Global CO2 emissions are a main cause of the climate changes and climate challenges globally. A large portion of these emissions can be eliminated through CO2 capture and storage. One common solution for storage is to re-use existing oil/gas wells or drill new ones into known reservoirs. CO2 will then be injected into the wells and sealed for storage. It is well known that wells tend to leak over time and different solutions have been and are being developed to remedy this. One method to remedy the cracks and debonding is to squeeze cement into cracks. Due to some serious limitations with cement, alternative materials are becoming important. Temperature activated resin, ThermaSet®, which will cure at a defined time and temperature has demonstrated significant potential for the application. The resin material is also resistant to CO2 and becomes an efficient and long-lasting solution for stopping CO2 leakages. The key development areas for this project is to understand what and how a crack, or debonding can be efficiently and permanently sealed. The project will also develop an environmentally friendly resin for remediation of CO2 leaks.
An environmentally friendly resin, EnvoSet®, has been developed and commercialized. 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 squeezing of resin proved to be successful for sealing the designed leak paths. Return permeability measurements was zero compared to initial permeability in the core sample. Resin formulation, such as viscosity and fillers are playing important roles in the efficiency of the solution. After a series of screening tests, the two resins ThermaSet® and EnvoSet® were selected and injected into artificial fractured cement cores. It was 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. Fractured cores which were sealed with ThermaSet® and EnvoSet® were exposed to supercritical CO2 for 38 days and then further exposed to CO2-brine for 55 days, in both cases at 75°C temperature and 100 bars pressure. The return permeability of cores remained zero, showing the cores were still sealed after 93 days exposure to CO2. This indicates that resins in the fractured cores were unaffected by CO2 exposure.
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. Testing of resin samples were done: 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 accelerates the resin ? water interactions that then resulted in faster changes to the resin samples. Such interactions reach equilibrium after some time and eventually resins retained very similar level of mechanical properties.
Based on the laboratory core flooding experimental results and long-term CO2 exposure study at realistic conditions, the evaluated thermal activated polymer resin systems were found to be promising candidates for remediation of leakages in CO2 wells. The results have also shown that the design of the polymer resin formulation is very important for the application.
Three new products (an environmentally friendly resin and two additives) have been developed and added in the portfolio. These products development has a positive environmental impact.
A novel method - consistency under applied pressure test (CAPT) for the determination of curing of resin under downhole conditions has introduced to the operation. CAPT could allow an accurate prediction of the curing process, thus enhance the value to the applications of resins in Oil & Gas wells.
Based on the laboratory core flooding experimental results and long-term CO2 exposure study at realistic conditions, the evaluated thermal activated polymer resin systems were found to be siutable candidates for remediation of leakages in CO2 wells. The results have also shown that the design of the polymer resin formulation is very important for the application.
Wells have been identified as a probable cause of leakage during CO2 storage, and failure of the annular cement sheath as well barrier element is a likely cause for well leakages. Cracking and debonding of the cement sheath occur as a result of repeated temperature and pressure cycles in the well, such as those experienced during injection, and is therefore likely to occur in CO2 injection wells. Furthermore, CO2 wells are often old, converted petroleum wells, where the cement sheaths have been damaged by such processes during decades of petroleum production.
The most common method for remediation of leakages through cement sheaths is squeeze cementing, but since cement has some series limitations in squeeze operations, an alternative is the use of temperature-activated polymer resins as sealing materials. The commercially available ThermaSet® developed by WellCem AS, has demonstrated significant potential for this application. Moreover, due to its resistance to CO2, ThermaSet® has a huge potential as remediation material for leakages in CO2 wells in particular.
The current version of Thermaset® can be squeezed into small fractures, however there are still several unanswered questions with respect to potential application as remediation material. Different mechanisms of cement failure (temperature or pressure cycles, CO2 leakage) may result in leak paths or fractures of different sizes and lengths, and requirements for successful remediation of fractured cement by using a polymer resin are unknown. It is necessary to determine to which extent the fractures need to be filled to achieve a complete seal. In addition, the fluid properties of Thermaset® need to be optimized for efficient squeezing into and sealing of small fractures.
The underlying idea of this project is therefore to develop a new version of the polymer resin ThermaSet® as an alternative remediation material for stopping leakages in CO2 wells.
CLIMIT-Forskning, utvikling og demo av CO2-håndtering