Reservoir

The proportion of pore space in the reservoir occupied by different fluids

Fluid Saturation

These refer to the state of the reservoir before any production begins

Initial Reservoir Conditions

What type of recovery can be defined as the extraction of oil or gas using the natural pressure of the reservoir

Primary recovery

What type of recovery involves the injection of fluids (usually water or gas) into the reservoir to maintain pressure and improve recovery?

Secondary recovery

A set of techniques (such as chemical injection, steam injection, or CO2 flooding) used to increase the amount of crude oil that can be extracted from a reservoir beyond primary and secondary recovery.

Enhanced Oil Recovery

• also: Tertiary Recovery

A measure of how much volume a given amount of oil or gas will occupy at reservoir conditions compared to surface conditions.

Formation Volume Factor

• For a gas reservoir → Gas Formation Volume Factor (B_g)

• For an oil reservoir → Oil Formation Volume Factor (B_o)

The reservoir drive mechanism in which water from an underlying aquifer pushes oil to the well.

Water Drive

The reservoir drive mechanism in which gas expands and pushes oil toward the well.

Gas Drive

The reservoir drive mechanism in which the expansion of oil itself helps drive production.

Oil Drive

The process of creating a computer model that represents the behavior of fluids in a reservoir.

Reservoir simulation

A measure of the ability of a particular fluid (oil, water, or gas) to flow through the porous rock in the presence of other fluids. It is a critical concept in multiphase flow.

Relative Permeability

A method used to predict future production rates and estimate reserves based on historical production data.

Decline Curve Analysis (DCA)

Reservoirs with very low permeability, which make it difficult for oil or gas to flow through them.

Tight Reservoirs

The percentage of produced fluid that is water, as opposed to oil or gas.

Water cut

A technique used to analyze pressure changes in a well over time to understand reservoir properties, such as permeability, porosity, and flow behavior.

Pressure Transient Analysis

The impairment of the reservoir's permeability due to the introduction of foreign materials (e.g., drilling mud, scale, or fines) during well completion or production.

Formation damage

The percentage of the total hydrocarbons in a reservoir that can be extracted using current or future technology. It is often influenced by reservoir properties, production methods, and techniques like enhanced oil recovery (EOR).

Recovery Factor

The minimum production rate at which a well can flow naturally without the need for artificial lifting. 

Critical Rate

The process of enhancing the flow of hydrocarbons from a reservoir by using techniques like hydraulic fracturing (fracking) or acidizing.

Stimulation

The pressure in the reservoir that is exerted by the weight of the overlying rock and fluid columns.

Geostatic Pressure

The pressure exerted by a reservoir rock when it absorbs water or other fluids.

Swelling Pressure

A modified version of the ideal gas law, which accounts for the real behavior of gases by considering intermolecular forces and the finite volume of gas molecules

Van der Waals Equation

Another term for the formation volume factor for oil (B_o)

Oil shrinkage factor

Refers to crude oil that has had its dissolved gas removed, typically due to a decrease in pressure during production

Dead oil

What is the term used to describe the oil that exists under pressure in a reservoir with associated gas?

Live oil

This is the general name given to the set of mathematical relationships between variables such as pressure, volume, and temperature that describe the behavior of a substance (typically a gas or liquid).

Equations of State

A term that refers to the ratio of the volume of produced gas to the volume of produced oil at surface conditions

Gas to Oil Ratio (GOR)

Refers to the ratio of the volume of gas dissolved in oil at reservoir conditions 

Solution Gas to Oil Ratio (Solution GOR)

Refers to the total volume of crude oil that is estimated to exist in a reservoir before any production has taken place

Original Oil in Place (OOIP)

• also: Initial Oil in Place (IOIP)

Refers to the total volume of gas that is estimated to exist in a reservoir before any production has

Original Gas in Place (OGIP)

• also: Initial Gas in Place (IGIP)