Tad Smith

Tad Smith
BSc	Geology
MSc	Geology
PhD	Geology
BSc university	Ohio Wesleyan University
MSc university	Washington State University
PhD university	Texas A&M University

Tad Smith is an American geologist and petrophysicist. He is currently the director of EPT - Geoscience at Apache Corporation. Throughout his career, Smith has worked as a petrophysicist, geologist, and manager at Apache Corporation, ConocoPhillips, CGGVeritas, and BP Amoco. Smith was the 2011 SEG North America Honorary Lecturer, 2013 Editoral Board Chair of The Leading Edge, and the 2013 President of the Geophysical Society of Houston. Smith received a Ph.D. in geology from Texas A&M University in 1991. In 1995–1996, he participated in the Amoco Petrophysics Training program, where he developed an interest in petrophysics and seismic rock properties (or, seismic petrophysics). He has been engaged in the process of integrating petrophysical data into geophysical work-flows ever since.^[1]

2011 SEG Honorary Lecturer, North America

Practical seismic petrophysics: The effective use of log data for seismic analysis

The conditioning and analysis of log data for quantitative seismic interpretation is often simply categorized as "rock physics." Unfortunately, rock physics workflows often overlook or oversimplify the proper editing and interpretation of log data, the result of which can be unrealistic expectations and interpretations of seismic amplitude responses. The more encompassing phrase "seismic petrophysics" better describes the necessary linkage between petrophysics and rock physics. Seismic petrophysics not only includes rock physics, but also includes the proper conditioning and interpretation of log data that should occur prior to the application of rock physics and seismic models. This is especially true in conditioning log data for shearwave velocity estimation, fluid substitution calculations, and AVO modeling.

This talk will focus on the important role of "seismic petrophysics" in the quest to extract additional information from subtle seismic responses. Topics covered will include various aspects of log editing, petrophysical interpretation (including integration of other data sources—core, fluids, pressures, etc.), and some common pitfalls associated with the "workhorses" of rock physics (invasion corrections, shear velocity estimation, and elements of fluid substitution). It is important to recognize that log data should not simply be recomputed to fit prior expectations as defined by a rock physics model. Instead, rock physics models should be used as templates, which allow the interpreter to better understand the underlying physics of observed log responses and how they are governed by local petrophysical properties. Case studies will be used to reinforce critical concepts.

Interview

Please tell us a little bit about yourself. I received a PhD in geology from Texas A&M in 1991, after which I went to work for Amoco Producion Company in Houston. My first assignment was working production geology in West Texas, as well as looking at nearby acreage for deeper exploration opportunities. It was during this time that I discovered petrophysics, which I recognized as the descipline that would allow me to link geology to reservoir performance. I therefore set my sights on the Amoco Petrophysics Program, which was a year-long training program in our Tulsa Research Lab. It was during my year in Tulsa (class of 1995-1996) that I met Carl Sondergeld, who was to become a good friend and mentor. It was Carl's infection enthusiasm for petrophysics and rock physics that got me started working in the world of "seismic petrophysics". Just as I had previously recognized that petrophysics links geology to reservoir performance, I also now recognized that rock physics provides the critical link between geology and geophysics. I have been almost exclusively engaged in the practice of "seismic petrophysics" since about 1997. It is my firm and unyielding belief that seismic amplitude interpretation cannot be reliably done in the absence of some knowledge of the local rock properties.

Would you like to mention anything about your personal attributes that helped you achieve the professional status you enjoy today; was it self-belief, hard work, a mentor, or something else? I'm not quite sure what professional "status" I enjoy, but if I've accomplished anything worthwhile it's been through a combination of passion and enthusiasm, hard work, reading the literature, and the willingness to try different things and make mistakes. I have also made it a point to publish and give presentations as much as possible. Nothing focuses the mind as much as public speaking or writing a paper for publication. Too often I find that people are reluctant to give presentations or publish a paper simply because they don't feel like they have the complete answer. My recommendation, especially to young geoscientists, is to present what you know, and do so in as many forums as possible. If you wait for the 90% solution, you will never experience the benefits of presenting your ideas to the geoscience community for feedback and review.

Why did you choose this lecture topic? Why is it important? A while back I came to the conclusion that the geophysical community often overlooks, or over-simplifies, the proper editing and interpretation of log data during the rock physics workflow. Unfortunately, improper log conditioning, and failure to properly understand the properties of the formations in the subsurface, can lead to unrealistic expectations and interpretations of seismic amplitude responses. One of the more distressing aspects of current rock physics workflows, at least as I see them applied, is the application of progressively more complex rock physics models without also taking the time to understand the complexities of the rocks in the subsurface. Just because your model predicts the in-situ velocities, doesn't mean that you understand the underlying controls on velocities. Basing forward models on these often-times flawed assumptions can lead to erroneous, and potentially expensive, results. I'm not sure we need new rock physics models, so much as we need to do a better job of applying and understanding the "workhorses" of rock physics. This means taking the time to integrate all sources of subsurface knowledge in the rock physics workflow.

Could you tell us in a few sentences what your course objectives are? This lecture will focus on the important role of seismic petrophysics in the quest to extract additional information from subtle seismic responses. Topics covered include various aspects of log editing, some key elements of petrophysical interpretation, and some common pitfalls associated with the "workhorses" of rock physics. I hope to illustrate, mostly through examples, the beneficial impact an integrated petrophysical interpretation can have on geophysical interpretation. One of my goals is to encourage geophysicists to work more closely with petrophysicists and geologists, and vice-versa. Frequently in the rock physics workflow, we don't ask enough questions about the underlying lithologies, and how they may affect the elastic response.

Are there any more specific areas that you want to emphasize? In this talk I'll revisit many of the key issues with regards to shear velocity prediction and application of Gassmann's equation. Although these techniques have been in use for many years, it has been my experience that we often make flawed assumptions about the rocks to which we are applying them. I will demonstrate (I hope) how his can lead us to incorrect assumptions about seismic responses.

What do you hope people will have learned after they attend your lecture? How is it different from other lectures? One of the most important themes that I will emphasize throughout my lecture is the need to calibrate to other sources of data and to make sure you understand the underlying geology of the reservoir. Too often we treat reservoir sands as simple quartz-dominated systems, when in fact many (most?) are far more complex. Failure to account for these complexities can lead to erroneous modeling results, which in turn can lead to flawed interpretations.

From a philisophical perspective, I doubt my lecture is any different than many of the other SEG lectures. That is, I will talk about the things I do on a daily basis, and in the process hope to have at least some small impact on the way people approach rock physics. From a purely technical perspective, I will probably incorporate more petrophysics and geology in my talk than most geophysicists are accustomed to seeing. I'm looking forward to some interesting, spirited, and fun discussions.

You have quite a busy year ahead. Do you enjoy traveling? Will it be difficult to balance the tour with your work? I do enjoy traveling, and am looking forward to visiting several cities, states, and provinces that I haven't yet been to. My employer, Apache Corporation, has been amazingly supportive of this tour, and has been very accomodating and with my workload this fall. I'm very grateful to them for granting their permission to go on this tour. I'm also grateful to my wife and son for giving me the time away from home to go on this tour.

Would you share with us one or two of your most exciting successes? Some of my most exciting successes have come from those times when I have made a breakthrough in my understanding of a petrophysics or rock physics issue. One example that comes to mind is when I fully started to realize the importance of pore microstructure (e.g., microcracks) on the velocity behavior of tight systems. This work lead to a paper in the January, 2010 issue of The Leading Edge, co-authored with Colin Sayers and Carl Sondergeld. Carl had been telling me about the importance of cracks for several years, but it wasn't until I was working on a tight gas sand project that I realized I had to incorporate crack theory into my thinking. For me, this was a period of rapid growth and learning.

How about a couple of disappointments? By the time you have worked in this business for over 20 years, and if you have continually pushed yourself to try new things and creatively solve difficult problems, you will probably have more disappointments than exciting successes. These disappointments can span the range from failed predictions to actual mistakes in your work. The challenge is to learn from the mistakes, and not get too confident from your successes (I like to remind people that even Michael Jordan, the great basketball player, recognized that he missed far more shots than he made). I encourage young geoscientists to keep this in mind when they feel reluctant to try new things or give a presentation that's not quite ready for prime time. Mother Nature is far too complex to get too confident or complacent in our work.

What advice would you give to geophysics students and professionals just starting out in the industry? I've addressed various aspects of this in a couple of other places in this interview. However, there are two additional pieces of advice that I offer up, as they have served me well over the years: 1) find some aspect of geophysics or geology that you find exciting and pursue it with a passion. Work hard and don't be afraid of long days and weekends (these are not 8 hour-a-day jobs!). 2) Find mentors and friends that will critically and honestly review your work. The former has a bearing on how much you learn and accomplish in your career, and the latter has a bearing on critical thinking skills. I have found that by working closely with my own "council" of mentors, I have been able to do things I never imagined possible when I started my career.