Controllable dissolution magnesium alloy ball and preparation method thereof

Abstract

The invention relates to the technical field of compact shale magnesium alloy balls, and particularly discloses a dissolution-controllable magnesium alloy ball and a preparation method thereof.The magnesium alloy ball is composed of magnesium-aluminum matrix powder and iron powder, the mass fraction of iron is 1-7 wt%, the mass fraction of aluminum is 5 wt%, and the balance is magnesium. According to the dissolution-controllable magnesium alloy ball and the preparation method thereof, the magnesium-aluminum matrix powder and the iron powder are subjected to powder configuration and mechanical dispersion and then are prepared and formed through electric spark rapid sintering, and a microstructure with a fine and compact structure is obtained; the prepared magnesium-aluminum-iron magnesium alloy ball has heat resistance when bearing high temperature at the bottom of a deep layer of the earth surface, keeps sufficient fracturing strength, has a galvanic corrosion effect, activates a magnesium matrix and accelerates corrosion.

Description

Technical Field

[0001] The invention relates to the technical field of dense shale magnesium alloy ball forming, and in particular to a controllable dissolution magnesium alloy ball and a preparation method thereof. Background Art

[0002] With the exhaustion of traditional energy resources, unconventional oil and gas resources with low and ultra-low permeability have gradually become the main source of increased production in oil and gas fields in various countries. However, the development of such oil and gas resources is extremely difficult and the collection efficiency is low, which has increased the cost of extraction and is not conducive to the development and utilization of resources.

[0003] Fracturing technology can use water pressure to create gaps in dense rocks, increase oil and gas channels, and facilitate the convergence and flow of oil and gas, thereby improving the flow level of oil and gas and significantly increasing production. Recently, staged fracturing uses magnesium alloy balls to divide the oil and gas reservoir into several sections, and the same pump truck is used to perform single-stage fracturing in sequence. This maximizes the reservoir's permeability, improves conductivity and productivity. The horizontal well open hole packer staged fracturing technology is widely used because of its simple construction, simple workflow, reduced operating costs, and high production efficiency. However, after the magnesium alloy ball completes the temporary plugging task, it is necessary to return the magnesium alloy ball to the ground. However, sometimes the magnesium alloy ball is stuck in the channel and cannot be returned to the ground due to insufficient formation pressure or ball deformation. In addition, the high temperature and high pressure environment underground has a strong destructive effect on the conical wall of the ball seat, making it easy to form defects in the wall material, resulting in the contact area between the ball seat and the ball being unable to achieve effective sealing. At this time, drilling and milling technology is required to clear the pipeline after the drilling operation. At the same time, the composition of the magnesium alloy ball must also be considered, which increases the cost and operation time.

[0004] The magnesium alloy balls for temporary plugging tasks need to have sufficient mechanical strength, especially high compressive strength to complete staged fracturing operations. Compared with polymer-based ceramic materials, magnesium alloys have comprehensive mechanical properties. At the same time, they can corrode in water and oxygen environments, but the corrosion rate is slow. In the deep underground of the surface, the temperature is getting higher and higher. The working temperature of magnesium alloy balls is around 100 degrees. When magnesium alloy balls are under pressure during high-temperature plugging, their creep resistance decreases, resulting in poor heat resistance and unstable high-temperature strength. Therefore, it is necessary to regulate the composition of magnesium alloy balls to accelerate corrosion and maintain heat resistance. Summary of the invention

[0005] The purpose of the present invention is to provide a controllably dissolvable magnesium alloy ball and a preparation method thereof. The prepared magnesium alloy ball has high compression strength during high-temperature plugging operations, meeting the heat resistance requirements of the magnesium alloy ball under different working conditions due to changes in bottom hole temperature. The corroded microscopic particles can be discharged from the pipeline along with the return fluid, eliminating the drawbacks of removing magnesium alloy balls in the downhole drilling and milling process.

[0006] To achieve the above objectives, the present invention provides a controllably dissolvable magnesium alloy ball having a compression strength of 370-455 MPa and comprising a magnesium-aluminum matrix powder and an iron powder, wherein the mass fraction of iron is 0.8-8wt%, the mass fraction of aluminum is 5wt%, and the remainder is magnesium.

[0007] Preferably, the mass fraction of iron is 1-7wt%.

[0008] Preferably, the mass fraction of iron is 5wt%.

[0009] Preferably, the size of the iron powder is 5-15 microns, and the size of the magnesium-aluminum matrix powder is 20-30 microns.

[0010] Preferably, the corrosion rate of the magnesium alloy ball in the potassium chloride solution is 11-35 mm / y.

[0011] Preferably, the hardness of the magnesium alloy ball is 55-115 HV.

[0012] A method for preparing a controllably dissolvable magnesium alloy ball comprises the following steps: Step 1: Powder preparation: weigh the refined iron powder, add it to the magnesium-aluminum matrix powder in 5-9 times, and use a stirring and mixing device to disperse the iron powder in a dry inert environment for 0.5-2.5 hours to obtain a mixed powder; Step 2: Mechanical dispersion: After mechanical mixing, the mixed powder is put into a ball mill for further ball milling dispersion and refinement, the ball-to-material ratio is 9:1, the inert protective gas is argon, the speed of the ball mill is 105-260r / min, and the ball milling time is 70-130 minutes; Step 3, electric spark sintering, the mixed powder after mechanical dispersion is solidified and formed by electric spark sintering process, the sintering temperature is 360-650 degrees, the sintering pressure is 2.2-3.8kN, and the insulation time is 8-14 minutes; the electric spark sintered blank is made into magnesium alloy balls of different diameters after grinding, polishing and machining.

[0013] The advantages and beneficial effects of the controllable dissolution magnesium alloy ball and the preparation method thereof are as follows: 1. The magnesium alloy ball of the present invention has high compression strength when subjected to high temperature load during high temperature plugging operation, thus meeting the heat resistance requirements of the magnesium alloy ball under different working conditions due to the change of bottom hole temperature.

[0014] 2. After completing the temporary plugging task, the magnesium alloy balls in the present invention produce rapid electrochemical corrosion due to the potential, and the corroded microscopic particles can be discharged from the pipeline along with the return fluid, eliminating the disadvantages of removing magnesium alloy balls in the downhole drilling and milling process.

[0015] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a microstructure diagram of the magnesium alloy ball prepared in Example 1 of the present invention; Figure 2 This is a microstructure diagram of the magnesium alloy ball prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0017] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0018] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0019] Example 1 A controllable dissolution magnesium alloy ball consists of magnesium-aluminum matrix powder and iron powder, wherein the mass fraction of iron is 5wt%, the mass fraction of aluminum is 5wt%, and the balance is magnesium.

[0020] A method for preparing a controllably dissolvable magnesium alloy ball comprises the following steps: Iron powder with a particle size of 5-15 microns is added to magnesium-aluminum matrix powder (aluminum mass fraction 5wt%) in 8 times at a mass ratio of 5wt%, and the iron powder is stirred and dispersed in a dry inert environment for 1 hour to obtain a mixed powder; the mixed powder is placed in a ball mill for further mixing and dispersion, the ball-to-material ratio is 9:1, the speed of the ball mill is 245r / min, the ball milling time is 80 minutes, and argon gas is used as a protective atmosphere during the ball milling process; the mixed powder is solidified and formed by an electric spark sintering process, the sintering temperature is 580 degrees, the sintering pressure is 2.8kN, and the insulation time is 10 minutes. After obtaining the blank, it is machined into magnesium alloy balls of different sizes.

[0021] The soluble magnesium alloy ball prepared by this method has a smooth surface, no obvious defects such as warping, a dense microstructure, a chemical composition close to the nominal composition, a density of 88%, a hardness of 102HV, a compressive strength of 412MPa, and a corrosion rate of 28mm / y in potassium chloride solution.

[0022] Example 2 A controllable dissolution magnesium alloy ball consists of magnesium-aluminum matrix powder and iron powder, wherein the mass fraction of iron is 3wt%, the mass fraction of aluminum is 5wt%, and the balance is magnesium.

[0023] A method for preparing a controllably dissolvable magnesium alloy ball comprises the following steps: Iron powder with a particle size of 5-15 microns is added to magnesium-aluminum matrix powder (aluminum mass fraction 5wt%) in 8 times at a mass ratio of 3wt%, and the iron powder is stirred and dispersed in a dry inert environment for 1 hour to obtain a mixed powder; the mixed powder is placed in a ball mill for further mixing and dispersion, the ball-to-material ratio is 9:1, the speed of the ball mill is 245r / min, the ball milling time is 80 minutes, and an argon protective atmosphere is used during the ball milling process; the mixed powder is solidified and formed by an electric spark sintering process, the sintering temperature is 580 degrees, the sintering pressure is 2.8kN, and the insulation time is 10 minutes. After obtaining the blank, it is machined into magnesium alloy balls of different sizes.

[0024] The soluble magnesium alloy ball prepared by this method has a smooth shape, no burning defects, dense microstructure, no defects such as pores and micropores, a density of 90%, a hardness of 84HV, a compressive strength of 378MPa, and a corrosion rate of 23mm / y in potassium chloride solution.

[0025] Example 3 A controllable dissolution magnesium alloy ball consists of magnesium-aluminum matrix powder and iron powder, wherein the mass fraction of iron is 15wt%, the mass fraction of aluminum is 5wt%, and the balance is magnesium.

[0026] A method for preparing a controllably dissolvable magnesium alloy ball comprises the following steps: Iron powder with a particle size of 5-15 microns is added to magnesium-aluminum matrix powder (aluminum mass fraction 5wt%) in 8 times at a mass ratio of 1.5wt%, and the iron powder is stirred and dispersed in a dry inert environment for 1 hour to obtain a mixed powder; the mixed powder is placed in a ball mill for further mixing and dispersion, the ball-to-material ratio is 9:1, the speed of the ball mill is 245r / min, the ball milling time is 80 minutes, and an argon protective atmosphere is used during the ball milling process; the mixed powder is solidified and formed by an electric spark sintering process, the sintering temperature is 580 degrees, the sintering pressure is 2.8kN, and the insulation time is 10 minutes. After obtaining the blank, it is machined into magnesium alloy balls of different sizes.

[0027] The soluble magnesium alloy ball prepared by this method has good molding quality, dense structure, microporous structure without thermal sintering cracks, shrinkage holes and pores, density of 92%, hardness of 80HV, compressive strength of 312MPa, and corrosion rate of 14mm / y in potassium chloride solution.

[0028] The electric spark sintering of the present invention has the characteristic of fast heating, which reduces the grain growth rate and refines the grains, thereby producing the effect of fine grain strengthening; at the same time, during the solidification of the magnesium-aluminum-iron alloy, the electric spark sintering can exert a certain extrusion force, avoiding structural defects such as micropores and pores in the conventional powder molding process, improving the density of the alloy, and then improving the compression strength.

[0029] In the present invention, the iron content needs to be strictly controlled. Too much addition may cause difficulty in mixing in the magnesium-aluminum matrix, easily produce uneven convergence and dispersion, and the dispersion strengthening effect and the bimodal second phase corrosion acceleration effect are limited. Therefore, the iron content and particle size, stirring and mixing, ball milling parameters and other steps play an important role; if the amount of iron added is small, the number of galvanic corrosion units is limited and the distribution range is very small, and it is difficult to activate the magnesium-aluminum matrix and cannot significantly accelerate corrosion.

[0030] Comparative Example 1 The other conditions are consistent with those in Example 1, except that: iron powder and magnesium-aluminum matrix powder (aluminum mass fraction 5 wt%) are weighed in a mass ratio of 18:82 to obtain a controllable dissolution magnesium alloy ball. Microstructure analysis shows that the iron particles are aggregated in flaky form. This is because the powder particles with different physical properties have poor flow properties and the iron powder content is high, requiring a longer stirring and dispersing time, a larger ball-to-material ratio, a faster ball milling speed and a longer ball milling time. After electric spark sintering, the mechanical properties are unstable and the hardness deviation is large, and the quality stability requirements cannot be guaranteed.

[0031] Comparative Example 2 The other conditions are consistent with those in Example 1, except that: iron powder and magnesium-aluminum matrix powder (aluminum mass fraction 5 wt%) are weighed in a mass ratio of 0.2:99.8 to obtain a controllable dissolution magnesium alloy ball. Microstructural analysis shows that the magnesium iron phase is not only small in quantity but also has a small distribution range. The hardness of the magnesium alloy ball is 68 HV, the compressive strength is 265 MPa, and the corrosion rate in potassium chloride solution is 5 mm / y.

[0032] Comparative Example 3 The other conditions are consistent with those in Example 1, except that the temperature applied during the electric spark sintering process is 370 degrees, the holding time is 2 minutes, the forming quality of the magnesium alloy ball is poor, a complete sample cannot be formed, debris will be generated after compression, and the room temperature yield strength is 98 MPa, which cannot meet the strength requirements for use.

[0033] Comparative Example 4 The other conditions are consistent with those in Example 1, except that: after sintering, it was observed that the iron powder with a particle size of 80-200 microns was extremely unevenly distributed, the iron in the microstructure was distributed in blocks, the dispersion strengthening effect was very limited, and in the hardness test, a large indentation was found on the loaded surface, and cracks appeared around the indentation. The hardness value was low, and it could not become a qualified magnesium alloy ball.

[0034] The microstructure of the magnesium alloy balls prepared in Example 1 and Comparative Example 1 was analyzed. Figure 1 and Figure 2 As shown. Figure 1It can be seen that the microstructure of the magnesium alloy ball prepared in Example 1 is dense. Figure 2 It can be seen that the magnesium alloy ball prepared in Comparative Example 1 has a dispersed microstructure.

[0035] It can be seen from Examples 1, 2, 3 and Comparative Examples 1, 2, 3, 4 that the components and preparation process of the present invention are an organic whole, and when any one or several key parameters are not within the protection scope of the present invention, the effect is significantly reduced. By comparing the internal structure of Example 1, Example 2 and Example 3 of the present invention, it is found that the preferred embodiment of the present invention has an unexpected effect.

[0036] Therefore, the present invention adopts the above-mentioned controllable dissolution magnesium alloy ball and its preparation method. The prepared magnesium alloy ball has high compression strength during high-temperature plugging operations, which meets the heat resistance requirements of the magnesium alloy ball under different working conditions due to the changes in bottom hole temperature. The corroded microscopic particles can be discharged from the pipeline with the return fluid, eliminating the disadvantages of removing magnesium alloy balls in the downhole drilling and milling process.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A controllable dissolution magnesium alloy ball, characterized in that: The magnesium alloy ball has a compression strength of 370-455MPa and is composed of magnesium-aluminum matrix powder and iron powder, wherein the mass fraction of iron is 0.8-8wt%, the mass fraction of aluminum is 5wt%, and the balance is magnesium.

2. The controllably dissolvable magnesium alloy ball according to claim 1, characterized in that: The mass fraction of iron is 1-7wt%.

3. A controllably dissolvable magnesium alloy ball according to claim 2, characterized in that: The mass fraction of iron is 5wt%.

4. The controllably dissolvable magnesium alloy ball according to claim 1, characterized in that: The size of the iron powder is 5-15 microns, and the size of the magnesium-aluminum matrix powder is 20-30 microns.

5. The controllably dissolvable magnesium alloy ball according to claim 1, characterized in that: The corrosion rate of magnesium alloy balls in potassium chloride solution is 11-35mm / y.

6. The controllably dissolvable magnesium alloy ball according to claim 1, characterized in that: The hardness of the magnesium alloy ball is 55-115 HV.

7. A method for preparing a controllably dissolvable magnesium alloy ball according to any one of claims 1 to 6, characterized in that: The following steps are involved: Step 1: Powder preparation: weigh the refined iron powder, add it to the magnesium-aluminum matrix powder in 5-9 times, and use a stirring and mixing device to disperse the iron powder in a dry inert environment for 0.5-2.5 hours to obtain a mixed powder; Step 2: Mechanical dispersion: After mechanical mixing, the mixed powder is put into a ball mill for further ball milling dispersion and refinement, the ball-to-material ratio is 9:1, the inert protective gas is argon, the speed of the ball mill is 105-260r / min, and the ball milling time is 70-130 minutes; Step 3: Electric spark sintering: the mixed powder after mechanical dispersion is solidified by electric spark sintering process, the sintering temperature is 360-650 degrees, the sintering pressure is 2.2-3.8kN, and the holding time is 8-14 minutes; The blanks sintered by electric spark are made into magnesium alloy balls of different diameters after grinding, polishing and machining.

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