SpoolSep for Subsea Produced Water Separation - Experimental Results

Abstract

Subsea Processing provides effective solutions to develop more and more challenging deepwater fields while maximizing oil recovery and optimizing the topsides. By removing most of produced water at the seabed, a subsea liquid/liquid separation station allows to eliminate the need to transport high volumes of water from deepwater mature fields production and then to debottleneck existing topside facilities and to reduce the required water treatment surface equipment. Moreover, the low subsea separation pressure reducing the back pressure on the subsea wellhead allows for an increase in oil recovery, which is a key driver for such a system. Dealing with the deepwater and high design pressures constraints, the SpoolSep, developed by Saipem for subsea gravity liquid-liquid separation, is made of several horizontal pipes working in parallel. The use of small and long diameter pipes for effective gravity separation of produced water combines robustness and efficiency. The pipes are designed as subsea spools which can be connected and disconnected individually for easy installation and maintenance. A first test campaign was performed in 2013 on a purpose built multiphase flow loop operating with air, water, and model oils at ambient conditions using a transparent SpoolSep model made of four parallel Plexiglas pipes of 200mm ID and 18m length each. Different inlet conditions, such as flowrates, water cut, gas-volume factor, shear rate on water/oil mixtures, water residence time, and spool inclination, were tested to qualify the separator efficiency and operability, resulting in a whole flow visualisation inside the pipes. Additional tests using several solid particle sizes were performed to qualify sand deposition and determine the limits of sand transport by fluid flowing inside a single spool. The paper presents the main findings of the experimental tests that validated the multiphase flow distribution inside the spools, levels control and symmetry. Moreover, the validation of the SpoolSep design criteria regarding required separation performances is presented. Main observations and key findings on tests with sand are also described. The presented work focused on the development and qualification of the fluid processing technology and does not make mention of any mechanical or structural design work.