The petrophysical properties of ultra-low permeability sandstone reservoirs near the injection wells change significantly after CO₂ injection for enhanced oil recovery (EOR) and CO₂ storage, and different CO₂ displacement methods have different effects on these changes. In order to provide the basis for selecting a reasonable displacement method to reduce the damage to these high water cut reservoirs near the injection wells during CO₂ injection, CO₂-formation water alternate (CO₂-WAG) flooding and CO₂ flooding experiments were carried out on the fully saturated formation water cores of reservoirs with similar physical properties at in-situ reservoir conditions (78 °, 18 MPa), the similarities and differences of the changes in physical properties of the cores before and after flooding were compared and analyzed. The measurement results of the permeability, porosity, nuclear magnetic resonance (NMR) transversal relaxation time (T₂) spectrum and scanning electron microscopy (SEM) of the cores show that the decrease of core permeability after CO₂ flooding is smaller than that after CO₂-WAG flooding, with almost unchanged porosity in both cores. The proportion of large pores decreases while the proportion of medium pores increases, the proportion of small pores remains almost unchanged, the distribution of pore size of the cores concentrates in the middle. The changes in range and amplitude of the pore size distribution in the core after CO₂ flooding are less than those after CO₂-WAG flooding. After flooding experiments, clay mineral, clastic fines and salt crystals adhere to some large pores or accumulate at throats, blocking the pores. The changes in core physical properties are the results of mineral dissolution and fines migration, and the differences in these changes under the two displacement methods are caused by the differences in three aspects: the degree of CO₂-brine-rock interaction, the radius range of pores where fine migration occurs, the power of fine migration.

Worldwide practices have proven that gas-assisted gravity drainage can obviously enhance oil recovery, and this technology can be especially effective for reservoirs with a thick formation and large inclination angle. For the successful implementation of this process, a key technology is the stable control of gas–oil interface during gas injection. For a detailed exploration of this technique, a three-stage permeable visual model was designed and manufactured, with permeability decreasing from top to bottom, thus, a reverse rhythm reservoir was effectively modeled. Then the experiment concerning CO₂-assisted gravity drainage was carried out with the adoption of a self-developed micro visual displacement device. This study mainly focused on the micro migration law of gas–oil interface and the development effects of CO₂-assisted gravity drainage. According to the experiments, CO₂ fingering somewhat happens in the same permeable layer from the beginning of gas injection. However, phenomena of “wait” and “gas–oil interface self-adjustment” occur instead of flowing into the next layer when the injected CO₂ reaches the boundary of the next lower permeability layer through the dominant channel. By the “gas–oil interface self-adjustment”, the injected CO₂ first enters into the pores of the relative higher permeability layer to the greatest extent, and thus expands the sweep volume. Futhermore, in the process of CO₂ injection, obvious gas channeling occurs in the low permeability layer directly connected to the outlet, resulting in low sweep efficiency and poor development effect. After connecting the core with lower permeability at the outlet, the development indexes of the model, such as the producing degree of the low permeability layer, the oil recovery before and after gas breakthrough, are significantly improved, and the recovery degrees of the medium permeability layer and the high permeability layer are also improved, and the overall recovery factor is increased by 12.38%. This “gas–oil interface self-adjustment” phenomenon is explained reasonably from the two scales of macroscopic flow resistance and microscopic capillary force. Finally, the enlightenments of the new phenomenon are expounded on the application of gas-assisted gravity drainage on site and the treatment of producers with gas breakthrough in gas injection development.

In order to improve the adaptability of low-salinity waterflooding technology in some areas where freshwater resources are scarce, we aimed at implementing the low-salinity effect (LSE) in carbonate reservoirs through tuning injection seawater composition. LSE of ion tuning water (ITW) was verified by the results of core flooding tests, obtaining a water-free recovery factor of 50.7% and cumulative oil recovery of 77.2%. The micro mechanisms behind it were revealed via direct force-measuring and Zeta parameter (Zeta_p) measuring. Our results are expected to provide a new LSW strategy via tuning injection seawater composition in the case of carbonate reservoirs.

With the increasing demand of natural gas in China, its production is extremely important to fulfill the requirement of society. However, in reality, the natural gas production from the gas well in the gas field is often accompanied by the production of formation water. For gas well with low production, the gas flow rate in the well is too low to carry out the formation water from the bottom of the well. The water will thus accumulate in the well bore and the gas production will be greatly diminished. To solve this problem, based on the developing status of M gas field in China, foaming surfactant Z301 is synthesized and then foaming agent ZK3012 is developed through combination of Z301 with CAT after optimization experiments. After that, the compatibility tests are conducted to ensure that ZK3012 can work together well with formation fluids, and the water carrying rate tests are conducted concerning the optimum concentration of ZK3012. Finally, pilot test is conducted in 2 gas wells on site in M gas field, good results are obtained that accumulated water is discharged by foam drainage and the gas well production is increased. Studies demonstrate the main steps involved for application of this technology. In regard to the high external dependence degree of China in gas supply, operators of gas fields should give prominence to related studies of this technology to achieve sustainable development.