Abstract:

In order to reduce injection pressure and increase water injection in ultra-low permeability oilfield, a system of depressurization and stimulation of injection well was developed. It is constituted by 320～850 mg/L gemini surfactant G12-3, 60～200 mg/L antiswelling agent NNR, 16～50 mg/L inhibition agent YJ and 4～20 mg/L ferric ion stabilizer QA. The interfacial activity, antiswelling performance, inhibition ability, and reverse wetting ability of this system were investigated under various conditions. When the mass concentration of the depressurization and stimulation of injection well system solution was 400～1 200 mg/L, the interfacial tension was reduced to 10-3 mN/m, the antiswelling rate is 81.2%～89.3%, and the inhibition rate was 84.7%, 83.5% and 81.7% for Ca2+, Ba2+ and Fe3+ respectively. With the increase of mass concentration of this system, mica surface wettability turned to weak water wettability, and oil-water relative permeability curve also shows that the system could improve the flow ability of formation fluid. At last, field test shows that the system made the injection pressure of injection well T214-16 reduced about 3.5 MPa, and the term of the validity of this measure was more than 6 months. It attained good application effect in this area.

Key words:  lowper meability, sandstone reservoirs, sedimentary facies, diagenesis, Chang8 oilreservoirset, Ordos Basin