Hardrock Seismic Reflection Through Cover: Defining Controls on Mineralization via Reflection Attribute Analysis

This study attempts to modify oil and gas industry seismic processing and interpretation techniques for use in Carlin-type deposit (CTD) gold exploration. Magmatic and deformation overprints on the Nevada carbonate platform-slope setting present challenges in seismic interpretation when compared to conventional seismic data, which is more commonly imaged in petroliferous basins with low levels of deformation. Barrick Gold Corporation provided 2D seismic reflection data for this case study, which assesses the viability of certain seismic practices when applied to hardrock seismic data collected in NE Nevada. Initial seismic interpretations of the pre-stack depth migrated (PSDM) sections located first-order structures and enhanced the geological model. This study uses derivatives of the PSDM, called seismic attributes, in an attempt to improve interpretability. Seismic attributes can reveal structural and stratigraphic features that are not apparent in the conventional PSDM amplitude data. Attribute analysis in this study leverages correlations made from a seismic response database of ~500 petrophysical drill core samples. These petrophysical measurements indicate that the ore zone exhibits a porosity, acoustic impedance, decarbonatization relationship that is distinguishable from unaltered rock. Down-hole geophysical data suggest an even larger contrast between altered and unaltered limestone. Given sufficient data quality, these observations make attribute analysis for detection of CTD alteration viable. An exhaustive calculation of attributes applied to one 2D reflection profile, which transects the Goldrush CTD resource, suggests that energy- and frequency-based attributes best highlight the ore zone, which is expressed as a chaotic zone of reduced amplitude within one 2D profile. RMS amplitude and instantaneous amplitude identify broad zones of low amplitude whereas an average frequency attribute highlights possible high-frequency attenuation effects in the vicinity of the ore-zone. The sweetness and frequency washout attributes combine frequency and amplitude attributes to more effectively highlight the ore zone. However, the erratic response of sweetness and frequency washout suggest that they may be negatively affected by noise. One structural model is also presented, which used the instantaneous phase attribute to better visualize possible thrust faulting

Summaries of physical research in the geosciences

The Department of Energy supports research in the geosciences in order to provide a sound foundation of fundamental knowledge in those areas of the geosciences which are germane to the Department of Energy's many missions. The Division of Engineering and Geosciences, part of the Office of Basic Energy Sciences of the Office of Energy Research, supports the Geosciences Research Program. The participants in this program include Department of Energy laboratories, industry, universities, and other governmental agencies. The summaries in this document, prepared by the investigators, briefly describe the scope of the individual programs. The Geosciences Research Program includes research in geology, petrology, geophysics, geochemistry, solar physics, solar-terrestrial relationships, aeronomy, seismology, and natural resource modeling and analysis, including their various subdivisions and interdisciplinary areas. All such research is related either directly or indirectly to the Department of Energy's long-range technological needs

Proceedings of the natural gas research and development contractors review meeting

The purpose of this meeting was to present results of the research in the DOE-sponsored Natural Gas Program, and simultaneously to provide a forum for real-time technology transfer, to the active research community, to the interested public, and to the natural gas industry, who are the primary users of this technology. The current research focus is to expand the base of near-term and mid-term economic gas resources through research activities in Eastern Tight Gas, Western Tight Gas, Secondary Gas Recovery (increased recovery of gas from mature fields); to enhance utilization, particularly of remote gas resources through research in Natural Gas to Liquids Conversion; and to develop additional, long term, potential gas resources through research in Gas Hydrates and Deep Gas. With the increased national emphasis on the use of natural gas, this forum has been expanded to include summaries of DOE-sponsored research in energy-related programs and perspectives on the importance of gas to future world energy. Thirty-two papers and fourteen poster presentations were given in seven formal, and one informal, sessions: Three general sessions (4 papers); Western Tight Gas (6 papers); Eastern Tight Gas (8 papers); Conventional/Speculative Resources (8 papers); and Gas to Liquids (6 papers). Individual reports are processed separately on the data bases

Submarine Landslides in the Central Mediterranean: Causes and Recurrences

This thesis (SLATE-project, https://www.itn-slate.eu/) is concentrated on submarine landslides in the central Mediterranean Sea. Commonly found in marine and lacustrine environments, submarine landslides represent one of the main mechanisms of sediment transport along continental margins, their volumes can be far larger than any terrestrial landslides and have potential to produce far-reaching tsunamis that can rival those produced by earthquakes. However, many uncertainties remain concerning their preconditioning factors, triggering mechanisms, return frequencies and relationship with climate change as well as their geohazard potential, which vary depending on their location. Newly identified submarine landslides emplaced in the Gela Basin (GB; south of Sicily, central Mediterranean Sea) were investigated where the particular geodynamic and oceanographic context and the limited extent basin is ideal for submarine landslides research. The investigation through multiple data types including deep boreholes, multi-channel and subbottom seismic profiles, sediment cores and swath bathymetry revealed the emplacement of multiple submarine landslides during the margin outbuilding in the Pliocene-Quaternary with a drastic transition in their volumes and emplacement location at the Middle-Pleistocene Transition (MPT). This change, accompanied by an accelerated margin outbuilding from 150 to 900 m/kyr and growth of the contourite deposits, has been related to the decreasing tectonic activity at the southern front of the Maghrebian fold-and-thrust belt and the climatic changes linked to the switch to the 100-kyr Milankovitch cyclicity. Numerical in-house codes used for the reconstruction of two small-size MTDs located at the ends of the GB show similar potential of generating high-wave tsunamis that can impact the coasts of Malta and Sicily but different triggering mechanisms based on the stability analysis. A multiproxy approach made on the sediment cores revealed that strong bottom currents and very-high sedimentation rate fluctuations, associated with sea-level changes, affected the stability of contourite deposits and contributed to the recurrent emplacement of MTDs

Seafloor gravity currents: flow dynamics in overspilling and sinuous channels

Turbidity currents are the largest agent of global sediment transport and their deposits, submarine fans, are the largest sedimentary structures on Earth. Submarine fans consist of networks of seafloor channels, which are vital pathways for sediment and nutrient transport to the deep ocean. This work focusses on flow dynamics within these channels, with the aim of understanding the role of the channel form on flow development and identifying implications for the development of channels and, ultimately, for submarine fans. Laboratory experiments have been conducted of continuous saline gravity currents traversing fixed-form channel models with a range of planform geometries. Both velocity and density data were gathered to investigate the effect of a channel on the flow field. Numerical simulations have also been conducted, using a Reynolds-averaged Navier Stokes model and a shear stress transport turbulence closure. These allow an extension of the laboratory analysis, both in terms of physical domain size, data resolution and measured variables. Velocity data reveal how partial confinement exerts a first order control on the vertical variation in flow structure. The channel half-depth acts to limit the height of the velocity maximum, resulting in the development of a confined, high-velocity flow core. The channel form also constrains the lateral and three-dimensional flow structure. Secondary flow rotation, characterised by a local reversal in the radial pressure gradient, is shown here to be inhibited by low channel sinuosity and large levels of overbank fluid losses. A change in cross-sectional channel profile is capable of switching the dominant cross stream basal flow direction of these structures. Furthermore, channels are shown to cause flow tuning, whereby flows of differing magnitudes entering a channel reach are rapidly modified to show a much restricted magnitude range, that remains quasi-stable thereafter. For the cases studied, this quasi-equilibrium state is characterised by a symmetrical cross channel basal stress profile. The existence of such a state could explain how seafloor channels can achieve a degree of planform stability

An experimental investigation into the stress-dependent mechanical behavior of cohesive soil with application to wellbore instability

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2009.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student submitted PDF version of thesis.Includes bibliographical references (p. 397-406).This thesis investigates the mechanical behavior of cohesive soils with reference to the applications of wellbore instabilities through an extensive program of laboratory element and model borehole tests. The laboratory tests use Resedimented Boston Blue Clay (RBBC) as an analog test material. Undrained triaxial shear tests have been performed on specimens that were K0-consolidated to stress levels ranging from 0.15 to 10.0 MPa in both compression and extension shear modes. Compression tests were also performed on overconsolidated specimens. Model borehole tests make use of two new automated, high pressure Thick-Walled Cylinder (TWC) devices to study the effects of the following parameters on the borehole response: mode of loading, specimen geometry, preshear lateral stress ratio, drainage conditions, consolidation stress level, stress history, and cavity volumetric strain rate. This testing program has been performed using small and large TWC devices with outer diameter, Do=7.6cm and 15.2cm, respectively. Both devices allow for independent control of the vertical stress and the radial pressures acting on the inner and outer walls of the cylinder, as well as pore pressure. The triaxial compression and extension test results demonstrate remarkable reductions in the undrained strength ratio (su/[sigma]'vc) with consolidation stress level, notable reduction in the stiffness ratio (Eu/[sigma]'vc), increase in the strain to mobilize the peak resistance (ef), and a significant decrease in the large strain friction angle (f'). The model borehole data indicate that most of the reduction in cavity pressure occurs at volume strains less than 5% before the borehole becomes unstable.(cont.) Increases in outer diameter and strain rate lead to a reduction in the minimum borehole pressure. The initial cavity stiffness ratio decreases as consolidation stress level increases. Drained tests have larger cavity strain at a given cavity pressure and lower minimum pressure than the undrained tests. The borehole closure curves were analyzed using a framework originally developed for interpreting undrained shear properties in model pressuremeter tests (Silvestri, 1998). Backfigured undrained strength ratios from these analyses range from su/[sigma]'vc=0.19-0.21 corresponding to an average between the measured triaxial compression and extension strength ratios. The relationship between su/[sigma]'vc and overconsolidation ratio is consistent with element tests.by Naeem Omar Abdulhadi.Ph.D