Note: Descriptions are shown in the official language in which they were submitted.
CA 02740060 2011-05-13
WATER TREATMENT METHOD FOR HEAVY OIL PRODUCTION
USING CALCIUM SULFATE SEED SLURRY EVAPORATION
RELATED PATENT APPLICATIONS
[0001] This application is a divisional of Canadian Patent Application
2,509,309 filed June 8, 2005.
COPYRIGHT RIGHTS IN THE DRAWING
[0002] A portion of the disclosure of this patent document contains
material that is subject to copyright protection. The applicant has no
objection
to the facsimile reproduction by anyone of the patent document or the patent
disclosure, as it appears in the Patent and Trademark Office patent file or
records, but otherwise reserves all copyright rights whatsoever.
TECHNICAL FILED
[0003] The invention disclosed and claimed herein relates to treatment of
water to be used for steam generation in operations which utilize steam to
recover
oil from geological formations. More specifically, this invention relates to
novel,
improved techniques for efficiently and reliably generating from oil field
1
CA 02740060 2011-05-13
produced waters, in high pressure steam generators, the necessary steam for
down-hole use in heavy oil recovery operations.
BACKGROUND
[0004] Steam generation is necessary in heavy oil recovery operations.
This is because in order to recover heavy oil from certain geologic
formations,
steam is required to increase the mobility of the sought after oil within the
formation. In prior art systems, oil producers have often utilized once-
through
type steam generators ("OTSG's). As generally utilized in the industry, once
through steam generators -OTSG's -usually have high blowdown rates, often in
the range of from about 20% to about 30% or thereabouts. Such a blowdown
rate leads to significant thermal and chemical treatment inefficiencies. Also,
once through steam generators are most commonly provided in a configuration
and with process parameters so that steam is generated from a feedwater in a
single-pass operation through boiler tubes that are heated by gas or oil
burners.
Typically, such once through steam generators operate at from about 1000
pounds per square inch gauge (psig) to about 1600 psig or so. In some cases,
once through steam generators are operated at up to as much as about 1800
psig. Such OTSG's often operate with a feedwater that has from about 2000
.mg/L to about 8000 mg/L of total dissolved solids. As noted in FIG. 1, which
depicts the process flow sheet of a typical prior art water treatment system
10,
such a once through steam generator 12 provides a low quality or wet steam,
wherein about eighty percent (80%) quality steam is produced. In other words,
the 80% quality steam 14 is about 80% vapor, and about 20% liquid, by weight
percent. The steam portion, or high pressure steam produced in the steam
generators is injected via steam injection wells 16 to fluidize as indicated
by
reference arrows 18, along or in combination with other injectants, the heavy
oil
formation 20, such as oils in tar sands formations. The injected steam 14
eventually condenses and an oil/water mixture 22 results, and which mixture
migrates through the formation 20 as indicated by reference arrows 24. The
2
CA 02740060 2011-05-13
oil/water mixture 22 is gathered as indicated by reference arrows 26 by
oil/water
gathering wells 30, through which the oil/water mixture is pumped to the
surface.
Then, the sought-after oil is sent to an oil/water separator 32 in which the
oil
product 34 separated from the water 35 and recovered for sale. The produced
water stream 36, after separation from the oil, is further de-oiled in a de-
oiling
process step 40, normally by addition of a de-oiling polymer 42 or by other
appropriate processes. Such a de-oiling process usually results in generation
of
an undesirable waste oil/solids sludge 44. However, the de-oiled produced
water
stream 46 is then further treated for reuse.
[0005] The design and operation of the water treatment plant which treats
the de-oiled produced water stream 46, i.e., downstream of the de-oiling unit
40
and upstream of injection well 16 inlet 48, is the key to the improvement(s)
described herein.
[0006] Most commonly in prior art plants such as plant 10, the water is
sent to the "once-through" steam generators 12 for creation of more steam 14
for
oil recovery operations. The treated produced water stream 12F which is the
feed stream for the once through steam generator, at time of feed to the steam
generator 12, is typically required to have less than about 8000 parts per
million
("PPM") of total dissolved solids ("TDS"). Less frequently, the treated
produced
water stream 12F may have up to about 12000 parts per million (as CaCO3
equivalent) of total dissolved solids, as noted in FIG. 8. Further, it is
often
necessary to meet other specific water treatment parameters before the water
can be reused in such once-through steam generators 12 for the generation of
high pressure steam.
[0007] In most prior art water treatment schemes, the de-oiled recovered
water 46 must be treated in a costly water treatment plant sub-system 10
before
it can be sent to the steam generators 12. Treatment of water before feed to
the
once-through steam generators 12 is often initially accomplished by using a
warm lime softener 50, which removes hardness, and which also removes some
3
CA 02740060 2011-05-13
silica from the de-oiled produced water feedstream 46. Various softening
chemicals 52 are usually necessary, such as lime, flocculating polymer, and
perhaps soda ash. Underflow 56 produces a waste sludge 58 which must be
further handled and disposed. Then, an "after-filter" 60 is often utilized on
the
clarate stream 59 to prevent carry-over of any precipitate or other suspended
solids, which substances are thus accumulated in a filtrate waste stream 62.
For
polishing, an ion exchange step 64, normally including a hardness removal step
such as a weak acid cation (WAC) ion-exchange system that can be utilized to
simultaneously remove hardness and the alkalinity associated with the
hardness,
is utilized. The ion exchange systems 64 require regeneration chemicals 66 as
is
well understood by those of ordinary skill in the art and to which this
disclosure is
directed. As an example, however, a WAC ion exchange system is usually
regenerated with hydrochloric acid and caustic, resulting in the creation of a
regeneration waste stream 68. Overall, such prior art water treatment plants
are
relatively simple, but, result in a multitude of liquid waste streams or solid
waste
sludges that must be further handled, with significant additional expense.
[0008] In one relatively new heavy oil recovery process, known as the
steam assisted gravity drainage heavy oil recovery process (the "SAGD"
process), it is preferred that one hundred percent (100%) quality steam be
provided for injection into wells (i.e., no liquid water is to be Provided
with the
steam to be injected into the formation). Such a typical prior art system 11
is
depicted in FIG. 2. However, given conventional prior art water treatment
techniques as just discussed in connection with FIG. 1, the 100% steam quality
requirement presents a problem for the use of once through steam generators 12
in such a process. That is because in order to produce 100% quality steam 70
using a once-through type steam generator 12, a vapor-liquid separator 72 is
required to separate the liquid water from the steam. Then, the liquid
blowdown
73 recovered from the separator is typically flashed several times in a series
of
4
CA 02740060 2011-05-13
flash tanks Fl, F2, etc. through FN (where N is a positive integer equal to
the
number of flash tanks) to successively recover as series of lower pressure
steam
flows Sl, S2, etc. which may sometimes be utilized for other plant heating
purposes. After the last flashing stage FN, a residual hot water final
blowdown
stream 74 must then be handled, by recycle and/or disposal. The 100% quality
steam is then sent down the injection well 16 and injected into the desired
formation 20. Fundamentally, though, conventional treatment processes for
produced water used to generate steam in a once-through steam generator
produces a boiler blowdown which is roughly twenty percent (20%) of the
10: feedwater volume. This results in a waste brine stream that is about
fivefold the
concentration of the steam generator feedwater. Such waste brine stream must
be disposed of by deep well injection, or if there is limited or no deep well
capacity, by further concentrating the waste brine in a crystallizer or
similar
system which produces a dry solid for disposal.
[0009] As depicted in FIG. 3, another method which has been proposed
' for generating the required 100% quality steam for use in the steam
assisted
gravity drainage process involves the use of boilers 80, which may be
packaged,
factory built boilers of various types or field assembled boilers with mud and
steam drums and water wall piping. Various methods can be used for producing
water of a sufficient quality to be utilized as feedwater 80F to a boiler 80.
One
method which has been developed for use in heavy oil recovery operations
involves de-oiling 40 of the produced water 36, followed by a series of
physical-
chemical treatment steps. Such treatment steps normally include a series of
unit
operations as warm lime softening 54, followed by filtration 60 for removal of
residual particulates, then an organic trap 84 (normally non-ionic ion
exchange
resin) for removal of residual organics. The organic trap 84 may require a
regenerant chemical supply 85, and, in any case, produces a waste 86, such as
a regenerant waste. Then, a pre-coat filter 88 can be used, which has a
precoat
filtrate waste 89. In one alternate embodiment, an ultrafiltration ("UF") unit
90 can
5 5
CA 02740060 2011-05-13
be utilized, which unit produces a reject waste stream 91. Then, effluent from
the
UF unit 90 or precoat filter 88 can be sent to a reverse osmosis ("RO") system
92, which in addition to the desired permeate 94, produces a reject liquid
stream
96 that must be appropriately handled. Permeate 94 from the RO system 92, can
be sent to an ion exchange unit 100, typically but not necessarily a mixed bed
demineralization unit, which of course requires regeneration chemicals 102 and
which consequently produces a regeneration waste 104. And finally, the boiler
80
produces a blowdown 110 which must be accommodated for reuse or disposal.
[0010] The prior art process designs, such as depicted in FIG. 3, for
utilizing packaged boilers in heavy oil recovery operations, have a high
initial
capital cost. Also, such a series of unit process steps involves significant
ongoing
chemical costs. Moreover, there are many waste streams to discharge, involving
a high and ongoing sludge disposal cost. Further, where membrane systems
such as ultrafiltration 90 or reverse osmosis 92 are utilized, relatively
frequent
replacement of membranes 106 or 108, respectively, may be expected, with
accompanying on-going periodic replacement costs. Also, such a process
scheme can be labor intensive to operate and to maintain.
[0011] In summary, the currently known and utilized methods for treating
, heavy oil field produced waters in order to generate high quality steam for
down-
hole use are not entirely satisfactory because:
such physical-chemical treatment process schemes are usually
quite extensive, are relatively difficult to maintain, and require significant
operator attention;
such physical-chemical treatment processes require many chemical
additives which must be obtained at considerable expense, and many of
which require special attention for safe handling;
such physical-chemical treatment processes produce substantial
quantities of undesirable sludges and other waste streams, the disposal of
6
CA 02740060 2011-05-13
which is increasingly difficult, due to stringent environmental and
= regulatory requirements.
[0012] lt is clear that the development of a simpler, more cost effective
approach to produced water treatment would be desirable in the process of
producing steam in heavy oil production operations. Thus, it can be
appreciated
that it would be advantageous to provide a new produced water treatment
process which minimizes the production of undesirable waste streams, while
minimizing the overall costs of owning and operating a heavy oil recovery
plant.
SOME OBJECTS, ADVANTAGES, AND NOVEL FEATURES
[0013] The new water treatment process(es) disclosed herein, and various
embodiments thereof, can be applied to heavy oil production operations. Such
embodiments are particularly advantageous in that they minimize the generation
of waste products, and are otherwise superior to water treatment processes
heretofore used or proposed in the recovery of bitumen from tar sands or other
heavy oil recovery operations.
[0014] From the foregoing, it will be apparent to the reader that one of the
important and primary aspects resides in the provision of a novel process,
including several variations thereof, for the treatment of produced waters, so
that
such waters can be re-used in producing steam for use in heavy oil recovery
operations.
= [0015] Another important aspect is to simplify process plant flow sheets,
i.e., minimize the number of unit processes required in a water treatment
train,
which importantly simplifies operations and improves quality control in the
manufacture of high purity water for down-hole applications.
7
CA 02740060 2011-05-13
[0016] Other important but more specific aspects reside in the provision
of various embodiments for an improved water treatment process for production
of high purity water for down-hole use in heavy oil recovery, which
embodiments may:
in one embodiment, eliminate the requirement for flash separation of the
high pressure steam to be utilized downhole from residual hot
pressurized liquids;
eliminate the generation of softener sludges;
minimize the production of undesirable liquid or solid waste streams;
minimize operation and maintenance labor requirements;
minimize maintenance material requirements;
minimize chemical additives and associated handling requirements;
increase reliability of the OTSG's, when used in the process;
decouple the de-oiling operations from steam production operations; and
reduce the initial capital cost of water treatment equipment.
[0016A] The present invention in one broad aspect pertains to a process
for treatment of a produced water stream resulting from the production of oil
from heavy oil reserves, the produced water stream comprising dissolved
solutes including calcium, sulfate, silica, alkalinity, and non-condensable
gases.
The process comprises acidification of the produced water stream, to remove
alkalinity by conversion to free carbon dioxide, steam stripping the produced
water stream to remove the non-condensable gases and the carbon dioxide
produced in the alkalinity removal step, evaporation of the produced water
stream to produce a slurry comprising water, dissolved solutes, calcium
sulfate,
and silica, to generate (i) a distillate stream at about 95% or more by volume
of
the produced water stream and (ii) a blowdown stream at about 5% or less by
volume of the produced water stream, and generating a steam stream at about
8
CA 02740060 2011-05-13
100% quality and at about 1000 pounds per square inch pressure or more from
the distillate stream, and wherein the steam stream comprises at least about
70% by weight of the distillate stream, and generating a blowdown stream of at
least about 30% or less by weight of the distillate stream.
[0017] Other important aspects, features, and additional advantages of
the various embodiments of the novel process disclosed herein will become
apparent to the reader from the foregoing and from the appended claims and
the ensuing detailed description, as the discussion below proceeds in
conjunction with examination of the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
[0018] In order to enable the reader to attain a more complete
appreciation of the novel water treatment process disclosed and claimed
herein,
and the various embodiments thereof, and of the novel features and the ad-
vantages thereof over prior art processes, attention is directed to the
following
8a
CA 02740060 2011-05-13
detailed description when considered in connection with the accompanying
figures of the drawing, wherein:
[0019] FIG. 1 shows one typical prior art process, namely a generalized
process flow diagram for a physical-chemical water treatment process
configured
for use in heavy oil recovery operations.
[0020] FIG. 2 shows another prior art process, namely a generalized
process flow diagram for a physical-chemical water treatment process as used
in
a steam assisted gravity drainage (SAGD) type heavy oil operation.
[0021] FIG. 3 shows yet another prior art physical-chemical treatment
process scheme, also as it might be applied for use in steam assisted gravity
drainage (SAGD) type heavy oil recovery operations.
[0022] FIG. 4 shows one embodiment of an evaporation based water
treatment process, illustrating the use of a seeded slurry evaporation based
process in combination with the use of packaged boilers for steam production,
as
applied to heavy oil recovery operations.
[0023] FIG. 5 shows another embodiment for an evaporation based water
treatment process for heavy oil production, illustrating the use of a seeded
slurry
evaporation process in combination with the use of once-through steam
generators for steam production, as applied to heavy oil recovery operations,
= 25 which process is characterized by feed of evaporator distillate to
once-through
steam generators without the necessity of further pretreatment.
[0024] FIG. 6 shows a common variation for the orientation of injection
and gathering wells as utilized in heavy oil recovery, specifically showing
the use
9
CA 02740060 2011-05-13
of horizontal steam injection wells and of horizontal oil/water gathering
wells, as
often employed in a steam assisted gravity drainage heavy oil gathering
project.
[0025] FIG. 7 shows the typical feedwater quality requirements for steam
[0026] FIG. 8 shows the typical feedwater quality requirements for steam
generators which produce steam in the 1000 pounds per square inch gauge
[0027] FIG. 9 provides a simplified view of a vertical tube falling film
evaporator operating in a seeded slurry mode in the treatment of produced
water
from heavy oil operations, for production of distillate for reuse in once
through
[0028] FIG. 10 shows further details of the use of evaporators operating in
a seeded slurry mode, illustrated by use of falling film evaporators, and
indicates
selected injection points for acidification of the feedwater and for control
of pH in
[0029] FIG. 11 illustrates the solubility of silica in water as a function of
pH
at 25 C when such silica species are in equilibrium with amorphous silica, as
well
[0030] FIG. 12 diagrammatically illustrates functional internal details of the
operation of a falling film evaporator operating in a seeded slurry mode,
which
10
CA 02740060 2011-05-13
evaporator type would be useful in the evaporation of produced waters from
heavy oil production; details illustrated include the production of steam from
a
falling brine film, by a heat exchange relationship from condensation of steam
on
a heat exchange tube, and the downward flow of such steam condensate
(distillate) by gravity for the collection of such condensate (distillate)
above the
bottom tube sheet of the evaporator.
[0031] The foregoing figures, being merely exemplary, contain various
elements that may be present or omitted from actual process implementations
depending upon the circumstances. An attempt has been made to draw the
figures in a way that illustrates at least those elements that are significant
for an
understanding of the various embodiments and aspects of the invention.
However, various other elements of the unique process methods, and the
combination of apparatus for carrying out the methods, are also shown and
briefly described to enable the reader to understand how various features,
including optional or alternate features, may be utilized in order to provide
an
efficient, low cost process design which can be implemented in a desired
throughput size and physical configuration for providing optimum water
treatment
plant design and operation.
11
CA 02740060 2011-05-13
DESCRIPTION
[0032] Many steam assisted heavy oil recovery schemes, such as a steam
assisted gravity drainage (SAGD) heavy oil recovery process injection and
recovery well arrangements of the type depicted in FIG. 6, most efficiently
utilize
a 100% quality steam supply 70. It would therefore be desirable to produce
such
a steam supply by an efficient process scheme such as I have found may be
provided by evaporation based heavy oil produced water treatment method(s).
Various embodiments and details of such evaporation based produced water
treatment method(s) are depicted in FIGS. 4, 5, 6, 9, 10 and 12.
[0033] As depicted in FIG. 6, in a SAGD process, horizontal injection
wells 16 and horizontal oil/water gathering wells 30 are advantageously.
utilized spaced apart within an oil bearing formation 20. As particularly
illustrated in FIGS. 4 and 5, a process for the use of an evaporation based
water
treatment system 120 has been developed to treat produced water, in order to
produce high quality steam for use in further heavy oil recovery.
Conceptually,
such an evaporative water treatment process may, in one embodiment, be
situated process wise - that is, water flow wise - between the point of
receipt of a
de-oiled produced water stream 46 and the point of steam injection at well
head
48 of injection well 16. The process, in combination with the steam injection
well
16, oil recovery well 30, and related oil water separation equipment 32 and de-
oiling equipment 40, and boilers 80 as shown in FIG. 4, or alternately, once
through steam generators 12 as shown in FIG. 5, can substantially reduce
capital
costs and can minimize ongoing operation and maintenance costs of heavy oil
recovery installations. Boilers 80 may be packaged, factory built boilers of
various types or field assembled boilers with mud and steam drums and water
wall piping, or more generally, conventional steam boilers. In some locales,
such
as northern Canada, the possibility of elimination of the need for handling of
waste sludges and other waste streams made possible by the evaporation based
12
CA 02740060 2011-05-13
water treatment system 120 may be especially important, since it may be
difficult
to work with such waste materials during the extremely cold winter months.
[0034] It has been observed that it may be desirable in some instances to
use a packaged boiler 80 to produce the required steam 70, rather than to
utilize
a traditional once-through type steam generator 12 to produce 80% quality
steam
14 and then utilize separator(s) 130 to separate steam 132 from liquid 134. It
is
noteworthy in such an economic process evaluation that packaged boilers 80 are
often less expensive on a capital cost basis and on an operating cost basis
than
once-through type oil-field steam generators 12. Also, package boilers can be
utilized to produce pure steam 70, and thus produce only a minimal liquid
blowdown stream 110. Also, as shown in FIGS. 4 and 5, boiler blowdown
stream can be either sent to the evaporator feed tank 210, or injected into
the
sump reservoir 152 of evaporator 140, such as via line 111, or into a
recirculating
brine via line 111'. One type of packaged boiler suitable for use in the
process
described herein is a water tube boiler having a lower mud drum and an upper
steam drum and water cooled sidewalls substantially extending therebetween in
a manner which encloses a combustion chamber. However, most such
packaged boilers require a much higher quality feed water 80F than is the case
with requirements for feedwater 12F fora once-through type steam generator.
As a result, in one embodiment, the process disclosed herein includes an
evaporation unit 140 based approach to packaged boiler 80 feedwater 80F
pretreatment. In other words, the de-oiled produced water 46 generated can be
advantageously treated by an evaporative process operating in a seeded slurry
mode, particularly if the oil in the de-oiled produced water is reduced
reliably to a
selected low level of less than about 20 parts per million, or more preferably
to
less than about 10 parts per million, and provides a significantly improved
method for produced water treatment in heavy oil production.
[0035] An oil/water mixture 22 is pumped up through oil gathering wells
30. The oil water mixture 22 is sent to a series of oil/water separators 32.
An oil
13
CA 02740060 2011-05-13
product 34 is gathered for further conditioning, transport, and sale. The
produced water 36 which has been separated from the oil/water mixture 22 is
then sent to a produced water de-oiling step 40, which may be accomplished in
dissolved air flotation units with the assistance of the addition of a de-
oiling
polymer 42, or by other appropriate unit processes, to achieve a preselected
low
residual oil level such as less than 20 parts per million.
[0036] In the water treatment method disclosed herein, the de-oiled
produced water 46 is treated and conditioned for feed to one or more
mechanical
vapor recompression evaporator units 140 (normally, multiple redundant units)
to
concentrate the incoming produced water stream 46. The necessary treatment
and conditioning prior to the evaporator unit 140 can be efficiently
accomplished,
but may vary somewhat based on feedwater chemistry - i.e. the identity and
distribution of various dissolved and suspended solids - and on the degree of
concentration selected for accomplishment in evaporator units 140.
[0037] In one embodiment, it may be necessary or appropriate to add acid
by line 144, or at an appropriate point upstream of the feed tank 210 when
desired such as via line 146'. A suitable acid may be sulfuric acid or
hydrochloric
acid, which is effective to lower the pH sufficiently so that bound carbonates
are
converted to free gaseous carbon dioxide, which is removed, along with other
no-n=condensable gases 148 dissolved in the feedwater 46 such as oxygen and
nitrogen, in an evaporator feedwater deaerator 150. However, use of acid 144
is
this manner is optional, and can sometimes be avoided if feedwater chemistry
and the concentration limits of scale forming species are sufficiently low at
the
anticipated concentration factor utilized in evaporator 140. For pH control,
as
seen in FIG. 101 it may be useful to add a selected base such as caustic 232
to
the concentrated brine recirculating in the evaporator 140, which can be
accomplished by direct injection of a selected base such as caustic 232 into
the
sump 141, as indicated by line 157, or by feed of a selected base such as
caustic
232 into the suction of recirculation pump 153, as indicated by line 159.
14
CA 02740060 2011-05-13
However, if the produced water contains an appreciable amount of calcium and
sulfate, the mechanical vapor recompression evaporator 140 may in one
embodiment be operated using a calcium sulfate seeded-slurry technique,
normally in a near neutral pH range. That mode of operation can be made
feedwater is introduced into the evaporator 140. Then, the evaporator 140 may
be operated a seeded-slurry mode wherein calcium sulfate and silica co
precipitated recirculating seed crystals, which avoids scaling of the heat
transfer
surfaces.
[0038] At feedwater heat exchanger, the feedwater pump 149 is used to
provide sufficient pressure to send feedwater from the evaporator feed tank
210
through the feedwater heat exchanger 148, prior to the deaerator 150. In the
opposite direction, the distillate pump 143 moves distillate 180 through the
feedwater heat exchanger 148, so that the hot distillate is used to heat the
feedwater stream directed toward the deaerator 150.
[0039] The conditioned feedwater 151 is sent as feedwater to evaporator
140. The conditioned feedwater 151 may be directed to the inlet of
recirculation
pump 153, or alternately, directed to the sump 141 of evaporator 140 as
indicated by broken line 151' in FIG. 10. Concentrated brine 152 in the
evaporator 140 is recirculated via pump 153, so only a small portion of the
recirculating concentrated brine is removed on any one pass through the
evaporator 140. In the evaporator 140, the solutes in the feedwater 46 are
=
concentrated via removal of water from the feedwater 46. As depicted in FIGS.
10 and 12, an evaporator 140 is in one embodiment provided in a falling film
configuration wherein a thin brine film 154 is provided by distributors 155
and
then falls inside of a heat transfer element, e.g. tube 156. A small portion
of the
water in the thin brine film 154 is extracted in the form of steam 160, via
heat
given up from heated, compressed steam 162 which is condensing on the
outside of heat transfer tubes 156. Thus, the water is removed in the form of
15 15
CA 02740060 2011-05-13
steam 160, and that steam is compressed through the compressor 164, and the
compressed steam 162 is condensed at a heat exchange tube 156 in order to
produce yet more steam 160 to continue the evaporation process. The
condensing steam on the outer wall 168 of heat transfer tubes 156, which those
of ordinary skill in the evaporation arts and to which this disclosure is
directed
may variously refer to as either condensate or distillate 180, is in
relatively pure
form, low in total dissolved solids. In one embodiment, such distillate
contains
less than 10 parts per million of total dissolved solids of non-volatile
components.
Since, as depicted in the embodiments shown in FIGS. 4, 5, 9, and 10, a single
stage of evaporation is provided, such distillate 180 may be considered to
have
been boiled, or distilled, once, and thus condensed but once.
[0040] Prior to the initial startup of the evaporator 140 in the seeded-slurry
mode, the evaporator, which in such mode may be provided in a falling-film,
mechanical vapor recompression configuration, the fluid contents of the unit
are
"seeded" by the addition of calcium sulfate (gypsum). The circulating solids
within
the brine slurry serve as nucleation sites for subsequent precipitation of
calcium
sulfate 272, as well as silica 274. Such substances both are precipitated as
an
entering feedwater is concentrated. Importantly, the continued concentrating
process produces additional quantities of the precipitated species, and thus
creates a continuing source of new "seed" material as these particles are
broken
up by the mechanical agitation, particularly by the action of the
recirculation
pump 153.
[0041] In order to avoid silica and calcium sulfate scale buildup in the
evaporator 140, calcium sulfate seed crystals 272 are continuously circulated
over the wetted surfaces, i.e., the falling film evaporator tubes 156, as well
as
other wetted surfaces in the evaporator 140. Through control of slurry
concentration, seed characteristics, and system geometry, the evaporator can
operate in the otherwise scale forming environment. The thermo chemical
operation within the evaporator 140 with regard to the scale prevention
16
CA 02740060 2011-05-13
mechanism is depicted in FIG. 12. As the water is evaporated from the brine
film
154 inside the tubes 156, the remaining brine film becomes super saturated and
calcium sulfate and silica start to precipitate. The precipitating material
promotes
crystal growth in the slurry rather than new nucleation that would deposit on
the
heat transfer surfaces; the silica crystals attach themselves to the calcium
sulfate
crystals. This scale prevention mechanism, called preferential precipitation,
has a
proven capability to promote clean heat transfer surfaces 260. The details of
one
advantageous method for maintaining adequate seed crystals in preferentially
precipitation systems is set forth in U.S. Pat. No. 4,618,429, issued Oct. 21,
1986
to Howard R. Herrigel, which may be referred to for further details.
[0042] It is to be understood that the falling film evaporator 140 design is
provided only for purposes of illustration and thus enabling the reader to
understand the water treatment process(es) taught herein, and is not intended
to
limit the process to the use of such evaporator design, as those in the art
will
recognize that other designs, such as, for example, a forced circulation
evaporator, or a rising film evaporator, may be alternately utilized with the
accompanying benefits and/or drawbacks as inherent in such alternative
evaporator designs.
[0043] In any event, in a falling film evaporator embodiment, the distillate
180 descends by gravity along tubes 156 and accumulates above bottom tube
sheet 172, from where it is collected via condensate line 174. A small portion
of
steam in equilibrium with distillate 180 may be sent via line 172 to the
earlier
discussed deaerator 150 for use in mass transfer, i.e, heating and steam
stripping descending liquids in a packed tower to remove non-condensable
gases 148 such as carbon dioxide. However, the bulk of the distillate 180 is
removed as a liquid via line 180', and may optionally be sent for further
treatment
in a distillate treatment plant, for example such as depicted in detail in
FIG. 4, or
as merely depicted in functional form as feed 181F for plant 181 in FIG. 5, to
17
CA 02740060 2011-05-13
ultimately produce a product water 181p which is suitable for evaporator
feedwater, such as feedwater 80F in the case where packaged boilers 80 are
utilized as depicted in FIG. 4. The plant 181 also normally produces a reject
stream 181 R which may be recycled to the evaporator feed tank 210 or other
suitable location for reprocessing or reuse. As shown in the embodiment set
forth in FIG. 5, the distillate treatment plant 181 is optional, especially in
the case
of the use of once through steam generators, and in such instance the
distillate
180 may often be sent directly to once-through steam generators as feedwater
12F (as distinguished from the higher quality from feedwater 12F
discussed
hereinabove with respect to prior art processes) for generation of 80% quality
steam 14. Also, as shown in FIG. 4, a distillate treatment plant 181 may also
be
optional in some cases, depending on feedwater chemistry, and in such cases,
distillate 180 may be fed directly to boiler 80 as indicated by broken line
81.
[0044] In an embodiment where boilers 80 are used rather than once
=
through steam generators 12, however, it may be necessary or desirable to
remove the residual organics and other residual dissolved solids from the
distillate 180 before feed of distillate 180 to the boilers 80. For example,
as
illustrated in FIG. 4, in some cases, it may be necessary to remove residual
ions
from the relatively pure distillate 180 produced by the evaporator 140. In
most
cases the residual dissolved solids in the distillate involve salts other than
hardness. In one embodiment, removal of residual dissolved solids can be
accomplished by passing the evaporator distillate 180, after heat exchanger
200,
through an ion exchange system 202. Such ion-exchange systems may be of
mixed bed type or include an organic trap, and directed to remove the salts
and/or organics of concern in a particular water being treated. In any event,
regenerant chemicals 204 will ultimately be required, which regeneration
results
in a regeneration waste 206 that must be further treated. Fortunately, in the
process scheme described herein, the regeneration waste 206 can be sent back
18
CA 02740060 2011-05-13
to the evaporator feed tank 210 for a further cycle of treatment through the
evaporator 140.
[0045] In another embodiment, removal of residual dissolved solids can be
accomplished by passing the evaporator distillate 180 through a heat exchanger
200 and then through electrodeionization (EDI) system 220. The EDI reject 222
is also capable of being recycled to evaporator feed tank 210 for a further
cycle
of treatment through the evaporator 140.
[0046] The just described novel combination of process treatment steps
produces feedwater of sufficient quality, and in economic quantity, for use in
packaged boilers 80 in heavy oil recovery operations. Advantageously, when
provided as depicted in FIG..4 a single liquid waste stream is generated,
namely
evaporator blowdown 230, which contains the concentrated solutes originally
present in feedwater 46, along with additional contaminants from chemical
additives (such as regeneration chemicals 204). Also, in many cases, even the
evaporator blowdown 230 can be disposed in an environmentally acceptable
manner, which, depending upon locale, might involve injection in deep wells
240.
Alternately, evaporation to complete dryness in a zero discharge system 242,
such as a crystallizer or drum dryer, to produce dry solids 244 for disposal,
may
be advantageous in certain locales.
[0047] Various embodiments for new process method(s), as set forth in
FIGS. 4 and 5 for example, are useful in heavy oil production since they
generally offer one or more of the following advantages: (1) eliminate many
physical-chemical treatment steps commonly utilized previously in handing
produced water (for example, lime softening, filtrating, ion exchange systems,
and certain de-oiling steps are eliminated); (2) result in lower capital
equipment
costs, since the evaporative approach to produced water treatment results in a
zero liquid discharge system footprint size that is about 80% smaller than
that
required if a prior art physical-chemical treatment scheme is utilized, as
well as
eliminating vapor/liquid separators and reducing the size of the boiler feed
19
CA 02740060 2011-05-13
system by roughly 20%; (3) result in lower operating costs for steam
generation;
(4) eliminate the production of softener sludge, thus eliminating the need for
the
disposal of the same; (5) eliminate other waste streams, thus minimizing the
number of waste streams requiring disposal; (6) minimize the materiel and
labor
required for maintenance; (7) reduce the size of water de-oiling equipment in
most operations; and (8) decouple the de-oiling operations from the steam
generation operations.
[0048] One of the significant economic advantages of using a vertical
tube, falling film evaporator such as of the type described herein is that the
on-
line reliability and redundancy available when multiple evaporators are
utilized in
the treatment of produced water. An evaporative based produced water
treatment system can result in an increase of from about 2% to about 3% or
more in overall heavy oil recovery plant availability, as compared to a
produced
water treatment system utilizing .a conventional prior art lime and clarifier
=
treatment process approach. Such an increase in on-line availability relates
directly to increased oil production and thus provides a large economic
advantage over the life of the heavy oil recovery plant.
[0049] In the process disclosed herein, the evaporator 140 is designed to
produce high quality distillate (typically 2-5 ppm non-volatile TDS) which,
after
temperature adjustment to acceptable levels in heat exchangers 200 or 200
(typically by cooling to about 452C., or lower) can be fed directly into
polishing
equipment (EDI system 220, ion exchange system 202, or reverse osmosis
system 224) for final removal of dissolved solids. The reject stream 221 from
the reverse osmosis system can be recycled to the evaporator feed tank 210 for
further treatment. Likewise, the reject from the EDI system may be recycled to
the evaporator feed tank 210 for further treatment. Similarly, the regenerant
from most ion exchange processes 202 may be recycled to the evaporator feed
tank 210 for further treatment. The water product produced by the polish
equipment just mentioned is most advantageously used as feedwater for the
20 20
CA 02740060 2011-05-13
packaged boiler 80. That is because in the typical once-though steam generator
12 used in oil field operations, it is normally unnecessary to incur the
additional
expense of final polishing by removal of residual total dissolved solids from
the
evaporator distillate stream 180. In some applications, final polishing is not
necessary when using conventional boilers 80. This can be further understood
by
reference to FIG. 6, where a typical boiler feed water chemistry specification
is
presented for (a) packaged boilers, and (b) once-through steam generators. It
may be appropriate in some embodiments from a heat balance standpoint that
the de-oiled produced waters 46 fed to the evaporator for treatment be heated
by
heat exchange with the distillate stream 180. However, if the distillate
stream is
sent directly to once-through steam generators 12, then no cooling of the
distillate stream 180 may be appropriate. Also, in the case of once-through
steam
generators 12, it may be necessary or appropriate to utilize a plurality of
flash
tanks F1, etc., in the manner described above with reference to FIG. 2.
[0050] Also, as briefly noted above, but significantly bears repeating, in
those cases where the ED! system 220 is utilized for polishing, the membrane
reject stream includes an EDI reject stream 222 that is recycled to be mixed
with
the de-oiled produced water 46 in the evaporator feed tank 210 system, for
reprocessing through the evaporator 140. Similarly, when reverse osmosis is
utilized the a membrane reject stream includes the RO reject stream which is
= recycled to be mixed with the de-oiled produced water 46 in the
evaporator feed
= tank 210 system, for reprocessing through the evaporator 140. Likewise,
when
ion-exchange system 202 is utilized, the regenerant waste stream 206 is
recycled to be mixed with the de-oiled produced water 46 in the evaporator
feed
tank system, for reprocessing through the evaporator 140.
[0051] Again, it should be emphasized that the blowdown 230 from the
evaporator 140 is often suitable for disposal by deep well 240 injection.
Alternately, the blowdown stream can be further concentrated and/or
crystallized
using a crystallizing evaporator, or a crystallizer, in order to provide a
zero liquid
21
CA 02740060 2011-05-13
discharge 242 type operation. This is an important advantage, since zero
liquid
discharge operations may be required if the geological formation is too tight
to
allow water disposal by deep well injection, or if regulatory requirements do
not
permit deep well injection.
[0052] Many produced waters encountered in heavy oil production are
high in silica, with values that may range up to about 200 mg/I as Si02, or
higher.
Use of a seeded slurry operational configuration in evaporator 140 co-
precipitates silica with precipitating calcium sulfate, to provide a process
design
which prevents the scaling of the inner surfaces 260 of the heat transfer
tubes
156 with the ever-present silica. This is important, since silica solubility
must be
accounted for in the design and operation of the evaporator 140, in order to
prevent silica scaling of the heat transfer surfaces 260.
[0053] Since the calcium hardness and sulfate concentrations of many
produced waters is low (typically 20-50 ppm Ca as CaCO3), it is possible in
many cases to operate the evaporators 140 with economically efficient
concentration factors, while remaining below the solubility limit of calcium
sulfate,
assuming proper attention to feedwater quality and to pre-treatment processes.
[0054] It is to be appreciated that the water treatment process described
herein for preparing boiler feedwater in heavy oil recovery operations is an
appreciable improvement in the state of the art of water treatment for oil
recovery
operations. The process eliminates numerous of the heretofore encountered
waste streams, while processing water in reliable mechanical evaporators, and
in
one embodiment, in mechanical vapor recompression ("MVR") evaporators.
Polishing, if necessary, can be accomplished in ion exchange,
electrodeionization, or reverse osmosis equipment. The process thus improves
on currently used treatment methods by eliminating most treatment or
regeneration chemicals, eliminating many waste streams, eliminating some types
of equipment. Thus, the complexity associated with a high number of treatment
steps involving different unit operations is avoided.
22
CA 02740060 2011-05-13
[0055] In the improved water treatment method, the control over waste
streams is focused on a the evaporator blowdown, which can be conveniently
treated by deep well 240 injection, or in a zero discharge system 242 such as
a
crystallizer and/or spray dryer, to reduce all remaining liquids to dryness
and
producing a dry solid 244. This contrasts sharply with the prior art
processes, in
which sludge from a lime softener is generated, and in which waste solids are
gathered at a filter unit, and in which liquid wastes are generated at an ion
exchange system and in the steam generators. Moreover, this waste water
treatment process also reduces the chemical handling requirements associated
with water treatment operations.
[0056] It should also be noted that the process described herein can be
utilized with once through steam generators, since due to the relatively high
quality feedwater¨treated produced water¨provided to such once through
steam generators, the overall blowdown rate of as low as about 5% or less may
be achievable in the once through steam generator. Alternately, as shown in
FIG. 5, at least a portion of the liquid blowdown 134 from the once through
steam
generator 12 can be recycled to the steam generator 12, such as indicated by
broken line 135 to feed stream 12F'.
[0057] In yet another embodiment, to further save capital and operating =
expense, industrial boilers of conventional design may be utilized since the
distillate¨treated produced water¨may be of sufficiently good quality to be an
acceptable feedwater to the boiler, even if it requires some polishing. It is
important to observe that use of such boilers reduces the boiler feed system
and
evaporative produced water treatment system size by twenty percent (20%),
eliminates vapor/liquid separation equipment as noted above, and reduces the
boiler blowdown flow rate by about ninety percent (90%).
[0058] In short, evaporative treatment of produced waters using a falling
film, vertical tube evaporator is technically and economically superior to
prior art
water treatment processes for heavy oil production. It is possible to recover
23
CA 02740060 2011-05-13
ninety five percent (95%) or more, and even up to ninety eight percent (98%)
or
more, of the produced water as high quality distillate 180 for use as high
quality
boiler feedwater (resulting in only a 2% boiler blowdown stream which can be
recycled to the feed for evaporator 140). Such a high quality distillate
stream
[0059] The overall life cycle costs for the novel treatment process
described herein are significantly less than for a traditional lime softening
and ion
crystallizer size when zero liquid discharge is achieved by treating blowdown
streams to dryness.
[0060] Although only several exemplary embodiments of this invention
have been described in detail, it will be readily apparent to those skilled in
the art
as illustrative and not restrictive. It will thus be seen that the objects set
forth
above, including those made apparent from the preceding description, are
efficiently attained. Many other embodiments are also feasible to attain
advantageous results utilizing the principles disclosed herein. Therefore, it
will
24
CA 02740060 2013-08-07
REPLACEMENT PAGE
be understood that the foregoing description of representative embodiments of
the invention have been presented only for purposes of illustration and for
providing an understanding of the invention, and it is not intended to be
exhaustive or restrictive, or to limit the invention only to the precise forms
disclosed.
[0061] All of the features disclosed in this specification (including any
accompanying claims, and the drawing) may be combined in any combination,
except combinations where at least some of the features are mutually
exclusive.
Alternative features serving the same or similar purpose may replace each
feature disclosed in this specification (including any accompanying claims,
and
the drawing), unless expressly stated otherwise. Thus, each feature disclosed
is
only one example of a generic series of equivalent or similar features.
Further,
while certain process steps are described for the purpose of enabling the
reader
to make and use certain water treatment processes shown, such suggestions
shall not serve in any way to limit the claims to the exact variation
disclosed, and
it is to be understood that other variations, including various treatment
additives
or alkalinity removal techniques, may be utilized in the practice of my
method.
[0062] The intention is to cover all modifications, equivalents, and
alternatives falling within the scope of the invention, as expressed in any
appended
claims. The scope of the invention, as descried herein and as indicated by any
appended claims, is thus intended to include variations from the embodiments
provided which are nevertheless described by the broad meaning and range
properly afforded to the language of the claims, as explained by and in light
of the
terms included herein, or the legal equivalents thereof.
2-5¨ 25
