CA2225297C

CA2225297C - Purification of broken frac fluid

Info

Publication number: CA2225297C
Application number: CA 2225297
Authority: CA
Inventors: Dwight N. Loree; Shaun Terrance Einar Mesher; Glenna L. Strickland
Original assignee: ENERCHEM INTERNATIONAL Inc
Current assignee: ENERCHEM INTERNATIONAL Inc
Priority date: 1997-12-19
Filing date: 1997-12-19
Publication date: 2009-02-10
Anticipated expiration: 2017-12-19
Also published as: CA2225297A1

Abstract

Phosphates are removed from a hydrocarbon stream by first contacting the hydrocarbon stream with a polar material, wherein the polar material chemically reacts with phosphates in the hydrocarbon stream and binds to the phosphates and then separating the hydrocarbon stream from the polar material. Contacting the hydrocarbon stream with the polar material preferably, particularly for large volume applications at a refinery, may comprise passing the hydrocarbon stream through a fixed filter bed composed of polar material that is insoluble in water or oil, wherein the hydrocarbon stream is separated from the polar material upon passage through the fixed filter bed. Contacting the hydrocarbon stream with the polar material may also comprises, particularly for use at a well site, mixing the hydrocarbon stream with an aqueous acid or base solution. Apparatus for carrying out the methods is also provided.

Description

TITLE OF THE INVENTION
Purification of Broken Frac Fluid NAME ( S) OF INVENTOR ( S) Shaun T. E. Mesher Glenna L. Strickland Dwight N. Loree FIELD OF THE INVENTION
This invention relates to apparatus and method used for the treatment of hydrocarbon streams, particularly hydrocarbon streams that include a broken frac fluid.
BACKGROUND OF THE INVENTION
In the treatment of oil and gas wells by fracturing, a frac fluid is applied to an underground formation under sufficient pressure to form fractures in the formation, and thus improve flow of oil and gas from the formation into a well. It is desirable to retain the frac fluid close to the well bore and for this reason the frac fluids are made to gel when pressure is applied at reservoir temperatures. The chemicals used to gel the frac fluids contain considerable phosphate and metal concentration. Upon completion of the fracturing treatment, pressure is released, the frac fluid breaks and the broken frac fluid is produced from the well along with reservoir fluid.
When the well is produced, the well production fluid is delivered to a refinery for refining into various hydrocarbon fluids. In the refining process, the phosphates have been found to cause contamination and plugging of the refinery equipment. It has thus been found necessary either to remove the phosphates from the chemicals used to gel the frac fluid or remove them in the refinery itself. Customers of Trysol Canada Ltd. have requested a solution to the problem of removing phosphates from hydrocarbon streams. So far as the applicant is aware, the producers of the hydrocarbons have been unable to provide a satisfactory solution.

SUMMARY OF THE INVENTION
The inventors have thus addressed the need for removing phosphates from a hydrocarbon stream, particularly a broken frac fluid.
Phosphates are removed from a hydrocarbon stream by first contacting the hydrocarbon stream with a polar material, wherein the polar material chemically reacts with phosphates in the hydrocarbon stream and binds to the phosphates and then separating the hydrocarbon stream from the polar material.
Contacting the hydrocarbon stream with the polar material preferably, particularly for large volume applications at a refinery, may comprise passing the hydrocarbon stream through a fixed filter bed composed of polar material that is insoluble in water or oil, wherein the hydrocarbon stream is separated from the polar material upon passage through the fixed filter bed.
Contacting the hydrocarbon stream with the polar material may also comprise, particularly for use at a well site, mixing the hydrocarbon stream with an aqueous acid or base solution.
Various polar materials may be used as described in the following.
Apparatus for carrying out the process, either with a filter bed in a pipe, or a container for mixing the hydrocarbon stream with an acid or base is also provided.

2a According to an aspect of the present invention, there is provided a method of purifying a well production fluid, wherein the fluid contains phosphates, the method comprising the steps of:
contacting the well production fluid with a polar material, wherein the polar material chemically reacts with phosphates in the well production fluid and binds to the phosphates; and separating the well production fluid from the polar material.
According to another aspect of the present invention, there is provided a method of purifying a hydrocarbon stream, wherein the hydrocarbon stream contains phosphates, the method comprising the steps of:
mixing the hydrocarbon stream with an aqueous acid or base solution, wherein the aqueous acid or base solution chemically reacts with phosphates in the hydrocarbon stream and binds to the phosphates; and separating the hydrocarbon stream from the aqueous acid or base solution.
According to a further aspect of the present invention, there is provided an apparatus for purifying a hydrocarbon stream, wherein the hydrocarbon stream contains phosphates, the apparatus comprising:
a pipe; and a filter bed in the pipe, the filter bed comprising a polar material that is insoluble in water or oil, wherein the polar material comprises alkaline carbonate and chemically reacts with phosphates in the hydrocarbon stream and binds to the phosphates.

2b According to another aspect of the present invention, there is provided an apparatus for purifying a hydrocarbon stream, wherein the hydrocarbon stream contains phosphates, the apparatus comprising:
a pipe; and a plurality of filter beds in the pipe, at least one of the filter beds comprising a polar material that is insoluble in water or oil, wherein the polar material comprises alkaline carbonate and chemically reacts with phosphates in the hydrocarbon stream and binds to the phosphates.
According to a further aspect of the present invention, there is provided an apparatus for purifying a hydrocarbon stream, wherein the hydrocarbon stream contains phosphates, the apparatus comprising:
a mixer connected to receive the hydrocarbon stream, wherein the mixer contains an acid or base which chemically reacts with phosphates in the hydrocarbon stream and binds to the phosphates.

These and other aspects of the invention are described in the detailed description of the invention and claimed in the claims that follow.

BRIEF DESCRIPTION OF THE DRAWINGS
There will now be described preferred embodiments of the invention, with reference to the drawings, by way of illustration only and not with the intention of limiting the scope of the invention, in which:
Fig. 1 shows a filter for use in treating hydrocarbon streams according to an aspect of the invention;
Fig. 2 shows a series of filter beds in a heat exchanger according to an aspect of the invention;
Fig. 3 shows apparatus for aqueous treatment of a hydrocarbon stream according to an aspect of the invention;
Fig. 4 is a graph showing metals present in a first untreated broken frac fluid;
Fig. 5 is a graph showing metals present in the first broken frac fluid after treatment according to an aspect of the invention in a continuous stirred tank reactor;
Fig. 6 is a graph showing metals present in the first broken frac fluid after treatment according to an aspect of the invention in a moving burden bed reactor;
Fig. 7 is a graph showing metals present in a second untreated broken frac fluid;
Fig. 8 is a graph showing metals present in the second broken frac fluid after treatment according to an aspect of the invention in a continuous stirred tank reactor;

Fig. 9 is a graph showing metals present in the second broken frac fluid after treatment according to an aspect of the invention in a moving burden bed reactor;
Fig. 10 is a graph showing phosphate removal from a continuous hydrocarbon stream passing through a first bed of alumina and calcium carbonate; and Fig. 11 is a graph showing phosphate removal from a continuous hydrocarbon stream passing through a second bed of alumina and calcium carbonate.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
This invention is particularly applicable to purification of a hydrocarbon stream in a refinery where production fluid from an oil reservoir is being refined.
The process may also be used elsewhere in the oil production process, including at an oil well site before introduction of the hydrocarbon stream into a pipeline. The hydrocarbon stream is contacted with a polar material that reacts with phosphates in the hydrocarbon stream and binds to the phosphates. For example, any alkali metal salt that is insoluble in water or oil is believed to work.
Exemplary polar materials are silica, silicates, alumina, aluminates and alkiline carbonates, particularly calcium carbonate. A base is preferred to an acid. Base or acid as used herein refers to a Bronsted acid or base or Lewis acid or base.
As shown in Fig. 1, a preferred manner of contacting the hydrocarbon stream with a polar material comprises passing a hydrocarbon stream A through a fixed filter bed 10 composed of polar material that is insoluble in water or oil. The filter bed 10 is formed within an enlarged pipe 12, enclosed within frits 14. The frits 14 are stainless steel plates perforated with holes having a small diameter, eg of about 2 m. The fixed filter bed 10 is preferably made from a packed powder form of the polar material held in place in the tubing 16 of a refinery, such that the hydrocarbon stream may be processed continuously.
The powder form of the polar material should have a 5 permeability that does not unduly block fluid flow through the filter, yet should present high surface area of the polar material to the hydrocarbon stream. Mesoporous polar material, particularly mesoporous silica and/or calcium carbonate is believed to provide satisfactory flow rates and phosphate removal rates. Mesoporous means a material having a mean hole diameter from 60 Angstroms to 150 Angstroms. The relative diameters of the pipes 16 and 12 are dependent on flow rate and desired residence time.
Greater diameter, and hence greater residence time, may be preferred for increased removal of phosphates.
The filter bed 10 may be a single homogenous polar material, may be formed of a mixture of one or more polar materials, may include a filler of non-polar material and may be formed of layered polar material. For example, the polar material may be powdered mesoporous alumina, which has been found to work well. A filler such as calcium carbonate may be used in a mixture with alumina (eg 75% by weight alumina and 25% by weight filler) to provide a flow path for the fluid. It has been found that the phosphate content of the hydrocarbon stream drops rapidly upon introduction to the filter bed 10 made of alumina, with removal of in the order of 98% of the phosphates, but the filter bed 10 appears to reach a saturation point after which a reduced level, eg. 50%, of phosphates is obtained.
The saturation point is believed to result from blocking of the pores of the polar material with contaminants in the hydrocarbon stream. This reduces the active surface area for phosphate binding reactions to occur.

Layers of filter material may be used. For example, an initial bed 18 of activated carbon may be used to clean contaminants from the hydrocarbon stream and prolong the efficacy of the filter material.
For increased time of high removal rates, several such filter beds 10 may be used in series, such as illustrated in Fig. 2. To further reduce the contamination of the filter bed, removable filter bed 22 with activated carbon may be used upstream of the other filter beds 10 to remove contaminants. The activated carbon is believed to bind the contaminants, which then do not block the pores of the polar material. These filter beds 10 may be housed in a heat exchanger 24, and the process operated at elevated temperature, for example 50 C.
Any of the filter beds 10 in a series may be made removable. Some kinds of filter material such as alumina may be reused by heating the filter medium to drive off carbon material.
In a further example of an aspect of the invention, shown in Fig. 3 schematically, an embodiment of the process may be operated using existing equipment at a well site configured uniquely. Acid is often used in well treatment operations. In this embodiment, the hydrocarbon stream B produced from the well is directed to an acid bath/mixer 30 where it is mixed with acid, such as hydrochloric acid.
A chemical reaction occurs in which the phosphate becomes polar and dissolves in the hydrochloric acid. The mixture of hydrocarbon stream and hydrochloric acid is then separated in for example a hydrocyclone 32. The hydrochloric acid may then be reused in the acid bath/mixer.
The hydrocarbon stream may then be dried conventionally to meet pipeline requirements. A base may be used in the acid mixer, though since use of acid is common at well sites, use of acid may be more convenient.

EXAMPLES
In example 1, a broken frac fluid from an oil well having total metal content of 199 ppm and total phosphate content of 101 ppm (as shown in Fig. 4) was treated by contact with a polar material consisting of calcium carbonate impregnated onto silica (Si02) in a continuous stirred tank reactor. Approximately 5 g of polar material was stirred with 100 g of hydrocarbons. After treatment, 0.8 ppm total phosphate remained and 1.7 ppm total metals remained (as shown in Fig. 5).
In example 2, the same broken frac fluid as in example 1 (Fig. 4) was treated by contact with a mixture of about 20 g fumed silica and calcium carbonate in a moving burden bed reactor. After treatment, 0.8 ppm total phosphate remained and 1.7 ppm total metals remained (Fig.
6).
In example 3, a broken frac fluid from a lab preparation which was gelled and broken in the lab, wherein the broken frac fluid had total metal content of 636 ppm and total phosphate content of 523 ppm (as shown in Fig. 7) was treated by contact with the same material as in example 1 in a continuous stirred tank reactor under the same conditions. After treatment, 8.7 ppm total phosphate remained and 10 ppm total metals remained (as shown in Fig.

8).
In example 4, a broken frac fluid as in example 3 (Fig. 7) was treated by contact with the same polar material as in example 2 in a moving burden bed reactor.
After treatment, 14.8 ppm total phosphate remained and 14.8 ppm total metals remained (Fig. 9).
In example 5, a hydrocarbon stream containing 65 ppm phosphate was passed at a flow rate of 0.5 mL/min through a filter bed containing 21.9 g of polar material consisting of 75 wt% alumina (A1203) and 25 wt% calcium carbonate (CaCO3). Samples were taken at 30 min intervals for a period of 6 hours. Initially, 100% phosphates were removed, and after 5 hours efficacy of the filter began to be degraded, with reduction in % removal.
In example 6, a hydrocarbon stream containing 65 ppm phosphate was passed at a flow rate of 0.5 mL/min through a filter bed containing 101 g of polar material consisting of 75 wt% alumina (A1203) and 25 wt% calcium carbonate (CaCO3). Samples were taken at 1 hr intervals for a period of 43 hours. Initially, 100% phosphates were removed, and after 5 hours efficacy of the filter began to be degraded, with reduction in % removal to 50% removal after about 29 hours.
The mechanisms according to which the phosphates become bound to the polar material is illustrated below for the following cases:
I Removal of trialkyl phosphate with basic silica.
Oxygen in the silica carries out a nucleophilic attack on the phosphorus. The resulting five member charged phosphorus species rearranges to reform the double oxygen bond and displace an alcohol.

II Removal of trialkyl phosphate with basic alumina. A
similar reaction occurs as with the silica.
III Removal of dialkyl phosphate with basic silica or basic alumina.

IV Removal of monoalkyl phosphate with basic silica or basic alumina V Removal of trialkyl phosphate with acidic silica or alumina. A lone pair of electrons on the oxygen/phosphorus member attracts a proton and creates a positive charge on the phosphorus. Nucleophilic attack is made by the oxygen on the alumina/silica on the phosphorus to create a five member phosphorus species. A double bond to the oxygen is reformed, which displaces a RO group.

VI Phosphate removal by Base Extraction. Calcium binds to an oxygen and displaces hydrogen.

Phosphate removal by acid extraction may be obtained when HC1 carries out the reaction shown in V, and generates an extremely acid soluble phosphate. Silica may also bond to the phosphate by hydrogen bonding, wherein the hydrogen is bound to both an oxygen on the silica and an oxygen in the phosphate.

- lo _ Removal of Phosphates with Basic or Acidic Silica or Alumina Basic: I i - Si -O-Ca+ -AI-O Ca' Trialkyl Phosphates ~O (:~O
RO-P-OR RO-P-OR
OR OR

I 1:
\ I- \ , si AI_ U= o O.
R ~P-OR RO-P-OR
OR OR
O"Si O~- AI-I I
ROCa + O=P-OR ROCa + 0=P-OR
OR OR -Dialkyl Phosphates Si ~
I ~
HO-P-OR ROCa + 0=P-OR or 0=P-OR ~
OR OH OH
Monoalkyl Phosphates I~
O O~Si O~-AI- I ~
HO-P-OR
, = ROCa + O=P-OH or O=P-OH
OH OH OH

- /pA -Phosphate Removal By Base Extaction O O
RO-P-OH CaCO3 . RO-P-O-Ca` v I
OR OR
Any alkaline metal should accomplish this task @ U

O
Ro=p -oR
~
o2 f~I-O
pH ~
R o -` P - 02 oR

L
vA

GP, ~

+
0= P - vK

(Zo+-t p= P -OK

o A person skilled in the art could make immaterial modifications to the invention described in this patent document without departing from the essence of the invention that is intended to be covered by the scope of the claims that follow.

Claims

1. A method of purifying a well production fluid, wherein the fluid contains phosphates, the method comprising the steps of:
contacting the well production fluid with a polar material, wherein the polar material chemically reacts with phosphates in the well production fluid and binds to the phosphates; and separating the well production fluid from the polar material.

2. The method of claim 1 in which contacting the well production fluid with the polar material comprises passing the well production fluid through a fixed filter bed composed of polar material that is insoluble in water or oil, wherein the well production fluid is separated from the polar material upon passage through the fixed filter bed.

3. The method of claim 1 in which contacting the well production fluid with a polar material comprises:
passing the well production fluid through a series of fixed filter beds, each filter bed being composed of polar material that is insoluble in water or oil, wherein the well production fluid is separated from the polar material upon passage through the fixed filter beds.

4. The method of claim 3 in which the fixed filter beds are contained within a heat exchanger.

5. The method of any one of claims 1 to 4 in which the polar material is selected from the group consisting of silica, silicates, alumina, aluminates and alkaline carbonates.

6. The method of any one of claims 1 to 5 in which the polar material is a packed powder.

7. The method of any one of claims 1 to 6 in which the polar material is silica or calcium carbonate or silica and calcium carbonate.

8. The method of any one of claims 1 to 7 in which the polar material comprises silica and calcium carbonate.

9. The method of any one of claims 1 to 8 in which the well production fluid further comprises a broken frac fluid.

10. The method of any one of claims 1 to 9 in which contacting the well production fluid with the polar material is carried out at greater than ambient temperature.

11. The method of any one of claims 1 to 10 in which, before contacting the well production fluid with the polar material, the well production fluid is treated to remove pore blocking contaminants.

12. The method of claim 11 in which treating well production fluid to remove pore blocking contaminants comprises passing the well production fluid through a bed of activated carbon.

13. The method of any one of claims 1 to 12 in which the well production fluid is treated for phosphate removal at a well site.

14. The method of any one of claims 1 to 13 in which the well production fluid is treated for phosphate removal at a refinery.

15. A method of purifying a hydrocarbon stream, wherein the hydrocarbon stream contains phosphates, the method comprising the steps of:
mixing the hydrocarbon stream with an aqueous acid or base solution, wherein the aqueous acid or base solution chemically reacts with phosphates in the hydrocarbon stream and binds to the phosphates; and separating the hydrocarbon stream from the aqueous acid or base solution.

16. The method of claim 15 in which separating the hydrocarbon stream from the aqueous acid or base solution comprises:
passing the hydrocarbon stream through a water-oil separator.

17. The method of claim 15 or 16 in which the aqueous acid or base solution is hydrochloric acid.

18. The method of any one of claims 15 to 17 in which the hydrocarbon stream comprises a broken frac fluid.

19. The method of any one of claims 15 to 18 in which contacting the hydrocarbon stream with the polar material is carried out at greater than ambient temperature.

20. The method of any one of claims 1 to 19 in which, before contacting the hydrocarbon stream with the polar material, the hydrocarbon stream is treated to remove pore blocking contaminants.

21. The method of claim 20 in which treating the hydrocarbon stream to remove pore blocking contaminants comprises passing the hydrocarbon stream through a bed of activated carbon.

22. The method of any one of claims 15 to 21 in which the hydrocarbon stream is treated for phosphate removal at a well site.

23. The method of any one of claims 15 to 22 in which the hydrocarbon stream is treated for phosphate removal at a refinery.

24. Apparatus for purifying a hydrocarbon stream, wherein the hydrocarbon stream contains phosphates, the apparatus comprising:
a pipe; and a filter bed in the pipe, the filter bed comprising a polar material that is insoluble in water or oil, wherein the polar material comprises alkaline carbonate and chemically reacts with phosphates in the hydrocarbon stream and binds to the phosphates.

25. The apparatus of claim 24 in which the pipe is in a refinery.

26. The apparatus of claim 24 or 25 in which the fixed filter beds are contained within a heat exchanger.

27. Apparatus for purifying a hydrocarbon stream, wherein the hydrocarbon stream contains phosphates, the apparatus comprising:

a pipe; and a plurality of filter beds in the pipe, at least one of said filter beds comprising a polar material that is insoluble in water or oil, wherein the polar material comprises alkaline carbonate and chemically reacts with phosphates in the hydrocarbon stream and binds to the phosphates.

28. The apparatus of claim 27 in which the pipe is in a refinery.

29. The apparatus of claim 27 or 28 in which the fixed filter beds are contained within a heat exchanger.

30. The apparatus of any one of claims 24 to 29 in which the polar material comprises at least one of silica, silicates, alumina, and aluminates.

31. The apparatus of any one of claims 24 to 30 in which the polar material is a packed powder.

32. The apparatus of any one of claims 24 to 31 in which the polar material comprises silica and calcium carbonate.

33. The apparatus of any one of claims 24 to 32 in which the apparatus further comprises a bed of activated carbon.

34. Apparatus for purifying a hydrocarbon stream, wherein the hydrocarbon stream contains phosphates, the apparatus comprising:
a mixer connected to receive the hydrocarbon stream, wherein the mixer contains an acid or base which chemically reacts with phosphates in the hydrocarbon stream and binds to the phosphates.

35. The apparatus of claim 34 in which the acid or base is aqueous and further comprising in series with the mixer:
a water-oil separator connected to receive fluid from the mixer; and a dryer connected to receive fluid from the water-oil separator.