Polymer resins for remediation of leakages in CO₂ wells

The R&D activities in the project address how to avoid leaks from CO₂ wells.
The primary objective of the project was to evaluate the potential for thermal activated polymer resin systems as remediation materials to repair cement failure at laboratory scale and representative reservoir temperature. In this project, core flooding experiments have been performed in cement plugs with varying crack sizes to determine the ability of the polymer resin to be squeezed into designed leak paths of different sizes and lengths. The sealing ability of polymer resin as a remediation material in cement cracks of different sizes and lengths was also tested. The effect of CO₂ on the integrity of the resin materials under realistic downhole conditions was also investigated.
- Determine ability of polymer resin to be squeezed into designed leak paths of different sizes. - Determine sealing ability of polymer resin in cement cracks. - Determine the long-term integrity of resin material under CO₂ exposure at downhole conditions. - Develop a more environmentally friendly polymer resin formulation with optimized fluid properties that enables use as remediation material.

The projec was completed in 2020.

Results achieved

New products in the portfolio
- An environmentally friendly resin, EnvoSet®, has been developed and commercialized. - A low toxic accelerator has been qualified to substitute the previous toxic chemical and already been used in the operations together with resin. - An ultra-fine filler material has been qualified as weight agent and already been used in the operations together with resin. It is a green product that pose no hazard to the environment.
These products development has a positive environmental impact.

Determine the penetration and sealing ability of Resins
Laboratory core flooding tests have been performed to determine the squeeze and sealing ability of resin products in fractured cement plugs at realistic downhole conditions.
- Results show that ThermaSet® and EnvoSet® can be easily squeezed into large size cracks (500 µm), small size cracks (72 µm) and multiple size cracks (91-500 µm). The squeeze of resin proved to be successful for sealing the designed leak paths. Return permeability measurements showed zero permeability in the core sample. Resin formulation, such as viscosity and fillers are playing important roles. - After a series of screening tests, the two resins ThermaSet® and EnvoSet® were selected and injected into artificial fractured cement cores. It has been shown that both resins are suitable as remediation materials and able to seal the fractures - Laboratory CO₂-flooding tests were performed including simulation of CO₂ leakages after resin remediation by flowing supercritical CO₂ and then CO₂-brine through the core samples, to investigate the effect of CO₂ on the resin sealing performance over time. Fractured cores which were sealed with resin ThermaSet® and EnvoSet® were exposed to supercritical CO₂ for 38 days and then further exposed to CO₂-brine for 55 days, in both case at 75°C temperature and 100 bars pressure. The return permeability of cores remained at zero, showing the cores were still sealed after 93 days exposure to CO₂. This indicated resins in the fractured cores were unaffected by CO₂ exposure.
Determine the long-term integrity of Resins
The long-term integrity was evaluated by determining physical and mechanical properties at given time interval in an accelerated testing system with simulated downhole conditions: 100°C and 500 bars. The ageing tests have been performed with two resins ThermaSet® and EnvoSet®: before exposure (0 day), after 1 month, 3 months, 6 months and 12 months of CO₂-brine exposure and pure brine (as a reference) exposure.

- Experimental results showed reductions in the mechanical properties after long-term exposure to brine and CO₂-brine. These reductions levelled off after 1 – 6 months exposure and the strength remained high after the levelling off. - Resins permeability to gas remained as low as initial, hence not measurable. - In comparison with the reference brine, CO₂-brine creates an acidic environment (pH 3.1) thus has accelerated the resin – water interactions and resulted in faster changes to the resin samples. Such interactions reach equilibrium after some time and eventually resins have retained very similar level of mechanical properties either exposed to CO₂-staurated brine or pure brine