- Technology Need

Re-injection of produced water is an environmentally sound and cost effective way of disposing of produced water and boosting hydrocarbons recovery. However, excessive oil concentration into a re-injection well can reduce the permeability of the reservoir, hinder re-injection and prevent full recovery of the hydrocarbons. There is therefore a requirement to continually monitor re-injection water quality both topsides and subsea. The usual specification for this service is 200-500ppm.
Monitoring of oil in water concentration in produced water re-injection lines has been identified as a key enabling technology for subsea processing systems. At present, the only available means of checking the quality of produced water subsea is through regular sampling - as employed on Norsk Hydro's Troll Pilot. This is expensive and does not facilitate a quick response to decreasing water quality. An oil in water monitor could be linked into the subsea control system to provide automatic adjustment to ensure water quality remains within specification and to signal an alarm to indicate process upsets.
In addition, it is an aim of the JIP to assess the monitor's capability to provide on-line measurement of discharge water quality. The duty for this is more onerous with a requirement to measure accurately down to <20ppm. Hence, the monitor's performance in this area will not determine the direction of the JIP.

 - Summary of Work to Date

Back in 1997 at the beginning of the CoSWaSS (Configurable Subsea Water Separation System) phase 2 JIP, the founding group of operators identified subsea oil in water monitoring as a major technology gap. A comprehensive study was undertaken to identify the best emerging or available technologies which CoSWaSS could support. The photoacoustic monitor scored very highly, particularly when later coupled with Kvaerner's proven subsea track record and commercial strength.
CoSWaSS supported conceptual design, initial laboratory characterisation and the detailed design, build and rigorous testing of a prototype OIWM at the Environmental Resource Technology flow loop in Orkney during the early part of 2000. It is considered that in the comprehensive programme of design, build and testing of this prototype, the majority of potential design issues have been encountered and either addressed or noted for further development work. The test work justified the confidence placed in the technology by the CoSWaSS participants (Amerada Hess, BP, Chevron, ExxonMobil, Norsk Agip, Norsk Hydro, Statoil, Texaco and TotalFinaElf).
Since then the huge amount of data generated has been analysed and used to profile the OIWM's operating capabilities and define remaining work to be carried out. In addition, with the surplus monies at the end of phase 2, CoSWaSS has funded a small fouling study which is looking at both cleaning mechanisms and a means of adjusting for fouling through the readout algorithm. This study is currently ongoing and the results will be made available to CoSWaSS phase 2 participants.
Concurrently with the CoSWaSS supported programme, a second prototype was built and tested at Norsk Hydro's facilities in Porsgrunn and Bergen. The results from this work yielded supporting data to the conclusions from the ERT data analysis and gave confidence in the capability of the OIWM to operate successfully within a real field development incorporating subsea pumps and valving. A small amount of study work has also been undertaken with the support of Demo 2000 to look at the feasibility of the technology being deployed downhole.
Kvaerner and Heriot-Watt are continuing to undertake assessment of the OIWM outside of the JIP particularly to confirm its response to particular parameters, such as velocity and noise.
This joint industry project aims to complete the development of Kvaerner Oilfield Products (Kvaerner) photoacoustic oil in water monitor (OIWM) through to field trials, marinisation and full commercialisation. The technical workscope is being performed by Kvaerner together with Heriot-Watt University, while JIP administration and management services are provided by OTM Consulting Ltd..