At the moment, Roxar is in the process of commercializing the AQUAHAWK online and in-line oil-in-water (OIW) monitor. The monitor is based on ultrasonic technology enabling high quality monitoring of produced water for both overboard discharge and re-injection applications. The project is run in collaboration with the TNO TPD Research Institute in Holland, and is sponsored by Statoil, PDO/Shell, ENI and through the Demo2000 program run by the Norwegian Research Council.

Why online monitoring of oil-in-water?

The industry has been searching for solutions for online OIW measurements for several years. With the legislative requirements and the drive towards development of subsea and downhole separation systems, there are clear, well defined industry needs for reliable, online OIW monitoring. Both regulatory authorities and operators consider the use of online OIW monitoring to be an important enabling tool to reach the environmental targets as well as for optimization of production through improved monitoring and understanding of the process.

One of the international frontrunners defining environmental requirements for the oil and gas industry, the OSPAR Commission, adopted a new recommendation in 2001 "OSPAR Recommendation 2001/1 for the Management of Produced Water from Offshore Installations." The recommendation was considered to be a breakthrough on the issue of offshore discharge of produced water.

Key points of the recommendation in relation to performance standards and reference OIW analysis method include:

• No individual offshore installation should exceed a performance standard for dispersed oil of 40.04 ppm (40 mg/l) for produced water discharged into the sea. By the end of year 2006 this will be reduced to 30.03 ppm (30 mg/l); and
• Each Contracting Party to achieve 15% reduction of oil overboard by year 2006 compared to the equivalent in the year 2000.

Current work related to produced water issues is mainly focused on meeting the OSPAR requirements and various national regulations including the Norwegian SFT, defining requirements to achieve "Zero harmful discharges" by end of 2005.

The technology behind

The Roxar AQUAHAWK is an ultrasonic particle monitor developed to quantitatively measure small amounts of oil and/or solid particles in water, based on a patented ultrasonic diffraction technique. The technology characterizes suspensions and is especially suitable for low to extremely low oil or solids concentrations. It covers a range where conventional techniques (e.g. ultrasonic transmission techniques) fail.

The development was initiated in the mid '80s, driven by the need of a method to detect yeast particles in the production of beer. The technology has been further developed by TNO in collaboration with Shell International E&P for OIW monitoring applications since the mid '90s.

This measurement technique is now being industrialized so that the AQUAHAWK OIW monitor will become available as a fully field acceptable product. The project is strongly focused towards industry requirements for field instruments, and ease of operation and maintenance through self-diagnostics and auto-calibration procedures, inline with Roxar's technology portfolio.

The AQUAHAWK technology is based on an acoustic pulse-echo method, utilizing a highly focused acoustic transducer. Acoustic reflection from individual particles like oil, gas and solids present in the measurement volume is used for the determination of both particle sizes and concentrations. This discrimination is based on distinct differences in the full waveform of the reflected acoustic signals. Hence, all three types of particles can be determined independently at the same time by the same sensor. This leads to the simultaneous determination of both the dispersed oil and the suspended solids content, unaffected by small gas bubbles that may be present.

What is being measured

The majority of the oil in produced water is normally carried as droplets, as opposed to dissolved components that will take significantly smaller and a much more un-predictive concentration in the water. In addition, the dissolved components in produced water have been shown to vary with different properties of the oil, and hence variation within the wells producing water might lead to deterioration in the measurement quality for such instruments. The AQUAHAWK measures the dispersed phase directly, i.e. the oil droplets.

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