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  • 1
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    Increasing seismicity in the U. S. midcontinent: Implications for earthquake hazard (2015)
    Society of Exploration Geophysicists (SEG)
    Details
    Publication Date: 2015-06-03
    Description: Earthquake activity in parts of the central United States has increased dramatically in recent years. The space-time distribution of the increased seismicity, as well as numerous published case studies, indicates that the increase is of anthropogenic origin, principally driven by injection of wastewater coproduced with oil and gas from tight formations. Enhanced oil recovery and long-term production also contribute to seismicity at a few locations. Preliminary hazard models indicate that areas experiencing the highest rate of earthquakes in 2014 have a short-term (one-year) hazard comparable to or higher than the hazard in the source region of tectonic earthquakes in the New Madrid and Charleston seismic zones.
    Print ISSN: 1070-485X
    Electronic ISSN: 1938-3789
    Topics: Geosciences
    Published by Society of Exploration Geophysicists (SEG)
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  • 2
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    Practical strategies for classification of unexploded ordnance (2013)
    Society of Exploration Geophysicists (SEG)
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    Publication Date: 2013-02-07
    Description: We have developed practical strategies for discriminating between buried unexploded ordnance (UXO) and metallic clutter. These methods are applicable to time-domain electromagnetic data acquired with multistatic, multicomponent sensors designed for UXO classification. Each detected target is characterized by dipole polarizabilities estimated via inversion of the observed sensor data. The polarizabilities are intrinsic target features and so are used to distinguish between UXO and clutter. We tested this processing with four data sets from recent field demonstrations, with each data set characterized by metrics of data and model quality. We then developed techniques for building a representative training data set and determined how the variable quality of estimated features affects overall classification performance. Finally, we devised a technique to optimize classification performance by adapting features during target prioritization.
    Print ISSN: 0016-8033
    Electronic ISSN: 1942-2156
    Topics: Geosciences , Physics
    Published by Society of Exploration Geophysicists (SEG)
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  • 3
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    Seismic-frequency loss mechanisms: Direct observation (2014)
    Society of Exploration Geophysicists (SEG)
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    Publication Date: 2014-06-04
    Description: Direct measurement of seismic attenuation (1/ Q ) and velocity dispersion in the laboratory point to several independent loss mechanisms. A forced-deformation technique allows measurement at seismic frequencies and amplitudes. Fluid motion is the primary mechanism in porous, permeable clastics. In shales, bulk-fluid motion is inhibited, and clay-particle interaction with bound water might dominate. Another mechanism usually not considered is losses in the fluid phase alone. Heavy, viscous fluids show bulk losses independent of a rock matrix. All these loss mechanisms are frequency dependent, so observations of 1/ Q made at seismic frequencies usually will not agree with ultrasonic data. Attenuation and velocity dispersion are coupled processes, and validity of the frequency-dependent 1/ Q values can be checked by comparison with observed velocity dispersion over a broad frequency range.
    Print ISSN: 1070-485X
    Electronic ISSN: 1938-3789
    Topics: Geosciences
    Published by Society of Exploration Geophysicists (SEG)
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  • 4
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    High-order finite-difference approximations to solve pseudoacoustic equations in 3D VTI media (2017)
    Society of Exploration Geophysicists (SEG)
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    Publication Date: 2017-07-23
    Description: Pseudoacoustic algorithms are very fast in comparison with full elastic ones for vertical transversely isotropic (VTI) modeling, so they are suitable for many applications, especially reverse time migration. Finite differences using simple grids are commonly used to solve pseudoacoustic equations. We have developed and implemented general high-order 3D pseudoacoustic transversely isotropic formulations. The focus is the development of staggered-grid finite-difference algorithms, known for their superior numerical properties. The staggered-grid schemes based on first-order velocity-stress wave equations are developed in detail as well as schemes based on direct application to second-order stress equations. This last case uses the recently presented equivalent staggered-grid theory, resulting in a staggered-grid scheme that overcomes the problem of large memory requirement. Two examples are presented: a 3D simulation and a prestack reverse time migration application, and we perform a numerical analysis regarding computational cost and precision. The errors of the new schemes are smaller than the existing nonstaggered-grid schemes. In comparison with existing staggered-grid schemes, they require 25% less memory and only have slightly greater computational cost.
    Print ISSN: 0016-8033
    Electronic ISSN: 1942-2156
    Topics: Geosciences , Physics
    Published by Society of Exploration Geophysicists (SEG)
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  • 5
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    Electrical properties and its correlation to the petrology of the Upper Yangtze organic shales (2017)
    Society of Exploration Geophysicists (SEG)
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    Publication Date: 2017-05-31
    Description: Shale gas is a particularly important research target on Chinese energy resources, especially in the Upper Yangtze region. Complex topography and geologic conditions challenge seismic exploration of shale gas in this area, and ground-based electromagnetic (EM) methods are used to aid recognition of the best reservoirs. However, the electrical properties of organic shale (EPOS) and its correlation to shale-gas petrology remain poorly understood. We studied EPOS and their correlation to shale petrology by measuring and analyzing the petrochemical features and complex impedance of rock samples from the Silurian Longmaxi and Cambrian Niutitang Formations in the Upper Yangtze, southwest China. Our study indicates that the organic shale in the Upper Yangtze features low resistivity and high polarizability in terms of a high negative phase, but no obvious low resistivity is observed among shaly sandstone and shales with lower and higher total organic carbon. Pyrite and quartz contents in the organic shale dominantly contribute to the EPOS with different mechanisms. Our result indicates that the EPOS bear relations to the petrology parameters of organic shale, which is essential for shale-gas evaluation and exploration. The correlation between EPOS and the shale-gas petrology promoted a new way for shale-gas exploration with complex geology, topography, and surface conditions in China, especially in the Upper Yangtze region, by using the ground-based EM method to evaluate the parameters of shale gas and to aid to delimit the productive reservoirs ("sweet spots").
    Print ISSN: 0016-8033
    Electronic ISSN: 1942-2156
    Topics: Geosciences , Physics
    Published by Society of Exploration Geophysicists (SEG)
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  • 6
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    Interpreting direct hydrocarbon indicators of low-API biodegraded oils -- A case study from a deepwater South Atlantic Basin (2016)
    Society of Exploration Geophysicists (SEG)
    Details
    Publication Date: 2016-06-23
    Description: Strong seismic flat spots are typically associated with the oil/water contact (OWC) in many amplitude-supported deepwater South Atlantic Basin (SAB) discoveries, particularly in relatively shallow (~2000 mbml), high-porosity unconsolidated Eocene-age reservoirs. These reservoirs contain biodegraded oils that have low API gravity, low gas-oil ratios, high viscosities, and fluid acoustic velocities between 4500 and 5000 ft/s. Often, a mismatch in amplitude is noted when comparing an observed seismic-amplitude response with a synthetic forward model generated using sonic logging data. These observations can be attributed to the high viscosity (low API gravity) of biodegraded oil that can lead to wave-induced heterogeneous pore pressure at logging frequencies, thus deviating from a key assumption in Gassmann's fluid-substitution theory. These dispersion effects can lead to significantly slower acoustic velocities of these oil-bearing reservoirs at seismic frequencies than those measured at logging frequencies. Using a generalized fluid/solid-substitution theory, we model this change in acoustic velocity and find that the theory can explain the observed bright-spot response.
    Print ISSN: 1070-485X
    Electronic ISSN: 1938-3789
    Topics: Geosciences
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  • 7
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    Monitoring CO2 injection for carbon capture and storage using time-lapse 3D VSPs (2013)
    Society of Exploration Geophysicists (SEG)
    Details
    Publication Date: 2013-09-27
    Description: Carbon capture and storage (CCS) is the process through which a nearly pure carbon dioxide (CO 2 ) stream is captured, separated from flue gas or other industrial processes, compressed, transported to an appropriate storage site, and injected deep underground into a geological formation where it can be safely stored for long-term geologic storage (Benson, 2005). Large sedimentary basins, such as the Illinois, Michigan, and Western Canadian sedimentary basins are good targets for CCS, as they are in close proximity to large CO 2 emitters and are composed of the appropriate saline formations and overlying nonpermeable formations. In 2003, the U.S. Department of Energy's National Energy Technology Laboratory (DOE-NETL) created a nationwide network of federal, state, and private sector partnerships to determine the most suitable technologies, regulations, and infrastructure for future CCS in different areas of the North America (Office of Fossil Energy, 2013).
    Print ISSN: 1070-485X
    Electronic ISSN: 1938-3789
    Topics: Geosciences
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  • 8
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    Revealing new hydrocarbon potential through Q -compensated prestack depth imaging at Wenchang Field, South China Sea (2019)
    Society of Exploration Geophysicists (SEG)
    Details
    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉Wenchang Field in the South China Sea contains a well-developed fault system, resulting in complex subsurface geology. Imaging the complex fault system plays an important role in hydrocarbon exploration in this area since the fault system forms a link between the source rocks and reservoirs. However, it is difficult to obtain a high-quality depth image of the fault system due to the effects of complex velocity and seismic absorption. Inaccurate depth velocities lead to fault shadows and structure distortions at the target zone. Absorption effects further deteriorate seismic imaging as they cause amplitude attenuation, phase distortion, and resolution reduction. We demonstrate how a combination of high-resolution depth velocity modeling and 〈span〉Q〈/span〉 imaging work together to resolve these challenges. This workflow provides a step change in image quality of the complex fault system and targeted source rocks at Wenchang Field, significantly enhancing structure interpretation and reservoir delineation. A couple of commercial discoveries have been made, and several other potential hydrocarbon reservoirs have been identified based on the reprocessed data, which reveal new hydrocarbon potential in this region.〈/span〉
    Print ISSN: 1070-485X
    Electronic ISSN: 1938-3789
    Topics: Geosciences
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  • 9
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    Summer of Applied Geophysical Experience (SAGE): Training for our future geoscientists (2015)
    Society of Exploration Geophysicists (SEG)
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    Publication Date: 2015-10-07
    Description: Energy and natural resources are crucial to the sustainability of worldwide economies, security, and overall well-being. However, the future workforce in the energy and natural-resources sector is at risk, and meeting the challenges of this dwindling workforce requires well-educated geoscientists in exploration and applied geophysics and related geoscience and technology disciplines. Programs such as geophysical field courses that are supported by SEG and industry, in partnership with academic institutions and government laboratories, are important approaches to maintaining and enhancing expertise in exploration geophysics. One example of a geophysical field course devoted to educating our future workforce is the Summer of Applied Geophysical Experience (SAGE), a four-week program based in Santa Fe, New Mexico, designed to actively engage students in all phases of applied geophysical research. SAGE is a unique educational experience that combines teaching and research as a partnership among universities, industry, government agencies, and professional societies. SAGE teaches the principles and applications of refraction and reflection seismology, magnetics, gravity, GPS, heat flow, several electromagnetic (EM) methods, and ground-penetrating radar (GPR) in a field-based, hands-on setting. More than 850 students and qualified professionals have attended SAGE, many of whom have gone on to become leaders in academia, industry, and government. SAGE students are exposed to the exciting challenges that face earth scientists today, and they develop skills that are necessary to address the world's growing energy demands. Examples of SAGE research projects include mapping archaeological sites and tectonic structure and investigating water and geothermal resources in the Rio Grande rift.
    Print ISSN: 1070-485X
    Electronic ISSN: 1938-3789
    Topics: Geosciences
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  • 10
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    ATV magnetometer systems for efficient ground magnetic surveying (2011)
    Society of Exploration Geophysicists (SEG)
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    Publication Date: 2011-04-01
    Description: Ground magnetic data contain information, not pre-sent in aeromagnetic data, which may be useful for precisely mapping near-surface faults and contacts, as well as constraining or aiding interpretation of other geophysical methods. However, collecting ground magnetic data on foot is labor-intensive and is therefore limited to small surveys. In this article, we present two newly developed all-terrain vehicle (ATV) magnetometer systems that significantly expand the survey area that is possible in a ground magnetic survey without greatly reducing the quality of data.
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    Electronic ISSN: 1938-3789
    Topics: Geosciences
    Published by Society of Exploration Geophysicists (SEG)
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