Gas Hydrate Formation in Drilling Mud Characterized With DSC Technique

摘要

Gas hydrates have been studied by petroleum industry forrnmore than 60 years, but up to now, the major part of thernresearch was linked to the problem of oil transportation,rnprevention or remediation of pipe lines plugging. Therndevelopment of deep offshore drilling has extended gasrnhydrate problem to drilling muds area. The consequences ofrnhydrate formation in drilling muds can be dramatic: loss ofrnmud rheological properties, accumulation of hydrate crystalsrnleading to plugging of the lines, the BOP or the annular,rninterruption of the drilling operations and even destruction ofrnrig equipment. To prevent these problems, operators must userndrilling muds (WBM or OBM) with thermodynamic inhibitorsrnof hydrate formation as salts and glycols, which causernimportant problems of density adjustment, corrosion andrntoxicity. The usual way to determine the thermodynamicrnconditions of hydrate formation in drilling mud formulations isrnto use batch reactors or thermodynamic models validated fromrnPVT experiments on simple or model fluids.rnAn innovative methodology was elaborated using DifferentialrnScanning Calorimetry (DSC) to determine the thermodynamicrnequilibrium properties and kinetics of hydrate formation inrnmud formulations, particularly in the presence of largernamounts of mineral. This technique allows the measurement ofrnheat transfers as a function of time, temperature and pressurernand thus detects phase transitions. We have shown recentlyrnthat this rapid, versatile, easy to use technique permits torndetermine the dangerous zones for hydrate appearance. Wernpresent here new results of hydrate characterization. UsingrnDSC, hydrate appearance in several drilling mudsrnformulations (WBM or OBM) was shown and quantified. Therninfluence of gas composition I.e. methane or natural gas onrnhydrate formation has been studied for different mudrncontinuous phases, the effectiveness of several inhibitors wasrnmeasured. A methodology using isothermal experiments tornquantify kinetics of the formation of hydrate was proposed, thernbubbling of gas into the measuring cell allowing to simulaternagitation and progressive gas incorporation. Effect of time andrntemperature are by this way quantified. Through this work,rnDSC has proven to be an efficient technique for characterizingrnhydrate formation in drilling muds.