Designing a seismic program for an industrial CCS site: Trials and tribulations

AbstractDesigning a seismic characterization and monitoring program for a site with high levels of industrial and cultural infrastructure is by not trivial. At the MGSC Phase III project site, a combination of 3D surface seismic and VSP surveys will be used for site characterization and to monitor the injected CO2. The sparse existing data have been carefully analyzed to design 3D surface seismic and VSP surveys that will fit within the surface constraints at the site and meet the greater objectives of the project. The seismic data will be used to map formation heterogeneities and characterize fractures

Microseismic source inversion in anisotropic media

Sedimentary rocks and shales in particular are known to be anisotropic, sometimes strongly so, and hydraulic fracturing is now common practice in shale plays to enhance the extraction of hydrocarbons. One of the ways to understand the hydraulic fracturing process is through the micro--earthquakes that it generates; it is therefore of interest to study the impact that anisotropy may have on hydraulically induced seismicity. This thesis is concerned with the inclusion of anisotropy into the geophysical forward and inverse problems of microseismic sources. Ray theory is used for the forward problem --- dynamic ray tracing in a medium composed of homogeneous layers with vertical transverse isotropy (VTI) is used and the possibility of qSv triplication is considered. Novel approaches to the inverse problem are introduced, including waveform fitting in the frequency domain to recover the source function as well as moment tensor. Uncertainties in estimated moment tensor components are quantified with multi--variate normal sampling utilizing the full covariance matrix from the linear inversion. A new decomposition of the moment tensor is described that removes the distortions due to anisotropy local to the source and a new way to visualize an earthquake source is also introduced. The impact of anisotropy on moment tensor inversion and decomposition is shown to be significant. Field data recorded by two downhole arrays of multicomponent receivers are analyzed using the new techniques. The event collection suggests a source mechanism dominated by cylindrical dilatation. This is unexpected but is supported by results from another code. Future directions include extensions to lower symmetry forms of anisotropy and application to surface arrays. Preliminary analysis of downhole recordings of aftershocks of the 2008 Mw=7.9 Wenchuan earthquake is shown.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat

Multiple dynamic matching and median filters applied to sonic well logs

Nonlinear signal matching is a generalization of cross correlation in that a discrete lag between signals is replaced with a variable lag function or 'matching function', m(x). Two methods are reviewed which attempt to solve for m(x), namely the dynamic programming approach and the inverse theory approach. Both methods suffer from pitfalls and require the input of prior constraints to ensure convergence to the correct solution. The goal of this work has been to develop a method that can handle simple or complex matching problems and can succeed without any prior knowledge constraints. The multiple dynamic matching method is the result. It uses a significance threshold to extract a set of ridge points from a similarity matrix and applies dynamic programming to obtain a set of matched sections. These significant matched sections or 'subpaths' are then combined into a set of complete matching functions and a 'mean local confidence' norm is evaluated to determine the best overall match. It is argued through a model of change between signals, that given that the correct matching function is known, the presence of large amplitude changes between signals can cause the correct matching function to appear suboptimal under similarity norms. Multiple dynamic matching, because it generates suboptimal solutions as well, does not overlook the correct matching function. Typically the top three interpretations as ranked by mean local confidence will contain the expert's choice for the correct matching function. The use of median filters to preprocess the data and enhance well log features for matching has been investigated. A new 'median decomposition' is discussed as well, and in the context of a scale - space point of view to filtering, it is argued that median scale space is the proper choice for blocky waveforms. Finally, the connection between multiple dynamic matching and pattern recognition is explored, and matching iteratively through scale is proposed as a means of further generalizing the multiple dynamic matching method, making efficient high resolution matching possible.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat