Hydrate saturation

Naphthalenedithiol can be prepared by adding 1,5-naph-thalenedisulfonyl chloride to an ethanol solution of tin (II) chloride 2-hydrate saturated with hydrogen chloride.6 An 80% yield of the crude dithiol melting at 103° was previously reported using zinc dust and sulfuric acid.7... 

Fig. 1. Log data showing the variation of porosity, permeability, and gas hydrate saturation for the Mallik Gas Hydrate Research Program Well-5L-38 (Uddin et al. 2008b).

Kleinberg et al. (2005) and Takayama et al. (2005) show that NMR-log measurement of sediment porosity, combined with density-log measurement of porosity, is the simplest and possibly the most reliable means of obtaining accurate gas hydrate saturations. Because of the short NMR relaxation times of the water molecules in gas hydrate, they are not discriminated by the NMR logging tool, and the in situ gas hydrates would be assumed to be part of the solid matrix. Thus the NMR-calculated porosity in a gas-hydrate-bearing sediment is apparently lower than the actual porosity. With an independent source of accurate in situ porosities, such as the density-log measurements, it is possible to accurately estimate gas hydrates saturations by comparing the apparent NMR-derived porosities with the actual reservoir porosities. Collett and Lee (2005) conclude that at relatively low gas... 

Progressing from each of the above levels to the next saves 2-3 orders of magnitude in financial and time expense. So, for example, if one wished to perform a sensitivity study of methane production rate response to reservoir permeability or hydrate saturation, it is many orders of magnitude easier to do so via a model, than via a field test. 

Many modern scientific tools were applied to Mallik that were not available at the time of Messoyakha. For example, well logs had advanced substantially so that it was possible to determine, for example, the porosity, permeability, and hydrate saturation of the sediments at Mallik, which were not available at Messoyakha. In addition, reservoir models for hydrate production could be based upon well-constrained Mallik 2002 production data, such as pressure stimulation tests over constrained well intervals or thermal stimulation tests. 

Zone C (1070-1107 m) consisted of sandy silt of 3(M0% porosities and hydrate saturations of 80-90% of pore volumes. With hydrates in sand, the permeability ranged from 0.01 to 0.1 mD, becoming less than 0.1 mD in silt. 

In addition to the above suite of well logs, the newest type of log was obtained via NMR (here called CMR) as shown in Figure 7.37. In this new method, the capillary, clay-bound, and free water (on the right) as determined by the NMR log, are subtracted from the total porosity as determined by the density tool (not shown) to obtain the hydrate saturation in the middle column. 

Figure 7.41 Mallik 5L-38 gas hydrate saturations at point of thermal stimulation test. (From Hancock, S.H., et al., in Scientific Results from the Mallik 2002 Gas Hydrate Production Research Well Program, Mackenzie Delta, Northwest Territories, Canada, Geological Survey of Canada Bulletin 585, including CD (2005b). With permission.)...

Fig. 8.3 shows the mass and volume relationships for a fully hydrated, saturated paste of w/c ratio 0.5, calculated using the above expressions and values. Following Powers and Brownyard, the hydrated cement is treated from a purely volumetric standpoint as a composite of reacted cement, non-evaporable water and gel water. The specific volume of the non-evaporable water was assumed to be 0.73 x I0 -gel water to be 1.00 x 10 m kg several reasons for example, the pore solution is in reality not pure water, but an alkali hydroxide solution with a specific volume (for 0.3 M KOH) of... 

In this connection it is vitally important to carry out experiments to study the CO2 hydrate formation in freezing soils and the behaviour of frozen hydrate saturated samples under non-equilibrium conditions. 

This work presents experimental data on the CO2 hydrate formation in gas saturated wet samples under cooling conditions as well as on the hydrate decomposition kinetics in frozen C02-hydrate saturated samples. 

Our approach for studies of gas hydrate formation and decomposition in sedimentary pore space consists of two steps. The first one is devoted to the hydrate accumulation kinetics in pore space of frozen soils to obtain frozen hydrate-saturated samples. The second one concentrates on the pore hydrate dissociation kinetics in frozen soils under non-equilibrium conditions. 

As a result we have obtained frozen C02-hydrate-saturated samples. The analysis of the thermo-baric changes in the pressure chamber during the process of hydrate and ice formation allows us to localized any phase transition in the soil samples as well as to calculate the water content, the volumetrical hydrate content (Hy) and the hydrate coefficient Kh (fraction of liquid water transformed into hydrate). 

Apart from a direct observation of the gas content of frozen samples in the course of time, the study of gas releases from the frozen hydrate saturated samples at atmospheric pressure were carried out with the help of DC-1 gas meter. 

Figure 3 Kinetics of CO2 hydrate accumulation in pore media (sand with 7%o of kaolinite clay, Win=10%), Gh - hydrate saturation, - water saturation...

Decomposition kinetics of frozen hydrate-saturated samples at non-equilibrium pressure... 

In the course of the experiments described above frozen hydrate-saturated samples were obtained at temperatures of -8°C. According to our petrographic analysis they feature quite homogeneous structures and a uniform distribution of hydrate and ice in the pore space of samples. The porosity of these samples was 0.37-0.41. The hydrate saturation of the samples in equilibrium conditions before the pressure release was 0.36-0.46. The volumetric hydrate content was 15-17 %, and the hydrate coefficient between 0.7-0.75. 

An vigorous CO2 hydrate dissociation was observed in frozen hydrate saturated samples after the pressure release in the pressure chamber. The hydrate coefficient decreased 1.5-3.0 fold in 30 minutes after a pressure drop to atmospheric values. The maximum decrease was observed in the sand sample with 14% of kaolinite particles, the minimum decrease in the sand sample with 7% montmorillonite particles with 17% of initial water content. In the course of time the intensity of CO2 hydrate dissociation in frozen samples dropped sharply with even a complete stop of the dissociation process as a consequence of gas the hydrates self-preservation effect at sub-zero temperatures A... 

The mineral composition of the soil will also influence the kinetics of gas hydrates dissociation in frozen soils. Our results show, that gas hydrate formations in pore space of samples with montmorillonite particles dissociate less markedly as compared to the samples with kaolinite admixture. This influence may be explained by microstructural specificities of pore hydrate saturated samples but undoubtedly requires additional micro-morphological studies for a full understanding. 

Figure 4 Hydrate coefficient (Kh) in artificial hydrate-saturated samples (Win lO%) at a temperature of -8 C in equilibrium and non-equilibrium conditions (30 min after pressure release) 1- sand 2- sand with 7% montmorillonite clay (Win=17yo) 3- sand with 7% montmorillonite clay 4- sand Math 14% kaolinite clay...

Figure 5 CO 2 hydrate dissociation kinetic in frozen hydrate-saturated sample (sand with 7% montmorillonite clay, Wirj=10%) after pressure release to 0.1 MPa, Gh -hydrate saturation, Gj - ice saturation...

The frozen hydrate-saturated media formed during these experiments were used for a study of the CO2 hydrate decomposition kinetics in the pore space. The influence of soil mineral composition, ice content and temperature on the CO2 hydrate self-preservation effect was established. It is revealed, that a temperature decrease slows down the CO2 hydrate dissociation low negative temperatures (below -13 C) cause a complete stop of the CO2 hydrate dissociation process. It is also shown that ice forming in the remaining pore space from freezing of unreacted water enhances the CO2 hydrate self-preservation effect. 

Fig. 2. Gas isotope compositions, gas hydrate saturation and TOC in the Nankai Trough, (a) Depth-trends of of CH4 and CO2. Open symbols, PTCS samples solid symbols, headspace gas samples.

Some of the data are from Waseda et al (1998) and Waseda and Uchida (2002). (b) Depth-trend of gas hydrate saturation estimated from Cl anomalies. Data are from Uchida et al (2004). (c) Depth-trend of TOC. Some of the data are from Waseda et al (1998). 

Blake Ridge ODP Leg 164 Thick (250 m) zone (200-450 mbsf) Low (av. 5-6%, max. 25% in pore) Mud Microbial CO2 reduction 1.5% (roughly enough to explain the average hydrate saturation) Passive margin Slow pervasive flow... 

Triaxial compression test of SI hydrate bearing coal used gas 1, and the one of SII used gas 2. We adopt heating and cooling of repeated during the course of the experiment, to make distribute hydrate in coal uniformly. We adopt gas consumption calculating and resistance measuring method to controlling gas hydrate saturation at about 70%. 

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