An increasing number of offshore oil and gas developments can be made viable with long-distance tiebacks by eliminating the need to add expensive topside facilities. The main challenge in longer tiebacks is flow assurance. The temperature reduction as the fluid is transported longer distances may lead to wax deposits on the pipe wall and hydrate formations during operating or reset conditions. Waxing occurs when oil cools and solidifies in the pipeline while hydrates form at high pressures and low temperatures.
The traditional method to combat this is active heating, whether that is direct electrical heating, electrically heat traced flowline or hot water circulation in a pipeline bundle. However, Subsea 7 is pioneering an innovative cold flow system that can reduce costs.
“As tieback distances increase beyond the effective capability of active heating systems, the flow assurance strategy moves from maintaining the temperature above hydrate formation temperature to transporting under ambient seawater temperature conditions,” said Sigbjørn Daasvatn, technology program manager for Subsea 7. “We are currently assessing the boundaries of applicability for cold flow systems for various tieback distances and host platform alternatives, but the concept enables longer tiebacks at a significantly lower cost than with FPSO or platform-based processing solutions.
“Cold flow systems have game-changing potential in remote regions where there is a lack of existing infrastructure or where manned processing facilities are not possible,” Daasvatn added.