As Exciting as Watching Scale Grow: Real-Time Observations Generate New Control Ideas

Abstract

Anne Neville wants engineers to look at scale buildup differently. A pipe-clogging buildup of calcium carbonate is not simply the product of reactions in a chemical stew found in a hot, pressured space to the professor at the University of Leeds. The factors controlling how and where scale grows into a problem are also a function of how fast the gas and fluids are moving, whether the flow is smooth or turbulent, and critically, the surface at the edge of the flow. A rough surface is more likely to allow scale to take hold and an oil coating can limit calcium carbonate scale, as can corrosion competing for surface space. Coatings on the pipe have an effect depending on differences that can be microscopic. As the director of the Institute of Functional Surfaces at the university’s engineering school, Neville is upfront about an obsession with every little detail related to surfaces, from new steel in the ground to the top of scale growth. “The word we keep coming back to is surface, surface, surface,” Neville said during the keynote speech at the SPE International Conference on Oilfield Chemistry. Her message at the recent meeting in Galveston, Texas, was that in the future those managing scale growth will consider many more variables. There is value in classic lab tests designed to measure which crystals form—clear glass jars are filled with water, scale-creating components, and perhaps a chemical designed to inhibit growth. But other testing will be needed because the environment in a glass jar cannot replicate the effect of all the surfaces that can alter growth in a well. “When I predict scale I want to know what kind of things make things grow and what things predict how it grows,” Neville said. To do so, the institute has developed devices to observe and measure the growth of scale crystals as it is happening. High-power magnification and ultrasensitive scales are used to quantify the results. The institute’s 75 scientists are interested in a range of topics beyond scale on surfaces, including lubrication, developing new coatings, and studying corrosion. Neville said rust provides a benchmark for the scale study work. While there are rules of thumb to estimate the rate of corrosion, there are no similar formulas for scale. With flow assurance problems such as calcium carbonate buildup, the answer depends on many variables, including competition from rust for a place on the surface. Things To Consider Researchers are looking for answers at institutions around the world. A paper by scientists from the Institute of Functional Surfaces summarizing recent advances in the understanding of scale growth offered three pages of citations. Much of this work is fundamental research, which commonly is delivered with the warning that further work is likely to complicate early findings. Rough surfaces encourage scale development, but some are more welcoming than others. Multiple theories have been offered to explain why molecules thrive on irregular surfaces, at least when viewed under magnification.