Aqueous fracturing fluid composition and fracturing process using the composition

Abstract

Fracturing fluid comprising, in solution in water, a proppant and an associative amphoteric polymer, the said polymer and comprising: 0.01 to 10 mol % of at least one cationic monomer containing a hydrophobic chain, from 0.09 to 89.99 mol % of at least one anionic monomer, and from 10 to 99.9 mol % of at least one nonionic water-soluble monomer, the total amount of monomer being 100 mol %. Fracturing process using this fluid.

Claims

1. A fracturing fluid comprising a proppant and an associative amphoteric polymer, the said polymer comprising: 0.01 to 10 mol % of at least one cationic monomer containing a hydrophobic chain; from 0.09 to 89.99 mol % of at least one anionic monomer; and from 10 to 99.9 mol % of at least one nonionic water-soluble monomer; the total amount of monomer being 100 mol %, wherein the at least one cationic monomer containing a hydrophobic chain has general formula I: ##STR00002##  in which: R.sub.1 is an alkyl or arylalkyl chain of 16 to 18 carbons, X is a halide chosen from the group consisting of bromide, chloride, iodide, fluoride, and a counterion of negative charge.

2. The fracturing fluid according to claim 1, comprising up to 500 ppm of at least one surfactant.

3. The fracturing fluid according to claim 2, wherein R.sub.1 is a linear alkyl chain of 16 to 18 carbons.

4. The fracturing fluid according to claim 1, wherein R.sub.1 is an alkyl chain of from 16 to 18 carbons.

5. The fracturing fluid according to claim 4, wherein R.sub.1 is a linear alkyl chain of 16 to 18 carbons.

6. The fracturing fluid according to claim 1, wherein X is chloride.

7. The fracturing fluid according to claim 1, wherein the proppant is chosen from the group consisting of sand, ceramic, bauxite, glass beads and resin-impregnated sand.

8. The fracturing fluid according to claim 1, wherein the proppant represents from 0.5% to 40% of the fluid.

9. The fracturing fluid according to claim 8, wherein the proppant represents from 1% to 25% of the fluid.

10. The fracturing fluid according to claim 9, wherein the proppant represents from 1.5% to 20% by weight of the fluid.

11. The fracturing fluid according to claim 1, wherein the associative amphoteric polymer represents from 0.05% to 2% by weight of the fluid.

12. The fracturing fluid according to claim 11, wherein the associative amphoteric polymer represents from 0.1% to 1% by weight of the fluid.

13. The fracturing fluid according to claim 12, wherein the associative amphoteric polymer represents from 0.1% to 0.75%, by weight of the fluid.

14. The fracturing fluid according to claim 1, wherein the associative amphoteric polymer has an average molecular weight by weight comprised between 1 million g/mol and 30 million g/mol.

15. The fracturing fluid according to claim 1, wherein the anionic monomer is selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, crotonic acid, maleic acid, fumaric acid, 2-acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, vinylphosphonic acid, allylsulfonic acid, allylphosphonic acid, styrenesulfonic acid, alkali metal, alkaline-earth metal and ammonium salts thereof, and mixtures thereof.

16. The fracturing fluid according to claim 1, wherein the nonionic monomer is selected from the group consisting of acrylamide, methacrylamide, N-isopropylacrylamide, N,N-dimethylacrylamide, N-tert-butylacrylamide, N-vinylformamide, N-vinylacetamide, N-vinylpyridine and/or N-vinylpyrrolidone, acryloylmorpholine, acryloylpyrrolidone, alkyl-polyethylene glycol methacrylates, and mixtures thereof.

17. The fracturing fluid according to claim 1, wherein the associative amphoteric polymer comprises: from 0.05 to 5 mol % of hydrophobic cationic monomer of formula (I), from 5 to 54.95 mol % of at least one anionic monomer selected from acrylic acid, methacrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and salts thereof, and from 45 to 90 mol % of at least one water-soluble nonionic monomer selected from acrylamide, N-isopropylacrylamide, N-N-dimethylacrylamide, N-tert-butylacrylamide, N-vinylformamide, N-vinylpyrrolidone, acryloylmorpholine, and acryloylpyrrolidone, the total amount of monomer being 100 mol %.

18. The fracturing fluid according to claim 1, wherein the associative amphoteric polymer comprises: from 0.05 to 2 mol % of hydrophobic cationic monomer of formula (I), from 5 to 24.95 mol % of 2-acrylamido-2-methylpropanesulfonic acid or a salt thereof, from 0 to 30 mol % of acrylic acid or a salt thereof, and from 45 to 90 mol % of acrylamide, the total amount of monomer being 100 mol %.

19. A process for fracturing an unconventional oil or gas reservoir, said process comprising: preparing the fracturing fluid according to claim 1, and injecting the fracturing fluid according to claim 1 into an oil or gas reservoir under pressure so as to create fractures distributed perpendicularly to a production well.

20. The process according to claim 19, wherein, after said injecting the fracturing fluid, at least one oxidizing compound and/or at least one surfactant is then injected into the reservoir.

Description

EXAMPLES

(1) 1/Preparation of the Polymer by Gel Polymerization

(2) In a beaker, dissolve x mol % of a hydrophobic cationic monomer, y mol % of acrylic acid, z mol % of acrylamide in water to obtain a 30 wt % active ingredient content. The aforementioned additives may advantageously be added at this point to improve the solubilization of the monomers. The sum of x+y+z is equal to 100. The solution is then stirred, cooled and neutralized by adding soda. The solution is then placed in a Dewar vessel and degassed with a nitrogen flow to remove oxygen.

(3) Polymerization is initiated using Ter-butyl hydroperoxide/sodium persulfate as red/ox pair. The temperature rises adiabatically.

(4) The resulting polymer is then isolated by filtration, dried, grinded and sieved to obtain a powder.

(5) The polymers of the present invention are numbered from 1 to 4. The respective comparative polymers made according to WO 2013/150203 are numbered from 5 to 8. For comparative purposes, a non-associative anionic polymer of very high molar mass is also evaluated: polymer 9, an amphoteric and non-associative polymer as described in WO 02/084075: polymer 10,

(6) The monomeric composition of polymers 1 to 10 is described in table 1.

(7) TABLE-US-00001 TABLE 1 Monomeric composition of polymers 1 to 10 in mol %. Associative Associative monomer of monomer of the invention, C.sub.12H.sub.25 type Mw ATBS R.sub.1 = C16 linear described in WO (millions Products AM ANa Na DADMAC alkyl chain 2013/150203 g/mol) Polymer 1 85 14.8 0 0 0.2 0 6-8 (Invention) Polymer 2 85 0 14.8 0 0.2 0 4-7 (Invention) Polymer 3 85 4.8 10 0 0.2 0  7-10 (Invention) Polymer 4 80 4.8 15 0 0.2 0 6-8 (Invention) Polymer 5 85 14.8 0 0 0 0.2 6-8 (Comparative) Polymer 6 80 0 14.8 0 0 0.2 4-7 (Comparative) Polymer 7 85 4.8 10 0 0 0.2  7-10 Comparative) Polymer 8 80 4.8 15 0 0 0.2 6-8 (Comparative) Polymer 9 75 25 0 0 0 0 18-20 (Comparative) Polymer 10 80 18 0 2 0 0 6-8 (Comparative)

(8) AM: Acrylamide

(9) ANa: Sodium Acrylate

(10) DADMAC: Diallyl dimethyl Ammonium Chloride

(11) ATBS Na: Sodium acrylamido-tert-butyl sulfonate

(12) 2/Preparation of the Aqueous Polymer Solution

(13) The dry extract of the polymer is determined in order to know the percentage of active material: weigh accurately to within 0.001 g a glass vial. Note this mass M.sub.C. Weigh out 10 g of powder in a glass vial and notes the cumulative mass M.sub.C+P. Place this glass vial in an oven at 120° C. for 2 hours. After the 2 hours at 120° C., allow the vial to cool in a desiccator. Weigh the vial with the mass of dry recovered solid, noted M.sub.C+PS. The percentage of dry matter X is given by the calculation:
X=[(M.sub.C+PS−M.sub.C)/(M.sub.C+P−M.sub.C)]*100 expressed as a percentage

(14) The polymer solution is prepared according to the following general protocol:

(15) Preparation of a Stock Solution Containing 10 g/L of Polymer (Product of the Invention or Guar Gum in Powder Form)

(16) Weigh out 200-(20/(X/100)) g of brine, representative of the injection water used on a fracturing field, in a 400 mL beaker. Using a mechanical stirrer, stir the solution at a speed of 500 rpm. 20/(X/100) g of dry polymer in powder form are added slowly in the vortex wall formed by the stirring at room temperature. The solution is left stirring for 2 hours.

(17) Dilution of the Stock Solution to Obtain a Solution Diluted to a Final Polymer Concentration of Y %

(18) Y*100 g of the 10 g/L stock solution are taken up by syringe and transferred into a 400 mL beaker. 100-Y g of brine prepared beforehand are added to beaker. The solution is then stirred using a magnetic bar at 250 rpm for 20 minutes.

(19) 3/Rheological Evaluation of the Polymers

(20) Polymers 1 et 10 and a guar gum Ecopol™ 500 are evaluated. This guar gum corresponds to guar gum used on fracturing fields in the United States.

(21) The rheological properties are determined using for example a Malvern Bohlin Gemini rheometer with cone/plate geometry of angle 2°, 6 cm in diameter. A Peltier heating and cooling system is used to be able to take measurements at different temperatures.

(22) The polymers and the guar gum are tested at two temperatures: 40° C. and 70° C., and in two different brines. The first brine contains 10 g/L of NaCl and 2 g/L of CaCl.sub.2, and the second brine contains 40 g/l of NaCl and 4 g/L of CaCl.sub.2. The polymer concentration is 2000 ppm by weight. For each rheological test the viscosity at shear rates of 1 s.sup.−1 and 10 s.sup.−1 are noted such as the viscosity loss in percentage, and Table 2 to 5 recapitulate the results in each condition.

(23) TABLE-US-00002 TABLE 2 Viscosity at 40° C. with brine 10 g/L of NaCl and 2 g/L of CaCl.sub.2. Viscosity Viscosity Viscosity at 1 s.sup.−1 at 10 s.sup.−1 loss (%) Polymer 1 290 195 32.8 Polymer 2 580 400 31 Polymer 3 1160 760 34.5 Polymer 4 2070 1350 34.8 Polymer 5 210 80 61.9 Polymer 6 450 210 53.3 Polymer 7 890 350 60.7 Polymer 8 1550 420 72.9 Polymer 9 90 44 51.1 Polymer 10 74 36 51.4 Ecopol ™ 500 40 18 55

(24) TABLE-US-00003 TABLE 3 Viscosity at 70° C. with brine 10 g/L of NaCl and 2 g/L of CaCl.sub.2. Viscosity Viscosity Viscosity at 1 s.sup.−1 at 10 s.sup.−1 loss (%) Polymer 1 221 156 29.4 Polymer 2 671 450 32.9 Polymer 3 957 620 35.2 Polymer 4 1612 1050 34.9 Polymer 5 168 72 57.1 Polymer 6 360 170 52.8 Polymer 7 712 290 59.3 Polymer 8 1240 150 63.7 Polymer 9 72 36 50 Polymer 10 59.2 28 52.7 Ecopol ™ 500 32 14 56.3

(25) TABLE-US-00004 TABLE 4 Viscosity at 40° C. with brine 40 g/L of NaCl and 4 g/L of CaCl.sub.2. Viscosity Viscosity Viscosity at 1 s.sup.−1 at 10 s.sup.−1 loss (%) Polymer 1 196 141 28.1 Polymer 2 413 279 32.4 Polymer 3 800 525 34.4 Polymer 4 1503 1010 32.8 Polymer 5 147 62 57.8 Polymer 6 315 138 56.2 Polymer 7 623 235 62.3 Polymer 8 1085 410 62.2 Polymer 9 63 31 50.8 Polymer 10 51.8 25 51.7 Ecopol ™ 500 28 13 53.6

(26) TABLE-US-00005 TABLE 5 Viscosity at 70° C. with brine 40 g/L of NaCl and 4 g/L of CaCl.sub.2. Viscosity Viscosity Viscosity at 1 s.sup.−1 at 10 s.sup.−1 loss (%) Polymer 1 185 122 34.1 Polymer 2 384 251 34.6 Polymer 3 678 450 33.6 Polymer 4 1365 890 34.8 Polymer 5 126 54 57.1 Polymer 6 270 118 56.3 Polymer 7 534 210 60.7 Polymer 8 930 356 61.7 Polymer 9 54 25 53.7 Polymer 10 44.4 21 52.7 Ecopol ™ 500 24 11 54.2

(27) From these results, we note that all conditions being equal, the use of the hydrophobic cationic monomer of the invention allows a significant improvement of the rheological properties of the polymers of the prior art. More precisely, in all conditions of salinity and temperature, when polymers 1 to 4 are compared to respective polymer 5 to 8, it is showed that the performances are improved.

(28) The polymers of the invention (1 to 4) give better results in terms of rheologic properties in all the conditions compared to the polymer 9 and 10. They are also better than the guar gum Ecopol™ 500.

(29) The polymers of the invention also offer lower viscosity loss than the prior art polymers. Viscosity loss is below 35% for polymers 1 to 4, whereas the viscosity loss is always higher than 50%, sometimes higher than 60% for prior art polymers. A lower viscosity between the viscosity at 1 s.sup.−1 and viscosity at 10 s.sup.−1 is favorable in the fracturing operation because the polymer has a more stable behavior in the formation and gives better and more predictable performances.

(30) In contrast, it is known that at a higher shear rate stage, it is better to have low viscosity to ensure good pumping properties. It has been found that at high shear rate (50 s.sup.−1 to 100 s.sup.−1), the viscosities are low for all the evaluated products.

(31) These results show that the polymers of the invention (1 to 4) are very good candidates for fracturing application because they are able to keep the proppant in suspension, even when the temperature and the salinity of the reservoir are high and ensure good pumping of the injected fluid.

(32) 4/Degradation of the Viscosity by Adding Surfactant After Fracturing

(33) During the production step, once the sand has been inserted, the viscosity of the polymer must be lowered in order to facilitate the placing of the sand in the fractures. Generally, the injection of oxidizing agent is used to destroy the polymer and to re-establish a fluid viscosity close to that of water.

(34) In order to demonstrate the impact of the surfactants on the polymer solutions in the presence of sand, the same sedimentation protocol was used. A 10 wt % solution of surfactant (sodium dodecyl sulfate (SDS)) is added (5 g, i.e. 2000 ppm) with stirring 30 seconds before the transfer into the measuring cylinder. The time corresponding to total sedimentation of the sand is recorded and is given in the following table 6:

(35) TABLE-US-00006 TABLE 6 Sedimentation Test with SDS. Products Sedimentation time for the 20 g of sand Ecopol 500 Less than 2 minutes Polymer 1 Less than 2 minutes Polymer 2 Less than 2 minutes Polymer 3 Less than 2 minutes Polymer 4 Less than 2 minutes Polymer 5 Less than 2 minutes Polymer 6 Less than 2 minutes Polymer 7 Less than 2 minutes Polymer 8 Less than 2 minutes Polymer 9 Less than 2 minutes Polymer 10 Less than 2 minutes

(36) It is noted by comparing this table with the preceding results that the addition of a sufficient quantity of SDS after fracturing drastically reduces the sand sedimentation time. It is thus advantageous to use the polymer of the present invention for its sand proppant properties, but also for the ease of subsequently reducing the viscosity of the solution by adding surfactant after fracturing.

(37) It is to be noted that the same very good performances, superior to the prior art polymers, are obtained with the same associative monomer wherein R.sub.1=C18 linear alkyl chain, and with mixtures of thereof.