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Introduction to Special Issue on “Rock Physics ‐ from microstructure to seismic signatures”

Rock physics has received increased attention in the last decade due to the revolutionary exploitation of energy resources from unconventionals (shale gas, oil shales, tar sands). In particular, the investigations of nanoand microscale features of these types of reservoirs have proven to be an important part of the successful production of oil and gas from these plays. Also in the last decade, quantitative interpretation (QI) workflows, where rock physics constitutes a fundamental part, have become standard procedures in the petroleum industry. One of the big challenges in rock physics is to bridge the gap between the different scales, from nanoand micro-scale, where most of the experimental work is done, to the well log and seismic scale, where most of the applications are made. Also, with recent applications of seismic geomechanics, there is a need to better understand the relationship between static and dynamic rock physics properties. One of the key topics of discussion at the 4th International Workshop on Rock Physics (4IWRP), held in Trondheim, Norway, between 29th of May and 2nd of June 2017, was whether we are able to honour fundamental rock physics in our integrated and upscaled QI workflows. There has been much technology transfer and many benefits from experimental rock physics and geomechanics work on unconventional shale resources for quantitative interpretation studies of conventional petroleum resources. In particular, the increased knowledge on shale properties has had a positive impact on amplitude variation with offset (AVO) and QI studies around the world. However, a key concern that was raised at the workshop was that geophysicists and rock physicists are not playing the strong role we should in applying our field methods and QI tools on unconventionals, leaving the task to the drilling engineers. With recent focus on machine learning and big data analytics, there is also a question of the future role of rock physicists themselves, and how we integrate rock physics with computer science. With increasingly data-driven and automated workflows, and use of artificial intelligence, to predict geology and reservoir properties from geophysical data, how can we ensure that physical bounds and rigorous theories are not violated? At the end of the day, in order to extract information reliably from geophysical observables, we still need to understand the physics of the rocks, the uncertainties in the measurements, and the validity of the methods we are using, at all scales. The 22 papers in this special issue are representative of the 79 papers presented at 4IWRP and of wider contributions from the rock physics community,. 4IWRP sessions included the topics of poroelasticity, seismic dispersion and attenuation, shale rock physics and anisotropy, quantitative interpretation, geomechanics, computational rock physics, 4D rock physics, experimental rock physics, CO2 sequestration, unconventionals, upscaling and petrophysics. Most of these topics are also covered by the 22 papers presented in this special issue, and this compilation gives a good overview of the current, cutting edge, research focus within the global rock physics community.