Oil and Gas Glossary

effective permeability

The ability to preferentially flow or transmit a particular fluid when other immiscible fluids are present in the reservoir (e.g., effective permeability of gas in a gas-water reservoir). The relative saturations of the fluids as well as the nature of the reservoir affect the effective permeability. In contrast, absolute permeability is the measurement of the permeability conducted when a single fluid or phase is present in the rock.

effective porosity

The interconnected pore volume or void space in a rock that contributes to fluid flow or permeability in a reservoir. Effective porosity excludes isolated pores and pore volume occupied by water adsorbed on clay minerals or other grains. Total porosity is the total void space in the rock whether or not it contributes to fluid flow. Effective porosity is typically less than total porosity.

electromagnetic propagation tool

EPT. The EPT is a device that measures the propagation time (TP1) and attenuation rate (A1) of a microwave frequency electromagnetic wave that is propagated through the formation near the borehole. These two measurements can be related to the (composite) dielectric constant of the formation close to the borehole. The EPT is a shallow investigation device that has a depth of investigation of 1 to 4 in., depending on the formation conductivity. As a result, the EPT responds primarily to the flushed or invaded zone of the formation. The utility of the EPT arises from two basic facts. First, the dielectric constant of earth formations is dominated by the amount of water contained in the rock pores. That results from the fact that the dielectric constant of water is an order of magnitude greater than that of the other constituents of reservoir rocks; namely, oil, gas, and the rock matrix. Second, at microwave frequencies, the dielectric constant of water saturated rocks is relatively independent of water salinity, except in ranges corresponding to very high salt concentrations. Those two facts imply that the dielectric constant inferred from the EPT measurements is effectively a salinity independent datum capable of distinguishing between water and oil in the zone of investigation. Also, these measurements can be used to derive values for formation porosity and water saturation that are essentially salinity independent. EPT is a mark of Schlumberger.

emulsion

A stable mixture of two immiscible fluids in which one phase is dispersed in droplets or globules in a continuous phase of the other. The continuous phase is said to be external; and the discontinuous phase, internal.

enhanced oil recovery

EOR. An enhancement of the conventional methods of oil recovery at any stage of their application. Enhanced oil recovery method refers to any recovery method other than primary and the conventional secondary recovery methods of flooding by injecting water or gas. All tertiary recovery methods are enhanced, but not all enhanced methods are tertiary.

evaporite

A sediment resulting from the evaporation of saline water.