Monitoring production


Oil in Water Monitoring – A Key Element of Production Separation Technology Today

                                                    By Erlend Blanchard, Mirmorax


The accurate measurement of oil in water is a critical element of operations today for one main reason – the continued increase in produced water as a by-product of oil & gas operations.

With 70% of the world’s production coming from mature fields and with a renewed focus on enhanced recovery techniques, such as Produced Water Re-Injection (PWRI) and water flooding, the oil & gas industry today is producing more water than oil. The growing increase in water cuts, for example, is a direct result of water flooding techniques as injected water eventually reaches the production wells.

The total discharge of produced water on the Norwegian continental shelf during 2011, for example, was 131 million m3 with the Norwegian Petroleum Directorate (NPD) predicting that this number will increase in the period up until 2015. Looking worldwide and in 2010, produced water rates exceeded hydrocarbon globally by as much as 50% and on the UK Continental Shelf this figure reached over 130% between 2011 and 2012 (Source: Genesis).

So what does this mean for oil & gas operators and oil in water monitoring?

There are two key arguments for the case for accurate oil in water monitoring today – one economic and one environmental.

The Economic Case for Oil in Water Monitoring

From an economic perspective, accurate information on the size and amount of sand and oil in produced water – whether it is reinjection, discharged or processed water – means more optimal operations, particularly during the water and oil separation and treatment processes.


The greater the detail on the specific components, concentrations and respective size distributions, for example, the more likely there will be optimum production through the enhanced design and use of separators and filters throughout the separation process.

Having accurate information and being able to control water/oil content also improves oil recovery and oil quality as well as ensuring reliable oil production estimates and the long-term economic future of the field. Such information can also negate lost revenues through produced water discharge.

There also remains a real danger to production if produced water is not carefully monitored – not just during the separation phase but throughout production. Typical problems might include the plugging of disposal wells by solid particles and suspended oil droplets, and the plugging of lines, pumps and valves due to inorganic scales.

To this end, information on sand and oil size distributions and concentrations will minimize effects such as plugging and decline in formation permeability that can have a highly negative economic effect on the field, reducing reservoir pressure and injectivity in water flooding operations and negating PWRI’s effectiveness as a secondary recovery technique.

The Environmental Case

The environmental case for oil in water monitoring is strong today also. Today, there are a number of regulators and bodies ensuring minimal oil discharge.

These include the OSPAR (Oslo/Paris) Convention, the main legal instrument overseeing international cooperation on the protection of the marine environment of the North-East Atlantic through to federal regulations in the Gulf of Mexico and bodies, such as the Norwegian State Pollution Control Authority (SFT) and US Environmental Protection Agency (EPA).

OSPAR, for example, has already set a target of ‘zero harmful discharge’ from produced water by 2020 and today, the current OSPAR limit is 30 mg of dispersed oil per litre of produced water. In the United States, according to the Environmental Protection Agency (EPA), produced water discharges must not exceed an oil daily maximum limitation of 35 mg per litre of produced water (40 CFR 435.52(b)).

In addition, OSPAR has also recently set out a new risk-based approach for operators as a means of integrating the assessments of all substances in produced water and identifying those posing the greatest unacceptable risk.

According to OSPAR, “where unacceptable environmental risks have been identified, contracting parties should review management options, evaluate measures and develop and implement site-specific actions to reduce the risks to an acceptable level.” In such circumstances, oil in water monitoring will be even more important.

From international regulations through to a company’s reputation and the importance of protecting the marine environment, the environmental argument for oil in water monitoring and reducing the liability of environmental discharges is every bit as strong as the economic one.

Oil in Water Monitoring Technologies Today

So are today’s oil in water monitoring technologies providing operators with all the information they need to meet both the economic and environmental criteria?

Traditionally, oil in water monitoring was manual, with samples taken from the produced water discharge, acidified to a low PH and then extracted through chemicals. Infrared quantification would then take place with oil content determined by the infrared absorbance of the sample extract and the total methylene (CH2) present.

Manual sampling has its limitations, however. As well as the fact that it is a highly labour-intensive process, there can be inconsistencies in the results. For example, spot samples rather than continuous samples over time are taken at just one moment in time with operators not getting the full real-time picture.

There is also potential confusion as to what constitutes ‘dissolved’ and ‘dispersed’ oil with both extracted by the extracting solvent. The result is that dissolved oil is often included in the dispersed oil content, making it more difficult for operators to effectively and accurately meet environmental requirements.

The recent emergence of online, inline oil in water monitoring technologies, however, has negated many of these limitations.

Online, inline monitoring can provide direct measurements at the dispersed and suspended phase and generate more detailed information on the size distribution and concentration of oil and sand in water. The fact that the monitoring is able to take place in real-time also provides a highly effective early warning system in terms of any production threats.

Real-time monitoring also optimizes the ongoing separation process. With any deviation, one can quickly step in so that production can continue. Separators, hydro cyclones and the type and regularity of chemical injection can all be run seamlessly with significant benefits to production.

Yet, even these technologies have their drawbacks – particularly in remote, offshore environments where there are often complex mixtures of produced water and dangers of scaling and possible contamination. In such circumstances, the accuracy and robustness of oil in water monitoring technologies are pushed to the limit.

The Rise in Acoustic-based Monitoring

It’s with these issues in mind that Mirmorax has developed an oil in water monitoring solution based on an ultrasonic measurement technique in which individual acoustic echoes from both solids and oil droplets are analyzed.

This is achieved through advanced signal processing that provides accurate information on size distribution and concentration. The amplitude of the scattered signals from each passing particle is used to characterize the produced water.

The way the system works is that a highly focused ultrasonic transducer is inserted directly into the produced water flow, enabling direct measurements on the suspended particles and dispersed oil phase. In the transducer focus, particles passing through the measurement volume will scatter the transducer beam and generate reflected waves or acoustic echoes. These acoustic signatures contain particle specific information. A large number of measurements are then performed to generate a distribution and from the distribution of these amplitudes, the particle size distribution and particle concentration can be calculated from accurate acoustic scattering models.

Furthermore, by being an ‘inline’ instrument, the monitor can provide direct measurements at the dispersed and suspended phase with more detailed information on the size distribution and concentration of oil and sand in water. The monitor caters for concentrations of 0 – 1000 + parts per million (ppm) and can provide complete size distributions ranging from two to three micrometers.

Meeting Scaling and Contamination Challenges

Many monitors, however, struggle to generate accurate measurements when there is scaling. To counteract this, the Mirmorax monitor is able to ‘sound penetrate’ material as opposed to optical based monitoring solutions that can’t. If there is an issue of oil film or scaling, the ultrasonic technology can work just as effectively and accurately because the ultrasonic energy will penetrate the layer and still transmit a signal into the produced water flow.

In addition, we have also introduced a new auto calibration feature to compensate for scale build-up and that allows for several millimeters of scale and oil to grow on the ultrasound transducer without affecting accuracy

Other recent developments include self-cleaning mechanisms that prevent the danger of thick oil clogging the system, and enhanced salinity detection, where salinity can be compensated for in the final measurements. Salinity measurement is a valuable source of data when determining the origin of water coming from multiple wells. Information about the salinity and density mix also provides the operator with verification of how much of the separation capacity is being used for each of the fields.

It is through developments such as these that the monitor can cover a wider measurement range and compensate for layers of scaling, possible contamination and salinity – issues that are particularly prevalent in offshore fields.

North Sea Installations

Last year, Mirmorax provided three of its oil-in-water monitoring units to Statoil’s Kristin Platform, where the ultrasonic pulse echo technology provides Statoil with highly accurate oil ppm measurements allowing them to monitor and optimize their produced water treatment process.

A number of other North Sea orders have also been recently signed and a trial is currently taking place in the Orkney Islands in partnership with leading operators. In another North Sea oil field, where three Oil in Water monitors were installed, the monitors managed to reduce the overall oil content in discharge water by more than 30%.

A ‘Must’ for Operators

With increased water production and discharges in the North Sea, the growth in brownfields, and stricter environmental regulations, the detailed information on the size and amount of sand and oil in produced water is an absolute ‘must’ for operators today. It’s encouraging to see that the latest in oil in water monitoring technologies are rising to the challenge.