High-purity graded quartz sand fracturing propping agent and preparation method thereof

Abstract

The invention discloses a high-purity graded quartz sand fracturing propping agent and a preparation method thereof.The preparation method comprises the following specific steps that after natural quartz stone is crushed, calcined and subjected to water quenching, the quartz stone is immersed into a mixed acid solution composed of hydrochloric acid and hydrofluoric acid for a reaction, and high-purity slurry is obtained; then adding quartz sand and a ceramic ball medium into the slurry, carrying out mechanical scrubbing, and carrying out graded screening by virtue of a hydrocyclone and a multi-stage ultrasonic vibrating screen, so as to obtain quartz sand with concentrated particle size distribution; finally, the screened sand and an organic silane coupling agent are mixed, modified and dried at the high temperature, and a finished product is prepared. Through deep impurity removal with mixed acid, particle morphology optimization with mechanical scrubbing and surface silanization modification, the proppant has excellent properties such as high silicon dioxide content (greater than or equal to 99.4%), good sphericity degree (greater than or equal to 0.91), high compressive strength (greater than or equal to 85 MPa), low breakage rate (less than or equal to 4.3%) and the like, the flow conductivity and durability are effectively improved, and the proppant is suitable for fracturing exploitation of deep high-pressure oil and gas reservoirs.

Description

Technical Field

[0001] This invention relates to the field of fracturing proppant materials, and in particular to a high-purity graded quartz sand fracturing proppant and its preparation method. Background Technology

[0002] In the field of oil and gas extraction, hydraulic fracturing technology is the core means of developing low-permeability reservoirs, and the performance of fracturing proppant directly determines the long-term conductivity of fractures and the extraction efficiency. Currently, the mainstream proppants on the market include natural quartz sand and artificial ceramsite, both of which have obvious limitations: Although natural quartz sand is low in cost and low in density, it generally suffers from insufficient purity (SiO2 content is usually below 99%), many surface impurities, and poor sphericity and roundness, resulting in high acid solubility and weak resistance to breakage, especially under deep formation pressure, the breakage rate increases significantly, seriously affecting the propping effect; although ceramsite proppant has high strength, it has high production cost and high density, has strict requirements on the proppant carrying capacity of fracturing fluid, and the preparation process is energy-intensive, which does not conform to the trend of green manufacturing. In addition, existing quartz sand purification processes mostly rely on simple water washing, magnetic separation or single acid treatment, which is difficult to completely remove surface thin film iron and embedded impurities, and also lacks systematic optimization of particle morphology and surface functionalization treatment. Therefore, there is an urgent need to develop a quartz sand fracturing proppant that combines high purity, excellent sphericity, ideal anti-fracture performance, and hydrophobic and corrosion-resistant surface properties, while also being economical and environmentally friendly, to meet the increasingly severe demands of unconventional oil and gas extraction. Summary of the Invention

[0003] To address the aforementioned issues, this invention proposes a high-purity graded quartz sand fracturing proppant and its preparation method. This fracturing proppant retains the cost and density advantages of natural quartz sand while significantly improving its strength and stability, thus better meeting the needs of modern oil and gas field development, especially fracturing stimulation of unconventional and deep oil and gas reservoirs.

[0004] The present invention proposes a method for preparing a high-purity graded quartz sand fracturing proppant, comprising the following steps: Step 1: Add natural quartz stone to the crusher, crush, calcine, quench in water, then immerse in mixed acid solution, stir and react to obtain slurry; Step 2: Add quartz sand and ceramic ball media with a diameter of 10-30 mm to the slurry, mechanically scrub for 20-40 minutes, then perform preliminary classification using a hydrocyclone, and use a multi-stage series ultrasonic vibrating screen to remove coarse particles and fine powder. Mix the screened quartz sand with organosilane coupling agent in a high-speed mixer and dry at 120-180℃ to obtain high-purity graded quartz sand fracturing proppant.

[0005] Preferably, the calcination temperature in step 1 is 850-1000℃, and the time is 1-3 h.

[0006] Preferably, the method for preparing the mixed acid solution in step 1 is as follows: add water, hydrochloric acid, and hydrofluoric acid to a flask, mix well, and obtain the mixed acid solution.

[0007] Preferably, the mass ratio of hydrochloric acid to hydrofluoric acid is (3-5):1.

[0008] Preferably, the temperature of the stirring reaction in step 1 is 50-80℃, and the time is 2-4 h.

[0009] Preferably, in step 2, the mass ratio of quartz sand, ceramic ball medium, and organosilane coupling agent is 1:(2-4):(0.1-0.5).

[0010] Preferably, the mixing temperature in step 2 is 80-120℃ and the mixing time is 5-15 min.

[0011] The beneficial effects of this invention are: The silica content of the quartz sand fracturing proppant prepared by this invention is as high as 99.4%, significantly improving its purity. Through mechanical scrubbing and the synergistic effect of ceramic ball media, the particle sphericity reaches 0.91-0.98 and the roundness reaches 0.89-0.97, exhibiting excellent morphology and effectively reducing the risk of embedding and migration when filling fractures. After surface modification with a silane coupling agent, the interparticle friction is reduced, and the compressive strength is increased to over 85 MPa. Under a closure pressure of 52 MPa, the breakage rate is less than 4.3%, significantly enhancing durability and conductivity. This process combines green, economical, and efficient characteristics, overcoming the shortcomings of traditional quartz sand (low purity, poor morphology, insufficient strength) and ceramic proppant (high cost and high energy consumption). It is particularly suitable for efficient fracturing and exploitation of deep, high-pressure unconventional oil and gas reservoirs. Attached Figure Description

[0012] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0013] Figure 1 The silica content of the proppant; Figure 2 For the sphericity and roundness of the proppant; Figure 3 The compressive strength and breakage rate of the proppant. Detailed Implementation

[0014] The following provides a detailed description of the embodiments of the present invention: These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and processes. However, the scope of protection of the present invention is not limited to the following embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions.

[0015] Example 1 This embodiment describes a method for preparing a high-purity graded quartz sand fracturing proppant, comprising the following steps: Step 1: Add 300 mL of water, 15 g of hydrochloric acid, and 5 g of hydrofluoric acid to the flask, mix well, and obtain a mixed acid solution; Step 2: Add 2 kg of natural quartz to the crusher, crush, calcine at 850℃ for 3 h, quench with water, then immerse in a mixed acid solution, stir and react at 50℃ for 4 h to obtain a slurry; Step 3: Add 1.5 kg of quartz sand and 3 kg of ceramic ball media with a diameter of 10 mm to 1.5 kg of slurry, mechanically scrub for 20 min, then perform preliminary classification by hydrocyclone, and use a multi-stage series ultrasonic vibrating screen to remove coarse particles and fine powder. Mix the screened quartz sand with 150 g of KH550 in an 80℃ high-speed mixer for 15 min, and dry at 120℃ to obtain high-purity graded quartz sand fracturing proppant.

[0016] Example 2 This embodiment describes a method for preparing a high-purity graded quartz sand fracturing proppant, comprising the following steps: Step 1: Add 300 mL of water, 20 g of hydrochloric acid, and 5 g of hydrofluoric acid to the flask, mix well, and obtain a mixed acid solution; Step 2: Add 2 kg of natural quartz to the crusher, crush, calcine at 1000℃ for 1 hour, quench in water, and then immerse in a mixed acid solution. Stir and react at 80℃ for 2 hours to obtain a slurry. Step 3: Add 1.5 kg of quartz sand and 6 kg of ceramic ball media with a diameter of 30 mm to 1.5 kg of slurry, mechanically scrub for 40 min, then perform preliminary classification by hydrocyclone, and use a multi-stage series ultrasonic vibrating screen to remove coarse particles and fine powder. Mix the screened quartz sand with 750 g of KH550 in a high-speed mixer at 120℃ for 5 min, and dry at 180℃ to obtain high-purity graded quartz sand fracturing proppant.

[0017] Example 3 This embodiment describes a method for preparing a high-purity graded quartz sand fracturing proppant, comprising the following steps: Step 1: Add 300 mL of water, 25 g of hydrochloric acid, and 5 g of hydrofluoric acid to the flask, mix well, and obtain a mixed acid solution; Step 2: Add 2 kg of natural quartz to the crusher, crush, calcine at 900℃ for 2 h, quench in water, then immerse in a mixed acid solution and stir at 65℃ for 3 h to obtain a slurry. Step 3: Add 1.5 kg of quartz sand and 4.5 kg of ceramic ball media with a diameter of 20 mm to 1.5 kg of slurry, mechanically scrub for 30 min, then perform preliminary classification by hydrocyclone, and use a multi-stage series ultrasonic vibrating screen to remove coarse particles and fine powder. Mix the screened quartz sand with 450 g of KH550 in a high-speed mixer at 100℃ for 10 min, and dry at 150℃ to obtain high-purity graded quartz sand fracturing proppant.

[0018] Comparative Example 1: The difference between this comparative example and Example 1 is that hydrochloric acid was used instead of mixed acid for treatment.

[0019] The preparation method of the quartz sand fracturing proppant in this comparative example includes the following steps: Step 1: Add 300 mL of water and 15 g of hydrochloric acid to the flask to obtain a single hydrochloric acid solution; Step 2: Add 2 kg of natural quartz to the crusher, crush, calcine at 850℃ for 3 h, quench with water, then immerse in a single hydrochloric acid solution, stir and react at 50℃ for 4 h to obtain a slurry. Step 3: Add 1.5 kg of quartz sand and 3 kg of ceramic ball media with a diameter of 10 mm to 1.5 kg of slurry, mechanically scrub for 20 min, then perform preliminary classification by hydrocyclone, and use a multi-stage series ultrasonic vibrating screen to remove coarse particles and fine powder. Mix the screened quartz sand with 150 g of KH550 in an 80℃ high-speed mixer for 15 min, and dry at 120℃ to obtain quartz sand fracturing proppant.

[0020] Comparative Example 2: The difference between this comparative example and Example 1 is that no ceramic ball medium is added and no mechanical scrubbing is performed.

[0021] The preparation method of the quartz sand fracturing proppant in this comparative example includes the following steps: Step 1: Add 300 mL of water, 15 g of hydrochloric acid, and 5 g of hydrofluoric acid to the flask, mix well, and obtain a mixed acid solution; Step 2: Add 2 kg of natural quartz to the crusher, crush, calcine at 850℃ for 3 h, quench with water, then immerse in a mixed acid solution, stir and react at 50℃ for 4 h to obtain a slurry; Step 3: Add 1.5 kg of quartz sand to 1.5 kg of slurry, perform preliminary classification directly through a hydrocyclone, and then remove coarse particles and fine powder by ultrasonic vibrating screen. Mix the screened quartz sand with 150 g of KH550 in an 80℃ high-speed mixer for 15 min, and dry at 120℃ to obtain quartz sand fracturing proppant.

[0022] Comparative Example 3: The difference between this comparative example and Example 1 is that the sieved quartz sand is not subjected to KH550 surface treatment.

[0023] The preparation method of the quartz sand fracturing proppant in this comparative example includes the following steps: Step 1: Add 300 mL of water, 15 g of hydrochloric acid, and 5 g of hydrofluoric acid to the flask, mix well, and obtain a mixed acid solution; Step 2: Add 2 kg of natural quartz to the crusher, crush, calcine at 850℃ for 3 h, quench with water, then immerse in a mixed acid solution, stir and react at 50℃ for 4 h to obtain a slurry; Step 3: Add 1.5 kg of quartz sand and 3 kg of ceramic ball media with a diameter of 10 mm to 1.5 kg of slurry, mechanically scrub for 20 min, then perform preliminary classification by hydrocyclone, and use a multi-stage series ultrasonic vibrating screen to remove coarse particles and fine powder. Dry the screened quartz sand directly at 120℃ to obtain quartz sand fracturing proppant.

[0024] Performance testing 1. Purity and silica content Take 100 g of quartz sand fracturing proppant, reduce it to 10 g using the quartering method, and grind the sample using a ceramic mortar until it passes through a 200-mesh standard sieve to ensure sample homogeneity. Take 5 g of the ground powder, dry it at 105℃ for 2 h, and cool it to room temperature in a desiccator for later use. Place a portion of the dried powder sample into a special pressing mold and press it into a flat, smooth disc under a pressure of 30 MPa. Place the pressed disc into the sample chamber of an XRF spectrometer, start the instrument, select the "oxide analysis" mode according to the instrument operation manual, scan the disc, and record the silica content as the main purity indicator.

[0025] Weigh 0.5 g of the prepared powder sample into a platinum crucible, add 5 g of anhydrous sodium carbonate, mix well, and melt in a muffle furnace at 1000℃ until transparent. After cooling, immerse the melt in a beaker with hot water and hydrochloric acid solution. Place the beaker on a water bath to evaporate to a wet salt state. Add hydrochloric acid and animal glue to coagulate the silicic acid. Filter, and then wash with hot dilute hydrochloric acid and water until no iron ions are present. Transfer the precipitate and filter paper into the weighed platinum crucible, ashing it, and then ignite it in a muffle furnace at 1100℃ until constant weight. Silica content (%) = (mass of precipitate after ignition / mass of sample) × 100%.

[0026] Table 1. Test Results of Purity and Silica Content

[0027] As shown in Table 1, Examples 1-3, treated with a mixed acid, effectively removed surface iron and silicate impurities, resulting in a silica content higher than 99.3%. In contrast, Comparative Example 1, using only hydrochloric acid, failed to effectively dissolve silicate inclusions, leading to a significant decrease in purity. Comparative Example 2, without mechanical scrubbing, did not completely remove surface impurities, further reducing purity.

[0028] 2. Sphericity and Roundness One hundred proppant particles were randomly selected and evenly dispersed on a glass plate with a graduated scale. A high-resolution digital camera was used to capture images of the particles vertically from directly above. These images were then imported into Clemex Vision, where its thresholding and particle analysis functions were used to automatically identify the contour of each particle and measure its projected area (A), perimeter (P), and minimum circumscribed circle radius (R). min and the maximum inscribed circle radius R max .

[0029]

[0030] Roundness = 2 × R max / (R) min +R max ) The closer the sphericity is to 1, the closer the particles are to a perfect sphere. The closer the roundness is to 1, the fewer the sharp edges and the smoother the surface of the particles.

[0031] Table 2. Test Count of Sphericity and Roundness

[0032] As shown in Table 2, due to the mechanical scrubbing and ceramic ball media, the particle morphology of all embodiments is closer to spherical, with reduced edges and corners, and the sphericity and roundness are close to 1. Comparative Example 1 has a rough surface due to incomplete acid treatment, which affects the roundness. Comparative Example 2 did not undergo mechanical scrubbing, so the particle morphology is irregular, and the sphericity (0.82) and roundness (0.78) are poor.

[0033] 3 Compressive strength Fifty intact, crack-free proppant particles were selected. Each particle was placed at the center of the lower platen of the testing machine and loaded at a constant displacement speed of 0.2 mm / min until the particles broke. The approximate compressive strength at break was recorded. Compressive strength (MPa) = F / ( ×r 2 ), where r is the average radius of the particle (mm).

[0034] Weigh 50 g of proppant sample and spread it evenly between the upper and lower steel plates of the flow chamber. Install the flow chamber onto the hydraulic pressure testing machine, apply a closing pressure of 52 MPa, and maintain this pressure for 2 minutes. After depressurization, remove the proppant sample and sieve it using a 70-mesh sieve. Weigh the mass of fine powder passing through the sieve. Breakage rate (%) = (mass of fine powder / total mass of sample before testing) × 100%.

[0035] Table 3 Compressive strength and breakage rate test data

[0036] As shown in Table 3, all examples, due to their high purity, optimized sphericity, and surface modification, produced fracturing proppants with high compressive strength (>58.6 MPa) and low breakage rate (<4.3%). Comparative Example 1, due to its low purity and poor morphology, exhibited a significant decrease in compressive strength (72.1 MPa). Comparative Example 2, lacking washing, had microcracks and stress concentration points in its particles, resulting in low compressive strength and a high breakage rate. Comparative Example 3, lacking surface modification, had high inter-particle friction, making it prone to breakage under closure pressure, leading to a relatively high breakage rate.

[0037] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-purity graded silica sand fracturing proppant, characterized in that, Includes the following steps: Step 1: Add natural quartz stone to the crusher, crush, calcine, quench in water, then immerse in mixed acid solution, stir and react to obtain slurry; Step 2: Add quartz sand and ceramic ball media with a diameter of 10-30 mm to the slurry, mechanically scrub for 20-40 min, then perform preliminary classification using a hydrocyclone, and use a multi-stage series ultrasonic vibrating screen to remove coarse particles and fine powder. Mix the screened quartz sand with organosilane coupling agent in a high-speed mixer and dry at 120-180℃ to obtain high-purity graded quartz sand fracturing proppant.

2. The method for preparing high-purity graded quartz sand fracturing proppant according to claim 1, characterized in that, The calcination temperature in step 1 is 850-1000℃, and the time is 1-3 h.

3. The method for preparing high-purity graded quartz sand fracturing proppant according to claim 1, characterized in that, The method for preparing the mixed acid solution in step 1 is as follows: add water, hydrochloric acid, and hydrofluoric acid to a flask, mix well, and obtain the mixed acid solution.

4. The method for preparing high-purity graded quartz sand fracturing proppant according to claim 3, characterized in that, The mass ratio of hydrochloric acid to hydrofluoric acid is (3-5):

1.

5. The method for preparing high-purity graded quartz sand fracturing proppant according to claim 1, characterized in that, The stirring reaction in step 1 is carried out at a temperature of 50-80℃ for 2-4 hours.

6. The method for preparing high-purity graded quartz sand fracturing proppant according to claim 1, characterized in that, In step 2, the mass ratio of quartz sand, ceramic ball media, and organosilane coupling agent is 1:(2-4):(0.1-0.5).

7. The method for preparing high-purity graded quartz sand fracturing proppant according to claim 1, characterized in that, The mixing temperature in step 2 is 80-120℃, and the time is 5-15 min.

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