Fracturing fluids based on associative polymers and on labile surfactants

Abstract

The present invention relates to a fracturing fluid comprising, in an aqueous medium: an associative polymer; and a labile surfactant, in an amount sufficient to reduce or inhibit the effect of increasing the viscosity induced by said associative polymer.

Claims

1. A process for recovery of hydrocarbons in a hydrocarbon reservoir, comprising a step where a fracturing fluid comprising, in an aqueous medium: an associative polymer suitable for increasing the viscosity of the aqueous medium; and a labile surfactant, wherein the labile surfactant comprises an ethoxylated fatty acid ester, in an amount sufficient to reduce or inhibit the effect of increasing the viscosity induced by said associative polymer; is injected into a hydrocarbon reservoir where the temperature and/or pH conditions are suitable for lyzing all or some of the labile surfactant; wherein the associative polymer is made by micellar radical polymerization in which the following are placed in contact, in an aqueous medium: hydrophilic monomers, dissolved or dispersed in said aqueous medium; hydrophobic monomers, in the form of a micellar solution that comprises micelles of such hydrophobic monomers dispersed in the aqueous medium; at least one radical polymerization initiator; and at least one radical polymerization control agent.

2. The process according to claim 1, wherein the labile surfactant comprises an ethoxylated fatty acid ester of formula RCOO(CH.sub.2CH.sub.2O).sub.nH, where R is a linear or branched hydrocarbon chain.

3. The process according to claim 1, wherein the associative polymer is present in an amount of 0.1% to 3% by weight relative to the total weight of the fracturing fluid.

4. The process according to claim 1, wherein the micelles further comprise at least one surfactant.

5. The process according to claim 1, wherein the initiator comprises a water-soluble or water-dispersible initiator.

6. The process according to claim 1, wherein the radical polymerization control agent comprises a thiocarbonylthio group.

7. The process according to claim 6, wherein the radical polymerization control agent is a xanthate compound.

Description

EXAMPLE

Synthesis of an Associative Polymer (Poly Acrylamide/AMPS/LMA 2 000 000 g/Mol)

(1) 29.3 g of a 30% SDS solution, 89.03 g of distilled water and 1.66 g of lauryl methacrylamide (LMA monomer) were introduced into a 500 ml round-bottomed flask at room temperature (20 C.). The mixture was stirred using a magnetic stirrer bar for 6 hours, until a clear micellar solution was obtained.

(2) 32.9 g of the micellar solution thus prepared, 7.53 g of water, 40.7 g of acrylamide (aqueous solution at 50% by weight), 32 g of AMPS (aqueous solution at 51% by weight), 0.454 g of Rhodixan A1 (ethanol solution at 1.0% by weight) and 6.00 g of ammonium persulfate (aqueous solution at 0.67% by weight) were introduced into a 250 ml round-bottomed flask at room temperature (20 C.). The mixture was degassed by sparging with nitrogen for 20 minutes. 1.5 g of sodium formaldehyde sulfoxylate, in the form of an aqueous solution at 0.13% by weight, were added to the medium, in a single portion. The mixture was degassed by sparging with nitrogen for 15 minutes.

(3) The polymerization reaction was then left to proceed with stirring for 16 hours at room temperature (20 C.).

(4) Reduction in the Viscosity by Addition of Labile Surfactant

(5) The polymer prepared above was placed in solution at 0.5% by weight of polymer in an aqueous solution of NaCl at 15% by weight in the presence of Alkamuls PSML20 labile surfactant at various concentrations.

(6) For each of the concentrations, the viscosity of the mixture was measured at 80 C., using an AR2000 rheometer (TA Instruments, Surrey, Great Britain), equipped with a Couette-type geometry. The results are reported in the table below:

(7) TABLE-US-00001 viscosity concentration at 1 s.sup.1 (ppm) (mPa .Math. s) 0 3430 50 1140 100 360 250 168 500 48 1000 10

(8) The reduction in viscosity by addition of labile surfactant is demonstrated here above 500 ppm.

(9) Hydrolysis of the Labile SurfactantEffect on the Viscosity

(10) The polymer from example 1 was placed in solution at 0.5 wt % in 15% NaCl in the presence of 0.5% Alkamuls PSML20. Sodium hydroxide is added in order to obtain a concentration of 83 mmol/I. The viscosity of the solution thus obtained is 10 cP at 25 C. (at 1 s.sup.1).

(11) The solution was placed in an oven at 80 C. for 16 h. At the end of this treatment, the viscosity of the solution was measured as equal to 4200 cP at 1 s.sup.1 (versus 3600 cP for a polymer solution without surfactant obtained after hydration by heating for 4 h at 80 C.).