Petroleum Engineering

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15C-1
The Lease Pumper’s Handbook
Chapter 15
Enhancing Oil Recovery
Section C
SECONDARY RECOVERY
C-1. Secondary Recovery.
In simple terms, secondary recovery is the
addition of basic water flood or gas flood
(i.e., pressure maintenance) as a continuous
force. Secondary recovery methods should
be introduced very early in the life of a field
while the income and profits from the wells
are high enough to pay for the additional
equipment and installation costs.
As noted in the following sections, there
are many problems with water and gas as
drive mechanisms. Nevertheless, they both
contribute greatly to enhanced recovery.
They can double the amount of oil produced
from the reservoir during the life of the
wells.
Water flood is the term used to describe
the increase in oil recovery by injecting
water into an oil-producing reservoir. When
gas is injected, it is not referred to as gas
flood, but instead is referred to as pressure
maintenance.
The term injection well is a general term
that means that either water or gas is
injected into a well.
Water disposal is a term used when water
does not enter an oil-producing zone.

operation. It provided a way to dispose of
undesirable water without the water being
used to stabilize firewalls around tank
batteries, control vegetation growth, and
water lease roads. At the same time, the
water raised production of the available oil
in the reservoir.
Water flood remains a keystone to many
methods of enhanced recovery. It is an
excellent second-stage recovery technique
and is also a major factor in slugging and
blending and extends deeply into many
tertiary recovery procedures throughout the
producing life of the reservoir.
One problem with water flood is that it is
difficult to push water through the formation
as a vertical wall—that is, the water will
spread out in the formation rather than move
through it evenly. Gravity pulls the leading
edge of the water down and causes it to
move downward as it progresses through the
reservoir. It can travel under the oil and
leave a large amount of oil behind.

C-2. Water Injection and Water Flood.
In the early years of experimenting with
enhanced recovery, water flood was
introduced.
This secondary recovery
practice solved a major problem of well

Figure 1. Wellhead set up for water
injection.

15C-2
Nevertheless, water continues to be one of
the best enhanced recovery tools available.
Water flood should be carefully designed
and properly installed because it will
probably be in place for the life of the well
or until equipment needs major changes.
C-3.
Preparing a Well for Water
Injection.
Downhole preparation. When preparing
an injection well, the casing must be tested
for leaks, a packer added near the casing
perforations to seal the annulus space, and
the space filled with a packer fluid to protect
it from corrosion. This process must receive
formal approval before it can be placed in
operation and must be witnessed by
regulating agencies when installed.
Pressure in the annulus is checked
regularly to determine that the casing or
tubing has no leaks and that the injection
pressure in the tubing is not excessive.

Figure 2. A wing valve used for water
injection.
(courtesy of Baker SPD, a Baker Oil Tools
company)

Wellhead preparation. When preparing
the wellhead for water injection, the pumper
will typically have a full opening master gate
on the tubing. The wing assembly, as
pictured in Figure 2, includes a valve, a
solids screen, volume meter, throttling valve
to regulate volume, a pressure gauge, and a
check valve to prevent fluid loss from the
injection well in the event of a line breaking.
C-4. Operating the Water Flood System
and Typical Problems.
Some water injection systems require a
collection system to gather all water from
several tank batteries. This may involve
large water holding tanks, filters, a highvolume injection pump...
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