A wood-based proppant and preparation method thereof

Abstract

The present 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 present invention is at least two of granular proppant, hydrophobic sawdust proppant and hydrophilic sawdust proppant prepared from wood as raw material; the wood-based proppant presents a floating, suspended and sedimentation state in the fracturing fluid according to the difference in density, supports areas of different heights in the crack, and forms an oil and gas flow channel in the crack; the granular proppant is obtained by subjecting natural wood to delignification treatment, densification treatment, cutting and hydrophobic treatment in sequence; the hydrophobic sawdust proppant is obtained by subjecting the wood raw material to crushing treatment, delignification treatment and hydrophobic treatment. The hydrophilic sawdust proppant is obtained by subjecting the wood raw material to crushing treatment, and then subjecting it to hydrophilic treatment. The wood-based proppant provided by the present invention has low density, high strength, low cost, and does not produce powder residue when crushed.

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 keeping fractures open and promoting efficient oil and gas flow. Traditional proppants, such as quartz sand and ceramsite, have very high bulk densities, generally exceeding 1.49 g / cm³, requiring the use of high-viscosity fracturing fluids to slow proppant settling during transport. However, high-viscosity fracturing fluids are often associated with issues such as fracturing costs and production efficiency. Although low-viscosity fracturing fluids have been proposed as an alternative, this can lead to significant proppant settling near the wellbore, resulting in low proppant transport efficiency and even sand production under high proppant loading conditions. Therefore, developing proppants that are compatible with low-viscosity fracturing fluids and can be efficiently transported and deployed is crucial for advancing unconventional reservoir fracturing technology.

[0003] Self-suspending proppants are a type of proppant material that spontaneously suspends in fracturing fluids, effectively reducing proppant sedimentation and providing an ideal solution for low-viscosity sand-carrying systems. Self-suspending properties are typically achieved by coating conventional proppants with polymeric materials or by designing them into hollow cores to reduce proppant density. However, under formation closure stress, the coating or matrix of the self-suspending proppant, when broken down, can clog fractures and impair reservoir conductivity. Complex preparation processes and high costs 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 low density, high strength, low cost, and does not produce powder residue when crushed.

[0005] The first object of the present invention is to provide a wood-based proppant, which is at least two of a granular proppant, a hydrophobic wood chip proppant, and a hydrophilic wood chip proppant prepared from wood as raw material; the wood-based proppant floats, suspends, and settles in the fracturing fluid depending on its density, supporting areas of different heights within the fracture, forming oil and gas flow channels in the fracture.

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

[0007] The natural wood is one or more combinations of basswood, poplar, pine, elm, beech, paulownia, oak, cherry, rosewood, fir, nanmu, and camphor wood.

[0008] The hydrophobic wood chip proppant is obtained by crushing the wood raw material, performing delignification treatment and hydrophobic treatment.

[0009] The hydrophilic wood chip proppant is obtained by crushing the wood raw material and then performing a hydrophilic 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, particle board, fiberboard, wood chip board and composite board.

[0011] The wood residues are one or more combinations of bark, roots, shredded veneer, sawn timber ends, shavings, sawdust, and scraps.

[0012] The wood-based proppant of the present invention can be transported to a designated location within a fracture solely under the action of water, without the need to add a thickener to the sand-carrying fluid; the granular proppant can maintain structural integrity under the closure stress of the formation without producing powder residue, thereby reducing the risk of sand blockage during oil and gas production; the granular proppant is prepared and regulated by hot pressing based on the porous structure of natural block wood to obtain granular proppant of different densities. The sawdust-like proppant is compressed in situ under the closure stress of the formation to form a support pile. The wood-based proppant has excellent migration performance, which enables long-distance transport of the wood-based proppant in the fracture and a relatively large laying area, and can form oil and gas channels with high conductivity coefficients in the fracture.

[0013] The second object of the present invention is to provide a method for preparing the above-mentioned wood-based proppant. The preparation of the granular proppant comprises the following steps:

[0014] Delignified wood is obtained by delignifying natural wood.

[0015] The delignified wood is mechanically hot-pressed at 1.4 MPa ~ 10 MPa and 70 ℃ ~ 100 ℃, and then fully dried to obtain dense wood.

[0016] The densified wood is cut to obtain the densified wood particles.

[0017] Densified wood particles were hydrophobically treated at room temperature to obtain particle proppants.

[0018] In a preferred embodiment of the present invention, the mechanical hot pressing time is 8 hours to 12 hours.

[0019] In a preferred embodiment of the present invention, the cutting process is performed using a laser cutting machine or a micro lathe.

[0020] The cutting parameters of the laser cutting machine are as follows: laser power of 13W~24W, cutting speed of 25mm / min~30mm / min, and cutting size of 1300μm~1500μm.

[0021] The cutting parameters of the micro lathe are: spindle speed of 1000 r / min, and cutting size of 1200 μm.

[0022] The third object of the present invention is to provide a method for preparing the above-mentioned wood-based proppant. The preparation of the hydrophobic sawdust proppant comprises the following steps:

[0023] The wood raw materials are crushed to obtain raw wood chips.

[0024] The original sawdust is subjected to delignification treatment to obtain delignified sawdust.

[0025] The delignified sawdust was hydrophobized at room temperature to obtain a hydrophobic sawdust proppant.

[0026] When wood raw materials are crushed, for natural wood and engineered wood, a cutting crusher is directly used for mechanical crushing.

[0027] For wood residues, they are first screened and the parts that do not pass through the screen are mechanically crushed using a cutting crusher.

[0028] The size of the screen during screening is 1 mm.

[0029] In a preferred embodiment of the present invention, the hydrophobic treatment method of the granular proppant and the hydrophobic sawdust proppant is the same.

[0030] During the hydrophobic treatment, the solute used in the hydrophobic solution is dimethyl silicone oil, polydimethylsiloxane, perfluorooctanoic acid or octadecylamine; the solvent is tetraethyl silicate, acetone, chloroform or ether.

[0031] The reaction time of the hydrophobic treatment is 0.5h~2h.

[0032] The mass concentration of the hydrophobic solution is 0.5%~3%.

[0033] The mass ratio of the wood to the hydrophobic solution is 1:30-70, and the wood is dense wood particles or delignified wood chips.

[0034] In a preferred embodiment of the present invention, the delignification treatment method of the granular proppant and the hydrophobic wood chip proppant is the same.

[0035] The delignification treatment method is sodium chlorite method, alkaline sodium sulfite method, hydrogen peroxide method or deep eutectic solvent method.

[0036] In a preferred embodiment of the present invention, the sodium chlorite treatment method is as follows: placing wood in an acetic acid / sodium chlorite aqueous solution and reacting at 80° C. to obtain a delignified product, wherein 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.

[0037] The treatment method of the alkaline sodium sulfite method is: placing the wood in a sodium hydroxide / sodium sulfite aqueous solution and reacting at 120°C to obtain a delignified product; wherein 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.

[0038] The hydrogen peroxide treatment method is as follows: the wood is placed in an alkaline hydrogen peroxide aqueous solution and reacted at 90°C to obtain a delignified product; wherein 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 alkali is 1%, and the alkali in the alkaline hydrogen peroxide aqueous solution is ammonia water.

[0039] The treatment method of the deep eutectic solvent method is: a hydrogen bond acceptor and a hydrogen bond donor are mixed evenly to obtain a deep eutectic solvent, and then the wood is placed in 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; wherein, the mass ratio of wood to the deep eutectic solvent is 1:30, the hydrogen bond acceptor is choline chloride, and the hydrogen bond donor is ethylene glycol.

[0040] The wood material is natural wood or wood raw material.

[0041] A fourth object of the present invention is to provide a method for preparing the above-mentioned wood-based proppant. The preparation of the hydrophilic sawdust proppant comprises the following steps:

[0042] The wood raw materials are crushed to obtain raw wood chips.

[0043] The original sawdust is added into the solution for hydrophilic treatment to obtain a hydrophilic sawdust proppant.

[0044] 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.

[0045] The reaction temperature of the hydrophilic treatment was 220 °C, the reaction time was 3 h, and the mass ratio of the original sawdust to the solvent was 1:100.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] The present invention uses wood as raw material to effectively reduce the preparation cost, and based on the characteristics of wood being light in weight and having orderly fiber arrangement, the main chemical components of the processed wood are cellulose, etc.; for the granular proppant, the wood can be softened after delignification treatment, so that it can be compressed to form densified wood. At this time, the wood pores collapse and the wood fibers are closely arranged. This dense physical structure and the chemical components of delignified wood fibers give the granular proppant the characteristics of low density, high strength and no powder and slag generation; for the wood chip proppant, since it has not been densified, it itself has low density. After the treated wood chips enter the formation cracks, they can be pressed into piles under the action of the formation closing stress, thereby showing high strength.

[0048] The advantages of the wood-based proppant prepared by the present invention are as follows:

[0049] (1) The wood-based proppant of the present invention has high compressive strength, which is as high as 145.2 MPa. The wettability of the wood-based support can be customized according to needs, such as hydrophilicity and hydrophobicity. The density range is 0.16 g / cm³~1.27 g / cm³. It has the characteristics of low density and high compressive strength. It is 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.

[0050] (2) The granular proppant of the present invention has three different density ranges: less than 1.00 g / cm³, approximately equal to 1.00 g / cm³, and greater than 1.00 g / cm³. It can spontaneously float, suspend, and settle in the fracturing fluid, and is laid at the top, middle, and bottom of the fracture, respectively. This discrete distribution maximizes the proppant laying height, forming high-conductivity oil and gas channels in the fracture.

[0051] (3) The wood chip proppant of the present invention is a low-density wood chip proppant with different wettability injected into the fracture. The hydrophobic wood chip proppant floats on the top of the fracture, while the hydrophilic wood chip proppant sinks to the bottom of the fracture. Under the action of formation closure stress, the wood chip proppant aggregates are compressed in situ to form support piles, thereby keeping the fracture open and creating a wide flow channel for oil and gas. Depending on the requirements of the proppant, the density of the wood-based proppant is controlled by the synergistic effect of different woods and hot pressing processes during preparation.

[0052] (4) The wood-based proppant of the present invention is different from traditional proppant such as quartz sand. This type of proppant can maintain structural integrity under the action of formation closure stress and does not produce powder residue, thereby preventing the risk of backflow and sand blockage during oil and gas production. The low density of the proppant is also conducive to the long-distance transmission of the proppant in the fracture and a larger laying area, and has good application prospects in unconventional reservoir fracturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 The processing pressure and density curves of particle-B1, particle-P1 and particle-B2.

[0054] Figure 2 Density plots of commercial quartz sand and sawdust after different treatments.

[0055] Figure 3 The compressive strength diagram of particle-B1, particle-P1 and particle-B2.

[0056] Figure 4 Figure 2 is the compressive strength diagram of support piles made of hydrophobic sawdust-PSBT1, hydrophilic sawdust-EP1, and mixed sawdust-PSBT1 / EP1.

[0057] Figure 5 The wettability diagrams for the densities of dense wood-B1 and particles-B1.

[0058] Figure 6 Figure 3 is the wettability diagram of the hydrophobic sawdust-PSBT1 and hydrophilic sawdust-EP1 support piles, where a is the wetting angle diagram of the hydrophobic sawdust-PSBT1 support pile, b is the wetting angle diagram of the hydrophilic sawdust-EP1 support pile, c is the distribution diagram of the hydrophobic sawdust-PSBT1 in water, and d is the distribution diagram of the hydrophilic sawdust-EP1 in water.

[0059] Figure 7 This is the size distribution diagram before and after the quartz sand crushing experiment.

[0060] Figure 8 This is the size distribution diagram before and after the ceramsite crushing experiment.

[0061] Figure 9 The size distribution diagram of particles B1, particles P1 and particles B2 before and after the crushing experiment.

[0062] Figure 10 Photos of commercial quartz sand, expanded clay, and particles B1, P1, and B2 before and after crushing, as well as a graph showing the crushing rates.

[0063] Figure 11 The size distribution of sawdust.

[0064] Figure 12 The water stability diagram of particles-B1 and particles-B2, where a is 0h, b is 2h, and c is 24h.

[0065] Figure 13 is the dynamic water stability diagram of particle-P1, where a is the equilibrium state diagram floating on the water surface, b is the imbalance state diagram subjected to downward force, and c is the equilibrium state diagram sinking to the bottom of the water.

[0066] Figure 14is the static water stability diagram of particle-P1, where a1 is the state diagram of particle-P1 floating on the water surface for 0 h, a2 is the state diagram of particle-P1 floating on the water surface for 2 h, a3 is the state diagram of particle-P1 floating on the water surface for 24 h, b1 is the state diagram of particle-P1 sinking to the water bottom for 0 h, b2 is the state diagram of particle-P1 sinking to the water bottom for 2 h, and b3 is the state diagram of particle-P1 sinking to the water bottom for 24 h.

[0067] Figure 15 The water stability diagram of hydrophobic sawdust-PSBT1 and hydrophilic sawdust-EP1.

[0068] Figure 16 Viscosity diagram of water, hydrophobic sawdust-PSBT1 and hydrophilic sawdust-EP1 fracturing fluid.

[0069] Figure 17 Figure 2 is a static sedimentation performance diagram of different wood-based proppants, where a is particle-B1, b is particle-P1, and c is particle-B2.

[0070] Figure 18 Figure 3 is the dynamic migration performance diagram of hydrophobic sawdust-PSBT1, hydrophilic sawdust-EP1 and mixed sawdust-PSBT1 / EP1, where a1 is the state diagram of hydrophobic sawdust-PSBT1 in 3 mm crack, a2 is the state diagram of hydrophobic sawdust-PSBT1 in 1.5 mm crack, b1 is the state diagram of hydrophilic sawdust-EP1 in 3 mm crack, b2 is the state diagram of hydrophilic sawdust-EP1 in 1.5 mm crack, c1 is the state diagram of mixed sawdust-PSBT1 / EP1 in 3 mm crack, and c2 is the state diagram of mixed sawdust-PSBT1 / EP1 in 1.5 mm crack.

[0071] Figure 19 Graph showing the silicone oil modification amount of particles B1, P1, and B2.

[0072] Figure 20 Figure 2 shows the acid solubility of Particle-B1, Particle-P1, and Particle-B2, as well as the standard acid solubility of commercial quartz sand and ceramic proppants.

[0073] Figure 21 Statistical diagram of the sizes of particles B1, P1 and B2 before and after acid treatment, where a is before acid treatment and b is after acid treatment.

[0074] Figure 22 Acid solubility diagram of hydrophobic sawdust-PSBT1 and hydrophilic sawdust-EP1. DETAILED DESCRIPTION

[0075] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0076] Example 1

[0077] This embodiment provides a method for preparing a wood-based proppant. The prepared proppant is a granular proppant, the wood raw material is basswood, the delignification method is an alkaline sodium sulfite method, and mechanical cutting is performed using a laser cutting machine. The specific steps are as follows.

[0078] Step 1. Place natural basswood in a sodium hydroxide / sodium sulfite solution, wherein the mass ratio of natural basswood to the sodium hydroxide / sodium sulfite solution is 1:50, the mass concentration of sodium hydroxide in the sodium hydroxide / sodium sulfite solution is 1%, the mass concentration of sodium sulfite is 4%, and the mass ratio of the sodium hydroxide solution to the sodium sulfite solution is 1:2. Treat at 120° C. for 3 hours, and then wash with deionized water until neutral; obtain delignified wood.

[0079] 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.

[0080] Step 3: The dense wood was laser cut with a laser power of 24 W, a cutting speed of 30 mm / min, and a cutting size of 1500 μm to obtain dense wood particles with a size of 1120-1629 μm.

[0081] Step 4: Perform hydrophobic modification on the dense wood particles at room temperature. Place the dense wood particles in a dimethyl silicone oil / acetone solution with a mass concentration of 2% and a mass ratio of the dense wood particles to the dimethyl silicone oil / acetone solution of 1:40. React at 600 r / min for 1 h, and then fully dry at 60 °C to obtain a particle proppant.

[0082] Example 2

[0083] This embodiment provides a method for preparing 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 performed using a laser cutting machine. The specific steps are as follows.

[0084] Step 1. Place natural poplar wood in an acetic acid / sodium chlorite aqueous solution, wherein the mass ratio of natural poplar wood to the acetic acid / sodium chlorite aqueous solution is 1:70, the mass concentration of acetic acid in the acetic acid / sodium chlorite aqueous solution is 0.1%, the mass concentration of sodium chlorite is 4%, and the mass ratio of the acetic acid solution to the sodium chlorite solution is 1:4. The mixture is treated at 80° C. for 6 hours, and then washed with deionized water until neutral; thereby obtaining delignified wood.

[0085] Step 2: Mechanically hot-press the delignified wood at 2.9 MPa and 70° C. for 12 hours, and obtain dense wood after sufficient drying.

[0086] Step 3: The dense wood is subjected to laser cutting with a laser power of 13 W, a cutting speed of 25 mm / min, and a cutting size of 1300 μm, to obtain dense wood particles with a size of 980 μm to 1560 μm.

[0087] Step 4: Perform hydrophobic modification on the dense wood particles at room temperature, place the dense wood particles in a polydimethylsilane / ether solution, the mass concentration of polydimethylsilane in the ether solution is 0.5%, the mass ratio of the dense wood particles to the polydimethylsilane / ether solution is 1:30, react at 100 r / min for 0.5 h, and then fully dry at 80°C to obtain a particle proppant.

[0088] Example 3

[0089] This embodiment provides a method for preparing a wood-based proppant. The prepared proppant is a granular proppant, the wood raw material is beech, the delignification method is a hydrogen peroxide method, and the mechanical cutting is performed using a micro lathe. The specific steps are as follows.

[0090] Step 1. Place natural beech wood in an ammonia / hydrogen peroxide aqueous solution, wherein the mass ratio of natural beech wood to the ammonia / hydrogen peroxide aqueous solution is 1:60, and the mass concentration of ammonia water and hydrogen peroxide in the ammonia / hydrogen peroxide aqueous solution is 1%, and the mass concentration of hydrogen peroxide is 8%. Treat the wood at 90° C. for 4 h, and then wash the wood with deionized water until the wood is neutral. Delignified wood is obtained.

[0091] Step 2: Mechanically hot-press the delignified wood at 10 MPa and 75° C. for 10 h, and obtain densified wood after sufficient drying.

[0092] Step 3: The dense wood is cut using a micro lathe with a spindle speed of 1000 r / min and a cutting size of 1200 μm to obtain dense wood particles with a size of 1080-1510 μm.

[0093] Step 4: Perform hydrophobic modification on the dense wood particles at room temperature, place the dense wood particles in 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 at 100 r / min for 0.5 h, and then fully dry at 40°C to obtain a particle proppant.

[0094] Example 4

[0095] This embodiment provides a method for preparing a wood-based proppant. The prepared proppant is a hydrophobic sawdust proppant, the wood raw materials are elm and pine, and the delignification method is a deep eutectic solvent method. The specific steps are as follows.

[0096] Step 1: Use a cutting crusher to directly crush the elm and pine wood, and pass through a 1mm sieve to obtain original wood chips.

[0097] Step 2: Choline chloride and ethylene glycol are mixed at a molar ratio of 1:1 at 80°C for 30 minutes to obtain a low eutectic solvent, and the original sawdust is placed in the low eutectic solvent at a mass ratio of 1:30. The mixture is reacted at 100°C for 1 hour, and then washed with deionized water to remove residual reagents. The delignified sawdust is obtained after drying.

[0098] Step 3: Perform hydrophobic modification on the delignified sawdust at room temperature, place the delignified sawdust in an octadecylamine / tetraethyl silicate solution, the mass concentration of octadecylamine in the tetraethyl silicate solution is 3%, the mass ratio of the delignified sawdust to the octadecylamine / tetraethyl silicate solution is 1:70, react at 1000 r / min for 2 hours, and then fully dry at 30°C to obtain a hydrophobic sawdust proppant.

[0099] Example 5

[0100] This embodiment provides a method for preparing a proppant. The prepared proppant is a hydrophilic sawdust proppant, and the wood raw materials are plywood, wood shavings, bark, and sawn timber ends. The specific steps are as follows.

[0101] Step 1: Screen the wood raw materials, and screen the particleboard, bark and sawn timber ends. The parts that do not pass through the screen are crushed together with the plywood using a cutting crusher. The crushed wood chips are mixed with the parts that pass through the screen to obtain original wood chips.

[0102] Step 2: Place the original sawdust in mixed oil and heat treat it at 220°C for 3 hours. The mass ratio of the original sawdust to the mixed oil is 1:100. The mixed oil is composed of palm oil, soybean oil and corn oil in a mass ratio of 1:1:4. Then filter the sawdust with a 100-mesh sieve until the excess oil is drained to obtain a hydrophilic sawdust support.

[0103] It should be noted that in the 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.

[0104] Densified wood-B1 refers to the product prepared in step 2 of Example 1.

[0105] The hydrophobic sawdust-PSBT1 corresponds to the hydrophobic sawdust proppant prepared in Example 4.

[0106] The hydrophilic sawdust-EP1 corresponds to the hydrophobic sawdust proppant prepared in Example 5.

[0107] In the following test data, the original sawdust refers to the product prepared in step 1 of Example 4, and the delignified sawdust refers to the product prepared in step 2 of Example 4.

[0108] The unit ppa in the present invention means pounds per gallon.

[0109] The wood-based proppant prepared by the present invention is subjected to characterization tests.

[0110] (1) Proppant water stability test

[0111] Water stability test of granular proppant: dry granular proppant was placed in water, left to stand at room temperature for 2 hours and 24 hours, and the distribution position of the granular proppant was observed.

[0112] Water stability test of sawdust proppant: 5.0 g of dry hydrophilic and hydrophobic sawdust proppant were placed in water and stirred at 90°C for 1 hour to test their water stability. After stabilization, the sawdust proppant floating on the water surface was collected, dried, and weighed.

[0113] (2) Viscosity test

[0114] The viscosity of the wood chip proppant / water mixture was measured at room temperature using a rotational viscometer. The viscosity test was performed using a No. 0 spindle at a speed of 6 rpm. The wood chip proppant addition level was 0.25 ppa.

[0115] (3) Compression test

[0116] The crushing resistance of quartz sand, ceramsite, and granular proppants was tested. 5 g of granular proppant was placed in a 60 mm × 30 mm mold and a force was applied continuously for 2 minutes. The crushed granular proppant was sieved through a 150-mesh vibrating screen for 10 minutes. The resulting oversize particles and undersize powder were collected and weighed. The test pressures of the granular proppant were 91.6, 120.2, and 145.2 MPa, respectively. Quartz sand and ceramsite were tested at 91.6 MPa. The sieve sizes of quartz sand and ceramsite were 40 / 70 mesh and 20 / 40 mesh, respectively.

[0117] (4) Acid solubility test

[0118] The granular proppant was immersed in a hydrochloric acid solution with a mass concentration of 10% for 30 min under external pressures of 91.6 MPa, 120.2 MPa, and 145.2 MPa, respectively.

[0119] The sawdust proppant was soaked in a hydrochloric acid solution at 65°C for 30 min. The acid-treated sample was washed with water until neutral and then completely dried in an oven at 60°C overnight.

[0120] The initial mass is m0, the final mass is m1, and the acid solubility is calculated as (m0-m1) / m0.

[0121] (5) Proppant transport and settlement test

[0122] The static settling characteristics of granular proppant were tested using a transport device with dimensions of 240 mm × 190 mm × 1.5 mm.

[0123] The dynamic transport characteristics of sawdust proppant were tested using a transport device with a size of 700mm×200mm×1.5mm~3.0mm and a peristaltic pump.

[0124] The sand-carrying fluid was pumped at an injection velocity of 10 cm / s. The addition rate of wood-based proppant was 0.25 ppa, and the sand-carrying fluid consisted only of water and wood-based proppant.

[0125] (6) Evaluation of proppant density, morphology, size, compressive strength and wettability

[0126] The low density, high compressive strength and specific wettability of wood-based proppants ensure that the proppants are effectively transported to the designated location in the fracture only under the action of water and provide support. Unlike 40 / 70 mesh commercial quartz sand and 20 / 40 mesh ceramsite proppants, wood-based proppants can maintain structural integrity under closure stress and do not produce powder residue, thereby reducing the risk of backflow and sand blockage during oil and gas production.

[0127] from Figure 1 and Figure 2It can be seen that the density of the granular proppant prepared in Examples 1 to 3 is 0.83 g / cm 3 ~1.27g / cm 3 The density of the sawdust proppant prepared in Example 4 is 0.16 g / cm 3 , which is much lower than 40 / 70 mesh commercial quartz sand. The low density can effectively alleviate the sedimentation of the proppant during transportation and reduce the dependence of the proppant on the viscosity of the fracturing fluid.

[0128] Figure 3 The compressive strength of the granular proppants prepared in Examples 1 to 3 is as follows: as the density increases, the compressive strength of the granular proppants along the longitudinal, radial and tangential directions of the wood increases, and the strength ranges from 19.1 MPa to 144.4 MPa.

[0129] Figure 4 For the compressive strength of sawdust proppant, it should be noted that after the sawdust proppant enters the crack, it can be compressed into piles under the action of the formation closing stress. The dense sawdust pile can provide support strength. Figure 4 It can be seen that the hydrophilic sawdust-EP1 prepared in Example 5, the hydrophobic sawdust-PSBT1 prepared in Example 4, and the mixed sawdust-PSBT1 / EP1 obtained by mixing the hydrophilic sawdust-EP1 prepared in Example 5 and the hydrophobic sawdust-PSBT1 prepared in Example 4 in 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 sawdust proppant, the high temperature causes the hemicellulose components of the wood to be broken down into small fragments of active substances, which interact with the oils and form a gel under the conditions of a high temperature of 100°C and a compression of 35MPa~105MPa simulating the formation. The hydrophilic sawdust-EP1 support pile shows the highest strength, with a strength range of 65.3MPa~95.1MPa, while the opposite wettability of the sawdust makes the mixed sawdust-PSBT1 / EP1 support pile have the lowest strength, with a strength range of 51.3MPa~57.0MPa. It should be noted that, Figure 4 The medium processing pressures of 4.1MPa, 8.2MPa and 12.3MPa refer to the instrument input processing pressure for the support pile press preparation in the laboratory. After conversion and calculation of the actual force-bearing area of ​​the support pile processing mold, the actual force on the support pile surface is 35MPa, 75MPa and 105MPa. This pressure simulates the closure stress of the formation.

[0130] Figure 5The wettability of the dense wood of Example 1 before and after hydrophobic modification is demonstrated. It can be seen that after the hydrophobic modification, the wood surface is converted from hydrophilic to hydrophobic. Therefore, the modified particle proppant can maintain a water-repellent state in water, thereby maintaining a stable density. Particles-B1, Particles-P1, and Particles-B2 can respectively remain floating, suspended, and settled in water, thereby simultaneously supporting the top, middle, and bottom of the crack, forming an oil and gas flow channel with a high conductivity coefficient.

[0131] Figure 6 The wettability of the sawdust piles and the distribution of the sawdust proppant in water were demonstrated. The hydrophobic sawdust-PSBT1 proppant exhibited a large hydrophobic angle of 128.5°, with the hydrophobic sawdust-PSBT1 completely floating on the water surface. The hydrophilic sawdust-EP1 proppant had a water contact angle of 71.0°, with the hydrophilic sawdust-EP1 mostly sinking to the bottom. This ensured that the two sawdust proppants were independently distributed at the top and bottom, forming top and bottom proppant zones, thereby creating a large central oil and gas flow channel.

[0132] Figure 7 、 Figure 8 and Figure 9 The sizes of the commercial quartz sand proppant with a mesh size of 40 / 70, the commercial ceramsite proppant with a mesh size of 20 / 40, and the granular 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 ceramsite all 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.

[0133] Figure 11 From the size statistics of sawdust, it can be seen that the original sawdust has almost no effect on its size after delignification treatment, and its distribution range is 0.68μm~1620μm. After oil-heat treatment, the hemicellulose in the sawdust is cracked, which has an impact on the sawdust size. The sawdust size is reduced to a distribution range of 0.68μm~700μm. Small-sized sawdust proppants can enter narrower cracks and improve the proppant laying effect.

[0134] (7) Evaluation of proppant water stability

[0135] 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.

[0136] Figure 12 It shows that particles-B1 and particles-B2 float and sink in water, respectively. After 2 h and 24 h, the particle proppant still maintains its original distribution state.

[0137] Figure 13 Shows the dynamic distribution of particles-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 they reach equilibrium.

[0138] Figure 15 The water stability of sawdust after being treated at 90°C for 2 hours was demonstrated. 85% of the hydrophobic sawdust-PSBT1 after hydrophobic modification was guaranteed to float on the water surface, while only 13% of the hydrophilic sawdust-EP1 floated on the water surface, that is, 87% of the hydrophilic sawdust-EP1 still stably settled to the bottom.

[0139] Figure 16 The viscosity of clean water and sawdust fracturing fluid is shown in Figure 2. It can be seen that the addition of sawdust proppant has little effect on the viscosity of water. The viscosity of the hydrophilic sawdust-EP1 fracturing fluid is 0.95 mPa·s, and the viscosity of the hydrophobic sawdust-PSBT1 fracturing fluid is 1.46 mPa·s.

[0140] (8) Proppant migration performance evaluation

[0141] The low density, small size, specific wettability and water stability of wood-based proppants ensure long-distance transport and uniform placement of proppants.

[0142] Figure 17 The results show that the granular proppants prepared in Examples 1 to 3, due to their hydrophobicity and different densities, are primarily laid at the top, middle, and bottom of the fracture, respectively. However, not all proppants maintain their theoretical positions; Particles B1 and B2 are primarily distributed at the top and bottom, while Particle P1 is more evenly distributed. This uneven distribution is due to the rough fracture walls that hinder the movement of the proppant. These characteristics indicate that multi-density granular proppants can be effectively used in hydraulic fracturing using only water as the fracturing fluid. The hydrophobicity of the particles enables them to float and suspend in the fluid, moving with the fluid into the far field. This maximizes the proppant area of ​​the fracture and improves oil and gas recovery.

[0143] Figure 18The dynamic migration and distribution of sawdust proppant in fractures with widths of 3 mm and 1.5 mm are shown. In the 3 mm main fracture, hydrophobic sawdust (PSBT1) is primarily concentrated in the upper region, while hydrophilic sawdust (EP1) settles primarily in the lower region. Due to the obstruction of the rough fracture wall, some sawdust is randomly distributed. Due to the combined effects of the hydrophilicity and low density of hydrophilic sawdust (EP1), hydrophilic sawdust (EP1) has greater spatial dispersion than hydrophobic sawdust (PSBT1). When mixed sawdust is injected into the fracture, hydrophobic sawdust (PSBT1) is primarily located at the top of the fracture, while hydrophilic sawdust (EP1) is primarily located at the bottom of the fracture. Some hydrophilic sawdust (EP1) is carried to the top and middle of the fracture by the hydrophobic sawdust (PSBT1).

[0144] (9) Evaluation of proppant acid resistance

[0145] Another key factor in evaluating proppant stability is acid solubility—the degree to which the proppant dissolves in an acidic environment. Chemicals present in the wellbore and surrounding formation can corrode and degrade the proppant, leading to problems such as decreased proppant performance and fracture closure, ultimately impacting oil and gas production. Therefore, acid solubility has become a key indicator of proppant stability in acidic media. Crucially, the proppant must not chemically react with the fracturing fluid and reservoir fluids, with a maximum allowable acid solubility of less than 7%. These criteria ensure proppant stability and acid resistance under downhole conditions, thereby promoting efficient oil recovery.

[0146] Figure 19 It shows that only 17 kg to 25 kg of silicone oil are needed to produce one ton of granular proppant. These silicone oil coatings can ensure that the proppant is isolated from the water-based fracturing fluid, thereby minimizing dissolution and swelling in the acidic environment.

[0147] Figure 20 The acid solubility of the granular proppants prepared in Examples 1 to 3, along with commercial quartz sand and ceramic proppants, is demonstrated. The acid solubility of the granular proppants was evaluated in a 10 wt% hydrochloric acid solution at simulated external closure pressures of 91.6 MPa, 120.2 MPa, and 145.2 MPa. The acid solubility of these proppants was very low, with acid solubilities of 1.39%, 1.76%, and 1.28% for Granules B1, P1, and B2, respectively, below the standard acid solubility of commercial proppants.

[0148] Figure 21 The dimensional statistics of the granular proppants after acid dissolution testing are presented, showing no significant change in particle size, with size reduction and expansion not exceeding 3% and 16%, respectively. The hydrophobic coating and the stabilizing components of the wood protect the multi-density granular proppants from the acidic conditions, with minor deformation and dissolution not enough to affect the granular proppant's performance.

[0149] Figure 22 The acid solubility of sawdust proppants in a 10% hydrochloric acid solution at 65°C was demonstrated. The hydrophobic sawdust PSBT1 and the hydrophilic sawdust EP1 had lower acid solubilities of 8.15% and 6.52%, respectively, ensuring the chemical stability of the sawdust piles during the propping process.

[0150] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0151] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims and their equivalents, the present invention is intended to include such modifications and variations.

Claims

1. A wood-based proppant, characterized in that: Wood-based proppants are at least two of the following: granular proppants, hydrophobic wood chip proppants, and hydrophilic wood chip proppants made from wood. Wood-based proppants float, suspend, or settle in the fracturing fluid, depending on their density, supporting areas at different heights within the fracture, forming oil and gas flow channels within the fracture. Granular proppants are obtained by delignifying, densifying, cutting and hydrophobizing natural wood. The hydrophobic wood chip proppant is obtained by crushing the wood raw material, performing delignification treatment and hydrophobic treatment; The hydrophilic wood chip proppant is obtained by crushing the wood raw material and then performing a hydrophilic treatment.

2. A method for preparing the wood-based proppant according to claim 1, characterized in that: The preparation of granular proppant includes the following steps: Delignified wood is obtained by delignifying natural wood; The delignified wood is mechanically hot-pressed at 1.4 MPa to 10 MPa and 70°C to 100°C to obtain dense wood after sufficient drying; Cutting the dense wood to obtain dense wood particles; Densified wood particles were hydrophobically treated at room temperature to obtain particle proppants.

3. The method for preparing a wood-based proppant according to claim 2, wherein: The mechanical hot pressing time is 8h~12h.

4. The method for preparing a wood-based proppant according to claim 2, wherein: The cutting process is carried out using a laser cutting machine or a micro lathe; The cutting parameters of the laser cutting machine are as follows: laser power of 13W~24W, cutting speed of 25mm / min~30mm / min, and cutting size of 1300μm~1500μm; The cutting parameters of the micro lathe are: spindle speed of 1000 r / min, and cutting size of 1200 μm.

5. A method for preparing the wood-based proppant according to claim 1, characterized in that: The preparation of hydrophobic wood chip proppant comprises the following steps: The wood raw materials are crushed to obtain raw wood chips; Delignifying the original sawdust to obtain delignified sawdust; The delignified sawdust was hydrophobized at room temperature to obtain a hydrophobic sawdust proppant.

6. The method for preparing a wood-based proppant according to claim 2 or 5, characterized in that: The hydrophobic treatment method for granular proppants and hydrophobic sawdust proppants is the same; During the hydrophobic treatment, the solute used in the hydrophobic solution is dimethyl silicone oil, polydimethylsiloxane, perfluorooctanoic acid or octadecylamine; the solvent is tetraethyl silicate, acetone, chloroform or ether; The reaction time of hydrophobic treatment is 0.5h~2h; The mass concentration of the hydrophobic solution is 0.5%~3%; The mass ratio of the wood to the hydrophobic solution is 1:30-70, and the wood is dense wood particles or delignified wood chips.

7. The method for preparing a wood-based proppant according to claim 2 or 5, characterized in that: The delignification process for granular proppants and hydrophobic wood chip proppants is the same; The delignification treatment method is sodium chlorite method, alkaline sodium sulfite method, hydrogen peroxide method or deep eutectic solvent method.

8. The method for preparing a wood-based proppant according to claim 7, wherein: The sodium chlorite treatment method is as follows: wood is placed in an acetic acid / sodium chlorite aqueous solution and reacted at 80°C to obtain a delignified product, wherein the mass ratio of 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 alkaline sodium sulfite treatment method is as follows: wood is placed in a sodium hydroxide / sodium sulfite aqueous solution and reacted at 120°C to obtain a delignified product; wherein the mass ratio of wood to the sodium hydroxide / sodium sulfite aqueous solution 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 hydrogen peroxide treatment method is as follows: wood is placed in an alkaline hydrogen peroxide solution and reacted at 90°C to obtain a delignified product; wherein the mass ratio of wood to alkaline hydrogen peroxide solution is 1:60, the mass concentration of hydrogen peroxide is 8%, and the mass concentration of alkali is 1%, and the alkali in the alkaline hydrogen peroxide solution is ammonia water; The deep eutectic solvent method comprises the following steps: a hydrogen bond acceptor and a hydrogen bond donor are uniformly mixed to obtain a deep eutectic solvent; then, wood is placed in 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; wherein the mass ratio of wood to deep eutectic solvent is 1:30, the hydrogen bond acceptor is choline chloride, and the hydrogen bond donor is ethylene glycol; The wood material is natural wood or wood raw material.

9. A method for preparing the wood-based proppant according to claim 1, characterized in that: The preparation of hydrophilic sawdust proppant includes the following steps: The wood raw materials are crushed to obtain raw wood chips; The original sawdust is added into the oil solution for hydrophilic treatment to obtain the hydrophilic sawdust proppant.

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

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