Alkaline Surfactant Polymer / Surfactant Polymer Technologies
Surfactant flooding is a well known concept that has been practiced in the field for many decades. Current technology is a progressive and gradual development of technologies and ideas that have existed for a long time. The key difference is the amount of surfactant used in projects today is much lower due to high purity.
Surfactant flooding is usually carried out after a waterflood. There are two main types of surfactant flooding – Alkaline Surfactant Polymer (ASP) or Surfactant Polymer (SP) flooding.
ASP vs. SP
ASP formulation typically consists of about 0.5-1% alkali, 0.1% surfactant and 0.1% polymer, while a SP formulation consist of 1% surfactant and 0.1% polymer. The choice between ASP or SP depends on a number of factors.
- Acid value of the oil
- Quality of water – if divalent ion concentration is high, >100 ppm, SP may have to be used
- Economics of project
- Ability to carry out water softening or desalination (geographic location)
All components are injected together into the reservoir as a “slug” and it is not a sequential injection. Typically, the A/SP slug is injected at about 0.3-0.4 PV for effective performance. The alkaline component react with the acidic moieties that exist in the oil creating natural soap and also helps reduce the adsorption of the surfactant on the rock. The surfactant component helps in releasing the oil from the rock and reduces the interfacial tension between water and oil. The polymer (typically, partially hydrolyzed polyacrylamide or HPAM) acts as the viscosity modifier and helps mobilize the oil. Typically, an A/SP flood is followed up with an equivalent pore volume injection of a polymer “push” solution. This helps reduce the slope of oil recovery decline and helps extend the production for a longer period of time.