Offshore Natural Gas Hydrate Prevention: A Promising Cavitation Method

Abstract

The high-pressure, low-temperature environment prevailing in offshore gas production and transportation is prone to forming methane hydrates inside the tubings or pipelines, resulting in reduced production and flow assurance problems. Conventional hydrate prevention relies on the continuous injection of chemicals to alter the chemical potential of the mixture stream. Such a method has the disadvantages of high cost, high toxicity, and high environmental impact. Effective hydrate prevention methods are urgently needed in offshore petroleum engineering. When fluid in nozzles or near turbine blades experiences an abrupt pressure drop, cavitation bubbles form and accumulate in the fluid. Bubbles collapse as they move downstream along the flow. As the bubble collapse, extremely high temperature and high pressure are generated, and the ambient fluid around the bubble is heated. In this paper, the thermal effect of cavitation is introduced into methane hydrate prevention. A numerical simulation of cavitation inside an injector was performed, an experimental setup was established, and the influences of various working parameters such as injection pressure, injection frequency, and fluid temperature on the thermal effect of cavitation were analyzed. Computational fluid dynamics studies have revealed the bubble collapse process. The evolution of pressure and temperature inside and outside the bubble has been analyzed and validated by previous experimental observations. Different impact chambers have been tested for their cavitation performance, and the one with a cone shape shows superior performance over the other two. In the experimental observations, an increase in the injection pressure leads to an increase in the fluid temperature. An increase in injection frequency and chamber pressure facilitates the increase in ambient fluid temperature, while a further increase in fluid temperature hinders the cavitation heating process. A tubing configuration with a cavitation method is also proposed in this paper.