Using Sized Calcium Carbonate (CaCO3) Particles in Mature CO2 EOR Projects for Deep Conformance

Abstract Deep reservoir thief zone conformance has been one of the most challenging tasks in the oil industry for decades. The challenges are driven by finding a stable, cost-effective, and easy-to-apply conformance agent. One of the recent technologies, borrowed from treatment of drilling circulation losses, involves calcium carbonate (CaCO3) particles. This study presents a number of applications involving the use of calcium carbonate particles for conformance improvement for CO2 Water Alternating Gas (WAG) injection in Oxy Permian EOR. Two cases were selected; one involves an injector with a suspected karst/fracture with very high injectivity (3-4 times higher than neighboring wells with similar reservoir characteristics). The well was diagnosed with linear flow using a pressure transient analysis pressure fall-off test. The calcium carbonate particles treatment was applied in a pill injection scheme involving stages of particles, carried in a polymer solution, with polymer solution flush stages interbedded between pills. In total, 40,000 pounds of the particles (50 to 1200 microns) were pumped while gaining 300 psi of pressure above pre-job reference pressure. The other case selected was more of a matrix flow dominated high permeability zone to test the ability to place small calcium carbonate particles in fracture/matrix mix with high injection intake. In this second case, 14,500 pounds of the particles (50 to 150 microns) were injected while building around 700 psi above pre-job reference injection pressure. The first case study data has been showing a stable gas and water injectivity reduction of around 75% since the treatment date of October 2024. This equates to reducing injection gas processing from 16 MMscf/d to 4 MMscf/d. In the second case targeting matrix dominated thief zone, water and gas injectivity was reduced by about 25% and 5% respectively. The latest CO2 Injection Profile Logs (IPL) showed gas injection has been partially diverted from top zone to bottom zones that were previously taking limited CO2. The IPL shows gas intake to the bottom layers has increased from 1.8 MMscf/d to 4 MMscf/d. Nearby patterns are showing an indication of oil response because of this conformance. More data is being collected to further evaluate the response. CaCO3 particles conformance results in the Permian CO2 EOR floods are considered encouraging. This conformance technology can have large scalability in the Permian CO2 EOR operations to improve CO2 utilization or reduce CO2 cycling and surface processing in mature projects. Given its low cost, ease of application, and commercial availability, CaCO3 particle conformance can add value even if it introduces only a small disturbance to CO2 flow streamlines to flood un-swept zones. CaCO3 particles conformance can still be followed with traditional wellbore conformance, and it is expected to limit vertical connections between layers.