## 1 Introduction
As exploration ventures deeper into the earth's crust, the increasing reservoir depth and high pressures make thermal methods less efficient and economically unviable. Chemical EOR methods, while promising, often face challenges such as surfactant adsorption onto the reservoir rock, which reduces the active concentration of the chemicals and limits their effectiveness. In addition, gas injection methods like CO\({}_{2}\) flooding, though widely studied, suffer from low sweep efficiency and gas channeling in heterogeneous reservoirs, leading to incomplete oil displacement. Particularly, CO\({}_{2}\)-based EOR methods have emerged as a focal point of research due to their dual benefits: enhancing oil recovery and simultaneously providing a means for carbon storage, thus contributing to climate change mitigation. Despite these advances, there remains a need for innovative approaches that improve CO\({}_{2}\) utilization efficiency and address surfactant loss, interfacial tension reduction, and oil mobility, particularly in low-pressure reservoirs. To overcome these limitations, hybrid methods that combine chemical and gas-based EOR strategies have drawn significant attention [13; 14]. Particularly, CO\({}_{2}\)-based EOR methods have emerged as a focal point of research due to their dual benefits: enhancing oil recovery and simultaneously providing a means for carbon storage, thus contributing to climate change mitigation. Despite these advances, there remains a need for innovative approaches that improve CO\({}_{2}\) utilization efficiency and address surfactant loss, interfacial tension reduction, and oil mobility, particularly in low-pressure reservoirs. Oilfield devel-opment and CO\({}_{2}\) flooding have an impact on the development of the oil industry in terms of EOR [15; 16]. Many approaches related to CO\({}_{2}\) injection-based EOR are available, including continuous CO\({}_{2}\) injection, water alternate CO\({}_{2}\) injection, and a CO\({}_{2}\)-based huff-n-puff method. The huff-n-puff method is considered the most effective among all the CO\({}_{2}\)-based EOR methods [12]. In this method, high-pressure CO\({}_{2}\) is injected into the oil reservoir, and oil is mobilized. This is followed by a soaking period, during which the reservoir is sealed while CO\({}_{2}\) is dissolved into the oil [17; 18]. During this period, the oil swells and becomes less viscous due to CO\({}_{2}\) dissolution. In the final stage, the well is opened, and the swollen oil is recovered due to the driving force generated by injected CO\({}_{2}\) pressure [19]. This method could be further improved by integrating chemical flooding. Recently, the potential of the nonionic polyether surfactant-assisted huff-n-puff method was tested in the core-based flooding experimental research [20]. It was found that additional surfactant flooding improved 14-19% of oil recovery compared to only the huff-n-puff method [20]. These promising results led us to propose a novel method of using an anionic surfactant flooding with intermittent CO\({}_{2}\) swelling. The primary hypothesis of this study is that the strategic implementation of surfactant flooding before and after a CO\({}_{2}\)-induced oil swelling stage can significantly enhance oil recovery. Initially, surfactant flooding recovers more oil by using the wettability alteration mechanism, where the surfactant is absorbed by the immobile oil and changes the wettability of the reservoir rock to be more water-wet [21]. This absorption process not only aids in immediate oil recovery but also prepares the oil for subsequent stages. Following this, oil swelling is induced by CO\({}_{2}\) injection. The absorbed surfactant during the initial flooding helps to enhance the oil swelling process by improving the CO\({}_{2}\) solubility in oil, resulting in greater oil volume expansion and better mobilization within the reservoir. Finally, a second stage of surfactant flooding is performed to mobilize the swelled oil, which is easier to extract due to its reduced viscosity.