing signal which causes a transient signal at the receiver sites. Knowledge of the source and geometry allows the calculating of apparent resistivities from a single field component. Using the electric and magnetic components gives you different sensitivities.

Standard applications: MT is widely used in many parts of the world for a variety of applications. Its major use is for oil exploration in seismically-difficult areas, including karst in east and SE Asia, and for subsalt and subcarbonate exploration in the Mediterranean and Gulf of Mexico. At 'audio' frequencies it is used for mineral exploration at depths beyond the reach of TEM while, at still higher frequencies, it is being applied to a range of environmental problems. Case histories to be shown include applications in petroleum and minerals exploration, and in environmental problems.

Numerous case histories are shown where LOTEM measurements confirm independently other measurements and help getting better resolution in the interpretation. The applications range from coal applications, mapping porosities to sub-basalt exploration and deep crustal studies.

The future of electromagnetic measurements lies clearly in its combination with reflection seismics and getting a better definition of the fluid content. In addition EM results can be used to constrain the interpretation of seismic velocities.
 

      About the instructors:

      Keeva Vozoff started his professional career exploring for porphyry copper and groundwater in the southwestern United States, then went on to apply AEM and introduce IP in Canada. He has worked in industrial and academic R&D with an engineering flavor in several countries. While with Geoscience Inc. of Boston he led a group that introduced MT to Shell and Mobil. In the early 1980's, while Professor of Geophysics at Macquarie University in Sydney (1972-1994) he developed a digital AMT system that produced data of quality comparable with present systems. With Kurt Strack and Horst Rueter, Keeva set up HarbourDom GmbH in Cologne and operated an Australian branch from 1992 - 1999. Early in his career (1954) he produced the first ever computer inversion programs in geophysics, going on to introduce 2D and 3D computer modelling and inversion in electrical geophysics.

      Through PASSTECH Pty Limited (Snowy Mountains Engineering Corp. and V&A Geoscience) in Sydney, Keeva is now developing new applications of geophysics to major environmental problems. He is a Fellow of the Australian Academy of Technological Sciences & Engineering, was awarded a Humboldt Prize (1993), Honorary Member of the Society of Exploration Geophysicists and the Australian Society of Exploration Geophysicists, an Honorary Life Fellow of the Association of Exploration Geophysicists (India). He is also a member of AAPG, EAGE and Australian Institute of Geoscientists.

      Kurt-M. Strack is president of KMS Technologies- KJT Enterprises Inc. specializing on consulting in borehole geophysics, electromagnetics and Advanced Technologies. He was Chief Scientist for Baker Atlas in Houston after being Resistivity Product Line manager and Advanced Scientific Research Department manager. There he supported Logging Tool Development and Interpretation through Modeling yielding numerous new logging tools. Prior to that Kurt pioneered LOTEM development and research in Germany, Australia and the USA. Kurt received a Ph.D. from the University of Cologne, Germany and a M.Sc. from Colorado School of Mines. He worked over the past 20 years as a geophysical consultant and as university researcher and teacher as R & D manager in the geothermal and logging industry. Kurt has published over 100 publications, 1 textbook and holds several patents. He also received a Fulbright scholarship and numerous international grant/awards throughout his career. His main interest is integrated geophysics, inversion, and technology transfer and project development. He is a member of SPWLA, AAPG, ASEG, DGG, BDG, SPE, SEG and EAGE. He was 1998-1999 SPE distinguished lecturer on Through Casing Resistivity. He was co-chairman of 3 SEG Summer research workshops on: Integration of Seismic Data with Well Logs (1995), NMR Imaging of Reservoir Attributes (1998), and Effective Technology Transfer of Model-based GeoInversion Techniques (1999). He is also co-chairman of the SPWLA topical conference on Borehole Anisotropy (April 2000).

         


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