Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEMS AND METHODS FOR TREATING PRODUCED WATER
FIELD OF THE TECHNOLOGY
One or more aspects relate generally to energy production, and more
particularly to
systems and methods for treating water used in oil and gas extraction.
BACKGROUND
To meet energy and manufacturing needs, oil and gas are routinely extracted
from
underground sources. Conventional oil and gas extraction is a water intensive
process.
Produced water is typically unfit for discharge into local water sources and
may be injected into
underground wells for disposal. Alternatively, produced water may be treated
to render it
suitable for a variety of uses.
SUMMARY
In accordance with one or more aspects, integrated systems and methods for
energy
production are disclosed.
In accordance with one or more aspects, a method for treating produced water
may
comprise recovering heat energy from the produced water, and using the
recovered heat energy
to directly drive treatment of the produced water.
In some aspects, recovering heat energy from the produced water comprises
converting
heat energy to mechanical energy. The mechanical energy may be used to
separate oil and/or
contaminants from the produced water. Recovering heat energy from the produced
water may
further comprise converting the mechanical energy to electrical energy.
Recovering heat energy
from the produced water may comprise using a heat engine in fluid
communication with a
generator to convert the recovered heat energy to electrical energy.
Recovering heat energy from
the produced water may comprise using a thermoelectric generator to convert
the recovered heat
energy to electrical energy.
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In some aspects, the method may further comprise delivering excess recovered
heat
energy to an energy network. An energy network may be used to supplement the
recovered heat
energy or as a backup source of power. In at least some aspects, the heat
energy may be
recovered prior to separating oil from the produced water. In other aspects,
the heat energy may
be recovered during treatment of the produced water.
In accordance with one or more aspects, a system for providing energy to treat
produced
water may comprise a source of produced water having heat energy, a water
treatment subsystem
having an energy requirement and fluidly connected downstream of the source of
produced
water, and an energy recovery subsystem configured to convert a portion of the
heat energy from
the produced water to mechanical and/or electrical energy, and to supply at
least a portion of the
energy requirement of the water treatment system.
In some aspects, the energy recovery subsystem may comprise a generator
disposed in
communication with a turbine to generate electrical energy. In some non-
limiting aspects, the
turbine may comprise a two-phase turbine. In at least some aspects, the water
treatment
subsystem may comprise an oil-water separator and at least one of a
microfiltration unit, an
activated carbon media unit, a reverse osmosis unit, and an electrodialysis
unit. The energy
recovery subsystem may comprise a heat engine configured to operate in
accordance with a
trilateral thermodynamic energy conversion cycle.
Still other aspects, embodiments, and advantages of these exemplary aspects
and
embodiments, are discussed in detail below. Moreover, it is to be understood
that both the
foregoing information and the following detailed description are merely
illustrative examples of
various aspects and embodiments, and are intended to provide an overview or
framework for
understanding the nature and character of the claimed aspects and embodiments.
The
accompanying drawings are included to provide illustration and a further
understanding of the
various aspects and embodiments, and are incorporated in and constitute a part
of this
specification. The drawings, together with the remainder of the specification,
serve to explain
principles and operations of the described and claimed aspects and
embodiments.
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BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings, like reference characters generally refer to the same parts
throughout the
different views. Also, the drawings are not necessarily to scale, emphasis
instead generally
being placed upon illustrating the principles of the disclosed embodiments,
and are not intended
as a definition of the limits of such embodiments. For purposes of clarity,
not every component
may be labeled in every drawing. In the following description, various
embodiments are
described with reference to the following drawings, in which:
FIG. 1 presents a schematic of a conventional water cycle during oil and gas
extraction
operations in accordance with one or more embodiments;
FIG. 2 presents a schematic of a produced water treatment process in
accordance with
one or more embodiments;
FIG. 3 presents a schematic of a produced water treatment process in
accordance with
one or more embodiments;
FIG. 4 presents an energy flow diagram of systems and methods in accordance
with one
or more embodiments;
FIG. 5 presents an example of heat recovery using a working fluid to exchange
and
recover heat in accordance with one or more embodiments;
FIG. 6 presents a schematic of a generator suitable for transforming heat
energy
transferred from a well fluid to electrical energy in accordance with one or
more embodiments;
FIG. 7 presents an energy flow diagram of systems and methods in accordance
with one
or more embodiments; and
FIG. 8 presents a schematic of a thermoelectric generator in accordance with
one or more
embodiments.
DETAILED DESCRIPTION
Various embodiments described herein are not limited in their application to
the details of
construction and the arrangement of components as set forth in the following
description or
illustrated in the drawings. One or more embodiments are capable of being
practiced or carried
out in various ways beyond those exemplarily presented herein.
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Treatment of produced water has become increasingly attractive in view of the
expense
and potential environmental drawbacks relating to water use and disposal.
Onsite treatment of
produced water has various challenges, however, particularly the large energy
demand associated
with such operations. Gas wells are often located in remote locations,
limiting access to large
energy grids. Operating and fueling on-site generators to supply the energy
required for
treatment can be cost prohibitive. In accordance with one or more embodiments
disclosed
herein, systems and methods may beneficially extract heat energy from produced
water and use
it to power onsite treatment of the produced water. This integration may
enable greater
efficiency of overall oil and gas extraction operations. While some disclosed
embodiments relate
specifically to produced water associated with oil and gas extraction, one or
more aspects may be
applied to any source of water to be treated. For example, heat may be
extracted from water
associated with geothermal applications as well as from various industrial or
refinery water
streams. In some embodiments, heat may be recovered from process streams
associated with
metal casting or the manufacture of cement, iron, steel, aluminum and glass.
The recovered
energy may then be used to treat the water from which the heat was extracted.
The following
discussion regarding energy recovery and its use in water treatment may
therefore be applied to
any source of water to be treated.
A schematic of a water cycle in a conventional oil and gas extraction
operation is
presented in FIG. 1. In a first step 110, injected water may be used to drive
oil or gas to the
surface at a well head. The injected water and/or the existing water in the
formation surfaces as
a mixture, or emulsion, known as "produced water" that includes the oil and
gas products. A
typical water to oil ratio may be about 5-10:1 but may vary greatly.
Temperatures at the depth
under the earth's surface where oil and gas yielding formations exist are
generally high, which
causes the water to become heated. In some embodiments, the produced water may
be at a
temperature in the range of about 100 F to about 750 F. In some specific non-
limiting
embodiments, the produced water may be at about 170 F.
In a second step 120 of the water cycle, the water portion and oil portion of
the produced
water are separated by various unit operations, as discussed in greater detail
below with
reference to FIG. 2. In a third step 130 of the water cycle, portions of the
separated water stream
may undergo different treatment operations depending on their intended use. If
the water is
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intended for reinjection to permanent well disposal or for waterflooding, then
further treatment
may be minimal. For example, in a fourth step 140 of the illustrated water
cycle, a portion of the
produced water is reinjected for waterflooding to enhance water production.
Alternatively,
minimally treated produced water may be injected in an underground well for
disposal (not
shown). If the intended use requires an improved water quality, such as for
irrigation, then a
more robust water treatment may be required as discussed in greater detail
below with reference
to FIG. 3.
FIG. 2 presents a non-limiting schematic of a method for oil and gas
separation from
produced water in accordance with one or more embodiments. The produced water
210 may
enter an oil/water separation train 200 and may first undergo treatment in a
gravity separation
device 230 to separate the oil from the water. Various gravity separation
devices and other
appropriate unit operations will be readily apparent to those of ordinary
skill in the art.
Typically, gravity separation devices may operate based on the specific
gravity differences
between oil and water. Given time, the less dense oil will form an oil layer
240 that floats on top
of the denser water layer 230. Likewise, particulate matter will sink to the
bottom of the water
layer and will be drained out as part of a sludge 250. Hydrocarbons in a vapor
phase may, in
some embodiments, be directed through a vapor outlet towards a vapor
collection vessel (not
shown). The oil 240 and water layers 230 may then be directed to different
outlets, with the oil
layer collected as a commodity, and the water layer directed toward further
separation and
treatment. Passage through a single separation device may not complete the
separation of oil and
water to a satisfactory degree.
In accordance with one or more embodiments with further reference to FIG. 2,
the water
mixture effluent from device 230 may continue on to another oil water
separation unit, for
example, an inclined plate separator 260. In an inclined plate separator,
smaller oil droplets that
remained in the water layer coalesce on the inclined plates 265 into larger
droplets and separate
from the water layer to form an oil layer 240 separate from the water layer
230. The two layers
may then be directed to different outlets. The oil layer 240 produced by the
inclined plate
separator 260 may be removed from the train 200, and collected as a commodity.
The remaining
water mixture may continue on to another separation device, for example, an
induced gas
flotation device 270 and/or a membrane filter 290. In an induced gas flotation
device, gas or air
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is introduced into the water mixture, coalescing entrained oil particles and
bringing them to the
surface where they are separated from the water mixture, and reserved as a
commodity.
Conventional oil and gas well operations that involve the introduction of
water to drive
oil and gas to the surface will generally include oil and water separation
processes of which the
above are examples. Various unit operations and their arrangements for oil and
gas separation
may be selected by those skilled in the art with the embodiment described
above presented as a
non-limiting example. At this stage in the overall extraction operation, an
optimal amount of oil
has been recovered, the acquisition of which was the general purpose of the
operation. The
remaining water mixture at this point may be reinjected either into a working
oil or gas well, in a
process known as waterflooding, to drive out more oil and gas. Alternatively,
the water may be
reinjected into a disposal well for permanent disposal.
Further alternative uses for the water may be limited, however, because even
after oil and
water separation processes are complete, the water mixture may still contain
sufficient impurities
to make it unfit for most uses according to various state and/or federal water
quality standards.
After separation from the oil products is complete, the remaining water
mixture still retains a
high amount of total dissolved solids (TDS). Non-limiting species of TDS found
in produced
water may include bicarbonate, calcium, chloride, magnesium, potassium,
sodium, and sulfate
species among others. Therefore, the waste water mixture may also go through a
treatment
process to prepare it for other uses.
FIG. 3 presents a schematic of a method for further treatment of a water
mixture after oil
separation in accordance with one or more embodiments. The water treatment
train 300 of the
non-limiting embodiment presented may include microfiltration 310, activated
carbon media
320, and/or a desalination process such as reverse osmosis or electrodialysis
330 unit operations.
Microfiltration 310 typically refers to filtration with a membrane pore size
ranging from 0.1 to
10 microns. However, other filtration techniques, whether they involve larger
or smaller pore
sizes, may be substituted for microfiltration. Another method for filtering
which may be
employed in the water treatment train 300 involves activated carbon media 320,
e.g., activated
carbon, to remove contaminants through chemical adsorption. Reverse osmosis
330 may
separate contaminants by applying pressure to push a water stream through a
selective
membrane. Additional or alternative steps in the water treatment train 300 not
shown could
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include coagulation and flocculation, water softening, air stripping, or any
other process
generally known in the art for treating water. Various combinations of such
unit operations may
be used for treatment.
In accordance with one or more embodiments, the result of this water treatment
train 300
may be a concentrate flow 340 which comprises a reject stream that includes
the impurities, and
a product flow 350 which comprises purified water of a quality that may be
suitable for a variety
of uses. The product flow 350 may be appropriate for a number of end uses
which fall within
established water quality regulations. In some non-limiting embodiments, the
product flow may
be used to recharge aquifers, or for agricultural and irrigation purposes.
As mentioned above, the energy demands associated with water treatment may
serve as a
barrier to its implementation or the extent thereof. Energy delivery to remote
oil and gas fields
may be costly and of limited availability. Conventional energy supplies for
oil and gas fields
include electrical energy from an electricity grid or a series of onsite
generators. In an overall
extraction operation, energy is generally required to drive a variety of pumps
which may bring
the flow of produced water to the surface and move it through further unit
operations. Energy is
also demanded by oil/water separation processes, as well as by any further
water treatment
processes such as those described above.
In accordance with one or more embodiments, heat energy from well fluids or
other
sources of water to be treated may be harnessed to power oil/water separation
and other water
treatment processes. Treatment of produced water may be driven by heat energy
captured from
the produced water. Such integration may beneficially allow water treatment
and overall oil or
gas extraction operations to be performed in a more efficient manner.
In accordance with one or more embodiments, the temperature of the produced
water
may vary, such as may depend on geographical location, depth of extraction,
and other factors.
In some embodiments, the temperature may be relatively low, for example,
between about -10
and 200 F.
FIG. 4 presents a non-limiting schematic of an integrated system and method in
accordance with one or more embodiments. System 400 includes oil and gas
recovery 440 and
water treatment 450 operations. System 400 may also include an energy recovery
system 460,
electric generator(s) 470, and/or an energy supply 420 as discussed below. The
energy recovery
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system 460 may convert heat energy 480 from well fluids 475 to mechanical
energy 485 and/or
electrical energy 490. Mechanical energy 485 and electrical energy 490 may be
used to operate
unit operations of not only the oil/water separation processes 440 but also
the further water
treatment processes 450. As discussed further in association with FIGS. 5 and
6, the heated well
fluid, or heated produced water 475 may be directed to a heat exchanger which
may be part of
the energy recovery system 460. As the heat energy flow arrows 480 indicate,
the transfer of
heat from the well fluids 475 can occur at any point or multiple points along
its path. One or
more heat energy recovery units may be used. In some embodiments, the heat
energy may be
recovered prior to or during oil/water separation. Heat energy may be
recovered during a
downstream water treatment process. In some non-limiting embodiments, cooling
may generally
be required prior to surface discharge and upstream of any membrane filtration
or biological
treatment used for water treatment.
As will be discussed further below, at least a portion of the heat from the
well fluids may
be transferred to a working fluid in a heat exchanger as part of the energy
recovery system 460 in
accordance with one or more embodiments. Various heat exchangers may be
implemented which
are capable of operating at the involved process conditions. In some non-
limiting embodiments,
the inlet temperature to the heat exchanger may be about 40 to 100 F. In some
embodiments,
the outlet temperature from the heat exchanger may be about 45 to 110 F. The
heated working
fluid may then be vaporized to drive a turbine, or other mechanical transfer
device, thus
converting the heat energy to mechanical energy in some non-limiting
embodiments. Any
mechanical transfer device may be used. In some embodiments, a turbine may be
used. The
turbine should generally be suitable for operation at the involved process
temperatures as
discussed herein. For example, the turbine may be a Euler turbine or a
variable phase turbine. In
some non-limiting embodiments, the turbine may be a two-phase turbine
commercially available
from Energent Corporation (CA). In other embodiments, a screw expander or
other mechanical
transfer device may be used.
The mechanical energy of the turbine may then be used directly or to generate
electrical
energy via a generator 470. The mechanical energy may be used for driving
pump(s) 430,
oil/water separator 440 or water treatment process 450. Other applicable
methods for energy
extraction may be recognized by those of ordinary skill in the art. The
electrical energy 490 thus
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produced may then be used to directly supply or supplement the electrical
energy requirements
of the unit operations 440 and/or 450. If the produced electricity 490 exceeds
system
requirements, then the difference may be supplied to grid 420. Alternatively,
if the produced
electricity 490 is less than demand, then the difference may be supplied from
the grid 420.
In accordance with one or more embodiments, the turbine may be used to
generate
electricity. In some embodiments, the turbine may be used to provide
mechanical energy to a
water treatment process, for example, to directly move a pump, a mixer or
other device.
In accordance with one or more embodiments, the energy recovery system may
transfer
mechanical energy to an oil water separator and/or a water treatment process.
In some non-
limiting embodiments, a rotating shaft may be implemented such that shaft
energy may be used
directly in an oil separator, for example, to run a mixer, or a flotation
unit.
FIG. 5 presents a non-limiting schematic illustrating a system 500 for the
exchange of
heat from a well fluid to a working fluid to generate mechanical energy that
may be used to
operate a mechanical system or provide electricity in accordance with one or
more embodiments.
Heated fluid from a production well 510 passes through a heat exchanger 520
and transfers a
portion of its heat to a working fluid 540, for example a refrigerant. The
heated working fluid
vaporizes to turn a turbine 550. The mechanical energy of the turbine 550 is
transformed into
electrical energy in a generator 560. The embodiment depicted in FIG. 5 may
operate based on
an organic Rankine cycle or alternative thermodynamic energy conversion cycles
such as, for
example, a trilateral cycle, a variable phase cycle, or a Kalina cycle. The
trilateral cycle, for
example, is a thermodynamic cycle involving a substantially perfect
temperature matching
between the heat source and the working fluid to minimize irreversibility
associated with the
process and to maximize its efficiency. In contrast with more traditional
thermodynamic cycles
that encompass expansion of gases, the expansion of liquid may start in the
saturated liquid
phase forming a mixture of gas and liquid as a result. Alternative working
fluids or heat cycles
may be substituted for those in FIG. 5.
FIG. 6 presents a non-limiting schematic of a generator 600 suitable for
transforming heat
energy transferred from a well fluid to electrical energy in accordance with
one or more
embodiments. Generator 600 may convert heat energy to mechanical energy, which
may be
subsequently converted to electrical energy. A working fluid, as described
above, may evaporate
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in evaporator 610 after heat is transferred to it from extracted produced
water. The evaporated
fluid may perform work on a turbine 620, the mechanical energy of which may be
used to
produce electricity. The working fluid may then be condensed in condenser 640
before beginning
the cycle again.
In accordance with one or more embodiments, a thermoelectric conversion
process may
be used instead of a heat engine. FIG. 7 presents a non-limiting schematic of
one such
embodiment of an oil and gas recovery operation. System 700 includes a
thermoelectric
conversion process 760 and an energy supply 720. Rather than a heat engine
described above, a
thermoelectric conversion process 760 uses heat 785 from well fluid 795 to
produce electricity
790. In some embodiments, the thermoelectric conversion process 760 may
involve a
thermoelectric generator described below with reference to FIG. 8. The
electricity 790 may then
be used to power the operations of the system 700, either driving the pump
730, powering the
oil/water separations 740, or powering the water treatment process 750. If
more power is
produced than required by the system, the balance of the energy may be
transferred to the energy
supply 720, e.g. the grid. If the system requires more energy than that
produced by the
thermoelectric conversion process 760, then the energy supply 730 will supply
the difference.
FIG. 8 presents a schematic of a thermoelectric generator in accordance with
one or more
embodiments. Recaptured heat from the produced water may be used to operate a
thermoelectric
generator 800. In generator 800, heat is absorbed by a substrate 810 connected
to thermoelectric
couples 820. The thermoelectric couples 820 of thermoelectric semiconductors
may be
connected electrically in series and thermally in parallel to make a
thermoelectric generator. The
flow of heat may generally drive the free electrons to produce electrical
power from heat.
In accordance with one or more embodiments, energy may be harnessed from
produced
water and used to drive oil/water separation as well as treatment of the
produced water.
Recovered energy may be mechanical energy used directly to drive pumps used
for water
treatment. In other embodiments, mechanical energy may be converted to
electrical energy
directly used to drive motors used for water treatment. In some embodiments, a
thermoelectric
generator may be used to convert the recovered heat energy to electrical
energy. Recovered
energy may be more or less than that required for conveyance and treatment of
the produced
water. Excess energy may be delivered to an electric energy network which may
provide
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supplemental energy when needed or otherwise serve as a backup source of
power. The heat
energy from the produced water may be recovered prior to separating oil from
the produced
water. In other embodiments, the heat energy may be recovered during treatment
of the
produced water.
In accordance with one or more embodiments, the systems and methods may
generally be
described as having an energy recovery component or subsystem, followed by a
water treatment
component or subsystem.
The embodiments described herein will be further illustrated through the
following
example which is illustrative in nature and not intended to limit the scope of
the disclosure.
EXAMPLE
The following Table illustrates a prophetic example of the electric energy
that can be
recovered as an oil field is developed and produced water increases.
Item Unit Energy Generation Example
Temperature Inlet Water F 160 160
160
Temperature Outlet
Water F 135 135
135
Flow Rate bbl/day 500,000 2,500,000
7,000,000
los 920 4,601
12,882
Produced Power kW gross 2,600 13,000
36,000
kW net 2,200 11,000
31,000
Power for Desalination kW 2,500 12,300
34,500
Excess Power kW (300) (1,300)
(3,500)
Annual energy kWh/y 19,300,000 96,400,000
271,600,000
Energy Price $/kWh $0.17 $ 0.17
$ 0.17
Annual Avoided Cost MS/Y 3.3 16.4
46
Annual Avoided CO2 ton CO2/y 5,000 25,000
72,000
The results for power generation are based on pilot unit results for the same
temperature
while the results for desalination are based on a recently run pilot unit
using electrodialysis
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reversal technology for removing the salts. It is observed that in this case
with low salinity
waters the energy recovered supplies about 90% of the total energy required
for water
desalination and conveyance for treatment. Energy expenses for desalination
are the most
significant processing expense in treating the water to render it suitable for
reuse. The energy at
this site is generated by burning crude oil in a combustion engine. There are
also significant
environmental benefits by avoiding green house gas emissions from burning the
oil. The last
row on the Table indicates the Tons of CO2 that will be avoided with the
technology as a result
of displacing the use of a fossil fuel to generate electric power with a
renewable energy source
such as natural water heat. The results from the pilot energy recovery unit
indicate that the
systems are sensitive to the influent temperature to the unit. There is
therefore an incentive to
harvest the heat before it is dissipated.
The phraseology and terminology used herein is for the purpose of description
and should
not be regarded as limiting. The use of "including," "comprising,"
"involving," "having,"
"containing," "characterized by," "characterized in that," and variations
thereof herein is meant
to encompass the items listed thereafter, equivalents thereof, as well as
alternate embodiments
consisting of the items listed thereafter exclusively. Use of ordinal terms
such as "first,"
"second," "third," and the like in the claims to modify a claim element does
not by itself connote
any priority.
While exemplary embodiments have been disclosed, many modifications,
additions, and
deletions may be made therein without departing from the spirit and scope of
the disclosure and
its equivalents, as set forth in the following claims.
Those skilled in the art would readily appreciate that the various parameters
and
configurations described herein are meant to be exemplary and that actual
parameters and
configurations will depend upon the specific application for which the
embodiments are used.
Those skilled in the art will recognize, or be able to ascertain using no more
than routine
experimentation, many equivalents to the specific embodiments described
herein. It is, therefore,
to be understood that the foregoing embodiments are presented by way of
example only and that,
within the scope of the appended claims and equivalents thereto, the disclosed
systems and
methods may be practiced otherwise than as specifically described. The present
systems and
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methods are directed to each individual feature described herein. In addition,
any combination of
two or more such features, if not mutually inconsistent, is included within
the scope of the
present disclosure.
Further, it is to be appreciated that various alterations, modifications, and
improvements
will readily occur to those skilled in the art. Such alterations,
modifications, and improvements
are intended to be part of this disclosure, and are intended to be within the
spirit and scope of the
disclosure. For example, an existing system or method may be modified to
utilize or incorporate
any one or more aspects of the disclosure. Thus, in some embodiments,
embodiments may
involve configuring an existing energy extraction system or method to include
the integration
described herein. For example, an existing system or process may be
retrofitted to involve use of
heat from produced water to drive treatment of the produced water in
accordance with one or
more embodiments. Accordingly, the foregoing description and drawings are by
way of example
only. Further, the depictions in the drawings do not limit the disclosures to
the particularly
illustrated representations.
What is claimed is:
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