Institute of Petroleum Engineering

Centre for Gas Hydrate Research Publications



Abstract 110
Gas Hydrates: Challenges and Opportunities to Iran's Gas/Oil Industry?
Masoudi, R., and Tohidi, B.
The 12th Iranian Researchers Conference in Europe (12th IRCE), University of Manchester Institute of Science and Technology (UMIST), Manchester, UK, 3-4 July (2004).

Gas hydrates (or clathrates) are group ice-like crystalline compounds, which form through a combination of water and suitably sized 'guest' molecules under favourable conditions, usually at low temperature and moderate to elevated pressure conditions. The pressure-temperature conditions for their formation depends on several factors, most importantly the composition of the gas and the water-rich phase. Within the clathrate lattice, water molecules form a network of hydrogen-bonded cage-like structures, enclosing the guest molecules, which generally comprise of low-molecular diameter gases (e.g., methane, ethane, propane, carbon dioxide (CO2), etc). The known clathrate structures are I, II, and H with each lattice being composed of a number of large and small cavities. In gas and petroleum exploration and production operations, clathrates pose a serious economic and safety concern. Low seabed temperatures combined with high fluid pressures promote formation of clathrates in reservoir hydrocarbon-water fluid mixtures. Hydrates can make costly and dangerous blockages in the oil and gas pipelines, subsea transfer lines, and surface separation facilities. It is speculated that, in some parts of Iran in particular in the Caspian Sea, the naturally formed hydrates in marine sediments (and possibility of hydrate formation during offshore drilling) are a very important concerns to any exploration and production operations in such area. In the Caspian Sea, the presence of deep-seated hydrocarbon reservoirs and their seepage provides the suitable conditions for the formation of thermogenic gas hydrates. As these seepages contain significant quantities of intermediate compounds, their formation can occur at much lower pressures (depths) compared to well-documented methane hydrates. Despite its importance, very little research on gas hydrates in the Caspian Sea has been conducted in Iran (Tohidi, 2003). Although hydrate formation can pose serious flow assurance problems in oil and gas industry, gas hydrates have great potential for positive applications -� turning a long-standing problem into a potential benefit. One of the important property of hydrates which makes them very attractive to be used in gas storage and transportation is their very high gas to solid ratio; 1m3 of hydrate may contain 150-180 m3 of gas (at standard conditions) depending on the pressure and temperature of production. They thus present a novel means for gas storage, transportation and delivery, with consequent potential applications in a wide variety of areas, including exploitation of remote gas fields, natural gas processing, capturing associated gas, CO2 mitigation/sequestration, desalination and water treatment, volatile organic compounds (VOC) recovery, etc. In Iran, due to the presence of huge reserves of natural gas, gas storage and transportation is a challenge to the Iranian oil and gas industry. Gas hydrate technology (Gas-to-Solid technology) could be an appropriate alternative to the well-established liquefied natural gas (LNG) technology for natural gas storage and transportation from small to medium size gas fields as LNG is only economically feasible in large-scale gas projects. In this communication, we give a summary of our previous findings including the hydrate formation and prevention challenges, a comprehensive experimental investigation and thermodynamic modelling of various conditions of gas hydrate formations and inhibitions (Tohidi et al., 2003; Masoudi et al., 2004), and the potential application of gas hydrate technology to Iran's gas storage and transportation activities.

References
Tohidi, B. (2003). Gas Hydrates in the Caspian Sea: Their Potential Importance to Iran's Exploration Activities. The 12th International Oil, Gas and Petrochemical Congress, 24-26 February 2003, Tehran, Iran.

Masoudi, R., Tohidi, B., Danesh, A., and Todd, A.C. (2004). A new approach in modelling phase equilibria and gas solubility in electrolyte solutions and its applications to gas hydrates. Fluid Phase Equilibria, 215, 163-174.

Tohidi, B., Anderson, R., Masoudi, R., Arjmandi, M., Burgass, R.W., Yang, J.H. (2003). A Review of Clathrate Hydrate Research at Heriot-Watt University. Russian Chemical Journal, 47(3), 49-58.