U.S. patent application number 13/629258 was filed with the patent office on 2013-03-28 for methods for treatment and use of produced water.
This patent application is currently assigned to FLUOR TECHNOLOGIES CORPORATION. The applicant listed for this patent is Fluor Technologies Corporation. Invention is credited to Rafique Janjua, Robert Prieto.
Application Number | 20130075098 13/629258 |
Document ID | / |
Family ID | 47909973 |
Filed Date | 2013-03-28 |
United States Patent
Application |
20130075098 |
Kind Code |
A1 |
Janjua; Rafique ; et
al. |
March 28, 2013 |
METHODS FOR TREATMENT AND USE OF PRODUCED WATER
Abstract
Produced water is treated by raising the pH to a level that
significantly increases silica solubility and breaks emulsions. So
treated water is then de-oiled, filtered, and subjected to ion
exchange chromatography to reduce water hardness prior to feeding
into a steam generator to form an intermediate quality steam. If
desired, the intermediate quality steam is directly used in SAGD,
or separated into a high quality steam and condensate, which is
further treated to obtain additional water that can then be used in
the steam generator.
Inventors: |
Janjua; Rafique; (Sugarland,
TX) ; Prieto; Robert; (Princeton Junction,
NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Fluor Technologies Corporation; |
Aliso Viejo |
CA |
US |
|
|
Assignee: |
FLUOR TECHNOLOGIES
CORPORATION
Aliso Viejo
CA
|
Family ID: |
47909973 |
Appl. No.: |
13/629258 |
Filed: |
September 27, 2012 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61539883 |
Sep 27, 2011 |
|
|
|
61621145 |
Apr 6, 2012 |
|
|
|
Current U.S.
Class: |
166/303 |
Current CPC
Class: |
E21B 43/2406 20130101;
C02F 2101/325 20130101; C02F 9/00 20130101; C02F 1/4604 20130101;
C02F 1/385 20130101; C02F 2103/365 20130101; C02F 2001/425
20130101; C02F 1/682 20130101; E21B 43/40 20130101; C02F 1/66
20130101; C02F 2103/10 20130101; C02F 1/048 20130101; C02F 2101/32
20130101; C02F 1/38 20130101; C09K 8/58 20130101; C02F 1/004
20130101; C02F 1/441 20130101; C02F 2001/5218 20130101 |
Class at
Publication: |
166/303 |
International
Class: |
E21B 43/24 20060101
E21B043/24 |
Claims
1. A method of processing produced water, comprising: providing a
quantity of produced water, and de-oiling and removing solids from
the produced water to thereby form treated water; removing divalent
cations from the treated water using an ion exchange resin to
thereby produce softened water; increasing alkalinity of the
softened water to thereby form alkalinized water, and forming an
intermediate quality steam product from the alkalinized water; and
using at least a portion of the intermediate quality steam product
for injection into a formation.
2. The method of claim 1 wherein the step of using at least a
portion of the intermediate quality steam product comprises
separation of the intermediate quality steam product into a
condensate and a high quality steam product, and a further step of
injection of the high quality product into the formation.
3. The method of claim 2 further comprising a step of processing
the condensate to obtain additional water, and using the additional
water in the step of forming the intermediate quality steam
product.
4. The method of claim 3 wherein the step of processing the
condensate comprises feeding the condensate into a brine
concentrator.
5. The method of claim 1 wherein the step of using at least a
portion of the intermediate quality steam product comprises using
substantially all of the intermediate quality steam product for
injection into the formation.
6. The method of claim 1 wherein the step of forming the
intermediate quality steam is performed using a once-through steam
generator.
7. The method of claim 1 wherein the alkalinized water has a pH of
at least pH 10.
8. The method of claim 1 wherein the intermediate quality steam
product comprises between 10 and 30% condensate.
9. The method of claim 1 wherein the steps of increasing
alkalinity, removing divalent cations, and forming the intermediate
quality steam product are performed without a step of removing
silicate from the produced water, the treated water, the softened
water, and the alkalinized water, respectively.
10. The method of claim 1 further comprising a step of adding
previously isolated silica to the produced water, the treated
water, the softened water, or the alkalinized water.
11. The method of claim 1 wherein the ion exchange resin comprises
a weak acid cation ion exchange resin.
12. A method of processing produced water, comprising: providing
produced water comprising silica, and de-oiling and removing solids
from the produced water; removing divalent cations from the
produced water using an ion exchange resin; and adding a base to
the produced water to thereby form alkalinized water, wherein the
base is added in an amount that increases solubility of the silica
in the alkalinized water at least 25% as compared to the produced
water.
13. The method of claim 12 wherein the base is an alkaline metal
hydroxide or an alkaline earth metal hydroxide.
14. The method of claim 12 wherein the base is added in an amount
to achieve a pH of at least 10 in the alkalinized water.
15. The method of claim 12 wherein the step of de-oiling comprises
a step of chemically breaking an emulsion in the produced
water.
16. The method of claim 12 further comprising a step of forming an
intermediate quality steam product from the alkalinized water, and
still further comprising a step of using at least a portion of the
intermediate quality steam product for injection into a
formation.
17. A method of processing produced water, comprising: providing
produced water comprising silica; chemically breaking an emulsion
in the produced water, and removing oil and precipitate from the
produced water; removing divalent cations from the produced water
using an ion exchange resin; adding a base to the produced water to
thereby form alkalinized water, and forming an intermediate quality
steam product from the alkalinized water without a step of removing
silica from the produced water.
18. The method of claim 17 wherein the base is added in an amount
to achieve a pH of at least 10 in the alkalinized water.
19. The method of claim 17 further comprising a step of adding
previously isolated silica to the produced water or the alkalinized
water.
20. The method of claim 17 further comprising a step of using at
least a portion of the intermediate quality steam product for
injection into a formation.
Description
[0001] This application claims the benefit of priority to copending
U.S. provisional applications with Ser. Nos. 61/539,883, filed Sep.
27, 2011, and 61/621,145, filed Apr. 6, 2012.
FIELD OF THE INVENTION
[0002] The field of the invention is methods and use of treated
produced water, especially as it relates to treatment and use for
enhanced oil recovery (EOR) and steam assisted gravity drainage
(SAGD).
BACKGROUND
[0003] Enhanced Oil Recovery (EOR) of heavy thick oil or Bitumen is
often done by injecting steam into a formation, resulting in a
combination of condensed steam and oil and/or melted bitumen that
is later separated into the hydrocarbon product and "produced
water". For example, steam-based tar sands EOR, also known as steam
assisted gravity drain (SAGD), requires about three barrels of
water equivalent of steam to produce one barrel of liquid bitumen
product. Such relatively high quantities of water demand can
present significant challenges, especially where recovery and
recycling of the water is required.
[0004] Among other difficulties, produced water from SAGD has
frequently high quantities of emulsions of liquid bitumen and
dissolved solids, suspended solids, and free or floating oil, which
requires significant treatment for production of usable water.
Currently known treatment methods include de-oiling, filtration for
suspended solids removal, warm/hot lime softening for hardness or
silica removal, or primary and secondary weak acid cation ion
exchange. Typical examples of known treatment methods include those
described in U.S. Pat. No. 8,047,287 and WO 2012/122207 where one
or more membranes are used to remove silica and/or oil from
produced water. Similarly, as described in U.S. Pat. App. No.
2008/0135478, produced water is treated by a series of steps that
include degasification, chemical softening, filtration, ion
exchange, and reverse osmosis. In yet other known methods,
flotation processes are used as taught in U.S. Pat. App. No.
2009/0014368 while WO 2005/054746 teaches processing of de-oiled
produced water through a high pH/high pressure evaporator to
generate a vapor suitable for SAGD to so avoid use of once through
steam generators that would require extensive chemical
treatment.
[0005] In still further known methods, as described in WO
2012/048217 an evaporative process using a crystallizer is
disclosed. Yet further known methods are described in WO
2007/051167, WO 2009/006575, and WO 2012/024764. These and all
other extrinsic materials discussed herein are incorporated by
reference in their entirety. Where a definition or use of a term in
an incorporated reference is inconsistent or contrary to the
definition of that term provided herein, the definition of that
term provided herein applies and the definition of that term in the
reference does not apply.
[0006] Unfortunately, de-oiling of produced water containing tight
emulsions using commonly known industry practices (e.g., hydro
cyclone, induced or dissolved gas flotation, etc.) are often not
effective. Consequently, most of the oily emulsion will pass
through to the downstream units, which tends to undermine the
effectiveness of filtration, lime softening, or ion exchange
systems. As a result, poor quality water is injected into the high
pressure boiler for steam generation and leads in many cases to
frequent and very expensive break downs. Alternatively, high
gravity force centrifuges (e.g., exceeding 3,000.times.g force) can
be used to break an emulsion. However, such approach generally
requires a large number of centrifuges, which is often cost
prohibitive and consumes significant plot space. To circumvent such
difficulties, emulsions can be acidified to a pH of less than 3 as
low pH solutions can break the emulsion. However, such low pH will
require neutralization or alkalinization prior to further
treatment, and require large amounts of acid and caustic materials
and special metallurgy. Moreover, handling of large amounts of acid
and base will increase safety hazards.
[0007] Compounding the above difficulties in current SAGD reservoir
operations is the use of high quality steam (approaching 100%) from
which silica and other cations have been removed to a large degree.
The removal of silica has been previously driven by process
consideration and the removed silica has become a high volume
hazardous waste product of SAGD operations that must be properly
disposed of. Moreover, many operators are generally opposed to the
use of high silica water in SAGD due to concerns over silica
deposition and precipitation in high-value equipment (e.g., once
through steam generators and steam separators). Additionally, many
operators have raised concerns with respect to reduced produced
water flows as a result of silica deposition in the interstitial
region between horizontal injector and extraction wells, even
though these concerns were not subject to detailed assessment
(presumably because of the concerns associated with high-value
equipment protection). As a consequence, and due to the relatively
high silica content of most produced water, operators tend to rely
on expensive processing equipment for water treatment prior to
steam generation, which presents a significant economic impact.
Worse yet, steam generation and particularly high-quality steam
generation is energy intensive and further exacerbates the economic
challenges with continuous SAGD.
[0008] Thus, there is still a need for processes, devices, and
methods that break down or remove emulsions to enhance filtration
processes, reduce or even eliminate the need for hot/warm lime
softening, and improve methods of steam use in EOR and especially
in SAGD.
SUMMARY OF THE INVENTION
[0009] The inventive subject matter provides devices, systems and
methods in which produced water is processed by (preferably
chemically) breaking emulsions such that the produced water can be
de-oiled and filtered in simple processes, and by elevation of the
pH to a degree that substantially increases silica solubility. Once
de-oiled, filtered, and alkalinized, the treated water is fed to a
steam generator, most preferably a once through steam generator
(OTSG), to produce an intermediate quality steam. The intermediate
quality steam is then either directly used for injection for SAGD,
or separated in a condensate separator to thereby produce high
quality steam and a condensate that can then be processed to
produce a purified water product suitable for additional steam
generation.
[0010] In one aspect of the inventive subject matter, the inventor
contemplates a method of processing produced water that includes a
step of providing a quantity of produced water, and a further step
of de-oiling and removing solids from the produced water to thereby
form treated water. In another step, divalent cations are removed
from the treated water using an ion exchange resin (e.g., a weak
acid cation ion exchange resin) to thereby produce softened water,
and in a still further step, alkalinity of the softened water is
increased to form alkalinized water. In yet another step, an
intermediate quality steam product is formed from the alkalinized
water, and at least a portion of the intermediate quality steam
product is used for injection into a formation.
[0011] In some aspects, it is preferred that the step of using a
portion of the intermediate quality steam product comprises
separation of the intermediate quality steam product into a
condensate and a high quality steam product, and a further step of
injection of the high quality product into the formation. Here, the
condensate may be further processed to so obtain additional water,
which may be uses in forming the intermediate quality steam
product. The condensate may then be processed in a brine
concentrator. In other aspects, it is preferred that the step of
using at least a portion of the intermediate quality steam product
comprises use of substantially all of the intermediate quality
steam product for injection into the formation.
[0012] Regardless of the manner of use of the intermediate quality
steam (which typically comprises between 10 and 30% condensate), it
is generally preferred that the intermediate quality steam is
formed in a once-through steam generator, and that the alkalinized
water has a pH of at least pH 10. It is further especially
preferred that all process steps are performed without an active
step of removing silicate from the produced water, the treated
water, the alkalinized water, and/or the softened water (e.g.,
silicate removal via lime softening). Indeed, it is noted that the
methods presented herein are even suitable for adding previously
isolated silica to the produced water, the treated water, the
softened water, and/or the alkalinized water.
[0013] Viewed from a different perspective, the inventor also
contemplates a method of processing produced water that includes a
step of providing produced water comprising silica, and de-oiling
and removing solids from the produced water. In another step,
divalent cations are removed from the produced water using an ion
exchange resin, and in yet another step, a base is added to the
produced water to thereby form alkalinized water, wherein the base
is added in an amount that increases solubility of the silica in
the alkalinized water at least 25% as compared to the produced
water.
[0014] In especially preferred methods, the base is an alkaline
metal hydroxide or an alkaline earth metal hydroxide, and is added
in an amount to achieve a pH of at least 10 in the alkalinized
water. While not limiting to the inventive subject matter, it is
preferred that the step of de-oiling comprises a step of chemically
breaking an emulsion in the produced water. If desired, an
additional step may include forming an intermediate quality steam
product from the alkalinized water, and yet another step of using
at least a portion of the intermediate quality steam product for
injection into a formation.
[0015] Similarly, the inventor also contemplates a method of
processing produced water that includes a step of providing
produced water comprising silica. In another step, an emulsion is
chemically broken in the produced water, and divalent cations are
removed from the produced water using an ion exchange resin. In
still further contemplated steps, a base is added to the produced
water to thereby form alkalinized water, and an intermediate
quality steam product is formed from the alkalinized water without
a step of removing silica from the produced water.
[0016] Most preferably, the base is added in an amount to achieve a
pH of at least 10 in the alkalinized water, and where desired,
previously isolated silica may be added to the produced water, the
alkalinized water, and/or the softened treated water. Contemplated
methods may also include a further step of using at least a portion
of the intermediate quality steam product for injection into a
formation.
[0017] Various objects, features, aspects and advantages of the
inventive subject matter will become more apparent from the
following detailed description of preferred embodiments.
DETAILED DESCRIPTION
[0018] The inventor has now discovered that produced water can be
treated for subsequent use in a conceptually simple and effective
manner avoiding various expensive processing steps. Most
preferably, produced water is treated with one or more chemicals to
a degree that is effective to break emulsions that are present in
the produced water. So treated water is then de-oiled using
conventional separation, and most preferably by one or more
separation processes that do not require centrifugation or other
mechanically complex devices. Therefore, downstream processes
(e.g., filtration, ion exchange processes) that would otherwise be
adversely affected by emulsions are now easily implemented. Once
de-oiled and solids/precipitates have been removed, the water is
alkalinized to a degree that is effective to reduce, or even
entirely eliminate the need for silica removal, which in turn
allows use of the alkalinized, de-oiled, and filtered water in
downstream processes without further processing.
[0019] For example, the de-oiled, and filtered water can now be
softened using an ion exchange resin (most preferably a weak acid
ion exchange resin), which advantageously avoids use of hot/warm
lime softening, and the alkalinized, de-oiled, and filtered water
can be directly used in a steam generation process (and most
preferably in a once-through steam generator, with or without ion
exchange without softening).
[0020] In yet further preferred aspects, steam generation of the
alkalinized, de-oiled, and filtered water will provide an
intermediate quality steam product (typically about 70% steam) that
can be directly used for injection into a formation, or that can be
processed in a condensate separator to generate high-quality steam
and a condensate suitable for further processing (preferably using
an evaporator) to thereby produce additional water for the steam
generator or other purpose. Thus, it should be appreciated that the
silica content of the water that is being fed to the steam
generator is in many instances the same (or some instances even
higher) than the silica content of produced water entering the
process.
[0021] The following discussion provides many example embodiments
of the inventive subject matter. Although each embodiment
represents a single combination of inventive elements, the
inventive subject matter is considered to include all possible
combinations of the disclosed elements. Thus if one embodiment
comprises elements A, B, and C, and a second embodiment comprises
elements B and D, then the inventive subject matter is also
considered to include other remaining combinations of A, B, C, or
D, even if not explicitly disclosed.
[0022] In one preferred aspect of the inventive subject matter, a
method of processing produced water is contemplated that includes a
step of providing a quantity of produced water, and another step of
de-oiling and removing solids from the produced water to thereby
form treated water. After removal of divalent ions (preferably
using a weak acid ion exchange resin) alkalinity of the treated
softened water is increased to so form alkalinized water. It should
be noted that the step of de-oiling most preferably uses one or
more chemical agents that break emulsions, and all known chemical
emulsion breakers are deemed suitable for use herein.
[0023] With respect to the produced water it is generally
contemplated that all known manners of providing produced water are
deemed suitable for use herein. Thus, suitable produced water may
be derived from steam-assisted hydrocarbon recovery, from on-shore
and off-shore oil and gas production, and various other sources in
hydrocarbon processing. Consequently, produced water is typically
separated from a mixture of the produced water and a hydrocarbon
product, and in most cases such separation is via gravity/phase
separation is separators well known in the art. However, in
alternative aspects of the inventive subject matter, previously
stored or otherwise sequestered produced water may also be employed
in conjunction with the teachings presented herein.
[0024] Regardless of the source of the produced water, and
regardless of the order of various other possible treatment steps
(e.g., de-oiling, softening, filtration, etc.) it is generally
preferred that the produced water is alkalinized such that the pH
of the alkalinized water is at least 8.5, more typically between
8.5 and 9.5, even more typically between 9.5 and 10.5, and most
typically between 10 and 11 (and in some cases even higher). Viewed
from another perspective, it is preferred that the pH of the
alkalinized water is higher than the pH of the produced water prior
to alkalinization, and typically at least 0.5 pH units, more
typically at least 1.0 pH units, and most typically more than 1.5
pH units. Thus, the pH is raised in the produced water to a level
such that solubility of silica in the alkalinized water is
increased over the solubility of silica in the produced water, in
most cases at least 50% (at standard temperature 20.degree. C. and
atmospheric pressure), more preferably at least 100%, and most
preferably at least 200%. Viewed from a different perspective, it
is generally preferred to raise the pH such that silica removal as
practiced in heretofore known processes is no longer required.
Indeed, it is contemplated that the pH can be raised to a level
that allows adding previously isolated silica to the produced water
(the alkalinized water, and/or the softened treated water) before
the water is fed to the steam generator.
[0025] As should be readily appreciated, there are numerous methods
of alkalinization known in the art, and all of the known methods
are deemed suitable for use herein. However, in especially
preferred methods, alkalinization is performed by adding a strong
base to the produced water in an amount sufficient to raise the pH
to the desired level. For example, suitable bases include
hydroxides of alkaline metals or earth alkaline metals, which may
be provided in solid or liquid form.
[0026] It should further be appreciated that the produced water
will still contain significant quantities of hydrocarbons, most
typically in form of emulsions and even tight emulsions due to the
SAGD process. Thus, de-oiling will also typically include a step of
breaking an emulsion and removal of the oil from the broken
emulsion. There are numerous manners of emulsion breaking known in
the art, and all of those are contemplated suitable for use herein.
However, in especially preferred aspects, one or more chemical
agents are used to break emulsions. Once more, there are numerous
chemical agents for breaking emulsions known in the art, and all of
those are appropriate for use. Depending on the particular type and
oil content in the emulsion of the produced water, it should be
noted that the water may be subject to a resting period after
breaking of the emulsion (e.g., in a surge tank or other holding
vessel) to promote or allow for phase separation, or may be
directly processed in a de-oiling process. It should be noted that
the step of de-oiling is typically performed in conventional
manner. Thus, de-oiling may be done in an API-type separator, in a
demulsifier, in a skim tank, a centrifugal or hydrocyclone
separator, or using a plate- or enhanced-coalescers. Moreover,
de-oiling may also be performed using various absorption media well
known in the art.
[0027] Likewise, it should be noted that removal of solid phase
(e.g., sand or other minerals, or precipitates) may be performed as
part of de-oiling operation and so form sludge, and/or may be
separately performed by gravity separation or filtration using
settling or filtration devices well known in the art.
[0028] Consequently, it should be noted that the downstream
processes (e.g., filtration) are also enhanced as the liquid is
less prone to foul filters and/or filtration materials. Moreover,
due to the increased silica solubility attributable to the high pH,
hot/warm lime softening can be reduced, and even more typically
entirely eliminated. If hardness remains a concern, it is noted
that water softening of the (de-oiled and/or alkalinized) water can
be performed using ion exchange chromatography to so remove
divalent cations that contribute to water hardness and scaling in
equipment. There are numerous suitable ion exchange resins known in
the art to remove such ions, and all of those are deemed suitable
for use herein. Especially preferred resins include weak acid
cation exchange resins.
[0029] Consequently, it should be recognized that contemplated
processes and methods will significantly reduce scaling of steam
generators, require less equipment and chemicals to process, and
produce less solid waste. Moreover, it should be noted that plants
using contemplated methods and processes will require a smaller
real-estate footprint, require less water to produce an equivalent
amount of product, and will simplify operation or maintenance.
[0030] Viewed from another perspective, the inventor also
contemplates a method of processing produced water comprising
silica. In such methods, a base (and most preferably a alkaline or
earth alkaline hydroxide) is added to the produced water to form
alkalinized water, typically after a step of de-oiling and solids
removal, wherein the base is added in an amount that increases
solubility of the silica in the alkalinized water at least 25%,
more typically at least 50%, even more typically at least 100%, and
most typically at least 250% as compared to the produced water.
Where desired, divalent cations are then removed from the treated
water using an ion exchange resin to thereby soften the treated
water.
[0031] Likewise, it should also be appreciated that produced water
comprising silica can be processed chemically breaking an emulsion
in the produced water, removing oil and precipitate from the
produced water, removing divalent cations from the produced water
using an ion exchange resin, adding a base to the produced water to
thereby form alkalinized water, and forming an intermediate quality
steam product from the alkalinized water without a step of removing
silica from the produced water. It is especially preferred that all
process steps are performed without an active step of removing
silicate from the produced water, the alkalinized water, and/or the
softened treated water (e.g., via lime softening, precipitation, or
other known manner). Such active steps are typically performed on
the produced water to remove at least 10%, more typically 20%, even
more typically at least 50%, and most typically at least 90% of the
silica present in the produced water.
[0032] Contemplated treatment methods are especially remarkable as
the feed-water quality for OTSGs, the most common form of boiler
found in oilfield enhanced oil recovery projects and used in
generating steam at pressures up to about 2,000 psig with treated
produced waters was established twenty-five years ago and has
changed little (SAGD facilities typically operate at lower steam
pressures but often use the same quality criteria). Currently the
accepted quality for many OTSG requires total hardness of equal or
less than 0.5 mg/L (as CaCO3), Silica equal or less than 50 mg/L,
and oil equal or less than 10 mg/L. However, it should be
appreciated that silica solubility increase at high pH and high
temperature. Both conditions can be maintained in an OTSG, which in
most cases produces about 75% steam and about 25% liquid. Table 1
illustrates solubility of silica in water at standard temperature
(20.degree. C.) and pressure (1 atm) as a function of pH.
TABLE-US-00001 TABLE 1 pH mg/l SiO2 6-8 120 9 138 9.5 180 10 310
10.6 876
[0033] Thus, and provided that the pH is suitably high, it should
be noted that water entering the OTSG can contain significant
quantities of silica, and indeed can even have higher quantities of
silica per volume as the untreated produced water where silica is
added. It is therefore contemplated that the water entering the
steam generator will have at least 70% silica content, more
typically at least 80% silica content, and most typically at least
90% silica content as compared to the silica content of the
untreated produced water.
[0034] In further preferred aspects of the inventive subject
matter, it should be appreciated that the inventor discovered that
the alkalinized water can be used in a variety of ways after
de-oiling, solids removal, and softening, and especially for steam
generation. In particularly preferred aspects, the alkalinized
water is directly used in a steam generator, despite the relatively
high silica content as substantially all (i.e., typically at least
95%, more typically at least 98%, even more typically at least 99%,
and most typically at least 99.9%) of the silica is dissolved in
the softened treated water. Thus, the softened treated water may
have a dissolved silica content of at least 100 mg/l, more
typically at least 200 mg/l, even more typically at least 400 mg/l,
and most typically at least 600 mg/l at STP (standard temperature
(20.degree. C.) and pressure (1 atm)). Moreover, it should be
recognized that the solubility is even further increased at
elevated temperatures (up to 500.degree. F.) and pressures (up to
2,000 psig) commonly encountered in steam generators, and
particularly OTSGs.
[0035] As should be readily appreciated, use of the alkalinized
water in steam generation may be performed in various manners, and
all known manners are deemed suitable herein. However, it is
especially preferred that the alkalinized water is fed to a OTSG to
so produce an intermediate quality steam product. Most commonly,
the steam quality will be in the range of 60-90%, and in the
majority of cases between 70-80%. Where desired, the so produced
intermediate quality steam product can be directly used for
injection in EOR or SAGD operations, or may be processed by
separation in a condensate separator. In such case, the isolated
stream is a high quality steam product (i.e., at least 90%, more
typically at least 95% steam) that is then used for its intended
purpose (e.g., injection in EOR or SAGD operations). The remaining
condensate may be further processed to obtain additional water, for
example, by use of an evaporator, brine concentrator, crystallizer,
reverse osmosis or other filtration, electrolytic desalination,
etc. The additional water may be used for further steam generation,
disposition in a sewer system, or other use in a plant.
[0036] Therefore, it is contemplated that the quality of
intermediate quality steam product may vary, and will typically be
at least 60% quality, more typically at least 70% quality, and most
typically 75-80% quality. Likewise, the intermediate quality steam
product may be at various pressures, and especially suitable
pressures will typically be at least 500 psig, more typically at
least 700 psig, even more typically at least 1000 psig, most
typically at least 1500 psig. Consequently, the steam temperature
is temperature at least 470.degree. F., more typically at least
505.degree. F., even more typically at least 546.degree. F., most
typically at least 597.degree. F. The person of ordinary skill in
the art will readily determine suitable pressures and temperatures,
which will be at least in part be dictated by the type of
hydrocarbon and the depth of formation. Thus, it is noted that at
least a portion of the intermediate quality steam product and in
other instances substantially all (i.e., at least 90%) of the
intermediate quality steam product can be used for injection into
the formation. One should further appreciate that the systems and
methods presented herein may have applicability beyond EOR or SAGD
processes. For example, contemplated systems and methods can be
applied toward other waste water treatment processes, and
especially desalter mudwash wastewater operations to reduce COD/BOD
load on treatment plants.
[0037] In still further contemplated aspects of the inventive
subject matter, the inventor noted that in most conventional
operations, steam-water mixtures exiting the OTSG still often
require steam quality improvement. Remarkably, it has not yet been
appreciated in the art to eliminate the steam separator stage,
silica removal equipment, and the large amount of chemicals
required in utilizing high quality steam by using lower quality
steam directly in SAGD reservoir operations as already described
above.
[0038] Even more notably, using pre-treated lower quality steam
will also eliminate concerns related to silica build-up in the
interstitial region between injection and extraction wells as is
explained in more detail below. Viewed from a different
perspective, silica removal operations currently necessitate
extensive capital equipment, maintenance and disposal costs, which
can be avoided through the use of high silica wet steam mixture as
a lower quality stream, delivering the same BTU content as is
currently employed. Additionally the use of high silica steam-water
injection results in the return of silica to the in-situ
environment it originated from. Indeed, it should be appreciated
that silica that is currently being removed and treated as a waste
stream can now be re-injected into its source formation without
adverse effects on the oil extraction operations. This re-injection
of silica provides significant environmental and economic
advantages through elimination of one of the major waste streams
associated with SAGD operations.
[0039] More specifically, the inventor has discovered that the
steam separator stage, silica removal equipment, and large amount
of chemicals currently required in utilizing high silica make-up
water can be eliminated by use of lower quality steam from
pre-treated water streams directly in SAGD reservoir operations
while eliminating concerns related to silica build up in the
interstitial region between injection and extraction wells.
[0040] During the initial phases of SAGD steam chamber expansion,
oil flows from both the ceiling and slopes and its flow rate can be
described by Butler's LinDrain equation:
q = L 1.3 kg .alpha..phi..DELTA. S o h mv S | 1 - .pi. de
##EQU00001##
[0041] During this phase flow rates are proportional to h where h
reaches a maximum at the thickness of the reservoir (net pay
thickness). This flow rate model is applicable until the steam
chamber reaches the overlying cap rock at which point it spreads
horizontally and oil flows become slope flows only and heat loss to
the cap rock occurs. During this subsequent phase, the shape of the
steam chamber can be approximated by a triangular cross
section.
[0042] Total oil produced over the life of the facility is directly
proportional to the area of the triangle which can be calculated as
R.times.h, where R is the radial spread along the cap rock and h is
the reservoir thickness. R is related to .theta., where .theta. is
the angle between the horizontal and the SAGD reservoir steam
chamber. As .theta. decreases, R grows, total oil produced grows
and heat loss to the cap rock also grows. The area represented by
the SAGD steam chamber can be written as h.sup.2/tan .theta.. In
typical SAGD reservoirs, the lower point in this inverted triangle
can be treated as the producer well with the injector well located
some distance S above the producer well. For simplicity the region
between the two wells is treated as being filled with a
bitumen/water mixture and the volume occupied is similarly
described by the area of the triangle bounded by the SAGD reservoir
and bitumen/water level. This area can be written as S.sup.2/tan
.theta.. The ratio of this bitumen/water volume to total produced
oil volume is S.sup.2/h.sup.2 and is constant throughout the entire
reservoir development period. During initial reservoir development
(until cap rock is reached), reservoir volumes developed will be
less than what would be expected based in the height of the steam
chamber.
[0043] Similar to total oil produced, silica production is directly
related to the cross sectional area of the steam chamber along the
axis of the injection well. As such, in situ silica (soluble
fraction only), would be liberated from the produced portion of the
reservoir and concentrated in the bitumen/water reservoir between
the producer and injector wells. The degree of concentration is
represented by the ratio of these two areas or S.sup.2/h.sup.2 and
actual silica levels in the bitumen/oil mixture will be a function
of in situ levels (soluble fraction). The constant nature of this
relative concentration is the reason that one does not see an
increase in silica levels in produced water over time. Viewed from
a different perspective, it should be appreciated that the silica
deposition in the formation and dissolution from the formation are
equilibrium processes that ultimately do not materially affect the
silica content in produced water. Likewise, over-deposition of
silica will not occur due to re-dissolution of the silica material
from the formation.
[0044] For "thick" reservoirs one might expect total net pay
thickness to be on the order of 33 meters and spacing between
production and injection wells to be 5 meters, concentrations in
the lower regions would be expected to be 43.56 times the initial
in situ soluble concentrations. Return of silica removed from
produced water to the bitumen/water reservoir underground does not
increase total silica in the underground reservoir.
[0045] Consequently, it should be recognized that in the pool is an
equilibrium concentration that is a function of the pH and pool
temperature, and material that can not stay in solution will
precipitate out. It should be noted that this precipitation already
happens with the current silica removal practice, since any
reduction of silica below the solubility limit in the pool is
immediately offset by dissolution of the precipitate back into the
pool, sustaining pool silica concentrations at the saturation level
consistent with pool chemistry and temperature (which is observed
in operation). Produced water silica levels will not rise above
this equilibrium level all other things being equal. Conversely, if
the saturation level is not yet reached, pool chemistry is driven
by the ratio laid out times the initial soluble silica
concentration in the reservoir, and again the pool will reach an
equilibrium level and the silica concentrations in produced water
will remain unchanged. Thus, one operational concern should not
relate to silica concentration in the circulating loop, but rather
to the significance of the precipitate volume in the reservoir.
[0046] For example, in a case for a 1000 bpd facility operating for
5 years, about 250,000 metric tons of oil are removed plus some
other amount of dissolved solids which are stripped out at the
surface. Also displaced are 217 tons of silica, or about 0.1% of
the removed oil. Using the reservoir dimensions above, the volume
in the liquid region is about 2.5% of the total depleted volume
which means 2.5% of the oil came from this volume. Consequently, it
should be appreciated that the oil is replaced with a mass of
silica that is 25 times smaller, ignoring the amount that is
actually in solution in the loop. Some fraction of the silica in
the pool will be in solution, further influenced by higher pH in
those instances where higher pH steam-water flows from the OTSG are
utilized, as well so the actual precipitate volumes will be even
less.
[0047] Unless the context dictates the contrary, all ranges set
forth herein should be interpreted as being inclusive of their
endpoints and open-ended ranges should be interpreted to include
commercially practical values. Similarly, all lists of values
should be considered as inclusive of intermediate values unless the
context indicates the contrary.
[0048] It should be apparent to those skilled in the art that many
more modifications besides those already described are possible
without departing from the inventive concepts herein. The inventive
subject matter, therefore, is not to be restricted except in the
scope of the appended claims. Moreover, in interpreting both the
specification and the claims, all terms should be interpreted in
the broadest possible manner consistent with the context. In
particular, the terms "comprises" and "comprising" should be
interpreted as referring to elements, components, or steps in a
non-exclusive manner, indicating that the referenced elements,
components, or steps may be present, or utilized, or combined with
other elements, components, or steps that are not expressly
referenced. Likewise, as used herein, and unless the context
dictates otherwise, the term "coupled to" is intended to include
both direct coupling (in which two elements that are coupled to
each other contact each other) and indirect coupling (in which at
least one additional element is located between the two elements).
Therefore, the terms "coupled to" and "coupled with" are used
synonymously. Where the specification claims refers to at least one
of something selected from the group consisting of A, B, C . . .
and N, the text should be interpreted as requiring only one element
from the group, not A plus N, or B plus N, etc.
* * * * *