Formulations and methods

Abstract

Formulations for fracturing fluids that include (i) a fluid (D) including an oil phase in which the fluid (D) is an inverse emulsion including a water-soluble polymer (B) and said oil phase; and (ii) particles of a water-soluble polymer (C), which are different than water-soluble polymer (B), wherein the particles of polymer (C) are dispersed in said oil phase as solid discrete particles. The fluid (D) includes at least 15wt % polymer (B).

Claims

1. A formulation (A), for use in a fracturing fluid, comprising: (i) a fluid (D) comprising an oil phase, wherein said fluid (D) is an inverse emulsion comprising a water-soluble polymer (B) and said oil phase; and (ii) particles of a water-soluble polymer (C), which are different than water-soluble polymer (B), wherein said particles of said polymer (C) are dispersed in said oil phase as solid discrete particles; and wherein: fluid (D) comprises at least 15wt % polymer (B).

2. The formulation according to claim 1, wherein the formulation (A) includes: 70-90wt % of said fluid (D); 10-30 wt % of said particles: and 0 to 1wt % of suspending agent.

3. The formulation according to claim 2, wherein at least 90wt % of said particles of said water soluble polymer (C) have a diameter greater than 20 μm; and said particles of said water soluble polymer (C) have a diameter less than 2000 μm.

4. The formulation according to claim 1, wherein fluid (D) comprises at least 25wt % polymer (B).

5. The formulation according to claim 1, wherein said formulation (A) has a viscosity of less than 1000cP.

6. The formulation according to claim 1, wherein said polymer (B) includes a repeat unit which includes an optionally substituted acrylamide of formula I ##STR00004## wherein R.sup.5, R.sup.6 and R.sup.7 independently represent a hydrogen atom or an optionally-substituted C.sub.1-4 alkyl group in combination with: a repeat unit comprising a moiety of formula II ##STR00005## wherein the O* moiety is an O.sup.− moiety or is covalently bonded to another atom or group; a repeat unit comprising a vinyl pyrrolidone moiety; or a repeat unit comprising a moiety of formula III ##STR00006## wherein R.sup.1 and R.sup.2 are independently selected from a hydrogen atom and an optionally-substituted alkyl group.

7. The formulation according to claim 1, wherein the inverse emulsion comprises at least 15wt % of said oil phase; and less than 70wt % of said oil phase; said inverse emulsion comprises at least 15wt % and less than 50wt % of polymer (B); and polymer (B) incorporates up to 40wt % of water.

8. The formulation according to claim 1, wherein said inverse emulsion includes 15-40wt % of said oil phase, 15-40wt % of polymer (B) and 15-40wt % water.

9. The formulation according to claim 8, wherein said polymer (B) is an ionic polyacrylamide.

10. The formulation according to claim 1, wherein said polymer (B) includes 5-40 mol % of ionic repeat units.

11. The formulation according to claim 1, wherein said polymer (B) includes a repeat unit which includes an acrylate, sulfonate or pyrrolidone moiety.

12. The formulation according to claim 11, wherein said water soluble polymer (C) includes one or more moieties selected from —C(O)NH.sub.2, —COO.sup.−, and quaternary ammonium.

13. The formulation according to claim 12, wherein said particles of water soluble polymer (C) have a mean particle diameter of at least 100 μm.

14. The formulation according to claim 1, wherein said water soluble polymer (C), independent of said polymer (B), includes a repeat unit which includes an optionally substituted acrylamide of formula I ##STR00007## wherein R.sup.5, R.sup.6 and R.sup.7 independently represent a hydrogen atom or an optionally-substituted C.sub.1-4 alkyl group in combination with: a repeat unit comprising a moiety of formula II ##STR00008## wherein the O* moiety is an O.sup.− moiety or is covalently bonded to another atom or group; a repeat unit comprising a vinyl pyrrolidone moiety; or a repeat unit comprising a moiety of formula III ##STR00009## wherein R.sup.1 and R.sup.2 are independently selected from a hydrogen atom and an optionally-substituted alkyl group.

15. The formulation according to claim 1, wherein a ratio (X), defined as the parts by weight of said fluid (D) divided by the parts by weight of said particles is in the range 1-12; and/or wherein a ratio (Y), defined as the parts by weight of polymer (B) divided by the parts by weight of polymer (C) is in the range 5:1 to 1:5; and/or wherein a ratio (Z), defined as the parts by weight of said oil phase divided by the parts by weight of polymer (C) is in the range 0.1 -2.0.

16. The formulation according to claim 1, wherein a ratio (X), defined as the parts by weight of said fluid (D) divided by the parts by weight of said particles is in the range 1-12; and wherein a ratio (Y), defined as the parts by weight of polymer (B) divided by the parts by weight of polymer (C) is in the range 5:1 to 1:5; and wherein a ratio (Z), defined as the parts by weight of said oil phase divided by the parts by weight of polymer (C) is in the range 0.1-2.0.

17. The formulation according to claim 1, wherein at least 90wt % of said particles of said water soluble polymer (C) have a diameter greater than 20 μm; and said particles of said water soluble polymer (C) have a diameter less than 2000 μm.

18. A method of fracturing a subterranean formation, the method comprising contacting the formation with a fracturing fluid which comprises the formulation (A) of claim 1 in combination with an aqueous liquid.

19. The method of claim 18, further comprising contacting and/or mixing of formulation (A) with water so that the inverse emulsion inverts and polymer (C) mixes with and/or is solubilised by the water.

20. The formulation according to claim 1, wherein said particles of water soluble polymer (C) have a mean particle diameter of at least 100 μm and said particles are in the form of powder, granules or flake.

21. The formulation according to claim 1, wherein said polymer (B) includes a repeat unit which includes an optionally substituted acrylamide of formula I ##STR00010## wherein R.sup.5, R.sup.6 and R.sup.7 independently represent a hydrogen atom or an optionally-substituted C.sub.1-4 alkyl group in combination with: a repeat unit comprising a moiety of formula II ##STR00011## wherein the O* moiety is an O.sup.− moiety or is covalently bonded to another atom or group; a repeat unit comprising a vinyl pyrrolidone moiety; or a repeat unit comprising a moiety of formula III ##STR00012## wherein R.sup.1 and R.sup.2 are independently selected from a hydrogen atom and an optionally-substituted alkyl group; and wherein said water soluble polymer (C), independent of said polymer (B), includes a repeat unit which includes an optionally substituted acrylamide of formula I ##STR00013## wherein R.sup.5, R.sup.6 and R.sup.7 independently represent a hydrogen atom or an optionally-substituted C.sub.1-4 alkyl group in combination with: a repeat unit comprising a moiety of formula II ##STR00014## wherein the O* moiety is an O.sup.− moiety or is covalently bonded to another atom or group; a repeat unit comprising a vinyl pyrrolidone moiety; or a repeat unit comprising a moiety of formula III ##STR00015## wherein R.sup.1 and R.sup.2 are independently selected from a hydrogen atom and an optionally-substituted alkyl group.

22. The formulation according to claim 1, said formulation including: 70 to 90wt % of said fluid (D); 10 to 30wt % of said particles; and 0 to 1wt % of a suspending agent; wherein a ratio (Y), defined as the parts by weight of polymer (B) divided by the parts by weight of polymer (C) is in the range 3:1 to 1:3; and wherein the sum of the wt % of said fluid (D) and the wt % of said particles in formulation (A) is at least 95wt %.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Specific embodiments of the invention will now be described, by way of example, with reference to the accompanying figures, in which:

(2) FIG. 1 is a particle size distribution graph (percent volume v. particle diameter (μm)) for Granule Polyacrylamide (GP);

(3) FIG. 2 is a graph of % Friction Reduction v. time for formulations described in Example 3;

(4) FIG. 3 is a graph of % Friction Reduction v. time for formulations described in Example 4;

(5) FIG. 4 is a graph of % Friction Reduction v. time for formulations described in Example 5; and

(6) FIG. 5 is a graph of % Friction Reduction v. time for formulations described in Example 6.

WORKING EXAMPLES

(7) The following materials are referred to hereinafter:

(8) Emulsion polymer (EP)—commercially available emulsion friction reducer composition supplied as FliRate 605 available from Independence Oilfield Specialties and comprising approximately 20 wt % of an anionic partially hydrolysed polyacrylamide copolymer, present as an inverse emulsion with water and surfactant in approximately 25 wt % of a continuous oil phase comprising a hydro treated light petroleum distillate.

(9) Organophilic Clay (OC)—Claytone SF from BYK

(10) Granule polyacrylamide (GP)—commercially available particulate friction reducer composition comprising >90% of an anionic partially hydrolysed polyacrylamide copolymer. Particle size analysis of the material is provided in FIG. 1. Analysis was performed using a Beckman Coulter Laser Particle Size Analyser LS13320. The material has a volume median particle diameter of 320.8 μm, a volume mean particle diameter of 323.2 μm, the largest particles being 948 μm and the smallest being 27.4 μm

(11) Test Water (W)—refers to tap water having the following composition.

(12) TABLE-US-00001 Concentration Ions (mg/L) Calcium 13.80 Magnesium 1.64 Barium 0.05 Boron 0 Iron 0 Sodium 244.56 Chloride 226.27 Sulphate 16.50 Phosphates 0.06 Bicarbonate 280.60 Carbonate 6.40 Potassium 2.93 Silicon 9.42 pH 8.90 Specific Gravity 1.00 Total Dissolved Solids (ppm) 811.64

(13) In general terms, formulations for fracturing fluids are prepared by mixing a granulated water-soluble friction reducing polymer (Granule polyacrylamide (GP)) with an invert polymer emulsion friction reducing formulation (Emulsion Polymer (EP)), optionally in the presence of an organophilic clay, without the need for specialized field equipment. The mixture can be dosed into water to produce a fracturing fluid which is found to be technically highly advantageous and cost-effective.

(14) Example 1 describes the preparation of candidate formulations for testing, Example 2 describes a general procedure for Flow-loop testing. Examples 3 to 6 describe assessments undertaken and results for a range of formulations.

Example 1—Preparation of Candidate Formulations for Testing

(15) The following blends A-1, A-2, A-3 and B-1 were prepared by blending the components described in the table at the level indicated to produce slurries having densities and viscosities as detailed in Table 1. In general terms in the method, the clay is added to Emulsion Polymer (EP) to disperse and activate the clay. The Granule Polyacrylamide (GP) is added and mixture stored at ambient temperature and pressure.

(16) TABLE-US-00002 TABLE 1 Granule Emulsion Organo- Poly- Polymer philic acrylamide Slurry Formulation Density (EP) Clay (OC) (GP) Viscosity Identifier. (lb/gal) (wt %) (wt %) ((wt %)) (cP) Blend A-1 8.942 79.30 0.51 20.19 378 Blend A-2 8.946 79.42 0.35 20.22 349 Blend A-3 8.937 79.61 0.20 20.18 340 Blend B-1 8.875 81.55 0.35 18.11 320

Example 2—General Procedure for Flow-Loop Testing of Formulations

(17) A flow loop device used was composed of two 10 ft pipes in sequence, one ¾ inch and the other ½ inch. The water for the test was held in a 5 gallon reservoir tank, equipped with an overhead stirrer. The fluid was recirculated through the pipes and reservoir using a Moyno pump. The flow rate in each test was held constant at either 6 or 10 gal/min. Initially, Test Water (W) was pumped for two minutes at constant rate to establish a baseline. After two minutes, a friction reducer to be tested was added to the reservoir tank with 30 seconds of vigorous mixing to assure uniform distribution of friction reducer while also flowing through the flow loop plumbing. After the 30 seconds of vigorous mixing, the stirrer speed was reduced to gently mix components for the rest of the test.

(18) The pressure drop across the length of each pipe, the flow rate through each pipe and the fluid temperature was continuously recorded, with data being collected at a rate of one data point per second. Each test was run for about 18 minutes. At the completion of each test, the flow rate, temperature and the percent friction reduction (calculated as 1−(ΔP FR/ΔP water), were plotted against time.

Example 3—Assessment of Formulations (First Set of Experiments)

(19) In the first set of experiments, testing of formulations detailed in the Table 2 below was undertaken using the flow loop of Example 2, at a flow rate of 6 gal/min.

(20) TABLE-US-00003 TABLE 2 Inversion Max % Example Formulation Loading Viscosity Time Friction No. Identifier (gpt) (cP) pH (sec) Reduction 3a Emulsion 0.50 1.13 8.05 62 73 (Comparative) Polymer (EP) 3b Emulsion 0.25 0.98 8.09 70 69 (Comparative) Polymer (EP) 3c Blend A-1 0.25 1.17 8.02 22 73 3d Blend A-2 0.25 1.17 8.00 21 73 3e Blend A-3 0.25 1.16 8.03 22 73 Note that “gpt” refers to “gallons per thousand gallons” which is conventional in the art.

(21) Results of the flow loop test are provided in Table 1 and in FIG. 2. The results show that the maximum friction reduction for the base line 0.50 gpt (Example 3a) was 73%, and the inversion time was 62 sec. When half the amount, 0.25 gpt in Example 3b was compared, the maximum reduction was only 69% and the inversion time was 70 sec. However, by incorporating varying amounts of powdered friction reducer polymer (i.e. Granule Polyacrylamide (GP)) in the Emulsion Polymer (EP) as described in Examples 3c, 3d and 3e, the maximum friction reduction is 73% and the inversion time is significantly faster (21-22 sec) compared to the Example 3b formulation which does not include the Granule Polyacrylamide (GP), but only includes Emulsion Polymer (EP).

(22) FIG. 2 illustrates the slower inversion rates of the Example 3a and 3b formulations compared to the formulations of Examples 3c to 3e, which include various amounts of Granule Polyacrylamide (GP). In addition, the Example 3c to 3e formulations, each of which contains about 20 wt % powdered polyacrylamide and varying amounts of organophilic clay, show near identical performance with all three curves in FIG. 2 lying on top of one another.

Example 4—Assessment of Formulations (Second Set of Experiments)

(23) In a second set of experiments, testing of formulations detailed in Table 3 was undertaken following the procedure of Example 3, but using, as a base line, 0.25 gpt of a formulation which only includes Emulsion Polymer (EP). This is Example 4a (comparative). This is compared to Example 4b (comparative) which uses a reduced concentration of 0.1 gpt of Emulsion Polymer (EP) formulation and to a concentration of 0.1 gpt of Blends A-1, A-2 and A-3 as described in Examples 4c, 4d and 4e. Table 3 below summarises details of the formulations used in the experiments and results obtained which are represented graphically in FIG. 2.

(24) TABLE-US-00004 TABLE 3 Inversion Max % Example Formulation Loading Viscosity Time Friction No. Identifier (gpt) (cP) pH (sec) Reduction 4a Emulsion 0.25 0.98 8.09 70 69 (Comparative) Polymer (EP) 4b Emulsion 0.1 0.84 8.12 108 53 (Comparative) Polymer (EP) 4c Blend A-1 0.1 0.99 7.98 27 72 4d Blend A-2 0.1 0.99 8.16 29 72 4e Blend A-3 0.1 0.97 8.02 28 73

(25) The results detailed in Table 2 and FIG. 3 show, for Example 4a (which includes only the Emulsion Polymer (EP) at 0.25 gpt), a 60% maximum friction reduction and a 70 sec inversion time. When dropping the loading to 0.1 gpt of Emulsion Polymer (EP) (Example 4b), the performance suffered, with the maximum friction reduction declining to 53% and the inversion time increasing to 108 sec—both of these factors would cause high pumping pressure on a fracturing treatment. In contrast, Examples 4c, 4d and 4e show that Blends A-1, A-2 and A-3 provide 72% maximum friction reduction with an inversion time of 27-29 sec which results are superior to those for Examples 4a and 4b and even superior to Example 3a (Comparative) which uses Emulsion Polymer (EP) at the much higher loading of 0.5 gpt.

Example 5—Assessment of Formulations (Third Set of Experiments)

(26) The procedure of Example 3 was repeated using a higher flow rate of 10 gal/min. The results are detailed in Table 4 below and FIG. 3 and compare use of base emulsions (Emulsion Polymer (EP)) (Examples 5a and 5b) with formulations comprising blends of Emulsion Polymer (EP) and Granule Polymer (GP).

(27) Results show use of Emulsion Polymer (EP) alone at 0.5 gpt (Example 5a) produces 72% maximum friction reduction and 106 sec inversion. Reducing the loading of Emulsion Polymer (EP) to 0.25 gpt (Example 5b) produces 59% maximum reduction and an inversion time of 141 sec. In contrast, formulations which include Emulsion Polymer (EP) and Granule Polyacrylamide (GP) at 0.25 gpt shows 73-76% maximum reduction and an inversion time of 19-28 sec, this being both more effective and more affordable than higher loadings of the base emulsion.

Example 6—Assessment of Formulations (Fourth Set of Experiments)

(28) In the next experiment, the performance of Blend A-2 is compared to Blend B-1. The test was conducted at a flow rate of 10 gal/min using 0.25 gpt and 0.1 gpt of the emulsions. The data is shown in Table 4. As per the table, there are slight differences between blends B-1 and A-2 at 0.25 gpt. However, Blend A-2 gave slightly better performance than blend B-1 at 0.10 gpt loading.

(29) TABLE-US-00005 TABLE 4 Inversion Max % Example Formulation Loading Viscosity Time Friction No's Identifier (gpt) (cP) pH (sec) Reduction 6a Blend B-1 0.10 1.0 8.36 25 72 6b Blend A-2 0.10 0.96 8.17 26 74 6c Blend B-1 0.25 1.16 8.22 20 76 6d Blend A-2 0.25 1.18 8.10 19 76

(30) Results are also summarised in FIG. 5.

(31) As an alternative to the Granule Polyacrylamide (GP) being mixed with Emulsion Polymer (EP), the Granule Polyacrylamide (GP) may be added to other non-aqueous additives which are used in fracturing process. These may include non-aqueous guar slurries and non-aqueous cross-linking agents.

Example 7—Use in Horizontal Well

(32) The product blend defined in Example 1 as Blend A-1 was used on several horizontal wells as a way to achieve a significant decrease in treating pressure during the hydraulic fracturing completion process. A particular well was 12,300 ft and constructed with 5.5 inch diameter casing. The fracture design for these wells led with 8,400 gal slickwater pad followed by roughly 483,000 gal of slickwater fluid at a rate of 3,780 to 4,200 gal treating fluid per min using Blend A-1 to displace 600,000+ lbs of frac sand. The Blend A-1 product was pumped at rates ranging from 0.7 to 1.0 gal/1000 gal treating fluid, depending on treating pressure. In addition to the friction reducer, the treating fluid also comprised 0.15 gal/1000 gal organophosphonate scale inhibitor and 0.25 gal/1000 gal 50% aqueous glutaraldehyde solution as a biocide. The frac sand proppant concentration was ramped upward through the job from 0.5 to 2.25 lb/gal added.

(33) Blend A-1 was provided in 330 gal plastic “one-way” totes plumbed from the bottom of the tote via a 2″ cam lock connection. The totes were located on top of a flat-bed trailer or a tote rack which utilized the hydrostatic pressure to aid in product flow to the chemical pump. The 2 inch diameter chemical hoses were then run from the tote to a medium range Waukesha pump. A diaphragm pump was used at times to prime the chemical line, depending on distances from the chemical injection pumps. Once the line was primed, the diaphragm pump was removed. The preferable injection point for Blend A-1 was the suction side of the blender discharge pump. However, the pumping company blender did not have an available port, so Blend A-1 was pumped from the Waukesha pump into the tub portion of the pumping company's blender. The Waukesha pumps discharge the product through the 2 inch diameter chemical lines roughly 20 ft to the blender tub.

(34) Blend A-1 was pumped as the only friction reducer and achieved the operator's goal of significant reduction of treating pressure. The treating pressures range from 7,500-9,500 psi, averaging 8,800-9,200 psi at 3,780 to 4,200 gal of treating fluid per min. This pressure at these injection rates was a significant improvement over conventional emulsion-based friction reducers, typically these having the same pressures at lower rates, such as 2,940 to 3,360 gal per min.

(35) It will be appreciated from the above examples that use of formulations comprising Emulsion Polymer (EP) and Granule Polyacrylamide (GP), are significantly advantageous over use of Emulsion Polymer (EP) alone. For example, the time taken between initial introduction of the formulations into water and maximum friction reduction is lower than when Emulsion Polymer (EP) alone is used and the maximum % friction reduction achieved for the formulations is higher than for an equivalent loading of Emulsion Polymer (EP) alone. The aforementioned allows pumps used to inject fracturing fluids incorporating the formulations to be operated at reduced speeds and/or pressures; or greater friction reduction may be achieved for a given pump speed/pressure, thereby allowing fracture fluids to be delivered at a higher pressure at the fracture face.

(36) Additionally, since the formulations described use less of relatively costly Emulsion Polymer (EP), friction reducer costs can be significantly reduced without the need for specialist field equipment and associated fuel and personnel costs.

(37) The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.