Page 37 - Petroleum and Gas Field Processing

assignment of production rates to individual wells in the field, shutting off
certain wells for a specific duration, drilling of new wells at specific
locations, and implementing specific pressure maintenance or improved
recovery operations. The importance of reservoir management has been
recognized in recent years. This led to the formation of specialized groups
and departments for reservoir management in most major oil companies.

1.7.5 Improved Petroleum Recovery
The natural reservoir drive mechanisms described in Section 1.3.2
normally result in low-recovery factors. In fact, if reservoirs were
produced solely by the natural driving forces, very poor recoveries would
be obtained. The specific rock and fluids properties and the forces that
control the movements of the fluids within the reservoir are responsible for
such poor recoveries. Petroleum recovery by these natural drive
mechanisms is called primary recovery.
In order to achieve recoveries higher than the primary recovery, we
must intervene into the reservoir to artificially control, or alter, the natural
driving forces and/or the rock and fluids properties. Reservoir engineers
have developed, and continued research is being conducted for further
developments, refinement, and improvement, and various techniques to
achieve higher than primary recoveries. Some techniques involve
supplementing the natural driving force by injecting high-pressure fluids
into the reservoir. Other techniques aim at changing the fluids and/or rock
properties to enhance the mobility of the petroleum fluids and suppress the
forces that hinder their movements. All such techniques are known as
enhanced recovery methods or improved recovery methods. A brief
description of some of the improved recovery methods follows.

Pressure Maintenance
As oil is produced, the reservoir pressure declines at a rate that depends on
the reservoir drive mechanism, the strength of that drive, and the amount
of oil produced. Solution-gas-drive reservoirs experience the highest rate of
pressure decline, followed by the gas-cap-drive reservoirs, with the water-
drive reservoirs being the least affected. The decrease in reservoir pressure
reduces the ability of the formation to produce oil. The loss of
productivity becomes very severe if the reservoir pressure drops below the
bubble point pressure.
One way of maintaining a high reservoir pressure to maintain
productivity and increase recovery is to inject a fluid into the reservoir at
such quantities and pressure that it will keep the reservoir pressure at the

Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.