Estudo experimental de formação de hidratos de gás em simulação de parada e repartida de linhas de gás e óleo

Abstract

Gas hydrates are crystalline structures composed by water molecules interconnected by hydrogen bonds. These structures form cavities where gas molecules are occluded, stabilizing the structures. Hydrates can form at high pressure and low temperatures above ice-forming temperature, conditions frequently encountered in oil and gas production lines in subsea wells. Therefore, oil and gas production lines are designed in order to avoid hydrate formation plugs, in normal production (flow) operations, by adding inhibitors, installing thermal isolation and heating the pipelines. However, scheduled or emergency shutdowns, can result in conditions with a higher potential for hydrate plugs to form. Cooling of the stagnant fluid in the line due to thermal exchange with the seabed may cause the pressure and temperature conditions to enter the hydrate forming zone. During start-up of the line, the shearing caused due to the flow and the increased pressure can contribute to the rapid formation of hydrate plugs. Knowing the parameters that influence the formation of hydrates and the involved phenomena are important to develop and improve techniques of inhibition of hydrate plug formation in transient regime. The present work aims to study the formation of hydrate plugs in transient operations by performing experiments in two different experimental setups (the pressure cell coupled to the rheometer and the rocking cell), in a two-phase system (water and gas) and three-phase system (water, oil and gas). Variables such as temperature, pressure, water cut, shear and influence and efficacy of anti-agglomerants were evaluated. Based on the experimental results, the influence of variables tested were evaluated and trends of the morphology of the hydrate crystals formed were identified. Besides a theoretical model of how the formation of hydrate plugs occurs in transient operations was proposed.