Packer elements are crucial in maintaining well integrity in gas wells, providing reliable seals under extreme conditions. However, CO2 corrosion poses a significant threat to these elements, especially under compressive stress. A recent comprehensive study has given us valuable insights into the performance of hydrogenated nitrile butadiene rubber (HNBR) and nitrile rubber (NBR) in such environments. Here, we summarize the study’s findings and offer recommendations for engineers in the selection and maintenance of packer elements for gas wells.
Rubber samples exposed to liquid CO2 showed significantly greater degradation than those exposed to gaseous CO2. This was evident through increased weight change, reduced hardness, and higher compression set values. For instance, HNBR samples exposed to liquid CO2 showed a weight change rate of up to 0.28%, compared to 0.071% in gaseous CO2.
Compressive stress exacerbated the corrosion effects of CO2 on both HNBR and NBR. Under compressive loads ranging from 0 to 12 kN, both types of rubber showed increased degradation in mechanical properties, with liquid CO2 causing more severe damage than gaseous CO2. The study revealed that higher loads led to more significant material degradation.
After CO2 exposure, the weight of rubber samples increased, indicating material absorption and swelling. For example, NBR samples showed weight change rates from 0.015% to 0.28%, depending on the phase of CO2 and the applied load. Hardness reduction was more pronounced in liquid CO2, with HNBR samples showing a decrease from an initial hardness of approximately 90 Shore A to as low as 58 Shore A after exposure under high load conditions.
Compression set, which measures the permanent deformation of rubber after compression, increased significantly after exposure to CO2. For HNBR samples, compression set values ranged from 10.59% to 22.40% in liquid CO2, compared to 7.04% to 11.08% in the control group.
SEM analysis showed that rubber samples exposed to liquid CO2 exhibited severe structural damage, such as holes and fractures, particularly under higher compressive loads. This microstructural damage correlates with the observed deterioration in mechanical properties.
EDS analysis indicated significant changes in the elemental composition of the rubber materials after CO2 exposure. For instance, the carbon content in HNBR decreased from 67.58% to 57.87% in liquid CO2, reflecting the material’s chemical interaction with CO2.
Based on these findings, engineers should consider the following recommendations when selecting and maintaining packer elements for gas wells:
The study highlights the critical impact of CO2 corrosion on HNBR and NBR materials used in packer elements under compressive stress. By selecting the right materials, implementing preventive measures, and considering environmental control, engineers can significantly improve the reliability and performance of packer elements in gas wells. Adopting these detailed recommendations will help mitigate the risks associated with CO2 corrosion, ensuring safer and more efficient gas well operations.
Zhu, D., Lin, Y., Ma, H., Zhang, H., Li, Y., Zhang, L. and Deng, K., 2017. Experimental studies on CO2 corrosion of rubber materials for packer under compressive stress in gas wells. Engineering Failure Analysis, 80, pp.11-23.