The 14th RPI for November-December 2017

Ran Bachrach - Geophysics Advisor at Schlumberger, Houston, Texas, USA

About Ran Bachrach

Ran received his B.Sc. in geophysics and planetary science in 1993 at Tel Aviv University, and a

Ph.D. in Geophysics, with a Ph.D. Minor, in Civil Engineering, in 1998, from Stanford University. His doctoral dissertation was titled “High Resolution Shallow Seismic Subsurface Characterization”, and his Ph.D. advisor was Prof. Amos Nur. During his Ph.D. thesis he performed seismic imaging of tidal driven fluid flow and worked on velocities in unconsolidated sands, liquefaction and dynamic poroelasticity, as well as on near surface seismic acquisition.

From 1999-2003 Ran was an assistant professor of applied geophysics at the Dept. of Geological Sciences, Michigan State University where he worked on near surface geophysics. In 2002 he started consulting for Schlumberger-WesternGeco’s Reservoir Services. After joining Schlumberger (SLB) he managed new technology group for Schlumberger Reservoir Seismic Services, (2003-2006) developing reservoir characterization techniques. In 2006 Ran managed technologies for integrated technologies group, a group responsible for integrated seismic-geomechanics solutions as well as new technologies for joint analysis of new borehole techniques with seismic data. Ran also taught and advised MSc and Ph.D. students in Tel Aviv University and in various internal and external professional courses.

Ran is currently a scientific advisor in rock physics and geophysics in Schlumberger. His research interests include anisotropic reservoir characterization, high-resolution geophysics, rock physics and physics of porous media, geomechanics, fluid flow, and poroelasticity. In SLB, much of Ran’s works is on the integration of seismic data with different discipline for 3D/4D imaging of subsurface processes, Earth model building (EMB) and Seismic reservoir analysis.

Some of the recent advancements Ran is involved in are:

- Anisotropic seismic velocity model building,
- Orthorhombic AVAz and fracture characterization.
- Seismic geomechanics joint analysis
- Data assimilation techniques for 4D and multi physics

Pathways or recipes for your success in becoming a well-known name in the rock physics community

I was fortunate to be part of the Stanford Rock physics consortium (SRB) where I spent time both in the rock physics lab and in the field. I find the physics of porous media to be a challenging and rewarding field of study. However, during my Ph.D. I also learned that the rock, the physical experiment and the ability to use the experiment to learn about the material properties of interest, are all interleaved subjects. I then decided to broaden my horizons and study many aspects of the experiment (acquisition, sources, processing etc.), modelling and parameter estimation. I therefore tried to learn as much as I could on topics that may not have been traditionally within the traditional rock physics discipline, including numerical modelling, statistical inference theory as well as seismic wave and source theory. I was also fortunate to interact and learn from many of my peers and colleagues.

In general, I believe that scientific curiosity and hands on approach have contributed to my carrier. I often think of myself as a professional problem solver as I enjoy solving problems which arise in the field and have some impact.

Challenges you see in taking rock physics to the next level

There are many challenges in understanding the theory and practice of rock physics. From my perspective the top are:

1. Scales and scaling:

- The issue of scales in rocks and scaling of rocks is still a major challenge. The natural scaling laws are not easily used in our science. Also the support volume of the measurements is not an explicit parameter we use. Homogenization and effective medium theory do not come with both the rock scales and the measurement scales. Also, we do not handle well theoretically large material contrasts (which often break the homogenization assumption) while the geophysical measurement is very sensitive to large material contrasts.

2. Small to large strain theories and having failure as an explicit part of rock models:

- The mechanics of large deformation and failure often is not considered in rock physics. We are happy to estimate the elastic properties of stressed fractured media but we do not consider often the effect they have on failure. The stress path and memory in the rock is a large strain problem while the elastic signature of damage is often stronger than any fluid effect.
- We need to use more the DC component of the poroelastoplastic strain!

3. The regression risk:During the last few decades I have observed that the field of rock physics is in risk of becoming a set of regression techniques for data fitting where well logs and seismic are brought together. While statistical inference is important, rock physics is not only a way to generate functional forms for data fitting. It is our responsibility to demonstrate the value we get by understanding rocks and rock models in comparison to performing regression.

Advice for early career scientists (rock physicists, geophysicists, etc.)

I would recommend the following:

- Build yourselves a strong mathematics background and a healthy physical intuition.
  - However, always look for simple solutions
- Make sure you know how to tell a computer what to do (i.e., learn how to program by yourselves)
- Broaden your understanding and interact with other fields
  - Rock physics provide an opportunity to work on EM, geomechanics, fluid flow and estimation theory, mechanics of composites and nano-science, HPC and data analytics and much more.
  - Be both curious and critical.
- When solving a problem always ask yourselves what is the potential impact your solution will have.
  - Provide solutions which have impact
- Keep learning from other people in your field and in other fields of science.
  - We advance together. Faster to learn from each other rather then re-invent the wheel every time.
- Do not forget to review assumptions you make and be transparent.
- Make sure you provide a measure of confidence (or uncertainty) always.
  - This may be a subjective measure but make sure you provide information relevant for decision making.

My last comment is that the thin crust we all live on is a resource that needs to be explored and maintained in a sustainable manner. As population grows we need to better manage this shared resource. Geoscience and geo-engineering are here to stay even when society will slowly shift away from hydrocarbons. Rock physics will always be here to support the analysis of geophysical and geomechanical information as long as we provide society with tools for decision making based on technical understanding.

We thank Ran for his continuous contributions to the rock physics community

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