Gas hydrate inhibitors

Gas hydrate inhibitors For gas and multi-phase transport to prevent hydrate deposits... 

M. Angel, K. Neubecker, and A. Sanner. Grafted polymers as gas hydrate inhibitors (Pfropfpolymerisate als Gashydratinhibitoren). Patent WO 0109271, 2001. 

W. Halliday, D. K. Clapper, and M. Smalling. New gas hydrate inhibitors for deepwater filing fluids. In Proceedings Volume, pages 201-209. lADC/SPE Drilling Conf (Dallas, TX, 373-3/6), 1998. 

W. S. Halliday, D. K. Clapper, M. R. Smalling, and R. G. Bland. Glycol derivatives and blends thereof as gas hydrate inhibitors in water base drilling, drill-in, and completion fluids. Patent WO 9840446, 1998. 

M. A. Kelland, T. M. Svartaas, and L. Dybvik. Studies on new gas hydrate inhibitors. In Proceedings Volume, pages 531-539. SPE Offshore Europe Conf (Aberdeen, Scotland, 9/5-9/8), 1995. 

Gas hydrate inhibitors. Gas hydrates, solid water clathrates containing small hydrocarbons, are problematic for oil and gas production because they can precipitate and cause line blockage. Simple cationic surfactants containing at least two butyl groups were previously developed to inhibit formation of gas hydrate precipitates in gas production lines [87]. However, similar to the situation with cationic drag reduction additives, poor toxicity profiles prevent widespread commercial acceptance. Ester quaternaries with structures somewhat similar to those used in fabric care have been claimed as hydrate inhibitors [88 ]. Additionally, certain alkylether quaternary compounds, e.g. C12-C14 alkyl polyethoxy oxypropyl tributyl ammonium bromide, were shown to have hydrate inhibition properties [89]. 

Although there are no new methane VPO competitive processes, current technology may be usehil for the production of impure methanol in remote areas for use as a hydrate inhibitor in natural gas pipelines (119,120). 

Ethylene glycol—High vapor equilibrium with gas so tend to lose to gas phase in contactor. Use as hydrate inhibitor where it can be recovered from gas by separation at temperatures below 50 I ... 

As mentioned previously, the classic additive to prevent hydrate formation is alcohol. Traditional hydrate inhibitors such as methanol and glycols have been in use for many years, but demand for cheaper methods of inhibition is great. Therefore the development of alternative, cost-effective, and environmentally acceptable hydrate inhibitors is a technologic challenge for the oil and gas production industry [947]. 

L. D. Talley and G. F. Mitchell. Application of proprietary kinetic hydrate inhibitors in gas flowlines. In Proceedings Volume, volume 3, pages 681-689.31 st Annu SPE et al Offshore Technol Conf (Houston,... 

Currently, there are three possible gas recovery processes for hydrates (1) thermal stimulation, (2) depressurization and (3) inhibitor injection. Very limited thermal stimulation and depressurization tests were reported for the Mallik natural gas hydrate reservoirs, together with numerical simulations (Moridis et al. 2004,... 

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. 

Kinetic inhibitors exhibit unusual effects on hydrate formation with implications to processing (Lee and Englezos, 2006). Gas hydrate formation experiments were conducted... 

Lee, J.D. Englezos, P. (2005) Enhancement of the Performance of Gas Hydrate Kinetic Inhibitors with Polyethylene Oxide. Chem Eng Sci, 60, 5323-5330. 

Patil, S.L., Measurements of Multiphase Gas Hydrates Phase Equilibria Effect of Inhibitors and Heavier Hydrocarbon Components, M.S. Thesis, University of Alaska (1987). Patwardhan, V.S., Kumar, A., AIChE J., 32,1419 (1986). 

Yet until these methods can be extended to all common natural gas guest components and their thermodynamic inhibitors, it will be difficult to use the programs pragmatically. To date the programs have proved the ab initio concept from an academic perspective. While extension of ab initio methods to all natural gas hydrate components can be done in principle, that task awaits the generation and maintenance of a complete program. 

The above two examples serve to illustrate that more severe conditions of gas recovery require large expense in thermodynamic inhibitors. The high pressure and high water production at Canyon Express and the steeply upward sloping lines and subfreezing temperatures of Ormen Lange are harbingers of more severe conditions in the future. There are some cases in which the cost of hydrate inhibitors determine the project viability. 

Long, J., Lederhos, J., Sum, A., Christiansen, R., Sloan, E.D., Kinetic Inhibitors of Natural Gas Hydrates, in Proc. 73rd Annual Convention of Gas Processors Association, New Orleans, LA, March 7-9, p. 85 (1994). 

Some interesting simulations have been used to investigate crystallization and deposition processes, in order to obtain a fundamental understanding of how these processes can be inhibited. The inhibition of formation of waxes (mixtures of normal alkanes that form lamellar structures) was examined.302 Gas hydrate formation has been investigated, and it was demonstrated that inhibition of methane hydrate by a octomer of polyvinylpyrrolidone was able to be simulated,302 and simulations were used to assist in developing a new class of inhibitors of gas-hydrate formation.303... 

Hawtin, R. W., Moon, C., and Rodger, P. M., Simulation of Hydrate Kinetic Inhibitors The Next Level, in The Fifth International Conference on Gas Hydrates, Trondheim, Norway, 2005, pp. 317-321. 

Figure 3 Different methods of hydrate formation (1-5) each can give a distinct perspective on certain aspects of hydrate formation l-ice + gas at T< 273K 2- ice with the temperature ramped above T = 273K 3 - amorphous ice +gas at T < 13 OK 4 and 5, either quiescent or with agitation are usually used for phase equilibrium studies and the effect of inhibitors. Simulation of natural gas hydrate requires the addition of sediment at various levels of water-sediment content.

Of particular interest to those in the natural gas industry is the phase diagram of hydrate systems in the presence of inhibitors. Fig. 3 shows the phase diagram for methane hydrates in the presence of methanol and a NaCl and KCl mixture. The solid line is the three-phase equilibrium curve for methane in pure water. As seen from Fig. 3, forming hydrates in the presence of either an alcohol or salt increases the pressure required for gas hydrate formation, at a given temperature. 

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