US20140144626A1

US20140144626A1 - Superheated steam water treatment process

Info

Publication number: US20140144626A1
Application number: US14/078,634
Authority: US
Inventors: Scott Macadam
Original assignee: ConocoPhillips Co
Current assignee: ConocoPhillips Co
Priority date: 2012-11-29
Filing date: 2013-11-13
Publication date: 2014-05-29
Also published as: CA2892960A1; WO2014085096A1

Abstract

Methods and apparatus produce steam and, more particularly, utilize untreated feedwater as a source for steam used in steam assisted gravity drainage. Superheated steam, produced from treated feedwater in a boiler, is used to vaporize untreated feedwater that would otherwise foul a boiler. Contaminants in the untreated water can them be removed as solids or concentrated brine. The vaporization process occurs in stages to allow for the use of a higher fraction of untreated water.

Description

PRIORITY CLAIM

This application is a non-provisional application which claims benefit under 35 USC §119(e) to U.S. Provisional Application Ser. No. 61/731,242 filed Nov. 29, 2012, entitled “Superheated Steam Water Treatment Process,” which is incorporated herein in its entirety.

FEDERALLY SPONSORED RESEARCH STATEMENT

Not Applicable

FIELD OF THE INVENTION

The invention relates generally to a method and apparatus of producing steam and, more particularly, to a method utilizing untreated feedwater as a source for steam used in enhanced oil recovery. Superheated steam from treated water is contacted with untreated feedwater in multiple sequential stages to allow for a higher fraction of untreated water to be vaporized.

BACKGROUND OF THE INVENTION

Conventional oil reserves are preferred sources of oil because they provide a high ratio of extracted energy over energy used for the extraction and refining processes it undergoes. Unfortunately, due to the physics of fluid flow, not all conventional oil can be produced. Additionally, as conventional oil sources become scarce or economically non-viable due to depletion, unconventional oil sources are being explored as a potential supply of oil. However, unconventional oil production is also problematic because it consists of extra heavy oils having a consistency ranging from that of heavy molasses to a solid at room temperature and heavy oils may also be located in reservoir rocks. These properties make it difficult to simply pump the unconventional oil out of the ground. Thus, its production is a less efficient process than convention oil.
As a result, enhanced oil recovery (EOR) techniques are often employed to increase the amount of heavy crude oil extracted. Using EOR, 30-60% or more of the original oil in place can be extracted. Additionally, EOR techniques can be applied in both conventional and unconventional oil reserves.
During EOR, compounds not naturally found in the reservoir are injected into the reservoir to assist in oil recovery. Simply stated, EOR techniques overcome the physical forces holding the oil hydrocarbons underground. There are many types of EOR techniques that are categorized by the injection: gas injection, chemical injection, microbial injection or thermal recovery. While there are many types of EOR techniques, reservoirs containing heavier crude oils tend to be more amenable to thermal EOR methods, which heat the crude oil to reduce its viscosity and thus decrease the mobility ratio. The increased heat reduces the surface tension of the oil and increases the mobility of the oil.
A summary of various EOR techniques is presented in Table 1.

TABLE 1

Enhanced Oil Recovery (EOR) Techniques

CSS	Cyclic Steam Stimulation or “huff and puff.” Steam is injected into a well at a
	temperature of 300-340° C. for a period of weeks to months. The well is allowed
	to sit for days to weeks to allow heat to soak into the formation, and, later, the
	hot oil is pumped out of the well for weeks or months. Once the production rate
	falls off, the well is put through another cycle of steam injection, soak and
	production. This process is repeated until the cost of injecting steam becomes
	higher than the money made from producing oil. Recovery factors are around
	20 to 25%, but the cost to inject steam is high.
SAGD	Steam Assisted Gravity Drainage uses at least two horizontal wells--one at the
	bottom of the formation and another about 5 meters above it. Steam is injected
	into the upper well, the heat melts the heavy oil, which allows it to drain by
	gravity into the lower well, where it is pumped to the surface. SAGD is cheaper
	than CSS, allows very high oil production rates, and recovers up to 60% of the
	oil in place.
VAPEX	Vapor Extraction Process is similar to SAGD, but instead of steam, hydrocarbon
	solvents are injected into an upper well to dilute heavy oil and enables the
	diluted heavy oil to flow into a lower well.
ISC	In situ combustion involves a burning of a small amount of the oil in situ, the
	heat thereby mobilizing the heavy oil.
THAI	Toe to Heel Air Injection is an ISC method that combines a vertical air injection
	well with a horizontal production well. The process ignites oil in the reservoir
	and creates a vertical wall of fire moving from the “toe” of the horizontal well
	toward the “heel”, which burns the heavier oil components and upgrades some
	of the heavy bitumen into lighter oil right in the formation.
COGD	Combustion Overhead Gravity Drainage is another ISC method that employs a
	number of vertical air injection wells above a horizontal production well located
	at the base of the bitumen pay zone. An initial Steam Cycle similar to CSS is
	used to prepare the bitumen for ignition and mobility. Following that cycle, air is
	injected into the vertical wells, igniting the upper bitumen and mobilizing
	(through heating) the lower bitumen to flow into the production well. It is
	expected that COGD will result in water savings of 80% compared to SAGD.
EM	A variety of electromagnetic methods of heating oil in situ are also being
	developed.
GAS	A variety of gas injection methods are also used or being developed, including
INJECTION	the use of cryogenic gases.
COMBO	Any of the above methods can be used in combination.

While many EOR techniques involve injecting steam into underground formations, SAGD is the most favored form of EOR involving steam. It is especially useful for the recovery of semi-solid crude oil known as bitumen. In SAGD, steam is injected into an upper horizontal injection well, which creates a steam chamber, and mobilizes the oil at the edges of the chamber. The live oil then gravity drains to a lower horizontal production well, where the oil and water mixture is then collected. Large amounts of steam are needed for this operation, and in SAGD the steam to oil ratio (SOR) is typically about 3, and can easily go higher.
Currently, most steam generators used for EOR are small, portable, once-through type units fired with oil or gas. The most common type of SAGD boiler is the Once Through Steam Generator (OTSG), which generates steam through indirect heat transfer. As evidenced by the name, water/liquid enters the system and makes a single-pass by the heat exchanger, vaporizes as it travels and exits as a steam/vapor mix. The main advantage of OTSGs is its lower capital cost and ability to handle water with relatively high percentage of dissolved and suspended solids, and organic contaminants.
In SAGD, high-pressure saturated steam is produced in boilers and delivered to the wellpad, where it is injected into the SAGD reservoirs. However, the necessary water to oil ratio is very high. For every barrel of bitumen recovered, 2 to 4 barrels of water are needed.
Moreover, the steam condenses during contact and is coproduced with oil. Thus, both water separation and subsequent water treatment are necessary operations in heavy oil recovery. Because vast amounts of water are needed to generate the required steam, a method of recycling the produced water is essential for a cost effective, sustainable SAGD system. Furthermore, concerns about climate change have encouraged the development of ‘zero-emissions power generation.’
Produced water and brackish well water are the main boiler feedwater sources used for SAGD. But, both sources of water contain contaminants, particularly dissolved solids, which cause scaling or fouling of boiler systems. Fouling or scale from the contaminants can result in failure of boiler tubes, down time to blow-down of the boiler and/or loss of boiler efficiency.
Normally, an OTSG can produce about 75-80% quality steam from feedwater with total dissolved solid (TDS) levels of 3,000 to 8,000 ppm. This relatively low steam quality is necessary to maintain wet conditions in the OTSG tubes in order to reduce fouling and scaling, but results in high blow-down levels of 20-25%. Although OTSG feedwater has relatively high TDS levels, it still requires some treatment to reduce silica and hardness levels. This is typically accomplished by warm lime softening followed by ion exchange. This water treatment process represents a significant portion of surface facility capital costs, and has a significant economic impact on a SAGD operation. Thus, what is needed in the art is a method of recycling untreated water for steam generation without pretreatment, yet without fouling the boiler systems.
U.S. Pat. No. 4,398,603 describes a method of using low quality feedwater to produce steam. Here, feedwater is recycled and contacted with superheated steam to produce saturated steam and precipitated minerals. The precipitated minerals are removed by withdrawing a stream of waste water containing the minerals from the contacting vessel. However, this method requires a steam compressor that is not commercially available.
Other steam generating methods also result in large amounts of CO₂being formed and subsequently co-injected with the steam. US20120160187 discloses the use of an oxygen-fuel combustor as a steam generator, instead of a more traditional boiler system. This new steam generation system is able to use untreated water to produce 100% quality steam for EOR techniques. By using an oxygen-fuel steam generator, no chemicals are needed to treat the water, regardless of total solid content because the heating is direct, rather than indirect heating as in a boiler. The oxygen-fuel generator produces less than 100% quality steam and a brine containing contaminates. The brine is then removed via a steam separator, resulting in 100% quality steam. However, this process also generates CO₂that is used during the injection process.
Betzer-Zilevitch et al. (2010) disclose another “Direct Contact Steam Generation” system in which untreated water is heated by direct contact with combustion gases, as opposed to the non-direct heating seen in OTSGs. However, the resulting steam is again mixed with a high percentage of CO₂, which is then co-injected into the well.
The presence of CO₂in the steam injection can be problematic for particular types of underground formations, and the combination of CO₂and water can produce a corrosive mixture of carbonic acids that attack the carbon steel typically used in injection pipes.
US20110061610 discloses a method of using water from waste streams. Here, the untreated water is preheated in a heat exchanger before entering a dryer, wherein input steam is used to indirectly dry (evaporate) the heated untreated water. This method reduces the amount of energy need to dry the untreated water while still producing high-quality water. The resulting steam is recycled in the dryer. However, during the drying process, the contaminants form a solid cake that, upon further processing, can be used to backfill the reservoir.
Thus, what is needed in the art is a method for generating steam that lowers water treatment costs and still avoids boiler fouling and the resultant costs, preferably a method that requires no pretreatment of untreated water is needed. Preferably, this method will also utilize current steam generator and steam/water separation methods without expensive modifications.

SUMMARY OF THE INVENTION

Embodiments of the invention describe a method of utilizing superheated steam to vaporize untreated water for use in enhanced oil recovery techniques, preferably SAGD. The vaporization occurs in stages, thus allowing for a greater fraction of untreated water to be utilized. In doing so, the water treatment cost of SAGD surface facilities are decreased.
Some embodiments meet one or more of the following objectives.
A general objective is the design of an apparatus and method for generating steam that is simple in design, economic to build, maintain and operate, and is sufficiently rugged for wellpad use.
Another objective is the design of an apparatus and method for generating steam from untreated water to reduce water treatment cost.
Another objective is the ability to reduce boiler fouling and any resulting boiler blow-down time.
Another objective is the adaptability of the present invention to steam generating systems currently in use with little modification.
In one embodiment, superheated steam, generated by a boiler or a furnace, is directly contacted with untreated water to vaporize some or all of the untreated water. The contaminants in the untreated water are removed as solids if all of the water is vaporized. Otherwise, the contaminants can be removed as a concentrated brine if only partial vaporization occurs. Both can be removed simultaneously in a suitable steam/water separator (such as a cyclonic separator) or solid and liquid separators can be used sequentially.
This results in a larger amount of steam that is significantly cooled with respect to the original superheated steam. The steam is re-superheated in an indirect heat furnace, and then directly contacted with more untreated water in a second stage. Again, the contaminants are removed. The process is repeated for multiple stages. At each stage, successively larger amounts of untreated water are contacted with superheated steam.
The initial superheated steam is heated to about 900-1000° F. before mixing with the initial untreated feedwater. The boiler or furnace used to generate superheated steam can be any commercial available unit capable of superheating steam.
Later stages of superheated steam (initial steam+steam from untreated water) are reheated to 900-1000° F. via a furnace. The superheated steam can either by produced in superheater coils placed in the radiant section of a boiler (common practice in power generation boilers), or in a stand-alone fired steam superheater.
In another embodiment, the mixing of steam and untreated water results in a wet steam plus liquid. Contaminants are then removed as a concentrated brine. This concentrated brine, removed at each step, is vaporized in a single mixer and solids are removed in a single filter. The use of a single mixer and solid filtration device can lower overall costs.
The contaminants are removed using well-known methods. In particular, for solids removal devices, cyclones and/or filters can be used. For a concentrated brine, liquid/gas separation devices such as gravity separators, centrifugal separators, and filter vane separators can be used.
In one aspect of the invention, untreated water with high levels of total dissolved solids can be used without any pretreatment step.
The term “boiler,” as used herein, denotes any means of indirectly producing superheated steam from feedwater before the initial contact of superheated steam and untreated water, wherein the heat source is water.
The term “furnace” as used herein implies indirect heating of steam to increase its level of superheat; wherein the heat source is a hydrocarbon such as gas or oil.
The term “untreated water” encompasses all water used for SAGD that has not undergone significant pretreatment to e.g., remove dissolved solids before being heated and includes sources such as feedwater, brackish water and water recovered from a production fluid.
The term “separators,” as used herein, mean any type of separation device used to separate components in different phases, i.e. solids/liquids, or liquids/gases.
The term “filter” refers to a device that separates solids from liquids (or solids) on the basis of particle retention and thus is size based.
The terms “mixer” and “contacting vessel” are used interchangeable and refer to the vessel wherein the untreated water and superheated steam are contacted.
As used herein, the term “superheated steam” means a water vapor that is 100% vaporized and at a temperature higher than its boiling point or at least 482° C.
As used herein, “steam” refers generally to water vapor although there may be some amounts of liquid water, water mist and solids therein.
“Saturated steam” is steam at the temperature of the boiling point which corresponds to its pressure; the term is sometimes also applied to wet steam, and the terms are used interchangeably herein. “Slightly saturated steam” is steam at a temperature 2.5-16° C. higher than its boiling point.
The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims or the specification means one or more than one, unless the context dictates otherwise.
The term “about” means the stated value plus or minus the margin of error of measurement or plus or minus 10% if no method of measurement is indicated.
The use of the term “or” in the claims is used to mean “and/or” unless explicitly indicated to refer to alternatives only or if the alternatives are mutually exclusive.
The terms “comprise”, “have”, “include” and “contain” (and their variants) are open-ended linking verbs and allow the addition of other elements when used in a claim.
The phrase “consisting of” is closed, and excludes all additional elements.
The phrase “consisting essentially of” excludes additional material elements, but allows the inclusions of non-material elements that do not substantially change the nature of the invention.
The following abbreviations are used herein:


	BPD	Barrels per day
	OTSG	Once Through Steam Generator
	SAGD	Steam Assisted Gravity Drainage
	SEP	Separation device
	TDS	Total dissolved solids

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Block flow diagram of process that uses superheated steam for the staged vaporization of untreated water wherein solids are removed after each vaporization step.

FIG. 2. Block flow diagram of process that uses superheated steam for the staged vaporization of untreated water wherein concentrated brine is removed after each vaporization step.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Embodiments of the invention provide a novel method of producing steam to be used in enhanced oil recovery techniques. In general, steam produced from a treated water source is superheated, and the superheated steam then used in one or more stages to directly vaporize untreated water. The resulting steam is easily separated from any solid contaminants using well-known solid filtration devices.
The method thus uses multiple stages for superheated steam/untreated water contact. Essentially, the initial vaporized untreated water and steam are superheated after the solids are removed and then directed to a second stage to mix with more untreated water. Again, the resulting vaporized untreated water is superheated and contacted with more untreated water in a third stage. In some embodiments, this process repeats multiple times, for a minimum of 3 stages, preferably a minimum of 5 stages. By using a staged vaporization, a higher fraction of untreated water can be converted to steam, thereby reducing water treatment cost associated with SAGD surface facilities.
In more detail, a treated water source is superheated to about 482-538° C. using a boiler or fired steam superheater. This initial superheated steam is then mixed with an untreated feedwater stream in a 2.5 to 4.5 ratio in a contactor vessel. This mixing results in a less heated steam and solid minerals or concentrated brine. The brine and solid minerals are removed from the less heated steam using a solid/liquid separating device or a liquid/gas separating device. The less heated steam is then re-superheated to about 482-538° C. using a furnace. This larger volume of steam is then mixed with a new amount of untreated feedwater in another contacting vessel. The process repeats at least two times, resulting in larger quantities of untreated feedwater being converted into less heated steam. After the final mixing, the less heated steam is injected in a well for mobilizing heavy oil.
The present invention is exemplified with respect to FIGS. 1 and 2. However, these figures are exemplary only, and the invention can be broadly applied to any steam generating system and any source of untreated water. The following examples are intended to be illustrative only, and not unduly limit the scope of the appended claims.

Solid Precipitation

Exemplary results, generated by process modeling, of the basic steam generation system depicted in FIG. 1 for reducing the amount of treated feedwater is given in Table 2. Referring to FIG. 1, superheated steam is mixed with untreated water in five separate contacting vessels. Different contacting vessels have to be used at each stage because progressively lower operating pressures are necessary. In the initial mixing, superheated steam is mixed with untreated water in a 3.3 mass ratio. During mixing, the water is converted into a less heated steam, resulting in a final composition of steam and solid contaminants. The solids are filtered out using a solids separation device such as a cyclone separator and/or filter, and the steam flows into a furnace to reheat. The re-superheated steam is directed into a second contacting vessel with a new batch of untreated water and the mixing/separation process is repeated.
In this particular example, 20,000 barrel per day (bpd) of treated feedwater was converted into 538° C. superheated steam in a conventional boiler. That superheated steam is mixed with 6,000 bpd of untreated water in the first contacting vessel (‘mixer’). The resulting mixture is 26,000 bpd of slightly saturated steam that is about 316° C. and solid contaminants. As the slightly saturated steam is directed to the furnace, it passes a solids separation device (‘filter’). Once the solids are removed, the slightly saturated steam is re-superheated in the furnace to about 538° C. This superheated steam is directed into a second mixer with 7,900 bpd of fresh untreated water. The process repeats, with increasing amounts of untreated water being utilized at each stage.
Table 2 displays the fraction of treated and untreated water as a function of mixing stages. As shown, increasing the number of stages decreases the amount of treated feedwater needed. As such, more untreated water is utilized, thus reducing traditional water treatment cost of the facility.

TABLE 2

Relative quantities of treated and untreated feedwater
as a function of number of vaporization stages.

Number of Vaporization	Treated Water (% of	Untreated Water (% of
Stages	total feedwater)	total feedwater)

1	77%	23%
2	59%	41%
3	45%	55%
4	35%	65%
5	27%	73%

Concentrated Brine Removal

FIG. 2 depicts a steam generating system wherein a concentrated brine is filtered out, as opposed to actual solids. As in FIG. 1, the superheated steam is mixed with untreated water in a contacting vessel in five separate stages. During mixing, the untreated water is transformed into a less heated steam, resulting in a final composition of steam and concentrated brine contaminants.
The concentrated brine is separated out using a gas/liquid separator (‘Sep’). The brine can then be vaporized in a single mixer with the solids being removed via a single filter afterwards. Note, this differs from FIG. 1, in that only one solid removal device is needed for all five stages. A single filter reduces cost and system complexity.
After the brine is separated out, the remaining steam is directed into a furnace to be reheated. A second stream of superheated steam is added to the wet steam before it enters the furnace. This second stream is added to vaporize any droplets carried over from the mixers, which prevents the droplets from drying and fouling the furnace tubes. After being reheated, the superheated steam is streamed into a second contacting vessel with a new batch of untreated water and the mixing/separation process is repeated.

Concentrated Brine and Solids Removal

Some embodiments allow for the removal of both solids and concentrated brine. This design is similar to FIG. 2 except a solid/gas filter is located in-line after the gas-liquid separator in the ‘Sep’. Alternatively, the solid/gas filter could also be located in-line with the gas-liquid separator, but after the makeup steam line. This configuration would allow one system to separate out either solids or concentrated brine, depending on the needs of the technique.
The following references are incorporated by reference in their entirety.
Betzer-Zilvitch, M. “Integrated Steam Generation Process and System for Enhanced Oil Recovery,” Conference Paper, Society of Petroleum Engineers, GSUG/SPE 137633, 2010.

U.S. Pat. No. 4,398,603
US20120160187
US20110061610

Claims

What is claimed is:

1. A method of producing steam for heavy oil recovery, comprising:

a) introducing an initial superheated steam into a contactor vessel;

b) introducing a feedwater stream into said contactor vessel;

c) mixing said initial superheated steam and said feedwater to produce a less heated steam and contaminants in said contactor vessel;

d) separating said less heated steam from said contaminants;

e) again superheating said less heated steam in a furnace to create a superheated steam and repeating steps a-e in sequential contactor vessels of decreasing pressure;

f) flowing a final less heated steam from a final contactor vessel; and

g) injecting said final less heated steam into an injection well for the mobilization of heavy oil.

2. The method of claim 1, wherein said contaminants are solid minerals.

3. The method of claim 1, wherein separation of the less heated steam from said contaminants is preformed using a solids separation device.

4. The method of claim 1, wherein separation of the less heated steam from said contaminants is preformed using a cyclone or filter.

5. The method of claim 1, wherein said contaminants are in a liquid phase and separated by a gas-liquid separator.

6. The method of claim 1, where said contaminants are separated as concentrated brine that undergoes further vaporization in a single mixer and solids are thereafter removed via a separator.

7. The method of claim 1, where said contaminants are separated as concentrated brine that undergoes further vaporization in a single mixer and solids are thereafter removed via a cyclone or filter.

8. The method of claim 1, further comprising adding additional superheated steam to the less heated steam, between steps d and e, after being separated from the contaminants and before superheating again in the furnace.

9. The method of claim 1, wherein said initial superheated steam is heated to 482-538° C. using a power plant boiler or a fired steam superheater.

10. The method of claim 1, wherein said initial superheated steam is heated to 482-538° C. using a power plant boiler.

11. The method of claim 1, wherein the initial ratio of said superheated steam to said feedwater is 2.5-4.5.

12. The method of claim 1, wherein the initial ratio of said superheated steam to said feedwater is 3.3.

13. The method of claim 1, wherein said superheated steam is 482-538° C.

14. A steam production system for heavy oil recovery, comprising:

a) a boiler;

b) a furnace;

c) n mixers and n separators for separating steam from solid and/or liquids, wherein each of said n mixer is fluidly connected to an n separator which is fluidly connected to said furnace, and wherein the furnace is fluidly connected to each of said n mixer, and wherein n is at least 3;

d) n inlet lines connected to each of said n mixers for feeding untreated water to each mixer;

e) said boiler fluidly connected to a first one of the mixers; and

f) a last one of the mixers fluidly connected to a heavy oil injection well.

15. The system of claim 14, wherein the mixers contact the untreated water and superheated steam to produce a less heated steam and contaminants removed by the separators in a plurality of stages and the furnace superheats said less heated steam received from said mixers and separators and thereby generates additional superheated steam directed to a next stage of the mixers and separators.

16. The system of claim 14, further comprising a vessel for vaporizing said liquids removed from the steam by the separators and a solids removal device for separating solid-waste from resulting additional steam generated in the vessel.

17. The system of claim 14, wherein the separators are gas-liquid separators for removing brine from the steam generated in the mixers.

18. The system of claim 14, wherein the separators are solids separation devices for removing solid minerals from the steam generated in the mixers.

19. The system of claim 14, further comprising a pipe to combine an additional amount of superheated steam with the steam at an outlet from said separators but before said furnace.

20. A method of steam assisted gravity drainage (SAGD), comprising:

injecting steam into a horizontal injection well and recovering produced hydrocarbons from a lower horizontal production well; and

preparing the steam for said injection wells by i) superheating steam, ii) mixing said superheated steam with untreated water to produce steam and solids or concentrated brine or both, iii) separating said solids or concentrated brine from said steam in step ii), iv) re-superheating said steam in a furnace, and v) repeating steps ii-iv) at least two more times.