Due to poor temperature resistance and salinity tolerance of conventional polymers, the chemical flooding for high-temperature and high-salinity reservoir faces enormous challenges. This work studies the comprehensive performance of a polymer-surfactant system based on an associative polymer and verifies its availability and feasibility in Guan-109 fault-blocked reservoir, Dagang (China), which is a typical high-temperature, high-salinity, ordinary heavy oil reservoir.
The viscosifying property of different polymers (including two associative polymers), interfacial activity of different surfactants and the interaction and compatibility between the polymers and surfactants are investigated to initially determine an associative polymer (AP-P7) and the petroleum sulfonate surfactant (PS-985) as suitable candidates. Then, the adsorption, shear resistance, aging stability, injectivity, and oil displacement capacity of the combination system containing AP-P7 and PS-985 are further studied to obtain the optimal binary flooding system. Moreover, the field application scheme for Guan-109 reservoir is further obtained through optimizing injecting concentration, slug size and slug combination of binary flooding system.
The lab tests show that, under the reservoir condition of 26983 mg/L salinity and 78 °C, the viscosity of associative polymer varies from 31.7 to 88.5 mPa·s in a concentration range of 1500~2500 mg/L, and the oil/water interfacial tension of the petroleum sulfonate is up to 10-3 mN/m order of magnitude in a concentration range of 0.05wt%~0.5wt%. At fixed polymer concentration (2000 mg/L) and surfactant concentration (0.3wt%), the binary system presents significant viscosifying capability, interfacial activity, adsorption resistance, shear resistance, aging stability, etc. Meanwhile, the system has good injectivity at a gas permeability of 210×10-3 μm2 and can generate a high resistance factor (105.1). After optimizing injecting parameters, in laboratory, the binary system can improve the oil recovery by 26.37% after water flooding. During the binary flooding pilot in Guan-109 reservoir (7 injectors and 12 producers), from December 2016 to December 2017, the system has been injected for 0.102 PV. Thus, the pilot achieves expected results. The liquid production enhances from 364 to 521.1 m3/d, oil production enhances from 27.7 to 51.7 m3/d, and the water cut decreases from 92.3% to 90.1% (the maximum decreasing amplitude is up to 3.4%).
Both lab tests and field pilot show that the binary system based on the associative polymer is hopeful to solve the challenges faced by chemical EOR in high-temperature and high-salinity reservoir. In addition, the pilot also provides much practical experience for the successful application of this novel system.