Production of Heavy Crude Oil: Topside Experiences on Grane

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper OTC 18240, "Production of Heavy Crude Oil - Topside Experiences on Grane," by S. Husoy and S. Hatlem, Norsk Hydro A/S, prepared for the 2006 Offshore Technology Conference, Houston, 1–4 May. Grane field production started in September 2003. Oil is exported to the onshore terminal at Sture in a 28-in. 212-km-long pipeline. Gas for injection is imported in an 18-in. 50-km-long pipeline from the Heimdal field center. Grane is the first oil field on the Norwegian continental shelf producing heavy crude. Close cooperation between Norsk Hydro's operations department, project-development team, contractors, and partners forms the basis for completing the Grane facilities on schedule, below budget, and without any serious incidents. Introduction Grane is the tenth field put into production by Norsk Hydro and is the first heavy-crude-oil (19°API) field on the Norwegian Continental Shelf. The full-length paper presents some of the challenges and experiences that Norsk Hydro as an operator has faced during field development and the production ramp-up period. Most of the challenges were well known beforehand, and the facility and organization were prepared accordingly. However, some of these challenges were underestimated. The production facility, including the organization, has been able to use the flexibility present to adjust directly or prepare temporary solutions while permanent solutions were developed and implemented. Environmental Focus The platform was designed to meet the zero-discharge philosophy of the operator. A disposal well was drilled as part of the predrilling campaign. This well was completed with 13 3/8-in. casing to an Oligocene sand reservoir 500 m true vertical depth above the oil reservoir. A drill-cutting slurrification unit in the drilling module grinds all drill cuttings and creates a seawater-based slurry. This slurry is injected into the disposal well. A disposal well for produced water was drilled as the first platform-drilled well and delivers produced water to the same formation as the drill cuttings. No produced water is discharged to the sea under normal operation. Water treatment includes degassing and hydrocyclones. Grane is allowed to direct 10% of yearly produced water to sea; however, the water-injection system uptime was more than 95% in 2005. The energy requirement for heating the oil is met by use of a waste-heat recovery unit that recovers energy from the exhaust of the turbines. This energy is transferred into the separation process by use of compact heaters. Heat transfer also is achieved from produced water before injection and from the crude before it enters the export pumps. The wellstream has a 70°C temperature entering the first-stage separator. Because sufficient separation of the crude is not achieved at this low temperature, heat is supplied upstream of the second-stage separator where inlet temperature is increased to 90 to 110°C.