|
Use of chemicals in EOR can be the most complex enhanced oil recovery technique because how the surfactant partitions between oil, water, gas and minerals will drastically affect performance of the flood. There are several major uses of chemicals.
-
The simplest is polymer flooding where a large molecule that is dissolved in water increases its viscosity. The viscous water than can improve the sweep efficiency in a heterogeneous reservoir or of a more viscous oil.
-
Surfactants can be used to reduce the mobility of a gas, to increase the mobility of an oil or to reduce its residual oil saturation.
-
Surfactants reduce mobility of gas by forming a foam, just like foam forms between water and gas with a soap. The lamellae in the foam are harder to move through pores in a rock, so the foam reduces gas mobility.
-
Surfactants increase the mobility of oil by reducing the interfacial tension (IFT) between oil and water, changing wettability of oil and water, emulsifying oil in water and reducing the amount of oil trapped by water. Generally, the surfactant and oil are pushed or chased from the reservoir by a slug of polymer.
-
The surfactant can be either a natural surfactant produced from the oil by adding a base (alkali). This is called an alkali polymer (AP) flood if the surfactant is created with an alkali or an ASP flood if additional surfactant is added to reduce the IFT. If alkali is not used the process is called an SP (surfactant polymer) flood.
More details of these processes are explained in the Chemical EOR section of this website. |
|
