This paper summarizes the work conducted for the project "Development of Swelling-Rate-Controllable Particle Gels to Enhance CO2 Flooding Sweep Efficiency and Storage Efficiency", a three-year project funded by the US Department of Energy. The overall objective of this project is to develop a novel particle- based gel technology that can be used to enhance CO2 sweep efficiency and thus improve CO2 storage in mature oilfields. In this paper, we first provide our classification of conformance problems in CO2 flooding fields, and addresses the importance of developing novel particle gels to efficiently control CO2 flooding conformance in oilfields. Then, we highlighted our research results about the three types of novel preformed particle gels (PPGs) that we successfully developed, including AMPS-based PPGs, CO2 responsive PPGs (CR-PPG) and CO2 resistance PPGs (CRG). The developed particles is size controlled from nanometer to millimeters, and the swelling time can be controlled from a few hours to three months, depending on the type of conformance problems to be solved. The millimeter-sized PPGs (10 um to a few millimeters) are obtained through bulk gel synthetization, cutting and drying, mechanically crushing and screening process, and they are mainly used to solve the conduits, fractures, or fracture-like channels problems. The nano- and micro-sized polymer particles are synthesized through either emulsion polymerization or dispersion polymerization process under scCO2, and they are mainly designed to solve the matrix problem for far-wellbore conformance control. Overall, the project has provided a series of reliable and cost-effective swelling-rate-controllable particle gel products that can be used to solve the different reservoir conformance problems for CO2 flooding, which will not only aid in improving oil recovery for CO2 flooding projects but can also help to improve CO2 storage efficiency for CO2 storage projects.