Glossary of Terms - EOR
This glossary covers words, phrases, and acronyms that are commonly used in various processes for the CO2 enhanced oil recovery industry. Some words may have different meanings when used in other contexts.
Crude Oil: Crude oil is a complex mixture of naturally occurring hydrocarbon compounds discovered in formation rock buried deep underground. Petroleum has different forms including solid, liquid, and gas, but the term is generally used to refer to liquid crude oil. Impurities such as sulfur, oxygen and nitrogen are common in petroleum, while considerable variation is found in color, gravity, odor, sulfur content and viscosity in petroleum from different areas.
As for crude oil, it can be termed as light, medium, or heavy, depending on its density and viscosity.
Reservoir: Reservoir is a subsurface body of rock having sufficient porosity to store fluids and permeability to transmit them. Sedimentary rocks are the most common reservoir rocks for storing hydrocarbons due to higher porosity than most igneous and metamorphic rocks. A reservoir is a critical component of a complete petroleum system.
Oilfield: Oil field is an accumulation, pool or group of pools of oil in the subsurface. An oilfield is composited of a reservoir in a shape that will trap hydrocarbons and that is sealed by an impermeable or sealing rock at the top.
Reservoir Characterization: Reservoir characterization is a mathematical model of a reservoir that incorporates all the characteristics of the reservoir that are pertinent to its ability to store hydrocarbons as well as to produce them. Reservoir characterization models are used to model and simulate behavior of the reservoir fluids within the reservoir under various conditions so as to find the optimum production techniques for maximizing the production.
Enhanced Oil Recovery (EOR): Enhanced oil recovery (EOR) is the third stage of hydrocarbon production during which sophisticated techniques that alter the original properties of the oil are used. EOR can be initiated after a secondary recovery process or at any time during the productive life of an oil reservoir. Its purpose is not only to restore and maintain formation pressure, but also to improve oil displacement or fluid flow in the reservoir.
The three major types of EOR operations are chemical flooding (alkaline flooding, micellar-polymer flooding, and alkaline-surfactant-polymer flooding), miscible displacement (carbon dioxide injection or hydrocarbon injection), and thermal recovery (steamflood or in-situ combustion). The optimum application of each type of EOR methods strongly depends on reservoir properties (reservoir temperature, pressure, depth, net pay, permeability, residual oil and water saturations, and porosity) and fluid properties (oil API gravity and viscosity).
CO2 Injection: CO2 injection is an EOR method in which CO2 is injected into a reservoir to increase production by reducing oil viscosity and providing miscible or partially miscible displacement of the oil.
Miscible Flooding: Miscible flooding is a general term for injection processes that initiate miscible gases into the reservoir. A miscible flooding process not only estores and maintains reservoir pressure, but also improves oil displacement because the interfacial tension between oil and water is reduced. The effect of gas injection is similar to that of a solution gas drive.
Miscible flooding is a major branch of EOR processes. Injected gases include liquefied petroleum gas (LPG), such as propane, methane, methane enriched with light hydrocarbons, nitrogen, and CO2 under appropriate reservoir temperatures and pressures. The fluid most commonly used for miscible displacement is carbon dioxide because it reduces the oil viscosity and is less expensive than liquefied petroleum gas.
Minimum Miscibility Pressure (MMP): Minimum miscibility pressure (MMP) is the minimum pressure at which reservoir crude oil is miscible with the injected fluids. In general, the operating pressure should be maintained at or higher than the MMP to ensure miscibility is reached in a miscible flooding process.
Reservoir Modeling and Simulation: Reservoir modeling is the act of producing a model of a reservoir that could include any of the geological, fluid or other characteristics of the reservoir.
Reservoir simulation is a computer run of a reservoir model over time to examine the flow of fluid within the reservoir and from the reservoir. Reservoir simulators are built on reservoir models that include the petrophysical characteristics required to understand the behavior of the fluids over time. In general, a reservoir simulator is calibrated by using historic pressure and production data in a process referred to as "history matching." Once the simulator has been successfully history matched, it can be used to predict and optimize future reservoir performance under a series of potential scenarios (drilling new wells, injecting various fluids or stimulation) and certain geological and financial uncertainties.