Separate Molecular Weight and Pressure Injection Technology for ASP Flooding in Daqing Oilfield

The displacement target of the ASP flooding in Daqing Oilfield has gradually shifted to class II reservoirs, which are characterized by multiple layers and great difference in permeabilities. The percentage of 3-5 layer injection wells has reached more than 50%. Currently, there are two main problems existing with the separate injection technology. First, due to the different microscopic molecular structure of the ASP solution, the viscosity loss of the ASP solution is more than 1 times higher than that of the polymer under the same injection conditions, which affects the displacement effect of ASP flooding. Second, the ASP system of a single molecular weight cannot meet the displacement requirements of all oil layers. To solve the two problems, a separate molecular weight and pressure injection technology is developed for ASP flooding. Based on the microscopic mechanism and simulation study, the separate molecular weight and pressure injection technology for ASP flooding is developed in this paper. The injection string can inject different ASP solutions of different molecular weights into different layers at different injection rates as required to match different oil layer permeabilities. Thus, the control of molecular weight and injection rate for separate layers in ASP flooding can be achieved. At the flow rate of 50m3/d, the adjustment range of molecular weight is 20-50%, the maximum throttling pressure difference can reach 1.5MPa or more, and the maximum loss of viscosity is less than 7.8%. Up to now, this technology has been applied to the field tests of more than 800 wells. Since the application of this technology, the injection profile has been effectively improved, and the pay-gross thickness ratio has been increased by 8%. With this technology, the separate injection for 3-5 layers and control of molecular weight as well as injection rate for separate layers to match the different oil layer permeabilities in ASP flooding can be achieved. This technology will play an important role in the development of major oil fields in the future.