METHOD FOR INHIBITING WATER PERMEATION IN AN EXTRACTION WELL OF A HYDROCARBON FLUID FROM AN UNDERGROUND RESERVOIR

Abstract

A method for inhibiting water permeation in an extraction well of a hydrocarbon fluid from an underground reservoir containing: supplying a water-in-oil emulsion an oily continuous phase and an aqueous discontinuous phase containing a plurality of particles of at least one hydrogel containing a cationic polymer; and positioning the water-in-oil emulsion in contact with the underground reservoir. The present invention also concerns a treatment fluid for hydrocarbon fluid extraction wells containing the aforementioned water-in-oil emulsion and the related preparation process.

Claims

1. A method for inhibiting water permeation in an extraction well of a hydrocarbon fluid from an underground reservoir, the method comprising: supplying a water-in-oil emulsion comprising: an oily continuous phase, and an aqueous discontinuous phase comprising a plurality of particles of at least one hydrogel comprising a cationic polymer; and positioning the water-in-oil emulsion in contact with the underground reservoir.

2. The method according to claim 1, wherein the cationic polymer comprises a monomeric unit having at least one cationic group.

3. The method according to claim 2, wherein the at least one cationic group is a —N.sup.+—R.sup.1R.sup.2R.sup.3 group, wherein R.sup.1, R.sup.2 and R.sup.3 are independently H or a C.sub.1-C.sub.4 alkyl group.

4. The method according to claim 1, wherein the cationic polymer comprises at least one monomeric unit corresponding to a monomer selected from the group consisting of a water-soluble salt of [2-(methacryloyloxy)ethyl] trimethylammonium and a water-soluble salt of 2-(acryloyloxy) ethyl trimethyl ammonium.

5. The method according to claim 4, wherein the cationic polymer comprises a comonomeric unit corresponding to a monomer selected from the group consisting of: poly(ethylene glycol)methyl ether acrylate, poly(ethylene glycol)methyl ether methacrylate, acrylamide and methacrylamide.

6. The method according to claim 5, wherein a weight ratio of the comonomeric unit and the monomeric unit is within a range of 5%-50%.

7. The method according to claim 5, wherein the cationic polymer comprises poly(ethylene glycol)methyl ether acrylate or poly(ethylene glycol)methyl ether methacrylate and the poly(ethylene glycol)methyl ether acrylate or poly(ethylene glycol)methyl ether methacrylate has a molecular weight within the range 200-10000 Da.

8. The method according to claim 1, wherein the cationic polymer is a cross-linked polymer.

9. The method according to claim 1, wherein the continuous phase is present in a ratio with respect to the aqueous discontinuous phase within a range of from 50:50 to 95:5 by weight.

10. The method according to claim 1, wherein the hydrogel particles have an average diameter within a range of 1-1000 micrometers.

11. The method according to claim 1, wherein the hydrogel particles have an average diameter within a range of 10-500 nanometers.

12. The method according to claim 1, comprising: a. positioning a first aliquot of an oily fluid in contact with the underground reservoir; b. positioning the water-in-oil emulsion; c. positioning a second aliquot of the oily fluid; d. injecting a displacement fluid for producing the hydrocarbon fluid.

13. A treatment fluid comprising a water-in-oil emulsion comprising: an oily continuous phase, an aqueous discontinuous phase comprising water and a plurality of particles of at least one hydrogel comprising a cationic polymer.

14. The treatment fluid according to claim 13, wherein the cationic polymer comprises a monomeric unit corresponding to a monomer having at least one cationic group.

15. The treatment fluid according to claim 14, wherein the at least one cationic group is a —N.sup.+—R.sup.1R.sup.2R.sup.3 group, wherein R.sup.1, R.sup.2 and R.sup.3 are independently H or a C.sub.1-C.sub.4 alkyl group.

16. The treatment fluid according to claim 13, wherein the cationic polymer comprises at least one monomer selected from the group consisting of: a halogen salt of [2-(methacryloyloxy)ethyl] trimethylammonium and a halogen salt of 2-(acryloyloxy)ethyl trimethylammonium.

17. A process for preparing a water-in-oil emulsion comprising: an oily continuous phase, an aqueous discontinuous phase comprising water and a plurality of particles of at least one hydrogel comprising a cationic polymer, the process comprising the following sequential steps: supplying an oily continuous phase comprising an oily fluid; supplying an aqueous discontinuous phase comprising water and a monomer having at least one cationic group; emulsifying the aqueous discontinuous phase in the oily continuous phase in the presence of at least one surfactant and at least one radical polymerization initiator forming free radicals to polymerize the monomer having at least one cationic group and optionally the comonomer.

18. The process according to claim 17, wherein the radical polymerization initiator is a thermally-activable initiator and the emulsifying is carried out by means of a mechanical stirrer at a temperature equal to or higher than an activation temperature of the thermally-activable initiator.

19. The process according to claim 17, wherein: the initiator comprises at least one redox initiators pair comprising an oxidant initiator and a reducing initiator, one of the oxidant initiator and reducing initiator being incorporated in one of the oily continuous phase and the aqueous discontinuous phase, the remaining initiator being added to the water-in-oil emulsion during the emulsification; the emulsification is carried out by means of ultrasound.

Description

EXAMPLE 1—PREPARATIONS OF INVERSE WATER-IN-OIL Emulsions Containing Cationic Microgels

[0143] Water-in-oil emulsions containing cationic microgels were prepared by inverse suspension polymerization according to the following procedure.

[0144] An oily continuous phase was prepared by mixing under mechanical stirring LAMIX 30 as an oily fluid and a mixture of the commercial non-ionic surfactants SPAN80 and TWEEN80. The weight ratio between the two surfactants was selected so as to cause the polymerization reaction at the desired HLB value.

[0145] In the specific example of an HLB value equal to 6, the SPAN80 surfactant was used with a massive concentration, referring to the sum of the two surfactants, equal to 84%.

[0146] An aqueous discontinuous phase was prepared by dissolving in water, with the aid of an ultrasonic sonicator and keeping the temperature below 50° C., a cationic monomer ([2-(methacryloxy))ethyl] trimethylammonium chloride—MADQUAT), a cross-linking agent (N,N′-methylenbis(acrylamide)—MBA) and optionally a (poly(ethylene glycol)methyl ether methacrylate comonomer of molecular weight 500 Da (PEGMEMA 500) or 2000 Da (PEGMEMA 2000)).

[0147] An aqueous solution of 2,2′-azobis(2-methylpropianimidine) dihydrochloride (AAPH) (thermally activatable radical polymerization initiator) was prepared separately, using a minimum amount of water sufficient to dissolve the compound.

[0148] The oily continuous phase and the aqueous discontinuous phase were mixed in a reactor with a volume equal to 2 liters, heated by means of a thermostatic oil bath. The mixing took place by means of a mechanical stirrer. The reactor was equipped with a water cooling jacket to remove the heat generated during the polymerization reaction. During polymerization, the reactor was kept under constant N.sub.2 flow so as to remove the air inside it.

[0149] The weight ratio between the aqueous discontinuous phase and the total weight of the water-in-oil emulsion was selected equal to 16% for the PEG2 sample and 18% for the PEG4 and PEG11 samples.

[0150] The polymerization reaction was initiated by pouring the solution of the AAPH initiator drop by drop into the reaction mixture, previously heated to the polymerization temperature, equal to 70° C. or 80° C. The reaction duration was selected equal to 2 hours or 2.5 hours.

[0151] The following Table 1 shows the compositions of the prepared inverse emulsions of microgels.

TABLE-US-00001 TABLE 1 Composition of the emulsions of microgels PEGMEMA PEGMEMA MADQUAT 500 2000 MBA AAPH Surfactants Sample (%).sup.a (%).sup.a (%).sup.a (%).sup.a (%).sup.c (%).sup.b HLB 1 100 — — 0.35 0.5 7.0 6 (A4).sup.d 2 95 — 5 0.35 0.5 5.0 4.3 (PEG2).sup.e 3 90 — 10 0.35 0.5 5.0 4.3 (PEG4).sup.e 4 92.5 7.5 — 0.35 0.5 5.0 4.3 (PEG11).sup.e .sup.apercentage by weight with respect to the weight of MADQUAT + PEGMEMA comonomers; .sup.bpercentage by weight referred to the total weight of the emulsion; .sup.cpercentage by weight with respect to the total weight of MADQUAT + PEGMEMA comonomers + MBA; .sup.dpolymerization temperature = 80° C.; polymerizationduration 2.5 hours; .sup.epolymerization temperature = 70° C.; polymerization duration 2.0 hours.

EXAMPLE 2—PREPARATION OF INVERSE WATER-IN-OIL EMULSIONS CONTAINING CATIONIC NANOGELS

[0152] Water-in-oil emulsions containing cationic nanogels were prepared by inverse miniemulsion polymerization according to the following procedure.

[0153] An oily continuous phase was prepared by mixing under mechanical stirring Eni LAMIX 30 as an oily fluid and a mixture of the commercial non-ionic surfactants SPAN80 and TWEEN80. The weight ratio between the two surfactants was selected so as to cause the polymerization reaction at the desired HLB value.

[0154] In the specific example of an HLB value equal to 10, the SPAN80 surfactant was used with a massive concentration, referring to the sum of the two surfactants, equal to 47%. An aqueous discontinuous phase was prepared by dissolving in water, with the aid of an ultrasonic sonicator and keeping the temperature below 50° C., a cationic monomer ([2-(methacryloxy))ethyl]trimethylammonium chloride MADQUAT), a cross-linking agent (N,N′-methylenbis(acrylamide)—MBA) and ammonium persulfate as a first initiator of the pair of redox initiators, ammonium persulfate (APS)/sodium metabisulfite (SMBS).

[0155] After conditioning the oily continuous phase in an ice bath (T equal to about 0-5° C.), the aqueous discontinuous phase was added to the oily continuous phase by keeping the mixture of the two phases under sonication. A SMBS aqueous solution was then added drop by drop to the mixture to initiate the polymerization reaction (polymerization duration 50 minutes).

[0156] The following Table 2 shows the compositions of the prepared inverse emulsions of nanogels.

TABLE-US-00002 TABLE 2 Composition of the emulsions of nanogels MADQUAT MBA APS SMBS Surfactants Sample (%).sup.a (%).sup.b (%).sup.b (%).sup.b (%).sup.b HLB 5 (MZ17) 35 0.35 2.5 2.5 21 10 .sup.apercentage by weight with respect to the weight of LAMIX 30 ®; .sup.bpercentage by weight with respect to the tota weight of MADQUAT.

3. Characterization of Emulsions of Microgels and Nanogels

3.1 Swelling Test

[0157] The capacity of water absorption of the prepared microgels were determined by measuring the average particle diameter by means of a compound light microscope, before and after the swelling test. The swelling test was carried out by depositing a few drops of a water-in-oil emulsion in a vial previously filled with water with two different degrees of salinity or with Lamix 30®. The samples were allowed to rest for 24 hours to allow the thermodynamic equilibrium to be reached. The samples were then observed under a microscope to determine the final size of the microgel particles.

[0158] The average particle diameter and the polydispersion index (PDI) of the polymer of the nanogels of the MZ17 sample were determined by means of dynamic light scattering (DLS) measurements. The particle size distribution of the nanogels was monomodal. The results of the DLS measurements are shown in Table 5.

[0159] Table 3 shows the chemical compositions of the saline waters used in the test.

[0160] Table 4 shows the diameter values of the microgels determined in Lamix 30® and in the different waters tested.

TABLE-US-00003 TABLE 3 Composition of saline waters Na.sup.+ Ca.sup.2+ Mg.sup.2+ (g/L) (g/L) (g/L) Field A 85 5.8 0.6 Field B 85 7.9 1.5

TABLE-US-00004 TABLE 4 Microgel diameter Std. Std. Std. Lamix Dev. Field B Dev. Field A Dev. (μm) (μm) (μm) (μm) (μm) (μm) A4 10.17 2.44 35.95 11.59 39.73 10.52 PEG2 9.37 5.63 32.77 11.74 30.93 13.77 PEG4 10.42 2.07 45.72 26.18 61.86 34.69 PEG11 9.904 2.372 67.22 33.381 63.916 29.087

[0161] It has been observed that in the samples placed in contact with Lamix 30® the sizes of the microgels before and after the swelling test are substantially identical; this shows that the microgels do not swell in contact with oily fluids. On the other hand, in the samples in contact with water, the sizes of the microgels after the swelling test are greater than the sizes of the same microgels before the test.

TABLE-US-00005 TABLE 5 Nanogel diameter Diameter Polydispersity (nm) (PDI) 5 (MZ17) 299.2 0.226

[0162] 3.2 Compatibility Assessment of the Emulsions of Microgels with Production Fluids

[0163] The following test was conducted to assess the behaviour of cationic microgels in contact with production fluids (formation water and hydrocarbon fluids).

[0164] A 10 ml aliquot of saline water was placed in a glass container. A 2 g aliquot of oil was added to it. The container was closed and conditioned in a stove at a temperature of 85° C. (to simulate the temperature of the well bottom). The sample was then taken from the stove and added with the emulsion containing the microgels.

[0165] The tested emulsions, having different concentrations of microgel particles, were dosed in the respective containers containing water and oil in amounts such as to obtain a concentration by weight of microgels equal to 26-28% referring to the weight of the mixture.

[0166] The following waters with different salinity originating from extraction fields of hydrocarbon oils were used in the test: [0167] Field C (total salinity: 2.3 g/l) [0168] Field D (total salinity: 84 g/l) [0169] Standard Sea Water (total salinity: 35 g/l)

[0170] In tests a hydrocarbon oil having a density between 1.012 and 1.017 g/cm3 also originating from an extraction field of hydrocarbon oils was used as a heavy oil.

[0171] The glass containers containing the water-oil mixtures were placed in a stove and conditioned at 85° C. At the end of the conditioning, the emulsion containing the microgels in the amounts indicated above was added to each container. The containers were then overturned repeatedly to mix all the components thoroughly and put back in the stove at 85° C. for 24 hours.

[0172] At the end of the thermal conditioning, the degree of separation of the water and oil phases, the settlement of the microgels on the bottom of the container and the volume of the container occupied by the microgels following the swelling as a result of water absorption were assessed visually.

[0173] Samples 2, 3 and 4 all showed a good separation of the water and oil phases and the settlement of the particles of microgels with water absorption in all the tests, i.e. with all three of the aforementioned waters with different salinity. Sample 4, in particular, showed the best separation results of the water and oil phases (clearer aqueous phase and greater volume occupied by the swollen microgels).

[0174] The test therefore proved that the inverse emulsions containing microgels are compatible with the production fluids, in particular their contact with these fluids does not lead to the emulsion of oil with water that may be present, which in a real situation could worsen the oil extraction effectiveness, increasing the amount of co-produced water.

[0175] The tests also show the effectiveness of the emulsions prepared according to the present invention in a very wide range of water salinity.

[0176] 3.3 Assessment of the Emulsions of Microgels with Production Fluids in the Presence of Calcium Carbonate

[0177] The following test was performed to assess the effectiveness of the interaction of the inverse emulsions according to the present invention with a carbonatic rock.

[0178] 10 g of solid calcium carbonate was weighed in one vial. 3 g of saline water or 4.5 g (Standard Sea Water having total salinity equal to 35 g/l) were then added to the vial. The amount equal to 3 g was sufficient to completely cover the present calcium carbonate (Series 1). The amount equal to 4.5 g produced an excess water condition (Series 2). 2 ml of an oil phase (Field D) were slowly deposited on the water phase. The vials were then placed in a stove and conditioned at 85° C. At the end of the conditioning, the emulsion containing the microgels was slowly added to each vial, in an amount equal to 2 ml, taking care not to create turbulence.

[0179] The vials were then put back in the stove at 85° C. for 24 hours.

[0180] At the end, it was assessed visually whether the particles of microgels were able to cross the oil phase without causing any emulsion thereof and where these particles were positioned. The vials, after a period of 24 hours, were overturned so as to assess the degree of adhesion to the calcium carbonate.

[0181] For comparison, the test was repeated with an inverse emulsion of microgels containing copolymers of methacrylic acid (partially neutralized with NaOH) and poly(ethylene glycol)methyl ether methacrylate (HEMA-PEG, MW=2000 Da, 42 polyoxyethylene units) prepared as described in Example 2 of WO 2016/166672.

[0182] In the Series 1 samples added with the emulsions containing the cationic microgels No. 2, 3 and 4, the total penetration of the particles of microgels between the calcium carbonate grains was observed. This penetration was not observed substantially in the comparative sample.

[0183] Probably, the observed penetration is attributable to the electrostatic attraction between the positive charges of the cationic microgels and the negative charges of the calcium carbonate, as well as the smaller sizes of the particles of the cationic microgels (about 10 micrometers) with respect to the comparative microgel particles (about 20 micrometers).

[0184] Furthermore, after overturning the vials, it was observed that samples No. 2, 3 and 4 help to compact the carbonate grains together, such that the solid phase remains firm on the bottom of the vial even when it is overturned. On the contrary, in the comparative sample, when the vial was overturned, the grain break-up of the calcium carbonate grains was observed and their sliding downwards.

[0185] The same behaviour of the cationic microgels according to the invention and of the comparative one was observed in the Series 2 samples containing excess water.

[0186] The test has proved a greater capability of the particles of the microgels of the emulsions according to the present invention of interacting with the carbonatic rocks with respect to the emulsions of microgels of the prior art.

[0187] 4. Characterization of the Emulsions of Nanogels

[0188] 4.1 Test 1—Flushing of Cores Saturated with Oil and Saline Water

[0189] The injectability of sample 5 containing particles of nanogels inside a sandy medium (Berea Sandstone) and its ability to modify water permeability in a formation was assessed by means of flux measurements in porous medium. For this purpose, a cylindrical core with a length equal to 5.09 cm and a diameter equal to 2.47 cm, having a porosity of 16.5% was used. The core was placed in a core holder under confining pressure (40 bar) to avoid fluid leaks.

[0190] The core was initially filled with synthetic sea water (salinity: 33 g/L) and brought to the temperature of 40° C. in the stove. The core was then flushed with Lamix 30® until it reached the conditions in which water is no longer produced (Core under residual water saturation). At this point sample 5 was injected for about 24 times the pore volume. The core was then allowed to rest at 40° C. for 24 hours (shut-in) to allow for the action of the nanogels. At the end of the shut-in period, the core was again flushed with synthetic sea water, to verify the possible effect of reduction of permeability to water generated by the cationic nanogels.

[0191] Sample 5 was easily injectable and no pressure increases were observed during its injection.

[0192] The final flushing with saline water showed a reduction in the permeability of the core to water with respect to flushing with water before the treatment with the inverse emulsion according to the invention. The value of the initial water permeability was in fact 36 mD and drops to 1.4 mD at the end of the test, due to the desired behaviour of the cationic nanogels.