METHOD OF CONSOLIDATING SUBTERRANEAN FORMATIONS USING CATIONIC AND ANIONIC AND/OR NON-IONIC POLYMERS

Abstract

A method of consolidating a subterranean formation which comprises particles is provided. The method includes selecting a subterranean formation in need of consolidation, contacting the particles with a cationic polymer and then an anionic or non-ionic polymer, thereby agglomerating the particles and consolidating the formation, wherein the agglomeration increases the uniformity of the size of the particles. Methods of producing hydrocarbon wherein the formation is consolidated by the method herein described are also provided. Use of kits comprising cationic polymer and anionic polymer and/or non-ionic polymer to consolidate subterranean formations is further provided. Kits comprising the polymers used in the method are also provided.

Claims

1. A method of consolidating a subterranean formation which comprises particles, said method comprising: (i) selecting a subterranean formation in need of consolidation; (ii) contacting said particles with a cationic polymer; and then (iii) contacting said particles with an anionic polymer and/or a non-ionic polymer to agglomerate said particles and thereby consolidate said formation, wherein said agglomeration increases the uniformity of the size of said particles.

2. A method as claimed in claim 1, wherein said agglomeration increases the average diameter of said particles.

3. A method as claimed in claim 1, wherein said particles are sand particles.

4. A method as claimed in claim 1, wherein said cationic polymer is a copolymer.

5. A method as claimed in claim 1, wherein said cationic polymer is formed from monomers of formula (I): ##STR00032## wherein R.sup.1 is H, CH.sub.3; R.sup.2 is COY, C.sub.6-12 aryl or C.sub.3-12 heteroaryl; Y is OR or NR.sub.2; and each R is independently selected from H and C.sub.1-6 alkyl; and/or said cationic polymer is formed from monomers of formula (II) ##STR00033## wherein R.sup.1 is H or CH.sub.3 and A is C.sub.3-12 heteroaryl group; and/or wherein said cationic polymer is formed from monomers of formula (III): ##STR00034## wherein R.sup.1 is H or CH.sub.3; Y is OR or NR.sub.2; and each R is independently selected from H and C.sub.1-6 alkyl; and/or wherein said cationic polymer is formed from monomers of formula (IV): ##STR00035## wherein R.sup.1 is H or CH.sub.3; Y.sup.1 is O or NH; m is an integer from 1 to 6, preferably 2 or 3; each R.sup.2 is independently H or C.sub.1-6 alkyl, preferably each R.sup.2 is methyl; and X.sup. is a counter anion.

6-8. (canceled)

9. A method as claimed in claim 1, wherein said cationic polymer is formed from monomers selected from 2-(trimethylammonio)ethyl acrylate salt, 2-(trimethylammonio)ethyl methacrylate salt, 2-(triethylammonio)ethyl acrylate salt, 2-(triethylammonio)ethyl methacrylate salt, acrylamide propyltrimethylammonium salt, methacrylamide propyltrimethylammonium salt, acrylamide propyltriethylammonium salt, methacrylamide propyltriethylammonium salt, dimethyldiallyl ammonium chloride, 2-vinylpyridine salt, 4-vinylpyridine salt and 3-methyl-1-vinyl-1H-imidazole salt.

10. A method as claimed in claim 1, wherein said cationic polymer is formed from acrylamide and 2-(trimethylammonio)ethyl acrylate salt.

11. A method as claimed in claim 1, wherein said cationic polymer has a weight average molecular weight of 110.sup.5 to 2010.sup.6 g/mol; and/or said cationic polymer has a charge activity of 5 to 100 mol %.

12. (canceled)

13. A method as claimed in claim 1, wherein said anionic polymer is a copolymer.

14. A method as claimed in claim 1, wherein said anionic polymer is formed from monomers of formula (III): ##STR00036## wherein R.sup.1 is H or CH.sub.3; Y is OR or NR.sub.2; and each R is independently selected from H and C.sub.1-6 alkyl; and/or wherein said anionic polymer is formed from monomers of formula (VI): ##STR00037## wherein R.sup.1 is H or CH.sub.3; and R.sup.3 is CO.sub.2Z, SO.sub.3Z, PO.sub.3Z.sub.2, (CH.sub.2).sub.1-6CO.sub.2Z, (CH.sub.2).sub.1-6SO.sub.3Z, (CH.sub.2).sub.1-6PO.sub.3Z.sub.2, CONH(CR).sub.2CO.sub.2Z, CONH(CR).sub.2SO.sub.3Z, CONH(CR).sub.2PO.sub.3Z.sub.2 wherein R is H, CH.sub.3 or C.sub.2H.sub.5 and Z is H or a univalent metal atom.

15. (canceled)

16. A method as claimed in claim 14, wherein in formula (VI) R.sup.3 is CO.sub.2Z.

17. A method as claimed in claim 1, wherein said anionic polymer has a weight average molecular weight of 110.sup.5 to 4010.sup.6 g/mol; and/or said anionic polymer has a charge activity of 10-100 mol %.

18. (canceled)

19. A method as claimed in claim 1, wherein said non-ionic polymer comprises a homopolymer.

20. A method as claimed in claim 1, wherein said non-ionic polymer comprises monomers of formula (III): ##STR00038## wherein R.sup.1 is H or CH.sub.3; and Y is OR or NR.sub.2, wherein when Y is OR, R is independently selected from C.sub.1-6 alkyl and when Y is NR.sub.2 each R is independently selected from H and C.sub.1-6 alkyl, preferably wherein Y is NR.sub.2 and each R is H.

21. (canceled)

22. A method as claimed in claim 20, wherein said non-ionic polymer has a weight average molecular weight of 110.sup.5 to 4010.sup.6 g/mol.

23. A method as claimed in claim 1, wherein in step (ii) an anionic polymer is added.

24. A method as claimed in claim 1, wherein in step (ii) a non-ionic polymer is added.

25. A method as claimed in claim 1, wherein said cationic polymer, said anionic polymer and said non-ionic polymer are each provided as a solution or suspension in an aqueous carrier.

26. A method of producing hydrocarbon from an unconsolidated subterranean formation comprising: (i) consolidating said formation by a method as defined in claim 1; and (ii) producing hydrocarbon from said formation.

27. A method as claimed in claim 26, wherein the particle production rate (e.g. sand particle production rate) is reduced after consolidation is carried out.

28. (canceled)

29. (canceled)

Description

[0135] The invention will now be described with reference to the following non-limiting Figures and examples, wherein:

[0136] FIG. 1 is a photograph of gold coated sand, gold coated sand treated solely with a cationic polymer and gold coated sand treated by a method of the present invention;

[0137] FIG. 2 is SEM images (150 magnification) of gold coated sand (FIG. 2a), gold coated sand treated solely with a cationic polymer (FIG. 2b) and gold coated sand treated by a method of the present invention (FIG. 2c);

[0138] FIG. 3 is ParticleView Measurement (PVM) probe software images of agglomerates formed using the method of the invention; and

[0139] FIG. 4 is a plot showing cumulative particle size distribution achieved using the method of the invention compared to a reference sample.

EXAMPLES

[0140] The examples were performed using the following materials and equipment, unless otherwise stated:

Standard brine consisting of NaCl, Na.sub.2SO.sub.4, NaHCO.sub.3, SrCl.sub.2, BaCl.sub.2, KCl, MgCl.sub.2 and CaCl.sub.2 in deionised water
Chemicals: The following polymers were used:
cationic polymer: polymer comprising acrylamide and 2-(trimethylammonio)ethyl acrylate salt
anionic polymer: polymer comprising acrylamide and acrylic acid monomers non-ionic polymer: acrylamide polymer
All polymers are acrylamide based and were obtained commercially.
Rock substrate: The core material used was sand from an oil field.
Scanning Electron Microscope (SEM) analysis: A Hitachi TM-1000 scanning electron microscope (in its default settings) was used to visually inspect the effect of the method of the invention on sand particles. A sample of sand particles (either untreated (control), treated solely with cationic polymer (control) or treated by a method of the invention) was sputter coated with a thin film of gold. The coated samples were placed on the SEM stage and slotted into the vacuum chamber. The chamber was evacuated of air using a vacuum pump, and a beam of electrons targeted at the coated surface of the sand particles. The backscattered electrons were detected by electron detectors, and processed to afford visual representations of the specimen surface. The magnification used is indicated on the images.

SEM Analysis of Sand Particles Treated by the Method of the Present Invention

[0141] Sand samples were prepared in test tubes by adding polymers to a suspension of 0.6 g formation sand in 10 ml brine. Visual analysis of sand samples treated with the polymers as summarised in table 1 below was carried out using SEM analysis. The samples were prepared by adding a cationic polymer to a sand suspension, shaking the suspension for 5 minutes, followed by addition of the anionic or non-ionic polymer and shaking for a further 5 minutes. A sand sample, without any additional polymers, was used as a control. A sand sample, treated only with cationic polymer, was used as a further control. The sand samples were filtered and dried. The samples were dried in a 50 C. oven overnight with a towel to absorb the excess brine to prevent crystallisation.

[0142] Each of the treated samples was sputter coated with gold and analysed by SEM.

TABLE-US-00003 TABLE 1 Cationic polymer Anionic polymer Non-ionic polymer Example (ppm wt) (ppm wt) (ppm wt) 1 2000 2000 None 2 2000 None 2000 Comparative None None None Example 1 Comparative 2000 None None Example 2

[0143] The results are shown in FIGS. 1 and 2. FIG. 1 is a picture of the gold coated samples. This image shows that there is very little difference between the untreated control sample and the control sample treated only with cationic polymer. In contrast, the sand samples treated by the method of the invention, are remarkably different to the control samples and comprise much larger particles.

[0144] This is confirmed in FIG. 2 which is the SEM images obtained with 150 magnification. Even under magnification, it is difficult to observe any differences between the sand particles which are untreated (FIG. 2a) and the sand particles treated solely with cationic polymer (FIG. 2b). In contrast it is clear from the 150images that the sand particles treated by the method of the invention (FIG. 2c) undergo significant agglomeration and as a result comprise particles having a much larger average diameter size compared to the comparative samples. Additionally there are noticeably fewer smaller particles in the sand sample treated according to the method of the invention (FIG. 2c) compared to the comparative samples (FIGS. 2a and 2b).

Simulation of Reservoir Conditions

[0145] To study sand agglomeration under simulated reservoir conditions, a shear test rig was built based on a round bottomed vessel which was stirred at speeds just enough to keep the solids suspended. A Focused Beam Reflectance Measurement (FBRM) probe and a ParticleView Measurement (PVM) probe made by Mettler Toledo were each positioned in the vessel to measure changes in particle size distribution and collect images at various stages of the agglomeration process. Formation brine was used as the suspending medium and elevated temperatures up to 80 C. were used. The FBRM and PVM software were setup to collect data from the start until the end of the experiments. The formulation was introduced and changes were recorded after the introduction of each polymer (cationic polymer followed by anionic polymer followed by further cationic polymer). As a comparative, measurements were made with no treatment.

[0146] FIG. 3 shows images from the PVM probe software of the agglomerates formed during the experiment. The images show the agglomerates formed by treatment according to the invention. The particle sizes in the images range from 500 to 900 m.

[0147] FIG. 4 shows the FBRM cumulative particle size distribution following the addition of cationic polymer (primary polymer), followed by anionic polymer (secondary polymer) and then further cationic polymer (tertiary polymer). This shows that the particle size distribution increases in size after each polymer treatment.