WO2013158315A1

WO2013158315A1 - Method for producing water for enhanced oil recovery

Info

Publication number: WO2013158315A1
Application number: PCT/US2013/032626
Authority: WO
Inventors: Edward Beaudry; John R. Herron
Original assignee: Hydration Systems, Llc
Priority date: 2012-04-18
Filing date: 2013-03-15
Publication date: 2013-10-24

Abstract

A combination of membrane processes is disclosed which can produce designer salt brine for enhanced oil recovery using seawater as the only feed source. The membrane processes used are reverse osmosis, nanofiltration and electrodialysis. The chemistry of the brine can be tightly controlled in terms of TDS, low sulfate levels and ratio of monovalent cations to divalent cations.

Description

METHOD FOR PRODUCING WATER FOR ENHANCED OIL RECOVERY

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. provisional application serial no.

61/635,244 filed April 18, 2012, the entire disclosure of which is hereby incorporated by reference.

FIELD OF THE INVENTION

[0002] The invention relates to water used in the extraction of crude oil from oil fields.

SUMMARY OF THE INVENTION

[0003] The present invention provides a method for producing stimulation water from seawater. The method of the invention adjusts the water chemistry of the stimulation water, using a low energy membrane process. The method of the invention is particularly advantageous for use in off-shore oil production facilities, due to the abundance of seawater available and because it eliminates the need to transport chemicals to the drilling platform.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] FIGURE 1 is a process flow diagram illustrating one of the process steps, process number 3, used in the method of the invention.

[0005] FIGURE 2 is a process flow diagram illustrating an embodiment of the electrodialysis process for enhanced oil recovery that is used in the method of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0006] A method of increasing the amount of crude oil that can be extracted from oil fields involves the injection of water having specific controllable chemistry into the formation. This water is referred to as "stimulation water". The stimulation water's chemistry is tailored for each site; however, generally speaking, it is critical that the sulfate ion concentration is controlled to be very low (less than about 40 ppm), the total dissolved ionic species (TDS) concentration is controlled, and the ratio of divalent to monovalent cations is controlled. The range of TDS commonly used for enhanced oil recovery is from about 1000 to about 5000 ppm, and the ratio of divalent to monovalent cations on an equivalence basis is about 10% to about 20%. Very large amounts of this water are required to stimulate a depleted field. On land it is possible to produce water with the desired chemistry by adding trucked-in salts to fresh water.

[0007] The instant invention comprises at least three membrane processes to produce tailored stimulation water from seawater. The method of the invention may be used in a system on site at oil fields or offshore drilling platforms, and does not require the use of adding salts to fresh water. The method produces low sulfate, high calcium and magnesium containing brine, which may be further treated as described herein.

[0008] In a preferred embodiment, the method comprises at least four membrane processes. The method for producing water for use in enhanced oil recovery, comprises the following four steps:

(a) desalinating a first quantity of seawater to produce desalinated seawater;

(b) filtering a second quantity of seawater via sulfate rejecting nano filtration to produce a first retentate and a first permeate;

(c) adding water to the first retentate and filtering via divalent cation rejecting sulfate rejecting nano filtration to produce a second retentate; and

(d) subjecting four streams to electrodialysis, wherein the four streams are seawater, the desalinated seawater, the first permeate, and the second retentate, by feeding each stream to a separate channel of an electrodialysis device having at least four channels, to produce brine having very low sulfate ion content and a high content of calcium and magnesium.

[0009] In an alternative embodiment, step (c) may be modified to delete the step of adding water to the first retentate prior to filtering. Such an alternative method would comprise the following steps:

(a) desalinating a first amount of seawater to produce desalinated seawater;

(b) filtering a second amount of seawater via sulfate rejecting nano filtration to produce a first retentate and first permeate; and (c) subjecting four streams to electrodialysis, wherein the four streams are seawater, the desalinated seawater, the first retentate, and the first permeate, and wherein each stream is fed to a separate channel of an electrodialysis device having at least four channels, to produce brine having very low sulfate ion content and a high content of calcium and magnesium.

[0010] Step (a) is preferably performed using reverse osmosis (RO).

[0011] In a further embodiment of the invention, the water produced for use as stimulation water may be adjusted, by combining the brine having a very low sulfate ion content and a high content of calcium and magnesium that is produced in the methods described herein with a stream of the desalinated seawater and the second retentate. The ratio of the three components may be varied depending upon the geology of the formation from which the oil is being extracted. By varying the ratio to adjust the chemistry of the water produced, stimulation water may be tailored to the specific chemistry desired for the site it is used.

[0012] The following is a more detailed description of a preferred embodiment of the invention wherein four membrane processes are used. Each "process" corresponds to the "steps" described above.

[0013] Process 1 : RO of seawater. The bulk of the water needed to produce stimulation water is fresh water produced by standard reverse osmosis (RO) seawater desalination. The fresh water that is produced by RO has a total dissolved solids content (TDS) of less than about 1000 ppm, and is also referred to herein as "RO permeate".

[0014] Process 2: Sulfate rejecting nanofiltration (SRNF). A much smaller amount of seawater (than used in Process 1 above) will be filtered using a sulfate rejecting nanofiltration (SRNF) element, to produce the first retentate and a first permeate. The SRNF will operate with a recovery such that the retentate will avoid calcium scaling. The first retentate from the SRNF will be used as the feed to Process 3, and the first permeate (referred to in FIGURE 1 as "SRNF Permeate" and in FIGURE 2 as "SRNF Filtrate"), will be one of the feeds in Process 4.

[0015] Process 3: Diafiltration via divalent cation rejecting sulfate rejecting

nanofiltration. The first retentate from Process 2 will have RO permeate water from Process 1 added to it, and then will be filtered again (diafiltration) with divalent cation rejecting SRNF membranes, to produce a second retentate. This will have the effect of greatly increasing the ratio of divalent to monovalent cations in the diafiltered retentate (the second retentate). The diafiltered retentate will then be used as a feed to Process 4.

[0016] A diagram of Process 2 and Process 3 is shown in FIGURE 1. In FIGURE 1,

"ED Stack" refers to the electrodialysis stack.

[0017] Process 4: Electrodialysis. The desired end product, which is a stream having a very low sulfate level and a high ratio of divalent to monovalent cations, is then produced by feeding four (4) different streams to an electrodialysis stack. A schematic of this process is shown in FIGURE 2. In FIGURE 2, the four large, downward-pointing arrows towards the top of the figure represent the directional flow of the four different streams in the electrodialysis stack. The large, downward-pointing arrow at the bottom of the figure represents the flow of the output from the stack, which is a low sulfate, high calcium and magnesium containing brine. The smaller, horizontal-pointing arrows represent the flow of ions (e.g., chloride, sulfate, sodium, calcium, magnesium) through the membranes.

[0018] The desired end product of Process 4 (and of the method of the invention) is a brine containing high levels of calcium and magnesium, and low levels of sulfate. The separation is effected by passing a current through a stack of alternating anionic and cationic membranes. The fluids fed to the chambers between the membranes are as follows:

1. Seawater

2. SRNF filtrate/permeate from Process 2

3. RO permeate from Process 1

4. SRNF diafiltered retentate from Process 3

[0019] In FIGURE 2, the electrodialysis stack comprises five (5) membranes, and is structured to receive at least four different streams. In this illustration, the membranes from left to right are: a first anionic membrane, a first cationic membrane, a second anionic membrane, a second cationic membrane, and a third anionic membrane. Between the first anionic and first cationic membranes is a channel or chamber for receiving SRNF diafiltered retentate. Between the first cationic and the second anionic membranes is a channel or chamber for receiving RO water. Between the second anionic and second cationic membrane is a channel or chamber for receiving SR F filtrate. Between the second cationic and third anionic membrane is a channel or chamber for receiving seawater. The stream exiting the electrodialysis stack will be a brine that is very low in sulfates and high in calcium and magnesium.

[0020] In this process the RO permeate is loaded with cations from the SRNF retentate and chlorides from the SRNF permeate. Sulfates are not found in the SRNF filtrate/permeate, so none enter the RO permeate.

[0021] It is possible to achieve the desired water chemistries (low sulfate, about 1000-

5000 ppm total dissolved ionic species, about 10-20% divalent/monovalent cations) by blending the three below-listed component streams. The ratio of each of these components will be determined by the geology of the formation from which the oil is being extracted, and the specific chemistry desired for each site.

1. RO permeate

2. SRNF permeate

3. Product of Process 4, which is a low-sulfate brine containing high levels of calcium and magnesium.

[0022] The following is a description of an embodiment of the invention wherein three membrane processes are used instead of the four membrane process described above:

[0023] Processes 1, 2 and 4 described above are used in this embodiment of the invention. The diafiltration of the SRNF permeate is omitted. This is a less preferred embodiment than the four membrane process, because it requires a much larger volume of water from the ED system in order to produce the desired water chemistry for oil well stimulation.

[0024] Examples of water produced by each process are illustrated in Table 1. The figures shown may vary depending upon a number of factors, such as the type of filters used, the amount of recovery that a particular filter gives (i.e., the percentage of water one recovers of the amount fed into the system), etc. Table 1 shows the approximate chemistry of the water from each of the processes (ppm) in a one working example of an embodiment of the invention. [0025] Table 1. Approximate chemistry of the water from each of the processes (ppm) in an exemplary embodiment of the invention.

[0026] Example of blending to produce stimulation water:

[0027] Assume stimulation water is desired with the following chemistry:

5000 ppm TDS

• 20% divalent to monovalent equivalence ratio

• Less than 40 ppm sulfate.

[0028] The blend ratios are:

6.7% ED process water (produced after the 4 step process)

12% SRNF permeate

81.3% RO permeate

[0029] The amount of stimulation water produced by the method of the invention may be increased by increasing the amperage (the electrical current) applied to the ED stack and/or by increasing the flow rate to one or more channels in the ED stack. For example, referring to FIGURE 2, the flow rate of SRNF Filtrate through the channels may be increased, and/or the flow rate of one or more of the other streams shown in FIGURE 2 may be increased.

[0030] The invention further comprises a system for converting seawater to brine having a low sulfate content and a high content of calcium and magnesium, comprising the following: (a) apparatus for receiving a first amount of seawater and subjecting the seawater to reverse osmosis to produce fresh water;

(b) apparatus for sulfate rejecting filtering a second amount of seawater to produce a retentate and a permeate; and

(c) an electrodialysis stack comprising:

a first channel, defined by a first anionic membrane on one side, and a first cationic membrane opposite and parallel to the anionic membrane, for receiving a stream of untreated seawater,

a second channel, adjacent to the first channel, said second channel defined by the first cationic membrane on one side and a second anionic membrane opposite and parallel to the first cationic membrane, for receiving a stream of the permeate, a third channel, adjacent to the second channel, said third channel defined by the second anionic membrane on one side, and a second cationic membrane opposite and parallel to the second anionic membrane, for receiving a stream of the fresh water, and a fourth channel, adjacent to the third channel, said fourth channel defined by the second cationic membrane on one side and a third anionic membrane on the other side, for receiving the stream of the retentate.

Claims

CLAIMS:

1. A method for producing water for use in enhanced oil recovery, comprising the following steps:

(a) desalinating a first quantity of seawater to produce desalinated seawater;

2. The method of Claim 1, wherein step (a) is performed via reverse osmosis desalination.

3. The method of Claim 1, further comprising a step of blending portions of the first permeate, the second retentate and the brine produced in step (d).

4. The method of Claim 2, further comprising a step of blending portions of the first permeate, the second retentate and the brine produced in step (d).

5. A method for producing water for use in enhanced oil recovery, comprising the following steps:

(a) desalinating a first amount of seawater to produce desalinated seawater;

(b) filtering a second amount of seawater via sulfate rejecting nano filtration to produce a first retentate and first permeate; and

(c) subjecting four streams to electrodialysis, wherein the four streams are seawater, the desalinated seawater, the first retentate, and the first permeate, and wherein each stream is fed to a separate channel of an electrodialysis device having at least four channels, to produce brine having very low sulfate ion content and a high content of calcium and magnesium.

6. The method of Claim 5, wherein step (a) is performed via reverse osmosis desalination.

7. A system for converting seawater to brine having a low sulfate content and a high content of calcium and magnesium, comprising the following:

(a) apparatus for receiving a first amount of seawater and subjecting the seawater to reverse osmosis to produce fresh water;

(c) an electrodialysis stack comprising:

a second channel, adjacent to the first channel, said second channel defined by the first cationic membrane on one side and a second anionic membrane opposite and parallel to the first cationic membrane, for receiving a stream of the permeate,

a third channel, adjacent to the second channel, said third channel defined by the second anionic membrane on one side, and a second cationic membrane opposite and parallel to the second anionic membrane, for receiving a stream of the fresh water, and

a fourth channel, adjacent to the third channel, said fourth channel defined by the second cationic membrane on one side and a third anionic membrane on the other side, for receiving the stream of the retentate.