In this issue of E&P you'll find a feature on rock physics. There are those who question the importance of this topic and wonder if it warrants six pages of coverage in our magazine (seven, if you count this column). I would argue that understanding rock physics is one of the most important issues in the oil and gas industry.
Ultimately it's not the rocks that matter, of course; it's the hydrocarbons within those rocks that impact the bottom line. But everyone from the geologist to the production engineer has a vested interest in knowing what types of rocks house the oil and gas reservoirs. The more of that information that can be gleaned before the field is fully developed, the more is known about potential reserves, potential recovery and potential drilling hazards.
If you're still not convinced, I've called in an expert to help plead my case. Dr. Rob Simm runs a company called Rock Physics Associates in the United Kingdom, offering project consultancy and training for applying rock physics in oil and gas exploration and production. Simm offers several training courses, including "The Essentials of Rock Physics for Seismic Amplitude Interpretation." The idea of the course is to send geophysicists and other asset team members back to their jobs with the skills and tools necessary to apply the essential principles of rock physics to their everyday workflows.
"My definition of rock physics is very broad," he said. "It describes the acoustic properties of rock, the interaction of those properties with seismic energy and the description of rock properties from seismic analysis techniques such as amplitude variations with offset (AVO) and inversion. You're trying to make a physical connection between models based on well data and observed effects on seismic data.
Unraveling the various signatures of rocks and fluids can give a clue as to whether in fact the differences in the amplitude that you're seeing could be due to hydrocarbons. That's what we're after at the end of the day."
Simm argues that rock physics, the physical link between the well and the seismic data, is an essential part of seismic interpretation and prospect generation. This sounds easier than it is in practice. The challenge is to integrate physics-based models into a process which is as much art as science. "In this world, there are number people and there are pattern people," he said. "You have the pointy-headed geophysicists in the world, who are very number- and equation-oriented. The interpreters who are pattern thinkers and gave up physics in school don't really want to have to get back into it again." Part of his aim in teaching the courses, he added, is to bring in rock physics, which is fundamentally underlined by bunches of equations, and introduce those equations as part of the pattern.
Simm hopes to spread his gospel beyond seismic interpreters. The potential impact of rock physics-related interpretation in prospect risk means that the need for rock physics understanding permeates all levels of the asset team. "In oil companies, there are usually a couple of experts, and they're totally overworked," he said. "They can't do enough of the rock physics that's required at the company, and yet they're quite protective of their little patch. So they try to do it all, and they can't.
"Then there are the interpreters who need to know more about it, but they don't need to be trained as experts - they just need to know what significance certain workflows have and how to carry that through into risking, which is the end result. There's a substantial need for training."
A better scenario would be to have the interpreter know enough rock physics to understand his or her particular situation, then call in the experts, rather than handing off all rock physics issues to them at the start. "We try to give people a little framework from which to start," he said. "The class is designed to give them some confidence to approach certain datasets which they have not really looked at in this way before."
Well data is one example of that. Simm argues that geophysicists should have enough confidence to look at well logs and determine the implications for their models.
Part of the current interest in using rock physics in seismic interpretation, Simm said, stems from the fact that the seismic itself is much more sophisticated than it was even 10 to 15 years ago. High-fidelity seismic is now the norm. Equations that seemed largely irrelevant in the past can now be applied because amplitude can be better controlled and the subsurface better imaged.
It's that improved seismic that has brought rock physics out of the lab and into the oil and gas business. Simm said that current developments could not have happened had it not been for the huge amount of detailed work carried out at universities such as Stanford, which spent 20 years studying the interaction of rocks with acoustic phenomena.
"When the high-fidelity seismic came along it became clear that this work was important to us in the oil and gas industry," he said. "What appeals is that we never really knew how petrophysics tied in with seismic, and we now know the tie is rock physics. That's the bit in the middle. The people in our classes are from all disciplines, and rock physics is the glue that connects them together."
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