Seismoacoustic Study of the Shallow Gas Transport and ... - E-LIB

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Chapter 1 reflections, interpreted as minor accumulations of gas within thin and relatively porous sediment layers; (3) Pull-down, the effect presented on coherent reflections located below units of gas-charged sediments; (4) Gas chimneys, vertical zones shown on 2D and 3D seismic datasets and caused by the previous or on-going gas migration; (5) Bright Spots, which are characterized by high-amplitude and negative-phase reflections and regarded as key characteristics of gas accumulations; (6) Flat spots, coherent reflection occurring at the gas-water interface in a hydrocarbon reservoir; (7) Acoustic blanking and columnar disturbances, which indicate the presence of free gas. Some examples of seismic evidence are shown in Figure 2. Furthermore, focused fluid flow can also be indicated by the narrow vertical acoustic blanking zones (chimneys), faults and fractures, which are the potential conduits for fluid flow migration (Gay et al., 2003; Wagner-Friedrichs, 2007). Figure 3 Global distribution of gas hydrates, pockmarks, mud volcanoes and other gas/fluid related structures (gas seeps) (from http://www.awi.de) Gas and fluid flow within marine sediments can be significant in shaping the morphology of marine seafloor. Gas and fluid flow related structures are widely distributed throughout the world’s oceans (Fig. 3). Different types of seabed fluid seepage result from the extrusion of gas- and fluid-rich sediments, such as mud volcanoes and pockmarks (Judd and Hovland, 2007; Kopf, 2002). Therefore, gas- and fluid-charged sediments are considered a major hazard by the oil and gas industry. Scientific research has also revealed a close correspondence to climate and environmental issues and geological hazards with gas- and fluid-charged sediments. 1.2 Seabed fluid seepage Seabed fluid seepage can be formed by a wide range of fluids (gases and liquids), which originate from sediments and pass through the seabed to the seawater and to the atmosphere (Judd and Hovland 2007). It includes not only cold seeps, but also volcanic 7
Chapter 1 and hydrothermal fluid vents from ocean spreading centers, island arcs, and intra-plate volcanism, and groundwater flows in some coastal areas (Judd, 2003). In this dissertation, the direct link to seabed fluid seepage is through cold seeps, from which methane escapes. Seeps can occur in all geological contexts, e.g. active and passive continental margins and the deep oceans, where fluids and hydrocarbons are from sub-ducting sediments, or migrate from deep gas/oil reservoirs; such as the Gulf of Mexico (e.g. Sager et al., 2003, Ding et al., 2008; Ding et al., 2010), the Cascadia Continental Margin (e.g. Collier and Lilley, 2005), the Black Sea (e.g. Dimitrov, 2002a; Klaucke et al., 2006; Wagner- Friedrichs et al., 2008; Römer et al., 2012), the Sea of Okhotsk (e.g. Obzhirov et al., 2004), the West African Basins (e.g. Gay et al., 2003; Pilcher and Argent, 2007), the continental shelf of the U.K., including Torry Bay, Firth of Forth, Scotland (e.g. Judd et al., 1997, 2002b), the Costa Rican coast (e.g. Mau et al., 2006) and the Barbados accretionary complex (e.g. Henry et al., 1990; Le Pichon et al., 1990). It is clearly widespread (Fig. 3) and contributes greater amounts of gas and fluids, dominated by methane, to the biosphere, the hydrosphere and the atmosphere (Hovland and Judd, 1988; Judd, 2003). However, the exact distribution and number of seep sites remain uncertain due to the limited number of investigations restricted so far to only a small portion of the world's seas and oceans (Judd, 2003). The spectrum of morphologies can vary from pockmarks (King and MacLean, 1970; Hovland and Judd, 1988) to mud volcanoes of various sizes and seeps with little effect on the seafloor sediments (Fig. 4) (Dimitrov, 2002b; Judd and Hovland, 2007). 1.2.1 Importance 1.2.1.1 Climate and environment Emission products of seabed fluid seepage include solid, liquid and gaseous materials. The gaseous materials not only contain higher hydrocarbons but also methane. Methane is considered as the most important emission. Because methane is a powerful greenhouse gas, it can play an important role in global climate change. Solomon et al. (2007) pointed that each molecule of methane has 25 times the direct global warming potential of a molecule of CO 2 over a period of 100 years. And the atmospheric mixing ratio of methane has increased to more than double during the last century (Rowland, 1985). Methane can originated from both anthropogenic (360-430 x10 6 T/yr) and natural sources (160-240 x10 6 T/yr) of either biologic or geologic origin (Prather et al., 1995; Kvenvolden and Rogers, 2005). Although some of the emitted methane from marine seepage dissolves into the ocean during transit from the seabed to the sea surface (Leifer and Judd, 2002), a greater fraction of methane can reach the atmosphere when larger bubbles are generated during eruptive episodes (e.g. blowouts) or during more rapid upwelling flow (Leifer et al., 2004, 2006). Marine seeps are estimated to contribute about 31 to 48% of the annual global methane emission into the atmosphere from geological sources (53± 11×10 6 T/yr, Etiope and Ciccioli, 2009; Etiope et al., 2008). According to climatologists’ prediction, if the concentration of greenhouse gases in the atmosphere increases, the Earth’s temperature will increase considerably during the next decades. For this reason, it can cause changes in local climate, loss of arable land and a potential increase in sea level (Kopf, 2003). 8
Page 1: Seismoacoustic Study of the Shallow
Page 4 and 5: Table of contents Table of contents
Page 6 and 7: Abstract Abstract In recent years,
Page 8 and 9: Outline of the Dissertation Outline
Page 10 and 11: Chapter 1 Chapter 1. Introduction 1
Page 14 and 15: Chapter 1 Submarine gas seeps, pock
Page 16 and 17: Chapter 1 which have documented act
Page 18 and 19: Chapter 1 fluid migration related t
Page 20 and 21: Chapter 1 Evidence of gas seepage
Page 22 and 23: Chapter 1 The three main different
Page 24 and 25: Chapter 1 from deeper sources in th
Page 26 and 27: Chapter 1 numerous countries such a
Page 28 and 29: Chapter 1 1.5 Geological setting of
Page 30 and 31: Chapter 1 main sequences consist of
Page 32 and 33: Chapter 1 craterlike depressions wi
Page 34 and 35: Chapter 1 Jurassic - Paleogene, Upp
Page 36 and 37: Chapter 1 respectively, and one wat
Page 38 and 39: Chapter 1 During the seismic data p
Page 40 and 41: Chapter 1 1.6.2 The Parasound sedim
Page 42 and 43: Chapter 1 Caress, D.W., and Chayes,
Page 44 and 45: Chapter 1 Hovland, M., Gardner, J.V
Page 46 and 47: Chapter 1 Luo, X.R. and Vasseur, G.
Page 48 and 49: Chapter 1 Schroot, B.M., Klaver, G.
Page 50 and 51: Chapter 2 Chapter 2. Shallow Gas Tr
Page 52 and 53: Chapter 2 times. Seismically imaged
Page 54 and 55: Chapter 2 spike noise were marked a
Page 56 and 57: Chapter 2 The 2D high resolution se
Page 58 and 59: Chapter 2 Figure 4 A close-up of se
Page 60 and 61: Chapter 2 within the upper sediment
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Chapter 2 volcanoes between 66 and
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Chapter 2 Figure 7 Geo-seismic sect
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Chapter 2 In the study area, many b
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Chapter 2 volcanism could be calcul
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Chapter 2 along the feeder channel
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Chapter 2 Evpatoriya). Soviet Geol
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Chapter 3 Chapter 3. Sedimentary Ev
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Chapter 3 South (Fig. 2). The water
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Chapter 3 Figure 3 (a) Uninterprete
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Chapter 3 Seven seismic facies type
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Chapter 3 Seismic Unit 5 ranges in
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Chapter 3 3.4.3.5. Seismic Unit 2 A
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Chapter 3 Figure 11 (a) Uninterpret
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Chapter 3 Figure 13 (a) Uninterpret
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Chapter 3 boundary between the Plio
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Chapter 3 Seismic Unit 6 belongs to
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Chapter 3 subsidence was coincident
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Chapter 3 Acknowledgements We thank
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Chapter 3 Tugolesov, D.A., Gorshkov
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Chapter 4 study area at ~900 m wate
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Chapter 4 Figure 2 Bathymetry of th
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Chapter 4 University of Bremen). At
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Chapter 4 and Ridge R2 (GeoB07-139)
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Chapter 4 flares location. Anticlin
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Chapter 4 GeoB07-145. Green arrows
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Chapter 4 4.4.3.2.3. Other anomalou
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Chapter 4 Slope fan deposits with f
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Chapter 4 Figure 12 Possible locati
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Chapter 4 bulk hydrate or even high
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Chapter 4 may add to gas accumulati
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Chapter 4 The narrow-beam Parasound
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Chapter 4 River fan deposits. Being
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Chapter 4 Klaucke, I., Sahling, H.,
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Chapter 4 Wagner-Friedrichs, M., 20
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Chapter 5 deposited; during lowstan
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Chapter 5 accumulations. An acousti
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Acknowledgements Acknowledgements I
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