In subsea processing systems multiphase cooling is required to meet a variety of process needs and flow assurance challenges. Required functionality might include enhanced pipeline corrosion protection, pipeline temperature control, improved process efficiency, compressor anti-surge cooling, gas dehydration and hydrate formation control. The multiphase cooler is an integral building block of the subsea processing station and is now, after the first successful year of operation on the Åsgard Subsea Compression station, a proven technology with a solid track record.
This paper will present the development and qualification of the Åsgard Subsea Compression Station Inlet Cooler. In addition, operational experience and performance data from the first year in service will be analysed and compared to previously qualified CFD tools. The paper will furthermore focus on the multiphase tests carried out during project execution to qualify the liquid distribution philosophy undertaken to guarantee liquid distribution in the cooler inlet header. Significant effort was put into ensuring sufficient MEG distribution to all cooling pipes to avoid hydrate growth under prolonged operation within the hydrate formation envelope. Three phase testing was performed validating the CFD methods used to determine the functionality of the subsea product.
The Åsgard Subsea Compression Station is located about 200 kilometres off the west coast of mid-Norway on the sea floor at a water depth of 260 meters. The station consists of two identical compressor trains receiving multiphase wellstream from the Midgard and Mikkel fields and producing towards the Åsgard B platform. The main purpose of the compressor station is to maintain production above the minimum flow requirement for the pipelines to avoid slugging and thereby increasing the field output by 280 million barrels of oil equivalents.
