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Every oil and gas reservoir has an initial energy reserve.
This energy reserve is consumed in moving the oil and gas through
the formation to the well. The energy reserve of a reservoir
depends on the magnitude of formation pressure. In the general
case, the sources of reservoir energy, which cause oil and gas to
flow to the well are:
- the elastic energy of compressed reservoir rocks and fluids;
- the energy of free gas and of the gas evolving from the oil
when pressure is reduced;
- the potential energy of water encroachment;
- the potential energy of the static pressure of the oil itself due
to gravity.
During the exploitation of a field, the reserves of reservoir
energy are consumed in overcoming forces that resist the
movement of oil and gas through the formation: forces of internal
friction of liquids and gases and of their friction with the rock, and
also capillary forces. Frictional forces arise due to the viscosity of
the fluids.
There may be a single dominant type of reservoir energy,
driving the oil and gas, or else they may be driven by a number of
forces. Further on it will be shown that the energy characteristics
of a reservoir determine the entire process of development and
exploitation.
Let us consider in greater detail the nature and the
character of manifestation of the types of reservoir energy
mentioned above. There are 6 oil reservoir drives:
- elastic drive;
- solution gas drive;
- water drive;
- gas cap drive;
- gravity drive;
- combination drive.
The drive of a reservoir is determined both by conditions
created artificially as a result of the development and the

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