Jeffrey Shragge

Colorado School of Mines · Department of Geophysics

Seismic monitoring at injection wells relies on generating accurate location estimates of detected (micro-) seismicity. Event location estimates assist in optimizing well and stage spacings, assessing potential hazards, and establishing causation of larger events. The largest impediment to generating accurate location estimates is an accurate veloc...

Seismic imaging algorithms face significant practical and numerical challenges when migrating multicomponent seismic data acquired from irregular topography. Most of these issues can be avoided by abandoning the Cartesian coordinate system and migrating the data in a generalized topographic coordinate system that is conformal to surface topology. W...

Accurate implementation of correct fluid-solid boundary condition at sea-bottom is important for realistic simulation of elastic wavefield solutions, especially the waves associated with the interface. However in field settings, the sea-bottom is rarely flat and the associated undulating can seriously affect the generation of waves associated with...

Real-time microseismic monitoring is essential for understanding fractures associated with underground fluid injection in unconventional reservoirs. However, microseismic events recorded on monitoring arrays are usually contaminated with strong noise. With a low signal-to-noise ratio (S/R), the detection of microseismic events is challenging using...

Deformation-rate distributed acoustic sensing (DAS), made available by the unique designs of certain interrogator units, acquires seismic data that are theoretically equivalent to the along-fiber particle velocity motion recorded by geophones for scenarios involving elastic ground-fiber coupling. While near-elastic coupling can be achieved in cemen...

Full-wavefield elastic imaging of active-source seismic data acquired by downhole receivers commonly offers higher-resolution subsurface images in the vicinity of a borehole compared to conventional surface seismic data sets, which can lack higher-frequency wavefield components due to longer travel paths and increased attenuation. An increasingly u...

Long-time marine seismic recordings are becoming more common with the increased use of ocean-bottom nodes (OBNs), which can measure ambient seismic energy at frequencies lower than the typical minimum values in active-source compressed air-gun surveys. Interferometric processing on long-time ambient multicomponent data allows for the extraction of...

In this article, the Editor of Geophysics provides an overview of all technical articles in this issue of the journal.

Recent advancements and the widespread availability of low-cost microcontrollers and electronic components have created new opportunities for developing and using low-cost, open-source instrumentation for near-surface geophysical investigations. Geophysical methods that do not require ground contact, such as frequency-domain electromagnetics, allow...

We conducted near-surface geophysical surveys in and around the Majes I agricultural development (60 km west of Arequipa, Peru), where the nexus of geology and agriculture has increased landslide activity along the Majes–Siguas River Valley. Through DC resistivity, transient electromagnetics (TEM), and seismic surveys, we refined the understanding...

Gas hydrates are found in significant quantities on the North Slope of Alaska in subpermafrost sand units and intermixed in lower portions of permafrost within the hydrate stability window. While conventional surface seismic data and established imaging methods can indicate the presence of gas hydrate reservoirs, producing high-resolution images of...

No PDF available ABSTRACT True-phase distributed acoustic sensing (DAS), a technique which uses low-power laser pulses to monitor along-fiber strain in optical cable, has proven useful in many geophysical research areas, including down-hole monitoring in oil/gas extraction, near-surface characterization, detecting and locating regional and global e...

Recent advancements and the widespread availability of low-cost microcontrollers and electronic components have created new opportunities for developing and using low-cost, open-source instrumentation for near-surface geophysical investigations. Geophysical methods that do not require ground contact, such as frequency-domain electromagnetics, allow...

Against the backdrop of recent membership discussions focused on what SEG will look like in the next decade lies an important question: who will be the members of this future SEG? It should come as no surprise to most readers that the SEG membership is aging; having a mean membership age increase by nearly one year every year is not sustainable in...

Real-time microseismic monitoring is essential for understanding fractures associated with underground fluid injection in unconventional reservoirs. However, microseismic events recorded on monitoring arrays are usually contaminated with strong noise. With a low signal-to-noise ratio (S/R), the detection of microseismic events is challenging using...

Data-driven artificial neural networks (ANNs) demonstrably offer numerous advantages over conventional deterministic methods in a wide range of geophysical problems. For seismic velocity model building, judiciously trained ANNs offer the possibility of estimating subsurface velocity models; however, there are substantial challenges with effective a...

Data-driven artificial neural networks (ANNs) offer a number of advantages over conventional deterministic methods in a wide range of geophysical problems. For seismic velocity model building, judiciously trained ANNs offer the possibility of estimating high-resolution subsurface velocity models. However, a significant challenge of ANNs is training...

Elastic time-reverse imaging offers a robust wavefield-based approach for locating microseismic events; however, event location accuracy greatly depends on the veracity of the elastic velocity models (i.e., VP and VS) used for wave propagation. In this study, we propose a methodology for microseismic image-domain wavefield tomography using the elas...

Insufficient access to safe drinking water is one of the most challenging global humanitarian issues. The development of low-cost microcontrollers and the widespread availability of cheap electronics components raise the possibility of developing and using low-cost geophysical instrumentation with open-source designs and software solutions to circu...

Correctly implementing the fluid/solid boundary conditions at the seafloor is important for accurate full-wavefield imaging and inversion of marine seismic data. Because bathymetric profiles are rarely flat, the associated undulations influence wave modes interacting with the seafloor and, therefore, the ensuing imaging and inversion results. The c...

Salt interpretation is an essential step of velocity model building for seismic imaging workflows in many salt basins around the world. However, conventional techniques are labor intensive and prone to human error due to the inherent complexities of salt geometries, seismic data and the model building process. While deep learning (DL) frameworks us...

Data-driven artificial neural networks (ANNs) demonstrably offer a number of advantages over conventional determinis-tic methods in a wide range of geophysical problems. For seismic velocity model building, judiciously trained ANNs offer the possibility of estimating subsurface velocity models more efficiently than deterministic full-waveform inver...

Long-time seismic recordings are becoming more common with the increased use of ocean bottom nodes (OBN). These records allow for the use of ambient seismic wavefields at frequencies lower than the typical minimum values in active-source compressed airgun surveys (i.e., sub-3 Hz). Cross-coherence-plus-stack processing on three-component geo-phone d...

Introduction Seismic monitoring analyzes signals to gain insight into the distribution and properties of passive sources. One of the main objectives of fluid injection programs including hydraulic fracturing and waste-water disposal is to infer the locations of (micro) earthquakes caused by induced or triggered seismicity (Maxwell and Urbancic, 200...

Distributed acoustic sensing (DAS) increasingly is being used for permanent monitoring in completed downhole installations characterized by near-elastic fiber coupling and high data quality that, for some types of interrogator units (IUs), approaches the particle velocities recorded on single-component geophones. Surface DAS installations, though,...

Ambient wavefield data acquired on existing (so-called ‘dark fibre’) optical fibre networks using distributed acoustic sensing (DAS) interrogators allow users to conduct a wide range of subsurface imaging and inversion experiments. In particular, recorded low-frequency (<2 Hz) surface-wave information holds the promise of providing constraints on t...

Elastic wavefield solutions computed by finite-difference (FD) methods in complex anisotropic media are essential elements of elastic reverse-time migration and full waveform inversion analyses. Cartesian formulations of such solution methods, though, face practical challenges when aiming to represent curved interfaces (including free-surface topog...

In this article, the Editor of Geophysics provides an overview of all technical articles in this issue of the journal.

In microseismic monitoring, obtaining reliable information about the event properties, such as the location, origin time, and moment tensor components, is critical for evaluating the success of the fluid injection programs. Elastic wavefield-based migration approaches can robustly image microseismic sources by extrapolating data through an earth mo...

Accurately estimating event locations is of significant importance in microseismic investigations because this information greatly contributes to the overall success of hydraulic fracturing monitoring programs. Full-wavefield time-reverse imaging (TRI) using one or more wave-equation imaging conditions offers an effective methodology for locating s...

Accurately modeling full wavefield solutions at and near the seafloor is challenging for conventional single-domain elastic finite-difference (FD) methods. Because they treat the fluid layer as a solid with zero shear-wave velocity, the energy partitioning for body and surface waves at the seafloor is distorted. This results in incorrect fluid/soli...

Geophysicists seek to extract useful and potentially actionable information about the subsurface by interpreting various types of geophysical data together with prior geologic information. It is well recognized that reliable imaging, characterization, and monitoring of subsurface systems require integration of multiple sources of information from a...

Numerical solutions of 3D isotropic elastodynamics form the key computational kernel for many isotropic elastic reverse-time migration and full waveform inversion applications. However, real-life scenarios often require computing solutions for computational domains characterized by non-Cartesian geometry (e.g., free-surface topography). One solutio...

Between 1992 and 2017, the Antarctic Ice Sheet (AIS) lost ice equivalent to 7.6 ± 3.9 mm of sea level rise. AIS mass loss is mitigated by ice shelves that provide a buttress by regulating ice flow from tributary glaciers. However, ice-shelf stability is threatened by meltwater ponding, which may initiate, or reactivate preexisting, fractures, curre...

In this article, the Editor of Geophysics provides an overview of all technical articles in this issue of the journal.

An accurate estimation of microseismic event locations plays an important role in the success of fluid-injection programs. Wavefield-based elastic time-reverse imaging (TRI) o↵ers a robust approach to locate microseismic events that occur due to induced seismicity. The event location accuracy, though, is greatly dependent on the veracity of the ela...

In this article, the Editor of Geophysics provides an overview of all technical articles in this issue of the journal.

Limitations on the vertical resolution in seismic data and fluid-flow models challenges the accurate interpretation of time-lapse (4D) seismic signals to identify fluid saturation changes within hydrocarbon reservoirs. Conventional streamer seismic data typically have a vertical resolution of 10-20 m at reservoir levels due to the lack of both lowe...

Recognition of seismic unconformities is crucial for interpreting basin history from seismic reflection data sets in both siliciclastic and carbonate settings. While it is well established that non-erosional changes in sedimentary facies can create seismic reflections that mimic seismic unconformities (i.e., pseudo-unconformities), these features a...

Seismic data processing flows often ignore the spatial and temporal variations in the sea surface during marine seismic acquisition by assuming a flat free surface. However, weather patterns during data acquisition can generate rough sea conditions, which can significantly influence seismic full-wavefield source behaviour, including ghost reflectio...

Full-waveform inversion is an iterative data-fitting procedure used to resolve complex subsurface elastic property models. It has the potential to become a tool for quantitative interpretation at stratigraphic and reservoir scales. To illustrate, we make use of a geologically modeled data set, and conventional marine seismic from the Northern Carna...

A key goal in industry and academic seismic research is overcoming long-standing imaging, inversion and interpretation challenges. One way to address these challenges is to develop a realistic 3D geomodel constrained by local-to-regional geological, petrophysical and seismic data. Such a geomodel can serve as a benchmark for numerical experiments t...

Large-scale 3D modeling of realistic earth models is being increasingly undertaken in industry and academia. These models have proven useful for various activities such as geologic scenario testing through seismic finite-difference (FD) modeling, investigating new acquisition geometries, and validating novel seismic imaging, inversion, and interpre...

Improving the accuracy of seismic wave propagation for imaging and inversion purposes often requires evaluating the validity of any underlying anisotropic assumption. Over the previous decades different models have been proposed to address the assumption of azimuthally anisotropic media; however, to our knowledge there is no published comparative a...

Utilising ambient seismic energy naturally propagating in the Earth as an alternative approach to active body‐wave seismic investigations has been a topic of interest for a number of decades. However, because ambient surface‐wave arrivals typically are of much greater amplitude than ambient body‐wave energy, significant data signal processing and l...

The Challenge Although known to host world-class mineral deposits, the Eastern Yilgarn Craton and Albany-Fraser Orogen are largely covered by sediments that post-date mineralisation and shield the highly-endowed regional geology from view. Recognising mineralisation through this cover to target exploration investment effectively requires the deve...

Utilising ambient seismic energy naturally propagating in the Earth as an alternative approach to active body-wave seismic investigations has been a topic of interest for a number of decades. However, because ambient surface-wave arrivals typically are of much greater amplitude than ambient body-wave energy, significant data signal processing and l...

Extracting body-wave arrivals from ambient seismic recordings remains a challenging task, largely because ambient records are usually dominated by surface-wave energy. Most ambient seismic data processing strategies aimed at enhancing body-wave energy focus on a cross-correlation plus stack (CC+S) methodology. While this approach is useful for inte...

The double absorbing boundary (DAB) is a novel extension to the family of high-order absorbing boundary condition operators. It uses auxiliary variables in a boundary layer to set up cancellation waves that suppress wavefield energy at the computational-domain boundary. In contrast to the perfectly matched layer (PML), the DAB makes no assumptions...

In passive seismic monitoring of microseismicity, fullwavefield imaging offers a robust approach for the estimation of source location andmechanism.Withmulticomponent data and the full 3D anisotropic elastic wave equation, the coexistence of P- and S-modes at the source location in timereversal wavefield extrapolation allows the development of imag...

Early recognition of concrete deterioration is an important engineering task with many associated monitoring challenges. Ground penetrating radar (GPR) is an important non-destructive testing tool commonly used by engineers to locate internal reinforcement and voids within concrete. However, the general standard of interpreting subsurface condition...

The heterogeneous distribution of reservoir properties is one of the most important uncertainties in static and dynamic reservoir modelling. Petrophysical properties are usually interpolated within reservoir models from sparse well-log data, which can lead to highly uncertain estimates at inter-well locations that directly affect the reliability of...

The heterogeneous distribution of reservoir properties is one of the most important uncertainties in static and dynamic reservoir modelling. Petrophysical properties are usually interpolated within reservoir models from sparse well-log data, which can lead to highly uncertain estimates at inter-well locations that directly affect the reliability of...

Photoacoustic (PA) imaging may be advantageous as a safe, non-invasive imaging modality to image the carotid artery. However, calcification that accompanies atherosclerotic plaque is difficult to detect with PA due to the non-distinct optical absorption spectrum of hydroxyapatite. We propose reflection-mode all-optical laser-ultrasound (LUS) imagin...

Monitoring for the deterioration of concrete infrastructure is an important assessment tool for an engineer and difficulties can be experienced with monitoring for deterioration within an infrastructure. If a failure crack, or fluid seepage through such a crack, is observed from the surface often the source location of the deterioration is not know...

Microseismic event locations obtained from seismic monitoring data sets are often a primary means of determining the success of fluid injection programs, such as hydraulic fracturing for oil and gas extraction, geothermal projects and waste-water injection. Event locations help decision makers evaluate whether operations conform to expectations or...

We conducted geophysical surveys on Beacon Island in the Houtman Abrolhos archipelago offshore Western Australia, to investigate areas of archaeological interest related to the 1629 Batavia shipwreck, mutiny, and massacre. We used three complementary near-surface geophysical survey techniques (total magnetic intensity, electromagnetic induction map...

Generating accurate numerical solutions of the acoustic wave equation (AWE) is a key computational kernel for many seismic imaging and inversion problems. While finite-difference time-domain (FDTD) approaches for generating full-wavefield solutions are well developed for Cartesian computational domains, a number of challenges remain when applying F...

Time-lapse (4D) seismic data sets have proven to be extremely useful for reservoir monitoring. Seismic-derived impedance estimates are commonly used as a 4D attribute to constrain updates to reservoir fluid flow models. However, 4D seismic estimates of P-wave impedance can contain significant errors associated with the effects of seismic noise and...

Biomedical imaging systems incorporating both photoacoustic (PA) and ultrasound capabilities are of interest for obtaining optical and acoustic properties deep in tissue. While most dual-modality systems utilize piezoelectric transducers, all-optical systems can obtain broadband high-resolution data with hands-free operation. Previously described r...

Simulating two-way acoustic wavefield propagation directly from a free-surface boundary in the presence of topography remains a computational challenge for applications of reverse time migration (RTM) or full-waveform inversion (FWI). For land-seismic settings involving heavily reworked geology (e.g., fold and thrust belts), two-way wavefield propa...

Wavefield imaging o↵ers a robust approach for source evaluation in microseismic monitoring. The coexistence of P- and S- wavemodes at the source location after time-reversal leads to an imaging condition from which the source position and radiation pattern can be identified. We propose a new imaging condition that is based on energy conservation an...

Direct imaging of ambient seismic data will require body waves to be extracted from the recordings. We use a dataset from an mine site in Manitoba, Canada, and a number of data analysis techniques aimed at extracting body waves from ambient seismic recordings. The four tools used here are data audification, power spectral density plots, cross-corre...

Biomedical image reconstruction using photoacoustic (PA) and -- more recently -- laser-ultrasound (LU) data is an active area of investigation. Previously, we demonstrated that a framework for LU image reconstruction can be developed based on reverse-time migration (RTM), an approach originally developed for seismic imaging. When combined with a mu...

While faults have long been known as primary pathways for fluid migration in sedimentary basins, recent work highlights the importance of fault zone internal architecture, lateral variation, transmissivity, and impact on migration and trapping. The impacts of fault zone architecture and properties on seismic images are investigated to facilitate ac...

SUMMARY The double absorbing boundary (DAB) is a new highorder absorbing boundary condition for the scalar acoustic wave equation. It suppresses scattered waves at the edge of a boundary layer in computational domain boundary by using destructive interference analogous to a noise-cancelling headphone. This method has advantages in that it addresses...