PNNL

When geothermal wells are made using PNNL-developed self-healing cement, cracks and breaks in the well can heal automatically. This technology has the potential to eliminate excavation, repair, and replacement costs associated with cracked cement wells.

With an average life span of 30-40 years, the cement around geothermal production wells eventually cracks over time. Because wells with cracked cement are vulnerable to leakage, reduced strength, and corrosion, it's important to repair them in a timely fashion. However, repairs can easily top $1.5 million dollars; the cost of new materials, excavation, installation, and halting power production adds up fast.

Researchers at PNNL developed cement that can heal itself when cracks occur. Using self-healing cement for geothermal wells would save geothermal plants millions of dollars and would reduce the amount of downtime necessary for repairs.

Super to the Power of Three

PNNL chemist Carlos Fernandez and his team discovered that by adding a strong and flexible and powerful ingredient, called polymers, they could create self-healing cement. Naturally found in the human body, plant structures, and more, these large, chain-like molecules work to hold substances together. The team discovered by mixing in 5 to 20 percent of man-made polymers into typical cement before it is poured and cured, the cement can repair itself when cracks occur. PNNL’s research team has successfully proven this cement can repair itself in a few days, and they predict it has the potential to heal itself in just a matter of hours. Just as impressive, is the cement’s projected ability for continuous self-healing, meaning it can repair itself many times over and maintain the rheological and mechanical properties necessary for geothermal wells.

And another superpower? Self-adhering properties. By using one of nature's strongest glue—covalent and hydrogen bonds—researchers will investigate if the cement can re-adhere to the well’s steel pipe and surrounding rock. If the cement is separated from the steel pipe or the rock surrounding the well, it can become vulnerable to cracks, or create pathways for the fluid inside the well to escape. Together with the self-healing properties and the potential to re-adhere, this cement could significantly reduce well failure at geothermal sites and the downtime associated with repairs.

This work is part of a collaborative project between PNNL, Brookhaven National Laboratory, and National Energy Technology Laboratory funded by DOE's Geothermal Technology Office.

PNNL Research Staff: Carlos Fernandez, Wooyong Um, Phillip K. Koech, M. Ian Childers, Kenton Rod, Vanda Glezakou, Manh T. Nguyen, Jaehun Chun, and Diana Linn