Microseismic imaging has become a useful tool in monitoring and analyzing fractures generated by hydraulic-fracturing stimulation in unconventional reservoirs. Although this technology has become more mature, there are still challenges in the processing of downhole microseismic data. First, intrinsic anisotropic reservoir rock-like-shale stacked with man-made fractures resulted in more complicated anisotropy than seen in more commonly used vertical transverse isotropy (VTI). However, a more accurate low-symmetry anisotropic model cannot be constrained from conventional P and fast S-wave travel times alone due to relatively sparse ray coverage. Second, for single monitoring well, event azimuths, which are obtained by a P-wave hodogram, must be added to data to determine event locations. However, typical weak P-wave arrivals usually cause heavy azimuth measurement uncertainties. To address these issues, we introduced new data, full S-wave-splitting parameters (delay time of the slow S-wave and fast S-wave polarization direction), to improve velocity models and microseismic locations. To solve the first problem, instead of assuming a higher-symmetry anisotropic model, we attempted to add S-wave splitting data, which is very helpful to constrain anisotropy. A Genetic Algorithm (GA) inversion was adopted to simultaneously determine event locations and stiffness coefficients of anisotropic media. We applied this approach to synthetic waveforms and successfully recovered the input event locations and velocity model. The effectiveness of this method is further demonstrated from real microseismic data acquired in the Bakken shale reservoir. The determined microseismic events are aligned in E15N direction, which agrees with the azimuth of the fast symmetric axis in the resulting anisotropic model in the area. Another study in this dissertation is the development of a new method of determining microseismic event azimuths using S-wave splitting analysis. This approach is based the positive correlation between the effectiveness of S-wave splitting measurements and the accuracy of the event azimuth. We applied a grid search to find the optimal azimuth. The obtained event azimuths agree well with the input ones in the synthetic experiments and with those determined from clear P wave particle motions in the field data tests. In summary, S-wave splitting data contain valuable information about seismic anisotropy and were significantly useful in resolving the velocity model and locating microseismic events. To the best of our knowledge, this dissertation is the first study using full S-wave splitting parameters in microseismic imaging. We have demonstrated the success of our new methods using synthetic and field data and envision their broad application in the future.

Downhole microseismic monitoring of stimulation and production of unconventional reservoirs has resulted in renewed industry interest in seismic anisotropy. This occurred not only because anisotropy of hydrocarbon-bearing shales is among the strongest in rocks but also because downhole microseismics shifts the focus from the standard exploration of P-waves to shear waves. The consequences of the difference in wave type are profound for geophysicists because everyone involved -- from theoreticians to developers and users of microseismic data-processing software -- must be aware of shear-wave splitting, singularities, and multivalued wavefronts, which have been largely irrelevant for P-waves propagating in relatively simple geologic settings. Anisotropy and Microseismics leads readers on a path of discovery of rarely examined wave phenomena and their possible usage. Most of the chapters begin by formulating a question, followed by explanations of what is exciting about it, where the mystery might lie, and what could be the potential value of answering the question. Importantly, the findings entail useful applications, as showcased by the unmistakably practical flavor of the chapters on microseismic event location, moment tensor inversion, and imaging. As an investigation of microseismic methodologies and techniques is conducted, it often yields unexpected results.

Provides essential background on anisotropic wave propagation, introduces efficient notation for transversely isotropic (TI) and orthorhombic media, and identifies the key anisotropy parameters for imaging and amplitude analysis. Particular attention is given to moveout analysis and P-wave time-domain processing for VTI and TTI.

Following the breakthrough in the last decade in identifying the key parameters for time and depth imaging in anisotropic media and developing practical methodologies for estimating them from seismic data, Seismic Signatures and Analysis of Reflection Data in Anisotropic Media primarily focuses on the far reaching exploration benefits of anisotropic processing. This volume provides the first comprehensive description of reflection seismic signatures and processing methods in anisotropic media. It identifies the key parameters for time and depth imaging in transversely isotropic media and describes practical methodologies for estimating them from seismic data. Also, it contains a thorough discussion of the important issues of uniqueness and stability of seismic velocity analysis in the presence of anisotropy. The book contains a complete description of anisotropic imaging methods, from the theoretical background to algorithms to implementation issues. Numerous applications to synthetic and field data illustrate the improvements achieved by the anisotropic processing and the possibility of using the estimated anisotropic parameters in lithology discrimination. Focuses on the far reaching exploration benefits of anisotropic processing First comprehensive description of reflection seismic signatures and processing methods in anisotropic media

This thesis presents an impressive summary of the potential to use passive seismic methods to monitor the sequestration of anthropogenic CO2 in geologic reservoirs. It brings together innovative research in two distinct areas – seismology and geomechanics – and involves both data analysis and numerical modelling. The data come from the Weyburn-Midale project, which is currently the largest Carbon Capture and Storage (CCS) project in the world. James Verdon’s results show how passive seismic monitoring can be used as an early warning system for fault reactivation and top seal failure, which may lead to the escape of CO2 at the surface.

Accompanying CD-ROM contains plates (chiefly maps) in Adobe Acrobat files, and contents in pdf format.

Shear-wave splitting observations can provide insight to mantle flow due to the link between the deformation of mantle rocks and their direction dependent seismic wave velocities. We identify shear-wave anisotropy in the Cook Inlet segment of the Alaska subduction zone by analyzing splitting parameters of S phases from local intraslab earthquakes between 50 and 200 km depths and SKS waves from teleseismic events. These earthquakes were recorded from 2015–2017 (local S) and 2007–2017 (SKS) by stations from SALMON (Southern Alaska Lithosphere and Mantle Observation Network), TA (EarthScope Transportable Array), MOOS (Multidisciplinary Observations Of Subduction), AVO (Alaska Volcano Observatory), and the permanent network. Automatic phase picking (dbshear) of 12095 local earthquakes (Ml ≥ 1.5) recorded at 84 stations yielded 678 high-quality splitting measurements (filtered 0.2–1 Hz). Teleseismic SKS phases recorded at 112 stations with 26,143 event–station pairs resulted in 360 high-quality SKS splitting measurements (filtered 0.02–1 Hz and 0.01–1 Hz). Measurements for both datasets were made using the SC91 minimum eigenvalue method with software package MFAST. We compare local S and SKS splitting patterns both from previous studies and our own analysis and find that they are most similar in the far forearc, at the Kenai Peninsula, below which there is no mantle wedge. Anisotropy in the subducting Pacific lithosphere and subslab asthenosphere is likely here as both S and SKS display plate convergence fast directions and SKS measurements exhibit delay times too long (∼2 s) to be explained solely by lithospheric anisotropy. Large splitting delay times (∼0.5 s) for local measurements that mainly sample slab further indicate that the Pacific slab lithosphere contains significant anisotropy. We also observe anisotropy in the mantle wedge indicated by an increase in delay time as focal depth increases for stations with ray paths dominantly sampling wedge. These measurements display trench-perpendicular and plate convergence fast directions consistent with 2D corner flow in the mantle wedge. Both datasets show trench-parallel splitting directions in select areas of the arc/forearc that overlie parts of the mantle wedge and nose. B-type olivine in the mantle nose, subslab asthenospheric flow, flow around the slab edge, and anisotropy in the Pacific lithosphere all could be invoked to explain this pattern. While we are unable to distill the anisotropy to a single responsible structure, the sharp transition in the local S data splitting pattern from trench-perpendicular in the backarc to trench-parallel across the arc suggests B-type olivine in the mantle nose. For an overall model, we favor 2D corner flow of A-type olivine in the mantle wedge induced by downdip motion of the slab, B-type olivine in the nose, and plate convergence parallel anisotropy in the subslab asthenosphere and subducting Pacific lithosphere to explain the observed splitting patterns. It is clear that the subducting slab’s structure and motion are the dominant influence on anisotropy and mantle flow regimes here. The differences in local S and SKS splitting results motivate further study on frequency dependence of splitting measurements and emphasize the need for a better understanding of which earth structures are responsible for the observed splitting patterns globally. This study constitutes the first comprehensive local splitting study in Alaska and refutes the common interpretation of along arc flow in the mantle wedge proposed by many previous splitting studies in Alaska.

An overview of the geophysical techniques and analysis methods for monitoring subsurface carbon dioxide storage for researchers and industry practitioners.