Li Changjun

A review of natural gas hydrates and itspipeline transportation technologies in deep water

Gas hydrates are non-stoichiometric crystalline compounds that consist of host water molecules to form cages through hydrogen bond and hydrate formation gas molecules to fill inside, and thus stabilize the crystal lattice by weak van der Waals forces. Hydrate formation gas molecules, also called as guest molecules can be methane, ethane, propane, carbon dioxide and so on which are suitable in sizes for being adsorbed in water cages. Natural gas hydrates in deep water are the unconventional natural gas resources with wide development prospects. Pipeline transportation is the key point to realize the development and utilization of natural gas hydrate resources. During the transportation, the pressure and temperature in the pipelines would change continuously which lead to the complex gas-liquid-solid three-phase flow coupled with natural gas hydrates formation and decomposition. In this paper, research progress in four main aspects were analyzed which included the distribution conditions of natural gas hydrates resources in the world, the methods of exploitation, the kinetics of natural gas hydrates formation and decomposition and the gas-liquid-solid multiphase flow. Based on the four aspects, the safety of natural gas hydrate pipeline transportation in deep water was analyzed.

Modeling and Simulation for Steady State and Transient Pipe Flow of Condensate Gas

Condensate gas is mainly demonstrated by methane. However, it also contains a lot of heavier contents like C5 or C5+ and some non-hydrocarbon mixture as well (Mokhatab et al, 2006). After recovering from gas wells, condensate gas needs liquid separation, gas purification and condensate stabilization treatment in the processing plant to meet the quality requirements. Processing plants far away from the gas well with long distances of two-phase flow in one condensate gas pipeline will take less investment than adjacent process plant with two single phase pipelines which are dry gas pipeline and liquid phase pipeline (Li, 2008). If the operation temperature somewhere in the condensate gas pipeline is lower than the gas dew point, liquid condensation would occur, subjecting the pipeline to two phase flow (Potocnik, 2010). While gas and its condensate flow simultaneously, mass transfer takes place continuously due to the change in pressure and temperature conditions. This leads to compositional changes and associated fluid property changes and also makes the hydraulic and thermal calculations of condensate gas more complex than normal gas. The condensate gas pipeline model which is established and solved based on the principle of fluid mechanics can simulate hydraulic and thermal parameters under various operation conditions. By means of technical support, this model is of great importance in the pipeline design and safety operation aspects (Mokhatab, 2009).