Differential Scanning Calorimetry: A New Technique To Characterize Hydrate Formation in Drilling Muds

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Abstract
Summary: With the increasing number of deep offshore drilling operations, operators and service companies are confronted by technical challenges ever growing in complexity. Extreme conditions encountered at these depths require an adaptation of the drilling muds. In particular, the range of temperatures and pressures encountered (as low as ‒1°C and up to 400 bar) is favorable for the formation of gas hydrates. Gas hydrates are solid structures formed from water and gas; water contained in drilling muds under certain temperature and pressure conditions will form solid cages that entrap the gas molecules. Formation of these solid gas hydrates is liable to plug kill and chokelines as well as the annular and may cause interruption of the drilling operation and even destruction of rig equipment. Deep offshore drilling operators are aware of this problem, and some operational solutions and drilling mud formulations have been proposed and utilized, but when extreme water depths are attained, classical inhibitor solutions alone may be ineffective. The usual way to determine the thermodynamic conditions of the formation of gas hydrates in drilling mud formulations is to use a pressure/volume/temperature (PVT) cell. This technique requires heavy instrumentation and often does not permit work with a whole formulation (especially in the presence of solids). Moreover, PVT cells do not give a quantitative evaluation of the kinetic properties of gas hydrate formation. In this work, we present experiments using differential scanning calorimetry (DSC) to determine the thermodynamic equilibrium properties of methane hydrate in calcium chloride solutions. Additionally, thermograms of an emulsion and a complete drilling mud are presented that show the possibility of characterizing hydrate thermodynamics in complex systems as synthetic mud formulations. This technique is easy to use, and, when correctly interpreted, it enables the dangerous zones for hydrate formation to be determined.

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