Environment-friendly high-strength low-density oil well cement and preparation process thereof

Abstract

The invention relates to the field of cement, and particularly discloses environment-friendly high-strength low-density oil well cement and a preparation process thereof. 35 to 60 parts of composite ecological lightweight aggregate; the composite ecological lightweight aggregate comprises waste glass micro powder activated by microwaves. 0.8 to 3.5 parts of a hyperbranched polycarboxylate drag reducer; 1.5-6 parts of a composite reinforcing agent (composed of modified chitosan and nano cerium oxide according to a mass ratio of 4: 1); 2-7 parts of a stabilizer (a nano barium titanate and magnesium aluminum silicate compound); 0.2 to 1.2 parts of a retarder (a compound of zinc polyaspartate and trisodium phosphate); the preparation process mainly comprises microwave treatment of glass micro powder. According to the scheme, the oil well cement which is environment-friendly and relatively high in strength is mainly provided.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of cement, and particularly discloses an environment-friendly high-strength low-density oil well cement and a preparation process. BACKGROUND

[0002] Traditional oil well cement production relies on high-energy heat treatment process, and the problems of carbon emissions and resource consumption are prominent. A large amount of natural resources such as limestone and clay are needed in the production process, which leads to ecological destruction, and the solid waste and greenhouse gas emissions intensify the environmental pressure.

[0003] Oil well cement is a special cement specially used for oil and gas well cementing engineering, and its core requirements revolve around the complex downhole environment and engineering needs. First, during the construction phase, the cement slurry needs to have appropriate fluidity and density control to ensure smooth injection into the casing and annulus. Second, the setting time and early strength are key indicators, and it is usually required to reach the initial consistency within 15-30 minutes and to form sufficient compressive strength within 24 hours. After hardening, the cement stone must have long-term stability, including impermeability, corrosion resistance (especially sulfate corrosion), and high temperature and high pressure resistance (up to 200℃ or more, tens of megapascals pressure). Therefore, the quality requirements of oil well cement are particularly high.

[0004] Patent No. 201710165226.0 discloses a low-density oil well cement, which belongs to the field of oil and gas well cementing technology. The oil well cement comprises the following raw materials in percentage by weight: cement clinker 82-90%, gypsum 1-8%, hollow glass microbeads 5-10%, dispersing agent 0-0.3%, and retarder 0.5-0.8%. The cement clinker is one of sulphoaluminate cement clinker and high belite sulphoaluminate cement clinker. The specific surface area of the sulphoaluminate cement clinker is 470-520 cm2 / g, and the content of anhydrous calcium sulphoaluminate C4A3 in the sulphoaluminate cement clinker mineral is 50-75%. The cement of the present application is mainly used for offshore drilling operations in shallow formations, has high early strength and long thickening time, and can meet the pressure stabilization requirements before, during and after well cementing. The cement clinker accounts for a large proportion in the above-mentioned patent, and the environmental protection is relatively poor. SUMMARY

[0005] Therefore, the present application aims to provide an environment-friendly high-strength low-density oil well cement and a preparation process to solve the technical problem of how to use environmentally friendly materials while ensuring the indicators of oil well cement, especially the strength.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0007] An environment-friendly high-strength low-density oil well cement is composed of the following weight fractions:

[0008] G-grade oil well cement 35-60 parts;

[0009] Composite ecological lightweight aggregate 35-65 parts; the composite ecological lightweight aggregate comprises microwave-activated waste glass micro powder;

[0010] Hyperbranched polycarboxylate drag reducer 0.8-3.5 parts;

[0011] Composite reinforcing agent 1.5-6 parts;

[0012] Stabilizer 2-7 parts;

[0013] Retarder 0.2-1.2 parts.

[0014] The scheme has the advantages that it is environmentally friendly, the microwave-activated waste glass micro powder is used to replace traditional high-cost lightweight materials (such as vitrified microbeads and floating beads), the surface activity of the micro powder is activated by the microwave technology, and the combination ability of the micro powder with the cement matrix is enhanced, so that the industrial solid waste is recycled and used, and carbon emissions are reduced. Compared with expanded perlite, the glass micro powder has a lower density and a significantly improved compressive strength, so that the problem of insufficient strength of traditional low-density materials is solved. The hyperbranched polycarboxylate drag reducer improves the dispersion efficiency and the flowability through the steric hindrance effect, and the composite reinforcing agent makes the cement have good high-temperature retention, which is significantly better than the high-temperature strength decay problem of conventional cement.

[0015] Optionally, the composite ecological lightweight aggregate comprises microwave-activated waste glass micro powder, volcanic rock fiber composite aerogel and biomass carbonized ash at a mass ratio of 7:2:1; the volcanic rock fiber composite aerogel can be replaced by activated coke powder ash; the composite reinforcing agent is composed of modified chitosan and nano cerium oxide at a mass ratio of 4:1; the stabilizer 2-7 parts is magnesium aluminum silicate or a composite of nano barium titanate and magnesium aluminum silicate; and the retarder is a compound of polyaspartic acid zinc and trisodium phosphate.

[0016] The scheme has the advantages that the surface activity of the glass micro powder is improved by the microwave activation technology, the combination of the glass micro powder with the cement matrix is enhanced, traditional high-cost lightweight materials are replaced, the raw material cost is reduced, and the use of waste glass is more environmentally friendly. The glass micro powder can inhibit the strength decay of the cement stone at high temperature, the lightweight property of the volcanic rock fiber composite aerogel is combined, the slurry density is 1.45-1.60 g / cm 3 , and the high compressive strength is maintained. The chelation of chitosan and the catalytic effect of nano cerium oxide can improve the strength. Polyaspartic acid zinc and trisodium phosphate regulate the pH value, form a double retardation path, make the thickening time 100-220 min adjustable, adapt to the cementing requirements of shallow wells to ultra-deep wells, and enhance the sulfur corrosion resistance of the cement stone by zinc ions.

[0017] Optionally, the microwave-activated waste glass powder is activated by crushing and acid washing (0.5-5% hydrofluoric acid treatment) of construction waste glass, and then irradiating in a microwave reactor at a power of 800 W and a frequency of 2.45 GHz for 15 minutes. The specific surface area of the activated microwave-activated waste glass powder is ≥2500 m 2 / kg, the SiO2 content is ≥90%; the volcanic rock fiber composite aerogel has a porosity of ≥85% and a density of 0.25-0.35 g / cm 3 The biomass carbonized ash is obtained by grinding rice husk and coconut shell to a particle size of ≤5 μm after carbonization under nitrogen protection.

[0018] The advantages of the present scheme are: 1% hydrofluoric acid is used for acid washing to remove impurities, and then the surface is activated by 800 W, 2.45 GHz microwave irradiation for 15 minutes, and the specific surface area is ≥2500 m 2 / kg (far more than the 500-800 m 2 / kg of conventional glass powder), which greatly improves the reactivity with the cement matrix; the SiO2 content is ≥90% (close to the purity of the original glass), which significantly enhances the chemical stability and compressive strength of the cement stone; the compressive strength of the recycled glass is very high, and the microwave-activated recycled glass performs better. The porous structure of the aerogel can absorb environmental heat and improve the high-temperature resistance of the cement-based material, adapting to extreme temperature environments. The carbonization temperature of rice husk and coconut shell under nitrogen protection can be 900℃, avoiding oxidation loss, which can improve its dispersibility and filling effect in cement, and the microporous structure of the biomass ash can adsorb harmful ions and inhibit cement corrosion.

[0019] Optionally, the hyperbranched polycarboxylate friction reducer is an acrylic acid-allyl polyoxyethylene ether-maleic anhydride terpolymer with a molecular weight distribution index ≤1.2, which can reduce the viscosity of the cement slurry and improve the salt resistance.

[0020] The acrylic acid-allyl polyoxyethylene ether-maleic anhydride terpolymer has a hyperbranched structure forming a three-dimensional spherical network, and a molecular weight distribution index ≤1.2 (narrow distribution), which significantly improves the regularity and reaction efficiency of the molecular chain; compared with traditional linear polycarboxylic acid water reducing agent, the space steric effect is enhanced, effectively inhibiting the agglomeration of cement particles and reducing the viscosity of the slurry.

[0021] The preparation process of the environment-friendly high-strength low-density oil well cement comprises the following steps:

[0022] S1, microwave-activated glass powder preparation: crushing construction waste glass to a particle size of ≤2 mm, soaking in 1% hydrofluoric acid for 30 minutes, then washing to neutral, and then putting into a microwave reactor for activation at a power of 800 W and a frequency of 2.45 GHz for 15 minutes;

[0023] S2, synthesis of composite ecological lightweight aggregate: microwave-activated waste glass powder, volcanic rock aerogel or activated coke ash, biomass carbonized ash were mixed in proportion, 3% silane coupling agent KH-560 ethanol solution was added, ultrasonic dispersion for 45 minutes, and then dried;

[0024] S3, in-situ polymerization of hyperbranched polycarboxylate drag reducer: acrylic acid, allyl polyoxyethylene ether, maleic anhydride were mixed in a molar ratio of 5:3:2 in a reaction kettle, ammonium persulfate was added as initiator, and the mixture was reacted at 60℃ for 6 hours to form a hyperbranched polymer;

[0025] S4, gradient grinding and activation: G-grade cement, composite ecological lightweight aggregate and stabilizer were put into a vertical mill to grind to 100μm sieve residue≤2%, then the hyperbranched polycarboxylate drag reducer, composite reinforcing agent, retarder and water (water-cement ratio 0.40-0.55) were put into the plasma activated ball mill, and argon plasma (power 300W) was applied to assist grinding to 45μm sieve residue≤1%;

[0026] S5, performance control: by adjusting the proportion of retarder and plasma treatment time, the accurate matching of thickening time and rheological parameters is realized.

[0027] Optionally, in S4, plasma activated ball milling technology is used to generate high energy electron bombardment on the surface of particles during grinding, so that nano-scale active sites are formed on the surface of particles.

[0028] In this scheme, the vertical mill is combined with the plasma activated ball mill, and the argon plasma (300W) excites the surface activity of the material to optimize the particle size distribution.

[0029] The acid pickling discharging equipment in the preparation process of the environment-friendly high-strength low-density oil well cement comprises a discharging device, the discharging device comprises a discharging box, a plurality of strip-shaped discharging ports are uniformly arranged on the bottom of the discharging box along the length direction, a material blocking frame is arranged in the discharging box, the material blocking frame can move vertically in the discharging box, the bottom of the material blocking frame comprises a blocking strip, and the blocking strip can completely block the discharging port; an inlet is arranged on the top of the side surface of the discharging box, a positioning seat capable of moving downward under the action of gravity is arranged in the discharging box, and a positioning strip is connected between the two positioning seats; a plurality of laser ranging sensors are mounted on the inner top wall of the discharging box, and the laser ranging sensors are arranged above the positioning strip. In the process, the particle size of the glass powder is small, and a large amount of powder is accumulated on one side after being poured into the acid pickling tank, which may cause uneven acid pickling, especially after the glass powder is poured into the acid pickling tank, the amount of hydrofluoric acid liquid in the acid pickling tank is reduced, and the acid pickling effect is more likely to be poor. However, the prior art does not mention the related problems, so the acid pickling tank does not have a related uniform discharging device, and the content of the present scheme mainly solves the technical problem of how to uniformly discharge.

[0030] Optionally, the inner wall top of the blanking box is provided with a main electromagnet, the top of the material blocking frame is opposite to the main electromagnet, and the spacing between the two is less than 2 cm, and the main electromagnet can attract the material blocking frame to move upward when activated.

[0031] Optionally, the positioning strip is made of flexible plastic material, and the positioning strip is provided with a laser reflection area.

[0032] The working principle and advantages of the present scheme are that:

[0033] 1. Environmental protection: using microwave-activated waste glass powder (construction waste glass) and biomass carbonized ash (agricultural and forestry waste) as the core lightweight aggregate, realizing solid waste resource utilization and reducing carbon emissions;

[0034] 2. High performance: low density and high strength: density 1.20-1.50 g / cm 3 , compressive strength ≥11 MPa, breaking through the technical bottleneck of insufficient strength of lightweight materials; resistant to deep well high temperature environment; corrosion resistance: in CO2 / H2S / Cl- composite corrosion medium, strength loss rate ≤6%.

[0035] 3. Low cost: using low-cost raw materials such as waste glass and agricultural and forestry straw to replace high-priced floating beads / fly ash to reduce cost. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 It is a structural schematic view of the pickling equipment in the embodiment.

[0037] In the drawings, the following marks are marked: blanking box 1, material blocking frame 2, main electromagnet 3, blocking strip 4, positioning seat 5, positioning strip 6, laser ranging sensor 7, blanking port 8. DETAILED DESCRIPTION

[0038] The following will be further described in detail through specific embodiments:

[0039] Example 1

[0040] An environmentally friendly high-strength low-density oil well cement, consisting of the following components by weight:

[0041] G-grade oil well cement 50 parts;

[0042] Composite ecological lightweight aggregate 40 parts; wherein the ratio of microwave-activated waste glass powder: activated coke ash: biomass carbonized ash is 7:2:1; wherein the biomass carbonized ash is rice husk and coconut shell carbonized under nitrogen protection and ground to a particle size of ≤5 μm;

[0043] Hyperbranched polycarboxylate drag reducer 3 parts;

[0044] Composite reinforcing agent (modified chitosan and nano cerium oxide at a mass ratio of 4:1) 3 parts;

[0045] Stabilizer (magnesium aluminum silicate) 2.5 parts;

[0046] Retarder (polyaspartic acid zinc: trisodium phosphate = 3:1) 1.5 parts.

[0047] In this formula, the main creation point is the microwave activation of waste glass micro powder. The microwave-activated waste glass micro powder has the characteristics of light weight, low density, high strength, etc. Especially the combination ability of microwave-activated waste glass micro powder and cement matrix. In this formula, the volcanic rock fiber composite aerogel has excellent high temperature resistance, but its application in refractory materials and cement has been the existing technology. However, the combination ability of the existing technology of volcanic rock fiber composite aerogel and cement matrix is poor, which will affect the strength of cement to some extent, so this kind of cement has not been mass-produced and is still in the laboratory stage. After adding microwave-activated waste glass micro powder, the deficiency can be greatly improved, which provides a basis for the large-scale production of this material in cement.

[0048] The preparation process of the environment-friendly high-strength low-density oil well cement comprises the following steps:

[0049] S1, microwave activation of glass micro powder preparation: building waste glass is crushed to a particle size of ≤2mm, soaked in 0.8% hydrofluoric acid for 30 minutes, then washed with water to neutral, and then put into a microwave reactor for irradiation at 800W, frequency 2.45GHz for 15 minutes for activation; until the specific surface area of the glass micro powder is ≥2500m 2 / kg, wherein the SiO2 content of the glass micro powder is ≥90%;

[0050] S2, synthesis of composite ecological lightweight aggregate: mix the activated glass micro powder, volcanic rock fiber composite aerogel and biomass carbonized ash according to the proportion, add 3% mass fraction of silane coupling agent KH-560 ethanol solution, ultrasonic dispersion for 45 minutes, and then dry;

[0051] S3, in-situ polymerization of drag reduction agent: mix acrylic acid, allyl polyoxyethylene ether and maleic anhydride in a molar ratio of 5:3:2 in a reaction kettle, add initiator ammonium persulfate, and react at 60°C for 6 hours to form a hyperbranched polymer;

[0052] S4, gradient grinding and activation: put G-grade cement, composite ecological lightweight aggregate and stabilizer into a vertical mill to grind to 100μm residue ≤2%, then put it into a plasma activated ball mill together with the drag reduction agent, the reinforcing agent, the retarder and water, and apply argon plasma (power 300W) to assist the grinding to 45μm residue ≤1%; In the grinding process, high-energy electron bombardment is generated on the surface of the particles, forming nano-scale active sites on the surface of the particles;

[0053] S5, performance regulation: by adjusting the proportion of retarder and plasma treatment time, the accurate matching of thickening time and rheological parameters is realized.

[0054] Example two, three:

[0055] The difference between example two, three and example one is the component formula;

[0056] Comparative example one:

[0057] In the composite ecological lightweight aggregate, only glass microbeads are used, and the rest of the component formula and process remain unchanged.

[0058] Comparative example two:

[0059] Unactivated glass powder is used to replace microwave activated waste glass powder, and the rest of the component formula and process remain unchanged.

[0060] Comparative example three:

[0061] The resistance reducing agent in example one is replaced by ordinary polycarboxylic acid water reducing agent.

[0062]

[0063]

[0064] Test design:

[0065] 1. Cement density test: reference GB / T 19139-2012 oil well cement test method, select instrument as pressurized liquid densimeter;

[0066] 2. Rheological property test: reference GB / T 19139-2012 oil well cement test method, rotary viscometer measurement; environmental conditions: 52℃, 35.6MPa, rotation speed 600r / min, consistency time range 15-30min; consistency standard can refer to the relevant standards in API;

[0067] 3. Thickening time detection test: high temperature and high pressure thickening instrument, the related equipment and detection method is very mature, so it is not repeated here;

[0068] 4. Strength detection test under high temperature and high pressure environment: according to the corresponding standard test, the test method is relatively simple, the condition is generally 110℃ / 20.7MPa for 24 hours;

[0069] 5. Salt invasion test: in acidic environment (CO2 / H2S / Cl-composite corrosion medium environment), cement 90 days corrosion resistance after strength, this test standard is higher than the national relevant standard.

[0070]

[0071] The experimental data above demonstrates that the formulation in Example 2 meets national standards in all indicators and outperforms Examples 1, 3, Comparative Examples 1, 2, and 3. In particular, the cement incorporating microwave-activated waste glass powder demonstrates outstanding density, compressive strength, and post-salt erosion strength. In practice, using activated coke ash instead of volcanic rock fiber composite aerogel offers lower costs, a more efficient manufacturing process, and comparable cement quality, making the use of activated coke ash more practical.

[0072] like Figure 1 As shown, the pickling and blanking equipment for microwave-activated waste glass powder includes a blanking device, which includes a blanking box 1. The bottom of the blanking box 1 is evenly provided with a number of strip-shaped blanking openings 8 along the length direction. A blocking rack 2 is provided in the blanking box 1, and the blocking rack 2 can move vertically in the blanking box 1. A baffle 4 is fixedly provided at the bottom of the blocking rack 2, and the two ends of the baffle 4 are vertically slidably provided inside the blanking box 1, and the baffle 4 can completely cover the blanking opening 8. A feeding port is provided at the top of the side of the blanking box 1, and a positioning seat 5 that can move downward under the action of its own weight is provided in the blanking box 1. A vertical slide is provided on the blocking rack 2, and two positioning seats 5 are respectively slidably provided in two slides. A positioning bar 6 is fixedly connected between the two positioning seats 5. The positioning bar 6 is made of flexible plastic material and is provided with a number of laser reflection areas. Several laser distance measuring sensors 7 are installed on the inner top wall of the blanking box 1. The laser distance measuring sensors 7 are arranged above the positioning bar 6 and can detect the height of the positioning bar 6. An active electromagnet 3 is set on the top of the inner wall of the blanking box 1. The top of the material stopper 2 is opposite to the active electromagnet 3 with a distance of less than 2 cm between them. When the active electromagnet 3 is activated, it can attract the material stopper 2 to move upward.

[0073] During the experiment, microwave-activated waste glass powder is very easy to accumulate due to its small particle size. A large amount of glass powder is not easy to disperse after entering the pickling tank, resulting in uneven pickling. Therefore, the existing pickling tank is modified. When in use, add the glass powder into the discharge box 1, and then start the active electromagnet 3. The active electromagnet 3 attracts the top of the material stop frame 2 to move upward, and the discharge port 8 is exposed, and the material can be discharged. Start the laser ranging sensor 7. When the laser ranging sensor 7 detects that the height of any positioning bar 6 is low, the glass powder at that location on the surface flows out too quickly. At this time, the active electromagnet 3 is controlled to close, and the material stop frame 2 descends and blocks the discharge port 8. When the height of the remaining positioning bars 6 is consistent with the height of the positioning bar 6, start the active electromagnet 3 again.

[0074] The above-mentioned are only embodiments of the present application, and the common knowledge of specific structures and characteristics in the scheme is not described in detail. It should be pointed out that for those skilled in the art, without departing from the structure of the present application, a number of modifications and improvements can be made, which should be considered as the protection scope of the present application, which will not affect the effect and practicability of the present application.

Claims

1. An environmentally friendly high-strength low-density oil well cement, characterized by: It is composed of the following parts by weight: 35-60 parts of G-grade oil well cement; 35-65 parts of composite ecological lightweight aggregate; the composite ecological lightweight aggregate contains microwave-activated waste glass powder; 0.8 to 3.5 parts of hyperbranched polycarboxylate drag reducer; 1.5-6 parts of composite reinforcing agent; 2-7 parts of stabilizer; 0.2 to 1.2 parts of retarder.

2. The environmentally friendly high-strength, low-density oil well cement according to claim 1, characterized in that: The composite ecological lightweight aggregate contains microwave-activated waste glass powder, volcanic rock fiber composite aerogel and biomass carbonized ash in a mass ratio of 7:2:1; the volcanic rock fiber composite aerogel can be replaced by activated coke powder ash; The composite reinforcing agent is composed of modified chitosan and nano-cerium oxide in a mass ratio of 4:1; The stabilizer is 2 to 7 parts of magnesium aluminum silicate or a composite of nano-barium titanate and magnesium aluminum silicate; The retarder is a compound of zinc polyaspartate and trisodium phosphate.

3. The environmentally friendly high-strength, low-density oil well cement according to claim 2, characterized in that: The microwave activated waste glass powder is made of building waste glass that has been crushed and pickled (treated with 0.5% to 5% hydrofluoric acid) and then irradiated in a microwave reactor at a power of 800W and a frequency of 2.45GHz for 15 minutes to activate it. The specific surface area of ​​the activated microwave activated waste glass powder is ≥2500m 2 / kg, SiO2 content ≥90%; Volcanic rock fiber composite aerogel, porosity ≥ 85%, density 0.25~0.35g / cm 3 ; The biomass carbonized ash is made of rice husk and coconut shell that are carbonized under nitrogen and then ground into a particle size of ≤5μm.

4. The environmentally friendly high-strength, low-density oil well cement according to claim 1, characterized in that: The hyperbranched polycarboxylate drag reducer is an acrylic acid-allyl polyoxyethylene ether-maleic anhydride terpolymer, and has a molecular weight distribution index of ≤1.

2.

5. The process for preparing the environmentally friendly high-strength low-density oil well cement according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1, preparation of microwave-activated glass powder: crush construction waste glass to a particle size of ≤2 mm, soak in 1% hydrofluoric acid for 30 minutes, then wash with water until neutral, and activate in a microwave reactor at 800 W power and 2.45 GHz frequency for 15 minutes; S2, synthesis of composite ecological lightweight aggregate: microwave-activated waste glass powder, volcanic rock aerogel or activated coke ash, and biomass carbonized ash were mixed in proportion, 3% by mass of silane coupling agent KH-560 ethanol solution was added, ultrasonically dispersed for 45 minutes, and then dried; S3, in-situ polymerization of a hyperbranched polycarboxylate drag reducer: acrylic acid, allyl polyoxyethylene ether, and maleic anhydride were mixed in a reaction kettle at a molar ratio of 5:3:2, and ammonium persulfate as an initiator was added, and the mixture was reacted at 60° C. for 6 hours to form a hyperbranched polymer; S4, gradient grinding and activation: G-grade cement, composite ecological lightweight aggregate, and stabilizer are put into a vertical mill to coarsely grind to a 100μm sieve residue of ≤2%, and then put into a plasma-activated ball mill together with a hyperbranched polycarboxylate drag reducer, a composite reinforcing agent, a retarder, and water (water-cement ratio of 0.40-0.55). Argon plasma (power 300W) is applied to assist in grinding to a 45μm sieve residue of ≤1%; S5, performance control: By adjusting the retarder ratio and plasma treatment time, a precise match between thickening time and rheological parameters can be achieved.

6. The process for preparing the environmentally friendly high-strength, low-density oil well cement according to claim 5, characterized in that: S4 uses plasma activated ball milling technology to simultaneously generate high-energy electrons to bombard the particle surface during the grinding process, forming nano-scale active sites on the particle surface.

7. The process for preparing the environmentally friendly high-strength, low-density oil well cement according to claim 6, characterized in that: The pickling unloading equipment for the pickling process of microwave-activated waste glass micropowder includes a unloading device, which includes a unloading box. The bottom of the unloading box is evenly provided with a plurality of strip-shaped unloading openings along the length direction. A material blocking rack is provided in the unloading box, and the material blocking rack can move vertically in the unloading box. The bottom of the material blocking rack includes a baffle, and the baffle can completely cover the unloading opening; an inlet is provided at the top of the side of the unloading box, and a positioning seat that can move downward under the action of its own weight is provided in the unloading box, and a positioning bar is connected between two relative positioning seats; a plurality of laser ranging sensors are installed on the inner top wall of the unloading box, and the laser ranging sensor is arranged above the positioning bar.

8. The process for preparing the environmentally friendly high-strength, low-density oil well cement according to claim 7, wherein: An active electromagnet is provided on the top of the inner wall of the material discharge box. The top of the material stopper is opposite to the active electromagnet and the distance between the two is less than 2 cm. When the active electromagnet is started, it can attract the material stopper to move upward.

9. The process for preparing the environmentally friendly high-strength, low-density oil well cement according to claim 8, characterized in that: The positioning bar is made of flexible plastic material and is provided with a laser reflection area.

Images