Note: Descriptions are shown in the official language in which they were submitted.
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SEPARATION OF WATER AND OIL FROM A PRODUCTION STREAM
TECHNICAL FIELD
[0001] This
relates to a method of enhancing the separation of oil and water from fluids
produced from a hydrocarbon producing well by diffusing microbubbles into the
production
fluid.
BACKGROUND
[0002]
Fluids that are produced from an underground formation containing hydrocarbons
generally include multiple phases, such as water, crude oil, gaseous product,
and sand or other
solids. Often, a well site will have separation equipment downstream of the
wellhead to
separate the majority of the phases in order to make the downstream processing
more
efficient. Separation equipment may include separators that separate the
physical phases,
such as separating the liquid phases from the solids and/or the gaseous phase.
Other
separators may separate liquid phases, such as separating water and oil.
Depending on the
characteristics of the well, there may be any number of separators that may be
required to
achieve the desired level of separation.
SUMMARY
[0003] According to an aspect, there is provided a method of separating oil
and water
from a production stream, comprising the steps of producing a production fluid
from a
hydrocarbon producing well, the production fluid comprising a gas phase, a
water phase, an
oil phase, and sand phase, passing the production fluid directly from the
hydrocarbon
producing well through a series of separators, the series of separators
comprising at least one
water/oil separator that separates at least the water phase and the oil phase,
and injecting
microbubbles into the production fluid upstream of or into the first water/oil
separator relative
to the hydrocarbon producing well.
[0004]
According to another aspect, the water/oil separator may further separate the
gas
phase, the sand phase, or the gas phase and the sand phase.
[0005]
According to another aspect, the microbubbles may be injected upstream of the
first water/oil separator, directly into the water/oil separator, or upstream
of the series of
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separators.
[0006]
According to another aspect, the microbubbles may be injected into a
circulation
loop of the water/oil separator.
[0007]
According to another aspect, the microbubbles may be injected by passing the
entire stream of production fluid through a diffusion tower.
[0008]
According to another aspect, the entire stream of production fluid may be
passed
through the diffusion tower prior to passing through the first separator in
the series of
separators.
[0009]
According to an aspect, there is provided a method of separating oil and water
from a production stream, comprising the steps of receiving a production fluid
directly from a
hydrocarbon producing well, the production fluid comprising at least an oil
phase and a water
phase, passing all of the oil phase and the water phase of the production
fluids through a
separator for separating the water phase from the oil phase, the separator
having an oil outlet
and a water outlet, and injecting microbubbles into the production fluid
upstream of the oil
outlet and the water outlet.
[0010]
According to another aspect, the production fluid may further comprise sand, a
gas phase, or sand and a gas phase.
[0011]
According to another aspect, the production fluid may be passed directly from
the
hydrocarbon producing well to the separator.
[0012]
According to another aspect, the production fluid may be passed directly from
the
hydrocarbon producing well to a series of phase separators, and the separator
may be the first
phase separator that separates the water phase from the oil phase.
[0013]
According to another aspect, the microbubbles may be injected upstream of the
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separator or directly into the separator.
[0014]
According to another aspect, the microbubbles may be injected into a
circulation
loop of the separator.
[0015]
According to another aspect, the microbubbles may be injected by passing the
entire stream of production fluid through a diffusion tower.
[0016]
According to another aspect, the entire stream of production fluid may be
passed
through the diffusion tower prior to passing through the first separator in
the series of
separators.
[0017] In
other aspects, the features described above may be combined together in any
reasonable combination as will be recognized by those skilled in the art.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] These
and other features will become more apparent from the following
description in which reference is made to the appended drawings, the drawings
are for the
purpose of illustration only and are not intended to be in any way limiting,
wherein:
FIG. 1 is a schematic view of a separator with a microbubble diffuser
upstream.
FIG. 2 is a schematic view of a separator with a microbubble diffuser attached
to a
separator.
FIG. 3 is a schematic view of a separator with a microbubble diffuser within
the
separator.
FIG. 4 is a schematic view of a separator with additional preliminary
separators
prior to a microbubble diffuser upstream of the separator.
FIG. 5 is a schematic view of a separator with a microbubble diffuser upstream
of
additional preliminary separators and a separator.
DETAILED DESCRIPTION
[0019] A
method of separating oil and water in a production stream of fluids from a
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hydrocarbon producing well will now be described with reference to FIG. 1
through 5.
[0020] FIG.
1 depicts a general layout of a wellhead 12 and separation equipment,
generally indicated by reference numeral 14, which receives the fluids
produced from
wellhead. The production fluids may be conventional production fluids, or may
be produced
in other circumstances, such as a water flood, polymer flood, etc. The
production fluids
generally have various components, including a gas phase, which consist
primarily of lighter
hydrocarbons such as methane and may also be referred to as a vapour phase; a
liquid phase,
which consists primarily of a water phase and an oil phase; and a solid phase,
which is
granular and generally referred to as sand, although it may include solids
other than silicates,
such as rock particles, clay, etc. that may be present in the underground
formation. The sand
is generally those solids that are carried by or suspended within the other
liquid or gas phases
as they are produced. After the production fluids exit wellhead 12, it is
necessary to separate
the various phases to isolate the oil phase for further processing. The other
phases are also
generally separated and used or disposed of as is known in the art. The
downstream
processing of the various components is well known in the art, and will not be
described
further.
[0021] At
the wellsite, an initial separation of oil and water occurs. It will be
understood
that a complete separation may not be possible, and that there may be some
emulsions or
suspended solids that are difficult to remove using onsite equipment. Instead,
the final
separation occurs elsewhere, such as in a refinery. However, a better
separation on site results
in a more efficient process, as a higher concentration of oil is being
collected and transported
to the refinery.
[0022]
Generally speaking, there are various separators that may be used at a
wellsite.
Examples may include a three phase separator, which is used to separate the
gaseous phase,
the liquid phase and the solid phase. Another type of separator is a sand
knockout, which is
used to remove sand from the production stream, with the liquid and gaseous
phases
continuing. Removing the sand is important, particularly in high pressure
situations, as the
sand acts as an abrasive and can erode equipment. Yet another separator is the
water/oil
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separator, which separates the oil and water phases present in the liquid
phase, such as a free
water knockout tank. The separation scheme and separators that are used will
generally
depend on the composition of the produced fluid, such as the relative
proportion of each
phase, and the way in which the production fluids will be transported, such as
the fluids being
5 stored in
a production tank for future transport by a tanker truck, or transported by
pipeline.
The presently described method was primarily designed for high pressure
applications,
however, it will be understood that it may be applied in a variety of other
applications.
[0023] The
presently described method relates to enhancing the initial separation of
water
and oil from the production stream by injecting microbubbles at the initial
stage. As will be
understood, the microbubbles may be injected in various ways and the actual
position of the
separator may vary depending on the configuration of the wellhead separator
equipment.
Some examples are given below. In each of the examples the microbubbles are
injected
upstream of, the first separator that is used to separate the water phase and
the oil phase. It
will be understood that this includes the scenario shown in FIG. 3, where the
microbubble
diffusion tower 18 is contained within the water/oil separator 16, as in this
case the fluid flow
is still passing through microbubble diffusion tower 18 prior to entering
separator 16. For the
situations described herein, this will still be considered upstream as the
fluid has not yet
entered the separation area of separator 16. The first water/oil separator may
be downstream
of a three phase separator, a sand knockout tank, or other type of separator,
or may be
integrated within the separator. The first separator where this occurs will be
described herein
as a water/oil separator. It should be kept in mind that, while the process
may be discussed in
terms of injecting the entire water and oil phases into the oil/water
separator, there may be
some ancillary, inherent removal of water or oil when separating the gas phase
or the solid
phase, as the gas phase may entrain water or oil droplets, and the sand may be
wet with water
or oil, as each phase is removed from a separator. As no separation can result
in 100%
separation, the residual amounts of phases that will be found in other phases
after separation
will not be considered to be part of the water or oil phase. Alternatively, it
may be considered
that the water/oil separator is the first separator that is designed to
separate water from oil, and
has separate outlets for outputting the water phase and the oil phase from the
separation
vessel.
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[0024] It
will also be noted that the fluid entering the water/oil separator will also
likely
include some sand, as it is difficult to fully remove the solid phase without
more robust
separation techniques. As such, even if water/oil separator is downstream of a
sand separator
(such as a three phase separator, sand knockout tank, etc.), there will likely
still be some
solids content in the fluid entering the water/oil separator.
[0025]
Referring now to FIG. 1, there is shown an example of a separation scheme in
which there is a separator 16 downstream of a microbubble diffusion tower 18.
Diffusion
tower 18 injects microbubbles of a gas into the stream of production fluids.
Preferably, the
gas is a gas that is non-reactive with the oil in the fluid stream, such as
methane, nitrogen, or
the like. An example of a suitable diffusion tower for injecting the
microbubbles includes the
diffusion systems produced by Seair Inc. of Alberta, Canada. Some of these
systems apply
shear forces to the fluids when injecting microbubbles, which may help
destabilize any
oil/water emulsions, i.e. emulsions that may exist in a "rag layer" at the
oil/water interface,
and may also help separate any entrained or emulsified sand.
[0026]
Preferably, the system is used in situations where the oil content is between
30 ¨
70%, and preferably 40 ¨ 60%, but may also used with production flows having
an oil content
of down to 2% or less, or up to 80% or more. Generally speaking, for higher
concentrations
of oil, more gas will be required, and the impact of the diffused gas is more
noticeable.
[0027]
Separator 16 is a water/oil separator that has a production fluid inlet 20, an
oil
outlet 22 and a water outlet 24. Separator 16 may vary and may be selected
from among
commercially available separators, or custom manufactured based on known
design
principles, that are known able to separate oil from water. A further example
is shown in
FIG. 2, where diffusion tower is connected in a circulation loop 26 of
separator 16, which
draws fluid out of separator 16, aerates the liquid using diffusion tower 18,
and reintroduces
the fluid into separator 16. Referring to FIG. 3, another example is shown,
where diffusion
tower 18 is positioned within separator 16. In this example, with diffusion
tower 18
surrounded by separator 16, the flow through inlet 20 is still directed
through diffusion tower
18 in which a gas/water mixture may be sheared before entering the full volume
of separator
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16. This eliminates a vessel that would normally be required for diffusion
tower 18. It will be
understood that separator 16 may require some modifications to be able to
handle the gas that
will be injected into the production fluid. For example, separator 16 may be
provided with an
additional gas outlet or vent (not shown), or may be designed to allow the gas
to exit through
one of the existing liquid outlets.
[0028] The
method is accomplished by passing all of the oil phase and the water phase of
the production fluids from wellhead 12 through separator 16 for separating the
water phase
from the oil phase, while injecting microbubbles into the production fluid
upstream of oil
outlet and water outlets 22 and 24. In one configuration, referring to FIG. 1-
3, the production
fluid is passed directly from wellhead 12 to separator 16. In another
configuration, referring
to FIG. 4, the production fluid is passed directly from wellhead 12 to a
series of phase
separators, with the microbubbles being injected upstream of the first phase
separator that
separates the water phase from the oil phase. This is represented by
additional separator 28,
which may represent multiple separators in series or parallel, connected
between wellhead 12
and water/oil separator 16. Referring to FIG. 5, diffusion tower 18 may also
be used prior to
additional separator 28. For example, the fluid flow may pass through
diffusion tower 18 prior
to entering a three phase separator at 28, which separates the gas, liquid,
and sand phases,
after which the fluid enters separator 16.
[0029] While
microbubbles have been commonly injected to treat or separate fluids in
separation tanks, this is generally seen as a polishing step. Contrary to
current industry
practice, it has been found that the efficiency of the separation of oil and
water in this initial
separator can be enhanced by injecting microbubbles at the initial stage,
where the gross
separation occurs, and where other solids may also be present. When performing
bulk
separation of oil and water using other separation techniques, it is common
for there to be
high oil concentration carry-overs, known as excursions, in the water phase.
For example, a
free water knock out separator may have about 2% oil in the separated water
stream, but an
excursion may be 30 ¨ 50% oil. By passing the fluid through diffusion tower
18, the shearing
force and the microbubbles serve to break up these excursions and aid in
separation of the oil
and water. It has also been found that by passing fluid flows with high
concentrations of oil
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through diffusion tower 18 prior to separation, the oil tends to collect, and
the small remaining
amounts of oil in the water is reduced relative to fluid flows with low
concentrations of oil.
As such, applying diffusion tower 18 to the fluid flow early in the separation
process is more
effective in separating the oil and water phases than if diffusion tower 18 is
used later in the
process.
[0030] In
addition to the effects described above, it has been found that, by passing
the
entire stream of production fluid through the diffusion tower, interaction
between the oil and
the microbubbles of gas is enhanced. In a typical injection situation, where
microbubbles are
injected into a separator tank such as by using compressed gas, the
microbubbles rise through
the tank and may not contact the oil particles. In this type of system, the
oil is attached to the
gas through incidental contact only. By passing the production fluid through a
diffusion
tower, the microbubbles are generated within the production fluid flow and
interaction
between the gas and the fluid is enhanced. Instead of passive or incidental
interaction, this
results in active contact and interaction being created between the oil and
gas and enhances
the separation of the oil and water. This technique may be beneficial as it
can be applied to
"dirty" fluid streams that have either had no separation of the sand and other
solid
components, or have had minimal separation.
[0031] In this patent document, the word "comprising" is used in its non-
limiting sense to
mean that items following the word are included, but items not specifically
mentioned are not
excluded. A reference to an element by the indefinite article "a" does not
exclude the
possibility that more than one of the elements is present, unless the context
clearly requires
that there be one and only one of the elements.
[0032] The
scope of the following claims should not be limited by the preferred
embodiments set forth in the examples above and in the drawings, but should be
given the
broadest interpretation consistent with the description as a whole.