Heat Transfer and Well Bore Stability Analysis in Hydrate Bearing Zone in the East Sea, South Korea.

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Abstract For sustainable development and to feed the world's energy demand continuous supply of fuel resources is of utmost important. Wells drilled in deep waters and permafrost regions contain challenging gas hydrate bearing formations. The oil industry has made certain advancements by drilling and casing gas hydrates bearing formation safely. However, when a well gets deeper gas hydrates start dissociation behind the casing due to heat transfer from the heated mud. The objective of this study is to analyze the heat transfer to these formations and drilling parameters effecting heat transfer. We developed a wellbore temperature simulator to model the temperature profile in deep formations and to determine the disturbance due to the circulation of the heated mud. We used the range of hydrate dissociation for the wellbore stability analysis to monitor the disturbance caused in gas hydrate bearing formations. The stability analysis shows that a well is in a great danger, if we are drilling deep formations through gas hydrates. On the basis of wellbore stability analyses we suggest to insulate the outer surface of casing for controlling the heat transfer and dissociation of gas hydrates. The suggested approach is found to be very useful for decreasing heat transfer and consequently reducing gas hydrates dissociation and for stabilizing the well in deep water and permafrost regions. Introduction Gas hydrates are the solid crystalline compounds with a well-defined structure that consists of a cage network of water molecules with hydrocarbon mainly methane trapped inside these cages. These hydrates form at certain temperature and pressure conditions. The temperature for gas hydrate formation is above the freezing point of water. These naturally occurring gas hydrates can exist in deep water at relatively shallow depths, below the sea floor or at terrestrial locations within and beneath deep permafrost (Sloan, 1998). Major portion of gas hydrates occur in oceans due to the methanogenesis in sub-ocean sediments. The parameters which affect the formation of gas hydrates in the subsea sediments are temperature, pressure, organic content, water salinity, sediments characteristics and presence of geological features. Worldwide increasing energy demand, raising energy prices and declining hydrocarbon reserves are increasing the exploitation of oil and gas. For this, a number of Exploration and Production companies are searching for hydrocarbons in terrestrial and harsh environments. These environments lie at low temperature and high pressure conditions which coexist in sediments, making gas and water to form a gas hydrate.