OFFLOADING NORNE OIL (WAXY OIL) FROM STORAGE TANKS ON THE NOFO OIL SPILL RESPONSE VESSELS

Abstract

ABSTRACT The oil from the Norne field at the Norwegian continental shelf presented new challenges to the Norwegian oil spill contingency. Because of its high wax content and high pour point, under some conditions the oil could not be collected with the weir skimmers that traditionally are used in Norwegian offshore oil spill contingency. An intensive development project was carried out through which new recovery concepts were developed for the collection of this oil. Having found a satisfying solution to the oil recovery problem, there were concerns with the ability to offload Nome oil from the storage tanks on the Norsk Oljevernforening For Operatorselskap (NOFO) oil spill response vessels. Det Norske Vertias (DNV) was contracted to assess the offloading capability of four of the vessels in the NOFO pool. Because of the oil's unique properties, it was not trusted that standard methodology for calculating pressure drop in pipes and fittings would provide satisfying accuracy for this oil. Therefore, a pumpability test was conducted on a full-scale copy (somewhat simplified) of one of the offloading systems, in which pressure drops and pumping rates were measured using 30 m3 of emulsified Nome oil. Based on the test findings, a modified method for estimating pressure drop in pipes pumping the Nome oil was established, taking into account the highly non-Newtonian behavior of the oil. The new method was later applied to estimate Nome offloading capacity from a number of tanks on four NOFO vessels. This paper describes the work conducted and the methodology that was established for estimating offloading capability. As an example, the results obtained applying the method to one of the oil spill response vessels are outlined.