Feasibility study of crude oil mobilizing with nano emulsion in low oil saturation reservoir

Abstract

The Chang 8 low oil saturation reservoir in Changqing Oilfield is highly heterogeneous and rich in organic matter, resulting in complex pore wettability. At present, when guar fracturing fluid is used for development, the wetting modification capacity of fracturing fluid is weak, the effect of imbibition on enhancing oil recovery (EOR) is poor, and the mobilization ratio of large pores oil is only 5.40%, and the total recovery rate in lab is less than 25%. There is an urgent need for a highly efficient oil mobilization reagent with strong modification capacity and capable of simultaneously mobilization core micro and nano-pore crude oil. Through relative permeability displacement and forced imbibition, it is found that the residual oil saturation of core is 29.87%. However, the oil saturation range of Chang 8 reservoir is only 12.2%–33.2%, and it is the main reason for the difficulty in mobilizing crude oil. Then, based on different types of chemical reagents, 0.10% KX-7 oil mobilization reagent is optimized through the nuclear magnetic resonance (NMR) method. The particle size of 0.10% KX-7 nano emulsion is about 10 nm, the imbibition recovery rate is 44.24%, and the mobilization ratio of small pores (nano-scale) and large pores (micro-scale) is 45.52% and 35.73% respectively, and the wettability angle of core is modified to 44°, which can reduce the residual oil saturation of the core to 18.20%. Its main mobilization mechanism is wetting modification and solubilization. Increasing reagent concentration, temperature, and pressure can promote the mobilization and modification capacity of KX-7 nano emulsion, and the mobilization ratio of crude oil is further increased by more than 10%. The optimized KX-7 nano emulsion has a good performance in the field test with a daily output of 28.2 tons, which can guide the highly efficient development of low oil saturation reservoirs.