Definition
This is the process of enhancing oil production by the injection of a fluid into the reservoir, specifically EOR is done using engineered fluids that utilize methods beyond natural energy and augmented natural energy. EOR is the result of the injection of gases or liquid chemicals and/or the use of thermal energy. The injected fluid supplements natural energy and interacts with the rock/oil system to create a favourable environment for oil recovery.
The process can be grouped into 5 main categories:
Mobility Control
Based on maintaining favourable mobility ratios to improve the magnitude of macroscopic displacement efficiencies.
This is the generic term describing any process where an attempt is made to alter the relative rates at which injected and displaced fluids move through a reservoir. The aim is to improve the volumetric sweep efficiency of a displacement process. Usually expressed in terms of Mobility Ratio M. If M≤1.0 then the process exhibits mobility control. Generally as M is reduced volumetric sweep efficiency increases.
Most mobility control processes concentrate on improving the characteristics of the injected fluids. In many cases mobility control involves the addition of polymers to augment the fluid being injected.
Chemical
The addition of chemical agents to affect the interfacial tension (IFT) and phase behavior to displace oil by improving microscopic displacement efficiency.
Miscible
To inject fluids that are directly miscible with the oil or that generate miscibility in the reservoir through composition alteration.
Thermal
Methods that rely on the injection of thermal energy or the in-situ generation of heat to improve oil recovery.
Other
A catch all category that addresses any other process that is NOT covered by the other categories.
1.1.1. Permeability
The ability of a porous medium (in this case a hydrocarbon reservoir) to allow fluids to flow through. The rock permeability usually denoted by the symbol “k”, is important because it controls the directional movement and the flow rate of the fluid through the rock. Permeability id mathematically defined by Darcy’s Law, it is the standard tool of the petroleum engineer when one considers the flow of hydrocarbons through a porous medium.
Absolute
Permeability when saturated with only one fluid.
Effective
Permeability to one fluid when two or more fluids are present.
Relative
The ratio of effective permeability of one phase to some base permeability.
1.1.1. Capillary Pressure
The pressure difference across the interface, f a fluid system, the wetting and the non-wetting phase.
Interfacial Tension
The energy required to increase the area of the interface by one unit.
Displacement Efficiency
It is the fraction of moveable oil that has been recovered from the swept zone at any given time.
Microscopic
How well the oil displacing fluid moves once in contact.
Macroscopic
How well the displacing fluid has contacted the reservoir containing oil.
