Coating technologies extend the operation of geothermal power plants – without chemicals
Learning from the oil and gas industry, geothermal operators apply internal coatings to mitigate corrosion and scaling.
As interest in geothermal energy for electric power grows, lessons learned in the oil and gas industry become more important and relevant. Geothermal production and oil and gas production are similar in many ways. Both require drilling in harsh environments, protecting existing groundwater, efficiently moving liquid through an extensive network of tubes and pipelines, and handling massive amounts of produced water.
For decades, oil and gas production operations have struggled with two major water-related problems: corrosion and scaling. Reservoir waters generally contain high concentrations of dissolved minerals and sparingly soluble salts. As reservoir fluids are pumped from the ground, changes in temperature, pressure, and chemical composition alter the solution balances of dissolved species, causing them to precipitate and settle as scale. Scaling occurs at all stages of hydrocarbon production (upstream, midstream, and downstream). If left unchecked, scale builds up and causes blockages in wellbore perforations, casing, pipelines, pumps, valves and other equipment.
Because they deal with similar reservoir waters, geothermal operations face many of the same scaling risks. Geothermal power plant generation is typically accompanied by corrosion damage and scale formation in pipelines and electrical equipment, leading to significant reductions in system reliability and efficiency. 
A new approach to optimize the performance of geothermal power plants
Methods of controlling and preventing corrosion and scaling in industrial applications have evolved over the past 50 years. Empirical approaches and “after the fact” treatments (including chemical and/or mechanical removal of scale and replacement of heavily scaled/corroded sections) are replaced. Systematic research aims to understand the complex phenomena behind these problems and to identify measures to prevent them. Knowledge acquired in other sectors, notably oil production, contributes significantly to mitigation practices in geothermal energy.
For over 70 years, liners have played an important role in maintaining flow in hydrocarbon production systems. NOV Tuboscope’s Tube-Kote (IPC) internal plastic liners have been proven to reduce or eliminate deposits and scale buildup in many oilfield environments. By using the appropriate IPC for the application, operators are assured of a coating that provides a smooth surface, low surface energy, corrosion protection and improved flow characteristics for longer life. actives.
A proven solution in extreme production environments
Tube-Kote IPCs have extended the life of many high temperature sour oil producing fields. A producing oil well in Canada provided a unique opportunity to evaluate the effectiveness of IPCs compared to bare steel. Due to lack of inventory, the operator designed the lower part of the shaft with 884 m (2,900 ft) of IPC-lined tubing and the upper 1,882 m (6,175 ft) with L-tube. 80 nudes.
The production tube exhibited pressure loss after one year of service, which was attributed to a hole in an unlined tube joint. As a result, the entire production column was pulled and inspected. The uncoated tube contained a layer of oil and solids deposits, while the IPC tube was almost free of deposit (Figure 1).
Inspection of the pipe wall, which was performed in accordance with a color coding system designed by the American Petroleum Institute (API) known as API Spec 5CT, classified the uncoated pipe in a blue band , green and red at 46%. This indicated that the remaining wall thickness of the uncoated tube was between 70% and less than 50% of the original nominal wall thickness. The remaining uncoated tube was designated yellow band, meaning the remaining wall thickness was 85%. The hole was found in the third joint of the tube above the internally lined section of the rope.
All joints of internally coated tubes have been inspected to API standards and rated as yellow tape with at least 85% wall remaining. As a result, the original lined pipe was driven downhole with an additional 6,175 feet (1,882 m) of lined pipe. The use of IPC along the entire length of the downhole tube extended the life of the asset by more than a year without the need for additional intervention.
Figure 1 – Inspection of the casing extracted from the Canadian well showed deposits of inorganic and organic solids on the uncoated pipe, while the IPC-coated pipe was largely free of deposits.
TK-15XT L-80 coated
Such results are common in other oil operations using IPCs – and geothermal operators are taking note. NOV is currently working with several operators in the United States to research ways to extend the life and production performance of their geothermal power plants with IPC.
For more information on NOV’s IPC solutions, visit https://www.nov.com/products/internal-tk-coatings.
 GV Tomarov, DV Kolesnikov, VN Semenov, VM Podverbny and AA Shipkov, “Prevention of corrosion and scaling in geothermal power plant equipment”, JSC “Geothem-EM”, Lefortovsky val. ul. 24, 111250 Russia.
 N. Andritsos, P. Ungemach and P. Koutsoukos, “Scale formation in geothermal plants”, International Summer School on Direct Application of Geothermal Energy, under the auspices of the Division of Earth Sciences, UNESCO, IGA. 2002. https://www.researchgate.net/publication/248390587_SCALE_FORMATION_IN_GEOTHERMAL_PLANTS
Source: NOV tuboscope