Modeling and simulation of hydrate thermal dissociation around gas production pipe from suboceanic sediment

• Modeling and simulation of hydrate thermal dissociation zone around the vertical buried pipe.
• The resulting differential equations were solved using orthogonal collocation method and finite element method.
• Due to lack of empirical data we compared the results of two different mathematical methods.
• The effect of parameters such as gas flow velocity in pipes was also examined.

Uncontrolled and spontaneous decomposition of methane hydrates in ocean floors can pose risks and potential problems, including damage to equipment that extracts fuel from underwater tanks. Since one of the main factors in hydrate decompositions is their heat up by oil and gas extraction and transportation pipes, this heating and decomposition of it are examined in this paper. After introduction to control volume and mathematical modeling, the developed equations of math model were solved via orthogonal collocation and finite element method and the results were compared. The results concluded to decomposed hydrate volume, released gas volume and its relevant pressure on sediment layer. In this research, the effect of gas flow velocity in pipes, porosity of sediment layers and thermal conductivity constant in pipes on two important parameter of volume of hydrate and its decomposition pattern were studied and it was realized that rising gas velocity in pipe could increase the volume of decomposed hydrate. A side of this enhancing the porosity leads to reduce the radius and volume of decomposed hydrate. Furthermore enhancing the porosity could increase conduction coefficient of heat transfer in gas media, as the increased velocity of gas shows similar effect on heat transfer rate and hydrate decomposition.