Recently, carbon dioxide injection into deep sea sediments has become one of the carbon dioxide mitigation methods since carbon dioxide hydrates are stable at the prevailing pressure and temperature conditions. The Black Sea, which is one of the major identified natural methane hydrate regions of the world, can be a good candidate for carbon dioxide storage in hydrate form. Injected carbon dioxide under the methane hydrate stability region will be in contact with methane hydrate which should be analyzed thoroughly in order to increase our understanding on the gaseous carbon dioxide and methane hydrate interaction. For the storage of huge amounts of CO2, geological structure must contain an impermeable barrier. In general such a barrier may consist of clay or salt. In this study, sealing efficiency of methane hydrate and long term fate of the CO2 disposal under the methane hydrate zone is investigated. In order to determine the interaction of CO2 and CH4 hydrate and the sealing efficiency of CH4 hydrate, experimental setup is prepared and various tests are performed including the CH4 hydrate formation in both bulk conditions and within sand particles, measurement of the permeability of unconsolidated sand particles that includes 30% and 50% methane hydrate saturations and injection of CO2 into the CH4 hydrate. Results of the experiments indicate that, presence of hydrate sharply decreases the permeability of the unconsolidated sand system and systems with hydrate saturations greater than 50% may act as an impermeable layer. Also, CO2-CH4 swap within the hydrate cages is observed at different experimental conditions. As a result of this study, it can be concluded that methane hydrate stability region in deep sea sediments would be a good alternative for the safe storage of CO2. Therefore, methane hydrate stability region in the Black Sea sediments can be considered for the disposal of CO2.

Hydrocarbon deposits in the form of petroleum, natural gas, and natural gas hydrates occur offshore worldwide. Electromagnetic methods that measure the electrical resistivity of sediments can be used to map, assess, and monitor these resistive targets. In particular, quantitative assessment of hydrate content in marine deposits, which form within the upper few hundred meters of seafloor, is greatly facilitated by complementing conventional seismic methods with EM data. The North-East Pacific Time-series Undersea Network Experiment (NEPTUNE) is an underwater marine observatory that provides power and network connection to a host of instruments installed on the seafloor on the Cascadia Margin offshore Vancouver Island. The observatory’s aim is to provide a platform for very long-term studies in which access to data is available on a continuous basis. For this thesis project, a transient dipole-dipole time-domain EM system was constructed and deployed on the NEPTUNE network with the goal of long-term monitoring of a well-studied hydrate deposit in the area. The instrument includes a source transmitter of electrical current and individual receivers to measure small electric field variations. The instrument is powered by the NEPTUNE observatory and data can be collected remotely by connecting to the instrument through the web. Data collected so far from the instrument are consistent with a resistive structure. The best fitting model from 1D inversion is a 36 ± 3 m thick layer of 5.3 ± 0.3 Ωm resistivity, overlaying a less resistive 0.7 ± 0.1 Ωm halfspace. Average hydrate concentration, deduced with the aid of ODP-889 well-log derived Archie’s parameters, is approximately 72% of pore space in the resistive layer, consistent with the very high concentration of gas hydrates (~80%) recovered from seafloor cores. The weekly collection of data from the instrument shows that the resistive structure has changed little since monitoring began in October of 2010.

Hydrocarbon deposits in the form of petroleum, natural gas, and natural gas hydrates occur offshore worldwide. Electromagnetic methods that measure the electrical resistivity of sediments can be used to map, assess, and monitor these resistive targets. In particular, quantitative assessment of hydrate content in marine deposits, which form within the upper few hundred meters of seafloor, is greatly facilitated by complementing conventional seismic methods with EM data. The North-East Pacific Time-series Undersea Network Experiment (NEPTUNE) is an underwater marine observatory that provides power and network connection to a host of instruments installed on the seafloor on the Cascadia Margin offshore Vancouver Island. The observatory’s aim is to provide a platform for very long-term studies in which access to data is available on a continuous basis. For this thesis project, a transient dipole-dipole time-domain EM system was constructed and deployed on the NEPTUNE network with the goal of long-term monitoring of a well-studied hydrate deposit in the area. The instrument includes a source transmitter of electrical current and individual receivers to measure small electric field variations. The instrument is powered by the NEPTUNE observatory and data can be collected remotely by connecting to the instrument through the web. Data collected so far from the instrument are consistent with a resistive structure. The best fitting model from 1D inversion is a 36 ± 3 m thick layer of 5.3 ± 0.3 Ωm resistivity, overlaying a less resistive 0.7 ± 0.1 Ωm halfspace. Average hydrate concentration, deduced with the aid of ODP-889 well-log derived Archie’s parameters, is approximately 72% of pore space in the resistive layer, consistent with the very high concentration of gas hydrates (~80%) recovered from seafloor cores. The weekly collection of data from the instrument shows that the resistive structure has changed little since monitoring began in October of 2010.

Gas hydrates have been recently recognized as a key factor affecting a number of global processes such as the climatic change, sea floor stability, etc. In this thesis we present the multidisciplinary study of gas hydrate rich sediments recovered during ODP Leg 204. The main objective of this thesis is to study how the textural characteristics of marine sediments can affect the main pathways and intensity of fluid flow and how fluid flow determines the distribution of gas hydrates in the continental margins, as well as the main geochemical processes that occur during early diagenesis.To reach these objectives, a complete sedimentary and geochemical study of 581 sediment samples from southern Hydrate Ridge was carried out. The methods and techniques that were applied include: complete textural analyses, mineralogy, physical properties and geochemistry.The southern Hydrate Ridge sediments are mainly made up of four lithofacies defined as: hemipelagites, turbidites, ash layers and debrites. Mass‐transport deposits such as turbidites and debrites are more abundant in Lithostratigraphic Unit III and II, as well as in Lithostratigraphic Unit IA in the slope basin of southern Hydrate Ridge. Some increasing trends with depth can be observed in the smectite content in the clay mineral assemblages. These features suggest that the transport in suspension of fine sediments through the California Current was more effective during the Pliocene and early Pleistocene period. Bedload transport of coarse material from local and distal areas was more effective during the middle Pleistocene and Holocene due to the tectonic reactivation of the southern Hydrate Ridge uplift. During the Pleistocene and owing to the pervasive fluctuation of sealevel, gas hydrate dissociation together with the seismic movements in the Oregon margin seems a plausible triggering mechanism for mass‐movements.The results presented here confirm that the sedimentation patterns in the Hydrate Ridge region are controlled by climate and tectonic parameters such as the regional intensity of the California Current or the local tectonic movements that lead to the uplift of the Ridge. These parameters mainly control the clay mineral distribution as well as the sedimentary facies that were produced.The sedimentary fabric of gas hydrate‐rich intervals is disturbed during core recovery due to gas hydrate dissociation. The two main disturbance fabrics generated through this process are mousselike and soupy. The gas hydrate‐rich sediments analyzed for this thesis are coarser grained in respect to the hemipelagite sediments. The coarse‐grained layers such as turbidites and ash layers could act as conduits for fluids in the southern Hydrate Ridge region because of their higher porosity and permeability. In this context, methane‐rich fluids migrate through these layers from deep in the sedimentary sequence and into the gas hydrate stability zone. A number of barium fronts have been identified in southern Hydrate Ridge sediments and interstitial waters. Barite fronts were formed as a result of the barite recycling process during early diagenesis, which is controlled by the availability of methane‐rich fluids, in situ decomposition of organic matter and the sulphate gradient. Modelling of these data shows that these processes were active at southern Hydrate Ridge for a period of up to one thousand years.A number of geochemical and sedimentological processes are proposed in this thesis as plausible mechanisms to allow the survival of the barite fronts during diagenesis. The sedimentary texture plays an important role in controlling the major fluid flow pathways in the continental margins. The temporal evolution of the fluid flow can be studied in a given area through the distribution of the mineral phases that form during early diagenesis, as well as the interstitial water composition. / EXTRACTE DE TESI:Aquesta tesi integra els resultats de l'anàlisi sedimentológica i geoquímica de sediment marins rics en hidrats de gas, recuperats durant la campanya "Ocean Drilling Program" Leg 204 en el marge d'Oregon (USA). L'objectiu principal d'aquest estudi és conèixer les característiques sedimentàries que afecten el fluxe de fluids i gasos a través del sediment i com els fluids afecten la distribució d'hidrats de gas en aquesta àrea, així com alguns processos geoquímics que operen durant la diagènesi inicial. Els mètodes i tècniques aplicats inclouen l'anàlisi de sedimentològia, mineralogia, susceptibilitat magnètica i geoquímica.Els sediments de southern Hydrate Ridge estan formats per 4 litofàcies: hemipelagita, turbidita, cendra volcànica i debrita. La sedimentació està controlada per factors climàtics i tectònics com ara la intensitat del corrent oceànic Californià o moviments tectònics locals. Aquests paràmetres exerceixen un control fonamental en la distribució dels minerals d'argila i de les fàcies sedimentàries en el marge continental. La seva evolució des del Pliocè és discutida en aquesta tesi.Els sediments analitzats rics en hidrats de gas són més grollers que els sediments hemipelàgics. Els sediments més grollers actuen com a conductes preferents per a la circulació de fluids degut a la seva porositat i permeabilitat. En aquest context, fluids rics en metà migren des dels sediments profunds cap a la zona d'estabilitat dels hidrats de gas, on possibiliten la seva formació.Diversos fronts de barita han estat identificats en els sediments de southern Hydrate Ridge. Es formen com a resultat del reciclatge de barita durant la diagènesi inicial, controlada per la presència de fluids rics en metà, la degradació de matèria orgànica i la presència de sulfat. La modelització de les dades obtinguda mostra que aquest procés va ser actiu durant un període de >1000 anys. En aquesta tesi, es discuteixen els possibles processos geoquímics i sedimentaris que permetrien la supervivència de la barita durant la diagènesis.La textura sedimentària juga un paper molt important en el flux de fluids als marges continentals. La seva evolució temporal en una àrea determinada pot ser deduïda estudiant les fases minerals que es formen durant la diagènesi.

The aim of this study is to demonstrate the possibility of production of nanocables as an alternative to the other one dimensional metal/polymer composite structures like nanowires and nanorods. There is no certain definition of nanocables / however they could be considered as assemblies of nanowires. Nanocable structure can be defined as a core-shell structure formed by a polymeric shell and a metal core that runs continuously within this shell. To produce nanocables, two main steps were carried out. Firstly, monodispersed silver metal nanoparticles to be aligned within the cable core were produced. Investigations on reduction reactions in the presence of strong and weak reducing agents and different capping agents revealed the importance of the kinetics of reduction in the production of monodispersed nanoparticles. Use of capping agents to give a positive reduction potential, resulted in the slow reduction rates that was critical for fine tuning of the final particle sizes between 1-10 nm. Hydrazine hydrate and oleylamine/ oleic acid systems were used as strong and weak reducing agents, respectively. By using weak reducing agent, monodisperse spherical silver nanoparticles with the diameter of 2.7 nm were produced. It was shown that particles with controlled diameter and size distribution can be obtained by tuning the system parameters. Secondly, particles produced as such were electrospun within the core of the polymer nanofibers and long continuous nanocables were produced. Polyvinyl pyrrolidone and polycaprolactone were used in shell part of nanocables. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), photon correlation spectroscopy (PCS), X-ray diffraction (XRD) and surface plasmon resonance spectroscopy (SPR) analyses were carried out in order to understand the mechanism by which the nanoparticles were reduced and for further characterization of the product.

Drilling operation expanded through deep water environments starting from mid-1980. As water depth increased, hydrate bearing formation in the shallow ocean floor is observed and that started to cause problems during drilling and production operations. Problems due to hydrate dissociation and forming during operations are also reported by the companies working in those environments many times. Although there are several factors affect the dissociation of shallow hydrate bearing sediments, heat flux from deeper sections of the well through shallower section during the operation is the major one. In order to mitigate that risk in this study, Black Sea is taken as a reference drilling environment. Hydrate phase boundary of the region is calculated via using actual temperature and pressure data gathered during drilling operations. Generic wellbore is defined and common drilling operation sequence is simulated in this defined wellbore. Heat transfer from section target depths to the shallow wellbore section is observed during simulations. Reducing effect of low inlet temperatures and a low circulation rate on wellbore temperatures are determined. In addition positive effect of riser boosting on depressing wellbore temperature in the well head is determined. Black Sea deep water hydrate stability zone is determined between 2210-2275m. Target depth limitation for generic well designed in drilling operations is determined as 4600m.

Gas hydrate consists of guest gas molecules encaged in water molecules. Methane is the most common guest molecule in natural hydrates. Methane hydrate forms under high fluid pressure and low temperature and is found in marine sediments or in permafrost region. Methane hydrate can be an energy resource (world reserves are estimated in 20,000 trillion m3 of CH4), contribute to global warming, or cause seafloor instability. Research documented in this thesis starts with an investigation of hydrate formation and growth in the pores, and the assessment of formation rate, tensile/adhesive strength and their impact on sediment-scale properties, including volume change during hydrate formation and dissociation. Then, emphasis is placed on identifying the advantages and limitations of different gas production strategies with emphasis on a detailed study of CH4-CO2 exchange as a unique alternative to recover CH4 gas while sequestering CO2. The research methodology combines experimental studies, particle-scale numerical simulations, and macro-scale analyses of coupled processes.

The presence of structure H (sH) methane hydrate in natural environments, in addition to the well-known structure-I (sI) and II (sII) hydrates, has recently been documented. Methane in the presence of condensates (C5-C7) forms sH hydrate at lower pressure than the sI hydrate. Thus, the occurrence of sH methane hydrate is likely to have both beneficial and negative practical implications. On the negative side, in the presence of condensate, sH hydrate may form and plug gas transmission pipelines at lower pressures than sI hydrate. On the other hand, sH hydrate can be synthesized at lower pressures and exploited to store methane. The existence of natural hydrates containing sH hydrate may also be expected in shallow offshore areas. There are at least 26 large guest molecules known as sH hydrate formers and each of them produces a sH hydrates with different properties. The hydrate stability, the cage occupancies and the rates of hydrate formation depend on the type of large molecule selected. Consequently, it is essential to understand how the host and the guest molecules interact. Studies at the molecular-level are therefore indispensable in providing information that is not obtainable from experiments or too costly to acquire. Free energy calculations are performed to determine the relative stability among different sH hydrate systems and the preferable cage occupancy. The latter would give indications of how much methane gas can be stored in the hydrate. The interaction of guest molecule inside the hydrate cage is also investigated. The results are related to the physical and chemical properties of gas hydrates observed from the experiments or reported in the literature.

The presence of gas hydrates offshore of eastern Canada has long been inferred from estimated stability zone calculations, but the physical evidence is yet to be discovered. While geophysical evidence derived from seismic and borehole logging data provides indications of hydrate occurrence in a number of areas, the results are not regionally comprehensive and, in some cases, are inconsistent. In this study, the results of systematic seismic mapping along the Scotian and Newfoundland margins are documented. An extensive set of 2-D and 3-D, single and multi-channel, seismic reflection data comprising ~45,000 line-km was analyzed for possible evidence of hydrate. Bottom simulating reflectors (including one double BSR) were identified at five different sites, ranging between 300 and 600 m below the seafloor and in water depths of 1000 to 2900 m. The combined area of the five BSRs is 1720 km2, which comprises a small proportion of the theoretical stability zone area along the Scotian and Newfoundland margins (~635,000 km2). The apparent paucity of BSRs may relate to the rarity of gas hydrates on the margin or may be simply due to geophysical limitations in detecting hydrate.

The presence of gas hydrates in permafrost regions has been confirmed by core samples recovered from the Mallik gas hydrate research wells located within Mackenzie Delta in the Northwest Territories of Canada. Strong vertical variations of compressional and shear velocities and weak surface seismic expressions of gas hydrates indicate that lithological heterogeneities control the lateral distribution of gas hydrates. Seismic scattering studies predict that typical horizontal scales and strong velocity contrasts due to gas hydrate concentration will generate strong forward scattering, leaving only weak energy to be captured by surface receivers. In order to understand the distribution of gas hydrates and the scattering effects on seismic waves, heterogeneous petrophysical reservoir models were constructed based on the P-wave and S-wave velocity logs. Random models with pre-determined heterogeneity scales can also be used to simulate permafrost interval as well as sediments without hydrates. Using the established relationship between hydrate concentration and P-wave velocity, we found that gas hydrate volume content can be determined by correlation length and Hurst number. Using the Hurst number obtained from Mallik 2L-38, and the correlation length estimated from acoustic impedance inversion, gas hydrate volume fraction in Mallik area was estimated to be 17%, approximately 7x108 m3 free gas stored in a hydrate bearing interval with 250,000 m2 lateral extension and 100 m depth. Simulations of seismic wave propagation in randomly heterogeneous models demonstrate energy loss due to scattering. With the available modeling algorithm, the impact of heterogeneity scales on seismic scattering and optimum acquisition geometries will be investigated in future studies.