Practical model to predict gas hydrate formation, dissociation and transportability in oil and gas flowlines, A

Abstract

The oil and gas industry is facing very challenging production issues with offshore explorations in deeper and colder waters. Longer subsea tiebacks will be required to transport hydrocarbon fluids from the wellhead to production and processing platforms. The formation of solid deposits, such as gas hydrates, waxes, asphaltenes and scale, may plug the flowlines, preventing production and generating a safety hazard. The flow assurance of the produced hydrocarbon stream is a technical discipline that focuses on the design of facilities and procedures for the uninterrupted transport of reservoir fluids from the reservoir to the point of sale. The rapid formation of gas hydrates, which is promoted by typical high pressure/low temperature operation conditions in deep subsea facilities, is considered one of the most challenging flow assurance problems. A transient gas hydrate model, that predicts when and where hydrate plugs will form in flowlines, will have significant utility for the flow assurance engineers in the oil and gas industry. The Colorado School of Mines Hydrate Kinetics model (CSMHyK) was specially designed to predict hydrate formation in oil-dominated systems. The objective of this research work is to develop a comprehensive hydrate model, extending and improving the CSMHyK model for the prediction of hydrate formation and transportability in oil, water and gas-dominated systems. The mechanisms of hydrate formation and transportability in pipelines is studied through the analysis of experimental data obtained at the Center for Hydrate Research laboratory of the Colorado School of Mines and two large scale flow loops (ExxonMobil and Tulsa University flow loops). A set of conceptual pictures is developed to explain the physical phenomena of gas hydrate formation in flowlines. The mathematical models developed in this work represent a significant advancement for the prediction of hydrate plugging risk in the pipelines of oil and gas transport facilities, and can be used as a tool to design flow assurance strategies. These models improve our capability to predict hydrate formation, by considering dynamic aggregation phenomena in oil-dominated systems, flow regime transition in high water cut systems, and hydrate film growth in gas-dominated systems.