Douglas (Doug) Oldenburg's forty-year research career has focused upon the development of inversion methodologies and their application to solving applied problems. He, with students and colleagues at the University of British Columbia Geophysical Inversion Facility (UBC-GIF), have developed forward modelling and inversion algorithms for seismic, gravity, magnetic and electromagnetic data. The inversion techniques and software are widely used in resource exploration problems. In recognition for his work building collaborative interactions between industry and academia, he was awarded the NSERC Leo Derikx and the AMEBC Special Tribute awards as well as the J.Tuzo Wilson medal. In 2011, Doug was the SEG Distinguished Lecturer; his presentation was entitled Imaging the Earth's near surface: The why and how of applied geophysics for the 21st century.
Doug’s current research activities include: inversion of EM data and their application to a wide range of problems, development of practical methodologies for combined inversion of geophysical and geological data, development of software for unexploded ordnance discrimination, and the use of self-potentials for dam safety investigations. He is passionate about the development of open-source educational resources for applied geophysics and increasing the visibility and benefits of using quantitative geophysics to help solve geoscience problems (http://geosci.xyz). These efforts will form the cornerstone of the SEG 2017 DISC.
Doug received his BSc Honors degree in Physics in 1967, and his MSc in geophysics in 1969, from University of Alberta in Edmonton. He completed his PhD in 1974 at Scripps Institution of Oceanography (UCSD) in earth sciences. After a three-year postdoc in Alberta, he joined the Geophysics and Astronomy department at University of British Columbia. He remains at UBC where he is currently a Professor, Director of UBC-GIF and holder of the TeckCominco Senior Keevil Chair in Mineral Exploration. He is an honorary member of the CSEG and a Fellow of Royal Society of Canada. Hr was awarded SEG Honorary Membership in 2001.
Geophysical Electromagnetics: Fundamentals and Applications
Electromagnetics has applications in oil and gas exploration and production, mineral exploration, groundwater exploration and monitoring, and geotechnical and environmental industries. Although it has widespread applications as a geophysical technique, it is not generally understood by the geoscience community. As a result it is underutilized, and in some cases, misused, as a technology.
The goal of this course is to provide a fundamental understanding about EM geophysics so that practitioners can decide if an EM technique can help solve their problem, select which type of survey to employ, and set realistic expectations for what information can be gleaned. Case histories, spanning applications from many areas in the geosciences, are used as an underlying framework to bind the material together. For more information, please see our online resources at http://disc2017.geosci.xyz.
Case histories discussed pertain to problems in resource exploration, including oil and gas, minerals, water, environmental, and geotechnical areas and are contributed by experts worldwide (http://disc2017.geosci.xyz/). These include:
- resource detection (eg. methane hydrates) or de-risking (eg. offshore-hydrocarbons),
- imaging SAGD steam chambers or monitoring hydraulic fracturing,
- mineral exploration (on land, on the ocean floor sea floor massive sulfides),
- water issues (eg. monitoring salt water intrusion, imaging aquifers)
- imaging geothermal systems,
- detecting and discriminating unexploded ordnance,
- geotechnical characterization, including slope stability,
- and more (see http://em.geosci.xyz/content/case_histories/index.html for a growing list).
We use these applications as motivation for investigating fundamentals of electromagnetics. We successively look at applications that make use ofː
- Steady state fields (e.g., DC resistivity, induced polarization)
- Frequency domain EM (e.g., marine CSEM, airborne surveys)
- Time domain EM (e.g., airborne, ground, borehole surveys )
- Natural source EM (e.g., Magnetotellurics, Z-Axis Tipper/ZTEM)
The energy sources for these surveys can be man-made or natural. Man-made sources include inductive transmitters (loops of wire carrying a current) or galvanic sources where current is injected into the ground. The natural energy sources promote MT (magnetotellurics), which is important for characterizing deep conductivity structures for geothermal energy, and ZTEM which has proven to be valuable in geologic mapping and mineral exploration. The various surveys can be carried out in the air using helicopters or airplanes, on the earth’s surface, or underground; the geoscientific question to be addressed determines which survey is selected. Case histories and survey types presented will be tailored to each location at which the DISC is presented, and chosen based on the local problems of general interest.
Each case history is presented in a seven-step process that begins with the description of the geologic or geophysical problem to be solved and ends with the impact of the EM geophysical survey to help solve the problem. At points in the middle, we investigate the details of the particular EM survey, some fundamentals of electromagnetic induction, and techniques for processing/inverting the data. The ability to move seamlessly between these different levels of information, so that relevant questions or concepts can be addressed, is facilitated by new open-source numerical software, interactive simulations, and the “textbook” resource http://em.geosci.xyz. Although we work continually with Maxwell’s electromagnetic equations, the presentations are mathematically “light” and the learning aspect is facilitated by the use of open-source, interactive numerical software and visual aides.
The site http://disc2017.geosci.xyz contains further details on the course, its goals, links to the open-source resources that will be used, and ways to get connected!
Fall 2011 SEG Distinguished Lecturer
Imaging the Earth's near surface: The why and how of applied geophysics for the 21st century
The top few kilometers of the Earth's surface are of extreme importance to our society. This near-surface region houses mineral and hydrocarbon wealth that are crucial for industrialized development, contains water needed for life, and is an environment with which we must interact to build our infrastructure. Substantial insight about the structure and composition of this region can be gleaned by determining its physical properties. Density, magnetic susceptibility, electrical conductivity, and elastic parameters can be critically diagnostic and data from appropriate geophysical surveys can be inverted to generate 3D distributions of these.
This talk will look at problems in which applied geophysics has made a major contribution and review the essential elements of the inverse problem needed to map survey data into 3D images of physical properties. Characterization of Earth materials generally requires knowledge of multiple physical properties, and this talk will show examples of this for mineral exploration and unexploded ordnance discrimination. The emphasis is on surveys sensitive to electrical conductivity. It is only recently that we have developed the capability to invert electromagnetic survey data in 3D and a plethora of applications now exists for mineral and hydrocarbon exploration, environmental and geotechnical problems. The talk concludes with a vision for the future and a discussion of the skill set required by a new generation of quantitative geophysicists who want to tackle important practical problems so that we can live sustainably on this planet.
The top few kilometers of the Earth's surface are of extreme importance to our society. This near-surface region houses mineral and hydrocarbon wealth that are crucial for industrialized development, water needed for life, and it is an environment with which we must interact to build our infrastructure. To exploit these resources, and also to mitigate problems that arise from their exploitation, we need to image the earth's interior without direct sampling. Substantial insight about the structure and composition about the near-surface can be gleaned by determining its physical properties. Density, magnetic susceptibility, electrical conductivity and elastic parameters can be critically diagnostic, and data from appropriate geophysical surveys can be inverted to generate 3D distributions of these properties. Since each structure or object in the ground is defined by its own suite of physical properties, it follows that the most reliable information can be acquired by carrying out inversions from different types of geophysical surveys and examining the cumulative set of recovered physical properties.
The goal of inverting all types of geophysical data is laudatory but the computational ease of inverting different surveys varies with the amount of data and the intrinsic resolution of the survey. Gravity and magnetic surveys generate simple data sets that arise from a single source and hence full 3D inversions have been available for nearly two decades. DC resistivity and IP (induced polarization) data are more complicated because they involve a number of transmitters, but these too are regularly inverted. It is only recently, however, that electromagnetic data in frequency and time, using multiple transmitters and multiple component receivers, can be inverted on computational grids that are fine enough to capture the relevant geology. For this reason, and because electrical conductivity is often a diagnostic physical property used for geologic interpretation, I concentrate upon methods to recover electrical conductivity in my talk.
In a typical electromagnetic experiment a time-varying current in the transmitter induces currents in the earth which diffuse away from the transmitter. The data consist of electric and/or magnetic fields measured in time. Inverting these fields for an arbitrary waveform is analogous to carrying out full waveform inversion of seismic data. I illustrate some of the basic principles of the EM technique, and apply them to a mineral exploration problem where the location of a massive sulfide is sought. The field site is ideal because multiple geophysical survey methods have been performed over the site and there is substantial well information to provide ground truth with which to verify our inversion. The sulfide body is dense, magnetic, conductive and chargeable. Locating regions of high values of these physical properties indicates a likely location to spot a drill hole.
Electrical conductivity is diagnostic for a large range of problems that are characterized by different physical dimensions. For example, on the small scale we want to find a UXO that has dimensions of tens of centimeters. On the larger scale, we want to detect a deeply buried hydrocarbon deposit in a marine environment or detect a large mineral deposit. Fortunately, electromagnetic surveys are scalable. Small low-powered systems are appropriate for small items while large high-powered systems are required to look deeper. For some investigations, however, the energy that can be generated through a man-made source becomes inadequate, and we must appeal to natural sources. Of particular interest is the ZTEM (Z-Axis Tipper EM) survey which is a modern version of the AFMAG survey used in 1950s. In the ZTEM technique, measurements of the vertical component of the magnetic field are acquired in an airborne survey and transfer functions with respect to the magnetic fields at a base station are computed. Data, which are obtained over a range of frequencies, can be inverted to yield a 3D conductivity structure. The sensitivity of the data can extend to depths of a kilometer or more and hence this survey has considerable potential for resource exploration and geologic mapping.
Because this talk will be presented to SEG and affiliated societies, as well as to student chapters, details of the talk will change according to the audience. The goal for the society meetings is to illustrate current capabilities for 3D EM inversions and to stimulate the desire to acquire enough data, of sufficiently high quality, so that good results from an inversion can be obtained. An additional goal for the student chapters is to illustrate that real-world problems are solved within multidisciplinary teams. In order to carrying out his or her job effectively, the geophysicist needs high level computational skills, as well as a strong background in math, physics, and geology.
A recording of the lecture is available.
- Personal Home Page
- Oldenberg, D. and Y. Li (1994) Inversion of induced polarization data, GEOPHYSICS 59(9):1327.