Flow assurance

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

The chemical reactions creating buildups of scale that can clog a well can be replicated in a chemical lab, but researchers are finding many more variables on the surfaces of pipes that need to be considered.

Source: IPTC 17953.

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.

The explanations offered include: low spots between ridges provide points for strong attachments, raised surfaces shelter crystals in depressions from shear forces, and the differences in the elevation combined with a surface that repels water (hydrophobic or oil wet) can promote scale development.

Surfaces that repel water in a well are likely to acquire a coat of oil, which is a plus for scale avoidance. In lab tests where they changed the wettability, “that has a massive impact on scale,” she said.

But Neville said a student at the University of Leeds would soon be defending a thesis covering the “subtleties” of how an oily surface can affect scaling.

Those who follow the work by Neville and others said it will significantly change how the oil industry ensures its pipe remains flowing in the future. When teaching industry classes on analyzing the potential for scale growth, A.J. Gerbino, vice president for consumer success at OLI Systems, talks about research in progress and “I tell them this is the state of science. When you retire, this is the stuff you will have been looking at in your career.”

Work in Progress

While much of the work at the institute is long term, it has advised a joint industry project (JIP) formed by ConocoPhillips, Equinor, and Total to look for ways to reduce damage to subsea control valves.

Corrosion and scale growth that can freeze the moving parts in these valves designed to shut off the flow in an emergency are a safety hazard and a maintenance headache for offshore oil companies. To ensure the valves work, operators periodically replace them, which is an expensive job in deep water. A paper from the institute looked at a study it did for the JIP on how various coatings altered crystal attachment and growth. (IPTC 17953).

Scale crystals on coated surfaces after 2 hours in brines rich in carbonates and sulfates. Source: IPTC 17953.


Neville said researchers are trying to understand interactions observed on surfaces, and mentioned a paper in an earlier session on frontier chemical technologies that looked at the “synergies and antagonisms among different chemical treatments to treat scale growth.”

She was referring to a presentation by Myles Jordan, a principal consultant for Nalco Champion, who concluded that certain pairs of scale inhibitors were significantly more effective than when either component was used on its own. These cocktails could save money by using lower-cost ingredients or decreasing the volume required for treatment (SPE 193613).

Combinations could also allow chemicals that reduce the environmental impact. The testing showed that a mixture of a degradable scale inhibitor polyaspartic acid (PASP) and phosphate ester could exceed an 80% effectiveness level against sulfite scale, particularly barite sulfate, required by customers.

“The performance of an environmentally acceptable scale inhibitor chemical [PASP] can be enhanced. It will allow us to look at more environmentally friendly, effective materials,” said Jordan.

The paper cautioned that the lab testing done did not reveal why combinations were effective, and field testing will be needed to verify if a promising combination will be effective against specific brines in different wells.

Further Reading

Surface Inorganic Scale Formation in Oil and Gas Industry: As Adhesion and Deposition Processes by Mohsen Vazirian, Thibaut V.J. Charpentier, and Anne Neville, Institute of Functional Surfaces; Mônica de Oliveira Penna, Petrobras Research and Development Center.

IPTC 17953 Comparison of Characteristic of Anti-Scaling Coating for Subsurface Safety Valve for Use in Oil and Gas Industry by Salima Baraka-Lokmane, Total; Thibaut V.J. Charpentier and Anne Neville, University of Leeds; Christian Hurtevent, Total; et al.

SPE 193613 Investigation into the Synergistic Interaction of a Range of Generic Scale Inhibitors for Improved Sulphate Scale Control in North Sea Topside Processes by Myles Jordan, Erin Temple, Anita Sham, et al., Nalco Champion, An Ecolab Company.