By Josh Perry, Editor
Researchers from the Pacific Northwest National Laboratory (PNNL) and Brookhaven National Laboratory developed a self-healing cement material using a flexible polymer that could be an environmentally-friendly enhancement from the geothermal industry, according to a report from the PNNL.
Researchers created an alternative to cement using a flexible polymer. (PNNL)
“Cement used in geothermal wells is known to crack under pressure and in high-temperature environments associated with drilling for geothermal energy,” the report noted. “The objective of the team’s study was to see how its self-healing cement would hold up when tested against conventional cement in these extreme heat conditions.”
Experiments at PNNL and Brookhaven demonstrated that the self-healing cement’s flexibility and ability to autonomously fill cracks outperformed standard cement in mechanical stress tests.
“The flexibility is attributed to chemically ‘soft’ or flexible bonding between the atoms in the polymer and cement,” the article explained. “This soft bonding allows large deformations that can be contained within the cement without breaking the bonds.”
Reports indicate that the polymer provides 60-70 percent more elasticity. It detaches from the cement and reattaches at areas where cracks form, producing an 87 percent reduction in crack size. With repairs to cracking cement requiring an average of $12 billion per year, researchers estimate that this material could save the cement industry $3.4 billion for infrastructure projects.
“Self-healing cement could resolve major concerns about the sealing of wellbores for oil, gas, and geothermal heat production,” the article added. “Leaks in wellbores cause contamination and limit the ability to provide clean energy alternatives. These leaks contaminate aquifers and surface waters.”
The research was recently published in Cement and Concrete Composites. The abstract stated:
“To isolate injection and production zones from overlying formations and aquifers during geothermal operations, cement is placed in the annulus between well casing and the formation. However, wellbore cement eventually undergoes fractures due to chemical and physical stress with the resulting time and cost intensive production shutdowns and repairs.
“To address this difficult problem, a polymer-cement (composite) with self-healing properties was recently developed by our group. Short-term thermal stability tests demonstrated the potential of this material for its application in geothermal environments. In this work, the authors unveil some of the physical and chemical properties of the cement composite in an attempt to better understand its performance as compared to standard cement in the absence of the polymer.
“Among the properties studied include material's elemental distribution, mineral composition, internal microstructure, and tensile elasticity. Polymer-cement composites have relatively larger, though not interconnected, levels of void spaces compared to conventional cement. Most of these void spaces are filled with polymer. The composites also seem to have higher levels of uncured cement grains as the polymer seems to act as a retarder in the curing process.
“The presence of homogeneously-distributed more flexible polymer in the cement brings about 60–70% higher tensile elasticity to the composite material, as confirmed experimentally and by density-functional calculations. The improved tensile elasticity suggests that the composite materials can outperform conventional cement under mechanical stress.
“In addition, calculations indicate that the bonding interactions between the cement and polymer remain stable over the range of strain studied. The results suggest that this novel polymer-cement formulation could represent an important alternative to conventional cement for application in high-temperature subsurface settings.”