Wax/Hydrate Flow Assurance of North Sea Pipeline-Riser System Using Integrated Production Modelling

Abstract

Abstract Flow assurance problems usually impede fluid transfer across process facilities especially in low-temperature regions, where oil and gas produced contain more wax as fields mature, and hydrates form at certain temperatures and pressures in facilities transporting acidic gases produced along with hydrocarbons. This study undertook a mechanistic, compositional modelling of a subsea gas condensate pipeline-riser system in the Norwegian sector of the North Sea. The objectives were to forecast wax and hydrate problems; estimate the operating conditions necessary for formation; predict their impacts on facility throughput, well deliverability and reservoir performance; and inform the design of mitigation schemes to enhance flow assurance, production optimisation and asset integrity. Integrated production modelling (IPM) was deployed to process data extrapolated from the literature through a graphical user interface (GUI) that links different specialist software packages within the suite and considers the entire asset as a total production system from reservoir to point-of-sales. Fluid composition data from crude assays was fed into PVTp to generate the required PVT data, which was imported to GAP along with process parameters to predict wax and hydrate deposition in the pipeline-riser system. The GAP model was then connected to RESOLVE to run manual and automatic mitigation programs for wax and hydrate deposition in the system. Predicted data obtained were plotted against relevant functions to analyse the effects of these issues and the modelled mitigation schemes on production and asset integrity. A critical analysis of manual and automatic mitigation designs for each of wax and hydrate modelling is provided. Wax risk was detected by GAP at the pipeline section connecting two wells, while hydrate risk was detected at another pipeline section. Two sections were found to indicate both hydrate and wax risks. A proactive approach to wax-hydrate monitoring was thus recommended to enable the detection and troubleshooting of other production issues before they escalate. Though the present tools are based on steady state flow, they should find application in facilities operating in mature fields with declining production rates that approximate the flow regime of the simulator. The acquisition and incorporation of algorithms from dynamic simulators was also advocated to enable composite models to be built by future research and simulations run in the more practical transient state as the IPM suite undergoes regular upgrades. No previous study in the literature has been found to report the use of the modelling tools of this paper for wax-hydrate flow assurance. This study is hoped to provide unique approach to integrated flow assurance from reservoir to point of sales; a key advantage of IPM. The recommendations had informed the development of a transient simulator by the software provider.