WO2014058696A1

WO2014058696A1 - Boron removal system and method

Info

Publication number: WO2014058696A1
Application number: PCT/US2013/063196
Authority: WO
Inventors: Theodore BAUDENDISTEL; Jesse FARRELL
Original assignee: M-I L.L.C.
Priority date: 2012-10-10
Filing date: 2013-10-03
Publication date: 2014-04-17

Abstract

A method of forming a fracturing fluid includes selectively removing boron from water, the selectively removing boron including flowing water through a boron exchange resin to provide an effluent having a lower boron concentration than the water, and mixing the effluent with a thickening agent. A method includes drilling a borehole in an earth formation, producing a produced water from the borehole, and selectively removing boron from the produced water, the selectively removing including pumping the produced water through a vessel, the vessel having a boron exchange resin, and flowing an effluent having a lower boron concentration than the produced water out of the vessel to be used with a thickening agent.

Description

BORON REMOVAL SYSTEM AND METHOD

BACKGROUND

[0001] Hydrocarbons are found in subterranean formations. Production of such hydrocarbons is generally accomplished through the use of rotary drilling technology which includes the drilling, completing, and working over of wells penetrating producing formations.

[0002] The types of subterranean formations intersected by a well may include formations having clay minerals as major constituents, such as shales, mudstones, siltstones, and claystones. Shale may be a troublesome rock type to drill in order to reach oil and gas deposits. One aspect that makes shales troublesome is that they have a very low (nano-Darcy) permeability with relatively small (nanometer) sized pore throats, which makes profitable extraction of entrained hydrocarbons particularly difficult. Other low permeability formations include sandstone, carbonates, and coal bed methane.

[0003] Hydrocarbons may be produced from shale formations in various ways. For example, gas derived from organic content, such as kerogen, may be stored in the natural fractures inherently present in shale formations so that the shale formation may be a large repository for gas that has formed. Also, hydrocarbons may be produced from shale through desorption directly from the kerogen. Hydraulic fracturing has conventionally been used to recover hydrocarbons from shale formations.

[0004] Hydraulic fracturing is a common stimulation technique used to enhance production of fluids from subterranean formations, and it is often used in recovering hydrocarbon fluids from low permeability formations that produce mainly dry natural gas. Shale formations, in particular, have low permeability such that hydrocarbon fluid production in commercial quantities occurs when fractures exhibit permeability. For example, in the past, vertical wells have been drilled through shale formations and hydraulically fractured. This drilling and completion strategy has evolved so that horizontal wells are now commonly drilled through shale formations and include multistage fracturing. [0005] In a typical hydraulic fracturing treatment, fracturing treatment fluid containing a solid proppant material is injected into the formation at a pressure sufficiently high enough to cause the formation or enlargement of fractures in the reservoir. Various materials may be used as proppants including, but not limited to, sand, glass beads, walnut hulls, metal shot, resin-coated sands, ceramics, sintered bauxite, and deformable materials. A thickening agent (e.g., gel) may be used to help the proppant material stay in suspension as the proppant travels downhole. The proppant material is deposited in a fracture, where it remains after the treatment is completed. After deposition, the proppant material serves to hold the fracture open, thereby enhancing the ability of fluids to migrate from the formation to the wellbore through the fracture. Because fractured well productivity depends on the ability of a fracture to conduct fluids from a formation to a wellbore, fracture conductivity is a parameter in determining the degree of success of a hydraulic fracturing treatment.

SUMMARY

[0006] In one aspect, embodiments disclosed herein relate to a method of forming a fracturing fluid including selectively removing boron from water, the selectively removing boron including flowing water through a boron exchange resin to provide an effluent having a lower boron concentration than the water, and mixing the effluent with a thickening agent.

[0007] In another aspect, embodiments disclosed herein relate to a method including drilling a borehole in an earth formation, producing a produced water from the borehole, and selectively removing boron from the produced water, the selectively removing including pumping the produced water through a vessel comprising a boron exchange resin. The method further includes flowing an effluent having a lower boron concentration than the produced water out of the vessel and adding a thickening agent to the effluent.

[0008] In another aspect, embodiments disclosed herein relate to a method of treating boron-containing water for a fracturing fluid including disposing a boron exchange resin in a vessel having an inlet and an outlet, and pumping the boron-containing water into the inlet and through the boron exchange resin. The method further includes selectively removing boron from the boron-containing water, flowing an effluent out of the outlet, and adding a thickening agent to the effluent.

[0009] This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

DETAILED DESCRIPTION

[0010] Embodiments disclosed herein relate to systems and methods for removal of boron from water for oilfield applications. In particular, embodiments disclosed herein relate to removal of boron from freshwater or produced water. More specifically, embodiments disclosed herein relate to removal of boron from water using an ion exchange resin, and specifically a boron exchange resin. Furthermore, embodiments disclosed herein relate to methods of forming a fracturing fluid with water that is boron- free or that contains a low concentration of boron.

[0011] Water is often used in various oilfield applications. For example, water may be used as a base fluid or additive drilling fluids, often called "mud," or fracturing fluid (also called a "frac fluid"), for treatment of cuttings (solid pieces of the rock formation generated during drilling of a borehole), for cleaning of equipment, and for providing hydraulic pressure or actuation. Water may be obtained from freshwater sources, such as water wells, subsurface aquifers, brackish waters, streams, or lakes, or may be obtained from fluids produced during drilling a formation for production of oil and/or gas (i.e., produced water).

[0012] Depending on the location of a drill site, water obtained from freshwater sources may contain certain concentrations of boron in addition to other chemical elements, compounds and/or contaminants. Similarly, produced water may include boron, other chemical elements, hydrocarbons, chemical additives, drill cuttings, and other contaminants that may come from the drilling fluids used or from the formation being drilled. In order to use the water in certain oilfield applications, boron may be removed or the concentration of boron reduced. As used herein, boron refers to boron in any form, including borates and boric acid.

[0013] Water is often used in fracturing (or fracking) operations. In fracturing operations, fracturing fluids are injected into a well to stimulate the formation, which enhances production of fluids form subterranean formations. Fracturing is often used in low-permeability reservoirs. The fracturing fluid may be pumped at a high pressure and rate into the reservoir interval to be treated to cause a vertical fracture to be opened. The fracturing fluid may include water, proppant, and other frac fluid chemicals including a thickening agent. The proppant may include, for example, grains of sand, glass beads, walnut hulls, metal shot, resin-coated sands, ceramics, sintered bauxite, and deformable materials. The proppant is mixed with the water or fracturing fluid to keep the fracture open when the treatment is complete. The frac fluid chemicals may be used to reduce friction pressure while pumping the fracturing fluid into the wellbore or to adjust viscosity of the fracturing fluid. The frac fluid chemicals may include thickening agents, friction reducers, crosslinkers, breakers, and surfactants. Crosslinkers may be used to change the viscosity of the fracturing fluid as necessary.

[0014] Thickening agents, such as guar gum, derivatized guar, cellulose derivatives, xanthan gum, and polyacrylamide, for example, may be used in accordance with embodiments disclosed herein to thicken the fluid to help transport the proppant material. Crosslinkers (or crosslinking agents) in accordance with the present disclosure may be used to enhance the characteristics and ability of the thickening agent to transport the proppant material. Crosslinkers may be used independently or as a mixture of crosslinker compounds. Example crosslinking agents may include borates, zirconates, titanates, and aluminates. Friction reducing agents in accordance with the present disclosure may include, for example, potassium chloride or polyacrylamide-based compounds to reduce tubular friction and subsequently reduce the pressure to pump the fracturing fluid into the wellbore. Surfactants used in accordance with embodiments disclosed herein may include, for example, anionic, cationic, nonionic, and hydrotropic surfactants or one or more hydrophobic organic alcohols, in an aqueous medium. Surfactants which may be used in accordance with the present disclosure may be a low benzene or benzene-free surfactant. Other example surfactants may include sulfosuccinates, sulfosuccinamates, polyoxyethylene sorbitol fatty acids, sorbitan sesquioleate, polyoxyethylene sorbitan trioleate, sorbitan monooleate, polyoxyethylene (20) sorbitan monooleate, sodium dioctylsulfosuccinate, oleamidopropyldimethyl amine, sodium isostearyl-2-lactate, polyoxyethylene sorbitol monooleate or mixtures thereof and the like. Other additives may be added to the fracturing fluid, including, but not limited to, scale inhibitors, such as ethylene glycol, iron control/stabilizing agents, such as citric acid or hydrochloric acid, biocides or disinfectants, such as bromine -based solutions or glutaraldehyde, corrosion inhibitors, such as Ν,η-dimethyl formamide, oxygen scavengers, such as ammonium bisulfite, etc.

[0015] The presence of additional boron (or borate) in the water used to form the fracturing fluid may undesirably crosslink with other components of the fracturing fluid or otherwise negatively affect the fracturing fluid. Such crosslinking may destabilize the fracturing fluid. For example, if water used in forming a fracturing fluid includes boron, the boron may act as a crosslinking agent and change the viscosity of the fracturing fluid from a designed viscosity. In certain fracturing fluids where the fracturing fluid includes a crosslinking agent, such as boric acid, adding water having boron therein may speed up crosslinking of the thickening agent, which may adversely increase the viscosity of the fracturing fluid before the fracturing fluid is at a downhole location. A viscous fracturing fluid may make it difficult to pump the fracturing fluid downhole and may wear or damage the pump or other equipment. If boron is present in the water used to make the fracturing fluid, the boron may prematurely crosslink the thickening agent before it is able to sufficiently hydrate in the water. If not sufficiently hydrated, the thickening agent may lose its viscosity and ability to transport sand at elevated temperatures downhole. Above a given concentration of boron in water, the boron can interfere with the ability of the fract fluid to maintain the proper viscosity at wellbore temperatures to successfully transport proppant downhold.

[0016] Because the presence of boron in water may adversely affect a fracturing fluid, embodiments disclosed herein provide a system and method for removing boron or reducing the boron concentration in water. One of ordinary skill in the art will appreciate that the system and methods disclosed herein may be used for other oilfield applications where boron-containing water is problematic.

[0017] Embodiments disclosed herein relate to systems and methods for removing boron from water. In particular, boron may be selectively removed from water so that the water may be used in oilfield applications that may require low concentrations of boron (e.g., less than 30 ppm boron). As used herein, selectively removed refers to the removal of boron, specifically, while allowing other elements or ions to be retained within the water.

[0018] A system for removing boron from water may include a vessel having a specified volume. The vessel may include an inlet and an outlet. An ion exchange resin is disposed in the vessel. Specifically, a boron exchange resin is disposed in the vessel. As used herein, a boron exchange resin is a resin that is designed to remove borates and/or other forms of boron from a solution. Specifically, the boron exchange resin may include a matrix of macroporous polystyrene with a functional group of N-Methylglucamine. The resin may be formed as beads having a harmonic mean particle size of about 0.400 to 0.800 mm. The boron ion generates a stable complex with the glucamine group while other anions do not react as well. Thus, while typical ion exchangers remove, for example, magnesium and calcium before removing boron, the boron exchange resin disclosed herein removes boron while leaving magnesium and calcium in the solution. One example of a commercially available boron exchange resin is AMBERLITE IRA743 chelating resin from The Dow Chemical Company (Philadelphia, PA). In some embodiments, the boron exchange resin may include a macroporous polystyrene crosslinked with divinylbenzene. In this embodiment, the resin may be formed as beads having a mean particle size of about 0.400 to 0.800 mm. Another example of a commercially available boron exchange resin is ULTRACLEAN UCW 1080 polystyrene divinylbenzene tertiary amino saccharide from The PUROLITE Company (Bala Cynwyd, PA).

[0019] The boron exchange resin may be disposed in the vessel to provide a resin bed through which water (or a water-based solution) is passed. In some embodiments, the water is introduced through the inlet of the vessel, passed through the boron exchange resin, which removes the boron from the water, and the effluent is flowed out through the outlet of the vessel. In some embodiments, a pump may be coupled to the inlet of the vessel to provide a pressure differential across the boron exchange resin to facilitate a flow of the water through the boron exchange resin. For example, the pump may provide a steady flow of water at about 2 to 20 psi. In certain embodiments, the pump may provide a flow of water at approximately 10 psi. In other embodiments, the boron exchange resin may be disposed on a surface of the vessel (i.e., line the surface of the vessel) across which the water is passed.

[0020] The system for removing boron from water may also include one or more components of pre-treatment equipment. Specifically, before introducing water to the vessel, the water may be passed through pre-treatment equipment to remove other contaminants from the water. Specifically, contaminants that may damage the boron exchange resin may be removed from the water before the water is passed through the boron exchange resin. For example, hydrocarbons and particulate matter may be removed from the water before pumping the water to the vessel having the boron exchange resin disposed therein. The pre-treatment equipment may include one or more of a filter, a vibratory separator, a centrifuge, a settling tank, and a hydrocyclone. One of ordinary skill in the art will appreciate that other pre-treatment equipment may be used without departing from the scope of embodiments disclosed herein. In some embodiments, the removal or separation of hydrocarbons and/or solids may be facilitated by the addition of a chemical. For example, a coagulant, surfactant, polymer, or combinations thereof may be added to the water before the water is passed through the boron exchange resin in the vessel. The chemicals may be injected into the water in the pre-treatment equipment discussed above.

[0021] The system may also include components for providing a backwashing of the resin. Specifically, the system may include a second pump configured to pump a backwash fluid back through the boron exchange resin. The second pump may be coupled to the outlet of the vessel to introduce a backwash fluid to the vessel and create a pressure differential across the boron exchange resin to facilitate flow of the backwash fluid back through the boron exchange resin. In other embodiments, the pump coupled to the inlet of the vessel may also be coupled to the outlet of the vessel with a valve operatively coupled to the pump to direct the flow of fluids to the inlet and/or outlet. In some embodiments, the backwash fluid may be an acid. For example, the backwash fluid may be hydrochloric acid or sulfuric acid. The pump coupled to the inlet and/or the second pump may also be configured to provide a regenerant material to the vessel to regenerate the boron exchange resin. The regenerant material may be a base fluid that is added to the vessel and flowed through the boron exchange resin. In some embodiments, the base fluid may be sodium hydroxide.

[0022] A method of treating a boron-containing water for oilfield applications, such as for forming a fracturing fluid, includes disposing a boron exchange resin in a vessel. The boron exchange resin may be a resin as discussed above for selectively removing boron from water. The boron-containing water is pumped into the vessel and through the boron exchange resin. The boron-containing water may be pumped into an inlet of the vessel and a pressure applied by a pump may facilitate the flow of the boron-containing water through the boron exchange resin. As the boron-containing water flows through the boron exchange resin, boron is removed from the boron-containing water by the boron exchange resin. An effluent (i.e., water with a boron concentration lower than the boron-containing water introduced to the vessel) is flowed out of the vessel, for example, through an outlet of the vessel.

[0023] While boron is removed from the boron-containing fluid pumped through the boron exchange resin, other anions will not react with the boron exchange resin, and therefore are not removed from the boron-containing water. For example calcium and magnesium in the boron-containing fluid will pass through the boron exchange resin with the water. In other words, the calcium concentration of the boron-containing water and the effluent may be approximately equal. Similarly, the magnesium concentration of the boron-containing water and the effluent may be approximately equal.

[0024] In some embodiments, a continuous stream of boron-containing water may be passed through the boron exchange resin for a predetermined amount of time or volume of fluid. The size of the vessel, the amount of the boron exchange resin, and the flow rate of the boron-containing water through the vessel may be adjusted and optimized for a particular application to provide a certain boron concentration in the resulting effluent. For example, a boron-containing water may have a boron concentration of from about 80 to 100 ppm boron, from about 60 to 80 ppm boron, from about 40 to 60 ppm boron, or from about 20 to 40 ppm boron. To obtain such a specific boron concentration, the boron removal system may be designed such that the size of the vessel, the amount of the boron exchange resin, and the flow rate of boron-containing water through the system may provide an effluent having an optimal boron concentration. For example, in a fracturing fluid application a water having less than 30 ppm boron, less than 20 ppm boron, less than 10 ppm or less than 5 ppm boron may be desired.

[0025] In certain embodiments, the flow rate of boron-containing water into the vessel may be between 4 and 30 BV/h. As used herein, BV refers to bed volume. BV/h is the volume per hours of liquid to be treated over the volume of resin. For example, in certain embodiments, the flow rate may be 10 BV/h, 17 BV/h, 25 BV/h, or other flow rates to achieve an optimized flow rate for a desired boron concentration in the effluent water flow. Additionally, the size of the vessel, the amount of the boron exchange resin, and the flow rate of boron-containing water may also be selected so as to provide a desired cycle time for the boron removal process.

[0026] Specifically, continually flowing a boron-containing water through the boron exchange resin will exhaust the boron exchange resin, i.e., reduce or eliminate the ability of the boron exchange resin to effectively remove boron from the boron-containing water. Therefore, the boron removal process may be stopped and the regeneration process of the boron exchange resin may be initiated. In other words, the boron exchange resin may be regenerated or restored to its proper ionic form for continued use in the boron removal process. Regeneration of the boron exchange resin may include a backwash cycle and a base fluid cycle.

[0027] To regenerate the boron exchange resin, a backwash cycle may be used to pump an acid into the vessel. That is, an acid backflow is applied to the boron exchange resin. One of ordinary skill in the art will appreciate that various acids may be used as a backwash for the boron exchange resin without departing from the scope of embodiments disclosed herein. Examples of acids that may be used to backwash the boron exchange resin include hydrochloric acid and sulfuric acid. As discussed above, the backwash fluid may be pumped into the outlet, through the boron exchange resin, and out the inlet of the vessel. The backwash fluid may expand the resin bed from its settled and packed condition and may clean the resin by flushing out any suspended solids (that may have bypassed the pre -treatment equipment discussed above) and/or any damaged resin particles.

[0028] After the backwash cycle, regenerating the boron exchange resin may further include pumping a base fluid through the boron exchange resin. One of ordinary skill in the art will appreciate that various based fluids may be used to regenerate the boron exchange resin without departing from the scope of embodiments disclosed herein. One example of a regenerant fluid that may be used is sodium hydroxide. In order to ensure that the boron exchange resin is adequately regenerated, a predetermined regeneration cycle time may be selected. In some embodiments, replacement or additional boron exchange resin may be added to the vessel to replace any damaged resin.

[0029] In certain embodiments, a 1 day cycle time for the boron removal process may be desired. In this example, the regeneration cycle (including the backwash cycle and the base fluid cycle discussed above) may be 4 hours while the boron removal cycle (i.e., flow of boron-containing fluid through the boron exchange resin) may be 20 hours. By adjusting the size of the vessel, the amount of the boron exchange resin, and the flow rate of boron-containing water the desired cycle time for the boron removal process may be determined. One of ordinary skill in the art will appreciate that other cycle times may be desired and that the size of the vessel, the amount of the boron exchange resin, and the flow rate of boron-containing water may be adjusted to achieve a desired boron removal process cycle.

[0030] A method of forming a fracturing fluid according to embodiments of the present disclosure may include selectively removing boron from water, and mixing the effluent with a thickening agent. The selectively removing boron includes flowing water through a boron exchange resin to provide an effluent having a lower boron concentration than the water introduced to the boron exchange resin. In other words, an effluent obtained from the outlet of the boron removal system described above may be mixed with a thickening agent to form a fracturing fluid for pumping down hole. Because the effluent has a lower boron concentration, for example, less than 10 ppm boron, the effluent may be used in a fracturing fluid without adversely affecting the fracturing fluid or without causing premature crosslinking of the thickening agent of the fracturing fluid.

[0031] Other fluids or additives may be added to the water and thickening agent in forming a fracturing fluid, as discussed above. For example, at least one crosslinking agent may be added to the water and thickening agent to increase the viscosity of the fracturing fluid downhole. In one embodiment, the crosslinking agent may be boric acid. The fracturing fluid may then be pumped downhole and used to fracture the earth formation.

[0032] In some embodiments, the boron removed from the boron-containing water may be reused. For example, boron removed from the boron-containing water by the boron exchange resin may be collected during the backwash cycle. For example, during the backwash cycle, acids used to clean and flush the boron exchange cycle may be collected and treated to separate the removed boron. The boron may then be reused in other oilfield applications. For example, the removed boron may be used as a crosslinking agent in subsequent fracturing fluids.

[0033] In another embodiment, a method according to the present disclosure includes drilling a borehole in an earth formation, producing a produced water from the borehole, and selectively removing boron from the produced water. The selectively removing boron from the produced water includes pumping the produced water through a vessel, the vessel having an ion exchange resin, and flowing an effluent having a lower boron concentration than the produced water out of the vessel. The ion exchange resin is a boron exchange resin as discussed above. [0034] The produced water pumped through the boron exchange resin at a predetermined flow rate produces an effluent having no or low concentrations of boron. In some embodiments, the effluent may be further diluted by adding a volume of water having no boron or a concentration of boron less than the concentration of boron of the effluent. The effluent may then be used in various oilfield applications. For example, the effluent may be used to form a fracturing fluid. As discussed above, a fracturing fluid may be formed by mixing the effluent water with a thickening agent. Further, other chemical additives may be added to the fracturing fluid including crosslinking agents, friction reducing agents, etc. The fracturing fluid may then be pumped into a borehole and used to fracture the earth formation.

[0035] Although only a few example means, materials, and embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from the systems and methods disclosed herein. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. § 112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words 'means for' together with an associated function.

Claims

CLAIMS What is claimed:

1. A method of forming a fracturing fluid, the method comprising:

selectively removing boron from water; the selectively removing boron comprising: flowing the water through a boron exchange resin to provide an effluent having a lower boron concentration than the water; and

mixing the effluent with a thickening agent.

2. The method of claim 1, wherein the boron exchange resin comprises a polystyrene.

3. The method of claim 2, wherein the boron exchange resin further comprises methy lglucamine .

4. The method of claim 1, wherein a calcium concentration of the water and the effluent is approximately equal.

5. The method of claim 1, wherein a magnesium concentration of the water and the effluent is approximately equal.

6. The method of claim 1, further comprising adding at least one crosslinking agent to the effluent.

7. The method of claim 1 , wherein the water is produced from a well.

8. The method of claim 1, wherein the water is freshwater.

9. A method comprising:

drilling a borehole in an earth formation;

producing a produced water from the borehole; and

selectively removing boron from the produced water, the selectively removing comprising: pumping the produced water through a vessel comprising a boron exchange resin;

flowing an effluent having a lower boron concentration than the produced water out of the vessel; and

adding a thickening agent to the effluent.

10. The method of claim 9, wherein the boron exchange resin comprises at least a polystyrene and methylglucamine.

11. The method of claim 10, further comprising pumping the fracturing fluid into the borehole, and fracturing the earth formation.

12. The method of claim 10, further comprising adding a crosslinking agent to the fracturing fluid.

13. A method of treating boron-containing water for a fracturing fluid, the method comprising:

disposing a boron exchange resin in a vessel having an inlet and an outlet;

pumping the boron-containing water into the inlet and through the boron exchange resin;

selectively removing boron from the boron-containing water;

flowing an effluent out of the outlet; and

adding a thickening agent to the effluent.

14. The method of claim 13, wherein the boron exchange resin comprises at least a polystyrene and methyglucamine.

15. The method of claim 13, further comprising regenerating the boron exchange resin.

16. The method of claim 15, wherein the regenerating comprises pumping an acid into the outlet, through the boron exchange resin, and out the inlet.

17. The method of claim 16, wherein the acid is at least one selected from hydrochloric acid and sulfuric acid.

18. The method of claim 16, wherein the regenerating further comprises pumping a base fluid through the boron exchange resin.

19. The method of claim 18, wherein the base fluid is sodium hydroxide.

20. The method of claim 13, further comprising pre-treating the boron-containing water before pumping the boron-containing water into the inlet, the pre-treating comprising removing at least one of hydrocarbons and solids from the water.

21. The method of claim 20, wherein the removing at least one of hydrocarbons and solids from the water comprises flowing the water through at least one of a filter, a gravity separator, a centrifuge and a hydrocyclone.

22. The method of claim 20, wherein the removing at least one of hydrocarbons and solids from the water comprises injecting at least one of a coagulant, a surfactant, a polymer, and combinations thereof.