By: Kent Caudle/Champion Technologies
January/February 2011

Most Americans think of corrosion in the context of fretting about one of the many old pipelines snaking beneath or near their communities exploding without warning or suddenly releasing hazardous substances into the environment — and who can blame them?

Catastrophic failures of large-diameter pipelines transporting crude oil, natural gas and petroleum products are front-page news, especially when fatalities are involved. A recent front-page article in the Houston Chronicle proclaimed the snarl of pipelines underlying the coastal Texas city to be a “hidden menace,” with some old pipeline systems unwittingly constructed using inferior welding techniques or covered with protective coatings the industry learned later could actually make pipelines more susceptible to corrosion.

Decades of hands-on experience and solution-focused R&D have enabled corrosion inhibitors to meet and resolve new challenges.

Most workers in the upstream oil and gas industry appreciate how serious corrosion issues can become for production and processing operations, as well. Production tubing and equipment, processing equipment, separators, pumps and flow lines -- wellsite facilities are literally at risk during every step in the production-handling process.

Corrosion has been a problem in the domestic oil and gas industry since at least the 1930s, when corrosion-related issues were reported mainly in low-pressure oil-production systems; although they were apparently neither widespread nor of serious economic concern. But the industry learned quickly that corrosion is driven by many mechanisms. So as domestic oil and gas activity expanded after World War II and throughout the latter half of the 20th Century, corrosion problems became more common and more severe.

Fortunately, the oil and gas industry’s knowledge of and ability to combat corrosion have more than kept pace.

Corrosion failures are costly
Today, corrosion drains tens of billions of dollars from the oil and gas industry every year in lost income and treatment costs alone.

Conditions are numerous and circumstances frequently complex in which corrosion can occur in oil and gas production, processing and pipeline systems. The principal corrodents in oil and gas production are carbon dioxide (CO2), hydrogen sulfide (H2S), oxygen, chloride ions, and bacteria, all of which use water as a medium. In addition, almost any oxygen-rich environment can nurture corrosion.

Corrosion mechanisms include:
• Electrochemical reactions involving water and oxygen, high operating temperatures,
or galvanic reactivity between two metals immersed in an electrolyte
• Acidic gases such as H2S and CO2
• Biomass generated by the biological activity of microbes contained in produced fluids
• Mineral solids precipitated through interact ion of incompatible fluids
• Sludge or reactive liquids

No metal surface or metal-alloy component of a piece of upstream equipment is immune to corrosion issues, such as top-of-line corrosion, under-deposit corrosion (UDC), microbially influenced corrosion (MIC), or pitting.

Irregular fluid flows or evolving production characteristics over the life of a well can alter corrosion conditions or even change potential corrosion mechanisms. Multiphase flows complicate the task of mitigating corrosion.

When corrosion problems can be predicted or diagnosed in a timely manner, equipment can be protected from damage and lost production minimized with chemical or mechanical remedies. If a corrosion problem is not anticipated before failure causes environmental pollution or endangers public safety, lost income and treatment costs can be the least of an energy company’s worries.

Pitting that has occurred as a result of H2S corrosion.

Corrosion-control chemistry
Development of corrosion-prediction methods and corrosion-inhibition chemistries came into their own in the 1950s. In the beginning, what have become core competencies were mostly exercises in trial and error. However, sophistication and tools in both disciplines developed rapidly on numerous fronts.

Nascent oil field chemical companies first developed rules of thumb to predict corrosion and how to control it. Gradually, as evidence and experience accumulated, oilfield chemists began to create new testing protocols to evaluate the ability of chemical substances to inhibit corrosion and to construct flow models that better simulated operating conditions at the wellsite. This more scientific approach proved many early rules of thumb to be unreliable.

During the last half of the 20th Century and first decade of the 21st Century, oilfield chemical companies have been working non-stop to develop new, even more effective methods of predicting corrosion. New corrosion-inhibition chemistries and new application strategies have been introduced to fight corrosion in the oil and gas industry.

Flow models have been re-calibrated to better reflect wellsite conditions, and testing protocols have been refined and augmented with more powerful analytic tools, including:
• Bubble tests of field fluids to evaluate the partitioning properties of water-soluble and/ or dispersible formulae
• Static autoclaves to simulate the corrosive conditions of stagnant aqueous flows in oil and gas wells; to accurately duplicate field pressures, temperatures, and acid gas compositions; to measure corrosion inhibition under alternative corrosion mechanisms; and to help determine inhibitor effectiveness and fluid partitioning behavior
• Rotating cylinder electrodes to rapidly screen corrosion inhibitors; to generate data for evaluating inhibitor dispersibility in brine; to study the mechanistic of electro-chemical corrosion; and to simulate carbon steel behavior under flow conditions
• Rotating cylinder autoclaves to replicate high liquid-velocity conditions; to simulate field system partial pressures of CO2 and H2S at high pressures and temperatures; and to determine corrosion rates by mass loss and coupon physical inspection
• Flow loops to simulate flow hydrodynamics of field pipelines for evaluation of corrosion inhibitors under defined shear-stress conditions
• Jet impingement to evaluate corrosion inhibitors under extremely high shear conditions

Metal loss can occur due to CO2 flow-induced corrosion.

More advanced testing equipment and methods used to evaluate corrosion issues include scanning electron microscopes, energy-dispersive X-ray spectroscopy, X-ray diffraction, laser profilometers, ecoclaves, pit tests and weld tests.

Advances in computing power have had a profound effect upon the analytic capabilities of oilfield chemical companies. Developments include a variety of advanced software models to forecast fluid dynamics in production tubing and surface pipelines, taking into account such variables as topographical fluid dynamics, pipeline heat-loss, phase behavior of produced liquids and gases, internal corrosion risks, corrosion rates, scale deposition tendencies and elemental sulfur deposition. Analytic capabilities also include dispersibility and emulsion testing, materials compatibility testing, foaming and viscosity tests, and pour-point testing.

Armed with cutting-edge scientific capabilities, modern oilfield chemical companies can predict corrosion problems before they occur by identifying conditions that can lead to corrosion. They can detect corrosion mechanisms when they are present, develop chemistries that can control corrosion before it becomes problematic, and determine the best application strategy for placing corrosion-inhibition chemistry wherever it will be most effective in an oil and gas production, storage, or transmission system.

Responding to industry trends
Two prominent industry trends have emerged. On one hand, crude oil supplies are becoming steadily heavier and more sour with more basic sediment and water (BS&W) — all characteristics that contribute to several types of corrosion mechanisms. At the opposite extreme, recent advances in directional drilling and multi-stage hydraulic fracturing are enabling access to numerous low-permeability reservoirs previously considered too risky to develop.

Ultra-low-gravity oil (oil sands in Canada, for example), must be blended with a diluent to be transported via pipeline. However, heavy oil blends and diluted bitumen contain BS&W made up of complex mixtures of waxes, asphaltenes, clays, silica, water and bacteria in micro-emulsions. Lab tests have demonstrated that some solid particulates found in heavy oil are more corrosive than others, and researchers are focused on finding out why.

Champion Technologies is working to evaluate the corrosion tendencies of various solids matrices found in heavy oil. We also are working cooperatively with several pipeline companies to design tests that will better represent specific pipeline corrosion issues with regard to solids deposition. Research has revealed that some corrosion inhibitor-surfactant packages control internal corrosion within solids matrices. Tests have shown treating exposed metal surfaces with inhibitor before solids can accumulate is the most effective way to prevent internal corrosion.

The extremely high pressures generated by hydraulic fracturing of gas shale and other low-permeability reservoirs present a unique problem for delivering chemical treatments of all types. By formulating corrosion-inhibiting chemistries into stable chemical products with the physical properties required for injection downhole, Champion has been able to develop a simple-to-implement batch method for protecting hydraulically fractured wells from corrosion during flowback.

The treatment program allows preventative chemicals (for Wolfberry wells, the corrosion inhibitor most frequently prescribed is a water-soluble amine salt with excellent surfactant and anti-foulant properties), to be forced deep into stimulated zones as constituents of fluids injected during the fracturing process. Extremely small amounts of inhibitor are then produced back to the surface throughout the flowback period and for several more months after the well is placed on production.
Inevitably, new corrosion issues will arise as the oil and gas industry continues pursing prospects in more hostile, difficult-to-produce downhole environments. When corrosion challenges occur, oilfield specialty chemical companies will be there with the knowledge, experience, tools and resolve to formulate new corrosion-fighting chemistries and to develop methods of application necessary to enable a solution.

ABOUT THE AUTHOR: Kent Caudle a technical representative in the western region of Champion Technologies, where he serves as a project lead for major proposals and critical projects in the Permian Basin; provides technical training for company account representatives, and presents training seminars for various customers. A Champion employee for the past six years, Caudle focuses on problem solving, account profitability, and product line consolidation.