Anti-Corrosion Cement Slurry Technology for Deep CCUS-EOR Wells in Hetao Basin

CCUS is one of the key technologies for achieving carbon neutrality. CO₂ injection into a well causes the well temperature to change and hence produces micro fractures in the set cement. In a damp, high-temperature high-pressure environment CO₂ causes a long-term corrosion to the set cement, resulting in CO₂ leakage, failure of the integrity of the reservoir and the borehole, as well as production stoppage etc. As the deepest CCUS-EOR engineering in China, the Hetao Basin has long been faced with temperature and pressure changes as well as long-term CO₂ corrosion. To deal with these problems, a high-performance anti-corrosion cement slurry was developed by introducing corrosion inhibitive materials and active materials into the mature cement slurries commonly used in the field operations in the basin. This new cement slurry has those characteristics such as high strength, high resistance to CO₂ corrosion and micro expansion. Study results show that, compared with other cement slurries, the optimized cement slurry has long-term performance in a damp high temperature that meets the requirements of field operations. At 150℃ and CO₂ partial pressure of 40 MPa, the optimized set cement treated with corrosion inhibitors has a 120-d corrosion depth less than 2.00 mm, a compressive strength that declines only by 3.2%, and a permeability that only increases by 14.19%, indicating that the performance of the set cement has been greatly improved. As with the low-density set cement, the 120-d corrosion depth is 2.12 mm, the compressive strength declines by about 4.34%, and the permeability increases by 23.49%. This new cement slurry was used 30 well-times in field operations, with more than 90% of the job quality being excellent, and this has laid the foundation for the CCUS-EOR engineering in the Hetao Basin.