EXPLORATION, RECOVERY, AND TRANSPORTATION 79
The recovery of petroleum from the reservoir in properly operated
water drive pools may run as high as 80%. The force behind the
water drive may be hydrostatic pressure, the expansion of the reservoir water, or a combination of both. Water drive is also used in
certain submarine fields.
Gravity drive is an important factor when oil columns of several thousands of feet exist, as they do in some North American
fields. Furthermore, the last bit of recoverable oil is produced in
many pools by gravity drainage of the reservoir. Another source
of energy during the early stages of withdrawal from a reservoir
containing under-saturated oil is the expansion of that oil as the
pressure reduction brings the oil to the bubble point (the pressure
and temperature at which the gas starts to come out of solution).
For primary recovery operations, no pumping equipment is
required. If the reservoir energy is not sufficient to force the oil to
the surface, then the well must be pumped. In either case, nothing is added to the reservoir to increase or maintain the reservoir
energy or to sweep the oil toward the well. The rate of production
from a flowing well tends to decline as the natural reservoir energy
is expended. When a flowing well is no longer producing at an efficient rate, a pump is installed.
The recovery efficiency for primary production is generally low
when liquid expansion and solution gas evolution are the driving
mechanisms. Much higher recoveries are associated with reservoirs
with water and gas cap drives and with reservoirs in which gravity effectively promotes drainage of the oil from the rock pores.
The overall recovery efficiency is related to how the reservoir is
delineated by production wells. Thus, for maximum recovery by
primary recovery, it is often preferable to sink several wells into a
reservoir, thereby bringing about recovery by a combination of the
methods outlined here.
3.3.2 Secondary Recovery
Over the lifetime of the well, the pressure will fall, and at some
point there will be insufficient underground pressure to force the
oil to the surface. If economical, and it often is, the remaining oil in
the well is extracted using secondary oil recovery methods. It is at
this point that secondary recovery methods must be applied.
Secondary oil recovery methods use various techniques to aid in
recovering oil from depleted or low-pressure reservoirs. Sometimes
The recovery of petroleum from the reservoir in properly operated
water drive pools may run as high as 80%. The force behind the
water drive may be hydrostatic pressure, the expansion of the reservoir water, or a combination of both. Water drive is also used in
certain submarine fields.
Gravity drive is an important factor when oil columns of several thousands of feet exist, as they do in some North American
fields. Furthermore, the last bit of recoverable oil is produced in
many pools by gravity drainage of the reservoir. Another source
of energy during the early stages of withdrawal from a reservoir
containing under-saturated oil is the expansion of that oil as the
pressure reduction brings the oil to the bubble point (the pressure
and temperature at which the gas starts to come out of solution).
For primary recovery operations, no pumping equipment is
required. If the reservoir energy is not sufficient to force the oil to
the surface, then the well must be pumped. In either case, nothing is added to the reservoir to increase or maintain the reservoir
energy or to sweep the oil toward the well. The rate of production
from a flowing well tends to decline as the natural reservoir energy
is expended. When a flowing well is no longer producing at an efficient rate, a pump is installed.
The recovery efficiency for primary production is generally low
when liquid expansion and solution gas evolution are the driving
mechanisms. Much higher recoveries are associated with reservoirs
with water and gas cap drives and with reservoirs in which gravity effectively promotes drainage of the oil from the rock pores.
The overall recovery efficiency is related to how the reservoir is
delineated by production wells. Thus, for maximum recovery by
primary recovery, it is often preferable to sink several wells into a
reservoir, thereby bringing about recovery by a combination of the
methods outlined here.
3.3.2 Secondary Recovery
Over the lifetime of the well, the pressure will fall, and at some
point there will be insufficient underground pressure to force the
oil to the surface. If economical, and it often is, the remaining oil in
the well is extracted using secondary oil recovery methods. It is at
this point that secondary recovery methods must be applied.
Secondary oil recovery methods use various techniques to aid in
recovering oil from depleted or low-pressure reservoirs. Sometimes