An air-suspended proppant and a preparation method thereof, and a fracturing fluid

Abstract

This invention provides an air-suspended proppant, its preparation method, and a fracturing fluid, belonging to the field of oil and gas field fracturing technology. This invention chemically modifies the proppant, introducing hydrophobic and gas-philic groups onto its surface to form a monomolecular hydrophobic and gas-philic coating. During fracturing, the proppant adsorbs the gas during gas mixing. Simultaneously, the introduced surfactant acts as a foaming agent, achieving foaming and stabilizing effects and preventing rapid bubble dissipation. The buoyancy of the bubbles enables the proppant to self-suspend in low-viscosity slickwater fracturing fluid, improving the placement effect.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field fracturing technology, specifically relating to an air-suspended proppant and its preparation method, and fracturing fluid. Background Technology

[0002] During the fracturing process in oil and gas fields, fracturing fluid carrying proppant such as quartz sand and ceramsite is pumped to the fracture location. After the fracturing fluid is flushed back, the proppant remains in the fracture to prevent it from closing, enhance its conductivity, and increase oil and gas field production.

[0003] Water-based fracturing fluids mainly include guar gum fracturing fluid systems and polymer fracturing fluid systems. Guar gum solutions, after cross-linking, form gels with strong proppant carrying capacity, but the material cost is relatively high and the construction friction is relatively high. Polymer fracturing fluids, represented by slickwater, have good drag reduction effect and low cost, but as low-viscosity, low-density liquids, their proppant suspension effect is poor, and proppant carrying can only be achieved by increasing the discharge rate and pump pressure and accelerating the pumping speed.

[0004] The proppant is mainly composed of silicon-based materials such as quartz sand and ceramsite, with a density of 2.6 g / cm³. 3 In low-viscosity slickwater fracturing fluids, proppant cannot achieve independent suspension in fracturing fluids and requires viscoelastic proppant-carrying fluids or high-speed shear pumping for long-distance placement. Silicon-based materials have unsaturated surface coordination, tending to adsorb water molecules from the air. These adsorbed water molecules are prone to dissociation, resulting in hydroxylation. Hydroxylation leads to polarity and hydrophilicity, causing poor proppant placement in low-viscosity slickwater fracturing fluids. Therefore, it is necessary to improve the suspension properties of proppants. Summary of the Invention

[0005] This invention chemically modifies the proppant, introducing hydrophobic and anaerobic groups onto its surface to form a monomolecular hydrophobic and anaerobic coating. During fracturing, the proppant adsorbs the gas during gas mixing. Simultaneously, the introduced surfactant acts as a foaming agent to achieve foaming and stabilizing effects, preventing rapid bubble dissipation. The proppant achieves autonomous suspension in low-viscosity slickwater fracturing fluid through the buoyancy of the bubbles, thus improving the proppant placement effect.

[0006] One of the objectives of this invention is to provide a method for preparing an air suspension proppant.

[0007] The second objective of this invention is to provide an air-suspension proppant prepared by the method described above.

[0008] A third objective of this invention is to provide a fracturing fluid comprising the air-suspended proppant.

[0009] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0010] In a first aspect, the present invention provides a method for preparing an air-suspended proppant, comprising the following steps:

[0011] (a) The silicon-based material support is heated and acid-washed, then washed with water and dried to obtain the acid-washed silicon-based material support;

[0012] (b) The pH value of the ethanol-water mixture was adjusted, stirred and heated, and a silane coupling agent was added for hydrolysis. After hydrolysis, the acid-washed silicon-based material support agent was added, and the reaction was continued to be heated. After the reaction, the support agent was filtered out, and the unreacted solvent was washed away to obtain the treated silicon-based material support agent.

[0013] (c) The ethanol aqueous solution of the surfactant is sprayed onto the surface of the treated silicon-based material support, mixed and dried to obtain the air-suspended support.

[0014] In some embodiments, in step (a), the silicon-based material support is one or more of quartz sand, ceramsite, walnut shell, and glass beads, preferably quartz sand;

[0015] Preferably, the quartz sand is one or more of the following specifications: 20-40 mesh, 40-70 mesh, and 70-100 mesh, with 40-70 mesh quartz sand being the most preferred.

[0016] In some embodiments, in step (a), the acid solution used for pickling is a hydrochloric acid aqueous solution with a mass concentration of 2%-10%, preferably a hydrochloric acid aqueous solution with a mass concentration of 5%.

[0017] In some embodiments, in step (a), the pickling temperature is 60°C-90°C, preferably 70°C; the pickling time is 2-6 hours, preferably 3 hours.

[0018] In some implementations, in step (a), the washing is performed three or more times until the pH of the washing solution is >6.0;

[0019] In some embodiments, in step (a), the drying temperature is 100-115°C, preferably 105°C; and the drying time is 3-6 hours, preferably 4 hours.

[0020] In some embodiments, in step (b), the mass percentage of water in the ethanol-water mixture is 1-10%, preferably 5%;

[0021] In some embodiments, in step (b), the pH value is adjusted to 2.5-5.5, preferably 4.0;

[0022] In some embodiments, in step (b), the heating temperature is 50°C-90°C, preferably 60°C;

[0023] In some embodiments, in step (b), the silane coupling agent is one or more of butyltrimethoxysilane, pentyltrimethoxysilane, octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, hexadecyltrimethoxysilane, 1H,1H,2H,2H-perfluorooctyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-methacryloyloxypropyltrimethoxysilane.

[0024] Preferably, the amount of silane coupling agent used is 0.1-5% of the mass of the mixed solution of ethanol and water;

[0025] In some embodiments, in step (b), the hydrolysis time is 30-100 min, preferably 60 min.

[0026] In some embodiments, in step (b), the mass ratio of the pickled silicon-based material support to the silane coupling agent is 100:0.2 to 100:2.5;

[0027] In some embodiments, in step (b), the heating temperature is 55°C-80°C, preferably 65°C, and the reaction time is 2-6 hours, preferably 4 hours.

[0028] In some implementations, step (b) involves washing with ethanol at least three times.

[0029] In some embodiments, in step (c), the surfactant is one or more of OP-10 (octylphenol polyoxyethylene (10) ether), dodecyl betaine, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, and cocamidopropyl betaine;

[0030] Preferably, the surfactant in the ethanol aqueous solution accounts for 4-6% by mass, more preferably 5%, and the ethanol accounts for 40-50% by mass, more preferably 45%.

[0031] In some embodiments, in step (c), the amount of surfactant used accounts for 0.05%-0.9% of the mass of the treated silicon-based material support;

[0032] In some embodiments, in step (c), the drying temperature is 100-120°C, preferably 110°C, and the drying time is 2-8 hours, preferably 4 hours.

[0033] In some specific embodiments, the preparation method of the air suspension proppant includes the following steps:

[0034] (1) Place the quartz sand in a 2%-10% hydrochloric acid aqueous solution and heat it to 60℃-90℃ for acid washing. This can remove impurities and activate the surface silanol groups. After acid washing, wash with water until the pH test shows that the washing solution is neutral and then dry until there is no moisture.

[0035] (2) Adjust the pH of the ethanol and water mixture to 2.5-5.5 with acetic acid, stir and heat at 50℃-90℃, add silane coupling agent and hydrolyze for 30-100 min. After hydrolysis, add the quartz sand treated in step (1) into the solution and continue to heat at 55℃-80℃ for 2-6 h. After the reaction, filter out the support agent and wash away the unreacted solvent with ethanol.

[0036] (3) Prepare an ethanol-water solution of surfactant, spray the solution onto the surface of the quartz sand treated in step (2), mix well and dry to obtain the air suspension proppant.

[0037] The general structural formula of silane coupling agents is R m SiX n (m+n=4), where R represents non-hydrolyzable organic functional groups, such as alkyl, alkenyl, amino, epoxy, and mercapto groups, and X represents hydrolyzable groups, such as methoxy and ethoxy groups. After hydrolysis, the silane coupling agent can undergo a condensation reaction with the silanol groups on the surface of silicon-based materials, grafting the non-hydrolyzable groups onto the proppant surface and completing the surface modification of the proppant. After hydrophobic modification, the proppant surface can be transformed into a non-polar hydrophobic-aerophilic state. During fracturing, non-polar gases such as nitrogen, air, and carbon dioxide are pumped in, and the gases are adsorbed onto the proppant surface. At the same time, the addition of surfactants serves two purposes: firstly, as foaming agents to complete the foaming and stabilizing effects of the system; secondly, the hydrophobic groups in the surfactants can synergistically enhance the suspension effect and increase the laying area during pumping.

[0038] Secondly, the present invention provides an air-suspension proppant prepared by the above-described preparation method.

[0039] Thirdly, the present invention provides a fracturing fluid comprising the aforementioned air-suspended proppant.

[0040] Beneficial effects:

[0041] The air-suspension proppant provided by this invention modifies the surface of silicon-based proppant materials by hydrophobicity and aerophilicity through a silane coupling agent to adsorb air bubbles, and further enhances suspension performance by using surfactants to promote foaming and stabilize bubbles. During fracturing, the injection of non-polar gases such as nitrogen and air further improves suspension performance and increases the layup area after air bubbles are adsorbed on the proppant surface. This effectively solves the shortcomings of existing slickwater and quartz sand proppant systems, which suffer from poor suspension performance and small layup area.

[0042] The present invention has been described in detail above; however, the above embodiments are merely illustrative in nature and are not intended to limit the invention. Furthermore, this document is not limited to the foregoing prior art or the invention itself, or to any theory described in the following embodiments. Attached Figure Description

[0043] Figure 1 The reaction mechanism of 1H,1H,2H,2H-perfluorooctyltrimethoxysilane modification in Example 1;

[0044] Figure 2 The particle size distribution of quartz sand in Example 1;

[0045] Figure 3 The optical contact angle measurements are for the unmodified quartz sand and the modified air suspension proppant.

[0046] Figure 4 This diagram illustrates the air suspension effect and the bubble adsorption of the unmodified quartz sand and the modified air suspension proppant.

[0047] Figure 5 This shows the static suspension of the air suspension proppant in Example 1. Detailed Implementation

[0048] The present invention will be further described below with reference to the embodiments. It should be noted that the following embodiments are provided for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0049] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art.

[0050] Example 1

[0051] (1) Take 500g of 40-70 mesh quartz sand (the physicochemical parameters of the 40-70 mesh quartz sand substrate are shown in Table 1 below, and the particle size distribution is shown in Table 2 and...). Figure 2 As shown, (meeting the requirements for the preparation of air suspension proppant) was placed in 600ml of 5% hydrochloric acid aqueous solution, heated and acid-washed at 70℃ for 3h, then washed with water 4 times, and the pH of the washing solution was measured to be 6.2. The quartz sand was then dried at 105℃ for 4h.

[0052] (2) Prepare 500g of a mixture of 5% water and 95% ethanol, adjust the pH to 4.0 with acetic acid, stir and heat to 60℃, add 2g of 1H,1H,2H,2H-perfluorooctyltrimethoxysilane for hydrolysis and heating. After hydrolysis for 60min, add 500g of quartz sand treated in step (1) to the solution, and continue heating the reaction at 65℃ for 4h. After the reaction, filter out the support, wash with ethanol three times to remove unreacted solvent, and the total washing liquid is 1000ml. The reaction mechanism of silane modification is as follows: Figure 1 As shown.

[0053] (3) Prepare the solution: 5% OP-10 + 45% ethanol + 50% water. Spray 50g of the solution onto the surface of the quartz sand treated in step (2), mix well, and dry at 110℃ for 4h to obtain the air suspension proppant.

[0054] Table 1 Analysis of Physicochemical Parameters of Quartz Sand Base

[0055] chemical composition <![CDATA[SiO2]]> <![CDATA[Na2O]]> <![CDATA[K2O]]> <![CDATA[Fe2O3]]> <![CDATA[Al2O3]]> <![CDATA[TiO2]]> total measured data 99.38％ 0.008％ 0.010％ 0.036％ 0.22％ 0.045％ 99.70％ Physical properties Moisture content % mud content % square factor Acid consumption Loss on ignition % pH value Standard requirements ≤0.30％ ≤0.30％ ≤1.35 ≤5 ≤0.30％ 6.5-7.5 measured data 0.05％ 0.24％ 1.32 1.6 0.21％ 6.7

[0056] Table 2. Grain size distribution of quartz sand

[0057]

[0058] Optical contact angle measurements were performed on the unmodified quartz sand and the modified air suspension proppant. The results are as follows: Figure 3 As shown, the contact angle increased significantly, indicating successful hydrophobic modification.

[0059] The unmodified quartz sand and the modified air suspension proppant were added to slickwater (0.10% polyacrylamide solution) and stirred to incorporate air bubbles. Microscopic optical detection was performed to observe the bubble adsorption. The results are as follows: Figure 4 As shown. Before modification, almost no bubbles were adsorbed, but after modification, the quartz sand was able to adsorb bubbles and complete suspension. The middle image shows the state before modification, where the quartz sand could not adsorb bubbles and complete suspension, and the field of view shows tiny bubbles formed by stirring; the right image shows the state after modification, where the proppant is adsorbed below larger bubbles and completes suspension, and the field of view shows the adsorbed combination of the two.

[0060] Static suspension test was conducted on the air-suspension proppant. 50g of air-suspension proppant was added to 200g of slickwater and stirred to introduce air bubbles for adsorption. After standing for 1 hour, the proppant that had not settled in the upper solution was washed with water, dried, and weighed. The suspension ratio (suspension ratio = mass of unsettled proppant / 50g × 100%) was measured to be 81%.

[0061] Example 2

[0062] (1) Place 500g of 40-70 mesh quartz sand (same as in Example 1) in 600ml of 5% hydrochloric acid aqueous solution, heat and acid wash at 70°C for 3h, then wash with water 4 times, and the pH of the washing solution is measured to be 6.2. Dry the quartz sand at 105°C for 4h.

[0063] (2) Prepare 500g of a mixture of 5% water and 95% ethanol, adjust the pH to 4.0 with acetic acid, stir and heat to 60°C, add 2g of hexadecyltrimethoxysilane for hydrolysis and heating, after hydrolysis for 60min, add 500g of quartz sand treated in step (1) into the solution, continue heating the reaction at 65°C for 4h, filter out the support after the reaction, wash with ethanol to remove unreacted solvent 3 times, and the total washing liquid is 1000ml.

[0064] (3) Prepare the solution: 5% sodium dodecylbenzenesulfonate + 45% ethanol + 50% water. Spray 50g of the solution onto the surface of the quartz sand treated in step (2), mix well, and dry at 110℃ for 4h to obtain the air suspension proppant.

[0065] A static suspension test was conducted using the same method as in Example 1, and the suspension ratio was measured to be 79%.

[0066] Example 3

[0067] (1) Place 500g of 40-70 mesh quartz sand (same as in Example 1) in 600ml of 5% hydrochloric acid aqueous solution, heat and acid wash at 70°C for 3h, then wash with water 4 times, and the pH of the washing solution is measured to be 6.2. Dry the quartz sand at 105°C for 4h.

[0068] (2) Prepare 500g of a mixture of 5% water and 95% ethanol, adjust the pH to 4.0 with acetic acid, stir and heat to 60°C, add 2g of γ-glycidyl oxypropyltrimethoxysilane for hydrolysis and heating, after hydrolysis for 60min, add 500g of quartz sand treated in step (1) into the solution, continue heating the reaction at 65°C for 4h, filter out the support after the reaction, wash with ethanol to remove unreacted solvent 3 times, and the total washing liquid is 1000ml.

[0069] (3) Prepare the solution: 5% dodecyl betaine + 45% ethanol + 50% water. Spray 50g of the solution onto the surface of the quartz sand treated in step (2), mix well, and dry at 110℃ for 4h to obtain the air suspension proppant.

[0070] A static suspension test was performed using the same method as in Example 1, and the suspension ratio was measured to be 80%.

[0071] Comparative Example 1

[0072] Following the same method as in Example 1, a static suspension test was conducted on untreated 40-70 mesh quartz sand, and the suspension ratio was measured to be 3%, indicating that there was essentially no suspension effect.

[0073] Comparative Example 2

[0074] (1) Place 500g of 40-70 mesh quartz sand (same as in Example 1) in 600ml of 5% hydrochloric acid aqueous solution, heat and acid wash at 70°C for 3h, then wash with water 4 times, and the pH of the washing solution is measured to be 6.2. Dry the quartz sand at 105°C for 4h.

[0075] (2) Prepare 500g of a mixture of 5% water and 95% ethanol, adjust the pH to 4.0 with acetic acid, stir and heat to 60°C, add 2g of 1H,1H,2H,2H-perfluorooctyltrimethoxysilane for hydrolysis and heating, after hydrolysis for 60min, add 500g of quartz sand treated in step (1) into the solution, continue heating the reaction at 65°C for 4h, filter out the support after the reaction, wash with ethanol to remove unreacted solvent 3 times, and the total washing liquid is 1000ml.

[0076] (3) Solution preparation: 45% ethanol + 55% water. Spray 50g of the solution onto the surface of the quartz sand treated in step (2), mix well, and dry at 110℃ for 4h to obtain the control group of air suspension proppant without surfactant treatment.

[0077] A static suspension test was conducted using the same method as in Example 1, and the suspension ratio was measured to be 35%. This shows that the lack of surfactant leads to a significant decrease in the suspension effect.

[0078] Comparative Example 3

[0079] (1) Place 500g of 40-70 mesh quartz sand (same as in Example 1) in 600ml of 5% hydrochloric acid aqueous solution, heat and acid wash at 70°C for 3h, then wash with water 4 times, and the pH of the washing solution is measured to be 6.2. Dry the quartz sand at 105°C for 4h.

[0080] (2) Prepare 500g of a mixture of 5% water and 95% ethanol, adjust the pH to 4.0 with acetic acid, stir and heat to 60°C, and after 60min, add 500g of quartz sand treated in step (1) into the solution and continue heating the reaction at 65°C for 4h. After the reaction, filter out the support agent, wash with ethanol to remove unreacted solvent 3 times, and the total washing solution is 1000ml.

[0081] (3) Solution preparation: 5% OP-10 + 45% ethanol + 50% water. Spray 50g of the solution onto the surface of the quartz sand treated in step (2), mix well, and dry at 110℃ for 4h to obtain the control group of air suspension proppant without silane coupling agent treatment.

[0082] A static suspension test was performed using the same method as in Example 1, and the suspension ratio was measured to be 12%. This shows that the absence of silane coupling agent leads to a near loss of suspension effect.

[0083] The above embodiments are merely illustrative of the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and substance defined by the claims of the present invention; and such modifications or substitutions are still within the scope defined by the claims of the present invention.

Claims

1. A method for preparing an air-suspended proppant, characterized in that, Includes the following steps: (a) The silicon-based material support is heated and acid-washed, then washed with water and dried to obtain the acid-washed silicon-based material support; (b) The pH value of the ethanol-water mixture was adjusted, stirred and heated, and a silane coupling agent was added for hydrolysis. After hydrolysis, the acid-washed silicon-based material support agent was added, and the reaction was continued to be heated. After the reaction, the support agent was filtered out, and the unreacted solvent was washed away to obtain the treated silicon-based material support agent. (c) The ethanol aqueous solution of the surfactant is sprayed onto the surface of the treated silicon-based material support, mixed and dried to obtain the air-suspended support.

2. The preparation method according to claim 1, characterized in that, In step (a), the silicon-based material support is one or more of quartz sand, ceramsite, walnut shell, and glass beads, preferably quartz sand; Preferably, the quartz sand is one or more of the following specifications: 20-40 mesh, 40-70 mesh, and 70-100 mesh, with 40-70 mesh quartz sand being the most preferred.

3. The preparation method according to claim 1, characterized in that, In step (a), the acid solution used for pickling is a hydrochloric acid aqueous solution with a mass concentration of 2%-10%.

4. The preparation method according to claim 1, characterized in that, In step (a), the pickling temperature is 60℃-90℃; the pickling time is 2-6h.

5. The preparation method according to claim 1, characterized in that, In step (b), the mass percentage of water in the ethanol-water mixture is 1-10%. Preferably, in step (b), the pH value is adjusted to 2.5-5.5; Preferably, in step (b), the heating temperature is 50℃-90℃.

6. The preparation method according to claim 1, characterized in that, In step (b), the silane coupling agent is one or more of the following: butyltrimethoxysilane, pentyltrimethoxysilane, octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, hexadecyltrimethoxysilane, 1H,1H,2H,2H-perfluorooctyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-methacryloyloxypropyltrimethoxysilane. Preferably, the amount of silane coupling agent used is 0.1-5% of the mass of the mixed solution of ethanol and water; Preferably, in step (b), the hydrolysis time is 30-100 min.

7. The preparation method according to claim 1, characterized in that, In step (b), the mass ratio of the pickled silicon-based material support to the silane coupling agent is 100:0.2 to 100:2.5; Preferably, in step (b), the heating temperature is 55℃-80℃ and the reaction time is 2-6h.

8. The preparation method according to claim 1, characterized in that, In step (c), the surfactant is one or more of OP-10, dodecyl betaine, sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, and cocamidopropyl betaine; Preferably, the surfactant in the ethanol aqueous solution accounts for 4-6% by mass, and the ethanol accounts for 40-50% by mass. Preferably, the amount of surfactant used is 0.05%-0.9% of the mass of the treated silicon-based material support.

9. An air suspension proppant, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. A fracturing fluid comprising the air-suspended proppant as described in claim 9.

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