Wood-based proppant and preparation method thereof

Abstract

The invention discloses a wood-based proppant and a preparation method thereof, and belongs to the technical field of oil and gas development. The wood-based proppant provided by the invention is at least two of a granular proppant, a hydrophobic wood chip proppant and a hydrophilic wood chip proppant which are prepared by taking wood as a raw material; the wood-based proppant is in floating, suspending and settling states in the fracturing fluid according to different densities and supports areas with different heights in the crack, and an oil-gas flowing channel is formed in the crack; the granular proppant is obtained by sequentially carrying out delignification treatment, densification treatment, cutting and hydrophobic treatment on natural wood; the hydrophobic wood chip proppant is obtained after wood raw materials are subjected to crushing treatment, delignification treatment and hydrophobic treatment. The hydrophilic wood chip proppant is obtained by crushing wood raw materials and then performing hydrophilic treatment. The wood-based proppant provided by the invention is low in density, high in strength and low in cost, and powder slag cannot be generated during crushing.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas development, and more particularly to a wood-based proppant and a preparation method thereof. Background Art

[0002] Proppants are crucial for maintaining the opening of fracture cracks and promoting the effective flow of oil and gas. Traditional proppants, such as quartz sand and ceramic proppants, have a high bulk density, generally greater than 1.49 g / cm³, and high-viscosity fracturing fluids are required to slow down the settlement of proppants during transportation. However, high-viscosity fracturing fluids are often associated with problems such as fracturing costs and production efficiency. Although low-viscosity fracturing fluids have been proposed as an alternative, this may cause serious settlement of proppants near the wellbore, resulting in low proppant transportation efficiency and even sand production under high proppant loading conditions. Therefore, the development of proppants with good compatibility with low-viscosity fracturing fluids and capable of efficient transportation and placement is crucial for advancing unconventional reservoir fracturing technology.

[0003] Self-suspending proppants are a type of proppant material that can spontaneously suspend in fracturing fluids, effectively reducing the settlement of proppants and providing an ideal solution for low-viscosity sand-carrying systems. Generally, the density of proppants is reduced by coating traditional proppants with polymer materials or designing proppants in a hollow shape to obtain self-suspending properties. However, under the action of formation closure stress, the powder residues generated by the fragmentation of the coating or matrix of self-suspending proppants will block the fractures and damage the conductivity of reservoir fractures. The complex preparation process and high cost also limit the industrial production and application of self-suspending proppants. Summary of the Invention

[0004] In view of the above problems, the present invention provides a wood-based proppant and a preparation method thereof. The wood-based proppant provided by the present invention has a low density, high strength, low cost, and does not produce powder residues when broken.

[0005] The first object of the present invention is to provide a wood-based proppant, which is at least two of granular proppants, hydrophobic wood chip proppants, and hydrophilic wood chip proppants prepared from wood as raw materials; the wood-based proppant presents floating, suspending, and settling states in the fracturing fluid according to different densities, supports different height regions in the fracture, and forms an oil and gas flow channel in the fracture.

[0006] The granular proppant is obtained by sequentially subjecting natural wood to delignification treatment, densification treatment, cutting, and hydrophobic treatment.

[0007] The natural wood is one or a combination of more of Tilia tuan Szyszyl., Populus spp., Pinus spp., Ulmus pumila L., Zelkova schneideriana Hand.-Mazz., Paulownia fortunei (Seem.) Hemsl., Quercus spp., Cerasus pseudocerasus (Lindl.) G. Don, Dalbergia odorifera T. Chen, Cunninghamia lanceolata (Lamb.) Hook., Phoebe zhennan S. Lee & F. N. Wei, Cinnamomum camphora (L.) J. Presl.

[0008] The hydrophobic wood chip proppant is obtained by crushing wood raw materials, followed by delignification treatment and hydrophobic treatment.

[0009] The hydrophilic wood chip proppant is obtained by crushing wood raw materials and then performing hydrophilization treatment.

[0010] The wood raw material of the wood chip proppant is one or more combinations of natural wood, engineered wood, and wood residues. The engineered wood is one or more combinations of plywood, particleboard, fiberboard, wood chipboard, and composite board.

[0011] The wood residues are one or more combinations of bark, roots, veneer scraps, sawmill cuttings, wood shavings, sawdust, and offcuts.

[0012] The wood-based proppant of the present invention can be transported to a designated position within the fracture only under the action of water, without the need to add a thickening agent to the sand-carrying fluid; the granular proppant can maintain its structural integrity under the closing stress of the formation and does not produce fines, thereby reducing the risk of backflow sand plugging during oil and gas production; the granular proppant is prepared by hot pressing according to the porous structure of natural massive wood to obtain granular proppants with different densities. The wood chip proppant is in-situ compressed to form support piles under the closing stress of the formation. The wood-based proppant has excellent migration performance, can achieve long-distance transportation and a high laying area of the wood-based proppant in the fracture, and can form an oil and gas channel with a high conductivity coefficient in the fracture.

[0013] The second object of the present invention is to provide a preparation method of the above wood-based proppant. The preparation of the granular proppant includes the following steps: Perform delignification treatment on natural wood to obtain delignified wood.

[0014] Mechanically hot press the delignified wood at 1.4 MPa to 10 MPa and 70 °C to 100 °C, and obtain dense wood after sufficient drying.

[0015] Perform cutting treatment on the dense wood to obtain dense wood particles.

[0016] Perform hydrophobic treatment on the dense wood particles at room temperature to obtain granular proppant.

[0017] In a preferred embodiment of the present invention, the mechanical hot pressing time is 8 h to 12 h.

[0018] In a preferred embodiment of the present invention, the cutting treatment is carried out using a laser cutting machine or a micro lathe.

[0019] The cutting parameters of the laser cutting machine are as follows: the laser power is 13 W to 24 W, the cutting speed is 25 mm / min to 30 mm / min, and the cutting size is 1300 μm to 1500 μm.

[0020] The cutting parameters of the micro-lathe are as follows: the spindle speed is 1000 r / min, and the cutting size is 1200 μm.

[0021] The third object of the present invention is to provide the preparation method of the above-mentioned wood-based proppant. The preparation of the hydrophobic wood chip proppant includes the following steps: The wood raw material is crushed to obtain the original wood chips.

[0022] The original wood chips are delignified to obtain delignified wood chips.

[0023] The delignified wood chips are hydrophobized at room temperature to obtain the hydrophobic wood chip proppant.

[0024] When the wood raw material is crushed, for natural wood and engineered wood, a cutting crusher is directly used for mechanical crushing.

[0025] For wood residues, screening is first carried out, and the part that does not pass through the sieve is mechanically crushed by a cutting crusher.

[0026] The size of the sieve during screening is 1 mm.

[0027] In a preferred embodiment of the present invention, the hydrophobization methods of the granular proppant and the hydrophobic wood chip proppant are the same.

[0028] During hydrophobization, the solute used in the hydrophobic solution is dimethyl silicone oil, polydimethylsiloxane, perfluorooctanoic acid or octadecylamine; the solvent is tetraethyl orthosilicate, acetone, chloroform or ether.

[0029] The reaction time of hydrophobization is 0.5 h to 2 h.

[0030] The mass concentration of the hydrophobic solution is 0.5% to 3%.

[0031] The mass ratio of wood to the hydrophobic solution is 1:30 to 70, and the wood is dense wood particles or delignified wood chips.

[0032] In a preferred embodiment of the present invention, the delignification methods of the granular proppant and the hydrophobic wood chip proppant are the same.

[0033] The delignification method is sodium chlorite method, alkaline sodium sulfite method, hydrogen peroxide method or deep eutectic solvent method.

[0034] In a preferred embodiment of the present invention, the treatment method of the sodium chlorite method is as follows: the wood is put into an acetic acid / sodium chlorite aqueous solution and reacted at 80 °C to obtain a delignified product. Among them, the mass ratio of the wood to the acetic acid / sodium chlorite aqueous solution is 1:70; in the acetic acid / sodium chlorite aqueous solution, the mass concentration of the acetic acid solution is 0.1%, the mass concentration of the sodium chlorite solution is 4%, and the mass ratio of the acetic acid solution to the sodium chlorite solution is 1:4.

[0035] The treatment method of the alkaline sodium sulfite method is as follows: the wood is put into a sodium hydroxide / sodium sulfite aqueous solution and reacted at 120 °C to obtain a delignified product; among them, the mass ratio of the wood to the sodium hydroxide / sodium sulfite is 1:50, the mass concentration of the sodium hydroxide solution is 1%, the mass concentration of the sodium sulfite solution is 4%, and the mass ratio of the sodium hydroxide solution to the sodium sulfite solution is 1:2.

[0036] The treatment method of the hydrogen peroxide method is as follows: the wood is put into an alkaline hydrogen peroxide aqueous solution and reacted at 90 °C to obtain a delignified product; among them, the mass ratio of the wood to the alkaline hydrogen peroxide aqueous solution is 1:60, the mass concentration of hydrogen peroxide is 8%, the mass concentration of the base is 1%, and the base in the alkaline hydrogen peroxide aqueous solution is ammonia water.

[0037] The treatment method of the deep eutectic solvent method is as follows: the hydrogen bond acceptor and the hydrogen bond donor are mixed evenly to obtain a deep eutectic solvent, and then the wood is put into the deep eutectic solvent composed of the hydrogen bond acceptor and the hydrogen bond donor and reacted at 100 °C to obtain a delignified product; among them, the mass ratio of the wood to the deep eutectic solvent is 1:30, the hydrogen bond acceptor is choline chloride; the hydrogen bond donor is ethylene glycol.

[0038] The wood is natural wood or wood raw material.

[0039] The fourth object of the present invention is to provide the preparation method of the above-mentioned wood-based proppant. The preparation of the hydrophilic wood chip proppant includes the following steps: The wood raw material is crushed to obtain the original wood chips.

[0040] The original wood chips are added to the solution for hydrophilic treatment to obtain the hydrophilic wood chip proppant.

[0041] In a preferred embodiment of the present invention, during the hydrophilic treatment, the solution used is a combination of soybean oil, palm oil and corn oil.

[0042] The reaction temperature of the hydrophilic treatment is 220 °C, the reaction time is 3 h, and the mass ratio of the original wood chips to the solvent is 1:100.

[0043] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses wood as a raw material, effectively reducing the preparation cost. Based on the characteristics of wood being lightweight and having an orderly arrangement of fibers, the main chemical components of the treated wood are cellulose, etc. For particulate proppants, after delignification treatment, the wood can be softened and thus compressed to form densified wood. At this time, the pores of the wood collapse and the wood fibers are arranged tightly. This dense physical structure and the chemical components of the delignified wood fibers endow the particulate proppant with the characteristics of low density, high strength, and no generation of powder residue. For wood chip proppants, since they are not densified, they inherently have a low density. After being treated, the wood chips can be compressed into piles under the action of the formation closure stress when entering the formation fractures, thereby showing high strength.

[0044] The advantages of the wood-based proppants prepared by the present invention are as follows: (1) The wood-based proppants of the present invention have high compressive strength, with the compressive strength up to 145.2 MPa. The wettability of the wood-based support can be customized according to requirements, such as hydrophilic and hydrophobic. The density ranges from 0.16 g / cm³ to 1.27 g / cm³, featuring low density and high compressive strength, and being superior to ordinary self-suspending proppants and conventional proppants in terms of specific compressive strength. It should be noted that the specific compressive strength is the ratio of compressive strength to density.

[0045] (2) The particulate proppants of the present invention have three different density ranges, namely less than 1.00 g / cm³, approximately equal to 1.00 g / cm³, and greater than 1.00 g / cm³, and can spontaneously exhibit floating, suspension, and sedimentation states in the fracturing fluid, respectively laying at the top, middle, and bottom of the fracture. This discrete distribution maximizes the laying height of the proppant and forms an oil and gas channel with a high conductivity coefficient in the fracture.

[0046] (3) The wood chip proppants of the present invention are to inject low-density wood chip proppants with different wettabilities into the fracture. The hydrophobic wood chip proppants float on the top of the fracture, while the hydrophilic wood chip proppants sink to the bottom of the fracture. Under the action of the formation closure stress, the wood chip proppant aggregates are in-situ compressed to form support piles, thereby keeping the fracture open and creating a broad flow channel for oil and gas. According to different requirements of the proppant, the density regulation of the wood-based proppant is achieved through the synergistic action of different woods and hot pressing processes during preparation.

[0047] (4) The wood-based proppants of the present invention are different from traditional proppants such as quartz sand. Such proppants can maintain the structural integrity under the action of the formation closure stress and do not generate powder residue, thus preventing the risk of backflow sand plugging during oil and gas production. The low density of the proppant is also beneficial for realizing the long-distance transmission and a relatively large laying area of the proppant in the fracture, and has good application prospects in unconventional reservoir fracturing. Description of the Drawings

[0048] Figure 1It is the graph of processing pressure and density for Granule - B1, Granule - P1 and Granule - B2.

[0049] Figure 2 It is the density graph of commercial quartz sand and wood chips after different treatments.

[0050] Figure 3 It is the compressive strength graph of Granule - B1, Granule - P1 and Granule - B2.

[0051] Figure 4 It is the compressive strength graph of hydrophobic wood chip - PSBT1, hydrophilic wood chip - EP1 and mixed wood chip - PSBT1 / EP1 support piles.

[0052] Figure 5 It is the wettability graph of dense wood - B1 and Granule - B1 with density.

[0053] Figure 6 It is the wettability graph of hydrophobic wood chip - PSBT1 and hydrophilic wood chip - EP1 support piles, where a is the wetting angle graph of hydrophobic wood chip - PSBT1 support pile, b is the wetting angle graph of hydrophilic wood chip - EP1 support pile, c is the distribution graph of hydrophobic wood chip - PSBT1 in water, and d is the distribution graph of hydrophilic wood chip - EP1 in water.

[0054] Figure 7 It is the size distribution graph of quartz sand before and after crushing experiment.

[0055] Figure 8 It is the size distribution graph of ceramsite before and after crushing experiment.

[0056] Figure 9 It is the size distribution graph of Granule - B1, Granule - P1 and Granule - B2 before and after crushing experiment.

[0057] Figure 10 It is the photo and crushing rate graph of commercial quartz sand, ceramsite and Granule - B1, Granule - P1 and Granule - B2 before and after crushing.

[0058] Figure 11 It is the size distribution graph of wood chips.

[0059] Figure 12 It is the water stability graph of Granule - B1 and Granule - B2, where a is 0h, b is 2h, and c is 24h.

[0060] Figure 13 It is the dynamic water stability graph of Granule - P1, where a is the equilibrium state graph floating on the water surface, b is the unbalanced state graph under a downward force, and c is the equilibrium state graph sinking to the bottom of the water.

[0061] Figure 14Static water stability diagram of granule - P1. Among them, a1 is the state diagram of granule - P1 floating on the water surface at 0 h, a2 is the state diagram of granule - P1 floating on the water surface at 2 h, a3 is the state diagram of granule - P1 floating on the water surface at 24 h, b1 is the state diagram of granule - P1 settling at the bottom of the water at 0 h, b2 is the state diagram of granule - P1 settling at the bottom of the water at 2 h, and b3 is the state diagram of granule - P1 settling at the bottom of the water at 24 h.

[0062] Figure 15 Water stability diagrams of hydrophobic wood chips - PSBT1 and hydrophilic wood chips - EP1.

[0063] Figure 16 Viscosity diagrams of fresh water, hydrophobic wood chips - PSBT1 and hydrophilic wood chips - EP1 fracturing fluids.

[0064] Figure 17 Static settlement performance diagrams of different wood - based proppants. Among them, a is granule - B1, b is granule - P1, and c is granule - B2.

[0065] Figure 18 Dynamic migration performance diagrams of hydrophobic wood chips - PSBT1, hydrophilic wood chips - EP1 and mixed wood chips - PSBT1 / EP1. Among them, a1 is the state diagram of hydrophobic wood chips - PSBT1 in a 3 - mm crack, a2 is the state diagram of hydrophobic wood chips - PSBT1 in a 1.5 - mm crack, b1 is the state diagram of hydrophilic wood chips - EP1 in a 3 - mm crack, b2 is the state diagram of hydrophilic wood chips - EP1 in a 1.5 - mm crack, c1 is the state diagram of mixed wood chips - PSBT1 / EP1 in a 3 - mm crack, and c2 is the state diagram of mixed wood chips - PSBT1 / EP1 in a 1.5 - mm crack.

[0066] Figure 19 Diagrams of the silicone oil modification amounts of granule - B1, granule - P1 and granule - B2.

[0067] Figure 20 Diagrams of the acid solubilities of granule - B1, granule - P1 and granule - B2, as well as the standard acid solubilities of commercial quartz sand and ceramsite proppants.

[0068] Figure 21 Statistical size diagrams of granule - B1, granule - P1 and granule - B2 before and after acid treatment. Among them, a is before acid treatment and b is after acid treatment.

[0069] Figure 22 Diagrams of the acid solubilities of hydrophobic wood chips - PSBT1 and hydrophilic wood chips - EP1. Detailed implementation methods

[0070] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0071] Example 1 This embodiment provides a preparation method of a wood-based proppant. The prepared proppant is a granular proppant. The wood raw material is basswood, the delignification method is the alkaline sodium sulfite method, and the mechanical cutting is carried out by a laser cutting machine. The specific steps are as follows.

[0072] Step 1: Put natural basswood into a sodium hydroxide / sodium sulfite solution. The mass ratio of natural basswood to the sodium hydroxide / sodium sulfite solution is 1:50. In the sodium hydroxide / sodium sulfite solution, the mass concentration of sodium hydroxide is 1%, and the mass concentration of sodium sulfite is 4%. The mass ratio of the sodium hydroxide solution to the sodium sulfite solution is 1:2. Treat at 120 °C for 3 h, and then wash with deionized water until neutral to obtain delignified wood.

[0073] Step 2: Mechanically hot-press the delignified wood at 1.4 MPa and 100 °C for 8 h, and obtain dense wood after sufficient drying.

[0074] Step 3: Carry out laser cutting treatment on the dense wood. The laser power is 24 W, the cutting speed is 30 mm / min, and the cutting size is 1500 μm to obtain dense wood particles with a size of 1120 - 1629 μm.

[0075] Step 4: Carry out hydrophobic modification treatment on the dense wood particles at room temperature. Put the dense wood particles into a dimethyl silicone oil / acetone solution. The mass concentration of dimethyl silicone oil in the acetone solution is 2%. The mass ratio of the dense wood particles to the dimethyl silicone oil / acetone solution is 1:40. React at 600 r / min for 1 h, and then dry thoroughly at 60 °C to obtain granular proppant.

[0076] Example 2 This embodiment provides a preparation method of a wood-based proppant. The prepared proppant is a granular proppant. The wood raw material is poplar, the delignification method is the sodium chlorite method, and the mechanical cutting is carried out by a laser cutting machine. The specific steps are as follows.

[0077] Step 1: Put natural poplar wood into an acetic acid / sodium chlorite aqueous solution. The mass ratio of natural poplar wood to the acetic acid / sodium chlorite aqueous solution is 1:70. In the acetic acid / sodium chlorite aqueous solution, the mass concentration of acetic acid is 0.1%, and the mass concentration of sodium chlorite is 4%. The mass ratio of the acetic acid solution to the sodium chlorite solution is 1:4. Treat at 80°C for 6 h, and then wash with deionized water until neutral to obtain delignified wood.

[0078] Step 2: Mechanically hot-press the delignified wood at 2.9 MPa and 70°C for 12 h, and obtain dense wood after sufficient drying.

[0079] Step 3: Perform laser cutting on the dense wood. The laser power is 13 W, the cutting speed is 25 mm / min, and the cutting size is 1300 μm to obtain dense wood particles with a size of 980 μm - 1560 μm.

[0080] Step 4: Perform hydrophobic modification on the dense wood particles at room temperature. Put the dense wood particles into a polydimethylsiloxane / ether solution. The mass concentration of polydimethylsiloxane in the ether solution is 0.5%. The mass ratio of the dense wood particles to the polydimethylsiloxane / ether solution is 1:30. React at 100 r / min for 0.5 h, and then dry thoroughly at 80°C to obtain particle proppants.

[0081] Example 3 This example provides a preparation method of a wood-based proppant. The prepared proppant is a particle proppant, the wood raw material is beech wood, the delignification method is the hydrogen peroxide method, and mechanical cutting is carried out using a micro-lathe. The specific steps are as follows.

[0082] Step 1: Put natural beech wood into an ammonia / hydrogen peroxide aqueous solution. The mass ratio of natural beech wood to the ammonia / hydrogen peroxide aqueous solution is 1:60. In the ammonia / hydrogen peroxide aqueous solution, the mass concentration of ammonia is 1%, and the mass concentration of hydrogen peroxide is 8%. Treat at 90°C for 4 h, and then wash with deionized water until neutral to obtain delignified wood.

[0083] Step 2: Mechanically hot-press the delignified wood at 10 MPa and 75°C for 10 h, and obtain dense wood after sufficient drying.

[0084] Step 3: Perform micro-lathe cutting on the dense wood. The spindle speed is 1000 r / min, and the cutting size is 1200 μm to obtain dense wood particles with a size of 1080 - 1510 μm.

[0085] Step 4: Hydrophobically modify the dense wood particles at room temperature. Put the dense wood particles into a perfluorooctanoic acid / chloroform solution. The mass concentration of perfluorooctanoic acid in the chloroform solution is 0.8%. The mass ratio of the dense wood particles to the perfluorooctanoic acid / chloroform solution is 1:50. React under the condition of 100 r / min for 0.5 h, and then dry thoroughly at 40 °C to obtain the particle proppant.

[0086] Example 4 This example provides a preparation method of a wood-based proppant. The prepared proppant is a hydrophobic wood chip proppant. The wood raw materials are elm and pine. The delignification method is the deep eutectic solvent method. The specific steps are as follows.

[0087] Step 1: Directly crush elm and pine with a cutting crusher and pass through a 1-mm sieve to obtain the original wood chips.

[0088] Step 2: Mix choline chloride and ethylene glycol according to a molar ratio of 1:1 and mix at 80 °C for 30 min to obtain a deep eutectic solvent. Put the original wood chips into the deep eutectic solvent. The mass ratio of the original wood chips to the deep eutectic solvent is 1:30. React at 100 °C for 1 h, and then wash with deionized water to remove the residual reagents. After drying, obtain the delignified wood chips.

[0089] Step 3: Hydrophobically modify the delignified wood chips at room temperature. Put the delignified wood chips into an octadecylamine / tetraethyl orthosilicate solution. The mass concentration of octadecylamine in the tetraethyl orthosilicate solution is 3%. The mass ratio of the delignified wood chips to the octadecylamine / tetraethyl orthosilicate solution is 1:70. React under the condition of 1000 r / min for 2 h, and then dry thoroughly at 30 °C to obtain the hydrophobic wood chip proppant.

[0090] Example 5 This example provides a preparation method of a proppant. The prepared proppant is a hydrophilic wood chip proppant. The wood raw materials are plywood, wood shavings, bark, and sawmill cants. The specific steps are as follows.

[0091] Step 1: Screen the wood raw materials. Screen the wood shavings, bark, and sawmill cants. The part that does not pass through the sieve and the plywood are crushed together with a cutting crusher. The crushed wood chips are mixed with the part that passes through the sieve to obtain the original wood chips.

[0092] Step 2: Put the original wood chips into the mixed oil and heat-treat at 220 °C for 3 h. The mass ratio of the original wood chips to the mixed oil is 1:100. The mixed oil is composed of palm oil, soybean oil, and corn oil with a mass ratio of 1:1:4. Then filter the wood chips with a 100-mesh sieve until the excess oil is drained to obtain the hydrophilic wood chip proppant.

[0093] It should be noted that in the accompanying drawings of the specification, Particle-B1 refers to the hydrophobic particle proppant prepared in Example 1, Particle-P1 refers to the hydrophobic particle proppant prepared in Example 2, and Particle-B2 refers to the hydrophobic particle proppant prepared in Example 3.

[0094] Dense wood-B1 refers to the product prepared in Step 2 of Example 1.

[0095] Hydrophobic wood chips-PSBT1 corresponds to the hydrophobic wood chip proppant prepared in Example 4.

[0096] Hydrophilic wood chips-EP1 corresponds to the hydrophobic wood chip proppant prepared in Example 5.

[0097] In the following test data, the raw wood chips refer to the product prepared in Step 1 of Example 4, and the delignified wood chips refer to the product prepared in Step 2 of Example 4.

[0098] In the present invention, the unit ppa represents pounds per gallon.

[0099] The wood-based proppant prepared by the present invention is characterized and tested below.

[0100] (1) Proppant water stability test Particle proppant water stability test: The dried particle proppants are respectively placed in water and left standing at room temperature for 2 h and 24 h, and the distribution positions of the particle proppants are observed.

[0101] Wood chip proppant water stability test: 5.0 g of dried hydrophilic wood chip proppant and hydrophobic wood chip proppant are respectively placed in water and stirred at 90 °C for 1 h to test their water stability. After stabilization, the wood chip proppants floating on the water surface are collected, dried and weighed.

[0102] (2) Viscosity test At room temperature, a rotational viscometer is used to measure the viscosity of the mixture of wood chip proppant and water. The viscosity test uses a No. 0 rotor and the rotation speed is 6 r / min. The addition amount of the wood chip proppant is 0.25 ppa.

[0103] (3) Compressive test The anti-breakage rates of quartz sand, ceramsite and particle proppant are tested. 5 g of particle proppant is placed in a mold with dimensions of 60 mm × 30 mm, and force is continuously applied for 2 min. The broken particle proppant is sieved with a 150-mesh vibrating sieve for 10 minutes, and the fine particles on the sieve and the powder under the sieve obtained are collected and weighed. The test pressures of the particle proppant are 91.6, 120.2 and 145.2 MPa respectively. Quartz sand and ceramsite are tested at 91.6 MPa. The mesh sizes of quartz sand and ceramsite are 40 / 70 mesh and 20 / 40 mesh respectively.

[0104] (4)Acid Solubility Test The granular proppants were immersed in a 10% hydrochloric acid solution under external pressures of 91.6 MPa, 120.2 MPa, and 145.2 MPa for 30 min respectively.

[0105] The wood chip proppants were immersed in a hydrochloric acid solution at 65 °C for 30 min. The samples after acid treatment were washed with water until neutral, and then completely dried overnight in an oven at 60 °C.

[0106] The initial mass was m0 and the final mass was m1. The acid solubility calculation formula was (m0 - m1) / m0.

[0107] (5)Proppant Transportation and Settlement Test The static settlement characteristics of granular proppants were tested using a migration device with dimensions of 240 mm × 190 mm × 1.5 mm.

[0108] The dynamic transportation characteristics of wood chip proppants were tested using a migration device with dimensions of 700 mm × 200 mm × 1.5 mm - 3.0 mm and a peristaltic pump.

[0109] The sand-carrying fluid was pumped at an injection speed of 10 cm / s. The addition amount of wood-based proppants was 0.25 ppa, and the sand-carrying fluid consisted only of water and wood-based proppants.

[0110] (6)Evaluation of Proppant Density, Morphology Size, Compressive Strength, and Wettability The low density, high compressive strength, and specific wettability of wood-based proppants ensure that the proppants are effectively transported to the designated position in the fracture only under the action of water and provide a supporting effect. Different from 40 / 70 mesh commercial quartz sand and 20 / 40 mesh ceramsite proppants, wood-based proppants can maintain the structural integrity under the closing stress without generating powder residues, thus reducing the risk of sand plugging during the backflow in oil and gas production.

[0111] From Figure 1 and Figure 2 it can be seen that the density of the granular proppants prepared in Examples 1 - 3 was 0.83 g / cm 3 ~1.27 g / cm 3 and the density of the wood chip proppants prepared in Example 4 was 0.16 g / cm 3 , which was much lower than that of 40 / 70 mesh commercial quartz sand. The low density can effectively alleviate the settlement of proppants during transportation and reduce the dependence of proppants on the viscosity of the fracturing fluid.

[0112] Figure 3For the compressive strength of the particulate proppants prepared in Examples 1 to 3, as the density increases, the compressive strength of the particulate proppants in the longitudinal, radial, and tangential directions of the wood increases, and the strength range is 19.1 MPa to 144.4 MPa.

[0113] Figure 4 Regarding the compressive strength of the wood chip proppant, it should be noted that after the wood chip proppant enters the fracture, it can be compressed into a pile under the action of the formation closure stress, and the dense wood chip pile can provide support strength. As can be seen from Figure 4 the hydrophilic wood chips - EP1 prepared in Example 5, the hydrophobic wood chips - PSBT1 prepared in Example 4, and the mixed wood chips - PSBT1 / EP1 obtained by mixing the hydrophilic wood chips - EP1 prepared in Example 5 and the hydrophobic wood chips - PSBT1 prepared in Example 4 at a mass ratio of 1:1, as the processing stress increases, the compressive strength increases; at the same time, during the preparation of the hydrophilic wood chip proppant, high temperature causes the hemicellulose component of the wood to crack into small fragment active substances, which interact with oils to form a gel under the simulated formation temperature of 100 °C and the compaction conditions of 35 MPa to 105 MPa. The hydrophilic wood chips - EP1 support pile exhibits the highest strength, with a strength range of 65.3 MPa to 95.1 MPa, while the opposite wettability of the wood chips results in the lowest strength of the mixed wood chips - PSBT1 / EP1 support pile, with a strength range of 51.3 MPa to 57.0 MPa. It should be noted that Figure 4 the processing pressures of 4.1 MPa, 8.2 MPa, and 12.3 MPa in [the relevant context] refer to the input processing pressures of the instrument for preparing the support pile compaction in the laboratory. After conversion calculation based on the actual stress area of the support pile processing die, the actual stress on the surface of the support pile is 35 MPa, 75 MPa, and 105 MPa, and this pressure is the simulated formation closure stress.

[0114] Figure 5 shows the wettability of the dense wood before and after hydrophobic modification in Example 1. It can be seen that after hydrophobic modification, the wood surface changes from hydrophilic to hydrophobic. Therefore, the modified particulate proppant can maintain a water - repellent state in water, thereby maintaining the stability of the density. Particulate - B1, Particulate - P1, and Particulate - B2 can respectively maintain floating, suspension, and sedimentation states in water, thereby simultaneously supporting the top, middle, and bottom of the fracture to form a high - conductivity oil - gas flow channel.

[0115] Figure 6The wettability of sawdust piles and the distribution of sawdust proppants in water are shown. The hydrophobic sawdust-PSBT1 proppants show a large hydrophobic angle of 128.5°, and all the hydrophobic sawdust-PSBT1 floats on the water surface. The water contact angle of the hydrophilic sawdust-EP1 proppants is 71.0°, and most of the hydrophilic sawdust-EP1 sinks to the bottom of the water, ensuring that the top and bottom of the two sawdust proppants are independently distributed, forming top and bottom support pile belts, thereby forming a large oil and gas flow channel in the middle.

[0116] Figure 7 , Figure 8 and Figure 9 The sizes of the commercial quartz sand proppant of 40 / 70 mesh, the commercial ceramsite proppant of 20 / 40 mesh, and the particle proppant prepared in Examples 1 to 3 before and after crushing are respectively Figure 10 It can be seen that after crushing, traditional proppants such as quartz sand and expanded clay produced a large amount of fine particles and powder residue, with reduced size and crushing rates of 43.3% and 41.0%, respectively. However, the granular proppants prepared in Examples 1 to 3 only produced plastic deformation, increased size, and no powder residue was produced.

[0117] Figure 11 From the statistics of sawdust size, it can be seen that the original sawdust has almost no effect on its size after delignification treatment, and the distribution range is 0.68μm~1620μm. The hemicellulose in the sawdust after oil heat treatment is cracked, which affects the sawdust size. The sawdust size is reduced to a distribution range of 0.68μm~700μm. Small-sized sawdust proppants can enter narrower cracks to improve the proppant laying effect.

[0118] (7) Evaluation of proppant water stability The specific wettability of the proppant ensures its different distribution states and stability in water, thereby ensuring that the proppant can maintain its original distribution position during pumping and migration, forming an ideal oil and gas flow channel.

[0119] Figure 12 It shows that particle-B1 and particle-B2 float and sink in water, respectively. After 2 h and 24 h, the particle proppant still maintains its original distribution state.

[0120] Figure 13 Shows the dynamic distribution of particle-P1 in water, Figure 14 The static distribution state of particles-P1 in water is demonstrated. Since their density is close to that of water, they can remain stable at any position in the water. In the absence of external interference, they remain stable on the water surface, but when disturbed or collided, they will accelerate down until reaching equilibrium.

[0121] Figure 15The water stability of wood chips after being treated at 90 °C for 2 h was demonstrated. After hydrophobic modification, 85% of the hydrophobic wood chips - PSBT1 could ensure floating on the water surface, while only 13% of the hydrophilic wood chips - EP1 floated on the water surface, that is, 87% of the hydrophilic wood chips - EP1 still settled stably to the bottom.

[0122] Figure 16 $\mu_{w}$ and $\mu_{s}$ are the viscosities of clear water and the wood chip fracturing fluid, respectively. It can be seen that after adding the wood chip proppant, the viscosity of water is not affected much. The viscosity of the fracturing fluid with hydrophilic wood chips - EP1 is 0.95 mPa·s, and the viscosity of the fracturing fluid with hydrophobic wood chips - PSBT1 is 1.46 mPa·s.

[0123] (8)Evaluation of proppant migration performance The low density, small size, specific wettability and water stability of the wood - based proppant ensure the long - distance transmission and uniform laying of the proppant.

[0124] Figure 17 It shows that the particulate proppants prepared in Examples 1 - 3 are mainly laid at the top, middle and bottom of the fracture respectively due to their hydrophobicity and different densities. However, not all proppants can maintain their theoretical positions; Particulate - B1 and Particulate - B2 are mainly distributed at the top and bottom, and Particulate - P1 is more evenly distributed. This non - uniform distribution is due to the rough fracture wall hindering the movement of the proppant. These characteristics indicate that multi - density particulate proppants can be effectively used in hydraulic fracturing with only water as the fracturing fluid. The hydrophobicity of the particles enables them to float and suspend in the fluid and enter the far field with the fluid. This can maximize the support area of the fracture and improve the oil and gas recovery rate.

[0125] Figure 18 It shows the dynamic migration distribution of wood chip proppants in fractures with a width of 3 mm and 1.5 mm. In the 3 - mm main fracture, the hydrophobic wood chips - PSBT1 are mainly concentrated in the upper layer region, and the hydrophilic wood chips - EP1 mainly settle in the lower layer region. Due to the hindrance of the rough fracture wall, some wood chips form a random distribution. Affected by the comprehensive influence of the hydrophilicity and low density of the hydrophilic wood chips - EP1, the hydrophilic wood chips - EP1 have a greater spatial dispersion than the hydrophobic wood chips - PSBT1. When injecting a mixture of wood chips into the fracture, the hydrophobic wood chips - PSBT1 are mainly located at the top of the fracture, and the hydrophilic wood chips - EP1 are mainly located at the bottom of the fracture, and some of the hydrophilic wood chips - EP1 are carried to the top and middle of the fracture by the hydrophobic wood chips - PSBT1.

[0126] (9)Evaluation of proppant acid - resistance performance Note: In the translation of item , $\mu_{w}$ and $\mu_{s}$ are assumed to be the viscosities of clear water and the wood chip fracturing fluid respectively, which are not clearly defined in the original text but are necessary for a complete and accurate translation of the sentence.Another key factor in evaluating proppant stability is acid solubility, which refers to the degree of dissolution of proppants in an acidic environment. Chemical substances present in the wellbore and surrounding formations can corrode and degrade proppants, leading to problems such as decreased proppant performance and fracture closure, ultimately affecting oil and gas production. Therefore, acid solubility has become a key indicator of proppant stability in acidic media. Most importantly, proppants do not react chemically with fracturing fluids and reservoir fluids, and the maximum allowable acid solubility is less than 7%. These criteria ensure the stability and acid resistance of proppants under downhole conditions, thus promoting efficient oil production.

[0127] Figure 19 It is shown that only 17 kg to 25 kg of silicone oil is required for every ton of particulate proppant produced. These silicone oil coatings can ensure the isolation of proppants from water-based fracturing fluids, thus minimizing dissolution and swelling in an acidic environment.

[0128] Figure 20 The acid solubilities of the particulate proppants prepared in Examples 1 to 3, commercial quartz sand, and ceramic proppants are shown. In a 10 wt% hydrochloric acid solution, the acid solubilities of the particulate proppants were evaluated under simulated external closure pressures of 91.6 MPa, 120.2 MPa, and 145.2 MPa. The acid solubilities of these proppants are very low. The acid solubilities of Granule-B1, Granule-P1, and Granule-B2 are 1.39%, 1.76%, and 1.28% respectively, which are lower than the standard acid solubility of commercial proppants.

[0129] Figure 21 The size statistics of the particulate proppants after acid dissolution tests are shown. There is no obvious change in the particle size, and the degrees of size reduction and swelling do not exceed 3% and 16% respectively. The hydrophobic coating and the stable components of the wood protect the multi-density particulate proppants from acidic conditions, and the slight deformation and dissolution are not sufficient to affect the performance of the particulate proppants.

[0130] Figure 22 The acid solubilities of wood chip proppants in a 10% hydrochloric acid solution at 65°C are shown. The acid solubilities of the hydrophobic wood chip-PSBT1 and the hydrophilic wood chip-EP1 are relatively low, 8.15% and 6.52% respectively, ensuring the chemical stability of the wood chip piles during the propping process.

[0131] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they learn the basic creative concepts. Therefore, the appended claims are intended to be construed as including the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

[0132] Obviously, those skilled in the art can make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims

1. A wood-based proppant, characterized in that, The wood-based proppant is at least two of granular proppants, hydrophobic wood chips proppants and hydrophilic wood chips proppants prepared from wood; according to different densities, the wood-based proppants present floating, suspended and sedimentation states in the fracturing fluid, support different height areas in the fracture, and form oil and gas flow channels in the fracture; The granular proppant is obtained by successively subjecting natural wood to delignification treatment, densification treatment, cutting and hydrophobic treatment; The hydrophobic wood chips proppant is obtained by crushing wood raw materials and then performing delignification treatment and hydrophobic treatment; The hydrophilic wood chips proppant is obtained by crushing wood raw materials and then performing hydrophilic treatment.

2. A preparation method of the wood-based proppant according to claim 1, characterized in that, The preparation of the granular proppant includes the following steps: Subject natural wood to delignification treatment to obtain delignified wood; Mechanically hot-press the delignified wood at 1.4 MPa to 10 MPa and 70 °C to 100 °C, and obtain dense wood after sufficient drying; Perform cutting treatment on the dense wood to obtain dense wood particles; Perform hydrophobic treatment on the dense wood particles at room temperature to obtain a granular proppant.

3. According to the preparation method of the wood-based proppant according to claim 2, characterized in that, The mechanical hot-pressing time is 8 h to 12 h.

4. According to the preparation method of the wood-based proppant according to claim 2, characterized in that, The cutting treatment is carried out by a laser cutting machine or a micro-lathe; The cutting parameters of the laser cutting machine are that the laser power is 13 W to 24 W, the cutting speed is 25 mm / min to 30 mm / min, and the cutting size is 1300 μm to 1500 μm; The cutting parameters of the micro-lathe are that the spindle speed is 1000 r / min and the cutting size is 1200 μm.

5. A preparation method of the wood-based proppant according to claim 1, characterized in that, The preparation of the hydrophobic wood chips proppant includes the following steps: Crush wood raw materials to obtain original wood chips; Perform delignification treatment on the original wood chips to obtain delignified wood chips; Perform hydrophobic treatment on the delignified wood chips at room temperature to obtain a hydrophobic wood chips proppant.

6. According to the preparation method of the wood-based proppant according to claim 2 or 5, characterized in that, The hydrophobic treatment methods of the granular proppant and the hydrophobic wood chips proppant are the same; When performing hydrophobic treatment, the solutes used in the hydrophobic solution are dimethyl silicone oil, polydimethylsiloxane, perfluorooctanoic acid or octadecylamine; the solvents are tetraethyl orthosilicate, acetone, chloroform or ether; The reaction time of the hydrophobic treatment is 0.5 h to 2 h; The mass concentration of the hydrophobic solution is 0.5% to 3%; The mass ratio of wood to the hydrophobic solution is 1:30 to 70, and the wood is dense wood particles or delignified wood chips.

7. According to the preparation method of the wood-based proppant according to claim 2 or 5, characterized in that, The delignification treatment methods of the granular proppant and the hydrophobic wood chips proppant are the same; The delignification treatment methods are sodium chlorite method, alkaline sodium sulfite method, hydrogen peroxide method or deep eutectic solvent method.

8. According to the preparation method of the wood-based proppant according to claim 7, characterized in that, The treatment method of the sodium chlorite method is: put the wood into an acetic acid / sodium chlorite aqueous solution and react at 80 °C to obtain a delignified product. Among them, the mass ratio of the wood to the acetic acid / sodium chlorite aqueous solution is 1:70; in the acetic acid / sodium chlorite aqueous solution, the mass concentration of the acetic acid solution is 0.1%, the mass concentration of the sodium chlorite solution is 4%, and the mass ratio of the acetic acid solution to the sodium chlorite solution is 1:4; The treatment method of the alkaline sodium sulfite method is as follows: put the wood into an aqueous solution of sodium hydroxide / sodium sulfite, and react at 120 °C to obtain a delignified product; among them, the mass ratio of the wood to sodium hydroxide / sodium sulfite is 1:50, the mass concentration of the sodium hydroxide solution is 1%, the mass concentration of the sodium sulfite solution is 4%, and the mass ratio of the sodium hydroxide solution to the sodium sulfite solution is 1:2; The treatment method of the hydrogen peroxide method is as follows: put the wood into an aqueous solution of alkaline hydrogen peroxide and react at 90 °C to obtain a delignified product; among them, the mass ratio of the wood to the aqueous solution of alkaline hydrogen peroxide is 1:60, the mass concentration of hydrogen peroxide is 8%, the mass concentration of the base is 1%, and the base in the aqueous solution of alkaline hydrogen peroxide is ammonia water; The treatment method of the deep eutectic solvent method is as follows: mix the hydrogen bond acceptor and the hydrogen bond donor evenly to obtain a deep eutectic solvent, and then put the wood into the deep eutectic solvent composed of the hydrogen bond acceptor and the hydrogen bond donor, and react at 100 °C to obtain a delignified product; among them, the mass ratio of the wood to the deep eutectic solvent is 1:30, the hydrogen bond acceptor is choline chloride; the hydrogen bond donor is ethylene glycol; The wood is natural wood or wood raw material.

9. The preparation method of the wood-based proppant according to claim 1, characterized in that, The preparation of the hydrophilic wood chip support agent includes the following steps: Crush the wood raw material to obtain the original wood chips; Add the original wood chips to an oil solution for hydrophilic treatment to obtain a hydrophilic wood chip support agent.

10. The preparation method of the wood-based proppant according to claim 9, characterized in that, The oil solution is a combination of soybean oil, palm oil and corn oil; The reaction temperature for the hydrophilic treatment is 220 °C, the reaction time is 3 h, and the mass ratio of the original wood chips to the solvent is 1:100.

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