Composite scale inhibitor, high-strength composite scale-preventing proppant, and preparation method and application thereof

Abstract

The application discloses a composite scale inhibitor, a high-strength composite scale prevention propping agent and a preparation method and application thereof, and belongs to the technical field of oil and gas field development engineering. The composite scale inhibitor is prepared from the following raw materials in parts by weight: 10-15 parts of phosphate, 10-20 parts of phosphonate, 5-10 parts of polycarboxylic acid, 10-15 parts of sulfonate, 3-5 parts of zinc salt and 100-120 parts of deionized water. The components in the composite scale inhibitor are synergistic with each other, and the composite scale inhibitor has significant advantages in scale inhibition performance, core permeability retention capacity and the like compared with existing scale inhibitors. The high-strength composite scale prevention propping agent is prepared by adding the composite scale inhibitor into the propping agent, has good migration effect in a fracture, good pressure resistance, high-strength performance and long service life, and can realize long-term scale inhibition effect.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field development engineering technology, and specifically relates to a composite scale inhibitor, a high-strength composite scale inhibitor proppant, its preparation method and application. Background Technology

[0002] With the continuous development of oil fields, formation energy is gradually being depleted. To replenish formation energy, most oil reservoir blocks have begun water and gas injection development, which has brought about a series of problems affecting the normal production of oil wells. For example, scaling and corrosion of well tubing, rods, pumps, etc., is a thorny issue. Scale and corrosion can cause tubing rupture, wellbore collapse, pump failure, and in severe cases, reduced production or even shutdown. If oil well production is restored by replacing damaged tubing equipment, it will greatly prolong the production cycle, reduce production efficiency, indirectly affect oil well production, and increase production costs.

[0003] To address the aforementioned problems, existing technologies often employ oilfield scale inhibition chemical methods, periodically injecting acids or liquid chemical agents such as scale removers and scale inhibitors into the formation from the wellhead after the oil and gas wells are put into production. For example, patent CN113955868A discloses a multifunctional scale and corrosion inhibitor and its preparation method. This corrosion inhibitor is composed of the following components by mass percentage: phosphate 1-15%, sulfonate 5-10%, phosphonate 10-25%, polycarboxylic acid 10-20%, imidazole 1-10%, and ammonium salt 1-5%. This system is a multifunctional composite scale and corrosion inhibitor suitable for various water treatment systems and multiple water quality requirements. However, this method is time-consuming, expensive, and ineffective. It mainly utilizes the adsorption principle to form a hydrophobic layer on the pipe wall, preventing corrosive media from contacting the metal surface to achieve corrosion inhibition. However, this system is not effective against corrosive bacteria, leading to increased scaling.

[0004] For example, patent CN114106804B discloses a high-temperature resistant esterified composite scale inhibitor and its preparation method. This scale inhibitor is compounded with borate ester and 2-butane-1,2,4-tricarboxylic acid phosphate, etc. The pH value of the system is neutral, which can effectively reduce the corrosion of equipment and pipelines. It has strong stability, does not crystallize or precipitate in winter, and can effectively reduce scale formation in oil and water well tubing and increase the production of single oil wells. However, after aging at 120°C, the scale inhibition rate of calcium carbonate and calcium sulfate is only 85%-90%, and its scale inhibition rate and effective scale inhibition period still need to be improved. Summary of the Invention

[0005] To address the problems existing in the prior art, the main objective of this invention is to provide a composite scale inhibitor, a high-strength composite scale inhibitor proppant, its preparation method, and its application. Compared to existing scale inhibitors, the composite scale inhibitor provided by this invention exhibits significant advantages in scale inhibition performance and core permeability retention. Furthermore, the high-strength composite scale inhibitor proppant provided by this invention is prepared by adding the composite scale inhibitor of this invention to a proppant, achieving a long-term scale inhibition effect. Moreover, the high-strength composite scale inhibitor proppant of this invention maintains high strength performance under high closure pressure and is compatible with fracturing fluids such as guar gum and slickwater. In addition, this high-strength composite scale inhibitor proppant is dry-inert, long-lasting, and environmentally friendly.

[0006] To achieve the above objectives, a first aspect of the present invention provides a composite antiscalant, comprising, by weight, the following raw materials: 10-15 parts phosphate, 10-20 parts phosphonate, 5-10 parts polycarboxylic acid, 10-15 parts sulfonate, 3-5 parts zinc salt, and 100-120 parts deionized water.

[0007] Furthermore, the polycarboxylic acid is polyaspartic acid.

[0008] Furthermore, the zinc salt is selected from zinc chloride and / or zinc sulfate.

[0009] Furthermore, the sulfonate is sodium propylene sulfonate.

[0010] Furthermore, the phosphate is sodium tripolyphosphate.

[0011] Furthermore, the phosphonate is aminotrimethylphosphonic acid.

[0012] A second aspect of the present invention provides a high-strength composite anti-scaling proppant, comprising the following components: the aforementioned composite anti-scaling agent and proppant.

[0013] Furthermore, the mass ratio of the composite antiscalant to the proppant is 0.02 to 0.04:1.

[0014] Furthermore, the proppant is quartz sand.

[0015] Furthermore, the particle size of the proppant is 270–830 μm.

[0016] A third aspect of the present invention provides a method for preparing a high-strength composite anti-scaling proppant, comprising the following steps:

[0017] S1, phosphate, phosphonate, polycarboxylic acid, sulfonate, zinc salt and deionized water are mixed evenly in proportion to obtain a composite scale inhibitor;

[0018] S2, the composite anti-scaling agent is adhered to the surface of the proppant, and then subjected to high-temperature curing and cooling in sequence to obtain the high-strength composite anti-scaling proppant.

[0019] Furthermore, step S1 specifically includes the following steps:

[0020] S11, using deionized water as a solvent, phosphate and sulfonate are mixed evenly in a certain proportion to obtain a mixed solution; using deionized water as a solvent, phosphonate and polycarboxylic acid are mixed evenly in a certain proportion to obtain a viscous base liquid;

[0021] S12, add zinc salt to the viscous base liquid in proportion and stir to mix to obtain a slow-release solution;

[0022] S13, the slow-release liquid and the mixed solution are mixed evenly to obtain a composite anti-scaling agent.

[0023] Furthermore, in S11, the phosphate and the sulfonate are mixed under high temperature conditions of 50–70°C.

[0024] Furthermore, the phosphonate and the polycarboxylic acid are mixed at a high temperature of 50–70°C.

[0025] Further, step S2 specifically includes the following steps: using a jet pump to carry the composite anti-scaling agent to the upper end of the proppant in an umbrella shape and spray it into the proppant, so that the composite anti-scaling agent adheres to the surface of the proppant, and placing the proppant under a high temperature atmosphere, whereby the composite anti-scaling agent is cured at high temperature under the action of the high temperature atmosphere, and then cooled at room temperature to obtain the high-strength composite anti-scaling proppant.

[0026] Furthermore, the high-temperature curing temperature is 50–70°C, and the time is 0.5–1.5 h.

[0027] A fourth aspect of the present invention also provides the application of the above-mentioned high-strength composite anti-scaling proppant in fracturing operations, wherein the high-strength composite anti-scaling proppant is mixed with fracturing fluid and injected during fracturing operations.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The composite scale inhibitor of the present invention has a synergistic effect among its components, which shows significant advantages over existing scale inhibitors in terms of scale inhibition performance and core permeability retention. It has a high scale inhibition rate, a significantly lower core permeability reduction, and also has a better slow-release effect.

[0030] 2. The high-strength composite scale inhibitor proppant provided by this invention comprises a composite scale inhibitor component and a proppant component. The composite scale inhibitor component is adhered to the proppant surface as solid-phase scale inhibitor particles. Compared with liquid scale inhibitors, it releases at a lower rate and remains active for a long time, effectively preventing scale buildup throughout the fracturing process. Moreover, the high-strength composite scale inhibitor proppant exhibits good migration performance in fractures and excellent pressure resistance, with a breakage rate of less than 10% under a closure pressure as high as 86 MPa, indicating its high strength and long service life.

[0031] 3. The high-strength composite scale inhibitor proppant of this invention can be used in various operations, including gravel packing, fracturing packing, or fracturing operations in new wells and production wells. This product is suitable for linear guar gum fracturing fluids and slickwater fracturing fluids, and mixing with them does not affect the rheological properties of the fracturing fluid. No adverse reactions such as sedimentation, flocculation, emulsification, or viscosity changes occur. It has good compatibility with fracturing fluids. Adding the high-strength composite scale inhibitor proppant of this invention during fracturing operations can effectively prevent scale buildup over a long period, reducing the risk of wellbore damage.

[0032] 4. By placing the high-strength composite scale inhibitor of the present invention into the fracture, oil and gas wells can ensure minimal scale deposition, resulting in better returns. Moreover, after the high-strength composite scale inhibitor comes into contact with the formation fluid, it acts on the near-wellbore area to provide a long-lasting scale inhibition effect. Attached Figure Description

[0033] Figure 1 A lithological structure diagram of the artificial sandstone used in the fracturing sand layer flow experiment of the present invention is shown;

[0034] Figure 2 A schematic diagram of the experimental system structure in the fracturing sand layer flow experiment of the present invention is shown;

[0035] Figure 3 This diagram illustrates the static state of the high-strength composite anti-scaling proppant of the present invention after mixing with fracturing fluid;

[0036] Figure 4 The figure shows the trend of average daily oil production of well group H before and after the application of the high-strength composite anti-scaling proppant of the present invention to the fracturing operation of well H. Detailed Implementation

[0037] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included within this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range. The invention will now be described in detail with reference to embodiments.

[0038] To achieve the above objectives, a first aspect of the present invention provides a composite antiscalant comprising the following raw materials: 10-15 parts of phosphate, 10-20 parts of phosphonate, 5-10 parts of polycarboxylic acid, 10-15 parts of sulfonate, 3-5 parts of zinc salt, and 100-120 parts of deionized water.

[0039] The composite scale inhibitor of this invention exhibits synergistic effects among its components, demonstrating significant advantages over existing scale inhibitors in terms of scale inhibition performance and core permeability retention. After a 12-hour core displacement experiment, the scale inhibition rate reached 95.59%–99.57%, and further improved over time. A short-term 3-hour test showed a scale inhibition rate of 6.06%–7.67%, indicating superior slow-release effect. The minimum permeability reduction was 1.96%, significantly lower than the permeability reduction of existing scale inhibitors (10–15%).

[0040] In a preferred embodiment of the present invention, the polycarboxylic acid is polyaspartic acid. Its main functions are scale prevention and corrosion prevention. Polyaspartic acid is a biomolecular compound that can effectively remove metal ions such as iron and manganese from water, control water hardness, and prevent scale and corrosion. It has high reactivity, which can improve surface tension and wettability, thereby producing better coating adhesion and corrosion resistance. Simultaneously, the polyaspartic acid macromolecule contains abundant amide bonds, carboxyl groups, and other active groups. The amide bonds have high chemical stability and are not easily decomposed at high temperatures. In this system, it can firmly adhere to the proppant surface and, along with the fracturing fluid, carry the scale-inhibiting components into the deep well, exhibiting good slow-release performance.

[0041] In a preferred embodiment of the present invention, the zinc salt is zinc chloride and / or zinc sulfate. The present invention adds zinc salt to a high-strength composite scale inhibitor support system, which, when combined with aminotrimethylphosphonic acid, exhibits good synergistic effects and solubility limiting effects. This scale inhibitor particle system uses zinc salt; compared to existing azole compounds, zinc ions can rapidly generate Zn(OH)2 at high temperatures, depositing on the cathode surface and acting as a protective film. The film formation is relatively rapid, but this film is not durable. However, when used in combination with phosphonates, a corrosion inhibitor, a superior slow-release effect can be achieved, and the cost is lower than that of azole compounds.

[0042] In a preferred embodiment of the present invention, the sulfonate is sodium propylene sulfonate. Sodium propylene sulfonate, as a monomer of the corrosion and scale inhibitor, exhibits better scale inhibition effect when used in conjunction with phosphates, polycarboxylic acids, and sulfonates in this system. It also possesses superior dispersion and filtration loss reduction properties, significant high-temperature and salt resistance, and increased water solubility.

[0043] In a preferred embodiment of the present invention, the phosphate is sodium tripolyphosphate. Sodium tripolyphosphate is an amorphous, water-soluble, linear polyphosphate. By adding sodium tripolyphosphate to a high-strength composite scale inhibitor proppant system, the present invention can enhance the suspension and dispersion capabilities of scale inhibitor particles and chelate metal ions, thereby preventing pipeline corrosion and protecting the well wall.

[0044] In a preferred embodiment of the present invention, the phosphonate is aminotrimethylphosphonic acid. Aminotrimethylphosphonic acid has good chelating, lower limit inhibition, and lattice distortion effects. The addition of aminotrimethylphosphonic acid to this system prevents the formation of scale-forming salts in water, especially calcium carbonate scale. At high concentrations in water, it has a good corrosion inhibition effect, and the system exhibits good chemical stability, is not easily hydrolyzed, and can withstand high temperatures.

[0045] In some specific embodiments of the present invention, the aforementioned composite scale inhibitor is prepared by the following method: phosphate, phosphonate, polycarboxylic acid, sulfonate, zinc salt, and deionized water are mixed uniformly in a certain proportion to obtain the composite scale inhibitor. Further, using deionized water as a solvent, phosphate and sulfonate are mixed uniformly in a certain proportion to obtain a mixed solution; using deionized water as a solvent, phosphonate and polycarboxylic acid are mixed uniformly in a certain proportion to obtain a viscous base liquid; zinc salt is added to the viscous base liquid in a certain proportion and stirred to obtain a slow-release liquid; the slow-release liquid and the mixed solution are mixed uniformly to obtain the composite scale inhibitor. The phosphate and sulfonate are mixed at a high temperature of 50–70°C, and the phosphonate and polycarboxylic acid are mixed at a high temperature of 50–70°C.

[0046] A second aspect of the present invention provides a high-strength composite anti-scaling proppant, comprising the following components: the aforementioned composite anti-scaling agent and proppant.

[0047] The high-strength composite anti-scaling proppant of the present invention includes a composite anti-scaling agent component and a proppant component. The composite anti-scaling agent component coats the surface of the proppant to form a coating, which plays a certain role in lubrication and protection. Combined with the hardness of the proppant itself and the functionality of each component in the system, the composite anti-scaling proppant of the present invention has excellent strength and anti-fracture properties and anti-scaling properties. It will not cause a significant decrease in conductivity and permeability due to scaling of the proppant filling layer.

[0048] Furthermore, the preferred anti-scaling agent component of this invention has a stronger compatibility with solid proppant particles compared to existing chemical reagents of the same function. That is, it can efficiently combine with the proppant with strong binding force, providing better lubrication and protection for the proppant surface, and further improving the anti-breakage and anti-scaling properties of the high-strength composite anti-scaling proppant of this invention.

[0049] In a preferred embodiment of the present invention, the mass ratio of the composite antiscalant to the proppant is 0.02 to 0.04:1.

[0050] This invention controls the mass ratio between the composite scale inhibitor and the proppant components. At this ratio, when applied to fracturing operations, it simultaneously exhibits excellent scale inhibition and core permeability retention capabilities, resulting in optimal economic benefits. If the mass ratio of the composite scale inhibitor is too low (less than 0.02:1), the scale inhibition effect will be inconsistent and the reservoir conductivity will decrease. If the mass ratio is too high (greater than 0.04:1), although the scale inhibition rate will slightly improve, the increase will be insignificant, and it will adversely affect the system's fluidity and reservoir permeability, leading to a significant increase in the decrease in core permeability.

[0051] In a preferred embodiment of the present invention, the particle size of the proppant is 270–830 μm. The suitability of the particle size determines the effectiveness of reservoir fracturing. If the particle size is too small, it is impossible to create sufficiently large guiding fractures; if the particle size is too large, it will increase the construction cost and the risk of blockage during the construction process.

[0052] The proppant material of this invention is obtained through selection from various existing proppants, including ceramic particles, walnut shell fragments, plastic balls, glass microspheres, and quartz sand. More preferably, the proppant is quartz sand. Propane breakage rate tests showed that the structural strength of plastic balls, glass microspheres, and walnut shell fragments is inferior to that of quartz sand, and their breakage rates are much higher than quartz sand under reservoir conditions. Ceramic particles have a lower breakage rate but are more expensive, and their compatibility with scale inhibitor components is not as good as that of quartz sand. Quartz sand is used as the proppant because it has superior high-temperature resistance and wear resistance, as well as strong resistance to acidic media corrosion.

[0053] A third aspect of the present invention provides a method for preparing the aforementioned high-strength composite anti-scaling proppant, comprising the following steps:

[0054] S1, phosphate, phosphonate, polycarboxylic acid, sulfonate, zinc salt and deionized water are mixed evenly in proportion to obtain a composite scale inhibitor;

[0055] S2, the composite anti-scaling agent is adhered to the surface of the proppant, and then subjected to high-temperature curing and cooling in sequence to obtain the high-strength composite anti-scaling proppant.

[0056] In a preferred embodiment of the present invention, step S1 specifically includes the following steps:

[0057] S11, using deionized water as a solvent, phosphate and sulfonate are mixed evenly in a certain proportion to obtain a mixed solution; using deionized water as a solvent, phosphonate and polycarboxylic acid are mixed evenly in a certain proportion to obtain a viscous base liquid;

[0058] S12, add zinc salt to the viscous base liquid in proportion and stir to mix to obtain a slow-release solution;

[0059] S13, the slow-release liquid and the mixed solution are mixed evenly to obtain a composite anti-scaling agent.

[0060] More preferably, the phosphate and the sulfonate are mixed at a high temperature of 50–70°C; the phosphonate and the polycarboxylic acid are mixed at a high temperature of 50–70°C.

[0061] In a preferred embodiment of the present invention, step S2 specifically includes the following steps: using a jet pump to carry the composite anti-scaling agent and spray it onto the upper end of the proppant in an umbrella-like manner, causing the composite anti-scaling agent to adhere to the surface of the proppant; then placing the proppant under a high-temperature atmosphere, where the composite anti-scaling agent is cured at high temperature, followed by cooling at room temperature, thus obtaining the high-strength composite anti-scaling proppant. More preferably, the high-temperature curing temperature is 50–70°C, and the time is 0.5–1.5 hours.

[0062] During the process of the proppant being filled with a high-temperature atmosphere, the super strong coating adhesion of components such as polycarboxylic acid allows the anti-scaling components to adhere firmly to the surface of the proppant at high temperatures. At the same time, the gas has the ability to repeatedly absorb the anti-scaling components. After a period of repeated flushing, the anti-scaling components will be fully adsorbed onto the surface of the proppant. Then, by allowing it to stand and cool at room temperature, the high-strength composite anti-scaling proppant of the present invention can be obtained.

[0063] This high-strength composite scale inhibitor proppant is manufactured using a high-temperature atmosphere method, which is simple to operate, chemically stable, and environmentally friendly, with a biodegradability rate exceeding 60%. Compared to conventional scale inhibitor and proppant mixtures, this system has only two layers, which prevents the decrease in conductivity caused by excessively large particle size during injection into the formation and reduces the degradation time, making it environmentally friendly.

[0064] A third aspect of the present invention also provides the application of a high-strength composite anti-scaling proppant in fracturing operations, wherein the high-strength composite anti-scaling proppant is mixed with fracturing fluid and injected during fracturing operations.

[0065] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0066] Example 1

[0067] A composite scale inhibitor, by weight, comprises the following raw materials: 10 parts phosphate, 10 parts phosphonate, 5 parts polycarboxylic acid, 10 parts sulfonate, 3 parts zinc salt, and 100 parts deionized water. The phosphate is sodium tripolyphosphate, the phosphonate is aminotrimethylphosphonic acid, the polycarboxylic acid is polyaspartic acid, the sulfonate is sodium propylene sulfonate, and the zinc salt is zinc chloride.

[0068] Example 2

[0069] A composite scale inhibitor, by weight, comprises the following raw materials: 12 parts phosphate, 15 parts phosphonate, 7 parts polycarboxylic acid, 12 parts sulfonate, 4 parts zinc salt, and 100 parts deionized water. The phosphate is sodium tripolyphosphate, the phosphonate is aminotrimethylphosphonic acid, the polycarboxylic acid is polyaspartic acid, the sulfonate is sodium propylene sulfonate, and the zinc salt is zinc chloride.

[0070] Example 3

[0071] A composite scale inhibitor, by weight, comprises the following raw materials: 15 parts phosphate, 17 parts phosphonate, 7 parts polycarboxylic acid, 13 parts sulfonate, 5 parts zinc salt, and 100 parts deionized water. The phosphate is sodium tripolyphosphate, the phosphonate is aminotrimethylphosphonic acid, the polycarboxylic acid is polyaspartic acid, the sulfonate is sodium propylene sulfonate, and the zinc salt is zinc chloride.

[0072] Example 4

[0073] A composite scale inhibitor, by weight, comprises the following raw materials: 15 parts phosphate, 20 parts phosphonate, 10 parts polycarboxylic acid, 15 parts sulfonate, 5 parts zinc salt, and 100 parts deionized water. The phosphate is sodium tripolyphosphate, the phosphonate is aminotrimethylphosphonic acid, the polycarboxylic acid is polyaspartic acid, the sulfonate is sodium propylene sulfonate, and the zinc salt is zinc chloride.

[0074] Example 5

[0075] A composite scale inhibitor, differing from Example 1 only in that polyaspartic acid is replaced with polymaleic anhydride.

[0076] Example 6

[0077] A composite scale inhibitor, differing from Example 1 only in that polyaspartic acid is replaced with polyacrylic acid.

[0078] Example 7

[0079] A high-strength composite anti-scaling proppant includes the composite anti-scaling agent and proppant of Example 1, wherein the composite anti-scaling agent accounts for 3% of the mass percentage of the proppant, and the proppant is 20-50 mesh quartz sand.

[0080] The preparation method includes the following steps: (1) Using 50 parts of deionized water as solvent, 10 parts of sodium tripolyphosphate and 10 parts of sodium propylene sulfonate are mixed evenly at 60°C to obtain a uniformly dispersed mixed solution.

[0081] (2) Using 50 parts of deionized water as a solvent, mix 5 parts of polyaspartic acid and 10 parts of aminotrimethylphosphonic acid at 60°C to form a viscous base liquid with anti-scaling effect.

[0082] (3) Add 3 parts of zinc chloride to the viscous base liquid in step 2 and stir at 1000 rpm to allow zinc chloride and aminotrimethylphosphonic acid to react completely to form a corrosion inhibitor. Then mix it evenly with the dispersion in step 1 to obtain a composite scale inhibitor.

[0083] (4) Place the quartz sand in a high-temperature environment of 60°C and introduce inert nitrogen gas. Use a jet pump to carry the composite anti-scaling agent and spray it into the proppant in an umbrella shape at the top of the proppant so that the composite anti-scaling agent adheres to the surface of the quartz sand. The composite anti-scaling agent is cured for 1 hour under the action of the high-temperature atmosphere of 60°C, and then cooled at room temperature for 0.5 hours to obtain the high-strength composite anti-scaling proppant.

[0084] Example 8

[0085] A high-strength composite scale inhibitor proppant comprises the composite scale inhibitor of Example 2 and a proppant, wherein the composite scale inhibitor accounts for 3% of the mass percentage of the proppant, and the proppant is 20-50 mesh quartz sand. Its preparation method is as described in Example 7.

[0086] Example 9

[0087] A high-strength composite scale inhibitor proppant comprises the composite scale inhibitor of Example 3 and a proppant, wherein the composite scale inhibitor accounts for 3% of the mass percentage of the proppant, and the proppant is 20-50 mesh quartz sand. Its preparation method is as described in Example 7.

[0088] Example 10

[0089] A high-strength composite scale inhibitor proppant comprises the composite scale inhibitor of Example 4 and a proppant, wherein the composite scale inhibitor accounts for 3% of the mass percentage of the proppant, and the proppant is 20-50 mesh quartz sand. Its preparation method is as described in Example 7.

[0090] Example 11

[0091] A high-strength composite anti-scaling proppant differs from Example 10 only in that the composite anti-scaling agent accounts for 1% of the proppant by mass.

[0092] Example 12

[0093] A high-strength composite anti-scaling proppant differs from Example 10 only in that the composite anti-scaling agent accounts for 5% of the proppant by mass.

[0094] Comparative Example 1

[0095] A scale inhibitor whose component is sodium tripolyphosphate.

[0096] Comparative Example 2

[0097] A scale inhibitor whose component is aminotrimethylphosphonic acid.

[0098] To investigate the performance of scale inhibitors with different component types, fracturing sand flow experiments were conducted on the composite scale inhibitors of Examples 1, 5, and 6 and the scale inhibitors of Comparative Examples 1-2. Scale inhibition rate and core permeability were tested after different experimental times (3h, 6h, 9h, and 12h) (the permeability reduction was calculated based on the permeability test to study the effect of the scale inhibitor on reservoir conductivity). The test results are shown in Tables 1 and 2. The specific experimental steps and principles are as follows:

[0099] (1) Prepare several sets of artificial sandstone cores with the same properties and parameters. Each core has an artificial fracture at its center. The specific structure is as follows: Figure 1 As shown. This type of core is used to simulate the fractured environment of sandstone reservoirs, where the artificial fractures are designed to provide space for the scaling process of the injected fluids.

[0100] (2) Establish such Figure 2 Before the formal experiment, each core sample was water-driven to measure its absolute permeability. In the formal experimental stage, nine groups of experiments were set up, all involving fluid injection into the core fractures at a rate of 4 mL / min. This included injecting fracturing fluid containing the composite scale inhibitors of Examples 1-6, the scale inhibitors of Comparative Examples 1-2, and fracturing fluid without scale inhibitors. The injected fluid was allowed to remain in the artificial core fractures for a period to induce scaling. Each core sample was then water-driven again, and its absolute permeability was measured after the experiment. The decrease in core permeability before and after the experiment was calculated. After each group of experiments, the core was removed, cut, and the fluid-induced scale adhering to the fracture inner wall was extracted and its mass measured.

[0101] (3) In this study, the following equation was used to calculate the scale inhibition rate:

[0102] α=(1-M a / M o )*100%

[0103] In the equation, α is the scale inhibition rate, and M... aM represents the scale formation quality on the inner wall of the core fractures in the fracturing systems containing the scale inhibitors of the examples and comparative examples. o The quality of scale formation on the inner wall of core fractures in a fracturing system without scale inhibitors.

[0104] Table 1. Comparison of scale inhibition performance between the composite scale inhibitors of Examples 1, 5, and 6 and the scale inhibitors of Comparative Examples 1-2

[0105]

[0106] Table 2. Comparison of permeability performance between the composite scale inhibitors of Examples 1, 5, and 6 and the scale inhibitors of Comparative Examples 1-2

[0107]

[0108] As shown in Tables 1 and 2, the scale inhibitor of Example 1 of the present invention exhibits the best scale inhibition and permeability performance compared to the scale inhibitors of Examples 5-6 and Comparative Examples 1-2. After a 12-hour core displacement experiment, Example 1 showed a scale inhibition rate as high as 96.04%, and a short-term (3-hour) scale inhibition rate of 7.49%, indicating a good slow-release effect. The permeability reduction ranged from 1.96% to 9.17%. This is because the composite scale inhibitor of Example 1 contains polyaspartic acid, which has excellent slow-release properties. It contains macromolecular active groups (such as amide bonds and carboxyl groups), and the amide bonds have high chemical stability, making them difficult to decompose under high temperature and high pressure conditions. This allows it to effectively adhere to the surface of the proppant, providing long-term scale prevention. In Examples 5 and 6, the polycarboxylic acids used in the composite scale inhibitors were polymaleic anhydride and polyacrylic acid, respectively. Example 5, using a polymaleic anhydride scale inhibitor system, showed good scale inhibition performance against inorganic salts, but its effect on corrosive bacteria was not significant, unlike polyaspartic acid. Furthermore, its biodegradability was inferior to polyaspartic acid, easily leading to further scaling and affecting the duration of the scale inhibition effect. Under the same experimental conditions, its scale inhibition rate after 12 hours was approximately 85%, with a permeability reduction of 10%–15%, which impacted the reservoir's conductivity in actual fracturing operations. Example 6, using a polyacrylic acid scale inhibitor system, exhibited strong stability in medium-temperature environments, but its temperature resistance above 120°C was inferior to polyaspartic acid. Its effective period of scale inhibition was shorter than that of Example 1. Under the same experimental conditions, its scale inhibition rate after 12 hours was approximately 85%, with a permeability reduction of 8–12%. The scale inhibition rates of other single-type polyphosphate and phosphonate scale inhibitors (Comparative Example 1 and Comparative Example 2) were all below 85%, and the permeability reduction was between 8% and 15%. These single scale inhibitors are prone to decomposition or formation of by-products under high temperature conditions, resulting in low scale inhibition rate improvement and difficulty in effectively maintaining permeability.

[0109] To investigate the application effect of the composite scale inhibitors of Examples 1-4 of this invention on the surface of the proppant, specifically the high-strength composite scale inhibitors of Examples 7-10, on fracturing operations, the same fracturing sand layer flow experiment was conducted. Specifically, fracturing fluid containing the high-strength composite scale inhibitors of Examples 7-10 was injected into artificial core fractures for scale inhibition rate and permeability performance testing. A blank control group (ordinary proppant quartz sand was added to the fracturing fluid, i.e., the fracturing fluid did not contain the composite scale inhibitor components of this invention) was also set up for performance parameter comparison to evaluate the scale inhibition rate and permeability retention capacity of the high-strength composite scale inhibitors of this embodiment. Furthermore, two different pressure conditions, 30 MPa and 40 MPa, were set up in the experiment to evaluate the proppant breakage rate in the high-strength composite scale inhibitors, denoted as breakage rate A1 and breakage rate A2, respectively. The breakage rate was calculated as the percentage of broken proppant retained in the core fractures by mass, i.e., the mass ratio of broken proppant retained in the core to its total mass. In addition, the content of scale inhibitor components retained in the core was determined by measuring the phosphorus concentration in the produced fluid.

[0110] To investigate the effect of the injection equivalent of high-strength composite anti-scaling proppant on the reservoir's conductivity and the lifespan of solid proppant particles, performance evaluation experiments were conducted at different injection rates (2 mL / min, 4 mL / min, 6 mL / min, and 8 mL / min) based on fracturing sand layer flow experiments.

[0111] The test results are shown in Tables 3, 4 and 5.

[0112] Table 3. Performance of high-strength composite scale inhibitor proppant tested over 12 hours.

[0113]

[0114] As shown in the table above, the high-strength composite scale inhibitor proppant of this invention exhibits excellent scale inhibition rate, reaching up to 99.57%. Furthermore, the proppant breakage rate A1 under 30 MPa conditions is less than that under 40 MPa conditions, indicating that increased pressure has a destructive effect on solid proppant. However, under both experimental pressure conditions, the overall proppant breakage rate in the system is less than 10%, meeting the domestic proppant breakage rate evaluation standard (SY / T5108-2014). That is, the breakage rate of the proppant material meets the specified value for material breakage rate under a specific pressure under engineering background conditions. Simultaneously, the phosphorus content (P) in the produced fluid was detected to infer the remaining effective content in the scale inhibitor. The detection method for P in the produced water refers to the standard GB / T11893-1989, "Determination of Total Phosphorus in Water". The results show that the P content in the produced fluid of each experimental group remained at a low level, indicating a low content of scale inhibitor components in the produced fluid. This reflects that the injected high-strength composite scale inhibitor proppant can efficiently remain in the reservoir pores and exert a long-term scale inhibition effect. Furthermore, the decrease in permeability of the core samples before and after injection of the high-strength composite anti-scaling proppant was smaller than that of the core samples injected with conventional fracturing fluid, indicating the superior scale reduction ability of the high-strength composite anti-scaling proppant.

[0115] Table 4. Scale inhibition performance of high-strength composite scale inhibitor proppant at different experimental times

[0116]

[0117] The results showed that as time went on, the scale inhibition rate of the high-strength composite scale inhibitor in each embodiment gradually increased, and before the effect was fully realized (the experimental time reached 12 hours), the rate of increase of the scale inhibition rate of each system gradually accelerated, indicating that the scale inhibition effect of the system was gradually released with the increase of time and had a good application effect.

[0118] Table 5. Performance of core permeability reduction and proppant breakage rate A1 after 12 hours of experiment at different injection rates.

[0119]

[0120] The results showed that as the fracturing fluid injection rate increased, i.e., the equivalent of high-strength composite scale inhibitor proppant in the reservoir increased, the decrease in reservoir permeability gradually increased, while the proppant fragmentation rate A1 gradually increased. This indicates that excessively increasing the high-strength composite scale inhibitor proppant can lead to a decrease in reservoir conductivity and a reduction in the lifespan of solid particles.

[0121] To further investigate the effect of the content of the composite scale inhibitor component in the high-strength composite scale inhibitor proppant on its scale inhibition and permeability performance, this invention conducted fracturing sand layer flow experiments on high-strength composite scale inhibitor proppants of Examples 11 and 12 containing different concentrations of composite scale inhibitor component, and tested their scale inhibition rate and permeability performance, comparing their performance with that of the high-strength composite scale inhibitor proppant of Example 10. The test results are shown in Table 6.

[0122] Table 6. Comparison of scale inhibition rate and permeability performance of high-strength composite scale inhibitor proppants with different concentrations of composite scale inhibitor.

[0123]

[0124] The results showed that when the concentration of the composite scale inhibitor was within a suitable range (2-4% by mass of the composite scale inhibitor to the proppant), a uniform and stable scale inhibitor layer could be formed on the proppant surface, exhibiting optimal slow-release performance and achieving the best balance point in system performance. This resulted in both extremely high scale inhibition and effective protection of the reservoir's conductivity. However, when the concentration of the composite scale inhibitor was low (e.g., in Example 11, when the composite scale inhibitor accounted for 1% by mass of the proppant), the amount of scale inhibitor was insufficient to form a continuous and effective scale inhibitor coating on the reservoir fracture surface, leading to a significant decrease in scale inhibition rate compared to Example 10, and a relatively large decrease in core permeability. When the concentration of the composite scale inhibitor is high (as in Example 12, where the composite scale inhibitor accounts for 5% of the proppant by mass), although the scale inhibition rate is slightly improved, the increase is not significant. Moreover, excessively high concentrations will adversely affect the fluidity of the system and the permeability of the reservoir, resulting in a significant increase in the decrease in permeability. This is because excessively high concentrations cause particle aggregation, affecting the flow capacity of the reservoir. At the same time, the amount of scale inhibitor adsorbed on the proppant surface reaches saturation, making it difficult to improve the scale inhibition rate. Instead, it will lead to increased costs and increased complexity of the injection operation.

[0125] In addition, the high-strength composite scale inhibitor proppant prepared in Example 10 of this invention was mixed evenly with fracturing fluid to form a suspension, and then allowed to stand for a period of time to observe the dispersion state of the high-strength composite scale inhibitor proppant in the suspension. The dispersion state is as follows: Figure 3 As shown, the high-strength composite anti-scaling proppant has good compatibility with fracturing fluid, disperses evenly, and does not exhibit adverse reactions such as sedimentation, flocculation, emulsification, or viscosity changes.

[0126] In a fracturing operation at an oilfield in Xinjiang, the high-strength composite scale inhibitor proppant of Example 10 of this invention was applied. The high-strength composite scale inhibitor proppant was injected in units of 50 lb / bag. The injection parameters were set uniformly according to the construction plan on the control instrument of the sand mixing truck, and 5 tons of the system were injected. In the on-site test of fracturing construction at Well H, the fracturing construction process was smooth, and there was no obvious solid particle backflow during the flowback process, indicating that the high-strength composite scale inhibitor proppant has a good migration effect in the fracture and good pressure resistance.

[0127] Meanwhile, the flowback fracturing fluid in this well showed no abnormalities compared to adjacent wells, and the formation water produced was also normal compared to adjacent wells on the platform, indicating that the high-strength composite scale inhibitor proppant did not adversely affect the fracturing fluid and formation fluids in Well H. Since its commissioning four months ago, Well H has been the highest-producing well, with a cumulative production of 519.73 m³. 3 This is far higher than the 34.69m of the second-highest producing well, Hua H-4. 3 This indicates that the high-strength composite anti-scaling proppant did not adversely affect the flow conductivity of the propping cracks, and may even have a beneficial effect on increasing production.

[0128] Furthermore, the application effect of the on-site anti-scaling system at Well H shows that, for example Figure 4 Under the influence of this system, the well achieved a relatively long-term and highly stable oil production efficiency from 20 to 24 years. Moreover, the average daily oil production after construction was much higher than before construction. At this time, the average daily oil production stabilized at about 40t / d, which is a good result. This shows that the scale prevention particle system of the present invention has a better slow-release effect and a longer effective period compared with the traditional chemical injection method. The effective time can be up to about 5 years.

[0129] The embodiments described above are merely illustrative of implementation methods of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. The present invention can also be implemented in other specific ways or forms without departing from its spirit or essential characteristics. Therefore, the described embodiments should be considered illustrative rather than limiting in any respect. The scope of the present invention should be defined by the appended claims, and any variations equivalent to the intent and scope of the claims should also be included within the scope of the present invention.

Claims

1. A composite scale inhibitor, characterized in that, It is made from the following raw materials in parts by weight: 10-15 parts phosphate, 10-20 parts phosphonate, 5-10 parts polycarboxylic acid, 10-15 parts sulfonate, 3-5 parts zinc salt, and 100-120 parts deionized water.

2. The composite scale inhibitor according to claim 1, characterized in that, The polycarboxylic acid is polyaspartic acid; And / or, the zinc salt is selected from zinc chloride and / or zinc sulfate; And / or, the sulfonate is sodium propylene sulfonate; And / or, the phosphate is sodium tripolyphosphate; And / or, the phosphonate is aminotrimethylphosphonic acid.

3. A high-strength composite anti-scaling proppant, characterized in that, It comprises the following components: the composite antiscalant and the proppant as described in claim 1 or 2.

4. The high-strength composite anti-scaling proppant according to claim 3, characterized in that, The mass ratio of the composite antiscalant to the proppant is 0.02 to 0.04:

1.

5. The high-strength composite anti-scaling proppant according to claim 3, characterized in that, The proppant is quartz sand.

6. The high-strength composite anti-scaling proppant according to claim 3, characterized in that, The particle size of the proppant is 270–830 μm.

7. A method for preparing a high-strength composite anti-scaling proppant as described in any one of claims 3 to 6, characterized in that, Includes the following steps: S1, phosphate, phosphonate, polycarboxylic acid, sulfonate, zinc salt and deionized water are mixed evenly in proportion to obtain a composite scale inhibitor; S2, the composite anti-scaling agent is adhered to the surface of the proppant, and then subjected to high-temperature curing and cooling in sequence to obtain the high-strength composite anti-scaling proppant.

8. The method for preparing the high-strength composite anti-scaling proppant according to claim 7, characterized in that, Step S1 specifically includes the following steps: S11, using deionized water as a solvent, phosphate and sulfonate are mixed evenly in a certain proportion to obtain a mixed solution; using deionized water as a solvent, phosphonate and polycarboxylic acid are mixed evenly in a certain proportion to obtain a viscous base liquid; S12, add zinc salt to the viscous base liquid in proportion and stir to mix to obtain a slow-release solution; S13, the slow-release liquid and the mixed solution are mixed evenly to obtain a composite anti-scaling agent.

9. The method for preparing the high-strength composite anti-scaling proppant according to claim 8, wherein in S11, the phosphate and the sulfonate are mixed under high temperature conditions of 50-70°C; And / or, the phosphonate and the polycarboxylic acid are mixed at a high temperature of 50–70°C.

10. The preparation method of the high-strength composite anti-scaling proppant according to claim 7, characterized in that, Step S2 specifically includes the following steps: The composite anti-scaling agent is sprayed into the proppant in an umbrella shape using a jet pump, causing the composite anti-scaling agent to adhere to the surface of the proppant. The proppant is then placed in a high-temperature atmosphere, where the composite anti-scaling agent is cured at high temperature and then cooled to room temperature to obtain the high-strength composite anti-scaling proppant.

11. The method for preparing the high-strength composite anti-scaling proppant according to claim 7 or 10, characterized in that, The high-temperature curing temperature is 50-70℃, and the time is 0.5-1.5h.

12. The application of a high-strength composite anti-scaling proppant as described in any one of claims 3 to 6 in fracturing operations, characterized in that, The high-strength composite anti-scaling proppant is mixed with fracturing fluid and injected during fracturing operations.

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