Subsea Separation and Water Injection at Luno II - Conceptual Design and Control Assessment
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Subsea separation and water re-injection give rise to production from oil fields earlierconsidered economically unfit and give a longer production life to existing fields.This thesis addresses the design of a subsea separation process where the water willbe re-injected into the reservoir as pressure support. The separators have been sized,together with an evaluation of factors influencing the separation. An analysis ofpossible future field tie-ins has also been conducted. Furthermore, a design of abasic control system was proposed and verified through dynamic simulations in thechemical simulation software, Aspen HYSYS. The design basis for this thesis was theoil field Luno II.The separation design proposed was two gravity separators in series where the firstwill do the rough separation and the second will polish the water to its required purity.The first separator was sized to have a 3 meters diameter and a 15 meters length.A conclusion could not be made with regards to the size of the second separator asthe purity of water did not vary with changing separator size, which is due to usinga feed fraction carry over for this separator.The suggested control model has been tuned, and the system process variablesshow resilience to realistic disturbances. However, the water purity varies substantiallywith small variations in process variables.