Remote determination of the hydrate content of marine sediments remains a challenging problem. In the absence of boreholes, the most commonly used approach involves the measurement of Pwave velocities from seismic experiments. A range of seismic effective medium methods has been developed to interpret these velocities in terms of hydrate content, but uncertainties about the pore-scale distribution of hydrate can lead to large uncertainties in this interpretation. Where borehole geophysical measurements are available, electrical resistivity is widely used as a proxy for hydrate content, and the measurement of resistivity using controlled source electromagnetic methods shows considerable promise. However, resistivity is commonly related to hydrate content using Archie’s law, an empirical relationship with no physical basis that has been shown to fail for hydrate-bearing sediments. We have developed an electrical effective medium method appropriate to hydrate-bearing sediments based on the application of a geometric correction to the Hashin-Shrikman conductive bound, and tested this method by making resistivity measurements on artificial sediments of known porosity. We have adapted our method to deal with anisotropic grains such as clay particles, and combined it with a well-established seismic effective medium method to develop a strategy for estimating the hydrate content of marine sediments based on a combination of seismic and electrical methods. We have applied our approach to borehole geophysical data from Integrated Ocean Drilling Program Expedition 311 on the Vancouver Island margin. Hydrate saturations were determined from resistivity logs by adjusting the geometric factor in areas of the log where hydrate was not present. This value was then used over the entire resistivity log. Hydrate saturations determined using this method match well those determined from direct measurements of the methane content of pressurized cores.

Potential applications of gas hydrates, including carbon dioxide sequestration in the deep ocean, coal bed methane–produced water treatment, storage and transportation of natural gas, and gas separations, are based on continuous, large-scale production of gas hydrates. A novel three-phase injector/reactor was developed at Oak Ridge National Laboratory for the continuous synthesis of gas hydrates. The reactor receives water and a hydrate-forming species and rapidly forms hydrate with a residence time of a few seconds. The reactor was designed to maximize interfacial area between reactants, thus minimizing mass transfer barriers and thermal effects that negatively affect conversion of reactants into hydrate. The cohesiveness and the density of the hydrate product desired for specific applications can be controlled by slight variations in the geometry of an exchangeable internal piece of the reactor, the choice of the guest gas, and by the regulation of operating parameters such as pressure, temperature, reactant ratios, and degree of emulsification. In general, spraying one reactant into the other, within the jet-break up regime, results in the highest conversions. The reactor has been field tested for ocean carbon sequestration and in the laboratory for coal-bed methane produced-water treatment using liquid carbon dioxide. In this paper, the application of the reactor for ocean carbon sequestration will be discussed.

Modeling of the onset of permafrost formation and succeeding gas hydrate formation in the changing surface temperature environment has been done for the Beaufort-Mackenzie Basin (BMB). Numerical 1D modeling is constrained by deep heat flow from deep well bottom hole temperatures, deep conductivity, present permafrost thickness and thickness of Type I gas hydrates. Latent heat effects were applied to the model for the entire ice bearing permafrost and Type I hydrate intervals. Modeling for a set of surface temperature forcing during the glacial-interglacial history including the last 14 Myr, the detailed Holocene temperature history and a consideration of future warming due to a doubling of atmospheric CO2 was performed. Two scenarios of gas formation were considered; case 1: formation of gas hydrate from gas entrapped under deep geological seals and case 2: formation of gas hydrate from gas in a free pore space simultaneously with permafrost formation. In case 1, gas hydrates could have formed at a depth of about 0.9 km only some 1 Myr ago. In case 2, the first gas hydrate formed in the depth range of 290 – 300 m shortly after 6 Myr ago when the GST dropped from -4.5 °C to -5.5. °C. The gas hydrate layer started to expand both downward and upward subsequently. More detailed modeling of the more recent glacial–interglacial history and extending into the future was done for both BMB onshore and offshore models. These models show that the gas hydrate zone, while thinning will persist under the thick body of BMB permafrost through the current interglacial warming and into the future even with a doubling of atmospheric CO2.

A HP micro DSC-VII from SETARAM was used to study the efficiency and mechanism of action of commercial kinetic inhibitors for gas-hydrate formation in drilling fluids (OBM). The main objective was to find a suitable and reliable method of screening for these chemicals. The DSC technique consists in monitoring the heat exchanges, due to phase changes (here hydrate formation or dissociation), either versus time at constant temperature or versus temperature during a heating or cooling program. All products showed a gas hydrate dissociation temperature (at a given pressure) that matched with theoretical and previously published data. Nevertheless, for some additives two thermal signals were observed on the thermograms, one that corresponds to the theoretical value and another at a higher temperature (about +4°C). This second peak is insensitive to the heating rate applied for the dissociation, but the areas ratio (1stpeak/2nd peak) changes with the additive concentration and with the driving force applied during the hydrate formation. Additionally, additive/water and additive/water/THF systems were tested. In each case, two dissociation peaks were also measured. The results allow us to disregard any kinetic effects bonded to this thermal phenomenon, and lead us to infer that some additives may induce non-classical crystalline structures of gas hydrates. To verify these results, crystallographic and spectroscopic experiments must be performed. The stabilities of these new compounds are under study.

In this paper we will discuss the first successful molecular simulation studies exploring the statesteady crystal growth of sI and sII methane hydrates. Since the molecular modeling of the crystal growth of gas hydrates has proven in the past to be very challenging, we will provide a brief overview of the simulation framework we have utilized to achieve heterogeneous growth within timescales accessible to simulation. We will probe key issues concerning the nature of the solid/liquid interface for a variety of methane hydrate systems and will make important comparisons between various properties. For example, the interface demonstrates a strong affinity for methane molecules and we find a strong tendency for water molecules to organize into cages around methane at the growing interface. The dynamical nature of the interface and its microfaceted features will be shown to be crucial in the characterization of the interface. In addition to the small and large cages characteristic of sI and sII hydrates, water cages with a 51263 arrangement were identified during the heterogeneous growth of both sI and sII methane hydrate and their potential role in cross-nucleation of methane hydrate structures will be discussed. We will describe a previously unidentified structure of methane hydrates, designate structure sK, consisting of only 51263 and 512 cages, and will also show that a polycrystalline hydrate structure consisting of sequences of sI, sII and sK elements can be obtained. In this paper we will also detail a variety of host defects observed within the grown crystals. These defects include vacant cages, multiple methane molecules trapped in large cages, as well as one or more water molecules trapped in small and large cages. Finally, preliminary results obtains for THF and CO2 hydrates will be presented and their behaviour contrasted to that of methane hydrate.

Simulation of the system behavior of hydrate-bearing geologic media involves solving fully coupled mass- and heat-balance equations. In this study, we develop a domain decomposition approach for large-scale gas hydrate simulations with coarse-granularity parallel computation. This approach partitions a simulation domain into small subdomains. The full model domain, consisting of discrete subdomains, is still simulated simultaneously by using multiple processes/processors. Each processor is dedicated to following tasks of the partitioned subdomain: updating thermophysical properties, assembling mass- and energy-balance equations, solving linear equation systems, and performing various other local computations. The linearized equation systems are solved in parallel with a parallel linear solver, using an efficient interprocess communication scheme. This new domain decomposition approach has been implemented into the TOUGH+HYDRATE code and has demonstrated excellent speedup and good scalability. In this paper, we will demonstrate applications for the new approach in simulating field-scale models for gas production from gas-hydrate deposits.

In February 2007, the U.S. Department of Energy, BP Exploration (Alaska), Inc., and the U.S. Geological Survey conducted an extensive data collection effort at the "Mount Elbert #1" gas hydrates stratigraphic test well on the Alaska North Slope (ANS). The 22-day field program acquired significant gas hydrate-bearing reservoir data, including a full suite of open-hole well logs, over 500 feet of continuous core, and open-hole formation pressure response tests. Hole conditions, and therefore log data quality, were excellent due largely to the use of chilled oilbased drilling fluids. The logging program confirmed the existence of approximately 30 m of gashydrate saturated, fine-grained sand reservoir. Gas hydrate saturations were observed to range from 60% to 75% largely as a function of reservoir quality. Continuous wire-line coring operations (the first conducted on the ANS) achieved 85% recovery through 153 meters of section, providing more than 250 subsamples for analysis. The "Mount Elbert" data collection program culminated with open-hole tests of reservoir flow and pressure responses, as well as gas and water sample collection, using Schlumberger's Modular Formation Dynamics Tester (MDT) wireline tool. Four such tests, ranging from six to twelve hours duration, were conducted. This field program demonstrated the ability to safely and efficiently conduct a research-level openhole data acquisition program in shallow, sub-permafrost sediments. The program also demonstrated the soundness of the program's pre-drill gas hydrate characterization methods and increased confidence in gas hydrate resource assessment methodologies for the ANS.

Nucleation is a stochastic process, most accurately represented by a probability distribution. Obtaining sufficient data to define this probability distribution is a laborious process. Here, we describe a novel instrument capable of the automated determination of hydrate nucleation probability under non-equilibrium conditions for a range of natural gas mixtures at pressures up to 10MPa. The instrument is based on the automated lag time apparatus (ALTA) which was developed to study the stochastic nature of nucleation in ambient pressure systems [1].We demonstrate that the probability distribution represents a robust and reproducible tool for the quantitative evaluation of hydrate formation risk under pseudo-realistic pressure conditions.

The liquid-to-crystal nucleation temperature is measured for clathrate-forming mixtures of tetrahydrofuran and water using both an automatic lag time apparatus (ALTA) and a ball screening apparatus. Our results are conclusive evidence that no so-called “memory effect” exists. Either the solid form melts fully or it does not. If it does not, then no supercooling is possible on the next cooling down of that sample, and if it does then the second cooling run and freezing on a sample is just as likely to have a colder nucleation temperature as a hotter one.

The statistics of liquid-to-crystal nucleation are measured for clathrate-forming mixtures of tetrahydrofuran and water using an automatic lag time apparatus (ALTA). We measure the nucleation temperature where a single sample is repeatedly cooled, nucleated and thawed. This is done for a series of tetrahydrofuran concentrations and in several different sample tubes since the nucleation is heterogeneous and occurring on the tube wall. The measurements are also done at the same concentrations and tubes but with an added catalyst, a single crystal of silver iodide. We discuss the need for this type of measurement if the true nucleation temperature of the clathrate is to be found. Comparisons are also made with our high pressure data on real-world clathrate formers.