Study On Heavy Alkylbenzene Sulfonate/Alkyl Poly-oxyethylene Ether Mixtures As Surfactant Systems For Enhanced Oil Recovery

The effects of nonionic surfactants, alkyl polyoxyethylene ethers (AEO), on the properties of heavy alkylbenzene sulfonate (HABS) surfactant systems in enhanced oil recovery are studied. The possibility of improving the electrolyte tolerance of HABS by adding AEO is investigated by studying phase behaviors of microemulsions with n-nonane and s-butanol as oil and co-surfactant respectively. Then synergetic effects of anionic/nonionic mixtures in reducing water/oil interfacial tension, decreasing initial alkali or salt concentration and widening alkali or salt concentration range required for obtaining ultra-low interfacial tension are examined for n-nonane/water systems and crude oil/reservoir water systems, respectively.The study on microemulsion systems shows that with HABS or ABS as surfactant, at water/oil (v/v) -1/1 and co-surfactant/surfactant (mole/mole) = 18.5/1, microemulsions of Winsor I, Winsor II and Winsor III types can be obtained. Increasing salinity results in Winsor I-Winsor III-Winsor II phase transformation, and with the increase of surfactant concentration, the volume fraction of excessive oil and water decreases and finally an isotropic microemulsion phase can be obtained. The optimal salinity, however, decreases with increasing surfactant concentration. The lowest surfactant concentration required to form isotropic microemulsion increases with the decrease of surfactant molecular weight, or the solubilization capacity increases with increasing molecular weight. The salinity tolerance of surfactant, however, decreases with increasing molecular weight. By adding hydrophobic nonionics, AEO3, the optimal salinity of the system decreases. The solubilization capacity of the mixed surfactants shows a small increase when a small amount of AEO3 is added but decreases at high proportion of addition. The mixing with AEO9 and AEO20 can greatly increase the optimum salinity but the solubilization capacity of the system will decrease when the proportion of nonionics is over 10%.With individual HABS or ABS, or their binary mixtures with nonionics, the interfacial tension of water/n-nonane can not be reduced to ultra-low (10"3mN/m). The HABS2#-HABS1# binary mixtures and HABS2#-HABS1#-AEO9 and HABS2#-HABSl#-AEO20 ternary mixtures can all reduce the water/n-nonane interfacial tension to the order of 10-2mN/m, close to ultra-low (1O"3 mN/m), but the salinity range required for producing such a low interfacial tension widens, or the salinity tolerance of the system increases, with the addition of nonionics.For crude oil/reservoir water systems, HABS2#-HABS1#-AEO9 and HABS2#-HABSl#-AEO20 ternary mixtures can produce ultra-low interfacial tension at total surfactant concentration of 0.1-0.3% in the presence of Na2CO3. Compared with HABS2#-HABS1# binary mixtures, the addition of nonionics greatly widens the Na2CO3 concentration range required for obtaining ultra-low interfacial tension, say, from 1.0-1.4% to 0.4-1.2% and 0.6-1.4% respectively. The addition of NaCl can further reduce the alkali concentration required.In comparison with HABS2#-HABS1# binary mixtures, the addition of AEO9 or AEO20 will result in an increase of interfacial tension, which is in good agreement with the conclusion from microemulsion study that solubilization capacity decreases with the excessive addition of nonionics.