Oil Recovery Performance and CO₂ Storage Potential of CO₂ Water-Alternating-Gas Injection after Continuous CO₂ Injection in a Multilayer Formation

Abstract

In this study, oil recovery performance and carbon dioxide (CO2) storage potential of a CO2 water-alternating-gas (CO2-WAG) injection after continuous CO2 injection process for multilayer formation were experimentally determined under immiscible and miscible conditions. First, a slim-tube apparatus was used to measure the minimum miscibility pressure (MMP) of a CO2–crude oil system (MMP = 22.79 MPa), which was applied as a guide for follow-on investigations. Afterward, the CO2-WAG injection after the continuous CO2 injection for a triple-layer system, horizontally placed and parallel-connected, was conducted to evaluate the capacity of enhanced oil recovery and CO2 storage potential of the multilayer formation at different operating pressures and a reservoir temperature of 98 °C. Results revealed that the oil recovery of the entire system was determined by the recovery of a layer with the highest permeability, which was more than 90% of the entire system recovery provided by the highest permeability layer in the continuous CO2 injection. The ensuing CO2-WAG injection could further enhance the oil recovery of the system after the continuous CO2 injection. The contribution of the recovery produced by the highest permeability from 90 to 98.3% could also be reduced for the entire system recovery. The oil recovery factor of the multilayer system increased as the operating pressure increased (i.e., from 33.01% of the system at Pop = 15 MPa to 39.42% of the system at Pop = 25 MPa). From a view of CO2 storage potential, the ensuing CO2-WAG injection at immiscible and miscible conditions could also double the amount of stored CO2 after the continuous CO2 injection for the multilayer system. More than 75–80% of stored CO2 for the multilayer system was contributed by the highest permeability layer at the end of the CO2-WAG the CO2-WAG injection after the continuous CO2 injection process under immiscible and miscible conditions. Therefore, for a multilayer formation, such as the Jilin oilfield, the layer with medium and low permeability should be further developed after CO2-WAG injection.