Wavefield imaging and tomography with the energy norm Daniel Rocha & Paul Sava Center for Wave Phenomena Colorado School of Mines We seek to develop technology for imaging the interior of the Earth using seismic waves. Our work belongs to well-established technology in the exploration seismology community which has been proven to be effective at delineating deep Earth structure. Analogous technology is used in medical ultrasound imaging, with primary differences in the type of acoustic/elastic waves and the frequencies used for investigation. The two main types of structural imaging based on seismic imaging are: 1. Wavefield migration (slide 2): a process designed to identify and position in the subsurface the interfaces between rock formations characterized by different physical properties. 2. Wavefield tomography (slide 3): a process designed to characterize the physical properties (e.g. velocity and other elastic parameters) between the identified interfaces. Migration and tomorgraphy work together and iteratively, i.e advances in one facilitates advances in the other. Our specific implementation uses the so-called energy norm which closely matches the properties of the propagating elastic waves. For tomography, we also employ knowledge of physical observed in boreholes, thus constraining the inversion to feasible results throughout the investigated subsurface space. Both migration and tomography are computationally intensive. Typical datasets can be many TB in size and consist of multiple partially-redundant experiemnts (often tens of thousands). These experiments require expensive calculations of wavefields which can be best accomplied on a distributed computing infrastructure, as the experiments are independent of one-another. Moreover, modern processing uses iterative methods, and thus processing repeats multiple times over the same physical subsurface. It is not uncommon that least-squares migration or tomography take days/weeks of continuous processing over multiple compute nodes.

Wavefield migration Build high-resolution images with least-squares migration first iteration final iteration

conventional: recovered model with artifacts Wavefield tomography Constrain wavefield tomography using petrophysical information true model conventional: recovered model with artifacts new recovery method

Acknowledgements Center for Wave Phenomena Sponsors – research funding Shell Exploration and Production Company – field data Co-authors Jeffrey Shragge Antoine Guitton Nicolay Tanushev Ben Witten