As the demands of tight-oil Enhanced Oil Recovery (EOR) and the controlling of anthropogenic carbon emission have become global challenges, Carbon Capture Utilization and Sequestration (CCUS) has been recognized as an effective solution to resolve both needs. However, the influential factors of carbon dioxide (CO₂) geological storage in low permeability reservoirs have not been fully studied. Based on core samples from the Huang-3 area of the Ordos Basin, the feasibility and influential factors of geological CO₂ sequestration in the Huang-3 area are analyzed through caprock breakthrough tests and a CO₂ storage factor experiment. The results indicate that capillary trapping is the key mechanism of the sealing effect by the caprock. With the increase of caprock permeability, the breakthrough pressure and pressure difference decreased rapidly. A good exponential relationship between caprock breakthrough pressure and permeability can be summarized. The minimum breakthrough pressure of CO₂ in the caprock of the Huang-3 area is 22 MPa, and the breakthrough pressure gradient is greater than 100 MPa/m. Huang-3 area is suitable for the geological sequestration of CO₂, and the risk of CO₂ breakthrough in the caprock is small. At the same storage percentage, the recovery factor of crude oil in larger permeability core is higher, and the storage percentage decreases with the increase of recovery factor. It turned out that a low permeability reservoir is easier to store CO₂, and the storage percentage of carbon dioxide in the miscible phase is greater than that in the immiscible phase. This study can provide empirical reference for caprock selection and safety evaluation of CO₂ geological storage in low permeability reservoirs within Ordos Basin.

Aiming to solve the problems of poor CO₂ displacement efficiency and serious gas-channeling and low well-opening rates in ultra-low permeability reservoirs, we carry out CO₂ displacement experiments under different permeability reservoirs by using different development methods, water drive to gas drive procedures, and different fracture positions to clarify the effects of physical formation properties, injection methods, and fracture parameters on CO₂ displacement efficiency in C8 ultra-low permeability reservoirs. The experimental results show that the recovery degree of CO₂ miscible drive increases with an increase in permeability. When the gas–oil ratio is greater than 2000 m³/m³, serious gas channeling can be observed in both the miscible drive and immiscible drive. In addition, when the water drive is altered to be a gas drive, the water cut of 0.45 mD and 0.98 mD cores decreased, and the recovery degree increased by 13.4% and 16.57%, respectively. A long fracture length will deteriorate gas channeling and lower the CO₂ oil-displacement efficiency. However, the fracture location is found to have little impact on the recovery of CO₂ displacement.

From the experience of CO₂ storage in the past, the leakage part of CO₂ may be the wellbore, fractures, faults, and cap rocks in the formation. Once CO₂ leaks from the wellbore, it will pose a serious threat to the life safety of workers near the well pad in a short time. Therefore, from the perspective of single well leakage in the process of CO₂ storage, this paper studies the risk of single well CO₂ injection leakage in Changqing Oilfield, Ordos Basin, simulates CO₂ leakage from the wellbore, and simulates it with the diffusion model after toxic gas leakage, so as to obtain the CO₂ concentration at different distances from the leakage point. The range of affected area after CO₂ leakage is determined by the critical value of CO₂ leakage diffusion concentration. According to the calculation in this paper, the area near the leakage source is divided into (taking summer as an example: the wind speed is about 3.3 m/s): fatal area (2.2 m), serious injury area (4.3 m), inhalation reaction region (19.5 m) and safety area (> 50 m). The leakage risk of CO₂ injection buried wellbore in low-permeability reservoir in Ordos Basin is evaluated.