A composite proppant and fracturing fluid system thereof

Abstract

The present application relates to a kind of composite proppant and fracturing fluid system thereof, adopt secondary coating technology granulation forming.First coating is coated by high molecular polymer;Second coating is coated by water-soluble coating material with ecological environmental protection, low density, hydrolyzable, salt-resistant, acid-resistant and lubricating, which is coupled and coated on the surface of coated sand, and the proppant is produced by processes such as drying, forming and screening, which has the functions of self-suspension, self-friction reduction and self-hydrolysis.The proppant integrates proppant and main additives of fracturing fluid, and has the technical characteristics of high strength, low density, high suspension, low viscosity, high sand ratio, low friction, high yield and low damage.The composite proppant is suitable for hydraulic fracturing construction and reservoir reconstruction of medium-deep shale gas and tight gas, and has the advantages of functional integration, simple construction, clean water fracturing, cost reduction, full-slit sand placement, efficient yield increase, sufficient hydrolysis, damage reduction, liquid preparation diversity, strong adaptability, free-burning forming, energy saving and carbon reduction.

Description

Technical Field

[0001] This invention relates to the field of mineral mining technology, specifically to a composite proppant and its fracturing fluid system. Background Technology

[0002] With the large-scale development of oil and gas reservoirs in my country, volumetric fracturing technology, which increases the volume of the fracturing process and the complexity of the fractures, has become a key technology for the exploitation of shale gas and other oil and gas reservoirs. However, the use of conventional proppant (ceramsite, coated sand, quartz sand, etc.) and fracturing fluid (slickwater, etc.) in combination often results in excessively high pump pressure and poor proppant carrying capacity during fracturing operations due to factors such as high proppant density and high frictional loss. This also leads to premature proppant shedding, resulting in a short proppant migration distance in the fracture network and a short effective support radius. The proppant is mainly concentrated in near-wellbore fractures, while the distal fractures and secondary fractures are not effectively filled and supported. This makes it difficult to utilize the role of the micro-fracture network, such as secondary fractures. Consequently, fracturing operations in deep shale gas and tight gas reservoirs are difficult (high cost and risk), with high initial production (due to the main fractures playing a role) and rapid decline (due to the poor role of secondary fractures), making it difficult to achieve safe and efficient operation and long-term high and stable production. Summary of the Invention

[0003] (a) Technical problems to be solved

[0004] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a composite proppant and its fracturing fluid system, which solves the technical problems of excessive pump pressure, poor proppant carrying capacity, and premature proppant loss in fracturing operations in the prior art.

[0005] (II) Technical Solution

[0006] In a first aspect, the present invention provides a method for preparing a composite proppant, comprising the following steps:

[0007] S1. Mix polyvinyl methyl aldehyde and polyvinyl butyral powders to obtain a mixture;

[0008] S2. Mix the mixture and aggregate and / or pre-coated aggregate in a container, immerse it in an ethanol solution of phenolic resin, add azoaminobenzene solution, place it at room temperature for 24 hours, and then gradually raise the temperature to 150°C at a rate of 5°C every three minutes. During the heating process, spray the adhesive and curing agent and stir evenly to prevent the particles from clumping, and obtain the first coating.

[0009] S3. Take the solidified particles into a mixer, slowly add an ethanol solution of 8% modified polyvinyl alcohol hydrogel and 55% epoxy resin, dry, and obtain a second coating. The second coating encapsulates the first coating.

[0010] S4. Cool to room temperature, crush and sieve to obtain composite proppant.

[0011] According to a preferred embodiment of the present invention, in S2, the aggregate is selected from one or more of the following: quartz sand, ceramsite, metal particles, spherical glass particles, sintered bauxite, sintered alumina, sintered zirconium oxide, synthetic resin, and crushed particles; the pre-coated aggregate is obtained by coating the surface of the aggregate with resin material.

[0012] According to a preferred embodiment of the present invention, in S2, the resin used for the pre-coated aggregate may be, in addition to phenolic resin, at least one of furan resin, epoxy resin, aromatic polyamide resin, polyimide resin, and polyphenylene imidazole resin.

[0013] According to a preferred embodiment of the present invention, in S3, the adhesive is at least one selected from phenolic resin, epoxy resin, and unsaturated polyester resin adhesive; the curing agent is at least one selected from aliphatic amines, tertiary amines and their salts, aromatic amines, imidazoles, acid anhydrides, peroxide acyl, peroxide lipids, paraformaldehyde, and phenolic amines.

[0014] According to a preferred embodiment of the present invention, in S1, the ratio of polyvinyl methyl aldehyde and polyvinyl butyral is 1:2-3; in S2, the mass ratio of the mixture to aggregate and / or pre-coated aggregate is 5-8:100-120.

[0015] According to a preferred embodiment of the present invention, in S2, the volume ratio of the azoaminobenzene solution to the ethanol solution of the phenolic resin is 1:100.

[0016] According to a preferred embodiment of the present invention, in step S3, the preparation method of 8% modified polyvinyl alcohol hydrogel is as follows: 8% aqueous solution of polyvinyl alcohol is prepared, and then heated at 90 degrees Celsius for 3 hours until the polyvinyl alcohol is completely dissolved. The solution is poured into centrifuge tubes and cast into columns. The sample is then placed in a -15°C refrigerator for 8 hours, and then thawed at room temperature for 8 hours. The above freeze-thaw process is repeated three times to obtain 8% polyvinyl alcohol hydrogel.

[0017] According to a preferred embodiment of the present invention, in S3, the mass ratio of the adhesive and curing agent to the aggregate and / or pre-coated aggregate is 0.5:0.1:100; the mass ratio of the 8% modified polyvinyl alcohol hydrogel to the aggregate and / or pre-coated aggregate is 0.5:100.

[0018] Mixing polyvinyl methyl aldehyde and polyvinyl butyral powders allows for adjustment of viscosity and the degree of hydrolysis under high formation temperatures, thus controlling the viscosity of the fracturing fluid system to decrease within a preset range. The mixture exhibits water absorption and swelling properties, enabling the proppant to suspend directly in water upon mixing, demonstrating excellent self-suspension, long suspension time, and good conductivity.

[0019] The first coating alters the contact pattern between sand grains, forming a lightweight porous structure from azoaminobenzene solution, resin, and other materials. This structure exhibits high strength and low density. Because the resin-coated sand transforms the original point-to-point contact between sand grains into small-area contact, the increased contact area disperses the load acting on the sand grains, improving their resistance to closure pressure and enhancing their crushing resistance. Simultaneously, the resin coating encapsulates crushed sand grains or silt, reducing silt migration. The coated sand has lower bulk density and apparent density, which is beneficial for sand carrying capacity and increasing the sand-to-powder ratio. It also maintains high conductivity. Ordinary quartz sand suffers from high friction, increasing resistance as the proppant migrates to the fracture depth, affecting fracture-forming performance and consequently, conductivity. By using resin-coated quartz sand to prepare coated proppant, sand ejection and shedding are prevented, strength and corrosion resistance are improved, resulting in a significant increase in fracturing production and a long effective period.

[0020] The aggregate surface coated with a phenolic / epoxy resin secondary layer undergoes two cross-linking chemical reactions: firstly, cross-linking occurs between the functional groups of the phenolic resin itself; secondly, the phenolic hydroxyl and hydroxymethyl groups in the phenolic resin can undergo ring-opening reactions with the epoxy groups in the epoxy resin. The second coating layer overlaying the first layer provides better performance in preventing proppant backflow. Increased proppant movement resistance prevents proppant backflow. Simultaneously, the proppant's water absorption rate decreases, and its compressive strength is enhanced. It can fill surface pores and microcracks, thereby improving the proppant's mechanical properties.

[0021] The higher the density of the fracturing fluid, the greater the damage to the formation. Adding 8% modified polyvinyl alcohol hydrogel, which is then encapsulated by resin to form a coating, achieves clean fracturing, reduces fracturing costs, and minimizes environmental pollution.

[0022] The mixed use of polyvinyl methyl aldehyde and polyvinyl butyral powders can achieve fracturing with proppant-carrying fluid while increasing the proppant delivery distance in the formation.

[0023] Secondly, the present invention provides a fracturing fluid system with a composite proppant, wherein the raw material components are as follows: crosslinking agent: 3-5%; flow aid: 1%-2%; breaker: 3.5%; proppant is the above-mentioned proppant, and the proppant accounts for no more than 40%; the balance is water.

[0024] Composite proppant can be suspended in water for a long time without the aid of thickeners, thus reducing the damage of thickeners to the reservoir and the workload of solution preparation.

[0025] According to a preferred embodiment of the present invention, the drainage aid is alkylphenol polyoxyethylene ether OP-7.

[0026] According to a preferred embodiment of the present invention, the degelatinizing agent is amylase.

[0027] According to a preferred embodiment of the present invention, the crosslinking agent is one of organoboron or organotitanium.

[0028] Thirdly, the present invention provides a process for modifying a fracturing fluid system with a composite proppant, which uses the above-mentioned process for the fracturing fluid system.

[0029] (III) Beneficial Effects

[0030] The mixture of polyvinyl methyl aldehyde and polyvinyl butyral powders allows for self-suspension in water without the need for additional thickeners or other additives. This not only reduces damage to the formation but also lowers fracturing costs, and provides a larger support area at the fracture tip in the formation.

[0031] This fracturing fluid exhibits higher fracturing efficiency, thereby increasing oil and gas field production. Furthermore, the proppant demonstrates good shear resistance during the mixing process with fresh water, the pumping of the mixture into the formation, and the propping of fractures, resulting in lower pump pressure during fracturing operations. Additionally, the proppant preparation method is simple and easy to implement, allowing for real-time on-site preparation. After preparation, the proppant and initial fresh water are mixed together in a mixing truck before being pumped into the formation. After fracturing operations are completed, conventional breaker can be used to break the gel, leaving no solid residue. The proppant can be quickly flushed back with fresh water after breaking, exhibiting superior formation permeability and conductivity recovery capabilities compared to traditional fracturing fluids, with less formation damage, demonstrating promising application prospects.

[0032] The 8% modified polyvinyl alcohol hydrogel in the composite proppant external coating undergoes long-chain macromolecules breaking down into short-chain small molecules after being mixed with water for a certain period of time and under the catalytic action of high temperature. This results in the automatic degradation of the polymer, which in turn leads to a continuous decrease in the viscosity of the composite proppant fracturing fluid system.

[0033] In the initial stage of fracturing and proppant addition, hydration occurs when the composite proppant is mixed with the liquid, increasing its viscosity and improving its suspension performance, which facilitates efficient proppant carrying. In the later stage of fracturing and proppant addition, after the composite proppant migrates to the end of the reservoir fracture network, the composite proppant fracturing fluid system undergoes accelerated hydrolysis under the catalytic effect of higher formation temperatures. After about 5 hours, the viscosity of the fracturing fluid system can be reduced to close to that of clean water, thereby reducing the damage of residues to the reservoir and improving the proppant conductivity and oil and gas well production. Detailed Implementation

[0034] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to specific embodiments.

[0035] Example 1

[0036] This embodiment describes a method for preparing a composite proppant, the steps of which are as follows:

[0037] 1.1 Prepare a mixture of polyvinyl methyl aldehyde and polyvinyl butyral powders at a ratio of 1:2.

[0038] 1.2 Preparation of 8% polyvinyl alcohol hydrogel

[0039] An 8% aqueous solution of polyvinyl alcohol was prepared and then heated at 90°C for 3 hours until the polyvinyl alcohol was completely dissolved. The solution was poured into centrifuge tubes and cast into columns. The samples were then placed in a -15°C freezer for 8 hours, and then thawed at room temperature for 8 hours. The above freeze-thaw process was repeated three times to obtain an 8% polyvinyl alcohol hydrogel.

[0040] 1.3 Preparation of proppant

[0041] (1) Mix 50g of polyvinyl methyl aldehyde and polyvinyl butyral powder to obtain 50g of mixture material;

[0042] (2) Mix 50g of the mixture and 1000g of 60-100 mesh quartz sand in a container, immerse in an ethanol solution of phenolic resin, and add an azoaminobenzene solution. The volume ratio of the ethanol solution of phenolic resin to the azoaminobenzene solution is 1:100. After standing at room temperature for 24 hours, gradually raise the temperature to 150℃, with a heating rate of 5℃ every three minutes. During the heating process, spray 5g of adhesive and 1g of curing agent and stir evenly to prevent particles from clumping, thus obtaining the first coating.

[0043] (3) Take the solidified particles into a mixer, slowly add 5g of 8% modified polyvinyl alcohol hydrogel and 55% epoxy resin ethanol solution to immerse them, dry them to obtain a second coating, and the second coating wraps the first coating.

[0044] (4) Cool to room temperature, crush and sieve to obtain composite proppant.

[0045] The composite proppant properties, tested according to industry standard SY / T5108-2014, are as follows: 52 MPa breakage rate 0.68%, roundness 0.8, sphericity 0.8, acid solubility 1.37%, and bulk density 1.33 g / cm³. 3 The contact angle is 150 degrees, the suspension time is 3-8 seconds, the suspension time is greater than 48 hours, the settling time in mineralized water is greater than 48 hours, and the liquid viscosity is 1.17 MPa·s.

[0046] Example 2

[0047] This comparative example is based on Example 1.

[0048] 2.1 Prepare a mixture of polyvinyl methyl aldehyde and polyvinyl butyral powders at a ratio of 1:3;

[0049] 2.2 Preparation of 8% polyvinyl alcohol hydrogel

[0050] An 8% aqueous solution of polyvinyl alcohol was prepared and then heated at 90°C for 3 hours until the polyvinyl alcohol was completely dissolved. The solution was poured into centrifuge tubes and cast into columns. The samples were then placed in a -15°C freezer for 8 hours, and then thawed at room temperature for 8 hours. The above freeze-thaw process was repeated three times to obtain an 8% polyvinyl alcohol hydrogel.

[0051] 2.3 Preparation of composite proppant

[0052] (1) 66g of a mixture of polyvinyl methyl aldehyde and polyvinyl butyral powder;

[0053] (2) Mix 66g of the mixture and 1000g of 60-100 mesh quartz sand in a container, immerse in an ethanol solution of phenolic resin, and add an azoaminobenzene solution. The volume ratio of the ethanol solution of phenolic resin to the azoaminobenzene solution is 1:100. After standing at room temperature for 24 hours, gradually raise the temperature to 150℃, with a heating rate of 5℃ every three minutes. During the heating process, spray 5g of adhesive and 1g of curing agent and stir evenly to prevent particles from clumping, thus obtaining the first coating.

[0054] (3) Take the solidified particles into a mixer, slowly add 5g of 8% modified polyvinyl alcohol hydrogel and 55% epoxy resin ethanol solution to immerse them, dry them to obtain a second coating, and the second coating wraps the first coating.

[0055] (4) Cool to room temperature, crush and sieve to obtain composite proppant.

[0056] The composite proppant properties, tested according to industry standard SY / T5108-2014, are as follows: 52 MPa breakage rate 0.56%, roundness 0.8, sphericity 0.8, acid solubility 1.21%, and bulk density 1.31 g / cm³. 3 The contact angle is 150 degrees, the suspension time is 3-8 seconds, the suspension time is 40 hours, the settling time in mineralized water is greater than 40 hours, and the liquid viscosity is 1.08 MPa·s.

[0057] The composite proppant prepared by this method has better hydrophobic properties, better suspension effect, and higher strength. Therefore, it settles more slowly during use and supports longer fracture lengths, which is beneficial to increase the conduction area and improve the recovery rate. At the same time, its high strength makes it suitable for higher formation closure pressures.

[0058] Comparative Example 1

[0059] This comparative example uses quartz sand with an average particle size of 20-40 mesh as a proppant, and the rest is the same as in Example 1.

[0060] The composite proppant properties, tested according to industry standard SY / T5108-2014, are as follows: 52 MPa breakage rate 0.96%, roundness 0.8, sphericity 0.8, acid solubility 1.21%, and bulk density 1.09 g / cm³. 3 The contact angle is 150 degrees, the suspension time is 10-20 minutes, the suspension time is less than 3 hours, the settling time in mineralized water is less than 3 hours, and the liquid viscosity is 1.08 mPa·s.

[0061] Comparative Example 2

[0062] This comparative example is based on Example 1, except that the polyvinyl alcohol methyl aldehyde powder is omitted and replaced entirely with a mixture of polyvinyl alcohol ethyl butyral powder. All other steps are the same as in Example 1. The composite proppant performance was tested according to industry standard SY / T5108-2014: 52 MPa breakage rate 0.68%, roundness 0.8, sphericity 0.8, acid solubility 1.37%, and bulk density 1.33 g / cm³. 3 The contact angle is 150 degrees, the suspension time is 3-8 seconds, the suspension time is 20-30 hours, the settling time in mineralized water is greater than 20 hours, and the liquid viscosity is 1.17 MPa·s.

[0063] Example 3

[0064] This invention provides a fracturing fluid system with a composite proppant, wherein the raw material components are as follows: organic boron: 3%; alkylphenol polyoxyethylene ether OP-7: 1%; amylase: 3.5%; the proppant is the above-mentioned proppant, accounting for 30%; the balance is water.

[0065] Put water into the preparation tank, add the above mixture, stir at 200-400 r / min, raise the temperature to 80 degrees, maintain for 5 minutes, lower to room temperature, stir evenly, and then discharge.

[0066] Example 4

[0067] This invention provides a fracturing fluid system with a composite proppant, wherein the raw material components are as follows: organic titanium: 5%; alkylphenol polyoxyethylene ether OP-7: 2%; amylase: 3.5%; the proppant is the above-mentioned proppant, accounting for 40%; the balance is water.

[0068] Put water into the preparation tank, add the above mixture, stir at 200-400 r / min, raise the temperature to 80 degrees, maintain for 5 minutes, lower to room temperature, stir evenly, and then discharge.

[0069] Comparative Example 3

[0070] The composite proppant was prepared without the addition of 8% modified polyvinyl alcohol hydrogel; all other steps were the same as in Example 1. The fracturing fluid preparation process was the same as in Example 3. Performance tests were performed on Examples 3, 4, and Comparative Example 3. Details are shown in Tables 1 and 2.

[0071] Table 1.

[0072]

[0073] Table 2.

[0074]

[0075] Among them, the drag reduction rate in the fracturing fluid system is a characterization of the comprehensive drag reduction effect and its technical indicators generated when the solid-liquid two-phase material formed by the composite proppant and water flows through the pipeline at high speed during fracturing.

[0076] Among them, the proppant carrying capacity in the fracturing fluid system is a technical indicator that characterizes the ability of composite proppant to migrate in fracturing fluid.

[0077] The composite proppant, water, and other additives are mixed to form a fracturing fluid system. The supernatant is filtered out within a certain time, and the viscosity measured according to the prescribed steps is called the initial viscosity of the fracturing fluid system.

[0078] In this process, the composite proppant is mixed with water and other additives to form a fracturing fluid system. After a certain period of time, the proppant is swelled and thickened. A certain amount of supernatant is filtered out and placed in a 90°C water bath for 5 hours. The measured viscosity value is called the hydrolytic viscosity of the fracturing fluid system.

[0079] Among them, the fracturing fluid system with composite proppant will produce a hydrolysis effect with continuously decreasing viscosity. The hydrolysis rate of the fracturing fluid system is a technical indicator that quantitatively characterizes the degree and effect of hydrolysis of the composite proppant fracturing fluid system under specific conditions, and is used to evaluate the damage of fracturing fluid system residues to the reservoir.

[0080] The core damage rate comprehensively reflects the influence of fracturing fluid filtrate on the permeability of the core matrix. This index can be used to characterize the degree of damage to the core after multifunctional composite proppant is combined with water-based fracturing and enters the formation.

[0081] Under dynamic or short-term static conditions, the composite proppant can exhibit a "homogeneous suspension" function at different heights in clear water without the aid of an external thickener. This produces the unique phenomenon of high-density sand particles suspended in low-density clear water, without a clear "solid-liquid" interface, thus achieving the effect of "water and sand as one, sand moving with the water".

[0082] After the composite proppant is mixed with water and other additives, each proppant particle exhibits a "slippery effect," possessing both bulk lubrication and automatic drag reduction functions, thereby greatly reducing fracturing migration friction.

[0083] In the initial stage of fracturing and proppant addition, the composite proppant fracturing fluid system has a high initial viscosity in order to improve the suspension rate, drag reduction rate and proppant carrying effect. In the later stage of fracturing and proppant addition, when the composite proppant migrates into the fracture network at the end of the reservoir, under the action of high formation temperature, the composite proppant fracturing fluid system is accelerated to hydrolyze to a viscosity close to that of water, thereby reducing the damage of residues to the reservoir.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a composite proppant, characterized in that, It includes the following steps: S1. Mix polyvinyl methyl aldehyde and polyvinyl butyral powders to obtain a mixture; the ratio of polyvinyl methyl aldehyde and polyvinyl butyral powders in the mixture is 1:2-3. S2. The mixture of material and aggregate and / or pre-coated aggregate is placed in a container, immersed in an ethanol solution of phenolic resin, and azoaminobenzene solution is added. After standing at room temperature for 24 hours, the temperature is gradually increased to 150°C at a rate of 5°C every three minutes. During the heating process, adhesive and curing agent are sprayed and stirred evenly to prevent particle agglomeration, thus obtaining the first coating. The mass ratio of the mixture to the aggregate and / or pre-coated aggregate is 5-8:100-120. S3. Take the solidified particles into a mixer, slowly add an ethanol solution of 8% modified polyvinyl alcohol hydrogel and 55% epoxy resin, dry, and obtain a second coating. The second coating encapsulates the first coating. The method for preparing the 8% modified polyvinyl alcohol hydrogel is as follows: prepare an 8% aqueous solution of polyvinyl alcohol, and then heat it at 90 degrees Celsius for 3 hours until the polyvinyl alcohol is completely dissolved. The solution was poured into centrifuge tubes and cast into columns. The sample was then placed in a -15°C freezer for 8 hours. The sample was then removed and thawed at room temperature for 8 hours. The above freezing-thawing process was repeated three times to obtain 8% polyvinyl alcohol hydrogel. The mass ratio of the 8% modified polyvinyl alcohol hydrogel to aggregate and / or pre-coated aggregate was 0.5-0.8:

100. S4. Cool to room temperature, crush and sieve to obtain composite proppant.

2. The method for preparing a composite proppant according to claim 1, characterized in that, In S2, the volume ratio of the azoaminobenzene solution to the ethanol solution of the phenolic resin is 1:

100.

3. The method for preparing a composite proppant according to claim 1, characterized in that, In S2, the mass ratio of adhesive and curing agent to aggregate and / or pre-coated aggregate is 0.5:0.1:

100.

4. A fracturing fluid with a composite proppant, characterized in that, It contains the following components by weight percentage: 3-5% crosslinking agent, 1%-2% drainage aid, 3.5% degumming agent, proppant, and water; The proppant is prepared by any of the preparation methods described in claims 1 to 3, and the proportion of proppant does not exceed 40%; the remainder is water.

5. The fracturing fluid with composite proppant according to claim 4, characterized in that, The drainage aid is alkylphenol polyoxyethylene ether OP-7; the degreasing agent is amylase; and the crosslinking agent is organoboron or organotitanium.

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