U.S. patent application number 14/682191 was filed with the patent office on 2015-10-29 for liquid based boiler.
The applicant listed for this patent is CONOCOPHILLIPS COMPANY. Invention is credited to David W. LARKIN.
Application Number | 20150308231 14/682191 |
Document ID | / |
Family ID | 54334281 |
Filed Date | 2015-10-29 |
United States Patent
Application |
20150308231 |
Kind Code |
A1 |
LARKIN; David W. |
October 29, 2015 |
LIQUID BASED BOILER
Abstract
Methods and systems generate steam for oil recovery operations.
The systems may limit feedwater pretreatment expenses and fouling
issues. In the method, dirty feedwater introduced into a vessel
containing a hot liquid hydrocarbon, e.g., an already hot produced
hydrocarbon, contacts the hydrocarbon and is vaporized into steam.
The steam collects in a top of the vessel and may be conveyed to
the wellhead for downhole injection. The hydrocarbon remains heated
by a closed circulation loop passing back and forth through a lower
half of the vessel containing the hydrocarbon. The fluid in this
loop remains isolated from contaminates in the water to limit
fouling in tubes, which form the loop and can employ normal
metallurgy to save on capital costs. The hydrocarbon can be treated
as needed to remove accumulating salts and/or entrained water and
recycled.
Inventors: |
LARKIN; David W.; (Houston,
TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CONOCOPHILLIPS COMPANY |
Houston |
TX |
US |
|
|
Family ID: |
54334281 |
Appl. No.: |
14/682191 |
Filed: |
April 9, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61983742 |
Apr 24, 2014 |
|
|
|
Current U.S.
Class: |
166/303 ;
166/302; 166/57 |
Current CPC
Class: |
E21B 43/24 20130101;
E21B 36/025 20130101; F22B 9/12 20130101 |
International
Class: |
E21B 36/00 20060101
E21B036/00; E21B 33/068 20060101 E21B033/068; E21B 43/24 20060101
E21B043/24 |
Claims
1. A steam generator system for heavy oil production, comprising: a
vessel comprising a hydrocarbon; a closed heat transfer fluid
circulation loop that passes in part through the vessel to heat the
hydrocarbon; a pump for pressurizing a feedwater stream and fluidly
connected to nozzles in the vessel, wherein the nozzles spray the
feedwater onto the hydrocarbon to produce steam; and a wellhead
injection system for conveying the steam into an oil reservoir and
coupled to an exit port near a top of the vessel for collecting the
steam.
2. The steam generator system of claim 1, wherein the closed heat
transfer fluid circulation loop includes a heat transfer fluid, a
heater and a pump.
3. The steam generator system of claim 1, wherein the closed heat
transfer fluid circulation loop includes a heat transfer fluid
selected from butane, molten sodium, molten sodium-potassium,
DOWTHERM and THERMINOL.
4. The steam generator system of claim 1, further comprising a
hydrocarbon treatment loop in fluid connection with the vessel,
wherein the hydrocarbon treatment loop desalts the hydrocarbon.
5. The steam generator system of claim 2, further comprising a
hydrocarbon treatment loop in fluid connection with the vessel,
wherein the hydrocarbon treatment loop desalts the hydrocarbon.
6. The steam generator system of claim 3, further comprising a
hydrocarbon treatment loop in fluid connection with the vessel,
wherein the hydrocarbon treatment loop desalts the hydrocarbon.
7. A liquid steam generator, comprising: a vessel comprising a
hydrocarbon in a lower portion of the vessel; a closed heat
transfer fluid circulation loop containing a heat transfer fluid,
wherein the loop passes in part through the lower half of the
vessel to heat the hydrocarbon and a remainder of the loop passes
to a heater and a pump to heat and circulate the heat transfer
fluid; a hydrocarbon treatment loop for cleaning the hydrocarbon,
wherein the hydrocarbon treatment loop includes a pump and a
desalter; a pump for pressurizing a feedwater stream fluidly
connected to nozzles in an upper portion of the vessel, wherein the
nozzles spray the feedwater onto the hydrocarbon to produce steam;
and a wellhead injection system for conveying the steam into an oil
reservoir and coupled to an exit port near a top of the vessel for
collecting the steam.
8. The steam generator system of claim 7, wherein the hydrocarbon
heat transfer fluid is selected from butane, molten sodium, molten
sodium-potassium, DOWTHERM and THERMINOL.
9. The liquid steam generator of claim 7, wherein the feedwater is
untreated produced water.
10. The liquid steam generator of claim 9, wherein the hydrocarbon
fluid is a produced hydrocarbon separated from the produced
water.
11. The liquid steam generator of claim 7, wherein a mixture of the
steam and at least some of the hydrocarbons with less than eight
carbon atoms per molecule output the vessel through the exit
port.
12. The liquid steam generator of claim 7, wherein the treatment
loop includes a visbreaker.
13. A method of generating steam, comprising: circulating a heat
transfer fluid through a closed loop for transfer of thermal energy
from a heater along the loop to hydrocarbons in a vessel as a
portion of the loop passes through the vessel; and introducing
feedwater into contact with the hydrocarbons in the vessel to
vaporize the feedwater into steam.
14. The method of claim 13, wherein the feedwater is untreated
produced water.
15. The method of claim 13, wherein the feedwater is blowdown from
one of a steam generator and an evaporator.
16. The method of claim 13, wherein the heat transfer fluid is
selected from butane, molten sodium, molten sodium-potassium,
DOWTHERM and THERMINOL.
17. The method of claim 13, further comprising injecting the steam
into an oil reservoir.
18. The method of claim 13, further comprising desalting the
hydrocarbon in the vessel.
19. The method of claim 13, wherein an output from the vessel
includes a mixture of the steam and at least some of the
hydrocarbons with less than eight carbon atoms per molecule.
20. The method of claim 13, further comprising circulating the
hydrocarbons into contact with the steam output from the vessel.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of U.S. Patent Application
Ser. No. 61/983,742 filed Apr. 24, 2014 entitled "LIQUID BASED
BOILER," which is hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] The invention relates to method and system for generating
steam with minimal or eliminated fouling resulting largely from the
use of contaminated feedwaters. The invention limits fouling
problem by spraying dirty feedwater directly onto a hot hydrocarbon
for steam generation.
BACKGROUND
[0003] Steam Assisted Gravity Drainage (SAGD) is an enhanced oil
recovery technology for producing heavy crude oil and bitumen. It
is an advanced form of steam stimulation wherein a pair of
horizontal wells are drilled into the oil reservoir, one a few
meters above the other. High pressure steam is continuously
injected into the upper wellbore to heat the oil and reduce its
viscosity, causing the heated oil and any condensed steam (hot
water) to gravity drain into the lower wellbore, where it can be
pumped to the surface. The produced oil is a mixture of heated oil
plus water. Because water is as precious a resource as oil, the
"produced water" is then cleaned and returned to the boiler, where
it is converted into steam and injected back into the ground.
[0004] Due to the recycling of water in SAGD operations, and the
fact that the water encounters petroleum deposits as well as any
additives used in production, the feedwater used to make steam is
typically far from pure. Produced water and brackish well water are
the main boiler feedwater sources for SAGD and other steam based
oil recovery process. The water at time of being generated into the
steam may still contain: at least about 500 parts per million
(ppm), at least 1000 ppm, at least 10,000 ppm or at least 45,000
ppm total dissolved solids; at least 100 ppm, at least 500 ppm, at
least 1000 ppm or at least 15,000 ppm organic compounds or
organics; and at least 1000 ppm free oil.
[0005] "Fouling" is the contamination of heating surfaces by these
mineral scales, and the build-up of scale eventually decreases the
heat-flux and thus the heating efficiency. Therefore, the boiler
has to be shut down several times a year to remove the fouling
layer and/or repair the tubing. In addition to the repair cost, the
down-time further increases the cost of the SAGD operation. To
minimize fouling, boiler feed-water (BFW) quality is critical
because dissolved solids are the major cause of boiler failure and
efficiency losses. Therefore, the total dissolved solids (TDS) for
BFW needs to be controlled under a certain level to prevent or
alleviate the scaling issue, and this is usually done by
pre-treating feedwater prior to use to reduce TDS.
[0006] The two most common types of steam generators used for oil
sands recovery are once through steam generators (OTSG) and drum
boilers, which are also called water tube boilers. Coal-fired steam
generators, downhole steam generators, fluidized bed combustion
boilers and vapor therm steam generators have previously been
reported to be used in Alberta fields, but they are no longer found
in recent field applications.
[0007] The OTSG is a large continuous tube type steam generator
wherein steam is produced at the outlet of the continuous tube, as
shown in in FIG. 1. Feedwater supplied at one cold end of the tube
undergoes the preheating-evaporation cycle as it travels along the
continuous tube. As steam is produced in a traditional OTSG, the
steam quality is usually around 75-80%, i.e. not all the feedwater
vaporizes.
[0008] In drum type steam generators, in contrast, preheated water
evaporates as it circulates in heated tubes between the steam drum
and the feedwater drum, as shown in FIG. 2. Saturated steam and
water rises into the steam drum due to the lowered density compared
with the water in downcomer tube. Saturated steam is drawn off the
top of the drum and sent to the superheater section.
[0009] OTSG systems require frequent cleaning, which leads to the
increased down-time and costly repair. Fouling also reduces the
thermal efficiency 1% to 15% depending on the amount of deposits,
as they act as an insulating layer on the heating tubes. The
shutdown to clean the scale increases operating costs, and the
pre-treatments needed to de-oil and clean the feedwater before use
also contributes significantly to cost.
[0010] Therefore, there is a need for an improved steam production
scheme that can minimize fouling issues and reduce the downtime and
reduce both operating and initial capital costs for SAGD and other
steam based oil recovery operations.
SUMMARY OF THE DISCLOSURE
[0011] Embodiments of the invention use a hot liquid, such as the
produced heated hydrocarbons, or fractions thereof, to directly
vaporize non-treated boiler feedwater. This hot hydrocarbon
receives its thermal energy from another hot fluid, such as molten
sodium, molten sodium-potassium, or another hydrocarbon that may
include butane, DOWTHERM.TM. or THERMINOL.TM. heat transfer fluid,
within coils in a closed circulation loop traveling from a standard
heater to the vessel containing the hot hydrocarbon. Contaminants
from the water being vaporized may thus buildup in the hot liquid
requiring treatment of the hot liquid. The fluid in the coils
transfers heat to the hot liquid without relying on transfer of the
hot liquid to the heater. Thus, the fluid in the coils circulates
to maintain a desired heat balance providing a benefit by enabling
decoupled circulation of the hot liquid for treatment, such as
desalting, at a rate wanted for removal of the contaminants
independent of a flow needed for the heating.
[0012] The use of a hot hydrocarbon such as DOWTHERM.TM. enables
more conventional metallurgies to be used for the coils, thus
minimizing CAPEX costs. Further, the contaminants remain in the hot
liquid outside the coils without passing to the heater to avoid
problems inside the circulation loop.
[0013] The hydrocarbon heat steam generation system is a
replacement to the current OTSGs de-oiling and water treatment
facilities, which are otherwise essential to prevent rapid fouling
and tube corrosion that occurs in either drum boilers or OTSG
systems. Use of the oil and desalting of the oil mitigates
contaminant concentration buildup in the oil and fouling within the
steam generation system.
[0014] The hot hydrocarbon may give up some lighter molecular
weight elements to the steam, thus providing a small amount of
solvent, and essentially converting the SAGD process to an ES-SAGD
process, which may reduce steam usage since the solvent has the
effect of diluting and thinning the heavy oil or bitumen.
Typically, C1-C5 hydrocarbons, and even C6-C8 hydrocarbons, may
vaporize and be carried along with the steam, albeit in low
amounts.
[0015] The invention produces high pressure steam or
steam-plus-solvent which can be used in a SAGD reservoir or in
other steam stimulation processes, such as cyclic steam generation
(CSS) or steam drive (SD) also called steam flooding, and
combinations and variations thereof.
[0016] Of course, the hot hydrocarbon picks up the dissolved solids
and any entrained oil in the dirty feedwater, but the oils are not
a problem, and the dissolved solids (which may no longer be
dissolved) can be removed in a cleaning loop using known
technology. Treatment units can include one or more of a variety of
treatment units, including e.g., a filter, coalescer, desalter,
dehydrator, visbreaker or electrostatic separator.
[0017] Salts in crude oil feedstocks can cause severe problems
downstream, including corrosion by acids formed by chloride salt
decomposition in fractionator overhead equipment, fouling of heat
exchangers by salt deposition, and poisoning of catalysts in
down-stream units. Therefore, crude is typically desalted before
being charged to the distillation train. Crude can also contain
suspended solids, such as sand, clay, and iron oxide particles.
[0018] The two most typical methods of crude-oil desalting,
chemical and electrostatic separation, use hot water as the
extraction agent. In chemical desalting, water and chemical
surfactant (demulsifiers) are added to the crude, heated so that
salts and other impurities dissolve into the water or attach to the
water, and then held in a tank where they settle out. Electrical
desalting is the application of high-voltage electrostatic charges
to concentrate suspended water globules in the bottom of the
settling tank. Surfactants are added only when the crude has a
large amount of suspended solids. Both methods of desalting are
continuous. A third and less-common process involves filtering
heated crude using diatomaceous earth.
[0019] For example, an electrostatic dehydration system is an
efficient method to remove high salinity formation water from the
crude oil stream. This process relies on establishing a high
voltage AC electrical field in the oil phase of dehydrator/desalter
vessels. The electrical field imposes an electrical charge on water
droplets entrained in the oil stream, thus causing them to
oscillate as they pass through the electrodes. During this
oscillation the droplets are stretched or elongated and then
contracted during reversal of the imposing AC electrical field.
During this agitation, the water droplets co-mingle and coalesce
into droplets of sufficient size to migrate, by gravity, back into
the lower water phase of the vessel for disposal.
[0020] Alternatively, Ultrafiltration (UF) can be used primarily to
remove the emulsified oil droplets, followed by the removal of
total dissolved solids (TDS) via reverse osmosis (RO).
[0021] The liquid boiler system described herein improves SAGD
economics by: [0022] Eliminating the need for de-oiling, water
pre-treatment plants and conventional steam boiler plants. [0023]
Enhancing the heavy oil recovery by including lower molecular
weight hydrocarbons combined with the produced steam. These
hydrocarbons aid in reducing the heavy oil viscosity in the
reservoir along with the steam, thus, enhancing oil production.
[0024] Overall SAGD steam demand may also decrease due to the
presence of hydrocarbon within the steam, in much the same manner
that ES-SAGD reduces steam requirements.
[0025] The invention includes one or more of the following
embodiments, in any combination thereof:
[0026] A steam generator system for heavy oil production,
comprising: a vessel comprising a hot hydrocarbon; a pump for
pressurizing a dirty feedwater stream fluidly connected to nozzles
in said vessel, said nozzles spraying said dirty feedwater onto
said hot hydrocarbon; and an exit port near a top of said vessel
for collecting pressurized steam and transporting said pressurized
steam to a wellhead injection system for injecting steam into an
oil reservoir; wherein these elements are fluidly connected.
[0027] A closed heat transfer fluid circulation loop that passes in
part through said vessel can be used to heat said hot hydrocarbon.
The closed heat transfer fluid circulation loop can comprise a heat
transfer fluid, a heater, and a pump, circulating through closed
coils which pass, in part, through the liquid boiler vessel.
[0028] The liquid boiler vessel can also comprise a hot hydrocarbon
treatment loop in fluid connection with said vessel, wherein said
hot hydrocarbon treatment loop either clean or upgrades the hot
hydrocarbons. Exemplary treatments include filtering, desalting,
dehydrating, coalescing, visbreaking, electrostatic separating, and
the like.
[0029] A liquid steam generator, comprising a vessel comprising a
hot hydrocarbon in a lower portion of said vessel; a closed heat
transfer fluid circulation loop containing a heat transfer fluid,
said loop passing in part through said lower half of said vessel to
heat said hot hydrocarbon, the remainder passing to a heater and a
pump to heat and circulate said heat transfer fluid; a hot
hydrocarbon treatment loop for cleaning said hot hydrocarbon, said
hot hydrocarbon treatment loop including a pump and a desalter; a
pump for pressurizing a dirty feedwater stream fluidly connected to
nozzles in an upper portion of said vessel, said nozzles spraying
said dirty feedwater onto said hot hydrocarbon; and an exit port
near a top of said vessel for collecting pressurized steam and
transporting said pressurized steam to a wellhead injection system
for injecting steam into an oil reservoir; wherein the elements
(except for the closed circulation loop) are fluidly connected.
[0030] Exemplary hydrocarbon heat transfer fluids are selected from
butane, molten sodium, molten sodium-potassium, DOWTHERM or
THERMINOL.
[0031] The dirty feedwater can be any water that is not pretreated
before use, including produced water, brackish water, well water,
brine, surface water and combinations thereof. The dirty feedwater
may be produced water originating from any convenient source.
[0032] The hot hydrocarbon fluid can be any conveniently available
hot hydrocarbon, especially being a produced hydrocarbon separated
from said produced water, or a fraction thereof.
[0033] The liquid boiler can produce a pressurized steam that is a
mixture of steam and low molecular weight hydrocarbons, such as
butane, pentane, and the like.
[0034] One embodiment is an improved method of steam assisted
gravity drainage (SAGD), the method comprising pretreating produced
water for a steam generator to remove oil and salts, making
pressurized steam from said pretreated water, pumping said
pressurized steam into a wellbore in an amount sufficient to
mobilize heavy oil, and gravity draining said mobilized heavy oil
to a production well, the improvement comprising spray injecting
pressurized dirty water into a vessel containing a hot heavy oil
and collecting pressurized steam for use in SAGD, without said
water pretreating step.
[0035] Another improved method of steam production for the
mobilization of heavy oil, the method comprising pretreating
produced water for a steam generator to remove oil and salts,
making pressurized steam from said pretreated water, pumping said
pressurized steam into a wellbore in an amount sufficient to
mobilize heavy oil, and producing said mobilized heavy oil, the
improvement comprising spray injecting pressurized dirty water into
a vessel containing a hot hydrocarbon and collecting pressurized
steam for use in mobilizing heavy oil, without said water
pretreating step, wherein said hot hydrocarbon is heated with a
closed circulation loop comprising a pump and a furnace to
circulate a heat transfer fluid through said closed circulation
loop.
[0036] By "dirty water" what is meant is that the water can be
recycled from oil recovery processes and used as is, without
expensive de-oiling or desalting pre-treatments applied to it.
[0037] The use of the word "a" or "an" when used in conjunction
with the term "comprising" in the claims or the specification means
one or more than one, unless the context dictates otherwise.
[0038] The term "about" means the stated value plus or minus the
margin of error of measurement or plus or minus 10% if no method of
measurement is indicated.
[0039] The use of the term "or" in the claims is used to mean
"and/or" unless explicitly indicated to refer to alternatives only
or if the alternatives are mutually exclusive.
[0040] The terms "comprise", "have", "include" and "contain" (and
their variants) are open-ended linking verbs and allow the addition
of other elements when used in a claim.
[0041] The phrase "consisting of" is closed, and excludes all
additional elements.
[0042] The phrase "consisting essentially of" excludes additional
material elements, but allows the inclusions of non-material
elements that do not substantially change the nature of the
invention.
[0043] The following abbreviations are used herein:
TABLE-US-00001 ABBREVIATION TERM ATM Atmosphere BFW Boiler
feed-water CAPEX Capitol expenses CPF Central processing facility
CSS Cyclic steam stimulation ES-SAGD Expanding solvent SAGD OPEX
Operating expenses OTSG Once-through steam generator RO Reverse
osmosis SAGD Steam-assisted gravity drainage SD Steam drive TDS
total dissolved solids Ts Saturation temperature UF
Ultrafiltration
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] FIG. 1 illustrates a highly simplified view of a modern OTSG
system and used for SAGD steam production.
[0045] FIG. 2 presents a simplified drum boiler system.
[0046] FIG. 3 illustrates a simplified schematic of the liquid
boiler system of the invention, which can be beneficially used with
SAGD and other steam-based enhanced oil recovery methods
[0047] FIG. 4 is a schematic of an alternative arrangement to
contact a mixture of water and oil with more of the oil that has
been heated to thus vaporize the water and potentially result in
visbreaking of the oil, according to one embodiment of the
invention.
DETAILED DESCRIPTION
[0048] The disclosure provides a novel method for generating steam
with minimized or eliminated fouling. The disclosure also provides
a novel system for implementing the method.
[0049] In general, an improved method of generating steam for SAGD
and other heavy oil production uses is provided, wherein a hot
liquid hydrocarbon is used to convert water to steam, and wherein
the steam may thus contain lower molecular weight components
stripped from the hot liquid hydrocarbon.
[0050] FIG. 3 gives one example of a liquid boiler process for
SAGD. As seen in the figure, dirty feedwater 101 that is not
de-oiled or pre-treated to remove dissolved solids enters the
system. Pump 103 brings the dirty water to high pressure and then
it is injected via spray nozzles 105 into the liquid boiler vessel
109. Since the water is pressurized there is little fouling of the
components up to this point.
[0051] Hot liquid 113 (e.g., produced heavy hydrocarbons, etc.)
vaporizes the dirty boiler feed water sprayed into the vessel. The
resulting produced steam (with potentially some hydrocarbons in it)
exits 111 out the top of the liquid-boiler and is sent by line 113
to the SAGD reservoir. Any dissolved solids or oil from the dirty
feedwater remains with the hot liquid hydrocarbons.
[0052] The hot liquid receives its thermal energy from another heat
transfer fluid in a closed circulation loop 157 via heat transfer
within coils 155. The heat transfer fluid (such as butane, molten
sodium, molten sodium-potassium, DOWTHERM or THERMINOL) within the
coils receives its heat via an external furnace 151, and in that
sense the boiler is an indirect boiler, heat coming from an outside
source. In some embodiments, the heat transfer fluid, such as
butane, may be condensed for pumping prior to being vaporized in
the furnace 151 and circulated through the coils 155 in the vessel
109. To the extent that produced hydrocarbons are used in the
process, they already have a certain heat, decreasing initial
heating costs. The hot hydrocarbons used to vaporize the produced
water may be treated by an external hydrocarbon treatment unit 173,
such as a desalter, to remove the accumulating contaminants from
the dirty feedwater.
[0053] The method allows the boiler to produce steam with
non-treated (dirty) boiler feed water. This, therefore, reduces the
CAPEX and OPEX costs associated with de-oiling and water treatment
plants. Using a liquid such as DOWTHERM or THERMINOL as the heat
transfer liquid allows for conventional coil metallurgy, thus,
minimizing the CAPEX for the indirect boiler, as well as minimizing
any fouling of these coils.
[0054] FIG. 4 illustrates a hot hydrocarbon-based system with a
steam generator vessel 200, an injection well 201 and a production
well 202 that are operated for steam generation. A feed pump 216
pressurizes the dirty feedwater mixture 204 that can optionally be
preheated in a furnace or heat exchanger 217 prior to introduction
into the vessel 200. In some embodiments, the mixture 204 may
receive pre-heat from a sales portion 210 of the hydrocarbons.
[0055] Upon entry into the vessel 200, some flashing of the water
in the mixture 204 may occur upon expansion into relative lower
pressure conditions of the vessel 200. However, most of the water
in the mixture 204 vaporizes upon contact with hot hydrocarbon 220
collected in the lower half of the vessel 200. The hydrocarbons 220
may be partially heated, if for example, produced hydrocarbons are
used, and/or can be further heated in closed circulation loop 257
consisting of furnace 251, pump 253 and heating coils 255 that pass
through the hot hydrocarbon 220.
[0056] A second circulation loop 222 contains a recycle pump 221
that passes the hot hydrocarbon 220 from the vessel 200 to a
treatment unit 223 before returning the hot hydrocarbon 220 to the
vessel 200. Treatment unit 223 can include one or more of a variety
of treatment units, including e.g., a filter, coalescer, desalter,
dehydrator, visbreaker or electrostatic separator. The desalter or
other treatment unit 223 removes inorganic material from the hot
hydrocarbon 220. Some of the hot hydrocarbon 220 exiting the
desalter 223 can provide the sales portion 210 of the hydrocarbons
for pipeline or transport to a refinery for further processing.
[0057] For some embodiments, overhead from the vessel 200 passes
through a separation device 229 that may include demisters,
separators, fractionators and/or particulate filters. The device
229 removes entrained liquids and/or solids 233 and/or condensable
hydrocarbons 231 vaporized by the hot hydrocarbon 220 or resulting
from cracking of the hot hydrocarbon 220. The condensable
hydrocarbons 231 may mix back into the sales portion 210 of the
hydrocarbons or have a portion mixed back for injection into the
formation as a solvent. However, it is anticipated that the
overhead steam can be used as is, and that any light hydrocarbons
that may have evaporated along with the steam (e.g., naptha), will
reduce the steam oil ratio (SOR) needed to produce a barrel of
oil.
[0058] Steam 230 exits the device 229 and is conveyed to the
injection well 201. Since separation of the mixture 204 occurs with
the vessel 200, this approach eliminates need for independent
de-oiling equipment.
[0059] Residence time of the hot hydrocarbon 220 in the vessel 200
may even provide sufficient soak time for visbreaking of the
hydrocarbon 220. A visbreaker thermally cracks large hydrocarbon
molecules in the oil by heating in a furnace to reduce its
viscosity and to produce small quantities of light hydrocarbons
(LPG and gasoline). The process name of "visbreaker" refers to the
fact that the process reduces (i.e., breaks) the viscosity of the
residual oil, and generally the process is non-catalytic.
[0060] Alternatively, a visbreaker can be provided in the second
circulation loop 222. Exemplary soaking times may range from 5
minutes to 1 hour with the bitumen heated in the visbreaker to at
least 385.degree. C. The circulation loop 222 may incorporate
various approaches to enhance the visbreaking, such as radiation
thermal cracking or hydrodynamic cavitation. The visbreaking lowers
viscosity and density of the heavy oils or bitumen 220 and hence
the sales portion 210 making the sales portion 210 more valuable
and easier to transport while requiring less diluents than the
bitumen without such upgrading.
[0061] In some embodiments, the water supplied for generation of
the steam may include boiler blowdown from another steam generator,
such as a once-through steam generator. The methods disclosed
herein may provide for treatment of such blowdown. Further, the
steam generated by such treatment may be at pressures lower than
desired for injection and may be recycled for mixing with boiler
feed water prior to generation of steam for injection.
[0062] Based on the above illustrations, it is clearly shown that
the methods and systems herein described pressurize the feedwater
before it enters the heating mechanism and thereby avoids the
nucleate boiling phase that directly contributes to fouling.
Downtime for pigging/repairing the boiler and pipes can be greatly
reduced, therefore cutting down the operation cost.
[0063] The following documents are incorporated by reference in
their entirety:
Gwak et al., A Review of Steam Generation for In-Situ Oil Sands
Projects, Geosystem Engineering, 13(3), 111-118 (September
2010).
* * * * *