Tariq Ali Alkhalifah
Tariq A. Alkhalifah is a professor of geophysics in the division of Physical Sciences and Engineering at King Abdullah University for Science and Technology (KAUST). He assumed his duties there in June 2009. Prior to joining KAUST, Tariq was a research professor and director of the Oil and Gas Research Institute at King Abdulaziz City for Science & Technology (KACST). He has also been associate research professor, assistant research professor, and research assistant at KACST. From 1996 to 1998, Tariq served as a postdoctoral researcher for the Stanford Exploration Project at Stanford University, USA. Tariq received his doctoral degree in geophysics (1997) and master's degree (1993) in geophysical engineering from the Colorado School of Mines, USA. He holds a bachelor's degree (1988) in geophysics from King Fahd University of Petroleum and Minerals, Saudi Arabia. Tariq's research interests are in imaging and velocity model building for exploration seismic data with special emphasis on media that exhibit anisotropic behavior. He served as the SEG Honorary Lecturer, received the J. Clarence Karcher Award from the Society of Exploration Geophysicists (SEG) in 1998, and received the Conrad Schlumberger Award from the European Association for Geoscientists and Engineers (EAGE) in 2003. He is a member of SEG and EAGE.
2011 SEG Honorary Lecturer, Middle East and Africa
Seismic imaging: Kirchhoff, beam, WEM, RTM, anisotropy, what is next?
The lecture will include three parts:
- Seismic imaging made easy, really easy
- What do we learn from the past?
- The current status and the road ahead
Seismic imaging (migration) is arguably the single most important step in treating recorded seismic data; it is usually the "final say" in processing and it has contributed, single-handedly, to some of the most important finds in the petroleum industry. This wave-equation-based operation has typically the biggest influence on seismic data and, as a result, costs the most. It is also sadly responsible for the most acronyms (abbreviations) used in the seismic industry, which is sometimes confusing.
Any process that moves (migrates) the reflection (or scattered) energy of seismic data can be referred to as migration, with imaging accomplished through imposing the imaging conditions. Those are zero-offset and zero-time, applied separately in poststack migration, but, now commonly applied simultaneously in what is referred to as prestack imaging. Seismic-imaging algorithms can be divided into two broad categories: integral methods (e.g., Kirchhoff methods) and wavefield-continuation methods. Integral methods can be described by simple geometrical objects such as rays and summation surfaces. Wavefield-continuation methods can yield more accurate images of complex subsurface structures.
In the 1980s, the integral approach was king; its simplicity and adaptability made it the industry workhorse through the 1990s, where it was used mostly on 3D data. It also provided an explicit approach to evaluate the accuracy of the velocity model used in the prestack migration by allowing the offsets to be handled separately. Meanwhile, direct-wave (continuation) methods, despite their potential, were still just gaining their footing at the time and were used mostly in poststack migration utilizing the velocity-inhomogeneity-limited Fourier methods or the dip-limited depth extrapolators. In the late 1990s, a slew of wave-equation-migration (WEM) results, especially in 3D subsalt regions, revealed some of the power of this technique. This was helped with the advent of velocity verification methods for WEM such as subsurface offset gathers (SOCIG) and angle gathers (ADCIG). The reign of WEM, however, was short lived; as our computing capabilities matured, short-changing the wave equation was no longer required and reverse time migration (RTM) saw a huge revival in the first decade of the 21st century. From acoustic isotropic RTM, to acoustic VTI (vertically transversely isotropic), and finally acoustic and elastic TTI (tilted transversely isotropic), the sky was the limit. RTM, however, remains too expensive for velocity estimation processes, and thus, curvelets, beam, and other fast methods are still used widely. RTM also has a weakness imposed by the integral-based imaging condition.
Further advances in computing nevertheless will make more complicated methods feasible, and thus we have to prepare for them. A more complicated wave equation describing wavefield evolution in the prestack domain, with the wavefield given as a function of three independent parameters in 2D media and five in 3D, can help alleviate some of the limitations of RTM. The double square-root (DSR) equation provides us with such a formula; the challenge is to resolve the limitations of this equation. While most modern seismic imaging techniques perform imaging by separating input data into parts (shot gathers), this new formulation is able to incorporate all available data at once, while numerically propagating the recorded multi-dimensional wavefield backward in time. While computationally intensive, this approach has the potential of generating accurate images, free of artifacts associated with RTM. Also, unlike RTM, which requires an integral-based imaging condition, imaging using the double square-root equation avoids that requirement and thus provides an explicit relationship between the imaging operator and medium parameters. A numerical extrapolation shows the evolution of the wavefield in the prestack domain using a prestack exploding reflector modeling and migration (PERM) experiment.
Biography Citation for the J. Clarence Karcher Award
If anisotropic processing has matured from an elegant construction of a few visionaries to an effective tool applied on a production basis, it is in large part thanks to Tariq Alkhalifah's enthusiasm for new ideas. While at Colorado School of Mines, Tariq transformed his scholarly excitement about anisotropic theory into practical methods for anisotropic imaging. Most important. Tariq cut through the problem of determining which are the pertinent parameters and devised a practical inversion method for obtaining these parameters from conventional surface seismic data. Here is how Ken Larner describes Tariq's first encounter with anisotropy:
"This was the course (quantitative seismology) that interested both Tariq and me in anisotropy. What followed the end of the course was a professor's dream-the natural coming together of a student and professor whose interests were fully in common. We would bump into each other in the hallway every day or so and exchange thoughts on papers we had been reading, and it seemed that, by coincidence, we had chosen many of the same papers."
Shortly after, Tariq joined the Center for Wave Phenomena where, under the mentorship of Larner and Ilya Tsvankin, he had six impressively productive years.
As a scientist, Tariq is fiercely independent and confident, yet eager and willing to learn from new data and observations. This combination of qualities has been nowhere more evident than in his remarkable success at applying his methods to field data. He attacks each data set confident that he already knows how to solve its particular problems, is carried by that confidence deep into the reality of the data set, then adapts his methods to get the most out of the data. The resulting growth in both his understanding of field data and the sophistication of his methods is remarkable.
While at Stanford as a postdoctoral fellow in the last year, Tariq responded enthusiastically to the challenges of a new environment and began to think about issues of 3-D and depth. A glance at his latest projects shows how quickly he initiates new ideas: for 3-D processing he derived analytical solutions for the Cheops pyramid and AMO in weakly anisotropic 3-D media; for imaging in complex media he has contributed to the development of time-domain processing in arbitrarily inhomogeneous media. But even more important than his technical contributions, Tariq's energy and enthusiasm have been a stimulus for Stanford's students and faculty.
Tariq's forceful and colorful talks have become a mainstay of geophysical meetings. He gave two talks at each of the last four SEG Annual Meetings and has been an active participant in the last three workshops on anisotropy. His talks are direct, clear, and to the point. The audience is in no danger of walking away without knowing the significance of Tariq's work. And more likely than not, the audience is going to remember the main message of the talk for quite some time. Tariq is also a clear writer. He learned the trade at Ken Larner's school, and as Ken says, "Tariq is the one, more than anyone else, who has taken suggestions on ways to improve writing to heart." He has already published 10 papers in Geophysics, and one, "Velocity analysis using nonhyperbolic moveout in transversely isotropic media" received honorable mention for Best Paper in Geophysics.
Tariq was born in 1966 in Alrass, Saudi Arabia, a small village in the middle of the desert, far removed from modern life. But he has become the perfect example of world cultural globalization. He is an adept citizen of both the Western world and the Eastern world. His first experience in the West was as a young boy in California while his father was completing a Ph.D. at U.C. Santa Barbara. He says that nostalgia for the free-form California lifestyle was one of the main reasons he came back to the United States for his own Ph.D. studies. However, before coming back to the United States, Tariq had a full immersion education in the culture and traditions of his own country.
He graduated from the University of Petroleum and Minerals in Dhahran, which was followed by his first geophysical experience (in earthquake seismology) at the National Center of Technology in Riyadh. In 1991 he came back West to CSM, where he earned an M.S. and a Ph.D. in geophysics. After finishing his doctorate in 1997, he became a post-doc with the Stanford Exploration Project and consultant with Chevron Overseas Petroleum Company.
Tariq has three beautiful daughters Nada, Monira, and Sara. The family is planning to return to Saudi Arabia where Tariq hopes to contribute to the education and training of a new generation of young Saudi geophysicists. We will miss him, but we are sure that we will find Tariq again wherever around the world a new and challenging seismic imaging problem is being tackled.
- Society of Exploration Geophysicists (1998) Awards Citations of the SEG SEG Publications, Tulsa, Ok.
- Alkhalifah, T. A. (1997) Velocity analysis using nonhyperbolic moveout in transversely isotropic media, GEOPHYSICS 62(6):1839.
- Alkhalifah, T. and I. Tsvankin (1995 Velocity analysis for transversely isotropic media, GEOPHYSICS 60(5):1550.