This contribution aims to publicize the efforts made in the identification of gas hydrates in the Uruguayan continental shelf, analyze the most outstanding aspects related to its energy potential, as well as include this topic in other areas of knowledge for a comprehensive understanding of the subject. The hydrates, crystalline solid formed mainly by water and natural gas, are reservoirs of carbon that occur naturally in the continents in permafrost areas, and at sea, in the offshore basins of continental margins. They contain more than twice the total carbon in the world, surpassing the conventional hydrocarbon reserves. Principal energy programs foresee its commercial exploitation by 2015. International research programs include not only the energy aspect, but studying such systems considering their participation in the global carbon cycle, climate change and benthic communities associated with them. In our country, several seismic surveys showed evidence of the presence of gas hydrates in continental shelf and the surrounding area. The first survey was carried out by Brazil in the south of the Brazilian continental shelf, ANCAP then showed the continuity of the hydrate layer on the Uruguayan continental shelf and estimated the gas potential of the mineralized layer (87 TCF). Finally, the BGR survey verified the existence of seismic evidence of gas hydrates layer and the presence of free gas below these. The typical seismic response of gas hydrate and free gas is the BSR (Bottom Simulating Reflector) and is interpreted as a positive intensity reflection, followed by a negative intensity, showing the wave passage from a high acoustic impedance zone to a low acoustic impedance zone.

The reformation of methane-ethane hydrate was observed in situ using 13C MAS NMR spectroscopy. In all reformation experiments, structure I (stable state for the reformation conditions) reformed, and the hydrate cage occupancy ratios were found to be almost the same as those predicted by a statistical thermodynamics program CSMGem, suggesting that there is no preferential formation of large or small cages on the relatively long time scale of this NMR experiment. It was also found that the reformation rate of the sample with PVCap is several times faster compared with the pure system, indicating that the presence of PVCap promotes the hydrate reformation at a high subcooling though this chemical is well-known as a good hydrate inhibitor.

Fundamental understanding of the structural changes occurring during hydrate formation and inhibition is important in the development of new strategies to control hydrates in flowlines and in inhibitor design. Neutron diffraction coupled with Empirical Potential Structure Refinement (EPSR) simulation has been used to determine the hydration structure around propane molecules before and during sII hydrate formation. The EPSR simulation results were generated by fitting neutron data (with H/D isotopic substitution) obtained from the SANDALS diffractometer at ISIS. Using this combination of techniques, the structural transformations of water around propane can be studied during propane (sII) hydrate formation. The hydration structure was found to be different in the liquid phases of the partially formed propane hydrate compared to that before any hydrate formation. The effect of a kinetic hydrate inhibitor, poly-N-pyrrolidone on the hydration structure was also examined. No significant effect was observed on the water structure in the presence of this inhibitor.

Economic studies on simulated natural gas hydrate reservoirs have been compiled to estimate the price of natural gas that may lead to economically viable production from the most promising gas hydrate accumulations. As a first estimate, large-scale production of natural gas from North American arctic region Class 1 and Class 2 hydrate deposits will be economically acceptable at gas prices over $CDN2005 10/Mscf and $CDN2005 17/Mscf, respectively, provided the cost of building a pipeline to the nearest distribution point is not prohibitively expensive. These estimates should be seen as rough lower bounds, with positive error bars of $5 and $10, respectively. While these prices represent the best available estimate, the economic evaluation of a specific project is highly dependent on the producibility of the target zone, the amount of gas in place, the associated geologic and depositional environment, existing pipeline infrastructure, and local tariffs and taxes. Class 1 hydrate deposits may be economically viable at a lower natural gas price due largely to the existing free gas, which can be produced early in project lifetimes. Of the deposit types for which hydrates are the sole source of hydrocarbons (i.e. Class 2, 3, and 4 deposits), theoretical simulation studies imply that Class 2 deposits may be the most likely to be economically viable (with all else equal) due to assistance that removal of the underlying free water will provide to depressurization; thus $CDN2005 17/Mscf can be seen as a lower bound on the natural gas price that may render hydrate deposits economically acceptable in the absence of free gas. Results from a recent analysis of the production of gas from marine hydrate deposits are also considered in this report [6]. On a rate-or-return (ROR) basis, it is approximately $2008 3/Mscf more expensive to produce from a Class 3 marine hydrates than a conventional marine gas reservoir of similar size.

The inter-conversion of methane-ethane hydrate from metastable to stable structures was studied using Raman spectroscopy. To investigate factors controlling the inter-conversion, the rate of structural transition was measured at 59% and 93% methane in ethane. The observed slower structural conversion rate in the lower methane concentration atmosphere can be explained in terms of the differences in kinetics (mass transfer of gas and water rearrangement). Also, the effect of kinetic hydrate inhibitors, poly-N-vinylpyrrolidone (PVP) and polyethylene-oxide (PEO), on the hydrate metastability was investigated at 65% and 93% methane in ethane. PVP increased the conversion rate at 65% methane in ethane (sI is thermodynamically stable), but retarded the rate at 93% methane in ethane (sII is thermodynamically stable), indicating that the function of PVP depends on hydrate structure. PEO did not affect the structural transition considerably for either methane-ethane compositions.

Gas Hydrates Markup Language (GHML) has been under development since 2003 by the CODATA Task Group “Data for Natural Gas Hydrates” as an international standard for data storage and transfer in the gas hydrates community. We describe the development of this evolving communication protocol and show examples of its implementation. In describing this protocol, we concentrate on the most recent updates that have enabled us to include ThermoML, the widely used IUPAC XML communication standard for thermodynamic data, into the GHML schema for the representation of all gas hydrate thermodynamic data. In addition, a new GHML element for the description of crystal structures is described. We then demonstrate a new tool - Guided Data Capture for Gas Hydrates - for the rapid capture of large amounts of data into GHML format. This tool is freely available and publicly licensed for use by any gas hydrate data producer or collector interested in using the GHML format. An effort will be made to achieve a consensus between scientific journals publishing thermophysical and structural data for gas hydrates to recommend their authors use this new software tool in order to generate GHML data files at the time of the submission of scientific articles. Finally, we will demonstrate how this format can be used to advantage when accessing data from a web-based resource by showing on-line access to GHML files for gas hydrates through a web service.

The chloride anion is known to be the most abundant salt ion in sea water. At the regions such as ODP Sites 1249 and 1250 the highly enriched chloride concentration is observed in a zone extended from near the sediment surface (~1 mbsf) to depths about 25 mbsf. Here, we designed the in-situ electric circuit system for measuring chloride concentration within reliable accuracy. In the cylindrical cell the 5-10 tubes having holes on the wall and electrodes were equipped around clay mixture. The open holes were made to regulate to a certain degree the interface area between methane gas and clay sample. As may be anticipated, the chloride concentration abnormally increased under fast rate condition for forming methane hydrate, but no noticeable concentration change was detected under relatively low rate. In fact, the present experiment seems to be a lot deficient to investigate the ion diffusion and moreover does not fully reflect the real deep-sea floor condition, but the meaningful results for describing the abnormal salinity enrichment might be drawn. The physical effects of chloride anions on surface morphologies of methane hydrate formed in the sediments were additionally examined with the Field Emission-Scanning Electronic Microscope (FE-SEM).

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.

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.

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.