U.S. patent application number 14/524250 was filed with the patent office on 2015-04-30 for minimizing fouling in steam assisted oil production.
The applicant listed for this patent is CONOCOPHILIPS COMPANY. Invention is credited to Jim P. SEABA, Jingwei ZHANG.
Application Number | 20150114318 14/524250 |
Document ID | / |
Family ID | 52994008 |
Filed Date | 2015-04-30 |
United States Patent
Application |
20150114318 |
Kind Code |
A1 |
ZHANG; Jingwei ; et
al. |
April 30, 2015 |
MINIMIZING FOULING IN STEAM ASSISTED OIL PRODUCTION
Abstract
Methods and systems generate steam for heavy oil recovery
operations, wherein fouling is limited with the use of wire matrix
turbulators in tubes with tendencies to foul.
Inventors: |
ZHANG; Jingwei; (Sugar Land,
TX) ; SEABA; Jim P.; (Calgary, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CONOCOPHILIPS COMPANY |
Houston |
TX |
US |
|
|
Family ID: |
52994008 |
Appl. No.: |
14/524250 |
Filed: |
October 27, 2014 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61897517 |
Oct 30, 2013 |
|
|
|
Current U.S.
Class: |
122/1C ;
166/303 |
Current CPC
Class: |
F22B 37/18 20130101;
E21B 43/2406 20130101; F22B 1/02 20130101; F22B 1/18 20130101 |
Class at
Publication: |
122/1.C ;
166/303 |
International
Class: |
F22B 1/02 20060101
F22B001/02; E21B 43/24 20060101 E21B043/24 |
Claims
1. A steam generator system for oil production, comprising a once
through steam generator (OTSG) having: an economizer section for
pre-heating feedwater and fitted with a wire matrix turbulator; a
radiant section for converting said pre-heated feedwater to steam;
and an injection system for injecting steam into an oil reservoir,
wherein the economizer section, radiant section and injection
system are fluidly connected.
2. The steam generator system of claim 1, wherein said wire matrix
turbulator comprises a coiled wire, wherein subsequent coils are
radially shifted around a central axis, and wherein all coils slant
in a direction of fluid flow.
3. The steam generator system of claim 1, wherein said wire matrix
turbulator comprises stainless steel wire.
4. The steam generator system of claim 1, wherein said wherein wire
matrix turbulator comprises a polymer coated wire.
5. The steam generator system of claim 1, wherein said wire matrix
turbulator comprises a polymeric wire or mesh.
6. The steam generator system of claim 1, wherein said radiant
section also includes the wire matrix turbulator.
7. The steam generator system of claim 1, further comprising a
water and steam separator in fluid communication between the
radiant section and the injection system for injecting separated
steam into the oil reservoir.
8. An improved method of producing steam for heavy oil production,
the method comprising heating feedwater in a once-through steam
generator (OTSG) sufficiently to make steam to inject into a
wellbore and use in mobilizing heavy oil, the improvement
comprising outfitting tubes in said OTSG with a turbulator and thus
reducing fouling in said tubes as compared with the same OTSG
lacking said turbulator.
9. The method of claim 8, further comprising preheating feedwater
in an economizer of the OTSG, then further heating said feedwater
in the OTSG sufficiently to make the steam, wherein the tubes with
the turbulator are disposed in said economizer.
10. The method of claim 8, wherein the turbulator is a wire matrix
turbulator.
11. The method of claim 8, further comprising preheating feedwater
in an economizer of the OTSG, then further heating said feedwater
in the OTSG sufficiently to make the steam, wherein the tubes with
the turbulator that is a wire matrix turbulator are disposed in
said economizer.
12. The method of claim 8, further comprising injecting the steam
into the wellbore.
13. The method of claim 8, wherein the turbulator is disposed in an
economizer section of the OTSG and alters fluid flow direction near
the wall, thus decreasing the temperature gradient and limiting
nucleate boiling and fouling.
14. The method of claim 8, wherein the turbulator is disposed in a
radiant section of the OTSG to increase the heat transfer area and
lead to a more uniform temperature distribution so as to minimize
the risk of local burnout caused by high temperature gradients at
the wall.
15. A method of generating steam for oil production, comprising:
pre-heating feedwater in a steam generator within an economizer
section fitted with a wire matrix turbulator; converting the
feedwater pre-heated in the economizer section to steam in a
radiant section of the steam generator; and injecting the steam
into an oil reservoir.
16. The method of claim 15, wherein said wire matrix turbulator
comprises a coiled wire, wherein subsequent coils are radially
shifted around a central axis, and wherein all coils slant in a
direction of fluid flow.
17. The method of claim 15, wherein said wherein wire matrix
turbulator comprises a polymer coated wire.
18. The method of claim 15, wherein said wire matrix turbulator
comprises a polymeric wire or mesh.
19. The method of claim 15, wherein said radiant section also
includes the wire matrix turbulator.
20. The method of claim 15, further comprising separating liquid
from the steam output from the radiant section prior to the
injecting into the oil reservoir.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a non-provisional application which
claims the benefit of and priority to U.S. Provisional Application
Ser. No. 61/897,517 filed Oct. 30, 2013, entitled "Minimizing
Fouling in Steam Assisted Oil Production," which is hereby
incorporated by reference in its entirety.
FIELD OF THE INVENTION
[0002] The invention relates to methods and systems for generating
high-pressure steam with minimal or eliminated fouling resulting
largely from boiling nucleation.
BACKGROUND OF THE DISCLOSURE
[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 to gravity drain into the lower
wellbore, where it can be pumped to the surface.
[0004] Generally speaking, high quality, high temperature and high
pressure steam is required for the SAGD process. SAGD calls for
100% quality, 7,000-11,000 kPag and 238-296.degree. C. temperature
steam. Considering oil production volume, and the fact that at
least 2 barrels of water are needed for every barrel of oil, the
water requirements for SAGD are immense.
[0005] A once-through steam generator (OTSG), for example,
generates around 75% to 80% quality steam, which then goes through
a series of liquid-steam separators (also called "flash drums") to
increase the steam quality. An OTSG is a large, continuous tube
type steam generator in which wet steam is produced at the outlet
of the continuous tube. Feedwater is supplied at one end of the
tube having low temperature, and then undergoes a
preheating-evaporation cycle as it travels along the tube.
[0006] OTSG features a single pass of water through the generator
coil, where the feedwater is heated and eventually vaporized.
Typically an OTSG comprises a convection section (also called
economizer section) and a radiant section. In the convection
section, the feed water is pre-heated by heat exchange with a hot
combustion gas, usually flue gas. In the radiant section, the
majority of the feedwater/wet steam will be heated by the heat
radiated from the furnace, resulting in about 80% quality steam,
i.e. the mass ratio of water to steam at the outlet of the
generator is about 1:4.
[0007] A source of large amounts of fresh or brackish water and
large water recycling facilities are required in order to create
the steam for the SAGD process. Boiler feed-water (BFW) quality is
critical due to organic/inorganic contaminants in the water that
may cause fouling/scaling and lead to boiler tube failure.
[0008] Fouling is the contamination of the heating surface, and the
build-up of contaminant will eventually decrease 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 repairing cost, the downtime
increases the cost of the SAGD operation.
[0009] Nucleate boiling is considered one of the main reasons for
fouling in heat transfer tubes. Nucleate boiling is characterized
by the growth of bubbles on a heated surface, which rise from
discrete points on a surface, whose temperature is only slightly
above the liquid's temperature. In general, the number of
nucleation sites is increased by an increasing surface temperature
and by irregular surfaces of the boiling vessel.
[0010] Nucleate boiling takes place when the surface temperature is
hotter than the saturated fluid temperature by a certain amount but
where the heat flux is below the critical heat flux. For water,
nucleate boiling occurs when the surface temperature is higher than
the saturation temperature (T.sub.s) by between 4.degree. C. to
30.degree. C. The critical heat flux is the peak on the curve
between nucleate boiling and transition boiling.
[0011] If the heat flux of a boiling system is higher than the
critical heat flux (CHF) of the system, the bulk fluid may boil, or
in some cases, regions of the bulk fluid may boil where the fluid
travels in small channels. Thus, large bubbles form, sometimes
blocking the passage of the fluid. This results in a departure from
nucleate boiling (DNB) in which steam bubbles no longer break away
from the solid surface of the channel, bubbles dominate the channel
or surface, and the heat flux dramatically decreases. Vapor
essentially insulates the bulk liquid from the hot surface.
[0012] DNB is also known as transition boiling, unstable film
boiling, and partial film boiling. For water boiling as shown on
the graphs in FIG. 7-8, transition boiling occurs when the
temperature difference between the surface and the boiling water is
approximately 30.degree. C. (54.0.degree. F.) to 120.degree. C.
(216.degree. F.) above the T.sub.S. This corresponds to the high
peak and the low peak on the boiling curve. The low point between
transition boiling and film boiling is the Leidenfrost point. See
FIG. 8.
[0013] During transition boiling of water, the bubble formation is
so rapid that a vapor film or blanket begins to form at the
surface. However, at any point on the surface, the conditions may
oscillate between film and nucleate boiling, but the fraction of
the total surface covered by the film increases with increasing
temperature difference. As the thermal conductivity of the vapor is
much less than that of the liquid, the convective heat transfer
coefficient and the heat flux reduces with increasing temperature
difference.
[0014] Both forms of boiling can foul heat transfer surfaces,
although the majority of fouling comes from nucleate boiling.
Eventually, fouling will build to a level that it must be
addressed. Boiler cleaning employs physical or chemical means to
clean the water tubes, and those methods inevitably require shut
off period until the cleaning is completed.
[0015] Therefore, there is the need for an improved
heating/pre-heating scheme that can minimize or even eliminate
nucleate boiling in the steam generating process, thereby
minimizing the fouling issues and reduce the downtime and cost for
SAGD operation.
SUMMARY OF THE DISCLOSURE
[0016] When fluid flows through a plain tube the fluid nearest the
wall is subjected to frictional drag, which has the effect of
slowing down the fluid at the wall. This laminar boundary layer can
significantly reduce the tube side heat transfer coefficient and
consequently, the performance of the heat exchanger.
[0017] A "turbulator" is a device inserted into the tubes of
firetube boilers, shell and tube heat exchangers and other types of
heat transfer equipment that helps to increase heat transfer
efficiency. The heat transfer coefficient for liquids and gases
flowing through pipes in heat exchangers tends to be limited due to
a fluid boundary layer close to the pipe wall that is stagnant or
moves at slow speed, thus acting as an insulating layer. Such heat
exchangers are found, for example, in domestic central heating
systems. This boundary layer can be broken or reduced in thickness
if turbulators are placed in the pipe, which create a turbulent
flow that reduces the boundary-layer thickness and thereby increase
the heat-transfer coefficient along pipe walls.
[0018] Examples of turbulators for pipe flow are: [0019]
Twisted-tape turbulators, a twisted ribbon that forces the fluid to
move in a helicoidal path rather than in a straight line; [0020]
Brock turbulators, a zig-zag folded ribbon; [0021] Wire
turbulators, typically an open structure of looped and/or entangled
wires that extends over the entire pipe length. See e.g., U.S. Pat.
No. 4,481,154.
[0022] Turbulators can also be put to use in certain internal
combustion engines--particularly, a ramjet engine. A simple porous
wire mesh placed in the diffuser of the ramjet can increase
turbulence in the flow entering the combustion chamber, which aids
in fuel mixing.
[0023] In Steam Assisted Gravity Drainage (SAGD) oil production
operations, Once-Through-Steam-Generation (OTSG) boilers are widely
used to supply the steam needed to heat the hydrocarbons, thus
mobilizing them for production. Because of the poor quality of
boiler feed water in Surmont and other field operations, serious
fouling problems have always been a problem inside OTSG economizers
in the convection zone. To solve the problem, every 6 to 10 weeks,
a pigging interval must be introduced to clean the fouling. Thus,
the fouling problem greatly affects the productivity and economics
of producing Canadian bitumen.
[0024] In some embodiments, tube inserts are in wire spring-like
configurations (as shown in FIG. 1), and are a commercially
available technology that has been applied inside the tubes of
shell and tube heat exchangers used for heating tar oil when
dealing with laminar or transient flows. Operation results have
showed great success of increasing heat transfer and reducing
fouling.
[0025] The theory of these configurations is to introduce local
turbulent secondary flows, which enhance the overall heat transfer
coefficient and reduce the residence time of fouling precursors
close to the hot surface. However this technology has not been
applied in SAGD OTSG boilers to mitigate fouling, in which flows
are already very turbulent.
[0026] In Canadian OTSG boilers, more severe fouling is often
observed in economizer sections, which are composed of many heat
exchangers. One of the hypotheses is fouling occurs at boiling
nucleation sites with an increased concentration of foulants in
economizers when preheating the boiler-feed water. Introducing this
technology in economizer sections of the OTSG boilers to suppress
nucleate boiling may prove to be a promising way to reduce fouling
in these unique systems.
[0027] This technology may also help reduce the tube wall
temperature and increase the wall shear rates, which both lead to
fouling mitigation.
[0028] When using a coiled wire insert in the economizer, local
flow induced by the inserts forms a highly turbulent flow near the
tube wall. This will increase the shear stress at the wall,
mitigating bubble formation. The nucleate boiling will be greatly
reduced or even eliminated where the flow goes directly into a
fully boiling regime. The higher shear stress near the wall also
limits the adhesion of organics, thereby further decreasing the
fouling rate.
[0029] The present disclosure provides a method of minimizing the
fouling caused by nucleate boiling and/or transition boiling of the
feed water in a steam generator. The current invention may reduce
fouling by inserting a push-to-fit coiled wire insert into the
pipes of e.g., the economizer section of the OTSG in the direction
of flow, wherein the wires are coiled either regularly or
randomly.
[0030] Coiled wire turbulators are easily fitted and removed. They
are flexible along their length for ease of installation even where
access is restricted. Elements are simply guided into place along
the axis of the tube, although the exchanger tubes may require
being in a clean condition before the elements are installed, as it
is important that the loops on the elements have contact with the
tube wall.
[0031] Various coiling patterns are possible, and a few are shown
in FIG. 2. However, a wire turbulator where the wire forms
concentric circular loops that are twisted around a flexible
central wire spine is preferred. These circular loops all slant in
one direction, opposing the flow of the fluid. The slant of the
loops makes it very easy to pull the turbulator through the tube in
one direction, but is difficult to pull through the tube in the
opposite direction. The fluid in the tube also presses the loops
against the wall of the tube providing a tight pressure fit. The
wire loops in the face of the fluid flow provides good turbulation
at reasonable pressure drop given the low resistance of the
cylindrical wire redirects the fluid flow within the tube and
maximizes its impact with the tube wall.
[0032] Such turbulators can also be provided with a hook at one end
for pulling through the tube. At the other end, depending on the
fluid flow characteristics, an anchor can be provided. However,
depending on the coiling pattern and flow characteristics,
turbulators typically need no fixing in the tubes as wires grip
quite tightly and do not tend to move with a normal flow. Also,
where long lengths are needed, a tail can be left at the other end
for joining on any follow up length. If needed, the coiled wire
inserts can be removed, and the tubes pigged as needed. The coiled
wire inserts themselves can also be cleaned in a chemical bath, if
needed.
[0033] Wire can be any suitable metal, but should be nonreactive
with the hydrocarbon and brine in the reservoir, which can
contaminate feedwaters, as well as with any dissolved solids,
cations, anions, and the like present in the feedwater. Typically,
stainless steel wire turbulators are used, but copper, brass,
galvanized steel, galvanized mild steel, or monel metal is also
possible.
[0034] Because the feedwaters in SAGD applications are recycled and
can have significant dissolved total solids, as well as a number of
reactive contaminants, it may be beneficial to protect the wire
from reacting therewith. Wire can thus be coated with a
non-reactive, protective polymeric coating if needed. As another
alternative, the turbulator could be made with a flexible polymeric
wire or polymeric mesh, instead of metal.
[0035] The method therefore may minimize the fouling caused by
nucleate boiling in the boiler. This can minimize the downtime of
the boiler for repairing or removing the fouling, thereby increases
the operating time.
[0036] The invention comprises one or more of the following
embodiments, in any combination thereof: [0037] A steam generator
system for oil production, comprising a once through steam
generator (OTSG) having: an economizer section for pre-heating
feedwater said economizer fitted with a wire matrix turbulator; a
radiant section for converting said pre-heated feedwater to steam;
and an injection system for injecting steam into an oil reservoir;
wherein elements a through c are fluidly connected. [0038] A steam
generator system for oil production, comprising a once through
steam generator (OTSG) having: an economizer section for
pre-heating feedwater said economizer section fitted with a wire
matrix turbulator; a radiant section for converting said pre-heated
feedwater to steam said radiant section fitted with a wire matrix
turbulator; an water and steam separator; and an injection system
for injecting separated steam into an oil reservoir; wherein
elements a through d are fluidly connected. [0039] An improved
method of producing steam for heavy oil production, the method
comprising heating feedwater in an OTSG sufficiently to make steam
to pump into a wellbore and use in mobilizing heavy oil, the
improvement comprising outfitting tubes in said OTSG with a
turbulator and thus reducing fouling in said tubes as compared with
the same OTSG lacking said turbulator. [0040] An improved method of
producing steam for heavy oil production with reduced fouling of
steam generator systems, the method comprising heating feedwater
sufficiently in a steam generator system to make steam to pump into
a wellbore and use in mobilizing heavy oil, the improvement
comprising outfitting tubes in said steam generator system with a
wire matrix turbulator and thus reducing fouling in said tubes.
[0041] An improved method of producing steam for heavy oil
production, the method comprising preheating feedwater in an
economizer, then further heating said feedwater in an OTSG
sufficiently to make steam to pump into a wellbore and use in
mobilizing heavy oil, the improvement comprising outfitting tubes
in said economizer with a wire matrix turbulator and thus reducing
fouling in said tubes. [0042] A method of minimizing fouling in an
economizer section of an OTSG, comprising providing a wire matrix
tube insert in said economizer section to alter fluid flow
direction near the wall, thus decreasing the temperature gradient
and minimizing nucleate boiling and fouling. [0043] A method of
minimizing fouling in an radiant section of an OTSG, comprising
providing a wire matrix tube insert in said radiant section where
steam is generated to increase the heat transfer area and lead to a
more uniform temperature distribution so as to minimize the risk of
local burnout caused by high temperature gradients at the wall.
[0044] The wire matrix turbulator can comprise a coiled wire,
wherein subsequent coils are radially shifted around a central
axis, and wherein all coils slant in a direction of fluid flow.
[0045] The wire matrix turbulator comprises stainless steel wire,
or a polymer coated wire, or a polymeric wire or mesh.
[0046] As used herein, "heat flux" is the rate of heat energy
transfer through a given surface, in other words, the heat rate per
unit area, whereas "critical heat flux" describes the thermal limit
of a phenomenon where a phase change occurs during heating, which
suddenly decreases the efficiency of heat transfer, thus causing
localized overheating of the heating surface.
[0047] As used herein, "economizer" means the devices for reducing
energy consumption in a steam-generating operation by preheating
feedwater. Typically an economizer is in the form of heat exchanger
where the thermal energy is transferred from a high temperature
fluid (e.g., steam condensate, flue gas or other waste heat source)
to the feedwater such that less energy is required to vaporize it.
Economizers are mechanical devices intended to reduce energy
consumption or to perform another useful function such as
preheating a fluid. In boilers, economizers are heat exchange
devices that heat fluids, usually water, up to but not normally
beyond the boiling point of that fluid. Economizers are so named
because they can make use of the enthalpy in fluid streams that are
hot, but not hot enough to be used in a boiler, thereby recovering
more useful enthalpy and improving the boiler's efficiency. They
are fitted to a boiler and save energy by using e.g., the exhaust
gases from the boiler or other hot plant fluids to preheat the cold
feedwater. It has been reported that approximately 35 to 50% of the
total absorbed heat in OTSG is transferred in the economizer.
[0048] By "wire" herein what is meant is a long thin flexible thin
flexible thread or rod. Wires can be metal, plastic or both. Wires
can also adhere to each other at crossing points, e.g., to make a
"mesh."
[0049] By "wire turbulator" or "wire matrix turbulator" what is
meant is that the majority of the turbulence is provided by wire,
and not a zigzagged or twisted ribbon, although the central axis of
a wire turbulator may be twisted wire or ribbon.
[0050] 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.
[0051] The term "about" means the stated value plus or minus the
typical margin of error of measurement or plus or minus 10% if no
method of measurement is indicated.
[0052] 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.
[0053] 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.
[0054] The phrase "consisting of" is closed, and excludes all
additional elements.
[0055] 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.
[0056] The following abbreviations are used herein:
TABLE-US-00001 ABBREVIATION TERM ATM Atmosphere CPF Central
processing facility OTSG Once-through steam generator SAGD
Steam-assisted gravity drainage Ts Saturation temperature
BRIEF DESCRIPTION OF THE DRAWINGS
[0057] FIG. 1A illustrates fluid flow in a plain tube.
[0058] FIG. 1B illustrates a wire turbulator
[0059] FIG. 1C illustrates the resulting effects of fluid flow in
the plain tube of FIG. 1A.
[0060] FIG. 1D illustrates the resulting effects of fluid flow when
the turbulator is used as compared with the plain tube.
[0061] FIG. 2A illustrates a first wire coiling pattern.
[0062] FIG. 2B illustrates a second wire coiling pattern.
[0063] FIG. 2C illustrates a third wire coiling pattern.
[0064] FIG. 3 illustrates the operating principle for an OTSG.
[0065] FIG. 4 illustrates a typical OTSG system for SAGD, with
preheater, economizer evaporator.
[0066] FIG. 5A shows an OTSG system fitted with a wire matrix
turbulator. FIG. 5A shows a partial OTSG system with a dashed box
denoting the expanded portion used in FIG. 5B-5C to show two
embodiments of the present disclosure.
[0067] FIG. 5B illustrates the expanded portion in FIG. 5A with the
turbulator having concentric wire circles.
[0068] FIG. 5C illustrates the expanded portion in FIG. 5A with the
turbulator having a spiraling loop configuration of wire.
[0069] FIG. 6 shows another embodiment of an OTSG system as fitting
in with other equipment typically found at or near a well-pad.
[0070] FIG. 7 illustrates the behavior of water on a hot plate. The
graph shows heat transfer (flux) v. temperature (in degrees
Celsius) above TS, the saturation temperature of water, 100.degree.
C. (212.degree. F.). From WikiMedia Commons.
[0071] FIG. 8 illustrates the boiling curve for water at 1 atm.
From WikiMedia Commons.
DETAILED DESCRIPTION
[0072] The disclosure provides a novel method for generating steam
for enhanced oil recovery with minimized or eliminated fouling
caused by nucleate boiling and/or transition boiling. The
disclosure also provides a novel system for implementing the
method. It is believed that by using the method and system of the
methods described herein, fouling in the steam generator due to
nucleate boiling can be greatly reduced or eliminated, thereby
reducing the operational cost and downtime for repairing and
maintaining the steam generator.
[0073] In general, an improved method of generating steam for SAGD
and other heavy oil production uses is provided, wherein a wire
matrix turbulator is used in water heating tubing, thus minimizing
or eliminating nucleate boiling.
[0074] FIG. 3 illustrates the operating theory behind an OTSG. The
OTSG is a continuous tube heat exchanger wherein many tubes are
mounted in parallel and are joined by headers thus providing a
common inlet for feedwater and a common outlet for steam. Unlike
other systems which utilize a drum boiler and natural circulation
of water, the water in the OTSG is forced through the tubes by a
boiler feedwater pump, entering the OTSG at the "cold" end and
maintaining constant flow through the tube bundle. A heated gas,
flowing in the opposite direction of the water (counter current
flow), heats the tube bundle. As the water flows through the heated
bundle, it changes phase along the circuit as it extracts heat from
the gas flow.
[0075] FIG. 4 illustrates a typical OTSG system in simplified
schematic. The cool untreated water (414) flows from the storage
tank (406) into a preheater (405). The preheated feedwater (415) is
then pressurized by a pump (408) before being introduced into the
OTSG (401). The OTSG (401) has a continuous tube (407) for water
that contacts with the flue gas (arrow) generated by a burner
(402). After contact with the continuous tube (407), the flue gas
(413) can be recycled for use in the preheater (405).
Alternatively, the preheater can have its own burner and fuel feed
supply (not shown).
[0076] Because the OTSG (401) typically does not have defined
economizer and evaporator sections (though it can), these areas are
approximated by the dashed boxes. The actual point of evaporation
can occur at any point in the OTSG and is not confined to the boxed
areas. The economizer section (403) heats the water up to, but
normally not beyond, the boiling point. From there, the heated
water enters the evaporator (404) where most is converted to steam.
The resulting steam (416) can then be injected into a hydrocarbon
reservoir.
[0077] FIG. 5 shows an illustration of two wire matrix turbulator
designs from expanded portion (501) of the continuous tube (407).
In this section, the wire matrix turbulator extends the length of
the continuous tube (407). Though not shown, such a turbulator may
extend from water inlet through the economizer section and the
radiant section. The turbulator typically has hooks for retrieval
and for connecting lengths of turbulators, but usually nothing is
required for securing the device in the pipes. If necessary, the
hook or other securing member can be used for same. In FIG. 5B, the
flexible spine (503) of the wire matrix turbulator has concentric
wire circles (502). Though hard to see, the concentric circles
(502) are slanted in the opposite direction of the water flow, such
that water flow tends to open the arrow or chevron, increasing the
pressure of the wires against the tube walls. FIG. 5C shows a
spiraling loop configuration of wire (512) around the flexible
spine (513).
[0078] FIG. 6 displays another embodiment of a typical OTSG system
with equipment typically found at or near a well-pad. Here, the
OTSG (100) has a burner that converts fuel and air into heated flue
gas (101) for heating metals tubes (102). Untreated water from a
storage facility is pressurized and introduced into the OTSG (100).
The water (110) flows through the metal tubes (102), is heated, and
exits the OTSG (100) as a wet steam (112). A steam/water separator
(104) separates the wet steam (112) into a stream of steam (113) to
be injected into a well-pad and a blowdown stream (111). The
blowdown stream (111) is recycled but it can also be purged.
[0079] In an exemplary operation, a shell and tube heater (125a)
preheats a feedwater stream (124) after it has undergone a warm
lime softening/weak acid exclusion treatment (126). The preheated
feedwater (124) is then heat in exchangers (125d) and (125c) with
produced gas (122) and produced liquids (123), respectively, to
form stream (127). Separately, the blowdown stream (111) from the
steam/water separator (104) is flashed in a drum (120) to produce
stream (121), which is then heat exchanged with stream (127) in
another heater (125b) before stream (127) is pressurized and
introduced into the OTSG (100).
[0080] The following documents are incorporated by reference in
their entirety for all purposes: [0081] Gwak et al., A Review of
Steam Generation for In-Situ Oil Sands Projects, Geosystem
Engineering, 13(3), 111-118 (September 2010). [0082] U.S. Pat. No.
4,481,154
* * * * *