Materials Selection and Corrosion Considerations for Low Enthalpy Geothermal Wells

Leothermal power uses the naturally high temperatures below the Earth’s surface to produce energy. There are many ways to access this heat, but it commonly involves drilling wells about one to three kilometers into the Earth to access subterranean water reservoirs. High temperature reservoirs are found in several volcanic areas around the world such as New Zealand, Iceland, and in the United States. These high temperature reservoirs are hot enough that they produce steam at the surface. The steam is sent via pipelines to a central plant where the steam is converted to electricity. Low enthalpy (LE) geothermal resources are not as hot (< 150 °C) as the higher temperature resources, but nonetheless LE geothermal resources are capable of producing energy in an economically attractive way. The hot water source found in LE geothermal reservoirs can be used to generate vapour which turns a turbine to generate electricity. The hot water may also be used as a source of direct heating for buildings such as greenhouses.

There are a number of LE geothermal plants that have been in operation for many years around the world, particularly in Europe. In western Canada, reservoirs similar to European reservoirs are currently being evaluated for production of LE geothermal energy. The reservoirs associated with these resources vary in their water and gas compositions, particularly in brine content. The different compositions therefore require careful design consideration for their corrosion and scaling properties. This article will highlight the important parameters that affect corrosion and degradation mechanisms in producer and injector wells, the corrosion and material selection challenges that face the design team, and some of the potential solutions for mitigating corrosion. The equipment covered will therefore be the well casing, tubing, wellhead, and downhole components e.g., packer or ESP.

Firstly, a geothermal resource classification system will be examined to better understand degradation mechanisms and material experience with LE types of geothermal wells.

Secondly, the produced water and gas composition along with well conditions such as pressure and temperature will be used to understand potential degradation mechanisms that may occur in LE geothermal wells. Furthermore, both the producer well and injector well will be shown to have “zones” where the same set of degradation mechanisms is expected to occur.

Because LE geothermal resources have been produced for many years in Europe, the article will highlight some of the corrosion and material selection learnings from these resources.

Use of higher alloy materials, commonly classed as corrosion-resistant alloys (CRAs) are used for specific...