Multiphase polymer suspension and use thereof

Abstract

The present invention relates to an aqueous multiphase particulate suspension comprising a water-soluble polymer and to an enhanced oil recovery method using said suspension. The invention further relates to the use of the multiphase suspension in a drilling, hydraulic fracturing and mining effluent treatment operation.

Claims

1. An aqueous particulate multiphase suspension comprising: 15 to 60% by weight of at least one water-soluble polymer in the form of solid particles with average size comprised between 5 and 500 μm; 15 to 45% by weight of a mixture of CaCl.sub.2 and CaBr.sub.2 having a weight ratio CaCl.sub.2:CaBr.sub.2 of between 10:1 and 1:2; at least one viscosifying agent other than the water-soluble polymer; at least 10% by weight of water; and said suspension having a Brookfield viscosity comprised between 500 and 20,000 cps, and said suspension having a density comprised between 1.1 and 2 kg/l.

2. The particulate multiphase suspension according to claim 1, wherein the particulate multiphase suspension contains less than 1% by weight of solvent, and less than 0.5% by weight of surfactant.

3. The multiphase particulate suspension according to claim 1, wherein the average size of the particles of water-soluble polymer is between 10 μm and 400 μm.

4. The multiphase particulate suspension according to claim 1, wherein the water-soluble polymer is an acrylamide-based anionic polymer, optionally at least partially post-hydrolyzed, and wherein the water-soluble polymer has a molecular weight of between 2 and 40 million g/mol.

5. The multiphase particulate suspension according to claim 1, wherein the viscosifying agent other than the water-soluble polymer is a cellulose derivative.

6. The multiphase particulate suspension according to claim 1, wherein the quantity of viscosifying agent other than the water-soluble polymer is between 0.01 and 5%.

7. The multiphase particulate suspension according to claim 1, wherein the density of the suspension is between 1.3 and 1.9 kg/l.

8. A process for enhanced oil recovery comprising the following steps: preparing an injection fluid by mixing an aqueous particulate multiphase suspension according to claim 1 with water or a brine; injecting the injection fluid into a reservoir; and recovering an aqueous and oily and/or gaseous mixture.

9. The process according to claim 8, wherein the mixing of the suspension and the water or brine is done for less than 1 hour.

10. The process according to claim 8, wherein the multiphase suspension is mixed with water or a brine containing fewer salts than the multiphase suspension to yield an intermediate composition, said intermediate composition next being mixed with water or a brine containing fewer salts than the multiphase suspension to yield the injection fluid.

11. The process according to claim 8, wherein the multiphase suspension is added on-line in a pipe transporting water or a brine forming an injection fluid, said injection fluid being injected directly into the reservoir, with no mixing step other than the turbulences in the pipe.

12. The process according to claim 8, wherein the mixing between the multiphase suspension and the water or brine is done partially in a static or dynamic mixer, or in an agitated tank, or in a dispersion device for particulate polymer suspension.

13. The process according to claim 8, wherein the mixing of the suspension and the water or brine is done for less than 10 minutes.

14. The multiphase particulate suspension according to claim 1, wherein the ratio between CaCl.sub.2) and CaBr.sub.2 is between 8:1 and 2:1.

15. The multiphase particulate suspension according to claim 5, wherein the viscosifying agent other than the water-soluble polymer is hydroxyethyl cellulose.

16. A process for treating a mining effluent, comprising the following steps: combining the suspension according to claim 1, or an aqueous solution prepared from said suspension, with a mining effluent; and discharging the effluent thus treated into an aquatic zone, near the water level or below the water level, such that the treated effluent flows and falls into the aquatic zone in which the solid part settles at the bottom and the aqueous part is in the water of the aquatic zone.

17. The multiphase particulate suspension according to claim 1, wherein the average size of the particles of water-soluble polymer is between 50 μm and 200 μm.

18. The multiphase particulate suspension according to claim 4, wherein the water-soluble polymer is selected from a copolymer of acrylamide and acrylamide tertiary butyl sulfonic acid (ATBS) optionally at least partially post-hydrolyzed, and a terpolymer of acrylamide, acrylic acid and acrylamide tertiary butyl sulfonic acid (ATBS), optionally at least partially post-hydrolyzed.

Description

(1) The invention and resulting benefits will become clearer from the following examples, supported by the figures.

(2) FIG. 1 is a graph showing the evolution of the head loss as a function of the quantity of injection fluid measured in volume equivalent to the pore volume, for an injection fluid A containing 2000 ppm of water-soluble polymer, and prepared from suspension of particles of terpolymer of acrylamide, acrylic acid and ATBS with a molecular weight of 12 million g/mol, suspended in an oil.

(3) FIG. 2 is a graph showing the evolution of the head loss as a function of the quantity of injection fluid measured in volume equivalent to the pore volume, for an injection fluid B containing 2000 ppm of water-soluble polymer, and prepared from a particulate multiphase suspension according to the invention and in which the water-soluble polymer is an acrylamide, acrylic acid and ATBS terpolymer with a molecular weight of 12 million g/mol.

EXAMPLES

(4) The injection of polymer into a porous medium is a good method for ensuring the good propagation of molecules within the reservoir with minimal damage. Injectivity is evaluated through the measurement of head losses continually recorded via pressure sensors placed on either side of the system.

(5) A good propagation generally results in a rapid stabilization of the head losses over time. Conversely, a steady pressure climb is proof of gradual plugging of the porous medium, which can cause irreversible damage to the reservoir and the impossibility of continuing the injection, resulting in shutting down the enhanced oil recovery process.

(6) Injection of the injection fluids was done with water-saturated Bentheimer-type rocks.

(7) The procedure used is described below: Preparing the Bentheimer rock specimen (9 cm long, 2.4 cm diameter). The sample is dried in an oven at 50° C. overnight, then the dry weight measured; Saturating the rock sample with synthetic seawater containing 30,000 ppm of NaCl and 3000 ppm of CaCl.sub.2, using a vacuum pump. The wet weight is recorded and the porous volume deduced; The rock sample is placed in a sleeve within a sealed cell of the Hassler type at ambient temperature. A back-pressure of 30 bar is applied in the cell to constrain the rock in the sleeve; Different brine flow rates are applied using a pump, and the head losses within the porous medium are read. Permeability of the rock is calculated using Darcy's law; Q is the flow rate (cm.sup.3/s) K is the permeability (Darcy) (P1-P2) is the head loss within the specimen (atm/cm)

(8) $Q=\frac{K\left(P1-P2\right)A}{\mu L}$
where:  A represents the section of the rock specimen (cm.sup.2) μ is the viscosity of the injected fluid (centipoise) L is the length of the rock specimen (cm) Next, the injection of the injection fluid is done over several porous volumes (15) at a concentration of 2000 ppm. A porous volume corresponds to the empty volume within the rock, calculated by subtracting the dry weight from the wet weight of the rock.

(9) The head loss is recorded continuously. This results in a graph with the head losses in mbar on the y-axis and the number of injected porous volumes on the x-axis. The injections are done at 25° C.

(10) In both of the following cases, the average particle size of the water-soluble polymer is 160 μm.

(11) In a counterexample, an injection fluid A is prepared from a mixture of particles of acrylamide, acrylic acid and ATBS terpolymer having a molecular weight of 12 million g/mol, suspended in an oil doped with bentonite, said suspension comprising 30% by weight of polymer and 66% of organic solvent (Exxsol D100), and 4% by weight of bentonite.

(12) The injection profile of injection fluid A shows a constant increase in the head loss. This increase demonstrates the poor propagation of injection fluid A, which gradually plugs the rock. Applied in an oil field, this can cause irreversible damage and lead to a total loss of injectivity.

(13) In one example according to the invention, an injection fluid B is prepared from a particulate multiphase suspension according to the invention of particles of acrylamide acrylic acid and ATBS terpolymer having a molecular weight of 12 million g/mol, said suspension comprising (by weight): 36% terpolymer, 25% CaCl.sub.2, 18% CaBr.sub.2, and 0.05% hydroxyethyl cellulose.

(14) The injection profile of injection fluid B shows a stabilization of the head loss after the injection of fluid volume equivalent to 3 pore volumes. The head loss next remains stable during injection, demonstrating a very good propagation of injection fluid B.

(15) The multiphase suspension according to the invention has the advantage of being stable for more than 6 months. It does not contain any solvent or surfactant that can be harmful during injection. It is prepared quickly without the need for a complex solution preparation device.

(16) The use of this multiphase particulate suspension in an enhanced oil recovery method makes it possible to simplify the preparation step of the injection fluid and makes it possible to achieve excellent results in injectivity.