The Scotian margin of the east coast of Canada has a large theoretical gas hydrate stability zone (GHSZ) yet review of extensive industry seismic data reveals a prominent BSR at only one location. 3D seismic reflection and long offset (9 km) pre-stack 2D multichannel seismic data were used to study the velocity structure and geophysical characteristics of the hydrate zone and surrounding regions. The Mohican Channel study area shows a unique double BSR at 300 to 450 m below the seafloor in the western section of the study area immediately adjacent to the Mohican Channel in a water depth range of 1500- 1930m. The topmost BSR (BSR 1) is the more extensive of the two covering an area of 150 km2 in the 3D volume and a calculated area of 280 km2 using 2D industry and single-channel seismic profiles outside of the study area. BSR 2 covers an area of ~50 km2 and occurs approximately 80m below BSR 1. A system of polygonal faults is prominent in the area and some faults appear as conduits for gas leakage into the GHSZ. Fluid escape features are common on the surface of BSR 1 but rare on the seafloor suggesting that fluid flux is at lower levels than in the past.

Results of seismic surveys are routinely used to assess the presence of methane hydrate in deep ocean sediments. Accurate estimates of hydrate distribution and volume within the sediment are required to assess the potential of gas hydrate as an energy resource, driver for climate change or as a geotechnical hazard. However, seismic velocity may be affected not only by the quantity and morphology of the hydrate, but also by the properties of the host sediment, for example its particle size distribution and grain shape. This paper reports the results of experiments conducted to determine dynamic geophysical properties such as compressional wave velocity (Vp), shear wave velocity (Vs) and their respective attenuation measurements (Qp -1 and Qs -1) of specimens with varying amounts of disseminated methane hydrate within materials with different particle shapes and sizes. The results show that the impact of disseminated hydrate is affected both by mean particle size and by particle sphericity, with the surface area of the sediment grains influencing the spread of hydrate throughout a material and therefore it’s bonding capabilities. The sediments with 10% hydrate content show the highest surface areas correspond to the least increase in seismic velocity while sediments with low surface areas gives the most.

The effects of porous medium heterogeneity on methane hydrate formation, water flow through the heterogeneous hydrate-bearing sand, and hydrate dissociation were observed in an experiment using a heterogeneous sand column with prescribed heterogeneities. X-ray computed tomography (CT) was used to monitor saturation changes in water, gas, and hydrate during hydrate formation, water flow, and hydrate dissociation. The sand column was packed in several segments having vertical and horizontal layers with two distinct grain-size sands. The CT images showed that as hydrate formed, the water and hydrate saturations were dynamically redistributed by variations in capillary strength of the medium (the tendency for a material to imbibe water), which changed with the presence and saturation of hydrate. Water preferentially flowed through fine sand near higher hydrate-saturation regions where the capillary strength was elevated relative to the lower hydrate saturation regions. Hydrate dissociation initiated by depressurization varied with different grain sizes and hydrate saturations.

It is well known that water molecules at room temperature tend to form ‘iceberg’ structures around the hydrocarbon chains of surfactant molecules dissolved in water. The entropy reduction (times the absolute temperature T) associated with the iceberg structure can be considered as the net driving force for self-assembly. More recently, many investigators measured long-range attractive forces between hydrophobic surfaces, which are likely to result from structuring of the water molecules in the vicinity of the hydrophobic surfaces. Similarly, the hydrophobic nature of most gas hydrate formers may induce ordering of water molecules in the vicinity of dissolved solutes. In the present work, the surface forces between thiolated gold surfaces have been measured using an atomic force microscope (AFM) to obtain information on the structure of the thin films of water between hydrophobic surfaces. The results have been used to develop a new concept for the formation of gas hydrates.

Design and construction of long term gas hydrate production facilities will require assessment of the in situ formation response to production at a field scale. Key parameters such as temperature and pressure are critical for the determination of phase conditions, others such as formation resistivity, formation acoustic properties and fluid mobility support the inference of gas hydrate saturation, permeability and porosity. An ability to continuously monitor the response of these parameters during the course of a production test would facilitate tracking of the dissociation front and yield valuable information for engineering design and verification of numerical reservoir simulators. Such a monitoring system has been designed, developed and introduced as a part of the Japan Oil, Gas and Metals National Corporation and Natural Resources Canada gas hydrate production testing program carried out in the winter of 2007 in the Mackenzie Delta, Canada. While the deployment of some sensors and the acquisition of some data sets were limited due to operational problems encountered during the field program, considerable experience has been gained during all phases of the research program. In particular, the acquisition and interpretation of downhole temperature profiles and changes in formation electrical potentials during testing provide insight into the production response of the reservoir and may assist in the understanding of operational conditions and related decision-making processes.

The purpose of this study is to develop the production method of CO2 hydrate-slurry. In this paper, the production process of CO2 hydrates with pure water dissolved antifreeze proteins (AFPs) is discussed. CO2 hydrate-slurry can be transported from a production place to storage one with a small pressure loss. The AFPs have made the hydrate particles be small and well disperse. It is revealed that the Type III AFPs are effective for the inhibition of structure I hydrate production. By the present experiments, the induction time for the hydrate production increases, and moreover the formation rate of the hydrate and the increasing rate of an agitator torque decrease.

Depressurization is thought to be a promising method for gas recovery from methane hydrate reservoirs, but considerable water production is expected when this method is applied to the hydrate reservoir of high initial water saturation. In this case, the prediction of water production is a critical problem. This study examined relative permeability curves during hydrate dissociation by comparing numerical simulations with laboratory experiments. Data of gas and water volumes produced during depressurization were taken from gas recovery experiments using sand-packed cores containing methane hydrates. In each experiment, hydrates were dissociated by depressurization at a constant pressure. The surrounding temperature was held constant during dissociation. The volumes of gas and water produced, the temperatures inside of the core, and the pressures at the both ends of the core were measured continuously. The experimental results were compared with numerical simulations by using the simulator MH21-HYDRES (MH21 Hydrate Reservoir Simulator). The experimental results showed that considerable volume of water was produced during hydrate dissociation, and the simulator could not reproduce the large water production when we used typical relative permeability curves such as the Corey model. To obtain good matching for the volumes of gas and water produced during hydrate dissociation, the shape of relative permeability curves was modified to express the rapid decrease in gas permeability with increasing water saturation. This result suggests that the connate water can be easily displaced by hydrate-dissociated gas and move forward in the hydrate reservoir of high initial water saturation.

Stable isotope of natural gas hydrates provides useful information of their gas sources. We investigated the isotopic fractionation of gas molecules during the formation of synthetic gas hydrates composed of methane and ethane. The gas hydrate samples were experimentally prepared in a pressure cell and isotopic compositions (δ13C and δD) of both residual and hydratebound gases were measured. δD of hydrate-bound molecules of methane and ethane hydrates was several per mil lower than that of residual gas molecules in the formation processes, while there was no difference in the case of δ13C. Effect of temperature on the isotopic fractionation was also investigated and it was found that the fractionation was effective at low temperature.

Ice-associating proteins (IAPs) are proteins that interact directly with ice crystals, either by offering a site for nucleation, i.e. ice nucleating proteins (INPs), or by binding to nascent crystals to prevent addition of more water molecules, i.e. antifreeze proteins (AFPs). AFPs have been found to inhibit the formation of clathrate-hydrates, ice-like crystalline solids composed of water-encaged guest molecules. Study of AFP-hydrate interaction is leading to a greater understanding of AFP adsorption and of the mechanism behind the “memory effect” in hydrates, wherein previously frozen crystals reform more quickly after a brief melt. AFP is currently the only known memory inhibitor. Such a low-dosage hydrate inhibitor (LDHI) is of great interest to the oil and gas industry, as hydrate formation and reformation in the field is a huge problem. Bacterial AFPs, though largely uncharacterized, may be the best candidates for large-scale production of hydrate inhibitors, given the difficulties in obtaining AFP from other sources. The popular kinetic inhibitors (KIs) polyvinylpyrrolidone (PVP) and polyvinylcaprolactam (PVCap) were used for points of comparison in experiments exploring the hydrate-inhibition activity of several ice-associating bacteria and proteins. The addition of the soil microbe, Chryseobacterium, increased the average lag-time to tetrahydrofuran (THF) hydrate formation by 14-fold, comparable to PVP or PVCap. Samples containing Pseudomonas putida, a bacterium having both ice-nucleation protein (INP) and AFP activity, had lag-times double that of the control. Solutions with P. putida and Chryseobacterium sometimes formed hydrate slurries of stunted crystal nuclei instead of solid crystals. No inhibition of memory or nucleation was noted in bacterial assays, however bacteria with INP activity was linked to unusually rapid memory reformation. Quartz crystal microbalance experiments with dissipation (QCM-D) showed that a tight adsorption to SiO2 and resistance to rinsing are correlated with a molecule’s inhibition of hydrate formation and reformation. These results support a heterogeneous nucleation model of the memory effect, and point to the affinity of AFP for heterogeneous nucleating particles as an important component of memory inhibition. / Thesis (Master, Biology) -- Queen's University, 2008-05-30 15:20:38.749

This thesis examines the sensitivity of the marine controlled source electromagnetic (CSEM) method to sub-seafloor resistivity structure, with a focus on gas hydrate and free gas occurrences. Different analysis techniques are applied with progressive sophistication to a series of studies based on simulated and measured data sets. CSEM data are modelled in time domain for one-dimensional models with gas hydrate, free gas and/or permafrost occurrences. Linearized and non-linear inversion methods are considered to infer subsurface models from CSEM data. One study applies forward modelling and singular value decomposition to estimate uncertainties for permafrost models of the Beaufort Sea. This simulation study analyzes the resolution of the CSEM data for shallow water depth which is a challenging case because the electromagnetic signature of the air-water boundary may mask the sub-seafloor response. The results reveal a blind window as a function of water depth in which the CSEM data are insensitive to the sub-seafloor structure. However, the CSEM data are sensitive to the top and the bottom of the permafrost with increasing uncertainties with depth. The next study applies non-linear Bayesian inversion to CSEM data acquired in 2005/2006 on the Northern Cascadia margin to investigate sub-seafloor resistivity structure related to gas hydrate deposits and cold vents. Bayesian inversion provides a rigorous approach to estimate model parameters and uncertainties by probabilistically sampling of the parameter space. The resulting probability density function is interpreted here in terms of posterior median models, marginal and joint marginal probability densities for model parameters and credibility intervals. The Bayesian information criterion is applied to determine the amount of structure (number of layers) that can be resolved by the data. The parameter space is sampled with the Metropolis-Hastings algorithm in principal-component space. Non-linear, probabilistic inversion allows the analysis of unknown acquisition parameters such as time delays between receiver and transmitter clocks or unknown source amplitude. The estimated posterior median models and credibility intervals from Bayesian CSEM inversion are compared to reflection seismic data to provide a more complete geological interpretation. The CSEM data on the Northern Cascadia margin generally reveal a 1 to 3 layer sediment structure. Inversion results at the landward edge of the gas hydrate stability zone indicate a sediment unconformity as well as several potential cold vents which were previously unknown. The resistivities generally increase upslope due to sediment erosion along the slope. Inversion results on the middle slope infer several vent systems close to well-known Bullseye vent in agreement with ongoing interdisciplinary observations. Finally, a trans-dimensional (trans-D) Bayesian inversion is applied to CSEM data acquired in 2012 in the German North Sea to investigate possible free gas occurrences. Trans-D inversion treats the number of layers as an additional unknown sampled probabilistically in the inversion. %over the parameter space by evaluating probabilistically the transition to a higher or lower number of interfaces. Parallel tempering is applied to increase sampling efficiency and completeness. Inversion results for the German North Sea yield resistivities at the seafloor which are typical for marine deposits, while resistivities at greater depth increase slightly and can be correlated with a transition from fine-grained marine deposits (Holocene age) to coarse-grained, glacial sediments (Pleistocene age), which is observed in a sediment core. The depths of layer interfaces estimated from CSEM inversion match the seismic reflector related to the contrast between the two depositional environments. The CSEM survey targeted a strong, phase-reversed, inclined seismic reflector within the glacial sediments, potentially indicating free gas. While interface-depth estimates from CSEM inversion do not correlate closely with this reflector, resistivities are generally elevated above the strong seismic amplitudes and the thickness of the resistive layer follows the trend of the inclined reflector. However, the uncertainties of deeper interface depth estimates increase significantly and overlap with the targeted reflector at some of the measurement sites. Relatively low resistivities of a third layer correlate with sediments of late-Miocene origin with a high gamma-ray count indicating an increased amount of fine-grained sediments with organic material. The interface at the bottom of the third layer has wide uncertainties which relates to the penetration limit of the CSEM array. / Graduate