Composition and Method for Breaking Friction Reducing Polymer for Well Fluids

Abstract

A polymer breaking solution usable in fracking and other downhole applications comprises a solution of aqueous hydrogen peroxide, an anionic surfactant, a metal chelating agent, an acidic pH buffer, a soluble zinc compound, and in some embodiments, a viscosifying agent. In other embodiments, the solution may additionally comprise a linear hydrophobic surfactant. At treatment concentrations of between 500 ppm to 1,500 ppm, the solution is non-toxic and usable at a wide range of downhole temperatures (32° C. to 82° C.).

Claims

1. An aqueous polymer breaking solution comprising: hydrogen peroxide, in a concentration between 7 wt % and 20 wt %; a soluble zinc compound, in a concentration between 0.05 wt % and 0.5 wt %; a metal chelating agent; an acidic pH buffer; and an alkyl sulfate surfactant.

2. (canceled)

3. The solution of claim 1, wherein the soluble zinc compound is selected from the group comprising: zinc sulfate, zinc acetate, zinc citrate, zinc oxide, zinc chloride, or zinc gluconate.

4. The solution of claim 1, wherein the metal chelating agent is present in a concentration between 0.1 wt % and 0.5 wt %.

5. The solution of claim 1, wherein the metal chelating agent is selected from the group comprising: diethylenetriaminepentaacetate, n-(hydroxyethyl)-ethylenediaminetriacetic acid, ethylenediaminetetracetic acid, iminodissuccinic acid, itaconic acid, iminodisuccinic acid, iminodiacetic acid, glutamic acid n,n-diacetic acid, polyaspartic acid, nitrilotriacetic acid, citric acid, erythorbic acid, ascorbic acid, or any sodium or potassium salts thereof.

6. The solution of claim 1, wherein the alkyl sulfate surfactant is present in a concentration between 0.1 wt % to 0.8 wt %.

7. The solution of claim 1, wherein the alkyl sulfate surfactant is selected from the group comprising: sodium lauryl sulfate or sodium lauryl ethoxy sulfate.

8. The solution of claim 1, wherein the pH buffer is present in a concentration between 0.1 wt % to 0.8 wt %.

9. The solution of claim 1, wherein the pH buffer is selected from the group comprising: acetic acid, oxalic acid, sulfonic acid, sulfamic acid, toluene sulfonic acid, 2-ethyl hexanoic acid, methane sulfonic acid, tartaric acid, lactic acid, and propionic acid.

10. The solution of claim 1, further comprising a linear hydrophobe surfactant.

11. The solution of claim 10, wherein the linear hydrophobe surfactant is present in a concentration between 0.1 wt % to 0.8 wt %.

12. The solution of claim 10, wherein the linear hydrophobe surfactant is selected from the group comprising: disodium decyl(sulfophenoxy)benzenesulfonate, disodium oxybis(decylbenezenesulfonate), sodium alkyl diphenyl oxide disulfonate, sodium C10(linear) diphenyl oxide disulfonate, sodium decyl diphenyl oxide disulfonate, sodium hexadecyldiphenyloxide disulfonate, sodium C16(linear) diphenyl oxide disulfonate, or disodium dihexyldiphenyloxide disulfonate.

13. The solution of claim 1, further comprising polyethylene oxide.

14. The solution of claim 13, wherein the polyethylene oxide is present in a concentration between 0.005 wt % to 0.1 wt %.

15. The solution of claim 13, wherein the polyethylene oxide has a molecular weight between one million and eight million.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 depicts the results of viscosity measurements of a control blend and a blend including two embodiments of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] Before describing selected embodiments of the present disclosure in detail, it is to be understood that the present invention is not limited to the particular embodiments described herein. The disclosure and description herein is illustrative and explanatory of one or more presently preferred embodiments and variations thereof, and it will be appreciated by those skilled in the art that various changes in the design, organization, means of operation, structures and location, methodology, and use of mechanical equivalents may be made without departing from the spirit of the invention.

[0030] As well, it should be understood that the drawings are intended to illustrate and plainly disclose presently preferred embodiments to one of skill in the art, but are not intended to be manufacturing level drawings or renditions of final products and may include simplified conceptual views to facilitate understanding or explanation. As well, the relative size and arrangement of the components may differ from that shown and still operate within the spirit of the invention.

[0031] Moreover, it will be understood that various directions such as “upper”, “lower”, “bottom”, “top”, “left”, “right”, and so forth are made only with respect to explanation in conjunction with the drawings, and that components may be oriented differently, for instance, during transportation and manufacturing as well as operation. Because many varying and different embodiments may be made within the scope of the concept(s) herein taught, and because many modifications may be made in the embodiments described herein, it is to be understood that the details herein are to be interpreted as illustrative and non-limiting.

[0032] The present invention includes embodiments of a composition and method of using an aqueous surfactant-stabilized hydrogen peroxide-based polymer breaker for breaking down and removing polymer. The hydrogen peroxide is the active ingredient and, in a solution, is stabilized against decomposition of the hydrogen peroxide, which delays or retards the polymer-breaking action.

[0033] Embodiments of the present invention comprise chemical compositions that can comprise: a) hydrogen peroxide, b) a surfactant, c) metal deactivator, d) viscosifier, e) pH buffer and f) oxidizer stabilizer, which are usable to more effectively break down low to high molecular weight polyacrylamide friction-reducing polymers and/or viscosity building agents for use in water or water-containing fluids.

[0034] In an embodiment, an aqueous hydrogen peroxide solution is supplemented with one or more chemicals, including surfactants and stabilizers, which when applied into a water solution containing a low to high molecular weight polyacrylamide polymer, will work to break down the polymer. The additive, as described in the present invention, can be used in over a wide range of hydrogen peroxide concentrations e.g., seven percent (7%) to twenty percent (20%), and a wide range of temperatures, including downhole temperatures e.g., from about 90° F. to at least 180° F. (32° C. to 82° C.). At these temperatures, the chemical composition can be effectively advantageous downhole in degrading the molecular weight of the polyacrylamide to greatly improve the polymer removal during flowback and to increase regain permeability of a shale formation.

[0035] The hydrogen peroxide solution contains a number of ingredients, which can include: (a) hydrogen peroxide (H.sub.2O.sub.2) solution in a concentration between 7% and 20%; (b) an anionic surfactant selected from a group consisting of sodium lauryl sulfate (SLS), sodium lauryl ethoxy sulfate (SLES) with 1 to 4 moles of ethylene oxide per mole of alkyl sulfate at 0.1% to 0.8% concentration. The preferred alkyl sulfate is sodium lauryl ethoxy sulfate with 3 moles of ethylene oxide. Additionally, a hydrophobic anionic surfactant can be used in combination with the above, selected from a group of linear 6-carbon to 16-carbon hydrophobe at 0.1% to 0.8% concentration. Surfactant hydrophobes used in the invention can include disodium decyl(sulfophenoxy)benzenesulfonate; disodium oxybis(decylbenezenesulfonate); sodium alkyl diphenyl oxide disulfonate (ADPODS); sodium C10 (linear) diphenyl oxide disulfonate; sodium decyl diphenyl oxide disulfonate; sodium hexadecyldiphenyloxide disulfonate; sodium C16 (linear) diphenyl oxide disulfonate; disodium dihexyldiphenyloxide disulfonate. The preferred linear hydrophobe surfactant is a 16-carbon linear hydrophobe, commercially known as Dowfax 3B2 or Dowfax 8390. In an embodiment, an organic acid can be used at a quantity sufficient to lower the hydrogen peroxide solution to a pH of between 4.5 and 5.5; (c) a metal chelating agent, including one or more of the following: diethylenetriaminepentaacetate (DTPA), N-(hydroxyethyl)-ethylenediaminetriacetic acid (HEEDTA), ethylenediaminetetracetic acid (EDTA), iminodissuccinic acid, itaconic acid, iminodisuccinic acid (IDS), iminodiacetic acid (IDA), glutamic acid N,N-diacetic acid, (GLDA), polyaspartic acid (PA), nitrilotriacetic acid (NTA), citric acid, erythorbic acid, ascorbic acid, or their sodium or potassium salts, in a concentration from 0.1% to 0.5%, the preferred metal chelating agent is DTPA; (d) A high molecular weight polyethylene oxide (PEO) to improve the stability of the hydrogen peroxide. Polyethylene oxides are water-soluble polymers. The PEO provides binding, thickening, water retention and film formation. It is preferred to use a PEO with a molecular weight between 1 million and 8 million, and more specifically, a PEO molecular weight between 2 million and 5 million. The PEO has the ability to reduce friction due to its high molecular weight and polymeric form; however, the inventors have found that the viscosifying effect of the PEO is primarily indirect when initially applied, via the PEO acting as a stabilizer to reduce the degradation of the hydrogen peroxide, with the direct viscosifying or friction reduction properties dominating as the time advances. The PEO additive may be present in a concentration of about 0.005 to 0.1 wt %. (e) a pH buffer intended to lower the pH of the peroxide solution to less than pH 5.0. Buffers used in the invention can include: acetic acid; oxalic acid; sulfonic acid; sulfamic acid; toluene sulfonic acid; 2-ethyl hexanoic acid; methane sulfonic acid; tartaric acid; lactic acid; and propionic acid. The preferred buffer to lower the pH is methane sulfonic acid and toluene sulfonic acid. The pH buffer may be present in a concentration of about 0.1% to 0.8%. (f) a soluble compound containing zinc ions such as zinc sulfate, zinc acetate, zinc citrate, zinc oxide, zinc chloride, or zinc gluconate in a concentration of about 0.05% to 0.5%. The preferred zinc compound is zinc sulfate heptahydrate (ZnSO.sub.4.7H.sub.2O);

[0036] A composition containing the above-mentioned ingredients provides excellent polymer breaking of polyacrylamide polymer friction reducers in water. The composition can be used at downhole temperatures from 90° F. to 180° F. (32° C. to 82° C.). At these temperatures and treatment concentrations of 0.5 to 1.5 gallons per thousand gallons (500 ppm to 1,500 ppm), the composition is effective at degrading the molecular weight of the polyacrylamide to greatly improve polymer removal during flowback and to increase regain permeability of the shale formation.

[0037] The composition can comprise six components in an aqueous solution: a) hydrogen peroxide solution, b) a surfactant, c) a metal deactivator, d) a viscosifier, e) a pH buffer and f) an oxidizer stabilizer. Additional chemical additives can be added to buffer the pH of the hydrogen peroxide solution to aid in reducing the loss of activity over time.

[0038] It is preferred that all of the components of the composition be free or have low concentrations of materials that can contribute to the decomposition of hydrogen peroxide, such as organic matter, transition metals, and other material.

[0039] The hydrogen peroxide concentration can be at any level for which an effective breakdown of the viscosity is achieved. The preferred hydrogen peroxide concentration of the invention is in a range from 7% to 20% hydrogen peroxide concentration. The most preferred hydrogen peroxide concentration depends upon the individual well conditions and activity of friction reducer polymer in the water.

[0040] In general, the treatment activity for hydrogen peroxide required for effective polymer degradation and/or for viscosity reduction are 0.2 gallons per thousand gallons (GPT) up to 3.0 GPT of a 7% up to 20% by weight hydrogen peroxide activity. These rates of addition are sufficient for the majority of slickwater applications, without being corrosive or difficult to transport and store. Higher hydrogen peroxide activity in the treatment chemical may be too aggressive in breaking polymer, and require additional handling precautions in the field.

[0041] Turning now to FIG. 1, a graph (100) of viscosity in cP (102) over time in minutes (104) is shown comparing four samples 1 gpt of friction reducing polymer polyacrylamide and/or hydrolyzed polyacrylamide. Samples 1-3 (106, 108, 110) comprise additives, the components of which are listed below as Table 1:

TABLE-US-00001 TABLE 1 Sample 1 (106) 1 gpt 18% H.sub.2O.sub.2 Sample 2 (108) 1 gpt 18% H.sub.2O.sub.2 0.1-0.3% DTPA 0.2-0.5% SLES 0.1-0.2% methane sulfonic acid 0.1-0.4% ADPODS 0.1-0.2% Zn salt Sample 3 (110) Sample 2, plus 0.01-0.05% PEO Sample 4 (112) control (no additives)

[0042] As FIG. 1 shows, the additives considerably improve the characteristics of the hydrogen peroxide. The Sample 4 (112) control polymer shows no decline in viscosity, while the viscosity of the additive-less hydrogen peroxide blend (Sample 1) reduces too fast; this can adversely affect the initial viscosity of the polymer and cause the proppant to settle or fall out of the flowing water entirely, which is not desired. Samples 2 (108) and 3 (110) show considerably increased utility as the hydrogen peroxide stays present long enough to provide a controlled decrease of polymer viscosity return the proppant back through the formation; the PEO additive allows Sample 3 (110) to retain the same basic curve as the blend in Sample 2 (108), but with a considerably slower decline in viscosity. With Sample 3 (110) as an additive, the selectivity and degradation rate of polymer are high, the use of hydrogen peroxide is improved, and the fluid flowback is easily recovered.

[0043] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been described in detail and shown by way of example. It should be understood, however, that it is not intended to limit the invention to the particular forms disclosed, but, on the contrary, the invention is to cover all modifications and alternatives falling within the spirit and scope of the invention as expressed in the appended claims.