Method for inhibiting the permeation of water in an extraction well of a hydrocarbon fluid from an underground reservoir

Abstract

A method for inhibiting the permeation of water in an extraction well of a hydrocarbon fluid from an underground reservoir is described. The method includes the injection of at least one treatment fluid into the underground reservoir. The treatment fluid contains at least one emulsion or dispersion in an organic solvent of at least one copolymer of a first monomer of an acrylic monomer or a methacrylic monomer, and a second monomer having at least one ethylene unsaturation and at least one polyoxyethylene chain. The emulsion or dispersion of the copolymer used in the method is also described.

Claims

1. A method for inhibiting permeation of water in an extraction well of a hydrocarbon fluid from an underground reservoir, the method comprising: injecting into said underground reservoir, at least one treatment fluid comprising at least one inverse emulsion or one dispersion in an organic solvent of at least one copolymer obtained from at least one first monomer selected from the group consisting of an acrylic monomer and a methacrylic monomer, and a second monomer of formula (I) ##STR00001## wherein: R.sub.1 is H or CH.sub.3; R.sub.2 is H, a C.sub.1-C.sub.4 alkyl or an acrylate group COCR.sub.3CH.sub.2 wherein R.sub.3 is H or CH.sub.3; X is O or NH; and n is an integer ranging from 4 to 500; wherein the organic solvent has a water solubility at 25 C. lower than or equal to 5 g/L and a solubility in oil at 25 C. equal to or higher than 100 g/Ls, the ratio between the weight of the second monomer and the weight of the first monomer is at least 5%, and the discontinuous phase of said inverse emulsion is in the form of dispersed drops/droplets containing said copolymer.

2. The method according to claim 1, wherein R.sub.1 is CH.sub.3; R.sub.2 is H or a C.sub.1-C.sub.4 alkyl, X is O; and n is an integer ranging from 4 to 50.

3. The method according to claim 1, wherein said second monomer has a molecular weight of 200-10,000 Da.

4. The method according to claim 1, wherein said at least one first monomer is selected from the group consisting of acrylic acid and methacrylic acid.

5. The method according to claim 4, wherein said acrylic acid or methacrylic acid is at least partially neutralized with metal ions.

6. The method according to claim 1, wherein said copolymer is cross-linked.

7. The method according to claim 1, wherein said treatment fluid comprises a water-in-oil emulsion of said at least one copolymer in said organic solvent, wherein said at least one copolymer is in the form of particles having an average diameter of 10-500 nanometres.

8. The method according to claim 1, wherein said treatment fluid comprises a dispersion of said at least one copolymer in said organic solvent, wherein said at least one copolymer is in the form of particles having an average diameter of 1-1,000 micrometers.

9. The method according to claim 1, wherein a weight ratio of said second monomer to said at least one first monomer ranges from 5% to 50%.

10. The method according to claim 1, wherein said organic solvent is at least one selected from the group consisting of an aliphatic or aromatic C.sub.6-C.sub.25 hydrocarbon solvent; an amide having a total number of carbon atoms ranging from 7 to 25; an alcohol having a total number of carbon atoms ranging from 7 to 25; an ether having a total number of carbon atoms ranging from 7 to 25; an ester having a total number of carbon atoms ranging from 7 to 25; and a ketone having a total number of carbon atoms ranging from 7 to 25.

11. The method according to claim 1, further comprising: after said injecting the at least one treatment fluid into said underground reservoir, injecting at least one displacement fluid into said underground reservoir for one or more times.

12. The method according to claim 1, further comprising: extracting said hydrocarbon fluid from said underground reservoir.

13. The method according to claim 1, wherein said hydrocarbon fluid is a hydrocarbon oil.

14. An emulsion or a dispersion in an organic solvent of at least one copolymer of at least one first monomer selected from the group consisting of an acrylic monomer and a methacrylic monomer, and a second monomer of formula (I) ##STR00002## wherein: R.sub.1 is H or CH.sub.3; R.sub.2 is H, a C.sub.1-C.sub.4 alkyl or an acrylate group COCR.sub.3CH.sub.2 wherein R.sub.3 is H or CH.sub.3; X is O or NH; and n is an integer ranging from 4 to 500; wherein the ratio between the weight of the second monomer and the weight of the first monomer is at least 5%, the organic solvent has a water solubility at 25 C. lower than or equal to 5 g/L and a solubility in oil at 25 C. equal to or higher than 100 g/Ls, and when an emulsion is present, the emulsion is an inverse emulsion.

Description

EXAMPLE 1TREATMENT FLUID IN THE FORM OF WATER-IN-OIL EMULSION

(1) The oily continuous phase was prepared in a three-neck flask by loading 64 g of kerosene and 1.44 g of a mixture of commercial non-ionic surfactants SPAN80 (HLB=4.3) and TWEEN80 (HLB=15.0). The weight ratio percentage between the two surfactants was selected so as to have the polymerization reaction at predetermined HLB values of the formulation to be occurred.

(2) The discontinuous aqueous phase was prepared into a becker by mixing 6.97 g of water, 5 g of methacrylic acid and NaOH in an amount ranging as a function of the neutralization desired degree of the methacrylic acid. To the solution of neutralized methacrylic acid, 2.5 g of a 50% b.w. aqueous solution of the 2-idrossietil methacrylate monomer (HEMA-PEG of the company Sigma-Aldrich, MW=2000 Da, 42 polyoxyethylene units), 0.056 g of N,N-methylen-bis-acrylamide and 0.239 g of ammonium persulphate (first component of a couple of redox polymerization initiators) were added.

(3) The discontinuous aqueous phase was dropped into the oily continuous phase, so promoting the formation of the emulsion by a sonicator. The mixture temperature was maintained within the range of 0-5 C. through an ice-bath. After 20 minutes of sonication, 0.1992 g of sodium metabisulfite dissolved in 0.5 g of water (second component of the couple of redox polymerization initiators) were added. The polymerization reaction in the presence of the couple of redox initiators is carried out for 30 minutes under sonication into an ultrasonic bath.

(4) The above-described process was used for preparing the water-in-oil emulsions having the compositions LS1-LS4 reported in table 1.

(5) The LS5 and LS6 emulsions were prepared by the above-described procedure, wherein the polymerization reaction was carried out also in the presence of an anionic surfactant (sodium dodecyl sulfate (SDS)) in the aqueous discontinuous phase.

(6) The particle average diameter and the polydispersity index (PDI) of the polymer in the emulsion were determined by dynamic light scattering (DLS) measures (table 2)

(7) TABLE-US-00001 TABLE 1 Composition of the emulsions. Neutralization degree SPAN80* TWEEN80 SDS** NaOH methacrylic acid Sample (g) (g) (g) HLB (g) (%) LS1 1.44 4.3 2.323 100 LS2 1.211 0.229 6 2.323 100 LS3 0.942 0.498 8 2.323 100 LS4 0.673 0.767 10 2.323 100 LS5 0.666 0.759 0.014 n.a. 2.323 100 LS6 0.659 0.752 0.028 n.a. 2.323 100 n.a.: not applicable, as it is present an anionic surfactant

(8) TABLE-US-00002 TABLE 2 Particle average Sample HLB diameter (nm) PDI LS1 4.3 106 0.10 LS2 6 154 0.12 LS3 8 164 0.14 LS4 10 205 0.12 LS5 n.a. 198 0.11 LS6 n.a. 208 0.13 n.a.: not applicable, as it is present an anionic surfactant

(9) The results show that the copolymer obtained has a particle average diameter within the range of about 100-200 nm. The polydispersity index shows that particle distribution is substantially singlemode.

(10) The emulsions obtained result to be stable.

(11) The effect of the emulsion inversion by contact with water and the consequent polymer release was assessed by introducing the emulsion into a vial containing water in a emulsion/water volume ratio of 3:1. The test was repeated using water with different salt concentrations.

(12) After one week of contact in static conditions, the higher oily layer present in the vial was subjected to thermogravimetric analysis in order to determine the amount of copolymer present; on the lower aqueous layer the presence of the copolymer and the related PDI were determined by DLS analysis.

(13) Due to the contact with water, to the interface between the higher oily layer and the aqueous lower layer, it was observed the formation of a whitish layer having viscous consistency due to hydrogel particles formed after water absorption which concentrate.

(14) The phase inversion of the emulsion was assessed by the contact with: (i) distilled acqua, (ii) water-1 (concentration of Na+ ions=9 g/L; Ca++ ions=0.53 g/L; Mg++ ions=1.2 g/L) and (iii) water-2 (concentration of Na+ ions=34 g/L; Ca++ ions=5.8 g/L; Mg++ ions=0.6 g/L).

(15) The results of the contact tests carried out on the samples LS4-LS6 are reported in tables 3-5.

(16) TABLE-US-00003 TABLE 3 Sample LS4 Particle average Particle percentage diameter (nm) PDI in the emulsion (%) Distilled water 420 0.29 49% water-1 384 0.41 52% water-2 230 0.43 45%

(17) TABLE-US-00004 TABLE 4 Sample LS5 Particle average Particle percentage diameter (nm) PDI in the emulsion (%) Distilled water 435 0.31 21% water-1 377 0.39 18% water-2 240 0.55 24%

(18) TABLE-US-00005 TABLE 5 Sample LS6 Particle average Particle percentage diameter (nm) PDI in the emulsion (%) Distilled water 460 0.29 16% water-1 395 0.44 14% water-2 244 0.52 15%

(19) The increase of the average particle diameter after the crossing into the aqueous phase is an index of the fact that the polymers were released and absorbed water.

(20) The experimental results also show in all the cases that at least 50% of the copolymer particles migrated from the emulsion to the aqueous phase. The presence of increasing amounts of a surfactant added to the aqueous discontinuous phase containing the monomers (LS5 and LS6) significantly promotes such migration.

(21) The PDI values in salt water are higher than values in distilled water. That shows that the presence of salts promotes the formation of aggregates between polymer particles.

EXAMPLE 2POLYMER DISPERSION IN ORGANIC SOLVENT

(22) A polymer particle dispersion (D1) in an organic solvent was prepared in the following way.

(23) The oily continuous phase was prepared in a three-neck reactor by loading 404 g of Lamix 30, 5.388 g of Span 80 and 5.388 g of Atlox 4914, both being non-fat-soluble non-ionic surfactants and having steric action. The dissolution of such surfactants was ensured by mechanical stirring through an impeller. The system was brought to the reaction temperature of 70 C.

(24) Separately, the discontinuous aqueous phase was prepared into a beaker by mixing 37.879 g of methacrylic acid and 43.749 g of a solution of NaOH concentrated to 30% by weight. The neutralization of the methacrylic acid was carried out into an ice-bath. 25 g of a 50% b.w. aqueous solution of the monomer 2-hydroxyethyl methacrylate (HEMA-PEG of the company Sigma-Aldrich, MW=2,000 Da, 42 polyoxyethylene units), 0.379 g of N,N-methylen-bis-acrylamide and 0.253 g of ammonium persulfate (radical initiator) were added to the solution of methacrylic acid neutralized. To this aqueous phase, 16.164 g of an aqueous solution containing 33.33% b.w. of Dowfax 2A1 (steric anionic surfactant) was added.

(25) The discontinuous aqueous phase was injected within the three-neck reactor, after that it was subjected to vacuum-nitrogen inerting cycles. The reaction was carried out for a total time of 3 hours at a temperature of 70 C.

(26) The dispersion D1 showed to contain copolymer particles having an average diameter of about 15 micrometers.

(27) Oily Phase Crossing Test

(28) The efficacy of copolymer migration from the dispersion in organic solvent to a hydrocarbon oil and from the latter to an aqueous phase was assessed in the following manner.

(29) Water (having the composition of water-2 of example 1), an hydrocarbon oil (retrieved by an extraction well) and the copolymer dispersion were introduced into a vial having a height equal to 7 cm and a diameter equal to 2 cm, so as to make the overlap of three layers in the following order (from the top downwards): emulsion/oil/water.

(30) The ratio by weight of the emulsion/oil/water is 1:1:1. The test was carried out at room temperature and 90 C. in static conditions (without stirring).

(31) At room temperature it was observed that the polymer particles sediment through the oil up to come into contact with water within about 5 hours.

(32) At 90 C., the time necessary for crossing oil was minutes. Furthermore, it was observed that the copolymer particles cross the oil without any effect of dispersed or emulsified water absorption, possibly present in the latter, occurs.

(33) Aging Tests

(34) A portion of the dispersion D1 was introduced into a vial containing water-2 of example 1 in a weight ratio 1:1. After the contact between the dispersion and water, a significant increase of the aqueous phase viscosity, due to the crossing of the copolymer in this phase and the following water absorption, occurred.

(35) The sample was kept into a stove at 90 C. for one week. At the end of the aging period in the stove, the sample maintained substantially unchanged its consistency.

(36) Test of the Reversibility of the Water Adsorbing Effect

(37) A portion of the dispersion D1 was introduced into a vial containing water-2 of example 1 in a weight ratio 1:1 so as to form a hydrogel.

(38) Once the formation of the hydrogel was completed, hydrochloric acid was introduced into the vial up to achieve pH=2. Due to acid addition, a significant reduction of the aqueous phase viscosity was observed. The same behavior was observed following the addition of formic acid up to pH=2.

(39) Use of Organic Solvent Polymer Dispersion within a Capillary.

(40) The behavior of a treatment fluid into a fractured rock formation was stimulated by carrying out the following applicative test into a capillary tube.

(41) A vial was filled with a sample of water-2 and brought to 90 C. Then, a glass capillary tube (inner diameter 2.5 mm and length 40 cm) was inserted into the vial in vertical direction, so as to immerge one end thereof under the water surface.

(42) A sample of the dispersion D1 (8 mL) was then introduced into the capillary tube by a syringe. After hours, in the lower part of the tube, above the water level, the formation of a highly viscous phase having an height of about 2 cm was observed.

(43) A second portion (8 mL) of the dispersion D1 was then injected into the capillary tube and it was observed that: i. the viscous phase behaved as a plug, exerting a significant adherence on the capillary tube walls; ii. the adherence was such that the injection of the second portion of the dispersion required the application of a certain pressure by the syringe; iii. the second portion of the dispersion partially replaced the first one, causing the precipitation of a portion thereof in the vial; iv. after two days, the presence of an aqueous phase above the hydrogel layer was observed; v. the water block effect exerted from the viscous phase could be annulled by injecting formic acid or hydrochloric acid into the capillary tube.

EXAMPLE 3

(44) A polymer dispersion prepared according to the previous Example 2 was tested in the treatment of an open-hole partially depleted well in a partially fractured reservoir, for reducing the water production associated with the extraction of oil.

(45) The well depth was about 3000 m. Total volume of the well: 19 m.sup.3. Well bottom temperature 95-100 C. The well was equipped with an artificial lift pumping system Thomassen 5 holes. The average production conditions before the treatment of the oil well were as follows:

(46) Oil: 5 m.sup.3/d

(47) Water: 20 m.sup.3/d

(48) Flux: 6 m.sup.3/d

(49) The volumetric water content [Water Cut:(volume of produced water)/(total produced volume)] was 65%.

(50) 20 m.sup.3 of a polymer dispersion were prepared on a discontinuous pilot scale by using the same reagents in the same proportions and the same procedure as in the previous Example 2. The solid (polymer) content of the dispersion was 25% b.w. The average particle size was about 15 micrometers.

(51) The well production was stopped and the following fluids were pumped in bullheading (with a high pressure pumping equipment) in sequence: 1. 10 m.sup.3 of dry light gasoil (average boiling point 170 C., density 0.907 g/cc, water content <500 ppm b.w.) for displacing water; 2. 16 m.sup.3 of the polymer dispersion prepared according to the procedure of example 2; 3. 20 m.sup.3 of dry light gasoil as in step 1 for displacing the polymer dispersion into the reservoir.

(52) After the injection of the fluids the well was maintained in shut-in for 50 hours before starting the extraction again, in order to allow the polymer particles to settle and get in contact with the water in the reservoir and to swell.

(53) The well production was started again. After about 20 days the well production had stabilized to a total production rate of about 60 m.sup.3/d with a Water Cut of about 40% (20% decrease with respect to the initial conditions before treatment). The overall average oil production increased to 30 m.sup.3/d. The same production characteristics have been maintained for over 1 year.

(54) Thus the method according to the invention resulted very effective in practice in enhancing the oil recovery and reducing the water production in a partially depleted oil well.