| Low permeability oilfields are faced with such problems as low injection and low productivity because of the small throat radius, poor permeability and continuous damage during the process of development. The blockage associated with oil droplets or emulsified oil and the damage caused by water blocking are difficult to remove by conventional acidizing technology. So surfactant systems were selected to remove the interfacial pressure difference of disperse phase, thus attaining the purposes of improve injection or production.By optimizing the structure of surfactants, octadcylamine polyoxvethylene polyoxypropylene dicarboxylate with PO number of 9 and EO number of 6 was selected as the main surfactant to improve injection. Through studying its combinations with different alcohols, the optimal formulation was obtained as following: alkylamine polyether carboxylate/isopropanol/butanol with the mass ratio of 5/3/2. Then an overall evaluation of the formulation was made to determine its application condition. Its concentration should be equal to or larger than 10%. The salt content in the formation may be 0mg/L~103000mg/L and the optimal salt content in the formation is 0mg/L~30000mg/L. The depressurizing ratio ranges from 48.5% to 83.3% for different cores. The agent can decrease pressure and increase injection by changing wettability and reducing residual oil saturation.In order to remove water blocking damage, a low interfacial tension system was selected, which included CBET-17/CBET-13 with the mass ratio of 4/6. It could reduce the IFT to 10-3mN/m or lower. Then slelecting the maximum solubilization amount of water as the criteria, the reverse microemulsion formula was obtained as following: Span80/octadecyl trimethyl ammonium chloride/butarol with the ratio of 5/5/3. Results obtained from the core displacement experiment demonstrate that the two systems could both reduce the water blocking damage and improve the permeability of oil in the flooding process. |
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