Insulating material for downhole high-power heaters and its preparation method

Abstract

This invention discloses an insulating material for a high-power downhole heater and its preparation method. The insulating material is an insulating ceramic material prepared by ball milling, drying and granulation, aging and molding, and plastic sintering of a mixture comprising magnesium oxide, manganese-containing dopants, zirconium-containing dopants, and modifying agents. Because the manganese-containing and zirconium-containing dopants can form solid solutions with magnesium oxide, they activate the magnesium oxide crystal lattice, improve the material's density and strength, and enhance its insulation performance. The modifying agents reduce the vacancy defects in the MgO grains, making it less prone to moisture absorption and the formation of MgO-OH structures, thus increasing the volume resistivity. The resulting insulating ceramic material exhibits excellent high-temperature insulation properties and can be used as an insulating material for high-power downhole heaters.

Description

Technical Field

[0001] This invention relates to the field of downhole high-power heater technology, and in particular to an insulating material for downhole high-power heaters and its preparation method. Background Technology

[0002] With the increasing demand for oil and gas and the continuous depletion of conventional oil and gas resources, the effective development of unconventional oil and gas resources is of significant strategic importance for alleviating the pressure on oil and gas supply, promoting the low-carbon transformation of the energy structure, and achieving green development. Unconventional oil and gas mainly includes heavy oil, shale oil, shale gas, and coalbed methane. The application of downhole electric heater technology in new fields such as downhole heating assistance for heavy oil and underground in-situ coal gasification is of great significance for promoting the implementation of major projects such as downhole electric heating assistance for heavy oil thermal recovery, in-situ conversion of shale oil, and underground in-situ coal gasification.

[0003] Downhole high-power electric heating technology utilizes the heat generated by resistance heating to continuously heat the wellbore heat transfer medium (steam, water, or oil reservoir). The downhole high-power electric heater is the core equipment of this electric heating technology. The electric heater (mineral-insulated heating cable) mainly consists of one or more resistance heating alloy wires as the heat source, magnesium oxide as the thermally conductive insulator, and stainless steel or copper as the sheath, manufactured using a special production process. When current flows through the heating core wire, electrical energy is converted into heat energy to heat the oil reservoir.

[0004] Currently, electric heating technology mainly uses MI cables, with high-purity magnesium oxide as the insulation material. However, its thermal conductivity, thermal stability, insulation performance, and long-term service performance are limited by many factors such as purity, chemical properties, particle shape, particle size distribution, crystal shape, and filling process. Therefore, developing a method for preparing an insulation material for high-power downhole heaters, and endowing it with good insulation, mechanical strength, thermal conductivity, and stability, is of great practical significance. Summary of the Invention

[0005] In view of the above problems, the present invention proposes an insulating material for a downhole high-power heater and a method for preparing the same, which overcomes or at least partially solves the above problems.

[0006] In a first aspect, embodiments of the present invention provide an insulating material for a high-power downhole heater. The insulating material is an insulating ceramic material prepared by ball milling, drying and granulation, aging and molding, and plastic sintering of a mixture comprising magnesium oxide, manganese-containing dopants, zirconium-containing dopants, and modifying reagents.

[0007] Optionally, the mass content of manganese-containing dopant in the mixed material is 0.1-2.7%, the mass content of zirconium-containing dopant in the mixed material is 0.1-2.7%, and the mass content of modifying reagent in the mixed material is 1-9%.

[0008] Optionally, the manganese-containing dopant material is a manganese salt.

[0009] Optionally, the manganese-containing dopant material is a manganese oxide.

[0010] Optionally, the manganese-containing doping material is a manganate.

[0011] Optionally, the manganese-containing dopant material is a manganese coordination compound.

[0012] Optionally, the zirconium-containing doping material is a compound formed by zirconium and a nonmetal.

[0013] Optionally, the zirconium-containing doping material is an intermetallic compound formed by zirconium and a metalloid.

[0014] Optionally, the zirconium-containing doping material is a zirconium salt.

[0015] Optionally, the zirconium-containing doping material is a zirconate.

[0016] Optionally, the modifying agent is at least one of sodium stearate, sodium dodecyl sulfate, sodium dodecyl sulfonate, CTAB, and tetrabutyl titanate.

[0017] Secondly, embodiments of the present invention provide a method for preparing insulating materials for a downhole high-power heater, comprising:

[0018] A slurry raw material is obtained by wet ball milling of a mixture of materials containing magnesium oxide, manganese-containing dopants, zirconium-containing dopants, and modifying agents.

[0019] The slurry raw material is dried and then sieved to obtain powder material;

[0020] The binder is added to the powder material for granulation, and then pressed into a ceramic blank;

[0021] The ceramic blank is crushed, reshaped, and aged to obtain ceramic green sheets;

[0022] Insulating ceramic materials are obtained by sintering raw ceramic sheets through plastic extrusion.

[0023] Optionally, after obtaining the ceramic green sheet, the process further includes:

[0024] Determine whether the particle size of the current ceramic green chips meets the particle size requirements;

[0025] If not, use the current ceramic raw material as raw material and return to the step of obtaining slurry raw material through wet ball milling.

[0026] The beneficial effects of the above-mentioned technical solution provided by the present invention include at least the following:

[0027] (1) The insulating material for downhole high-power heaters provided by this invention is an insulating ceramic material prepared by ball milling, drying and granulation, aging and molding, and plastic sintering of a mixture containing magnesium oxide, manganese-containing dopants, zirconium-containing dopants, and modifying agents. Since the manganese-containing dopants and zirconium-containing dopants can form solid solutions with magnesium oxide, they can activate the lattice of magnesium oxide crystals, improve the density and strength of the material, and enhance the insulation performance. The modifying agents reduce the vacancy defects in MgO grains, making it less prone to moisture absorption and forming MgO-OH structures, thus improving the volume resistivity. The resulting insulating ceramic material has good high-temperature insulation performance and can be used as an insulating material for downhole high-power heaters.

[0028] (2) The method for preparing the manganese-doped high-power heater insulation material provided by the present invention is simple, easy to operate, and suitable for industrial production.

[0029] The technical solution of the present invention will be further described in detail below through embodiments. Attached Figure Description

[0030] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0031] Figure 1 This is a flowchart of the method for preparing insulating materials for a high-power downhole heater in this invention. Detailed Implementation

[0032] Exemplary embodiments of the present invention are described in detail below. While exemplary embodiments have been disclosed, it should be understood that the invention may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0033] To address the problems existing in the prior art, this invention provides an insulating material for a downhole high-power heater and a method for preparing the same.

[0034] This invention provides an insulating material for a high-power downhole heater, which is a uniform insulating ceramic material that still has good electrical resistance at high temperatures. It is made by ball milling, drying and granulation, aging and molding, and plastic sintering of a mixture containing magnesium oxide, manganese dopant, zirconium dopant and modifying reagent.

[0035] Since manganese-containing and zirconium-containing doped materials can form solid solutions with magnesium oxide, they can activate the lattice of magnesium oxide crystals, improve the density and strength of the material, and enhance its insulation performance. The modifying agent reduces the vacancy defects in MgO grains, making it less prone to moisture absorption and forming a MgO-OH structure, thus improving the volume resistivity. The resulting insulating ceramic material has good high-temperature insulation performance and can be used as an insulating material for high-power heaters in underground mines, ensuring that it will not break down at a high temperature of 650 degrees Celsius.

[0036] Optionally, the purity of magnesium oxide shall not be less than 80%.

[0037] Optionally, the mass content of manganese-containing dopants in the mixed material is 0.1–2.7%, the mass content of zirconium-containing dopants in the mixed material is 0.1–2.7%, and the mass content of modifying reagents in the mixed material is 1–9%.

[0038] Optionally, the manganese-containing doped material can be in the following forms:

[0039] (1) Manganese-containing dopants are manganese salts.

[0040] It can be manganese acetate or manganese stearate, or it can be manganese carbonyl, manganese tungstate, manganese citrate, manganese trifluoromethanesulfonate (II), manganese carbonate (II), manganese perchlorate, etc.

[0041] (2) The manganese-containing doping material is a manganese oxide.

[0042] It can be an oxide of manganese in various valence states, such as manganese monoxide, manganese dioxide, manganese trioxide, manganese tetroxide, etc.; it can also be an oxide form such as lithium manganese nickel oxide, lithium nickel manganese cobalt oxide, etc.

[0043] (3) The manganese-containing doped materials are manganates.

[0044] Examples include barium manganate, potassium permanganate, and lithium permanganate (III,IV).

[0045] (4) The manganese-containing doped material is a manganese coordination compound.

[0046] It can be tricarbonylcyclopentadienyl manganese (I), tetra-p-tolylporphyrin manganese, or di(ethylcyclopentadienyl)manganese (II), tris(2,2,6,6-tetramethyl-3,5-heptanediol)manganese (III), etc.

[0047] Optionally, the zirconium-containing doped material can be in the following forms:

[0048] (1) The zirconium-containing doped material is a compound formed by zirconium and a nonmetal.

[0049] It can be zirconium oxide or zirconium oxychloride, or zirconium iodide, zirconium chloride, zirconium fluoride, zirconium dichlorocerocene, tetra(dimethylammonium)zirconium, etc.

[0050] (2) The zirconium-containing doped material is an intermetallic compound formed by zirconium and a metalloid.

[0051] It can be zirconium carbide, zirconium nitride; it can also be zirconium sulfide, zirconium hydride, zirconium boride, etc.

[0052] (3) The zirconium-containing doping material is a zirconium salt.

[0053] Examples include zirconium n-propoxide, zirconium acetylacetonate, and zirconium silicate.

[0054] (4) The zirconium-containing doped material is a zirconate.

[0055] It can be ammonium fluorozirconate, barium zirconate, etc.

[0056] Optionally, the above-mentioned modifying agent may be at least one of sodium stearate, sodium dodecyl sulfate, sodium dodecyl sulfonate, CTAB, and tetrabutyl titanate.

[0057] This invention provides a method for preparing insulating materials for downhole high-power heaters, see [link to relevant documentation]. Figure 1 As shown, it includes the following steps:

[0058] Step S11: The mixture containing magnesium oxide, manganese dopant, zirconium dopant and modifying reagent is wet-milled to obtain a slurry raw material.

[0059] For details regarding the specific materials and their mass ratios of magnesium oxide, manganese-containing doped materials, zirconium-containing doped materials, and modifying reagents, please refer to the above description.

[0060] Alternatively, magnesium oxide raw material, manganese-containing dopant material, zirconium-containing dopant material, and modifying reagent can be wet-milled in agate balls and anhydrous ethanol for 6–12 hours to obtain a slurry raw material.

[0061] Step S12: After drying the slurry raw material, sieve it to obtain powder material.

[0062] After drying the slurry raw material, it is passed through a 40-100 mesh sieve to obtain the undersize powder material.

[0063] Step S13: Add the binder to the powder material for granulation, and then press it into a ceramic blank.

[0064] The binder is added to the powder for granulation. During the granulation process, the binder and the powder are thoroughly mixed and homogeneous, and then the mixture can be pressed into a ceramic blank.

[0065] Furthermore, the adhesive can be polyvinyl alcohol (PVA) with a mass fraction of 5-10 wt.%; alternatively, other adhesives can also be used.

[0066] Step S14: Crush, reshape and age the ceramic blank to obtain ceramic green sheets.

[0067] Optionally, after obtaining the ceramic green slabs, the following may also be included:

[0068] Determine whether the particle size of the current ceramic green sheet meets the particle size requirements; if not, use the current ceramic green sheet as raw material and return to the step of obtaining slurry raw material through wet ball milling.

[0069] In the process of re-preparing ceramic green sheets using the current ceramic green sheets as raw materials, the previous preparation process can be kept unchanged, or agate balls with higher hardness can be selected, and / or sieves with smaller mesh sizes can be selected.

[0070] Step S15: Perform plastic sintering on the ceramic green sheets to obtain insulating ceramic material.

[0071] This may include heating the formed ceramic green sheet to 500-700°C at a heating rate of 5°C / min, maintaining this temperature for 30-120 minutes for debinding; then heating it to 1000-2000°C in a high-temperature muffle furnace, maintaining this temperature for 1-48 hours for high-temperature sintering to obtain an insulating ceramic material.

[0072] The method for preparing insulating materials for downhole high-power heaters provided by this invention is simple, easy to operate, and suitable for industrial production.

[0073] Example 1

[0074] Weigh out and add 1000g of magnesium oxide (99.99% purity), 5g of manganese dioxide, 5g of zirconium dioxide, 30g of sodium dodecyl sulfate, and an appropriate amount of anhydrous ethanol to a star-shaped ball mill. Perform wet ball milling for 9 hours. Transfer the raw materials to an oven and dry at 120℃ for 24 hours. Pass the dried materials through a 40-mesh sieve. Add 5wt.% polyvinyl alcohol (PVA) as a binder to the powder for granulation. During granulation, ensure the binder and powder are thoroughly and evenly mixed. Then press the powder into a ceramic green body. Crush, reshape, and age the ceramic green body to obtain ceramic green sheets. Heat the shaped ceramic green sheets to 500℃ at a heating rate of 5℃ / min and hold for 30 minutes for debinding. Immediately afterwards, heat to 1400℃ in a high-temperature muffle furnace and hold for 48 hours to sinter the ceramic green sheets at high temperature to obtain ceramic samples.

[0075] Example 2

[0076] Weigh out 1000g of magnesium oxide (99.99% purity), 1g of manganese acetate, 9g of zirconium oxychloride, 10g of sodium dodecyl sulfate, and an appropriate amount of anhydrous ethanol, and add them to a star-shaped ball mill. Wet ball mill for 9 hours. Transfer the raw materials to an oven and dry at 120℃ for 24 hours. Pass the dried materials through a 40-mesh sieve. Add 5wt.% polyvinyl alcohol (PVA) as a binder to the powder for granulation. During granulation, ensure the binder and powder are thoroughly and evenly mixed. Then press the powder into a ceramic green body. Crush, reshape, and age the ceramic green body to obtain ceramic green sheets. Heat the shaped ceramic green sheets to 500℃ at a heating rate of 5℃ / min and hold for 30 minutes for debinding. Immediately afterwards, heat to 1400℃ in a high-temperature muffle furnace and hold for 48 hours to sinter the ceramic green sheets at high temperature to obtain ceramic samples.

[0077] Example 3

[0078] Weigh out and add 1000g of magnesium oxide (99.99% purity), 3g of manganese stearate, 7g of zirconium carbide, 10g of sodium dodecyl sulfate, and an appropriate amount of anhydrous ethanol to a star-shaped ball mill. Perform wet ball milling for 9 hours. Transfer the raw materials to an oven and dry at 120℃ for 24 hours. Pass the dried materials through a 40-mesh sieve. Add 5wt.% polyvinyl alcohol (PVA) as a binder to the powder for granulation. During granulation, ensure the binder and powder are thoroughly and evenly mixed. Then press the powder into a ceramic green body. Crush, reshape, and age the ceramic green body to obtain ceramic green sheets. Heat the shaped ceramic green sheets to 500℃ at a heating rate of 5℃ / min and hold for 30 minutes for debinding. Immediately afterwards, heat to 1400℃ in a high-temperature muffle furnace and hold for 48 hours to sinter the ceramic green sheets at high temperature to obtain ceramic samples.

[0079] Example 4

[0080] Weigh out and add 1000g of magnesium oxide (99.99% purity), 7g of lithium manganese nickel oxide, 3g of zirconium nitride, 20g of sodium dodecyl sulfate, and an appropriate amount of anhydrous ethanol to a star-shaped ball mill. Wet ball mill for 9 hours. Transfer the raw materials to an oven and dry at 120℃ for 24 hours. Pass through a 40-mesh sieve. Add 5wt.% polyvinyl alcohol (PVA) as a binder to the powder for granulation. During granulation, ensure the binder and powder are thoroughly and evenly mixed. Then press into ceramic blanks. Crush, reshape, and age the ceramic blanks to obtain ceramic green sheets. Heat the shaped ceramic green sheets to 500℃ at a heating rate of 5℃ / min and hold for 30 minutes for debinding. Immediately afterwards, heat to 1400℃ in a high-temperature muffle furnace and hold for 48 hours to sinter the ceramic green sheets at high temperature to obtain ceramic samples.

[0081] The preparation process of subsequent Examples 5-19 is the same as above, except that the composition and mass ratio of the raw materials used are different, as shown in Tables 1 and 2, which will not be repeated here.

[0082] The ceramic sheet is machined according to the sample size requirements of the performance to be tested. For samples for electrical performance testing, silver electrodes need to be coated on the surface of the machined ceramic sheet and the electrodes need to be fired at 800℃ for 30 minutes. Then, the corresponding electrical performance tests are carried out.

[0083] Using existing high-purity magnesium oxide ceramic materials as comparative examples, the electrical performance test results of the ceramic samples prepared in Examples 1-19 and the four comparative examples at corresponding temperatures are shown in Tables 1 and 2:

[0084] Table 1. Raw material composition of Examples 1-15 and statistical results of electrical performance tests of Examples 1-15 and the comparative example.

[0085]

[0086]

[0087] Table 2. Statistical table of raw material composition and electrical performance test results for Examples 16-19

[0088]

[0089] As can be seen, the ceramic samples prepared in Examples 1-19 still have a volume resistivity higher than 160 MΩ·cm even at a high temperature of 650℃. The ceramic samples prepared in this example have high insulation performance and can meet the requirements of not being broken down at high temperatures. In contrast, high-purity magnesium oxide ceramic materials have a high risk of being broken down at high temperatures.

[0090] The comparison of Examples 16-19 also reveals that the higher the purity of magnesium oxide in the mixed material, the better the insulation of the resulting insulating ceramic material.

[0091] Furthermore, in more embodiments, it was found that during the preparation process, at least two of the following modified reagents were selected: sodium stearate, sodium dodecyl sulfate, sodium dodecyl sulfonate, CTAB, and tetrabutyl titanate. A 40-100 mesh sieve was used. The formed ceramic green sheets were subjected to debinding treatment at a constant temperature of 500-700℃ for 30-120 minutes. The ceramic green sheets were then heated to 1000-2000℃ in a high-temperature muffle furnace and sintered at this temperature for 1-48 hours. All of these methods yielded insulating ceramic materials with satisfactory insulation properties.

[0092] It should also be noted that the raw materials used in the preparation of insulating ceramic materials in the embodiments of the present invention and the materials involved in the comparative examples are all commercially available products.

[0093] The foregoing description includes examples of one or more embodiments. Of course, those skilled in the art will recognize that the various embodiments can be further combined and arranged. Therefore, the embodiments described herein are intended to cover all such changes, modifications, and variations that fall within the scope of the appended claims. Furthermore, the term "comprising" as used in the specification or claims is interpreted in a manner similar to the term "including," as interpreted when used as a conjunction in the claims. Additionally, the use of any term "or" in the specification of the claims is intended to mean "non-exclusive or."

[0094] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from the concept and scope of the invention. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. An insulating material for a high-power downhole heater, characterized in that, The insulating material is an insulating ceramic material made by ball milling, drying and granulation, aging and molding, and plastic sintering of a mixture of magnesium oxide, manganese-containing dopants, zirconium-containing dopants and modifying reagents.

2. The insulating material for a high-power downhole heater as described in claim 1, characterized in that, The mass content of manganese-containing dopant in the mixed material is 0.1-2.7%, the mass content of zirconium-containing dopant in the mixed material is 0.1-2.7%, and the mass content of modifying reagent in the mixed material is 1-9%.

3. The insulating material for a high-power downhole heater as described in claim 1, characterized in that, The manganese-containing dopant material is a manganese salt.

4. The insulating material for a high-power downhole heater as described in claim 1, characterized in that, The manganese-containing dopant material is a manganese oxide.

5. The insulating material for a high-power downhole heater as described in claim 1, characterized in that, The manganese-containing doping material is a manganate.

6. The insulating material for a high-power downhole heater as described in claim 1, characterized in that, The manganese-containing dopant material is a manganese coordination compound.

7. The insulating material for a high-power downhole heater as described in claim 1, characterized in that, The zirconium-containing doping material is a compound formed by zirconium and a nonmetal.

8. The insulating material for a high-power downhole heater as described in claim 1, characterized in that, The zirconium-containing doped material is an intermetallic compound formed by zirconium and a metalloid.

9. The insulating material for a high-power downhole heater as described in claim 1, characterized in that, The zirconium-containing doping material is a zirconium salt.

10. The insulating material for a high-power downhole heater as described in claim 1, characterized in that, The zirconium-containing doped material is a zirconate.

11. The insulating material for a high-power downhole heater as described in claim 1, characterized in that, The modifying agent is at least one of sodium stearate, sodium dodecyl sulfate, sodium dodecyl sulfonate, CTAB, and tetrabutyl titanate.

12. A method for preparing insulating material for a high-power downhole heater, characterized in that, include: A slurry raw material is obtained by wet ball milling of a mixture of materials containing magnesium oxide, manganese-containing dopants, zirconium-containing dopants, and modifying agents. The slurry raw material is dried and then sieved to obtain powder material; The binder is added to the powder material for granulation, and then pressed into a ceramic blank; The ceramic blank is crushed, reshaped, and aged to obtain ceramic green sheets; Insulating ceramic materials are obtained by sintering raw ceramic sheets through plastic extrusion.

13. The method as described in claim 12, characterized in that, After obtaining the ceramic green sheet, the process further includes: Determine whether the particle size of the current ceramic green chips meets the particle size requirements; If not, use the current ceramic raw material as raw material and return to the step of obtaining slurry raw material through wet ball milling.

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