Subsea System Design for the HPHT Kristin Field Development. Thermal and Pressure Loads.

Abstract

The HPHT field Kristin is located 16 km south west of the Åsgard field in the North Sea. The reservo ir has a temperature of 170°C and a pressure of 911 barg. The field will be produced by pressure depletion from four subsea templates tied back to a dedicated floater. Kristin is the first subsea HPHT field development. First production will be autumn 2005. The production lines, flexible risers and the topside process are protected by three separate pressure protection systems including a subsea HIPPS system. Direct electrical heating will be installed for the production line as the main hydrate control measure. For the design of the subsea system and the operational procedures for the system, special attention must be given to the high temperature and pressure. The high and low temperatures imposed on the production system by the producing fluid during normal production, shutins, restarts and operational/system failures make the design challenging. This paper will give an overview of the flow assurance work. The design and operational consequences of the high pressure and temperature loads on the wells, templatepiping, production lines, electrical cable and flexible riser are presented. Introduction The Kristin field is located offshore approximately 160 km from the Norwegian coast in the Haltenbanken area. It is a gas/condensate field with estimated recoverable reserves of 42 billion Sm3 of gas and 35 million Sm3 of condensate. The gas will be exported through the 700 km Åsgard pipeline to Kårstø for onshore processing. The condensate will be sent to Åsgard C for storage and offloading. Production start -up is planned October the 15th 2005. Figure 1 Kristin field (Available in full paper) Figure 2: Kristin field location (Available in full paper) The Kristin field is a high pressure and high temperature (HPHT) field2. The producing formations Garn and Ile are located 4500 m and 4850 m below the seabed. The Ile formation has the highest reservoir temperature and pressure of 169°C and 911 bar. The Garn formation has a temperature and pressure of 164°C and 894 bar respectively. The field will be produced by pressure depletion. The Kristin field is the first HPHT field to be developed subsea. There will be 12 subsea wells and four templates (see Figure 3). There will be four wells at template R and S and two wells at template P and N. Six 10" ID flowlines will transport the produced fluid to the Kristin semi; two flowlines each from template R & S and one flowline each from template P &N. The flowline lengths vary between 6 and 6.8 km. Flexible risers with a length of approximately 700 m connect the flowlines to the process facility on the semi. The water depth on the field varies between 315 and 375 m. The design rate for the flowlines is 4 MSm3/d of gas. Depending on the flexible riser arrival temperature, the production can be increased to 5 MSm3/d. The receiving facility is a semi submergible roduction unit.