Determining reasonable formation pressure plays an important role in improving oil recovery, reducing water consumption and casing loss rate. Whether the formation pressure is reasonable or not is also related to the stable production and economic benefits of the oilfield. For ultra⁃high water cut reservoirs, the study of formation pressure is relatively rare, and the existing methods do not take into account the influence of different viscosity, recovery degree and gas⁃oil ratio on reasonable formation pressure. Therefore, material balance method, gas⁃oil ratio dynamic data analysis method and numerical simulation method, are used to study the variation law of different viscosities, recovery degree, gas⁃oil ratio and formation pressure. Reasonable formation pressure values of each block are calculated, considering the influence of dissolved gas on crude oil viscosity and recovery factor, and the reasonable formation pressure values in the west part of central block of Daqing Oilfield are determined. The results show that the reasonable formation pressure in the west of the central region is close to the saturation pressure, the reasonable formation pressure in Sapu formation is 9.11 MPa, and the reasonable formation pressure in Gaotaizi formation is 10.12 MPa, which has important guiding significance for the later waterflooding development of Daqing Oilfield.

The enhanced oil recovery technology of ASG (alkali, surfactant and nitrogen) composite foam and water alternating injection was studied in high temperature and high salinity low permeability reservoir. The ASG foam and water alternating injection experiments were carried out through indoor flooding experiments, and compared with water flooding nitrogen flooding and surfactant flooding. The results show that the enhanced oil recovery of the method adopted by this study is 16.61%, 10.26% and 9.21%, respectively, compared with water flooding, nitrogen flooding and surfactant flooding technology. Experimental study on injection parameters optimization of ASG foam and water alternating injection is carried out, and the parameters such as slug size, injection rate and gas fluid ratio of ASG composite foam are optimized by bench scale displacement test. The results show that under the condition of the same foam injection volume (1.2 times the pore volume), the effect of foam slug injection with 0.4 times pore volume is best. The foam injection rate has an optimum value of 1.5 mL/min. When the injection rate is too low, less foam is produced, gasliquid separation is easy to occur, and the blocking effect is poor. When the injection rate is too high, the size of the bubble is different, and it is easy to cause the bubble to merge, causing the bubble to burst, and at the same time, it is easy to cause the shear defoaming of the foam. When the gas fluid ratio is 3∶1, 2∶1 and 1.5∶1, respectively, the recovery rate is 2.04% higher than that of the single gas fluid ratio.