Phase change composite material for oil-based drilling fluid as well as preparation method and application of phase change composite material

Abstract

The invention provides a phase-change composite material for an oil-based drilling fluid as well as a preparation method and application of the phase-change composite material. The phase-change composite material for the oil-based drilling fluid comprises a phase-change basic substance, an amination modified porous material, modified asphalt and macrocyclic compound molecule cucurbituril [n]. The preparation method comprises the following steps: mixing NaNO3, KNO3 and LiNO3, heating, cooling and crushing to obtain a phase change basic substance; carrying out modification treatment on expanded graphite and / or montmorillonite to obtain an amination modified porous material; the preparation method comprises the following steps: adding macrocyclic compound molecule cucurbituril [n] into an aqueous solution of an amination modified porous material to obtain a first suspension, preparing a phase change basic substance into a solution, adding the solution into the first suspension to obtain a second suspension, and calcining the second suspension to obtain a first phase change composite material; and dissolving the modified asphalt in petroleum ether to obtain a third suspension, dispersing the first phase-change composite material in the third suspension, freezing, performing vacuum filtration, and drying to obtain the phase-change composite material for the oil-based drilling fluid.

Description

Technical Field

[0001] This invention relates to the field of oilfield drilling, and more specifically, to a phase change composite material for oil-based drilling fluids, its preparation method, and its application in oil-based drilling fluids. Background Technology

[0002] Currently, the demand for oil and natural gas is growing rapidly, and the exploitation of conventional oil and gas reservoirs has entered a depletion stage. There is a need to develop deep and ultra-deep oil and gas reservoirs to meet the ever-increasing energy demands of humankind. Oil-based drilling fluids possess advantages such as high-temperature stability, good lubricity, resistance to formation hydration and swelling, fast drilling speed, good sand carrying capacity, and strong anti-fouling ability, making them widely used in deep wells, high-temperature and high-pressure wells, complex wells, water-sensitive formations, and saline bottom layers. As drilling depth increases, formation temperature continues to rise, and a large amount of heat is generated during prolonged drilling. Traditional oil-based drilling fluids have poor heat transfer capacity and cannot effectively transfer this heat, leading to increased temperatures in the bottom hole tools and drilling fluid. This damages the drill bit and rotary steerable tools, preventing the transmission of effective information to the surface and hindering normal drilling operations. Particularly when drilling horizontal wells with oil-based drilling fluids, the failure rate of rotary steerable tools at the bottom hole temperature of 120–150°C reaches as high as 32%. Therefore, capturing and storing the heat energy generated by the formation and the friction between the drill bit and the formation is crucial for the successful completion of drilling operations. Currently, surface cooling devices can be used to reduce the temperature of drilling fluid returning from the wellbore. However, this method only indirectly reduces the circulating temperature of the drilling fluid within the wellbore by lowering the inlet temperature, failing to meet the cooling requirements of the high-temperature drilling fluid and drilling tools at the bottom of the well, and incurring significant energy losses. Phase change materials (PCMs) absorb or release heat during phase change. Utilizing this property effectively can reduce the temperature within the wellbore and alter the temperature field distribution of the fluid. However, leakage problems may occur when PCMs transform from a solid to a liquid state. Drilling fluid phase change temperature control materials often employ encapsulation methods such as microencapsulation, porous material molding, and coaxial classical spinning to prevent leakage. This method encapsulates the PCM within a certain space, isolating it from contact with the external environment. This solves the leakage problem during the solid-to-liquid transformation of PCMs and also controls the issue of increased volume, increased heat transfer area, and reduced temperature control effectiveness during the phase change process.

[0003] For example, patent CN115491183A, published on December 20, 2022, discloses a method for preparing high-temperature and high-pressure resistant microspheres for active cooling of high-temperature drilling fluids and their application. The phase change core material of the microspheres is an organic polymer material (paraffin-modified composite material), and the wall material is nano-silica. The organic polymer phase change material is modified and subjected to high-pressure spray treatment, and the high-temperature and high-pressure resistance of the microspheres is improved by in-situ polymerization. The nano-silica forms a dense shell through self-assembly deposition, and the particle size of the phase change microspheres is controllable. The phase change microspheres in this invention are used for cooling water-based drilling fluids, but cannot be used for cooling oil-based drilling fluids in deep wells and horizontal wells. Patent CN117701255A, published on March 15, 2024, discloses a phase change capsule for drilling fluid cooling, its preparation method, and its application. The capsule's core material is a mixture of NaNO3 and KNO3, and the shell material is silicon dioxide. Cellulose nanofibers are used to supplement the shell, which can improve the capsule's mechanical strength and thermodynamic properties. However, the phase change microspheres in this invention can only be used for cooling water-based drilling fluids and cannot be used for cooling oil-based drilling fluids in deep wells or horizontal wells. Patent CN116063996A, published on May 5, 2023, discloses a phase change heat storage microcapsule material suitable for drilling fluid cooling and its preparation method. The microcapsule's polymer wall material is polyethersulfone, and the core material is erythritol. Nano-graphite is incorporated to improve the capsule's thermal conductivity, heat transfer rate, latent heat of phase change, and encapsulation filtration. However, this invention does not clearly define the effect of phase change microcapsules on drilling fluid performance and is only applicable to water-based drilling fluids. Patent CN118206957A, published on June 18, 2024, discloses a phase change material for cooling the bottom of drilling wells and its preparation method. The preparation steps are as follows: heating the phase change material (paraffin, butyl stearate, or ethylene distearate) to melt, adding a thermally conductive material (at least one of carbon nanotubes, graphite, and alumina), then adding polyethylene, grinding into powder to obtain a modified phase change material; calcining and modifying montmorillonite, dispersing it in deionized water, adding nanomaterials (silver nanowires or nanographite), adding chitosan solution, drying to obtain a wall material; heating the modified phase change material to melt to obtain an oil phase; dispersing the wall material in deionized water to obtain an aqueous phase; adding the oil phase to the aqueous phase, then ultrasonically dispersing, drying, and then spraying with a polyurea waterproof coating (to prevent leakage) to obtain the phase change material for cooling the bottom of drilling wells. However, this invention uses a large amount of phase change material, resulting in limited cooling effect and a relatively complex preparation method. Furthermore, the impact of the phase change material on drilling fluid performance is not yet clear. Patent CN117821032A, published on April 5, 2024, discloses a phase change material for oil-based drilling fluids, comprising: tris(hydroxymethyl)aminomethane, tris(hydroxymethyl)ethane, graphite, rubber, and asphalt.It mainly improves the thermal conductivity of phase change materials through the combined effect of expanded graphite, rubber and asphalt. However, its phase change temperature only reaches 127.88℃, and the size of the phase change material is not clearly defined. There is a possibility that the size is too large to pass through a 200-mesh vibrating screen for recycling and reuse.

[0004] Furthermore, because oil-based drilling fluids have lower heat transfer efficiency and specific heat capacity than water-based drilling fluids, their heat absorption and cooling capabilities are inferior in high-temperature formations. When drilling with oil-based drilling fluids, the drill string and rotary steering tools inside the wellbore are more susceptible to damage, leading to reduced drilling efficiency. Current research has not yet solved the wellbore cooling problem for oil-based drilling fluids. Most disclosed phase change cooling materials are used with water-based drilling fluids, and their preparation processes are stringent, requiring a two-step method to prepare phase change microcapsules. Therefore, based on current research in high-temperature drilling, it is necessary to develop new phase change materials for cooling oil-based drilling fluids. In addition to reducing the temperature of the drilling fluid inside the wellbore and being reusable, the material's impact on drilling fluid performance must also be considered to ensure improved drilling efficiency and effectiveness. Summary of the Invention

[0005] The purpose of this invention is to overcome at least one of the aforementioned deficiencies in the prior art. For example, one objective of this invention is to improve a phase change composite material for oil-based drilling fluids.

[0006] To achieve the above objectives, the present invention provides a phase change composite material for oil-based drilling fluids.

[0007] The phase change composite material for oil-based drilling fluids includes: phase change base material, aminated modified porous material, modified bitumen, and macrocyclic compound cucurbita[n].

[0008] In an exemplary embodiment of the phase change composite material for oil-based drilling fluid of the present invention, the phase change base material may be a nitrate eutectic composed of NaNO3, KNO3 and LiNO3, the aminated modified porous material may be amino-expanded graphite and / or amino-montmorillonite, the modified asphalt may be one or more of acrylic resin modified asphalt, polyethylene modified asphalt and petroleum resin modified asphalt, and the macrocyclic compound molecule cucurbita[n] may be one or more of cucurbita[5], cucurbita[6] and cucurbita[7], wherein the molar ratio of NaNO3, KNO3 and LiNO3 may be 2:3:2 to 3:2:2.

[0009] In an exemplary embodiment of the phase change composite material for oil-based drilling fluid of the present invention, the phase change temperature of the phase change composite material for oil-based drilling fluid can be 133.9 to 143.2°C, and the particle size range of the phase change composite material can be 35 to 68 μm.

[0010] Another aspect of the present invention provides a method for preparing a phase change composite material for oil-based drilling fluids, the method comprising the following steps:

[0011] S1. The phase change basic material can be obtained by mixing, heating, cooling and pulverizing NaNO3, KNO3 and LiNO3.

[0012] S2. The aminated modified porous material can be obtained by modifying expanded graphite and / or montmorillonite.

[0013] S3. The macrocyclic compound molecule cucurbita[n] can be added to the aqueous solution of the aminated modified porous material to obtain a first suspension. The phase change basic material can be prepared into a solution and added to the first suspension to obtain a second suspension. The second suspension can be calcined to obtain a first phase change composite material.

[0014] S4. The modified asphalt can be dissolved in petroleum ether to obtain a third suspension. After dispersing the first phase change composite material in the third suspension, the oil-based drilling fluid phase change composite material can be obtained by freezing, vacuum filtration, and secondary drying.

[0015] In an exemplary embodiment of the preparation method of the phase change composite material for oil-based drilling fluid of the present invention, the molar ratio of NaNO3, KNO3 and LiNO3 can be 2:3:2 to 3:2:2; the molar ratio of the aminated modified porous material, the macrocyclic compound cucurbita[n], the modified bitumen and the phase change base material can be 1:1:2:10 to 1:2.5:5:10.

[0016] In an exemplary embodiment of the preparation method of the phase change composite material for oil-based drilling fluid of the present invention, the heating temperature can be 235-250°C, and the heating time can be 10-12 h; the dispersion stirring speed is 1000-1300 r / min, and the dispersion stirring time is 20-30 min; the freezing temperature is -5 to -8°C, and the freezing time is 1-3 h; the secondary drying temperature can be 80-100°C, and the secondary drying time can be 10-12 h.

[0017] In an exemplary embodiment of the preparation method of the phase change composite material for oil-based drilling fluid of the present invention, step S2 may further include the following steps:

[0018] S21. The aminated modified porous material can be dispersed in water, ultrasonically treated, and adjusted to an acidic solution to obtain a first solution.

[0019] S22. An aqueous solution of silane coupling agent can be added to the first solution to obtain a second solution.

[0020] S23. The first solution and the second solution can be mixed and subjected to an alkylation reaction, and the aminated modified porous material can be obtained by drying after removing unreacted silane coupling agent in one step.

[0021] In an exemplary embodiment of the preparation method of phase change composite material for oil-based drilling fluid of the present invention, the pH value of the acidic solution can be 3-5, the ultrasonic treatment time can be 30-50 min; the temperature of the alkylation reaction can be 80-100℃, the alkylation reaction time can be 22-24 h; the primary drying temperature can be 80-100℃, and the primary drying time can be 22-24 h.

[0022] In an exemplary embodiment of the preparation method of the phase change composite material for oil-based drilling fluid of the present invention, step S3 may further include the following steps:

[0023] S31. The first suspension may be stirred at 80-85°C for 8-12 hours.

[0024] S32. The second suspension may be stirred at 60-65°C for 7-9 hours.

[0025] In another aspect, the present invention provides the application of any of the above-described phase change composite materials for oil-based drilling fluids in oil-based drilling fluids, wherein, based on the total weight of the oil-based drilling fluid, the amount of phase change composite material added to the oil-based drilling fluid can be less than or equal to 6 wt.%.

[0026] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0027] (1) The phase change composite material for oil-based drilling fluid of the present invention introduces aminated modified porous structure material, and introduces modified asphalt and supramolecular compound cucurbita[n] with cavity structure, which can enhance the lubricity of phase change composite material, and optimize the porous structure of expanded graphite and / or aminomontmorillonite by self-assembly to recognize amino, adsorb more phase change basic materials, and improve the thermal conductivity and thermal cycling stability of phase change composite material.

[0028] (2) The phase change composite material prepared by the present invention can be directly used for cooling oil-based drilling fluid. It has little effect on the rheology and emulsification stability of drilling fluid, which is beneficial to reducing its high-temperature filtration loss and frictional resistance, and is beneficial to the filtration loss and lubricity of drilling fluid.

[0029] (3) The preparation method of phase change composite material for oil-based drilling fluid of the present invention directly immerses the phase change material into the porous material, which is simpler and lower in cost than the encapsulation technology commonly used in the prior art, such as microencapsulation, porous material molding, and coaxial classical spinning. Attached Figure Description

[0030] The above and other objects and / or features of the present invention will become clearer from the following description taken in conjunction with the accompanying drawings, in which:

[0031] Figure 1 The DSC and TGA curves of a test example of the phase change composite material for oil-based drilling fluids of the present invention, NIT / CB@EG-Asp-2, are shown.

[0032] Figure 2 The temperature curve of a test example of the phase change composite material for oil-based drilling fluid of the present invention, NIT / CB@EG-Asp-4, after a heating-cooling cycle is shown. Detailed Implementation

[0033] In the following sections, phase change composite materials for oil-based drilling fluids, their preparation methods, and applications will be described in detail with reference to exemplary embodiments.

[0034] It should be noted that "first", "second", "third"... "S1", "S2", "S3", "S4"... "once", "twice"... etc. are only for the convenience of description and distinguishing similar objects, and should not be interpreted as describing a specific order or sequence or indicating or implying relative importance.

[0035] While the scientific community is currently dedicated to solving the cooling challenges in high-temperature wellbore environments, a dedicated cooling solution for oil-based drilling fluids remains lacking. Therefore, we urgently need to innovatively develop a phase change cooling material specifically designed for oil-based drilling fluids, based on current research findings in high-temperature drilling technology.

[0036] To address the aforementioned problems, the inventors proposed a phase change composite material for oil-based drilling fluids to solve the issue of unsatisfactory wellbore cooling effect in existing oil-based drilling fluids. The phase change composite material for oil-based drilling fluids in this invention consists of a phase change base material, an aminated modified porous material, modified asphalt, and macrocyclic compound molecules. The phase change base material is a nitrate eutectic composed of NaNO3, KNO3, and LiNO3; the aminated modified porous material is aminated expanded graphite and / or aminomontmorillonite; the modified asphalt is one or more of acrylic resin modified asphalt, polyethylene modified asphalt, and petroleum resin modified asphalt; and the macrocyclic compound molecule is cucurbita[n]. This invention impregnates the phase change base material into the aminated modified porous material and introduces modified asphalt and the macrocyclic compound molecule cucurbita[n] with a cavity structure. Therefore, it enhances the lubricity of the phase change composite material and, through self-assembly and recognition of amino groups, optimizes the porous structure of expanded graphite and / or aminomontmorillonite, adsorbing more phase change base material and improving the thermal conductivity and thermal cycling stability of the phase change composite material.

[0037] To better illustrate the present invention and facilitate understanding of its technical solutions, typical but non-limiting exemplary embodiments of the present invention are as follows:

[0038] Exemplary Example 1

[0039] This exemplary embodiment provides a phase change composite material for oil-based drilling fluids, which includes a phase change base material, an aminated modified porous material, modified bitumen, and a macrocyclic compound cucurbita[n].

[0040] In this exemplary embodiment, the phase change base material may be a nitrate eutectic composed of NaNO3, KNO3, and LiNO3; the aminated modified porous material may be amino-expanded graphite and / or amino-montmorillonite; the modified asphalt may be one or more of acrylic resin modified asphalt, polyethylene modified asphalt, and petroleum resin modified asphalt; and the macrocyclic compound molecule cucurbituril[n] may be one or more of cucurbituril[5], cucurbituril[6], and cucurbituril[7]. The molar ratio of NaNO3, KNO3, and LiNO3 may be 2:3:2 to 3:2:2.

[0041] In this exemplary embodiment, the phase change temperature of the phase change composite material for oil-based drilling fluids can be 133.9–143.2 °C, and the particle size of the phase change composite material can be 35–68 μm. For example, the phase change temperature can be 133.9, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, and 143.2 °C, and the particle size can be 35, 40, 45, 50, 55, 60, 65, and 68 μm.

[0042] Exemplary Example 2

[0043] This exemplary embodiment provides a method for preparing a phase change composite material for oil-based drilling fluids, as in Exemplary Embodiment 1. The preparation method includes the following steps:

[0044] S1. NaNO3, KNO3 and LiNO3 are mixed, heated, cooled and pulverized to obtain the phase change basic material.

[0045] In this exemplary embodiment, the ratio of NaNO3, KNO3 and LiNO3 can be 2:3:2 to 3:2:2.

[0046] In this exemplary embodiment, the heating temperature can be 235 to 250°C, and the heating time can be 10 to 12 hours. For example, the heating temperature can be 235, 240, 245, or 250°C, and the heating time can be 10, 11, or 12 hours.

[0047] S2. Modify expanded graphite and / or montmorillonite to obtain aminated modified porous materials.

[0048] In this exemplary embodiment, step S2 may further include the following steps:

[0049] S21. Aminated modified porous materials can be dispersed in water, ultrasonically treated, and adjusted to an acidic solution to obtain a first solution.

[0050] In this exemplary embodiment, the pH range of the acidic solution may be 3 to 5, for example, the pH may be 3, 4 and 5.

[0051] In this exemplary embodiment, the ultrasonic treatment time can be 30 to 50 minutes, for example, 30, 35, 40, 45, or 50 minutes.

[0052] In this exemplary embodiment, hydrochloric acid can be used to adjust the solution to an acidic state.

[0053] S22. An aqueous solution of silane coupling agent can be added to the first solution to obtain the second solution.

[0054] In this exemplary embodiment, the silane coupling agent may be γ-aminopropyltriethoxysilane.

[0055] S23. The first solution and the second solution can be mixed and then subjected to an alkylation reaction. After removing the unreacted silane coupling agent, the material can be dried once to obtain an aminated modified porous material.

[0056] In this exemplary embodiment, the alkylation reaction temperature can be 80–100°C, and the alkylation reaction time can be 22–24 h. For example, the alkylation reaction temperature can be 80, 85, 90, 95, or 100°C, and the alkylation reaction time can be 22, 23, or 24 h. The primary drying temperature can be 80–100°C, and the primary drying time can be 22–24 h.

[0057] In this exemplary embodiment, filtration can be performed under vacuum conditions, and the mixture can be repeatedly washed with methanol and deionized water to remove unreacted silane coupling agent.

[0058] In this exemplary embodiment, a small amount of H2O may be retained during a single drying process.

[0059] S3. Add the macrocyclic compound molecule cucurbita[n] to the aqueous solution of the aminated modified porous material to obtain the first suspension. Prepare the phase change basic material into a solution and add it to the first suspension to obtain the second suspension. Calcine the second suspension to obtain the first phase change composite material.

[0060] In this exemplary embodiment, the ratio of the aminated modified porous material, the macrocyclic compound cucurbita[n], the modified bitumen, and the phase change base material can be 1:1:2:10 to 1:2.5:5:10.

[0061] In this exemplary embodiment, the aqueous solution of the aminated modified porous material may be an acidic solution.

[0062] In this exemplary embodiment, hydrochloric acid can be used to adjust the solution to an acidic state.

[0063] In this exemplary embodiment, step S3 may further include the following steps:

[0064] S31. The first suspension can be stirred at 80-85°C for 8-12 hours, for example, at 80, 81, 82, 83, 84, and 85°C for 8, 9, 10, 11, and 12 hours, respectively.

[0065] S32. The second suspension can be stirred at 60-65°C for 7-9 hours, for example, at 60, 61, 62, 63, 64, and 65°C for 7, 8, and 9 hours, respectively.

[0066] S4. Modified asphalt can be dissolved in petroleum ether to obtain a third suspension. After dispersing the first phase change composite material in the third suspension, it can be obtained by freezing, vacuum filtration, and secondary drying to obtain the phase change composite material for oil-based drilling fluid.

[0067] In this exemplary embodiment, the dispersion stirring speed is 1000 to 1300 r / min, and the dispersion stirring speed is 20 to 30 min. For example, the dispersion conditions are stirring at speeds of 1000, 1100, 1200, and 1300 r / min for 20, 25, and 30 min, respectively.

[0068] In this exemplary embodiment, the freezing temperature is -5 to -8°C, the freezing time is 1 to 3 hours, the secondary drying temperature is 80 to 100°C, and the secondary drying time is 10 to 12 hours. For example, the freezing temperature is -5, -6, -7, and -8°C, the freezing time is 1, 2, and 3 hours, the secondary drying temperature is 80, 85, 90, 95, and 100°C, and the secondary drying time is 10, 11, and 12 hours.

[0069] Exemplary Example 3

[0070] This exemplary embodiment provides the application of phase change composite materials for oil-based drilling fluids prepared by the preparation method of phase change composite materials for oil-based drilling fluids as in Exemplary Embodiment 1 or Exemplary Embodiment 2 in oil-based drilling fluids.

[0071] For example, an oil-based drilling fluid comprising a phase change composite material for oil-based drilling fluid, wherein the content of the phase change composite material for oil-based drilling fluid may be less than or equal to 6 wt.%.

[0072] To better understand the exemplary embodiments of the present invention described above, further descriptions are provided below in conjunction with specific examples, test cases, and accompanying drawings. However, the examples given are not intended to limit the present invention.

[0073] Example 1

[0074] This embodiment provides a phase change composite material for oil-based drilling fluids, the preparation method of which includes:

[0075] Step (1): Mix NaNO3, KNO3 and LiNO3 in a beaker at a molar ratio of 2:3:2, i.e., 2 parts NaNO3, 3 parts KNO3 and 2 parts LiNO3. Stir thoroughly and heat to 250℃ and maintain for 12h. Allow to cool naturally and pulverize thoroughly to obtain the phase change basic material (nitrate eutectic NIT).

[0076] Step (2): Disperse expanded graphite in deionized water, sonicate at room temperature for 30 min, and adjust the pH to acidic with hydrochloric acid, and stir thoroughly to form solution A; add silane coupling agent (γ-aminopropyltriethoxysilane) to deionized water and stir to form solution B; mix solutions A and B, stir at 100℃ for 24 h to complete the alkylation reaction, filter under vacuum, and wash repeatedly with methanol and deionized water to remove unreacted silane coupling agent; finally dry at 100℃ for 24 h to obtain aminated modified expanded graphite.

[0077] Step (3): Add the above-mentioned aminated modified expanded graphite to deionized water, adjust the pH of the solution to acidic with HCl, add the macrocyclic compound cucurbita[7], and stir the resulting suspension at 80°C for 12 hours; then prepare the above-mentioned nitrate eutectic into a solution and add it to the suspension, and stir at a constant temperature of 60°C for 7 hours before drying and calcining to obtain the first phase change composite material. The molar ratio of aminated modified expanded graphite: cucurbita[7]: nitrate eutectic is 1:1:10, that is, 1 part aminated modified expanded graphite, 1 part cucurbita[7] and 10 parts nitrate eutectic.

[0078] Step (4): Dissolve the acrylic resin modified bitumen in petroleum ether to obtain a third suspension. Disperse the first phase change composite material prepared in step (3) in the third suspension by stirring at 1100 r / min for 20 min. Then freeze at -5℃ for 3 h, vacuum filter, and dry to obtain the phase change composite material for oil-based drilling fluid. The molar ratio of acrylic resin modified bitumen to first phase change composite material is 2:1, that is, 2 parts acrylic resin modified bitumen and 1 part first phase change composite material.

[0079] Example 2

[0080] This embodiment provides a phase change composite material for oil-based drilling fluids, the preparation method of which includes:

[0081] Step (1): Mix NaNO3, KNO3 and LiNO3 in a beaker at a molar ratio of 3:2:2, i.e., 3 parts NaNO3, 2 parts KNO3 and 2 parts LiNO3. Stir thoroughly and heat to 250°C and maintain for 12 hours. Allow to cool naturally and pulverize thoroughly to obtain the phase change basic material (nitrate eutectic NIT).

[0082] Step (2): Disperse expanded graphite in deionized water, sonicate at room temperature for 30 min, and adjust the pH to acidic with hydrochloric acid, stirring thoroughly to form solution A; add silane coupling agent (γ-aminopropyltriethoxysilane) to deionized water and stir to form solution B; mix solutions A and B, stir at 80℃ for 24 h to complete the alkylation reaction, filter under vacuum, and wash repeatedly with methanol and deionized water to remove unreacted silane coupling agent; finally, dry at 80℃ for 24 h (retaining a small amount of H2O) to obtain aminated modified expanded graphite.

[0083] Step (3): Add the above-mentioned aminated modified expanded graphite to deionized water, adjust the pH of the solution to acidic with HCl, add macrocyclic compound molecules (cucurbita[7]), and stir the resulting suspension at 80°C for 8 hours; then prepare the above-mentioned nitrate eutectic into a solution and add it to the suspension, and stir at a constant temperature of 60°C for 7 hours before drying and calcining to obtain the first phase change composite material. Among them, the molar ratio of aminated modified expanded graphite: cucurbita[7]: nitrate eutectic is 1:1:10, that is, 1 part aminated modified expanded graphite, 1 part cucurbita[7] and 10 parts nitrate eutectic.

[0084] Step (4): Dissolve the acrylic resin modified bitumen in petroleum ether to obtain a third suspension. Disperse the first phase change composite material prepared in step (3) in the third suspension by stirring at 1100 r / min for 20 min. Then freeze at -5℃ for 3 h, vacuum filter, and dry to obtain the phase change composite material for oil-based drilling fluid. The molar ratio of acrylic resin modified bitumen to first phase change composite material is 2:1, that is, 2 parts acrylic resin modified bitumen and 1 part first phase change composite material.

[0085] The phase change composite material obtained in this embodiment is denoted as NIT / CB@EG-Asp-1.

[0086] Example 3

[0087] Steps (1) to (4) of this embodiment are the same as those of embodiment 2. The ratios of aminated modified expanded graphite: cucurbita[7]: nitrate eutectic in step (3) are changed to 1:1.5:10, 1:2:10 and 1:2.5:10 respectively, and the ratio of acrylic resin modified bitumen: first phase change composite material in step (4) is changed to 3:1, 4:1 and 5:1 respectively. Experimental schemes a, b and c can be obtained.

[0088] The phase change composite materials obtained by experimental scheme a, experimental scheme b, and experimental scheme c are respectively designated as NIT / CB@EG-Asp-2, NIT / CB@EG-Asp-3, and NIT / CB@EG-Asp-4.

[0089] Example 4

[0090] This embodiment also provides a phase change composite material. In its preparation method, steps (1) to (2) are the same as in Example 2. In step (3), aminated modified expanded graphite is weighed and dried at 80°C for 8 hours. Nitrate eutectic and aminated modified expanded graphite are mechanically stirred in deionized water for 6 hours to obtain a suspension. After slow evaporation, the suspension is maintained at 400°C for 3 hours, allowing the molten nitrate eutectic to penetrate into the porous material under the action of capillary force and surface tension. After cooling, the mixture is ground to obtain the phase change composite material, denoted as NIT@EG. The ratio of aminated modified expanded graphite to nitrate eutectic is 1:10. This phase change composite material does not contain macrocyclic compound molecules or modified bitumen.

[0091] Example 5

[0092] The steps in this embodiment are the same as steps (1) to (3) in embodiment 2, except for step (4) in embodiment 2, to obtain the first phase change composite material, denoted as NIT / CB@EG. The molar ratio of aminated modified expanded graphite: cucurbita[7]: nitrate eutectic is 1:1.5:10. This phase change composite material does not contain modified bitumen.

[0093] Example 6

[0094] The steps in this embodiment are the same as steps (1), (2), and (4) of Embodiment 2, and step (3) is the same as step (3) of Embodiment 4. The resulting phase change composite material is denoted as NIT@EG-Asp. The molar ratio of aminated modified expanded graphite, acrylic resin modified bitumen, and nitrate eutectic is 1:2:10. This phase change composite material does not contain macrocyclic compound molecules.

[0095] Example 7

[0096] The steps in this embodiment are the same as those in experimental scheme a in embodiment 3, except that the expanded graphite is replaced with montmorillonite.

[0097] Example 8

[0098] The steps in this embodiment are the same as those in experimental scheme a of embodiment 3, except that cucurbituril[7] is changed to cucurbituril[5] and cucurbituril[6], to obtain experimental scheme d and experimental scheme e respectively.

[0099] Example 9

[0100] The steps in this embodiment are the same as those in experimental scheme a of embodiment 3, except that the acrylic resin modified asphalt is replaced with polypropylene modified asphalt and petroleum resin modified asphalt, resulting in experimental scheme f and experimental scheme g, respectively.

[0101] Test Example 1

[0102] Thermal analysis of NIT / CB@EG-Asp-2 was performed using differential scanning calorimetry and thermogravimetric analysis. The test results are shown below. Figure 1 In the DSC curve, peak a has an area of ​​213.56 J / g, a peak location of 136.5℃, an initial point of 132.4℃, an ending point of 141.0℃, a width of 6.6℃ (37.000%), and a height of 0.1703 Mw / mg. Point b is the first starting point of the TG curve at 180.5℃; point c is the second starting point of the TG curve at 231.95℃; point d is the ending point of the TG curve at 248.6℃; point e is a numerical point of the TG curve with a value of 300.0℃ and 45.50%. Point f is the first peak point of the DTG curve with a peak value of 204.0℃ and a concentration of -4.38% / min; point g is the second peak point of the DTG curve with a peak value of 240.0℃ and a concentration of -3.22% / min.

[0103] It can be seen that the DSC curve of NIT / CB@EG-Asp-2 shows two endothermic reaction stages. The weight changes during the high-temperature endothermic stage in the thermogravimetric (TG) and DTG curves. Therefore, the phase transition temperature of NIT / CB@EG-Asp-2 is 136.5℃ and the latent heat of phase transition is 213.56J / g.

[0104] Test Example 2

[0105] The phase transition temperature, latent heat of phase transition, thermal conductivity, and particle size of the products obtained in Examples 1 to 9 were tested using differential scanning calorimetry (DSC), thermal conductivity analyzer, and laser particle size analyzer, as shown in Table 1 below.

[0106] Table 1 shows that the phase transition temperatures of NIT and the phase change composite material range from 133.9 to 143.2 °C, and the latent heat of phase transition ranges from 248.44 to 195.54 J / g. The thermal conductivity of the composite phase change material increases from 0.66 W / m·K for pure NIT to 4.14 W / m·K, with an average particle size range of 35–68 μm. It can be recycled using a 200-mesh (74 μm) vibrating screen at the drilling site. The introduction of porous materials reduces the latent heat of phase transition of NIT and increases its thermal conductivity. Compared with NIT, the phase change temperature and latent heat of phase change of the phase change composite material are lower. This is because the molecules of the aminated modified porous material, modified bitumen, and macrocyclic compound remain solid at high temperatures and do not undergo phase transition. Introducing these components reduces the proportion of NIT. The thermal conductivity of NIT / CB@EG-Asp-4 is increased to 1.32 times that of NIT@EG-Asp. This can be attributed to the fact that NIT is encapsulated in the three-dimensional mesh pores of NIT / CB@EG-Asp-4. Phonons of NIT can propagate through the inner cavity of CB[7], reducing phonon scattering, optimizing the heat transfer path, and achieving enhanced heat transfer effect. Since the thermal conductivity of montmorillonite is lower than that of expanded graphite, the thermal conductivity of the phase change composite material obtained by using montmorillonite in Example 7 is significantly lower than that of NIT / CB@EG-Asp-2. Furthermore, since the molecular cavities of cucurbituril[5] and cucurbituril[6] are smaller than those of cucurbituril[7], their ability to recognize amino groups through self-assembly is weaker than that of cucurbituril[7]. Due to the differences in functional group structures between polypropylene modified asphalt and petroleum resin modified asphalt and acrylic resin modified asphalt, the thermal conductivity, phase transition temperature, latent heat of phase transition, and average particle size of the phase change composite materials obtained in experimental schemes d, e, f, and g in Examples 8 and 9 are all different from those of NIT / CB@EG-Asp-2.

[0107] Table 1. Thermophysical properties and particle size of NIT and phase change composite materials

[0108]

[0109]

[0110] Test Example 3

[0111] The on-site density is 1.6 g / cm³. 3The effect of the phase change composite material NIT / CB@EG-Asp-3 on drilling fluid properties was tested in oil-based drilling mud. The results are shown in Table 2. Table 2 shows that with the increase of NIT / CB@EG-Asp-3 dosage, the viscosity and shear stress of the drilling fluid first decreased and then increased, the demulsification voltage decreased slightly, and the filtration loss and friction coefficient decreased significantly. This indicates that the phase change composite material has a positive effect on the lubrication performance of the drilling fluid and is beneficial for reducing frictional heat generation between the drilling fluid and drill string. When the dosage of NIT / CB@EG-Asp-3 is 6 wt.%, the viscosity and shear stress of the drilling fluid are higher than those of the oil-based drilling fluid without the addition of the phase change composite material. Therefore, it is recommended that the amount of NIT / CB@EG-Asp-3 added should not exceed 5 wt.%.

[0112] Table 2 Performance of drilling fluids with different NIT / CB@EG-Asp-3 dosages

[0113]

[0114]

[0115] Test Example 4

[0116] Table 3 shows the cooling effect of different concentrations of the phase change composite material NIT / CB@EG-Asp-4 in oil-based drilling fluids. As can be seen from Table 3, with increasing NIT / CB@EG-Asp-4 dosage, the heating rate of the drilling fluid in the 130–150 °C range decreases. At 200s and 400s, the temperature difference between the tested drilling fluids was not significant; at 600s, the temperature of the 0wt.%NIT / CB@EG-Asp-4 drilling fluid was 145.4℃, while the temperature of the 5wt.%NIT / CB@EG-Asp-4 drilling fluid was 136.9℃, a difference of 8.5℃; at 800s, the temperature of the 0wt.%NIT / CB@EG-Asp-4 drilling fluid was 154.7℃, while the temperature of the 5wt.%NIT / CB@EG-Asp-4 drilling fluid was 146.0℃, a difference of 8.7℃; at 1000s, the temperature difference between the 0wt.%NIT / CB@EG-Asp-4 and 5wt.%NIT / CB@EG-Asp-4 drilling fluids was 1.5℃, and both reached the set temperature of 160℃ at 1200s. The results show that the phase change composite material NIT / CB@EG-Asp-4 underwent phase change endothermic reaction in the phase change temperature range, which slowed down the heating rate of the drilling fluid.

[0117] Table 3. Temperature rise of drilling fluid (°C) under different NIT / CB@EG-Asp-4 dosages.

[0118]

[0119] In wellbore cooling operations, composite phase change materials must exhibit no structural damage during the heating-cooling cycle and retain their original thermophysical properties after multiple melting-solidification cycles. The temperature curves of NIT / CB@EG-Asp-4 after heating-cooling cycles are shown below. Figure 2 As shown, curve a is the temperature curve of pure drilling fluid, curve b is the temperature curve after adding 5.wt% NIT / CB@EG-Asp-4 and circulating for 0 cycles, curve c is the temperature curve after adding 5.wt% NIT / CB@EG-Asp-4 and circulating for 50 cycles, curve d is the temperature curve after adding 5.wt% NIT / CB@EG-Asp-4 and circulating for 100 cycles, and curve e is the temperature curve after adding 5.wt% NIT / CB@EG-Asp-4 and circulating for 200 cycles. Figure 2 It can be seen that after 50, 100 and 200 heating-cooling cycles, the cooling effect of the phase change composite material NIT / CB@EG-Asp-4 hardly changed, indicating that the phase change composite material has good thermal cycling stability.

[0120] Although the present invention has been described above in conjunction with exemplary embodiments and accompanying drawings, those skilled in the art should understand that various modifications can be made to the above embodiments without departing from the spirit and scope of the claims.

Claims

1. A phase change composite material for oil-based drilling fluids, characterized in that, The phase change thermal storage composite material for oil-based drilling fluids includes: phase change base material, aminated modified porous material, modified bitumen, and macrocyclic compound cucurbita[n].

2. The phase change composite material for oil-based drilling fluid according to claim 1, characterized in that, The phase change base material is a nitrate eutectic composed of NaNO3, KNO3 and LiNO3, the aminated modified porous material is amino-expanded graphite and / or amino-montmorillonite, the modified asphalt is one or more of acrylic resin modified asphalt, polyethylene modified asphalt and petroleum resin modified asphalt, the macrocyclic compound molecule cucurbita[n] is one or more of cucurbita[5], cucurbita[6] and cucurbita[7], wherein the molar ratio of NaNO3, KNO3 and LiNO3 is 2:3:2 to 3:2:

2.

3. The phase change composite material for oil-based drilling fluid according to claim 1, characterized in that, The phase change composite material for oil-based drilling fluid has a phase change temperature of 133.9–143.2 °C and a particle size range of 35–68 μm.

4. A method for preparing a phase change composite material for oil-based drilling fluid as described in any one of claims 1 to 3, characterized in that, The preparation method includes the following steps: S1. The phase change basic material is obtained by mixing, heating, cooling and pulverizing NaNO3, KNO3 and LiNO3; S2. Modify expanded graphite and / or montmorillonite to obtain the aminated modified porous material. S3. The macrocyclic compound molecule cucurbita[n] is added to the aqueous solution of the aminated modified porous material to obtain a first suspension. The phase change basic material is prepared into a solution and added to the first suspension to obtain a second suspension. The second suspension is calcined to obtain a first phase change composite material. S4. Dissolve the modified asphalt in petroleum ether to obtain a third suspension. Disperse the first phase change composite material in the third suspension, freeze, vacuum filter, and dry it a second time to obtain the phase change composite material for oil-based drilling fluid.

5. The method for preparing the phase change composite material for oil-based drilling fluid according to claim 4, characterized in that, The molar ratio of NaNO3, KNO3 and LiNO3 is 2:3:2 to 3:2:2; the ratio of the aminated modified porous material, the macrocyclic compound cucurbita[n], the modified bitumen and the phase change base material is 1:1:2:10 to 1:2.5:5:

10.

6. The method for preparing the phase change composite material for oil-based drilling fluid according to claim 4, characterized in that, The heating temperature is 235–250℃, and the heating time is 10–12 h; the dispersion stirring speed is 1000–1300 r / min, and the dispersion stirring time is 20–30 min; the freezing temperature is -5–-8℃, and the freezing time is 1–3 h; the secondary drying temperature is 80–100℃, and the secondary drying time is 10–12 h.

7. The method for preparing the phase change composite material for oil-based drilling fluid according to claim 4, characterized in that, Step S2 further includes the following steps: S21. The aminated modified porous material is dispersed in water, ultrasonically treated, and adjusted to an acidic solution to obtain a first solution; S22. Add the aqueous solution of silane coupling agent to the first solution to obtain the second solution; S23. The first solution and the second solution are mixed and subjected to an alkylation reaction. After removing the unreacted silane coupling agent, the mixture is dried once to obtain the aminated modified porous material.

8. The method for preparing the phase change composite material for oil-based drilling fluid according to claim 7, characterized in that, The acidic solution has a pH of 3-5, the ultrasonic treatment takes 30-50 minutes, the alkylation reaction takes 80-100°C and 22-24 hours, and the primary drying takes 80-100°C and 22-24 hours.

9. The method for preparing the phase change composite material for oil-based drilling fluid according to claim 4, characterized in that, Step S3 further includes the following steps: S31. Stir the first suspension at 80-85°C for 8-12 hours; S32. Stir the second suspension at 60-65°C for 7-9 hours.

10. The application of the phase change composite material for oil-based drilling fluids according to any one of claims 1 to 3 in oil-based drilling fluids, characterized in that, Based on the total weight of the oil-based drilling fluid, the amount of phase change composite material used in the oil-based drilling fluid added to the oil-based drilling fluid is less than or equal to 6 wt.%.

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