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§4 MAINTENANCE OF RESERVOIR PRESSURE BY
INJECTION INTO DEPOSIT OF WATER AND GAS

Everybody knows that the natural formation energy does
not always ensure complete recovery of the oil or the required
production rate. Maintenance of reservoir pressure for injecting
water or gas into the reservoir use to achieve higher recovery
factors and the necessary rate of oil production is very popular.

§4.1 MAINTENANCE OF RESERVOIR PRESSURE
BY WATER INJECTION

The oil recovery rate, the rate of withdrawal of its
reserves, is determined by its specific productivity index and by
the reserves. The specific productivity index is determined by size
and shape of reservoir, physical properties of rocks and fluids,
number of wells and their completion, external boundary and
bottom-hole pressures and distance from bottom holes to external
reservoir boundary. The number of wells and their arrangement as
well as bottom-hole pressure is generally controlled by the field
personnel; other factors are natural and uncontrollable.
When the loop pressure isn`t high and external reservoir
boundary is out of distance, assuming an optimum well spacing
and maintaining optimum bottom-hole pressure, a low withdrawal
rate can be maintained sometimes.
When applying marginal flooding external boundary can
be displaced up to the reservoir and sufficiently high pressure is
maintained in it.
Cap is the drainage area as it were and the gas-oil contact
may be taken as the drainage boundary in gas-cap reservoirs.
Injection of gas into the gas cap helps to maintain the pressure in it
and therefore it maintains a steady rate of production or increases
it.

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