Real time micelle detection in development

One important component of corrosion management is the use of corrosion inhibitors, which help protect infrastructure.

Organic film-forming corrosion inhibitors, the type of inhibitor commonly used in the upstream oil and gas industry, are unlikely to maintain their association with the metal surface for a very long time as they suffer physical forces from fluid flow.

Rather, the film is constantly being broken and must therefore be replenished by inhibitor from the bulk solution. It is important that an adequate bulk concentration is present to ensure that the film integrity is maintained.

However, what represents an adequate bulk concentration and how can this be monitored? Often the chemical dosage is determined from laboratory testing. Such testing can help in the identification of suitable chemicals and provide data on dosage. 

In the field, this dosage may then be checked with residual monitoring, which determines the amount of a formulation component in a sample of fluid. Yet conditions in the field may differ significantly from those that can be set up in the laboratory, for example with regard to pressure, temperature, and the complex mix of treatment chemicals, solids, oil, and water.

Furthermore, when systems change (for example with changing water cut, or wells being brought on or taken off line) dosage may need to be modified to remain optimal.

A tool, which determines optimum dose onsite, would be advantageous. The result would be improved integrity management, potential chemical savings, and potential benefits for oil—inwater separation, given the surfactant nature of the inhibitors.

The science

Reports have demonstrated a link between the critical micelle concentration (CMC) of surfactant-type corrosion inhibitors and the inhibitory effect. Below the CMC, the film consists of a non-continuous surface, which can be penetrated and allow corrosion to occur.

Above the CMC, the film is denser and multi-layers can form. There is a significant drop in increasing inhibitor performance at concentrations above the CMC, and so in most circumstances it can be thought of as the optimal dose of corrosion inhibitor.

Research Program

LUX Assure has worked with a major North Sea operator since 2009 to develop a corrosion inhibitor micelle detector that could be used in the field to generate near real-time data. The result of this project, CoMic, is a novel tool to improve corrosion management, which has been deployed at UK assets and further afield to improve corrosion management.

Case Study:

Production fluids may be transported between different platforms to most efficiently process them. These flow lines can be susceptible to corrosion and must be managed accordingly. In this example, the operator of a field in the North Sea had received conflicting information from traditional methods about the efficacy of the corrosion inhibitor dose.

Two corrosion detection methods were being used one of which suggested adequate protection at the pipeline exit and one which did not. The corrosion inhibitor micelle detection method was used to verify whether there was an optimum dose at entry and exit points.

Samples were taken from the sampling points at the pipeline’s entry and exit, and then transferred to the offshore laboratory. They were quickly analysed, using the CoMic instrument and LUX Assure personnel, for the presence of corrosion inhibitor micelles.

Timing is important as corrosion inhibitor micelles are known to change when left in a static oxygenated environment for the long periods associated with shipping samples, so onsite analysis is considered important to ensure accurate results.

During a first test, samples entering and exiting the pipeline were assessed. Corrosion inhibitor micelles were apparent in the brine phase of the fluids entering the pipeline, but the micelles had been consumed by the time they had arrived on the destination platform.

This analysis provided new information for the facility manager to understand the corrosion risks that existed in the pipeline.

On a follow-up visit, samples were measured from the same system again, but on this occasion a different chemical was being used to improve corrosion inhibition, and two different inhibitor dose rates were analysed (low and high).

Results suggested the presence of micelles both at the pipeline’s entry and the exit (adjustments to the instrument between analyses means that the scales on ordinate axes of figures cannot be directly compared).

The move to a higher dose resulted in an increase in micelles detected. Results of the other analyses (e.g. corrosion rate) were not available to LUX Assure, although they would have provided additional, complementary information to the operator and showed the difference in corrosion rates that can be brought about by an increase in micelle content.

Accurate results from corrosion probes are dependent on access to appropriate measurement locations and can be subject to inaccuracies due to scale formation and changing flow-regimes, for example. When combined with the effective chemical dose, knowledge provided by micelle detection, the limitations of such data can be strengthened and more informed decisions can be made.

LUX Assure applies life science concepts to monitor difficult to detect chemicals used in the oil industry. Having recently raised significant investment in 2013, LUX plans a period of growth and transformation into a service provider. OE

Emma Perfect is LUX Assure’s chief scientific officer and managing director. She manages a team of highly skilled scientists and heads research programmes within the company. With extensive experience in assessing new technology opportunities, she is instrumental in bringing new technology into LUX Assure to build up the company’s core skills. She has a first class honours degree in Biological Sciences from University of Oxford and a PhD in plant disease.