Special Report: POINT OF VIEW: New SEG chief keeps eye on nonseismic advances

Nov. 3, 2008
Moving new seismic methods from theory to practice can require attention to progress in separate but related scientific and engineering disciplines, says the incoming president of the Society of Exploration Geophysicists.

Moving new seismic methods from theory to practice can require attention to progress in separate but related scientific and engineering disciplines, says the incoming president of the Society of Exploration Geophysicists.

“A lot of time it takes experience with other data sets” to bring a new geophysical method into commercial application in the field, says Larry Lines, professor of geophysics at the University of Calgary.

The most innovative geophysical techniques often can take a decade to implement, notes Lines, who becomes president at SEG’s annual meeting in Las Vegas this week.

“Sometimes this involves the implementation of methods in a simple, robust manner,” he explains. “Sometimes there are issues of cost.”

In simplifying new techniques to the level required by everyday practice, “The key is to be aware of advances in other areas,” such as electronics, computing, other areas of science.

It was progress in computing technology, for example, that made possible the most important advance Lines has seen in his career: the widespread use of 3D seismic methods.

Within that category of practice there have been important strides in acquisition, processing (especially 3D prestack depth migration), and interpretation, with the advent of seismic workstations. (Prestack depth migration moves seismic reflections to their correct locations in space in areas where subsurface sound velocities undergo unusually rapid changes. Because the processing occurs before a summing of reflection data known as stack, the step requires considerable computing power.)

“At the beginning of my career in the 1970s, these methods were in their infancy, while today 3D seismic surveys are the norm,” Lines says. “These advances came about when we realized the limitations of conventional methods in oil and gas exploration.”

Advances in computer technology made 3D imaging feasible, he notes, adding, “It is instructive for us to keep abreast of advancing technologies to obviate our restrictive methods of the past.”

Improved simulation

With 17 years of experience with a major oil company and 15 years in academia, Lines has a broad view of past and current progress in seismic and other geophysical methods.

“In terms of oil and gas production,” he says, “I think that the most important area is the application of reservoir geophysics to reservoir engineering.”

Techniques such as time-lapse (4D) seismology and the use of rock physics to estimate significant parameters in reservoir simulation have become standard but ever-improving enhancements to oil-field decision-making.

“The improved reservoir simulations and matching of production history should allow us to understand the scheduling of infill drilling and enhanced oil recovery processes,” Lines says.

Inevitably, progress in some areas seems to have stalled.

“I have always wondered why the vector borehole gravimeter was not promoted or utilized more widely for finding density anomalies due to natural gas deposits,” Lines says.

Unlike the traditional instrument, the vector borehole gravimeter doesn’t assume only an anomalous vertical gravity field component and thus can identify density variations between masses positioned laterally in the subsurface.

“Perhaps this is a question of well spacing or the fact that people feel that seismic methods are adequate,” Lines says of the limited use of the vector gravimeter.

Promising areas

Asked about promising areas of geophysical progress, the new SEG president points to:

Elastic wave description of the earth through multicomponent recording.

Multicomponent technology allows geophones to record reflections of sonically induced elastic waves in which particle motion is not only parallel to the direction of travel (compressional waves) but also perpendicular to the direction of travel (shear waves). Interpretation based on a combination of compressional (P) and shear (S) wave data can provide a fuller picture of the wave’s movement through the subsurface than is available from traditional work based on P-wave data alone.

Multicomponent recording has improved through the application of microelectromechanical system (MEMS) technology to accelerometers, which enables geophones to record a broader spectrum of sonic frequencies than was available from earlier systems, Lines says. Greater bandwidth means more information about the subsurface.

From information on elastic-wave behavior available via multicomponent recording, interpreters now can make deductions about rock types and other formation characteristics. But multicomponent data, while nearly as cheap to acquire as P-wave-only data, are much more costly to process and interpret. A reason for this, Lines explains, is that S-wave reflections typically have more-limited bandwidth, lacking high frequencies, “basically due to Mother Earth.”

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“It is instructive for us to keep abreast of advancing technologies to obviate our restrictive methods of the past.”–Laurence (Larry) Lines, professor of geophysics, University of Calgary

Lines notes an irony in modern seismic work: Much productive multicomponent recording is done offshore. S-waves don’t propagate through water, but advances in ocean-bottom instruments allow for the recording of data from what geophysicists call converted waves, which are S-waves induced when P-waves in water impact the seabottom.

Wide-angle 3D surveys.

With broad receiver arrays and many receivers per shot, seismic contractors sample more of the reflected wave field than is available through conventional, more-oblong survey designs. The improvement in survey geometry enhances the ability of multicomponent recording to describe the elastic wave field in the earth.

• Generalized wave-equation imaging through reverse-time migration.

In reverse-time migration, interpreters model both downward-traveling sonic impulses and upward-traveling reflections through use of the wave equation, which describes the position of the seismic wave at any given time. Conventional wave-equation migration models only the impulse wave down to reflecting points in the subsurface.

Because it’s computationally intensive, reverse-time migration strains computer capacities. But it enables interpreters to use much more of the information available from seismic recording than they can with other migration methods. It thus improves imaging of subsurface features involving steep dips and abrupt changes in sonic velocities, such as salt bodies.

Geophysicists made limited use of reverse-time migration 25 years ago, Lines says. But the technique was costly because of the computational load.

“Now computers have caught up with the algorithm,” he says, noting “huge interest in this area” and adding, “Some of us feel vindicated.”

Extensions to rock physics models.

As the ability of geophysicists to describe rock layers improves with advances in techniques such as multicomponent recording, Lines says, basic tools of rock physics need to improve as well.

He cites Gassman’s equation, a tool for analyzing wave propagation that assumes a crucial elastic property, shear modulus, is the same for saturated and dry rock.

“We now see different rock physics problems that go beyond that model,” Lines says. “We need to go beyond Gassman.”

He sees the need for more measurements able to improve understanding of key factors of interpretation such as attenuation, or the earth’s filtering effect on seismic energy, and elastic moduli.

Lines calls rock physics the “key link between what we measure seismically and what we read in reservoir simulation.”

Use of electromagnetic methods and high-resolution potential field measurements.

Controlled-source electromagnetic imaging (CSEM), which makes use of resistivity differences between saline fluids and hydrocarbons, “is beginning to look productive,” Lines says.

He also notes improvements in resolution of aeromagnetic and aerogravity data, which like CSEM can “nicely complement the seismic methods” and help interpretation when rock properties differ from what seismic data show.

All these areas of promise, Lines says, “extend the conventional methods for geophysical exploration and obviate restrictions of conventional methods.”

Classrooms full

Integration of geophysics with other disciplines is important for reasons beyond the application of new methods, according to Lines.

It also raises the appeal of geophysics as a career to students and young professionals.

“The geophysics profession is more exciting than it has ever been when considering the potential to integrate with other fields in geoscience and engineering, not only in the oil industry but in other branches of earth sciences as well,” Lines says.

He cites the increasing combination of energy with environmental topics as an enrichment that students like.

For oil companies and geophysical contractors, the benefits of integrating disciplines offer a lesson: “It is imperative for us to share information within the geosciences and engineering,” Lines says. “We should not worry about proprietary restrictions too much.”

The industry needs more geophysical professionals and seems to be getting them.

“As a professor, I see burgeoning geoscience student populations with record enrollments,” Lines says. “The big challenge will be to provide such large classes with a quality education that will provide them with the tools needed by geophysical professionals.”

Important to that goal is communication between industry, academia, and government, which can help set teaching goals and prevent “reinventing the wheel,” Lines says.

And as scientific subjects develop and the importance of integrating them grows, the need for such communication becomes doubly important.

“You can’t know everything,” Lines says.



Career highlights

Laurence (Larry) Lines is a professor of geophysics at the University of Calgary.

Employment

Lines became a university professor in 1993 after working for 17 years with Amoco Corp. in Tulsa and Calgary. He was NSERC/Petro-Canada chair in applied seismology at Memorial University of Newfoundland in 1993-97 and became chair in exploration geophysics at the University of Calgary in 1997. At the same university, he served as head of the Department of Geology and Geophysics in 2002-07.

Education

He holds BSc and MSc degrees in geophysics from the University of Alberta and a PhD in geophysics from the University of British Columbia.

Affiliations

With SEG, Lines has served as editor of Geophysics, distinguished lecturer, Geophysics associate editor, translations editor, publications chairman, and member of The Leading Edge editorial board. He has served as editor and associate editor for Canadian Society of Exploration Geophysicists.

Lines and coauthors won SEG’s Best Paper in Geophysics Award in 1986 and 1998 and won honorable mention for best paper in 1986 and 1998. He is an honorary member of SEG, CSEG, and the Geophysical Society of Tulsa.

He also is a member of the Association of Professional Engineers, Geologists, and Geophysicists of Alberta, Canadian Geophysical Union, European Association of Geoscientists and Engineers, and American Association of Petroleum Geologists.