Injecting seawater into reservoirs for pressure maintenance and incremental enhanced oil recovery is a long established practice, normally involving water treatment processes and high pressure pumps located on platform topsides.
The next logical evolutionary step is moving closer to reality whereby the seawater would not have to make the lengthy return journey via the topsides for treatment. Instead the treatment processes would be performed alongside the injection pump at the subsea wellhead, giving operators greater flexibility in the optimal siting of subsea injection wells and removing the constraints imposed by the number of well slots available on the host platform.
Since its conception in 2002, the SWIT (Subsea Water Intake and Treatment) has gone through several phases of development. Phase 3 of the development process involved testing a full scale pilot plant on the bottom of Oslofjord in Norway from July 2009 to October 2010 (15 months). In order to monitor the solids reduction achieved by the SWIT process, an accurate method of monitoring particle sizes was required. It was felt that the ViPA had a lot to offer for monitoring of the seabed treatment system due to its on-line monitoring capabilities and its potential to be marinised for duty subsea. Of particular interest was to be able to obtain data for a range of solids variables including: solids concentration, particle sizes and optical density. This JIP enabled a topsides trial of this equipment, prior to its full marinisation.
During the test period, several different methods were used for measuring solids in the control and treated water pipelines:
• The Jorin ViPA
• Total Suspended Solids (TSS)
• Silt Density Index (SDI)
• Visual Inspection of 0.45 micron Millipore filters
• Visual inspection of solids settled out in the still room after retrieval
Dave Pinchin, CTO of Seabox, said “The most informative of the above methods was the Jorin ViPA. Live images from the ViPA video microscope system were available on a computer screen at all times. This allowed operators to physically see the solids particles, their sizes and the amounts present as well as the condition of the flow cell with respect to cleanliness. While vast amounts of data were generated it was easy to make comparisons between the influent and treated water and demonstrate the effectiveness of the SWIT.”Jorin’s Managing Director, Nick Roth, said “…we are very pleased that we have been able to participate in this trial and contribute useful information. Not only was a lot of information gathered relating to the solids removal capabilities of the SWIT treatment system, but other relevant information gathered related to the VIPA itself including remote online operation, flow cell condition and cell cleaning intervals for seawater applications, as well as methods of operation”
Dave Pinchin reported “…we are now exploring methods to enable more information to be derived from the data produced and believe we have a good understanding of how to identify biological cells and determine how effectively their cell structure is destroyed by the antioxidants generated within the SWIT. Together with Jorin we are looking to take the next logical step and enable a subsea version of the ViPA to be developed.”
Source: prlog, September 08, 2011; Image: Jorin