Prediction of Gas Hydrates Formation with DSC Technique

With the increasing number of deep offshore drilling operations, operators and service companies are now faced with new problems related to the possible formation of gas hydrates in drilling muds. Actually, the appearance of gas hydrate crystals in drilling fluids can lead to dreadful effects and safety problems, like modification of mud rheological properties, interruption of the drilling operations due to plugging and even destruction of rig equipment when gas hydrates dissociate. Propulsion of gas hydrate plugs at very high velocity is also a great risk. To prevent these problems, formulations of drilling muds (WBM or OBM) have to be optimized with thermodynamic inhibitors of hydrate formation (salts and glycols), which cause important problems of density adjustment, corrosion and toxicity. In previous papers (SPE 62962, 71379), an innovative calorimetric technique (DSC) was presented to characterize hydrate formation in drilling mud up to 100 bar. This rapid, easy and reliable technique was applied to fluids of increasing complexity, from solutions and emulsions to complete oil-base and water-base muds. Results were validated from classical PVT measurements. In this study, this work was continued on thermodynamic properties of hydrate formation in complex solutions. The main objective was to establish phase diagrams of ternary and quaternary mixtures (water-CH₄-salt and water-CH₄-salt-glycol) and also to understand the mechanisms that govern hydrate formation in such mixtures. In parallel, a new microcalorimeter was developed, that allows measurements on gas hydrates up to 400 bar, whatever the mud composition (WBM or OBM). This apparatus can analyze complete muds, in presence of solids, and is designed to be implemented on drilling platforms. Hence, it will be possible to follow the risk for hydrates formation as a function of drilling conditions on site. Furthermore, this apparatus will allow the establishment of a database on different muds. A coupling of this database with a software that calculates the thermal profile along the riser should give birth to a predictive method for gas hydrate formation risks.