Methane gas hydrate

J. S. Parent and P. R. Bishnoi. Investigations into the nucleation behaviour of methane gas hydrates. Chem Eng Commun, 144 51-64, February 1996. 

Natural gas (methane) can be obtained from gas hydrates. Gas hydrates are also called clathrates or methane hydrates. Gas hydrates are potentially one of the most important energy resources for the future. Methane gas hydrates are increasingly considered a potential energy resource. Methane gas hydrates are crystalline solids formed by combination of methane and water at low temperatures and high pressures. Gas hydrates have an iee-hke crystalline lattiee of water molecules with methane molecules trapped inside. Enormous reserves of hydrates can be foimd imder eontinental shelves and on land under permafrost. The amount of organic... 

Jamalludin, A.K.M. Kalogerakis, N. Bishnoi, PR. (1989). Modelling decomposition of a synthetic core of methane gas hydrate by coupling intrinsic kinetics with heat transferrates. Can. J. Chem. Eng., 67, 948-955. 

Other vast yet untapped reserves of natural gas (methane) are locked up as hydrates under the permafrost in Siberia. Methane gas hydrates are inclusion... 

Pecher, I.A., Waite, W.F., Winters, W.J., Mason, D.H., Physical properties and rock physics models of sediment containing natural and laboratory-formed methane gas hydrate. Am. Mineral., 89, 1221 (2004). 

The activation of methane [1] is also included as one of the most desired yet not technically viable reactions. Abundant amounts of methane occur with crude oil and as gas in remote locations it is also produced in large quantities during hydrocarbon processing. A large fraction of this methane is flared, because economical use or transportation is not possible. This gas and the abundant resources of methane gas hydrates would make a very suitable feedstock for higher hydrocarbons, if its activation to produce molecules other than synthesis gas were feasible. Despite enormous fundamental and practical efforts [1-5], no applicable method has yet been found for creation of ethylene, methanol, or formaldehyde from methane. 

Clarke, M.A. Bishnoi, P.R. Determination of the activation energy and intrinsic rate constant of methane gas hydrate decomposition. Can. J. Chem. Eng. 2001, 79, 143-147. 

Methane gas hydrates are formed from liquid water by the following reaction ... 

Winters W J, Pecher I A, Waite W F, et al. 2004. Physical Properties and Rock Physics Models of Sediment Containing Natural and Laboratory-Formed Methane Gas Hydrate. American Mineralogist, 89(8-9) 1221-1227. 

Winters W J, Waite W F, Mason D H, et al. 2007. Methane Gas Hydrate Effect on Sediment Acoustic and Strength Properties. Journal of Petroleum Science and Engineering, 56(1-3) 127-135. 

Keywords methane gas hydrate, centrifugal experiments, stratum stability, failure process... 

Englezos, P., Kalogerakis, N., Dholababhai, P.D. and Bishnoi, P.R., 1987a. Kinetics of fonuation of methane and ethane gas hydrates. Chemical Engineering Science, 42(11), 2647-2658. 

Methane gas-Ethylene liquid cross exchanger 25 20 26.2 Uq drops to 10 after fouling with hydrate... 

Methane gas-propane liquid cross exchanger 25 17.9 19.7 Uq drops to 13 after fouling with hydrate ice. 

Gas hydrates are an ice-like material which is constituted of methane molecules encaged in a cluster of water molecules and held together by hydrogen bonds. This material occurs in large underground deposits found beneath the ocean floor on continental margins and in places north of the arctic circle such as Siberia. It is estimated that gas hydrate deposits contain twice as much carbon as all other fossil fuels on earth. This source, if proven feasible for recovery, could be a future energy as well as chemical source for petrochemicals. 

Non-conventional gas is natural gas found in unusual underground conditions, such as very impermeable reservoirs which require massive stimulation in order to be recovered, or in underground occurrences of gas hydrates, or dissolved in formation water, or coal-bed methane, or gas from in-situ gasification of coal. 

For the gas hydrates it is not possible to make an entirely unambiguous comparison of the observed heat of hydrate formation from ice (or water) and the gaseous solute with the calculated energy of binding of the solute in the ft lattice, because AH = Hfi—Ha is not known. If one assumes AH = 0, it is found that the hydrates of krypton, xenon, methane, and ethane have heats of formation which agree within the experimental error with the energies calculated from Eq. 39 for details the reader is referred to ref. 30. 

Gas hydrates are a special form of clathrates. Here water is the host molecule. The first gas hydrate (with chlorine) was described in 1818 by Sir Humphrey Davy. Naturally-occurring gas hydrates in Siberia are methane hydrates. 

P. M. Rodger, T. R. Forester, and W. Smith. Simulations of the methane hydrate/methane gas interface near hydrate forming conditions. Fluid Phase Equilibria, 116(l-2) 326—332, 1995. 

Gas hydrates are non-stoichiometric crystals formed by the enclosure of molecules like methane, carbon dioxide and hydrogen sulfide inside cages formed by hydrogen-bonded water molecules. There are more than 100 compounds (guests) that can combine with water (host) and form hydrates. Formation of gas hydrates is a problem in oil and gas operations because it causes plugging of the pipelines and other facilities. On the other hand natural methane hydrate exists in vast quantities in the earth s crust and is regarded as a future energy resource. 

A mechanistic model for the kinetics of gas hydrate formation was proposed by Englezos et al. (1987). The model contains one adjustable parameter for each gas hydrate forming substance. The parameters for methane and ethane were determined from experimental data in a semi-batch agitated gas-liquid vessel. During a typical experiment in such a vessel one monitors the rate of methane or ethane gas consumption, the temperature and the pressure. Gas hydrate formation is a crystallization process but the fact that it occurs from a gas-liquid system under pressure makes it difficult to measure and monitor in situ the particle size and particle size distribution as well as the concentration of the methane or ethane in the water phase. 

Uddin et al. (2008b) conducted several depressurization simulations for the Mallik 5L-38 well. Their results showed that the Mallik gas hydrate layer with its underlying aquifer could yield significant amounts of gas originating entirely from gas hydrates, the volumes of which increased with the production rate. However, large amounts of water were also produced. Sensitivity studies indicated that the methane release from the hydrate accumulations increased with the decomposition surface area, the initial hydrate stability field (P-T conditions), and the thermal conductivity of the formation. Methane production appears to be less sensitive to the specific heat of the rock and of the gas hydrate. 

The combination of C02 injection and methane production over specific PT regimes allows the heat effects of C02 hydrate formation and methane hydrate decomposition to nullify each other resulting in a sustainable delivery process which both reduces C02 emissions to combat global warming and recovers methane to supplement the declining reserves of conventional natural gas (Fig. 4). This gas hydrate phase-behaviour in response to the dissociation and formation processes clearly demonstrates the potential of C02 enhanced CH4 recovery from the Mallik gas hydrate deposit. 

Just as oil, natural gas is also categorised as conventional and unconventional. Unlike crude oil, however, natural gas deposits are normally classified according to the economic or technical approach, i.e., all occurrences that are currently extract-able under economic conditions are considered conventional, whereas the rest are termed unconventional. Conventional natural gas includes non-associated gas from gas reservoirs in which there is little or no crude oil, as well as associated gas , which is produced from oil wells the latter can exist separately from oil in the formation (free gas, also known as cap gas, as it lies above the oil), or dissolved in the crude oil (dissolved gas). Unconventional gas is the same substance as conventional natural gas, and only the reservoir characteristics are different and make it usually more difficult to produce. Unconventional gas comprises natural gas from coal (also known as coal-bed methane), tight gas, gas in aquifers and gas hydrates (see Fig. 3.17). It is important to mention in this context so-called stranded gas , a term which is applied to occurrences whose extraction would be technically feasible, but which are located in remote areas that at the moment cannot (yet) be economically developed (see Section 3.4.3.1). 

Hydrates are also of research interest as a source of greenhouse gases resulting from the decomposition of the trapped methane as well as for their role as a submarine geohazard, as the destabilisation of gas hydrates may initiate submarine landslides, which may cause tsunamis. The formation of gas hydrates further poses problems for gas pipelines at low temperatures, such as in deep and cold waters. 

The key to establishing gas hydrates as a significant energy resource is whether the methane gas will ever be economically and safely producible. The current state of knowledge is still too limited to allow reliable estimates on the start of an economic gas hydrate production. The BGR (2003) estimates gas hydrate resources at 500 Tm3. 

Figure 25.1 indicates that a substantial amoimt of carbon is trapped in marine sediments as frozen methane. This gas is produced in the surfece sediments by methanogens from metabolism of detrital organic matter and abiotically in more deeply buried sediments. At sufficiently low temperatures, the methane becomes encased in a cage of water molecules, fitrming a solid gas hydrate. As shown in Figure 25.3, the stability... 

Although atmospheric methane concentrations appear to have stabilized over the past few decades, melting of gas hydrates in permafrost and shallow marine sediments have the potential to rapidly release large quantities of this potent greenhouse gas. As noted in... 

Models have been developed to evalnate natnral gas production from hydrates by both depressnrization and heating methods. There are three methods to obtain methane from gas hydrates (1) the depressurization method, (2) the thermal stimulation method, and (3) the chemical inhibition method. The thermal stimulation method and the chemical inhibitor injection method are both costly procedmes, whereas the depressurization method may prove useful when applied to more than one production. 

---