In Situ Hydrates

Recovering In Situ Hydrates from Permafrost , Geological Survey of Canada Report. 

Fundamentals of phase equilibria (i.e., phase diagrams, early predictive methods, etc.) are listed in Chapter 4, while Chapter 5 states the more accurate, extended van der Waals and Platteeuw predictive method. Chapter 6 is an effort to gather most of the thermodynamic data for comparison with the predictive techniques of Chapters 4 and 5. Chapter 7 shows phase equilibria applications to in situ hydrate deposits. Chapter 8 illustrates common applications of these fundamental data and predictions to gas- and oil-dominated pipelines. 

Collet presents analysis of ARCO-Exxon drilling logs study for hydrated core 1988 Makogon and Kvenvolden separately estimate in situ hydrated gas at 1016 m3... 

The determination of in situ hydrates spawned a wave of research to measure hydrate properties needed for geological research and gas recovery. Several measurements were made of sonic velocity and thermal conductivity of hydrates in sediments (e.g., Stoll and Bryan, 1979 Pearson et al., 1984 Asher, 1987 Waite et al., 2005), while others measured the calorimetric properties (e.g., Rueff, 1985 Handa, 1986a,b,c,d Rueff et al 1988) needed to estimate dissociation energy. Davidson (1983) summarized hydrate properties as being similar to ice, with a few notable exceptions. Chapter 2 presents comparisons of physical property measurements of ice and hydrate. 

Chapter 7 discusses in situ hydrates in the oceans and permafrost. Seven key concepts are presented for hydrates in nature. These concepts are illustrated in four field case studies for hydrate assessment (Blake Bahama Ridge, Hydrate Ridge) and production (Messoyakha and Mallik, 2002). 

Due to the difficulty of quantifying time-dependent phenomena, the present chapter deals with hydrate formation and dissociation in laboratory systems. The principles are extended to hydrate formation/dissociation/inhibition in pipelines in Chapter 8 on hydrates in production, processing, and transportation. Dissociation in porous media, such as the assessment of gas evolution from in situ hydrate reserves using hydrate reservoir models is discussed in Chapter 7 on hydrates in the earth. The present chapter is also restricted mostly to the time-dependent properties of structures I and II due to the limited time-dependent data on structure H. The experimental tools that have been applied to measure hydrate time-dependent phenomena are presented in Chapter 6. 

Only since 1965 has mankind recognized that the formation of in situ hydrates in the geosphere predated their artificial formation (ca. 1800) by millions of years. In addition to their age, it appears that hydrates in nature are ubiquitous, with some probability of occurrence wherever methane and water are in close proximity at low temperature and elevated pressures. 

Makogon (1965) announced the presence of gas hydrates in the permafrost regions of the Soviet Union. Since that time there have been two extreme views of in situ hydrate reserves. In one view, they have been ignored, presumably because they were considered to be too dispersed and difficult to recover, relative to the conventional supply of gas. In the other view, they were thought to be pervasive in all regions of the earth with permafrost (23% of the land mass) and in thermodynamically stable regions of the oceans (90% of the oceans areal extent). With further exploration and production of gas from a hydrate reservoir, a third, more realistic estimate of the hydrate resource has evolved, as the basis for this chapter. 

However, other researchers suggest that considerably less methane can be generated by in situ hydrate production. Hyndman and Davis (1992) indicated that an unaccountably high concentration of gas was required for hydrate formation. Minshull et al. (1994), Pauli et al. (1994), and Klauda and Sandler (2005) suggest that for in-place formation, under the best conditions the maximum amount of hydrate that can fill the sediments is 3%. 

When hydrates dissociate on core retrieval, the melting hydrates provide water that is lower in chlorinity than the surrounding seawater. In situ hydrates content can be determined by measuring the degree of prewater dilution relative to a baseline assumed to represent the in situ pore water Cl- concentration prior to gas hydrate dissociation (Hesse and Harrison, 1981 Egeberg and Dickens, 1999). 

In the first principle in this chapter, it was indicated that the state-of-the-art was moving away from in situ hydrate assessment, to hydrate production. In the next section we turn to hydrate production models, which are calibrated by a number of costly field and laboratory experiments. 

The hydrate recovered consisted of methane ( 99%), with minor to trace amounts of carbon dioxide (1.22%), ethane (86 ppmv), propane (2 ppmv), with a volumetric ratio of methane to water of 154. The chlorinity concentration (57.2 mM) of water collected indicated that the sample was a mixture of 10% pore water and 90% freshwater. The gas water ratio exceeded 170, higher than any previously reported for in situ hydrates. The C1/C2 ratio was 11,500, compared to a headspace value three times lower however, both gas ratios indicate biogenic gas. 

Currently, the techniques to recover natural gas from in situ hydrate deposits are in their infancy. Possible techniques include dissociating the in situ hydrates by pressure reduction, heating, or solvent injection. Two test wells were drilled for characterization and production testing in the Mackenzie Delta region of Canada, by international efforts in 1998 and 2002. The results of the first test well have been reported. The release of production test results from the second well is expected. On 25 August 2005 from the Geological Survey of Canada. ... 

As oil and gas exploration extends into progressively deeper waters, the potential hazard posed by gas hydrates to operations is gaining increasing recognition. Hazards can be considered as arising from two possible events (1) the release of high-pressure gas trapped below the hydrate stability zone, or (2) the destabilization of in situ hydrates. A major issue is how gas hydrates alter the physical properties of sediment. The link between seafloor failure and gas... 

BnX - BnNHAc. This transformation is related to the Ritter reaction. Activation of benzyl halides by FeClj in refluxing MeCN is sufficient to bring about the displacement (and in situ hydration). 

The water sequestered in the hydrate lattice is preferentially enriched in 0 and deuterium (D), thus the isotopic composition of the water in the pore spaces collected from gas hydrate bearing sediment can provide additional information on the abundance and the characteristics of these deposits. Pore fluid samples that had been modified by hydrate decomposition upon core recovery during ODP Legs 146 (Kastner et al. 1998), and 164 (Matsumoto and Borowski 2000) provided the first field data to derive the oxygen isotope fractionation factor for in situ hydrate formation. A more comprehensive sampling... 

The weak side of the Itypothesis of crystalhzation pressure is the well known phenomenon that crystals growing in the supersaturated solution carmot exert a pressure when the other crystals can grow free, with no obstacles. To elucidate this discrepancy the hypothesis explaining the expansion as the effect of in situ hydration of anhydrous phases was proposed. It is assumed that the crystals of anhydrous phase are surrounded by the colloidal hydration products. The solution of electrolyte can migrate through the pores in colloidal gel to the surface of anhydrous phase, but there is no empty space for the crystallization of l drates formed. The... 

Bentonite (geosynthetic clay liner) (pre-hydrated or dry bentonite requiring in situ hydration) - Hydrocarbon resistance - Lower maintenance - Self-sealing properties if punctured. - Pre-hydrated can be laid at performance specification required - Requires a protection layer. - Potential hidden problems at penetrations. - Potential for drying out on slopes - In situ hydration of dry systems to achieve performance specification required - Can be uncertain - Good as geotextile mat protected by layer of soil/ stone Medium... 

The calorimetric curve upon cement hydration, which is generally continuously monitored, provides valuable kinetic information. Thus, the hydration times can be identified when further discontinuous hydration experiments, e.g. using XRD or TGA, can be carried out. There have also been interesting combinations of isothermal calorimetry and other measurement techniques published (mainly in fields other than cement science), such as the measurement of pressure, ion concentration, pH, relative humidity, rheology and chemical shrinkage (Champenois et al. 2013 Johansson and Wadso 1999 Lura et al. 2010 Minard et al. 2007 Wadso and Anderberg 2002). Recent work focused also on the calculation of heat flow curves from in situ hydration experiments done by quantitative XRD analysis (Bizzozero 2014 Hesse et al. 2011 Jansen et al. 2012a,b). 

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