Solution of liquid-solid phase change autogenous hydroxyapatite microspheres and preparation method and application thereof

Abstract

The present application relates to a kind of liquid-solid phase change autogenic hydroxyapatite microspheres solution and its preparation method and application.The liquid-solid phase change autogenic hydroxyapatite microspheres solution includes calcium source solution, composite phosphorus source solution and composite regulator solution;The calcium source solution includes calcium salt;The composite phosphorus source solution includes phosphorus salt;The phosphorus salt includes the combination of any two or at least three of sodium tripolyphosphate, sodium hexametaphosphate, sodium trimetaphosphate or sodium hexametaphosphate;The composite regulator solution includes urea and organic acid.The liquid-solid phase change autogenic hydroxyapatite microspheres solution of the present application can generate hydroxyapatite microspheres in situ under specific temperature conditions by hydrothermal reaction, and can be used as proppant in the fracture after oil and gas reservoir fracturing, has good flow conductivity, thereby improving recovery efficiency.

Description

Technical Field

[0001] This invention relates to the field of oil and gas reservoir development technology, and in particular to a solution of self-generated hydroxyapatite microspheres by liquid-solid phase transformation, its preparation method, and its application. Background Technology

[0002] Currently, the main technical measure for enhancing production and increasing well output in unconventional oil and gas reservoirs is hydraulic fracturing. Hydraulic fracturing has been widely applied in the development of ultra-low permeability, tight, and shale oil and gas reservoirs in major oil and gas fields, making significant contributions to stable and increased production. Hydraulic fracturing involves pumping fluid into the reservoir. The high-pressure fluid flow generates stress in the reservoir. By continuously increasing the pumping pressure and injection volume, the stress generated by the injected fluid eventually exceeds the maximum stress required for reservoir rock fracturing, leading to formation fracturing and the creation of fractures of a certain length and width, as well as a complex fracture network. Solid proppant is then filled into the fractures. The proppant is continuously and uniformly distributed within the artificial fractures to prevent them from reclosing under high closure pressure. The pores between the proppant particles become the main channels for oil and gas flow. Oil and gas flow from the reservoir matrix through the fractures and the pores between the proppant particles into the wellbore, forming an industrial oil and gas flow.

[0003] Traditional hydraulic fracturing uses polymer solutions carrying solid proppant particles such as quartz sand and ceramsite as the injection fluid. The proppant transport process consumes the kinetic energy of the injection fluid, resulting in injection pressures far exceeding formation fracturing pressures. Currently, the injection volume of in-situ fluid has reached a high level, but it still falls short of the proppant transport requirements, and the proppant placement effect is poor, with most of the proppant being placed near the wellbore and failing to migrate further. Furthermore, the high viscosity of the fracturing fluid increases frictional resistance in the pipeline, wellbore, and formation fractures, increasing pumping difficulty. The proppant fracturing process is complex; high proppant loading necessitates high displacement, and high pump pressure places high demands on the wellhead, equipment, and tubing. Improper control during proppant loading can also cause sand blockage, posing significant potential engineering and personnel safety risks. All of these factors necessitate fundamental changes to existing hydraulic fracturing methods through innovation in solution chemistry materials.

[0004] In-situ self-generated proppant, which undergoes a chemical reaction after entering the reservoir fracture space, is one of the ways to transform hydraulic fracturing methods. Currently, the methods for in-situ self-generated proppant mainly employ organic reagents. US Patent US9834721(B2) discloses a chemical composition and method for in-situ conversion of injected fracturing fluid into a highly permeable proppant-filled layer. The hydraulic fracturing fluid includes a spherical bead-forming liquid composition comprising a primary liquid precursor and a secondary liquid precursor. The primary liquid precursor contains a micelle-forming surfactant, a bead-forming compound, and a non-solid bead liquid solvent, and the secondary liquid precursor contains one or more curing agents and one or more co-curing agents. Because the fracturing fluid itself forms the proppant, it can penetrate fractures and complex networks along its entire length, maximizing the effective fracture area and reservoir volume. The proposed particle size can be significantly larger than conventional proppants without considering screening. The in-situ formed proppant has sufficient strength to resist fracture closure stress. Furthermore, no polymer is needed to suspend the proppant, thus leaving no gel residue that could compromise fracture conductivity. Chinese patent CN111100620A discloses a hydraulic fracturing fluid and method thereof. The fracturing fluid comprises a liquid solvent, a surfactant, a proppant-forming compound, and a curing agent. The proppant-forming compound includes one or more of the following: aliphatic epoxides, acid anhydrides, glycidylamine epoxides, alicyclic epoxides, epoxy functional resins, polyurethane resins, phenolic resins, bisphenol A diglycidyl ether, polyglycidyl ether, acrylic resins, glycidyl ether, and bisphenol F diglycidyl ether aldehyde resin. The liquid solvent, surfactant, proppant-forming compound, and curing agent are mixed to form a liquid composition; under external pressure, the liquid composition is pumped into an injection well in the reservoir to create fractures; the liquid composition is allowed to react to form an in-situ proppant, which maintains the fracture open after the external pressure is released.

[0005] Compared to organic materials as in-situ proppants, inorganic materials are more stable, resistant to aging, and less prone to deformation. Therefore, this invention proposes a method for preparing and applying microspherical hydroxyapatite, which can function as an in-situ proppant during fracturing. Methods for preparing hydroxyapatite include solid-state reaction, sol-gel, hydrothermal, chemical precipitation, and dry methods (solid-state and mechanochemical methods). Hydrothermal-prepared hydroxyapatite is often columnar or short rod-shaped. For example, Chinese patent CN113307242A discloses a method for preparing hydroxyapatite nanorods. Diammonium hydrogen phosphate solution, calcium nitrate solution, and hydroxypropyl chitosan hydrogel are mechanically stirred for 3 hours at pH 10-11 and T 60℃. Then, the mixture is hydrothermally treated at 160℃ for 12 hours in a high-pressure reactor. After ultrasonication, centrifugation, washing, and drying, a hydroxyapatite preform is obtained. Finally, after heat treatment at 800℃ for 2 hours, rod-shaped hydroxyapatite nanoparticles with good dispersion and crystallinity are obtained. Chinese patent CN101343054A discloses a method for preparing high specific surface area hydroxyapatite microspheres. Under the action of a template agent, a spherical mixture of hydroxyapatite and calcium carbonate is first generated, and then completely converted to hydroxyapatite through ion exchange. Chinese patent CN1528468A discloses a method for preparing porous hydroxyapatite by converting coral calcium carbonate using a hydrothermal method. Chinese patent CN103466580A discloses a method for preparing hydroxyapatite microspheres by combining a hydrothermal method with a microwave radiation method, using calcium carbonate and phosphate. However, all of the above methods require a precursor and do not fully realize the phase transition from a liquid system to a solid product, making them unsuitable for the concept of in-situ self-generated proppant in fracturing processes.

[0006] Therefore, in order to address the above problems, it is of great significance to provide a method for preparing self-generated hydroxyapatite microspheres from liquid-solid phase transformation for supporting fractures in phase transformation fracturing. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a solution of self-generated hydroxyapatite microspheres via liquid-solid phase change, its preparation method, and its applications. The self-generated hydroxyapatite microspheres of this invention are prepared via a hydrothermal reaction using a specific solution of self-generated hydroxyapatite microspheres. The specific preparation method effectively generates microsphere-structured hydroxyapatite in solution through a liquid-solid phase change process. This allows for the in-situ proppant formation of self-generated hydroxyapatite microspheres within fractures after reservoir fracturing in oil and gas reservoirs. This overcomes the shortcomings of traditional hydraulic fracturing methods, such as insufficient proppant carrying capacity, short proppant migration distance, and difficulty in proppant entry into micro-fractures, providing a new approach for the efficient development of unconventional oil and gas.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a solution of self-generated hydroxyapatite microspheres by liquid-solid phase change, the solution comprising a calcium source solution, a composite phosphorus source solution, and a composite regulator solution;

[0010] The calcium source solution includes calcium salts;

[0011] The composite phosphorus source solution includes phosphate salts;

[0012] The phosphate salt includes any two or at least three of sodium tripolyphosphate, sodium hexadeciphosphate, sodium trimetaphosphate, or sodium hexadeciphosphate.

[0013] The composite regulator solution includes urea and organic acids.

[0014] In this invention, the solution of self-generated hydroxyapatite microspheres obtained by compounding a calcium source solution, a composite phosphorus source solution, and a composite regulator solution is a clear solution at room temperature. As an injection fluid, it ensures the injection fluid system is entirely liquid, containing no solids, thus effectively altering the proppant placement pattern and consequently reducing wellhead pressure. At reservoir temperatures, the solution of hydroxyapatite microspheres undergoes a hydrothermal reaction, generating hydroxyapatite microspheres in situ. This effectively supports fractures while maintaining high conductivity, thereby improving oil and gas recovery.

[0015] The mechanism of action of this invention is as follows: Hydroxyapatite is generated through a hydrothermal reaction of calcium and phosphorus sources under the regulation of urea and organic acids. This hydroxyapatite possesses a microspherical structure and high compressive strength, which can support complex fractures formed after fracturing, prevent fracture closure, and provide smooth oil and gas flow channels in the reservoir. Without the addition of urea and organic acids as regulators, the calcium and phosphorus sources mix to form an amorphous flocculent precipitate of calcium phosphate, resulting in a turbid liquid solution and an inability of the solid phase precipitate to provide support. The addition of organic acids to the system causes a complexation effect with calcium ions, altering the precipitation-dissolution equilibrium. After the mixed solution is prepared, it remains clear upon standing. Urea, acting as a precipitant, hydrolyzes at high temperatures to generate hydroxide ions. Under the combined action of hydroxyapatite and organic acids, the calcium and phosphorus sources slowly crystallize to form hydroxyapatite. During this process, the solution system is in the liquid phase under room temperature storage conditions, and hydroxyapatite spontaneously forms from the solution after a reaction time at high temperatures, completing the liquid-solid transition. Hydrothermal apatite produced typically occurs in nanoscale columnar, short rod-shaped, or fibrous forms due to limited calcium and phosphorus sources in the solution and short crystallization time. Increasing the concentration of calcium and phosphorus sources leads to a high ion concentration in the solution, resulting in supersaturated crystallization at room temperature. This rapid crystallization also causes the crystals to form two-dimensional plates, lacking supporting function. To prevent supersaturated crystallization, the conventional approach is to increase the concentration of organic acid to slow down the crystallization time. However, organic acid itself is a scale inhibitor; adding too much organic acid will cause the solution pH to be too low, making it difficult to initiate the crystallization process after heating. This reduces the ratio of solids produced to dissolved solids, increasing the cost of the well fluid system.

[0016] To resolve this contradiction, this invention uses a composite aqueous solution of any two or at least three of the following phosphate salts: sodium tripolyphosphate, sodium hexadecimalphosphate, sodium trimetaphosphate, and sodium hexametaphosphate, as a composite phosphorus source solution. Sodium tripolyphosphate crystallizes relatively quickly with a calcium source, while sodium trimetaphosphate crystallizes relatively slowly with a calcium source. The mixing of sodium trimetaphosphate and calcium source first undergoes a complexation reaction, similar to the effect of organic acids, which regulates the precipitation equilibrium and facilitates the transformation of amorphous calcium phosphate precipitate into hydroxyapatite crystals. Sodium trimetaphosphate not only acts as a phosphorus source but also regulates crystallization. Through this complexation effect, the concentrations of calcium and phosphorus sources in the liquid phase are increased without rapid crystallization, allowing the hydroxyapatite crystallization process to proceed in an orderly and slow manner. Furthermore, the sufficient replenishment of calcium and phosphorus sources enables hydroxyapatite to crystallize into microspheres during the liquid-solid phase transition, thereby meeting the requirements for supporting cracks. By utilizing the liquid-solid transformation process of this chemical reaction, existing fracturing technology can be transformed. The injection fluid at the wellhead is no longer a high-viscosity liquid carrying additional proppant such as quartz sand and ceramsite, but the injection fluid of this invention, which is a mixture of calcium source, phosphorus source, urea and organic acid. It is a liquid when injected, and after the fracture is created, it enters the fracture network. The fracture space that the injection fluid can enter is used as a reaction vessel, and a chemical reaction occurs at the reservoir temperature to generate hydroxyapatite microspheres, which can effectively support the fractures and improve the oil and gas recovery effect.

[0017] Preferably, the calcium salt content is 30-40% based on the total mass of calcium salt, phosphate salt, urea and organic acid as 100%, for example, it can be 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38% or 39%, etc.

[0018] Preferably, the calcium source is calcium nitrate and / or calcium chloride.

[0019] Preferably, the calcium source solution is an aqueous solution.

[0020] Preferably, the water in the aqueous solution is tap water, deionized water, or distilled water.

[0021] Preferably, the mass concentration of calcium salt in the calcium source solution is 24-35 g / L, for example, it can be 25 g / L, 26 g / L, 27 g / L, 28 g / L, 29 g / L, 30 g / L, 31 g / L, 32 g / L, 33 g / L or 34 g / L, etc.

[0022] Preferably, the content of the phosphate salt is 10-30% based on the total mass of calcium salt, phosphate salt, urea and organic acid as 100%, for example, it can be 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26% or 28%, etc.

[0023] Preferably, the phosphorus source solution is an aqueous solution.

[0024] Preferably, the water in the aqueous solution is tap water, deionized water, or distilled water.

[0025] Preferably, the phosphate salt includes phosphate salt A and phosphate salt B.

[0026] Preferably, the phosphate salt A comprises sodium tripolyphosphate and / or sodium hexapolyphosphate.

[0027] Preferably, the phosphate salt B comprises sodium trimetaphosphate and / or sodium hexametaphosphate.

[0028] Preferably, the mass ratio of phosphate salt A to phosphate salt B is (1-20):1, for example, it can be 1:1, 1.5:1, 2:1, 3:1, 4:1, 5:1, 8:1, 10:1, 15:1 or 20:1, and more preferably (1.5-4):1.

[0029] Preferably, the mass concentration of phosphate salt A in the phosphorus source solution is 5-20 g / L, for example, it can be 6 g / L, 8 g / L, 10 g / L, 12 g / L, 14 g / L, 16 g / L, 18 g / L or 19 g / L, etc.

[0030] Preferably, the mass concentration of phosphate salt B in the phosphorus source solution is 1-5 g / L, for example, it can be 1 g / L, 1.5 g / L, 2 g / L, 2.5 g / L, 3 g / L, 3.5 g / L, 4 g / L, 4.5 g / L or 5 g / L, etc.

[0031] This invention combines phosphate salt A and phosphate salt B in a specific ratio to obtain a composite phosphate source solution, which is then mixed with a calcium source solution. This allows the crystallization process of hydroxyapatite to proceed in an orderly and slow manner. Furthermore, due to the sufficient replenishment of calcium and phosphate sources, hydroxyapatite can crystallize into microspheres during the liquid-solid phase transition, thereby meeting the requirements for supporting cracks. This avoids the risk of oversaturation crystallization that occurs when a single phosphate salt system is mixed with a calcium source, resulting in columnar or short rod-shaped hydroxyapatite.

[0032] Preferably, the urea content is 20-30% based on the total mass of calcium salt, phosphate salt, urea and organic acid as 100%, for example, it can be 20-30%.

[0033] Preferably, the mass concentration of urea in the composite regulator solution is 20-30 g / L, for example, it can be 21 g / L, 22 g / L, 23 g / L, 24 g / L, 25 g / L, 26 g / L, 27 g / L, 28 g / L or 29 g / L, etc.

[0034] Preferably, the content of organic acid is 20-30% based on the total mass of calcium salt, phosphate salt, urea and organic acid as 100%, for example, it can be 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28% or 29%, etc.

[0035] Preferably, the organic acid includes any one or a combination of at least two of citric acid, alginic acid, tartaric acid, glutamic acid, or aspartic acid.

[0036] Preferably, the mass concentration of organic acid in the composite regulator solution is 10-20 g / L, for example, it can be 11 g / L, 12 g / L, 13 g / L, 14 g / L, 15 g / L, 16 g / L, 17 g / L, 18 g / L or 19 g / L, etc.

[0037] In this invention, urea and organic acids in the composite regulator solution mainly play a role in regulating precipitation equilibrium and crystal growth process, making the solution clear at room temperature, and generating precipitate crystals through hydrothermal reaction after heating.

[0038] In a second aspect, the present invention provides a method for preparing a solution of self-generated hydroxyapatite microspheres as described in the first aspect, the preparation method comprising the following steps:

[0039] A solution of the calcium source solution, the composite phosphorus source solution, and the composite regulator solution is mixed to obtain a solution of the self-generated hydroxyapatite microspheres by liquid-solid phase change.

[0040] Preferably, the mixing is carried out under stirring.

[0041] Preferably, the stirring speed is 350-450 r / min, for example, it can be 360 ​​r / min, 370 r / min, 380 r / min, 390 r / min, 400 r / min, 410 r / min, 420 r / min, 430 r / min or 440 r / min, etc.

[0042] Preferably, the preparation method further includes mixing until the solution becomes clear and then allowing it to stand.

[0043] Preferably, the settling time is 22-26 hours, for example, 22 hours, 22.5 hours, 23 hours, 23.5 hours, 24 hours, 24.5 hours, 25 hours, 25.5 hours, or 26 hours.

[0044] In this invention, after the solution of the prepared liquid-solid phase change self-generated hydroxyapatite microspheres was left to stand for 22-26 hours, it was observed that its state was still a clear liquid, indicating that the solution of the liquid-solid phase change self-generated hydroxyapatite microspheres of this invention does not precipitate at room temperature and can exist in a long-term stable solution form.

[0045] Thirdly, the present invention provides a method for preparing self-generated hydroxyapatite microspheres through liquid-solid phase transformation, the method comprising the following steps:

[0046] The liquid-solid phase change self-generated hydroxyapatite microspheres were obtained by hydrothermal reaction using a solution of the liquid-solid phase change self-generated hydroxyapatite microspheres described in the first aspect.

[0047] Preferably, the temperature of the hydrothermal reaction is 60-250℃, for example, it can be 80℃, 100℃, 120℃, 140℃, 160℃, 180℃, 200℃, 220℃ or 240℃, etc.

[0048] In this invention, the preset hydrothermal reaction temperature is consistent with the temperature at which the solution is injected into the reservoir. In the laboratory, the hydrothermal reaction temperature can reach 250°C, while in actual oil and gas reservoir development, the reservoir temperature generally does not exceed 200°C. Furthermore, the hydrothermal reaction vessel in the laboratory is a reaction vessel or a core plate device, while in oil and gas reservoir development and application, the reaction vessel refers to the underground fracture space of the reservoir.

[0049] Preferably, the hydrothermal reaction time is 2-12 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours.

[0050] Preferably, the preparation method further includes a post-processing step after the hydrothermal reaction is completed.

[0051] Preferably, the post-processing steps include filtration, washing, and drying.

[0052] Preferably, the filtration includes filtration of the reaction solution after the hydrothermal reaction is completed using a microporous membrane with a pore size of 0.1 μm.

[0053] Preferably, the washing process includes washing the filtered cake alternately with deionized water and anhydrous ethanol.

[0054] Preferably, the drying temperature is 85-95℃, for example, it can be 86℃, 87℃, 88℃, 89℃, 90℃, 91℃, 92℃, 93℃, 94℃ or 95℃, etc.

[0055] Preferably, the drying time is 22-26 hours, for example, 22 hours, 22.5 hours, 23 hours, 23.5 hours, 24 hours, 24.5 hours, 25 hours, 25.5 hours, or 26 hours.

[0056] Preferably, the particle size of the self-generated hydroxyapatite microspheres from the liquid-solid phase change is 0.5-100 μm, for example, it can be 0.5 μm, 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 50 μm, 80 μm or 100 μm, etc.

[0057] The method for preparing self-generated hydroxyapatite microspheres by liquid-solid phase transformation of the present invention produces spherical hydroxyapatite with a relatively large particle size, in the micrometer range. This allows it to be used as a proppant after fracturing in oil and gas reservoir development, exhibiting excellent flow conductivity.

[0058] Fourthly, the present invention provides a method for preparing self-generated hydroxyapatite microspheres by liquid-solid phase change as described in the third aspect.

[0059] Fifthly, the present invention provides a solution of self-generated hydroxyapatite microspheres as described in the first aspect or the application of self-generated hydroxyapatite microspheres as described in the fourth aspect in fracturing technology for oil and gas reservoir development.

[0060] Compared with the prior art, the present invention has at least the following beneficial effects:

[0061] (1) The solution of self-generated hydroxyapatite microspheres in liquid-solid phase change provided by this invention is a clear solution at room temperature, but can undergo hydrothermal reaction under specific temperature conditions to generate self-generated hydroxyapatite microspheres in situ, thus enabling it to be well used as a proppant in phase change fracturing to support fractures. Compared with existing hydraulic fracturing methods using quartz sand and ceramsite proppants and low-density proppant methods, the solution of self-generated hydroxyapatite microspheres in liquid-solid phase change of this invention ensures that the injection fluid system is completely free of solids, changing the proppant placement pattern and effectively reducing wellhead pressure. Compared with the technical defects of traditional methods where the space in which proppant can enter is limited, and some micro fractures reclose due to the lack of proppant entry, resulting in reduced fracturing effect, the proppant formed by the specific solution of this invention can be self-generated in the space in which the injection fluid enters, that is, proppant is laid to support fractures in the space in which the injection fluid can enter, meeting the need for supporting fractures longer and farther.

[0062] (2) Further, the solution of the self-generated hydroxyapatite microspheres by liquid-solid phase change provided by the present invention undergoes hydrothermal reaction under specific temperature conditions to generate hydroxyapatite microspheres in situ. These microspheres can be used as in-situ proppant for inorganic materials in oil and gas reservoir development. Compared with the technology of generating in-situ proppants from organic materials, the hydroxyapatite generated by the present invention can maintain stability underground for a long time and is not easy to age or deform. At the same time, the inorganic surface is polar and hydrophilic, which is more conducive to the flow of oil and gas. Attached Figure Description

[0063] Figure 1 This is a flowchart of the application of the solution of self-generated hydroxyapatite microspheres in liquid-solid phase change for supporting fractures in phase change fracturing according to the present invention.

[0064] Figure 2 This is the SEM image of the self-generated hydroxyapatite microspheres obtained from the liquid-solid phase change in Example 1;

[0065] Figure 3 The image shows the XRD pattern of the self-generated hydroxyapatite microspheres obtained from the liquid-solid phase change in Example 1. Detailed Implementation

[0066] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0067] The flowchart of the application of the solution of self-generated hydroxyapatite microspheres in liquid-solid phase change for supporting fractures in phase change fracturing is as follows: Figure 1 As shown.

[0068] Example 1

[0069] This embodiment provides a liquid-solid phase change self-generated hydroxyapatite microsphere, the preparation method of which is as follows:

[0070] (1) Dissolve 2.4g of anhydrous calcium chloride in 100mL of deionized water to prepare a calcium source solution;

[0071] (2) Add 1.07g of sodium tripolyphosphate (Na5P3O) 10 0.3g of sodium trimetaphosphate (NaPO4)3 was dissolved together in 100mL of deionized water to prepare a phosphorus source solution;

[0072] (3) Dissolve 1.7g of urea and 1.37g of citric acid together in 100mL of deionized water to prepare a compound regulator solution;

[0073] (4) Mix the three solutions prepared in steps (1)-(3) and stir at a rate of 400 r / min to obtain a clear mixed solution, and obtain a solution of self-generated hydroxyapatite microspheres by liquid-solid phase change.

[0074] (5) Let the solution of self-generated hydroxyapatite microspheres from the liquid-solid phase change in step (4) stand for 24 hours;

[0075] (6) Place the static solution from step (5) into an oven, adjust the temperature to 90°C, and react for 6 hours;

[0076] (7) The solution after the reaction was filtered by a microporous membrane with a pore size of 0.1 μm. The resulting filter cake was rinsed three times each with deionized water and anhydrous ethanol, and then dried in a constant temperature drying oven at 90°C for 24 h to obtain the liquid-solid phase change self-generated hydroxyapatite microspheres.

[0077] The microstructure of Example 1 was tested as follows:

[0078] like Figure 2As shown in the SEM image of the self-generated hydroxyapatite microspheres prepared in Example 1, the morphology of the obtained hydroxyapatite is spherical. The diameter of a single hydroxyapatite microsphere is approximately 10 μm, and the microspheres are tightly connected to form aggregates. The overall particle size is approximately 50 μm, corresponding to a mesh size of 300 mesh. These aggregates can act as a self-generated proppant to support the fractures formed after fracturing, maintaining high conductivity in the fractures.

[0079] like Figure 3 As shown in the XRD pattern of the self-generated hydroxyapatite microspheres obtained from the liquid-solid phase transformation in Example 1, it can be seen that they have the characteristic diffraction peaks of hydroxyapatite.

[0080] Example 2

[0081] This embodiment provides a liquid-solid phase change self-generated hydroxyapatite microsphere, the preparation method of which is as follows:

[0082] (1) Dissolve 2.4g of anhydrous calcium chloride in 100mL of deionized water to prepare a calcium source solution;

[0083] (2) Add 1.5g of sodium hexapolyphosphate (Na6P6O) 18 0.5 g of sodium trimetaphosphate (NaPO4)3 was dissolved together in 100 mL of deionized water to prepare a phosphorus source solution;

[0084] (3) Dissolve 1.6g of urea and 2g of glutamic acid together in 100mL of deionized water to prepare a compound regulator solution;

[0085] (4) Mix the three solutions prepared in steps (1)-(3) and stir at a rate of 350 r / min to obtain a clear mixed solution, thereby obtaining the solution of the liquid-solid phase change self-generated hydroxyapatite microspheres;

[0086] (5) Let the solution of self-generated hydroxyapatite microspheres from the liquid-solid phase change in step (4) stand for 24 hours;

[0087] (6) Place the static solution from step (5) into an oven, adjust the temperature to 90°C, and react for 8 hours;

[0088] (7) The solution after the reaction was filtered by a microporous membrane with a pore size of 0.1 μm. The resulting filter cake was rinsed three times each with deionized water and anhydrous ethanol, and then dried in a constant temperature drying oven at 85℃ for 26 h to obtain liquid-solid phase change self-generated hydroxyapatite microspheres with an average particle size of 15 μm.

[0089] Example 3

[0090] This embodiment provides a liquid-solid phase change self-generated hydroxyapatite microsphere, the preparation method of which is as follows:

[0091] (1) Dissolve 2.4g of anhydrous calcium nitrate in 100mL of deionized water to prepare a calcium source solution;

[0092] (2) Add 2g of sodium hexapolyphosphate (Na6P6O) 18 0.4 g of sodium hexametaphosphate (NaPO4)6 was dissolved together in 100 mL of deionized water to prepare a phosphorus source solution;

[0093] (3) Dissolve 2g of urea and 1.2g of citric acid together in 100mL of deionized water to prepare a compound regulator solution;

[0094] (4) Mix the three solutions prepared in steps (1)-(3) and stir at a rate of 380 r / min to obtain a clear mixed solution, thereby obtaining the solution of the liquid-solid phase change self-generated hydroxyapatite microspheres.

[0095] (5) Let the solution of self-generated hydroxyapatite microspheres from the liquid-solid phase change in step (4) stand for 24 hours;

[0096] (6) Place the static solution from step (5) into an oven, adjust the temperature to 60°C, and react for 12 hours;

[0097] (7) The solution after the reaction was filtered by a microporous membrane with a pore size of 0.1 μm. The resulting filter cake was rinsed three times each with deionized water and anhydrous ethanol, and then dried in a constant temperature drying oven at 95℃ for 22 h to obtain liquid-solid phase change self-generated hydroxyapatite microspheres with an average particle size of 13 μm.

[0098] Example 4

[0099] This embodiment provides a liquid-solid phase change self-generated hydroxyapatite microsphere, the preparation method of which is as follows:

[0100] (1) Dissolve 3.5g of anhydrous calcium nitrate in 100mL of deionized water to prepare a calcium source solution;

[0101] (2) Add 1.0g of sodium tripolyphosphate (Na5P3O) 10 0.35 g of sodium trimetaphosphate (NaPO4)3 was dissolved together in 100 mL of deionized water to prepare a phosphorus source solution;

[0102] (3) Dissolve 2.65g of urea and 1.5g of alginic acid together in 100mL of deionized water to prepare a compound regulator solution;

[0103] (4) Mix the three solutions prepared in steps (1)-(3) and stir at a rate of 450 r / min to obtain a clear mixed solution, thereby obtaining the solution of the liquid-solid phase change self-generated hydroxyapatite microspheres.

[0104] (5) Let the solution of self-generated hydroxyapatite microspheres from the liquid-solid phase change in step (4) stand for 24 hours;

[0105] (6) Place the static solution from step (5) into an oven, adjust the temperature to 120℃, and the reaction time to 6h;

[0106] (7) The solution after the reaction was filtered by a microporous membrane with a pore size of 0.1 μm. The resulting filter cake was rinsed three times each with deionized water and anhydrous ethanol, and then dried in a constant temperature drying oven at 90℃ for 24 h to obtain liquid-solid phase change self-generated hydroxyapatite microspheres with an average particle size of 18 μm.

[0107] Example 5

[0108] This embodiment provides a liquid-solid phase change self-generated hydroxyapatite microsphere, the preparation method of which is as follows:

[0109] (1) Dissolve 2.4g of anhydrous calcium chloride in 100mL of deionized water to prepare a calcium source solution;

[0110] (2) Add 0.5g of sodium tripolyphosphate (Na5P3O) 10 0.1 g of sodium hexametaphosphate (NaPO4)6 was dissolved together in 100 mL of deionized water to prepare a phosphorus source solution;

[0111] (3) Dissolve 1.8g of urea and 1.2g of tartaric acid together in 100mL of deionized water to prepare a compound regulator solution;

[0112] (4) Mix the three solutions prepared in steps (1)-(3) and stir at a rate of 450 r / min to obtain a clear mixed solution, thereby obtaining the solution of the liquid-solid phase change self-generated hydroxyapatite microspheres.

[0113] (5) Let the solution of self-generated hydroxyapatite microspheres from the liquid-solid phase change in step (4) stand for 24 hours;

[0114] (6) Place the static solution from step (5) into an oven, adjust the temperature to 180℃, and react for 2 hours;

[0115] (7) The solution after the reaction was filtered by a microporous membrane with a pore size of 0.1 μm. The resulting filter cake was rinsed three times each with deionized water and anhydrous ethanol, and then dried in a constant temperature drying oven at 90℃ for 24 h to obtain liquid-solid phase change self-generated hydroxyapatite microspheres with an average particle size of 21 μm.

[0116] Example 6

[0117] This embodiment provides a liquid-solid phase change self-generated hydroxyapatite microsphere, which differs from Example 1 in that the amount of sodium tripolyphosphate in step (2) is adjusted from 1.07g to 0.685g, and the amount of sodium trimetaphosphate is adjusted from 0.3g to 0.685g. Other raw materials, amounts, and preparation methods are the same as in Example 1, resulting in liquid-solid phase change self-generated hydroxyapatite microspheres with an average particle size of 17μm.

[0118] Example 7

[0119] This embodiment provides a liquid-solid phase change self-generated hydroxyapatite microsphere, which differs from Example 1 in that the amount of sodium tripolyphosphate in step (2) is adjusted from 1.07g to 0.822g, and the amount of sodium trimetaphosphate is adjusted from 0.3g to 0.548g. Other raw materials, amounts, and preparation methods are the same as in Example 1, resulting in liquid-solid phase change self-generated hydroxyapatite microspheres with an average particle size of 20μm.

[0120] Example 8

[0121] This embodiment provides a liquid-solid phase change self-generated hydroxyapatite microsphere, which differs from Example 1 in that the amount of sodium tripolyphosphate in step (2) is adjusted from 1.07g to 1.095g, and the amount of sodium trimetaphosphate is adjusted from 0.3g to 0.275g. Other raw materials, amounts, and preparation methods are the same as in Example 1, resulting in liquid-solid phase change self-generated hydroxyapatite microspheres with an average particle size of 16μm.

[0122] Example 9

[0123] This embodiment provides a liquid-solid phase change self-generated hydroxyapatite microsphere, which differs from Example 1 in that the amount of sodium tripolyphosphate in step (2) is adjusted from 1.07g to 1.12g, and the amount of sodium trimetaphosphate is adjusted from 0.3g to 0.25g. Other raw materials, amounts, and preparation methods are the same as in Example 1, resulting in liquid-solid phase change self-generated hydroxyapatite microspheres with an average particle size of 12μm.

[0124] Comparative Example 1

[0125] This comparative example provides a hydroxyapatite, the preparation method of which is as follows:

[0126] (1) Dissolve 1.5g of anhydrous calcium chloride in 100mL of deionized water to prepare a calcium source solution;

[0127] (2) Add 0.6g of sodium tripolyphosphate (Na5P3O) 10 Dissolve in 100 mL of deionized water to prepare a phosphorus source solution;

[0128] (3) Dissolve 1.8g of urea and 1.0g of citric acid together in 100mL of deionized water to prepare a compound regulator solution;

[0129] (4) Mix the three solutions prepared in steps (1)-(3) and stir at a rate of 400 r / min to obtain a clear mixed solution, and obtain a solution of self-generated hydroxyapatite microspheres by liquid-solid phase change.

[0130] (5) Let the solution of self-generated hydroxyapatite microspheres from the liquid-solid phase change in step (4) stand for 24 hours;

[0131] (6) Place the static solution from step (5) into an oven, adjust the temperature to 90°C, and react for 8 hours;

[0132] (7) The solution after the reaction was filtered by a microporous membrane with a pore size of 0.1 μm. The resulting filter cake was rinsed three times each with deionized water and anhydrous ethanol, and then dried in a constant temperature drying oven at 90℃ for 24 h to obtain nano-columnar hydroxyapatite.

[0133] Comparative Example 2

[0134] This comparative example provides a hydroxyapatite, the preparation method of which is as follows:

[0135] 100 mL of 0.108 mol / L calcium nitrate tetrahydrate, 100 mL of 0.02 mol / L sodium trimetaphosphate, and 50 mL of 1 mol / L urea were mixed in a beaker using deionized water as the solvent. The mixture was magnetically stirred, and the pH was adjusted to 3.5 with 0.05 mol / L dilute nitric acid. Then, glutamic acid was added to the solution, where n(calcium nitrate tetrahydrate):n(sodium trimetaphosphate):n(glutamic acid) = 10.8:2:15. After magnetic stirring for 0.5 h, the resulting solution was transferred to a high-pressure reactor. The reaction temperature was set to 180 °C, and the reaction time was 10 h. Finally, the resulting white precipitate was centrifuged and washed twice with deionized water and once with anhydrous ethanol, and then freeze-dried to obtain core-shell structured hydroxyapatite microspheres.

[0136] Comparative Example 3

[0137] This comparative example provides a hydroxyapatite, which differs from Example 1 only in that sodium tripolyphosphate (NaPO4)6 is not added in step (2), and sodium tripolyphosphate (Na5P3O)6 is added instead. 10 The amount of ) was adjusted from 1.07g to 1.37g, and the other raw materials, amounts and preparation methods were the same as in Example 1, resulting in flake-shaped hydroxyapatite.

[0138] Comparative Example 4

[0139] This comparative example provides a hydroxyapatite, which differs from Example 1 only in that sodium tripolyphosphate (Na5P3O3) is not added in step (2). 10 The amount of sodium trimetaphosphate (NaPO4)6 was adjusted from 0.3g to 1.37g, and the other raw materials, amounts and preparation methods were the same as in Example 1, resulting in flake-like hydroxyapatite.

[0140] Comparative Example 5

[0141] This comparative example provides a hydroxyapatite, which differs from Example 1 only in that the citric acid in step (3) is replaced with 0.05 mol / L dilute nitric acid. The other raw materials, dosages and preparation methods are the same as in Example 1, and liquid-solid phase change self-generated hydroxyapatite microspheres with an average particle size of 25 μm are obtained.

[0142] The hydroxyapatite obtained in Examples 1-9 and Comparative Examples 1-5 were tested for conductivity using a CDLY-2006 hydraulic fracturing fracture conductivity meter. The measuring medium was a 2% potassium chloride solution, and the concentration of hydroxyapatite was 10 kg / m³. 2 The experimental temperature was 90℃, the fluid flow rate was 2mL / min, and the closing pressure was 30MPa. The test results are shown in Table 1.

[0143] Table 1

[0144] <![CDATA[Average fracture conductivity (μm 2 ·cm)]]> Example 1 3.45433 Example 2 3.23465 Example 3 4.12754 Example 4 4.32052 Example 5 2.34327 Example 6 3.43764 Example 7 3.54336 Example 8 3.34322 Example 9 3.32398 Comparative Example 1 0.87342 Comparative Example 2 0.67543 Comparative Example 3 0.64532 Comparative Example 4 0.94345 Comparative Example 5 0.53235

[0145] The test results show that:

[0146] (1) As can be seen from Examples 1-9, the solution of the liquid-solid phase change self-generated hydroxyapatite microspheres of the present invention can generate hydroxyapatite microspheres in situ at a specific temperature, and thus can act as a self-generated proppant to support the fractures formed after fracturing, so that the fractures maintain a high conductivity (2.34327-4.32052 μm). 2 ·cm).

[0147] (2) By comparing Example 1 with Examples 6-9, it can be seen that the specific mass ratio of phosphate salts A and B in the composite phosphate source solution of the present invention can make the obtained hydroxyapatite microspheres have better conductivity. This is because the reaction rate can be controlled by the specific ratio of phosphate salts A and B, thereby regulating the crystallization time of hydroxyapatite, achieving the purpose of regulating the morphology of the obtained hydroxyapatite microspheres, and thus obtaining hydroxyapatite microspheres with better conductivity.

[0148] (3) By comparing Example 1 with Comparative Examples 1 and 2, it can be seen that the solution of the self-generated hydroxyapatite microspheres by liquid-solid phase change of the present invention can generate hydroxyapatite microspheres in situ, which has good conductivity and can be used as an in-situ proppant after fracturing of oil and gas reservoirs. However, the hydroxyapatite prepared in the prior art cannot stably obtain hydroxyapatite with a large spherical particle size, has poor conductivity, and is not suitable as an in-situ proppant for supporting fractures after fracturing of oil and gas reservoirs.

[0149] (4) By comparing Example 1 with Comparative Examples 3 and 4, it can be seen that the phosphate salt A and phosphate salt B in the composite phosphate source solution of the present invention can play a synergistic role through compounding, so that the solution of the liquid-solid phase change self-generated hydroxyapatite microspheres can undergo hydrothermal reaction at a specific temperature to generate hydroxyapatite microspheres that can be used to support fractures in phase change fracturing.

[0150] (5) By comparing Example 1 and Comparative Example 5, it can be seen that the selection of specific organic acids can be combined with urea to make the resulting composite regulator solution play a better regulatory role, and then be well combined with calcium source solution and composite phosphorus source solution, so that hydroxyapatite crystallizes into microspheres during the liquid-solid phase transition process, with better flow conduction effect, which can meet the requirements of supporting cracks; while non-specifically selected inorganic acids do not have this technical effect, and therefore cannot meet the requirements of supporting cracks.

[0151] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A solution of self-generated hydroxyapatite microspheres through liquid-solid phase change, characterized in that, The solution includes a calcium source solution, a composite phosphorus source solution, and a composite regulator solution; The calcium source solution includes calcium salts; The composite phosphorus source solution includes phosphate salts; The phosphate salt includes any two or at least three of sodium tripolyphosphate, sodium hexadeciphosphate, sodium trimetaphosphate, or sodium hexadeciphosphate. The composite regulator solution includes urea and organic acids.

2. The solution of self-generated hydroxyapatite microspheres by liquid-solid phase change according to claim 1, characterized in that, The calcium salt content is 30-40% based on the total mass of calcium salt, phosphate salt, urea and organic acid as 100%. Preferably, the calcium source is calcium nitrate and / or calcium chloride; Preferably, the calcium source solution is an aqueous solution; Preferably, the water in the aqueous solution is tap water, deionized water, or distilled water; Preferably, the mass concentration of calcium salt in the calcium source solution is 24-35 g / L.

3. The solution of self-generated hydroxyapatite microspheres according to claim 1 or 2, characterized in that, The content of the phosphate salt is 10-30% based on the total mass of calcium salt, phosphate salt, urea and organic acid as 100%. Preferably, the phosphorus source solution is an aqueous solution; Preferably, the water in the aqueous solution is tap water, deionized water, or distilled water; Preferably, the phosphate salt includes phosphate salt A and phosphate salt B; Preferably, the phosphate salt A comprises sodium tripolyphosphate and / or sodium hexapolyphosphate; Preferably, the phosphate salt B comprises sodium trimetaphosphate and / or sodium hexametaphosphate. Preferably, the mass ratio of phosphate salt A to phosphate salt B is (1-20):1, more preferably (1.5-4):1; Preferably, the mass concentration of phosphorus salt A in the phosphorus source solution is 5-20 g / L; Preferably, the mass concentration of phosphate salt B in the phosphate source solution is 1-5 g / L.

4. The solution of self-generated hydroxyapatite microspheres according to any one of claims 1-3, characterized in that, The urea content is 20-30% based on the total mass of calcium salts, phosphate salts, urea and organic acids, which is 100%. Preferably, the composite regulator solution is an aqueous solution; Preferably, the water in the aqueous solution is tap water, deionized water, or distilled water; Preferably, the mass concentration of urea in the composite regulator solution is 16-26.5 g / L.

5. The solution of self-generated hydroxyapatite microspheres according to any one of claims 1-4, characterized in that, The organic acid content is 15-25% based on the total mass of calcium salts, phosphate salts, urea, and organic acids, which is 100%. Preferably, the organic acid includes any one or a combination of at least two of citric acid, alginic acid, tartaric acid, glutamic acid, or aspartic acid; Preferably, the mass concentration of organic acid in the composite regulator solution is 12-20 g / L.

6. A method for preparing a solution of self-generated hydroxyapatite microspheres by liquid-solid phase change as described in any one of claims 1-5, characterized in that, The preparation method includes the following steps: A solution of the calcium source solution, the composite phosphorus source solution, and the composite regulator solution is mixed to obtain a solution of the self-generated hydroxyapatite microspheres by liquid-solid phase change. Preferably, the mixing is carried out under stirring; Preferably, the stirring speed is 350-450 r / min; Preferably, the preparation method further includes mixing until the solution becomes clear and then allowing it to stand; Preferably, the settling time is 22-26 hours.

7. A method for preparing self-generated hydroxyapatite microspheres through liquid-solid phase transformation, characterized in that, The preparation method includes the following steps: The liquid-solid phase change self-generated hydroxyapatite microspheres according to any one of claims 1-5 are subjected to a hydrothermal reaction to obtain the liquid-solid phase change self-generated hydroxyapatite microspheres. Preferably, the temperature of the hydrothermal reaction is 60-250℃; Preferably, the hydrothermal reaction takes 2-12 hours.

8. The method for preparing self-generated hydroxyapatite microspheres by liquid-solid phase change according to claim 7, characterized in that, The preparation method also includes a post-processing step after the hydrothermal reaction is completed; Preferably, the post-processing steps include filtration, washing, and drying; Preferably, the filtration includes filtration of the reaction solution after the hydrothermal reaction is completed using a microporous membrane with a pore size of 0.1 μm; Preferably, the washing includes washing the filtered cake with deionized water and anhydrous ethanol alternately; Preferably, the drying temperature is 85-95°C; Preferably, the drying time is 22-26 hours; Preferably, the particle size of the self-generated hydroxyapatite microspheres from the liquid-solid phase change is 0.5-100 μm.

9. Liquid-solid phase change self-generated hydroxyapatite microspheres prepared by the method described in claim 7 or 8.

10. The application of a solution of self-generated hydroxyapatite microspheres of liquid-solid phase change as described in any one of claims 1-5, or the application of self-generated hydroxyapatite microspheres of liquid-solid phase change as described in claim 9, in fracturing technology for oil and gas reservoir development.

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