Download or read book Sensitivity of Seismic Responses to Gas Hydrates written by United States. Department of Energy and published by . This book was released on 1992 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Sensitivity of Seismic Responses to Gas Hydrates written by and published by . This book was released on 1992 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt: The primary goal of this project was to determine the sensitivity of seismic responses to gas hydrate and associated free gas saturation within marine sediments. The development of a model to predict the physical properties of sediments containing hydrates was required. This model was used as the basis for predicting the sensitivity of P and S wave seismic velocities and waveform amplitudes to variations in hydrate and free gas saturation. Secondary goals of the project included: assessment of the usefulness of seismic shear waves in characterizing hydrate saturation and a review of potential complications in seismic modeling procedures.
Download or read book The Sensitivity of Seismic Responses to Gas Hydrates Final Report written by and published by . This book was released on 1992 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: The sensitivity of seismic reflection coefficients and amplitudes, and their variations with changing incidence angles and offsets, was determined with respect to changes in the parameters which characterize marine sediments containing gas hydrates. Using the results of studies of ice saturation effects in permafrost soils, we have introduced rheological effects of hydrate saturation. The replacement of pore fluids in highly porous and unconsolidated marine sediments with crystalline gas hydrates, increases the rigidity of the sediments, and alters the ratio of compressional/shear strength ratio. This causes Vp/Vs ratio variations which have an effect on the amplitudes of P-wave and S-wave reflections. Analysis of reflection coefficient functions has revealed that amplitudes are very sensitive to porosity estimates, and errors in the assumed model porosity can effect the estimates of hydrate saturation. Additionally, we see that the level of free gas saturation is difficult to determine. A review of the effects of free gas and hydrate saturation on shear wave arrivals indicates that far-offset P to S wave converted arrivals may provide a means of characterizing hydrate saturations. Complications in reflection coefficient and amplitude modelling can arise from gradients in hydrate saturation levels and from rough sea floor topography. An increase in hydrate saturation with depth in marine sediments causes rays to bend towards horizontal and increases the reflection incidence angles and subsequent amplitudes. This effect is strongly accentuated when the vertical separation between the source and the hydrate reflection horizon is reduced. The effect on amplitude variations with offset due to a rough sea floor was determined through finite difference wavefield modelling. Strong diffractions in the waveforms add noise to the amplitude versus offset functions.
Download or read book Quantitative Assessment of Gas Hydrate from Seismic Data written by Maheswar Ojha and published by LAP Lambert Academic Publishing. This book was released on 2012-04 with total page 124 pages. Available in PDF, EPUB and Kindle. Book excerpt: Gas Hydrate is solid compound of mainly methane and water, considered to be a huge energy resource, is still in research mode of delineation, distribution and estimation. Here, few methods/approaches have shown for quantitative assessment of gas hydrate from seismic amplitudes. Seismic attributes like reflection strength, blanking and instantaneous frequency have been computed to identify gas-hydrates in absence of BSR (Bottom simulating reflector) or to ascertain whether a BSR is related to gas-hydrates. Constrained amplitude versus offset (AVO) coupled with rock physics modeling employed here, could be an effective way for quantification of gas-hydrates and free-gas across a BSR.
Download or read book Gas Hydrate written by Umberta Tinivella and published by MDPI. This book was released on 2019-11-28 with total page 182 pages. Available in PDF, EPUB and Kindle. Book excerpt: This Special Issue reports research spanning from the analysis of indirect data, modeling, and laboratory and geological data confirming the intrinsic multidisciplinarity of gas hydrate studies. The study areas are (1) Arctic, (2) Brazil, (3) Chile, and (4) the Mediterranean region. The results furnished an important tessera of the knowledge about the relationship of a gas hydrate system with other complex natural phenomena such as climate change, slope stability and earthquakes, and human activities.
Download or read book Gas Hydrates written by J.-P. Henriet and published by Geological Society of London. This book was released on 1998 with total page 352 pages. Available in PDF, EPUB and Kindle. Book excerpt: From a geological perspective, gas hydrates are an important feature of the shallow geosphere. If current estimates are correct, gas hydrates contain more potential fossil fuel energy than is present in conventional oil, gas and coal deposits, although it is uncertain how much of this can be exploited. They are also geological agents that affect the physical, geophysical and geochemical properties of sediments. Oceanic gas hydrates are increasingly recognized as a major potential hazard for the stability of offshore structures in various deep-water hydrocarbon provinces. The possibility also exists that a large release of methane from gas hydrates may have a significant impact on the radiative properties of the atmosphere and thus influence global climate: past, present and future. Following an introduction and overviews, this book covers analysis and modelling of hydrate formation; exploration strategy and reservoir evaluation; regional case studies; relevance to margin stability and climate change. Hydrate research informatiloln is presented from the USA, Russia, South Asia and the European Union.
Download or read book Feasibility of High Resolution P and S Wave Seismic Reflection to Detect Methane Hydrate written by and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In March, 1999, a combined geophysical field team from the Kansas Geological Survey, Oak Ridge National Laboratory, and the Geological Survey of Canada, performed some experimental high resolution seismic testing at the Mallik drill site in the Mackenzie Delta, Northwest Territories, where drilling and sampling had previously identified gas hydrates at depth beneath a thick permafrost zone. In this information document, we show data from this seismic test, along with comparisons and observations significant to the effective use of high resolution imaging and important considerations about high resolution operations in this environment. Included are discussions and examples based on previous studies at this site, data acquisition, processing, correlation of results with other data sets and some recommendations for future surveying.
Download or read book Seismic Characterization of Marin Gas Hydrates and Free Gas at Northern Hydrate Ridge Cascadia Margin written by Carl Jörg Petersen and published by . This book was released on 2004 with total page 101 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract ; Zs.-Fassung.
Download or read book Study of the Electromagnetic Response of Gas Hydrates Using Forward CSEM 1 dimensional Models from Global Gas Hydrate Deposits written by James A. Lindsay and published by . This book was released on 2012 with total page 196 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Seismic Velocity Structure Associated with Gas Hydrate at the Frontal Ridge of Northern Cascadia Margin written by Caroll López and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: At the frontal ridge near the base of the slope off Vancouver Island, wide-angle ocean bottom seismometer (OBS) data were acquired in summer 2005, in support of the Integrated Ocean Drilling Program (IODP) Expedition 311. Marine gas hydrate is present beneath the ridge based on the observation of the 'Bottom Simulating Reflector' (BSR) that is interpreted to coincide with the base of the methane hydrate stability zone. Hydrate was also observed in downhole logs and drilling by IODP. The BSR has been identified on single-channel seismic data at -250-260 m depth beneath the ridge crest and on its seaward slope. The OBS data have been analyzed with the objective of determining the velocity structure in the upper portion of the accretionary wedge especially the hydrate stability zone and underlying free gas. As identified by a clear refracted phase, the velocity structure above the BSR shows anomalous high velocities of about 1.95 (?0.5) km/s at shallow depths of 80 - 110 m. On vertical incidence data, high amplitude reflectors are observed near this depth. Below the BSR, the velocities increase to -2.4 km/s at sub-seafloor depths of about 600 m. A strong refracted phase with a velocity of 4.0 km/s is generated at a depth of about 1700 mbsf. Velocities from traveltime inversion of OBS data are in general agreement with the Integrated Ocean Drilling Program (IODP) X311 downhole sonic velocities. In particular, on the log data, a layer with low porosity and high velocities of 2.4 - 2.8 km/s was observed at depths of 50 - 75 m. This probably corresponds with the 1.95 km/s layer at depths of 80-110 m interpreted from the OBS data. The refraction data thus suggest that this high-velocity layer varies laterally through the frontal ridge region, out to distances of at least 4 km from the drillhole. BSR depths (250-280 m) estimated in the present work also agree with the IODP X311 depths. From the velocity structure, we can make estimates of hydrate concentration in a region close to the deformation front, where fluid flow velocities are expected to be large. The gas hydrates concentrations vary from -35% for the shallow phase to -22% for the layer above the BSR. The deep refracted phase with a velocity of 4.0 km/s at 1700 m depth indicates the presence of highly compacted accreted wedge sediments. On the SW side of the frontal ridge, a collapse structure is observed in newly acquired multi-beam bathymetry data from the University of Washington and in seismic reflection data. The BSR is present in the region surrounding the slump. There are only weak indications of its presence within the slide region. Since hydrates may prevent normal sediment compaction, their dissociation in sediment pores is thought to decrease seafloor strength, potentially facilitating submarine landslides on continental slopes. The head wall of the frontal ridge slide is -250 m high, extending close to the BSR depth, and the slump has eroded a -2.5 km long section into the ridge, along strike. Migrated seismic reflection data image a set of normal faults in the frontal ridge striking NE-SW, perpendicular to the strike of the ridge and the direction of plate convergence. These faults outcrop at the seafloor and can be traced from the surface through the sedimentary section to depths well below the BSR in some locations. Seafloors scarps show that fault seafloor displacements of -25 m to 75 m are generated. The two faults with the largest seafloor scarps bound the region of slope failure on the frontal ridge, suggesting that the lateral extent of slumping is fault-controlled. The triggering mechanism for the slope failure may have been a combination of various effects. The possible mechanisms explored include gas hydrate dissociation, high pore pressure fluid expulsion along the faults, and salinity elevation in faults which would inhibit the formation of gas hydrates along the faults. However, an earthquake may induce initial slope failure, which can not only start gas hydrate dissociation but also increase fluid expulsion and pore pressure.
Download or read book Seismic Imaging of Gas Hydrate Reservoir Heterogeneities written by Jun-Wei Huang and published by . This book was released on 2009 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Natural gas hydrate, a type of inclusion compound or clathrate, are composed of gas molecules trapped within a cage of water molecules. The presence of gas hydrate has been confirmed by core samples recovered from boreholes. Interests in the distribution of natural gas hydrate stem from its potential as a future energy source, geohazard to drilling activities and their possible impact on climate change. However the current geophysical investigations of gas hydrate reservoirs are still too limited to fully resolve the location and the total amount of gas hydrate due to its complex nature of distribution. The goal of this thesis is twofold, i.e., to model (1) the heterogeneous gas hydrate reservoirs and (2) seismic wave propagation in the presence of heterogeneities in order to address the fundamental questions: where are the location and occurrence of gas hydrate and how much is stored in the sediments. Seismic scattering studies predict that certain heterogeneity scales and velocity contrasts will generate strong scattering and wave mode conversion. Vertical Seismic Profile (VSP) techniques can be used to calibrate seismic characterization of gas hydrate expressions on surface seismograms. To further explore the potential of VSP in detecting the heterogeneities, a wave equation based approach for P- and S-wave separation is developed. Tests on synthetic data as well as applications to field data suggest alternative acquisition geometries for VSP to enable wave mode separation. A new reservoir modeling technique based on random medium theory is developed to construct heterogeneous multi-variable models that mimic heterogeneities of hydrate-bearing sediments at the level of detail provided by borehole logging data. Using this new technique, I modeled the density, and P- and S-wave velocities in combination with a modified Biot-Gassmann theory and provided a first order estimate of the in situ volume of gas hydrate near the Mallik 5L-38 borehole. Our results suggest a range of 528 to 768x10 6 m3/km2 of natural gas trapped within hydrate, nearly an order of magnitude lower than earlier estimates which excluded effects of small-scale heterogeneities. Further, the petrophysical models are combined with a 3-D Finite Difference method to study seismic attenuation. Thus a framework is built to further tune the models of gas hydrate reservoirs with constraints from well logs other disciplinary data.
Download or read book A 3 D Seismic Investigation of the Distribution of Gas Hydrate and Free Gas and Their Relationship to the Structure and Stratigraphy of Hydrate Ridge written by Hao Xun and published by . This book was released on 2007 with total page 158 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Seismic Imaging of Gas Hydrate Reservoir Heterogeneities written by Jun-Wei Huang and published by . This book was released on 2009 with total page 394 pages. Available in PDF, EPUB and Kindle. Book excerpt: Natural gas hydrate, a type of inclusion compound or clathrate, are composed of gas molecules trapped within a cage of water molecules. The presence of gas hydrate has been confirmed by core samples recovered from boreholes. Interests in the distribution of natural gas hydrate stem from its potential as a future energy source, geohazard to drilling activities and their possible impact on climate change. However the current geophysical investigations of gas hydrate reservoirs are still too limited to fully resolve the location and the total amount of gas hydrate due to its complex nature of distribution. The goal of this thesis is twofold, i.e., to model (1) the heterogeneous gas hydrate reservoirs and (2) seismic wave propagation in the presence of heterogeneities in order to address the fundamental questions: where are the location and occurrence of gas hydrate and how much is stored in the sediments.Seismic scattering studies predict that certain heterogeneity scales and velocity contrasts will generate strong scattering and wave mode conversion. Vertical Seismic Profile (VSP) techniques can be used to calibrate seismic characterization of gas hydrate expressions on surface seismograms. To further explore the potential of VSP in detecting the heterogeneities, a wave equation based approach for P- and S-wave separation is developed. Tests on synthetic data as well as applications to field data suggest alternative acquisition geometries for VSP to enable wave mode separation.A new reservoir modeling technique based on random medium theory is developed to construct heterogeneous multi-variable models that mimic heterogeneities of hydrate-bearing sediments at the level of detail provided by borehole logging data. Using this new technique, I modeled the density, and P- and S-wave velocities in combination with a modified Biot-Gassmann theory and provided a first order estimate of the in situ volume of gas hydrate near the Mallik 5L-38 borehole. Our results suggest a range of 528 to 768x10 6 m3/km2 of natural gas trapped within hydrate, nearly an order of magnitude lower than earlier estimates which excluded effects of small-scale heterogeneities. Further, the petrophysical models are combined with a 3-D Finite Difference method to study seismic attenuation. Thus a framework is built to further tune the models of gas hydrate reservoirs with constraints from well logs other disciplinary data.
Download or read book Detection of Gas Hydrates in Garden Banks and Keathley Canyon from Seismic Data written by Idris Murad and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Gas hydrate is a potential energy source that has recently been the subject of much academic and industrial research. The search for deep-water gas hydrate involves many challenges that are especially apparent in the northwestern Gulf of Mexico, where the sub-seafloor is a complex structure of shallow salt diapirs and sheets underlying heavily deformed shallow sediments and surrounding diverse minibasins. Here, we consider the effect these structural factors have on gas hydrate occurrence in Garden Banks and Keathley Canyon blocks of the Gulf of Mexico. This was accomplished by first mapping the salt and shallow deformation structures throughout the region using a 2D grid of seismic reflection data. In addition, major deep-rooted faults and shallow-rooted faults were mapped throughout the area. A shallow sediment deformation map was generated that defined areas of significant faulting. We then quantified the thermal impact of shallow salt to better estimate the gas hydrate stability zone (GHSZ) thickness. The predicted base of the GHSZ was compared to the seismic data, which showed evidence for bottom simulating reflectors and gas chimneys. These BSRs and gas chimneys were used to ground-truth the calculated depth of the base of GHSZ. Finally, the calculated GHSZ thickness was used to estimate the volume of the gas hydrate reservoir in the area after determining the most reasonable gas hydrate concentrations in sediments within the GHSZ. An estimate of 5.5 trillion cubic meters of pure hydrate methane in Garden Banks and Keathley Canyon was obtained.
Download or read book Seismic Characterization of Gas Hydrate in the Gulf of Mexico Based on Rock Physics written by Zijian Zhang and published by . This book was released on 2011 with total page 292 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Feasability of High Resolution P and S wave Seismic Reflection to Detect Methane Hydrates written by and published by . This book was released on 2000 with total page 42 pages. Available in PDF, EPUB and Kindle. Book excerpt: In March 1999, a geophysical field team performed some experimental high-resolution seismic testing at the Mallik drill site in the Mackenzie Delta, Northwest Territories, where drilling & sampling had previously identified gas hydrates at depth beneath a thick permafrost zone. This document presents data from this seismic test, along with comparisons & observations significant to the effective use of high-resolution imaging and important considerations about high-resolution operations in this environment. Included are discussions & examples based on previous studies at the site, information on data acquisition, processing, correlation of results with other data sets, and some recommendations for future surveying.
Download or read book Seismic Attribute Analyses and Attenuation Applications for Detecting Gas Hydrate Presence written by Roberto Dominic Clairmont and published by . This book was released on 2021 with total page 149 pages. Available in PDF, EPUB and Kindle. Book excerpt:
