COATED PROPPANTS FOR FRACKING EXTRACTION METHODS

Abstract

The invention relates to coated support means for fracking mining methods, containing an inorganic substrate material and a coating containing polymers of one or more ethylenically unsaturated monomers from the group containing vinyl esters of unbranched or branched alkyl carboxylic acids with 1 to 15 C atoms, methacrylic acid esters and acrylic acid esters of alcohols with 1 to 15 C atoms, vinyl aromatics, olefins, dienes and vinyl halides, characterised in that the polymers are obtained by means of radical-initiated polymerisation in an aqueous medium, wherein 0.5 to 20 wt. % of ethylenically unsaturated and silane group-containing monomers are copolymerised, in relation to the total weight of the monomers.

Claims

1. A coated proppant for use in fracking, comprising an inorganic carrier material and a coating comprising polymers of one or more ethylenically unsaturated monomers selected from the group consisting of vinyl esters of unbranched or branched alkylcarboxylic acids having 1 to 15 carbon atoms, methacrylic esters and acrylic esters of alcohols having 1 to 15 carbon atoms, vinylaromatics, olefins, dienes, and vinyl halides, wherein the polymers are obtained by radically initiated polymerization in aqueous medium, wherein 0.5 to 20 wt % of ethylenically unsaturated monomers comprising silane groups are copolymerized, based on the total weight of the monomers.

2. The coated proppant as claimed in claim 1, wherein the ethylenically unsaturated monomers comprising silane groups are monomers with the general formula RSi(CH.sub.3).sub.0-2(OR.sup.1).sub.3-1, where R is CH.sub.2CR.sup.2(CH.sub.2).sub.0-1 or CH.sub.2CR.sup.2CO.sub.2(CH.sub.2).sub.1-3, R.sup.1 is an unbranched or branched, optionally substituted alkyl radical having 1 to 12 carbon atoms and may optionally be interrupted by an ether group, and R.sup.2 is H or CH.sub.3.

3. The coated proppant as claimed in claim 2, wherein the coating comprises polymers of vinyl esters and 0.5 to 20 wt % of ethylenically unsaturated monomers comprising silane groups, and optionally 0.1 to 10 wt % of ethylenically unsaturated carboxylic acids, wherein the polymers may optionally include 5 to 45 wt % of one or more monomer units from the group consisting of vinyl estersdifferent to the copolymerized vinyl estersof unbranched or branched alkyl carboxylic acids having 3 to 15 carbon atoms, methacrylic esters and acrylic esters of alcohols having 1 to 15 carbon atoms, styrene, ethylene, butadiene, and vinyl chloride; and wherein the figures in wt % add up to 100 wt % in each case.

4. The coated proppant as claimed in claim 1, wherein the coating comprises polymers of (meth)acrylic esters of alcohols having 1 to 15 carbon atoms and 0.5 to 20 wt % of ethylenically unsaturated monomers comprising slime groups, and optionally 0.1 to 10 wt % of ethylenically unsaturated carboxylic acids, and optionally 0.1 to 50 wt %, preferably 5 to 30 wt %, of styrene; wherein the figures in wt % add up to 100 wt % in each case.

5. The coated proppant as claimed in claim 1, wherein the coating comprises polymers in the form of composite particles composed of the organic polymer and at least one inorganic solid, wherein the weight fraction of inorganic solid is 15 to 40 wt %, based on the total weight of organic polymer and inorganic solid in the composite particle.

6. The coated proppant as claimed in claim 5, wherein the inorganic solid particles are metal oxides or semimetal oxides.

7. The coated proppant as claimed in claim 1, wherein the inorganic carrier materials are sand, rocks, glass beads, ceramic particles or ceramic spheres.

8. The coated proppant as claimed in claim 1, wherein particles of the inorganic carrier material have an average diameter of 50 to 5000 m.

9. A method for producing coated proppants as claimed in claim 1, wherein the polymer is applied as an aqueous polymer dispersion or aqueous composite dispersion to the inorganic carrier material and is subsequently dried.

10. The coated proppants as claimed in claim 1, wherein the coated proppant is used in fracking methods for mineral oil and natural gas.

Description

EXAMPLE 1 (POLYMER DISPERSION 1)

[0042] A reactor with a volume of 3 liters was charged with 1.0 g of deionized water, 4.6 g of sodium lauryl sulfate, and 1.4 g of potassium peroxodisulfate under a nitrogen atmosphere and this initial charge was heated to 40 C. with stirring. At that temperature a mixture with the following composition was introduced into the reactor:

TABLE-US-00001 Vinyltriethoxysilane 0.8 g Methacrylic acid 8.5 g Butyl acrylate 100.8 g Dodecyl mercaptan 0.3 g Methyl methacrylate 40.7 g Styrene 18.7 g

[0043] Subsequently the temperature was raised to 80 C. and, on attainment of this temperature, the initiator solution (1.4 g of potassium peroxodisulfate in 86.8 g of water) was metered in over the course of three hours; simultaneously but separately, over the course of 2.5 hours, a solution having the following composition was introduced into the reactor:

TABLE-US-00002 Vinyltriethoxysilane 3.7 g Methacrylic acid 37.1 g Butyl acrylate 440.8 g Dodecyl mercaptan 1.48 g Methyl methacrylate 177.8 g Styrene 81.5 g

[0044] After the end of the metered additions, stirring took place at 80 C. for two hours and at 85 C. for one hour.

[0045] The polymer dispersion was subsequently diluted with water and the pH was adjusted to 9 using an aqueous ammonia solution (12.5% strength). This gave a polymer solution having a solids content (DIN EN ISO 3251) of 43.0 wt %. The minimum film formation temperature (DIN ISO 2115) was 5 C.

EXAMPLE 2 (COMPOSITE DISPERSION 2)

[0046] A jacketed reactor was charged at 50 C. and with stirring with 1000 g of the 43%, aqueous polymer dispersion 1, and 460 g of an aqueous silica sol (solids content 40%, Bindzil 2040 from Akzo Nobel) were added.

[0047] The resulting dispersion had a solids content of 42.7% and a silica content of 30 wt %, based on the total solids content.

[0048] Production of Coated Proppants:

[0049] In a Ldige mixer, 2 wt %, based on sand, ox the dispersions from examples 1 and 2 were sprayed using a nozzle onto fracking sand of 12/18 mesh and, respectively, 20/40 mesh, and the dispersions were dried at 80 C.

[0050] Investigation of the Coating Quality of Fracking Sand by Electron Microscope (SEM):

[0051] A surface coverage of >95% was achieved in each case.

[0052] Investigation of the Pressure Stability of Coated Proppants:

[0053] The pressure stability of the coated proppants was investigated in each case in accordance with DIN EN ISO 13503-2 at 7500 psi and 10000 psi pressure.

[0054] The results are shown in tables 1 and 2.

TABLE-US-00003 TABLE 1 Fracking sand 12/18 coat- Amount of fine fraction formed ed with dispersion from in % example at 7500 psi at 10000 psi 1 7% 12% 2 3% 8% Comparative example, un- 15% 22% coated sand 12/18

TABLE-US-00004 TABLE 2 Fracking sand 20/40 coat- Amount of fine fraction formed ed with dispersion from in % example at 7500 psi at 10000 psi 1 3% 6% 2 1% 3% Comparative example, un- 6% 10% coated sand 20/40

[0055] With the proppants of the invention, the result in each case is a much smaller fine fraction after pressure loading.