Fire and Ice: Gas Hydrate Transportation - A Possibility for the Caribbean Region

Abstract

Abstract Natural gas hydrates, NGH, are crystalline solids composed of water and natural gas where individual gas molecules exist within cages of water molecules, CH4.nH2O where n 5.75. NGH can contain up to 160m3 of methane per 1 m3 of hydrate. Hydrate technology development has focused on using gas hydrates to convert gas to a solid (GtS) to transport natural gas to market as a low cost solution to managing associated gas in regions lacking in gas infrastructure and/or market. There could be possibilities for NGH for transport of natural gas from Trinidad to the Caribbean Islands at volumes much less than those normally considered for LNG, but still commercial to the whole transport chain from producer to consumer. Compared to alternative technologies such as LNG and gas to liquids, GtS hydrates conversion is relatively simple, low cost and does not require complex processes or extremes of pressure or temperature. It can be small-scale, modular and particularly appropriate for offshore associated gas applications. Put simply, the hydrate production concept amounts to adding water to natural gas and ‘stirring’. However, a comprehensive understanding of hydrate behaviour is necessary to design the technology for transoceanic gas transportation. This paper describes a hydrate slurry production process and its integration into a system for delivering gas for small scale utilities in regions of the world that lack gas pipeline infrastructure. In particular, we discuss the market potential of gas transport by hydrate, present some laboratory and pilot scale studies of results on the stability of hydrates produced in a continuous stirred tank reactor, and consider the implications of these results on the process design and overall economics and the challenges to be met before the technology can be commercialised. Introduction The Caribbean Islands currently use mainly diesel, fuel oil or coal for electricity generation as they are the cheapest energy sources available. However, these fuels are environmentally unfriendly, with emission of greenhouse gases, sulphur dioxide and particulates, all of which are becoming increasingly unacceptable. The introduction of gas would widen the fuel mix, which a number of Islands wish. Gas is also ideal for use in combined cycle power plants, whose efficiency is much greater than conventional steam-cycle plants, furthermore natural gas produces less than half the CO2 emissions per unit of electricity generated compared to conventional fuels. Gas is thus seen as the premier fuel for electricity generation, but only if it can be delivered cheaper per energy unit (excluding environmental compliance premium costs) than conventional fuels. It must be remembered that 1 bbl oil contains approximately the same amount of energy as 6000 scf (170 m3) of gas, so that if the oil price is $15/bbl then at equivalent energy rates, gas needs to be less than $2.5 per thousand scf. But getting natural gas to the Caribbean markets would be expensive by pipeline or Liquefied Natural Gas (LNG), so is not yet done. Current Trinidad's Routes for Monetising Its Gas Trinidad has substantial reserves of natural gas, much of it non-associated gas, with the current estimate being over 30 trillion scf, (~1 Tsm3) with potential for much more [1,2]. Because most of it is offshore, market delivery has been problematical and prevented reservoir exploitation for many years. Non-associated gas is gas from reservoirs where gas only is in the reservoir, and associated gas is the gas produced from an oil reservoir along with oil. Crude oil cannot be produced without some associated gas also being produced. Associated gas usually has a greater percentage of the heavier hydrocarbons than non associated gas [3]. Natural gas is regarded as stranded gas if there is no current accessible market (e.g. the onshore or offshore fields where there is no pipeline) or when governments restrict the flaring of associated gas as their public perceives that it is a waste of a valuable non-renewable resource.