|
| |
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)
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).
|
