Chemical flooding technique of alkali-surfactant-polymer (ASP) has been successfully applied in China for sandstone reservoir. However, challenges to develop chemical EOR formulations without alkali are significant and unique for both sandstone and carbonate reservoir. On the one hand, it is very difficult to achieve ultra-low interfacial tension and good oil displacement effect without the help of alkali. On the other hand, the oil types, rock mineral compositions, rock surface property, matrix pore structure and orientation are all different for sandstone and carbonate reservoir. In fact, the ASP technologies successfully used in Daqing sandstone oilfield cannot be simply extrapolated to SP combination flooding and carbonate reservoir. The key technology is development low cost and high efficiency surfactant and polymer.
In this paper, the new surfactant/polymer formulation has been developed, and show good properties for both sandstone and carbonate reservoir.
The novel sulfobetaine with intellectual property has been obtained with raw material of cheap fatty acid, and the carbon-carbon double bond can improve the solubility and emulsifying property.
The star-shaped polymer has been developed, and could effectively increase the rigidity of polymer molecular chain and the regularity of molecular structure, which can make the curliness of polymer chain become difficult, and increase the revolving hydraulic radius of molecular chain.
The new surfactant/polymer formulation had wide adaptability and could achieve ultra-low interfacial tension (IFT, less than 1.0×10−2mN/m) in different sandstone and carbonate reservoir conditions, and the temperature were from 45 ℃ to 90℃, and the salinity were from 4,500 mg/L to 100,000 mg/L.
The SP system has good long term stability at different reservoir conditions. The IFT results were in the range from 10−4mN/m to 10−3mN/m with duration of 180 days, and the retention rates of viscosity were more than 90%.
The new surfactant/polymer formulation had good emulsifying capacity, and emulsion Winsor III was observed. It could change the wettability from oil wet to water wet, and had good stripping film capacity.
The alkali-free SP formulation showed good oil displacement effect. After water flooding, it could increase oil recovery 21.5% (OOIP) in Daqing oilfield in China for sandstone reservoir; for carbonate reservoir, it could increase oil recovery 23.42% (OOIP) in the oilfield of Middle East.
This paper presents the new alkali-free surfactant/polymer combination flooding green technology, which provide promising chemical EOR technique for both sandstone and carbonate reservoir.