Reservoir energy – the energy of the reservoir bed and of the embedded fluid (oil, water, gas) which are stressed under the effect of rock pressure and reservoir pressure.

Main types of reservoir energy: produced water discharge, free gas and gas emitted when the pressure of the gas dissolved in oil is lowered, compressed formation and fluids tension, discharge energy defined by oil gravity. The more gases are dissolved in oil, the higher is the reservoir energy resource. When gas or fluid is recovered from the reservoir, the reservoir energy resource is spent on fluids movement and on overcoming the forces counteracting this movement (internal friction forces of fluids and gases and their friction on the rock, as well as capillary forces). Oil and gas movement in the reservoir is usually defined by various types of reservoir energy simultaneously (compressed formation and fluids tension and energy defined by oil gravity are always shown). Depending on geological features and the conditions of field development that or another type of energy shall prevail. According to the type of energy defining movement of gas and fluids to producing fields, different modes of operation are set for oil and gas deposits.

Reservoir energy resource spent during field development may be restored due to natural influx of water from surface sources into the pay zone (in outcrop locations), from aquifer (especially when external reservoir boundary is practically unlimited and has good hydro-dynamic connections with oil-saturated reservoirs) or by way of artificial injection of water, gas or other agent displacing reservoir fluid. Reservoir energy balance (ration of energy spent on production and external energy flowing into the reservoir) is one of the crucial parameters of oil field development. It is characterized by the difference between current and initial reservoir pressure, as well as by current and accumulated compensation of recovered fluid by injected working agent.