Micro-crack proppant and preparation method thereof

Abstract

The invention relates to a microfracture proppant and a preparation method thereof, and belongs to the technical field of oil exploitation. According to the preparation method of the microcrack proppant, on the basis of taking nano silicon dioxide as a carrier, high-strength epoxy resin is cured on the surfaces of nano silicon dioxide particles to prepare micron-sized particles, and the particle size of the micron-sized particles can be controlled within several to dozens of microns. The nano silicon dioxide particles are resistant to high pressure and high temperature, uniform in particle size and the like. The resin serving as the wrapping layer has the advantages of high temperature resistance, high compressive strength, easiness in wrapping and controllable curing. The particles are wrapped by atomized resin, the uniformity of a wrapping layer can be ensured, and the formed micro-crack propping agent has the characteristics of high compressive strength, high temperature resistance, uniform particle size and stable and reliable performance, not only can play a better filling and supporting role, but also can meet the state requirements of underground high temperature and high pressure. The problem that an existing proppant cannot ensure uniform wrapping of resin, and consequently performance is unstable is solved.

Description

Technical Field

[0001] The invention relates to a micro-crack proppant and a preparation method thereof, belonging to the technical field of petroleum extraction. Background Art

[0002] With the large-scale development and commercial expansion of shale gas reservoirs, shale gas development has long become a hot research topic and a focal point of significant attention. Due to the inherent limitations of shale gas reservoirs, they must undergo hydraulic fracturing to achieve commercial production value and achieve certain economic benefits. Hydraulic fracturing in shale oil and gas reservoirs often creates a network of micron-sized fractures. However, the large particle size of current proppants makes it difficult to penetrate these microfractures. After hydraulic fracturing, these microfractures naturally close under formation pressure, becoming no longer pathways for shale oil and gas flow and contributing nothing to production. This represents a significant waste of hydraulic fracturing investment and is a primary reason for the rapid decline in shale oil and gas production. To address this issue, a new proppant has been developed that can fill these microfractures. Pumped into the formation along with the fracturing fluid during hydraulic fracturing, it supports the microfractures and achieves high and stable shale oil and gas production.

[0003] U.S. Patent Publication No. 6,528,157A1 discloses proppant with fiber reinforced resin coatings, which is specifically disclosed in Example 1: The following general coating procedures were followed to prepare fiber-laden curable proppants using HEXA as a crosslinking agent. Into a 3 quart mixing bowl was placed one kilogram of 20 / 40 mesh sand available from and an appropriate amount of fiber to achieve the desired weight percent fiber, 20 / 40 sand has 90% of its particles between 20 and 40 mesh (US Standard Sieve Series) per American Petroleum Institute RP-60 procedure, Section 4 (1989). The sand and glass fiber were stirred with a Hobart C-100 mixer and heated with a gas flame to 280°F. 26.6 grams of EX5150 novolac resin (Borden, Inc.) and 0.4grams of A-1100silane (Union Carbide Corporation) were added and mixed for90seconds.At this time13.8grams of 32.6% water solution of hexamethylenetetramine was added.Mixingwas continuedand at 96seconds of total mixing time 8.1grams of waterwasadded.At 120seconds of mixing time 1.0gram of L 45silicon was added.Mixing was continued for another 180 seconds. At 300 seconds of total mixing time, the coated sand was discharged from the bowl as a free fowing product, consistent with individual sand grains coated with a curable resin coating. The stick melting point of this product was 232°F. A 3-minute, 450°F, hot tensile strength test was run and produced a specimen with a hot tensile of 200 psi. The proppant was coated with Plasti Flake EX5150, a commercial phenol-formaldehyde novolac manufactured by Borden, Inc. / North American Resins, Louisville, Ky. RP-60 Procedure, Section 4 (1989), 20 / 40 sand has 90% of its particles between 20 and 40 mesh (U.S. Standard Sieve Series). The sand and glass fiber were mixed in a Hobart C-100 mixer and heated to 280°F with a gas flame. 26.6 grams of EX 5150 novolac resin (Borden, Inc.) and 0.4 grams of A-1100 silane were added and mixed for 90 seconds. At this point, 13.8 grams of a 32.6% aqueous solution of hexamethylenetetramine was added. Mixing continued, and at a total mixing time of 96 seconds, 8.1 grams of water was added. At a total mixing time of 120 seconds, 1.0 grams of L45 siloxane was added. Mixing was continued for an additional 180 seconds. At a total mixing time of 300 seconds, the coated sand was discharged from the mixer as a free-flowing product consisting of individual sand particles coated with a curable resin coating.

[0004] The product has a melting point of 232°F in rod form. A hot tensile strength test was conducted at 450°F for 3 minutes and produced a sample with a hot tensile strength of 200 psi. The proppant was coated with Plasti Flake EX5150 (a commercial phenol-formaldehyde novolac manufactured by Borden, Inc. / North American Resins, Louisville, KY).

[0005] The aforementioned proppant forms a mixed coating of resin and fiber on the sand surface. However, due to the large sand mass (1 kg) and the relatively small resin mass (26.6 g), the resin coating cannot be evenly coated on the sand, and the thickness of the resin layer on the sand surface varies, resulting in poor performance. Therefore, it is necessary to develop a microfracture proppant and its preparation method to ensure stable and reliable performance. Summary of the Invention

[0006] The purpose of the present invention is to provide a micro-fracture proppant with stable performance, which can effectively support micro-fractures in underground wells and ensure the effective flow of oil and gas, and a preparation method thereof.

[0007] The technical solution of the present invention is: A micro-fracture proppant is composed of nano-silicon dioxide particles and a resin layer. The characteristic is that the nano-silicon dioxide particles are used as the core and are coated with the resin layer.

[0008] A method for preparing a micro-fracture proppant, characterized by comprising the following steps: 1) Calculate the dosage ratio of nano-silica particles and resin in the micro-fracture proppant according to the width of the micro-fracture downhole; 2) Heating the resin in a fluidized bed and then atomizing it under pressure, so that the atomized resin wraps the nano-silica particles to form an intermediate; 3) After the resin surface of the intermediate is solidified by hot air, it is cooled and shaped by cold air; 4) After the intermediate resin is completely solidified, it is screened to obtain a micro-fracture proppant product that meets the size requirements. The calculation steps in step 1) are: A. Through particle optimization, the diameter of the nano-silicon dioxide particles is determined to be Dn, then its volume is: For a unit volume of nano-silica particles, the porosity is generally 20%, so the total number of particles T n for:

[0009] B. According to actual needs, the diameter of the micro-fracture proppant to be provided should be Dw.

[0010] C. Theoretically, calculate the volume and mass of the resin; For a single nano-silica particle, when its diameter increases from Dn to Dw, the required resin volume V m It can be expressed as: The volume of resin required for unit volume of nano-silica is V T Expressed as: According to the density of the resin ρ h , its mass m can be calculated h for:

[0011] Using the above formula, the required resin volume and mass are calculated based on the diameter of the selected silica particles and the particle size requirements of the microfracture proppant.

[0012] In the step 2), the resin is atomized at a temperature of 60-150° C. and is atomized at a pressure of 0.8-0.9 MPa. Preferably, the resin is atomized at a temperature of 140° C.

[0013] In the step 2), the resin flow rate is controlled in sections, with low resin flow rate for pre-wrapping in the first 5 seconds and full flow rate for wrapping after 5 seconds; the particle size of the intermediate is monitored by a laser particle size analyzer, and the resin flow rate is adjusted when the particle size fluctuation is greater than 5%.

[0014] In the step 3), the hot air temperature is 300±3° C., the hot air speed is 0.5±0.4 m / s; the cold air temperature is -40±2° C., and the cold air speed is 0.7-0.8 m / s.

[0015] The fluidized bed includes a reaction chamber, a feed pipe, an atomizing nozzle and a cyclone separator. The reaction chamber is provided with a feed pipe, the end of the feed pipe extends into the reaction chamber, and the feed pipe extending into the reaction chamber is provided with an atomizing nozzle; a feed port is provided on the reaction chamber above the feed pipe; a plurality of hot air inlets are provided on the reaction chamber below the atomizing nozzle, and the hot air inlet is connected to the air source through a heater; a discharge port is provided on the side wall of the reaction chamber opposite to the atomizing nozzle, and a cold air inlet is provided at the bottom of the reaction chamber between the discharge port and the hot air inlet, and the cold air inlet is connected to the air source through a refrigerator; a cyclone separator is provided on one side of the reaction chamber, and the inlet of the cyclone separator is connected to the top center of the reaction chamber through a connecting pipe.

[0016] The beneficial effects of the present invention are: This microfracture proppant is prepared by curing the surface of nanosilica particles with a high-strength epoxy resin, using nanosilica as a carrier. The resulting micron-sized particles can be controlled to have a size ranging from a few to tens of microns. The nanosilica particles used as the core carrier offer advantages such as high-pressure and high-temperature resistance, and uniform particle size. The epoxy resin used as the coating layer on the particle surface offers advantages such as high-temperature resistance, high compressive strength, ease of coating, and controllable curing. The atomized resin coating ensures a uniform coating, combining the advantages of nanosilica and epoxy resin. The resulting microfracture proppant exhibits high compressive strength, high-temperature resistance, uniform particle size, and stable and reliable performance. It not only penetrates micron-sized fractures to provide effective filling and support, but also meets the high-temperature and high-pressure requirements of shale oil and gas reservoirs. This solves the problem of existing proppants that lack uniform resin coating, resulting in unstable performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic structural diagram of the fluidized bed of the present invention.

[0018] In the figure: 1. reaction chamber, 2. feed pipe, 3. atomizing nozzle, 4. cyclone separator, 5. feed port, 6. hot air inlet, 7. heater, 8. discharge port, 9. cold air inlet, 10. refrigerator. DETAILED DESCRIPTION

[0019] The preparation method of the micro-fracture proppant comprises the following steps: The particle size of the microfracture proppant is selected according to the width of the microfractures downhole. The particle size of the microfracture proppant should be less than or equal to the average width of the microfractures to ensure that the microfracture proppant can enter the microfractures and fill and support the microfractures.

[0020] Calculate the ratio of nano-silica particles to resin in the micro-fracture proppant. This example uses a micro-fracture proppant with a particle size of 50 μm, made with 500 nm nano-silica particles as the core and o-cresol epoxy resin (ECN series) as the coating. The specific calculation steps are as follows: Through particle optimization, the diameter of the nano-silica particles is determined to be Dn, then its volume is: For a unit volume of nano-silica particles, the porosity is generally 20%, so the total number of particles T n for: According to actual needs, the diameter of the micro-fracture proppant to be provided should be Dw; Theoretically, calculate the volume and mass of the resin; For a single nano-silica particle, when its diameter increases from Dn to Dw, the required resin volume V m It can be expressed as: The volume of resin required for unit volume of nano-silica is V T Expressed as: According to the density of the resin ρ h , its mass m can be calculated h for: Using the above formula, the required resin volume and mass are calculated based on the selected silica particle diameter and the required microfracture proppant particle size. Substituting the nanosilica particle diameter, resin density, and microfracture proppant particle size parameters into the above formula, the calculated resin to nanosilica particle volume ratio is 78.2:1. The ingredients are then proportioned according to this calculated ratio.

[0021] The o-cresol-formaldehyde epoxy resin is solid at room temperature, has a solid content greater than or equal to 95%, an epoxy value of 0.45-0.55 eq / 100 g, and a viscosity (at 100° C.) of 500-1500 mPa.s.

[0022] Nano-silicon dioxide particles with a purity greater than or equal to 99.5% and a specific surface area of 50-80 m2 / g are vacuum dried at 120°C for 4 hours and pre-treated by ultrasonic dispersion to prevent particle agglomeration.

[0023] The resin is heated to a temperature of 60-150°C, preferably 140°C. This heat liquefies the o-cresol epoxy resin. By appropriately increasing the heating temperature, the resin viscosity is reduced, facilitating resin liquefaction. After the resin is liquefied, a curing agent is added and pressurized into the fluidized bed.

[0024] The fluidized bed includes a reaction chamber 1, a feed pipe 2, an atomizing nozzle 3 and a cyclone separator 4. The reaction chamber 1 is provided with a feed pipe 2, the end of which extends into the reaction chamber 1. The feed pipe 2 extending into the reaction chamber 1 is provided with an atomizing nozzle 3 to atomize the resin under pressure through the atomizing nozzle. A feed port 5 is provided on the reaction chamber 1 above the feed pipe 2 to allow nano-silicon dioxide particles to be introduced into the reaction chamber through the feed port 5. A plurality of hot air inlets 6 are provided on the reaction chamber 1 below the atomizing nozzle 3. The hot air inlets 6 are connected to an air source through a heater 7 to allow hot air to be introduced into the reaction chamber 1 through the hot air inlets 6, thereby promoting the curing of the resin by heating. A discharge port 8 is provided on the side wall of the reaction chamber 1 opposite the atomizing nozzle 3. A cold air inlet 9 is provided at the bottom of the reaction chamber 1 between the discharge port 8 and the hot air inlet 6. The cold air inlet 9 is connected to the air source through a refrigerator 10 so as to introduce cold air into the reaction chamber 1 through the cold air inlet 9. The resin coated with nano-silica particles is cooled and shaped by the cold air. A cyclone separator 4 is provided on one side of the reaction chamber 1. The inlet of the cyclone separator 4 is connected to the top center of the reaction chamber 1 through a connecting pipe. The function of the cyclone separator 4 is to separate the fine particles carried by the wind. The fine particles are discharged and recovered from the bottom outlet of the cyclone separator 4, and the wind is discharged from the top center outlet of the cyclone separator 4. Distribution plates are provided on the hot air inlet 6 and the cold air inlet 9. The opening rate of the distribution plate is 12%-15%, the aperture of the distribution plate is 1-2mm, and the openings are arranged in an equilateral triangle to ensure uniform airflow.

[0025] Resin is introduced into reaction chamber 1 via feed pipe 2 and atomized by atomizing nozzle 3. The atomized resin coats the nano-silica particles introduced via fluidized bed feed port 5, forming an intermediate. The nano-silica particles and resin are introduced into the fluidized bed in batches, with each batch processing time lasting 10-20 seconds to avoid excessive resin deposition. The resin atomization pressure is 0.8-0.9 MPa, which diffuses the atomized resin upward, spreading it and expanding its range of action, allowing it to evenly coat the nano-silica particles. The droplet size of the atomized resin is controlled at 1-2 μm (measured by a laser particle size analyzer). During resin introduction, the resin flow rate is controlled in stages, with a low flow rate for pre-coating for the first 5 seconds and a full flow rate for coating after 5 seconds. The particle size of the intermediate is monitored using a laser particle size analyzer. When the particle size fluctuates by more than 5%, the resin flow rate is adjusted to maintain a particle size of approximately 50 μm.

[0026] After resin and nano-silicon dioxide particles are introduced, hot air is introduced into the reaction chamber through the hot air inlet 6 of the fluidized bed. The hot air is obtained by a heater 7 with an inert gas (such as nitrogen). The hot air temperature introduced is 300±3°C and the hot air speed is 0.5±0.4m / s. The resin surface of the intermediate is cured by the hot air, and the atomized resin and nano-silicon dioxide particles are suspended by the hot air. After the hot air is cured, cold air is introduced through the cold air inlet 9 of the fluidized bed. The cold air is cooled by a refrigerator. The cold air temperature is -40±2°C and the cold air speed is 0.7-0.8m / s. The surface-cured intermediate is cooled and shaped by the cold air to avoid excessive adsorption of the resin and control the particle size of the intermediate. The cooled and shaped intermediate is discharged by the discharge port 8 of the fluidized bed. The wind carries fine particles into the cyclone separator 4, which is then separated and recovered by the cyclone separator 4.

[0027] After the intermediate is discharged, it is allowed to stand to allow the resin in the intermediate to completely solidify. After the intermediate is completely solidified, it is screened by a cyclone classifier to obtain a micro-fracture proppant product that meets the size requirements (50±5μm).

[0028] This microfracture proppant is prepared by curing the surface of nanosilica particles with a high-strength epoxy resin, using nanosilica as a carrier. The resulting micron-sized particles can be controlled to have a size ranging from a few to tens of microns. The nanosilica particles used as the core carrier offer advantages such as high-pressure and high-temperature resistance, and uniform particle size. The epoxy resin used as the coating layer on the particle surface offers advantages such as high-temperature resistance, high compressive strength, ease of coating, and controllable curing. The atomized resin coating ensures a uniform coating, combining the advantages of nanosilica and epoxy resin. The resulting microfracture proppant exhibits high compressive strength, high-temperature resistance, uniform particle size, and stable and reliable performance. It not only penetrates micron-sized fractures to provide effective filling and support, but also meets the high-temperature and high-pressure requirements of shale oil and gas reservoirs. This solves the problem of existing proppants that lack uniform resin coating, resulting in unstable performance.

Claims

1. A method for preparing a microfracture proppant, characterized in that: The following steps are involved: 1) Calculate the dosage ratio of nano-silica particles and resin in the micro-fracture proppant according to the width of the micro-fracture downhole; 2) Heating the resin in a fluidized bed and then atomizing it under pressure, so that the atomized resin wraps the nano-silica particles to form an intermediate; 3) After the resin surface of the intermediate is solidified by hot air, it is cooled and shaped by cold air; 4) After the intermediate resin is completely solidified, it is screened to obtain a micro-fracture proppant product that meets the size requirements.

2. The method for preparing a micro-fracture proppant according to claim 1, wherein: The calculation steps in step 1) are: A. Through particle optimization, the diameter of the nano-silicon dioxide particles is determined to be Dn, then its volume is: For a unit volume of nano-silica particles, the porosity is generally 20%, so the total number of particles T n for: B. According to actual needs, the diameter of the micro-fracture proppant to be provided should be Dw; C. Theoretically, calculate the volume and mass of the resin; For a single nano-silica particle, when its diameter increases from Dn to Dw, the required resin volume V m It can be expressed as: The volume of resin required for unit volume of nano-silica is V T Expressed as: According to the density of the resin ρ h , its mass m can be calculated h for: Using the above formula, the required resin volume and mass are calculated based on the diameter of the selected silica particles and the particle size requirements of the microfracture proppant.

3. The method for preparing a micro-fracture proppant according to claim 1, wherein: In the step 2), the resin is atomized at a temperature of 60-150° C. and is atomized at a pressure of 0.8-0.9 MPa. Preferably, the resin is atomized at a temperature of 140° C.

4. The method for preparing a microfracture proppant according to claim 1, wherein: In the step 2), the resin flow rate is controlled in sections, with low resin flow rate for pre-wrapping in the first 5 seconds and full flow rate for wrapping after 5 seconds; the particle size of the intermediate is monitored by a laser particle size analyzer, and the resin flow rate is adjusted when the particle size fluctuation is greater than 5%.

5. The method for preparing a micro-fracture proppant according to claim 1, wherein: In the step 3), the hot air temperature is 300±3° C., the hot air speed is 0.5±0.4 m / s; the cold air temperature is -40±2° C., and the cold air speed is 0.7-0.8 m / s.

6. The method for preparing a microfracture proppant according to claim 1, wherein: The fluidized bed comprises a reaction chamber (1), a feed pipe (2), an atomizing nozzle (3) and a cyclone separator (4); the reaction chamber (1) is provided with a feed pipe (2), the end of the feed pipe (2) extends into the reaction chamber (1), and the feed pipe (2) extending into the reaction chamber (1) is provided with an atomizing nozzle (3); the reaction chamber (1) above the feed pipe (2) is provided with a feed port (5); the reaction chamber (1) below the atomizing nozzle (3) is provided with a plurality of hot air inlets (6 ), a hot air inlet (6) is connected to an air source via a heater (7); a discharge port (8) is provided on the side wall of the reaction chamber (1) opposite to the atomizing nozzle (3); a cold air inlet (9) is provided at the bottom of the reaction chamber (1) between the discharge port (8) and the hot air inlet (6), and the cold air inlet (9) is connected to an air source via a refrigerator (10); a cyclone separator (4) is provided on one side of the reaction chamber (1), and an inlet of the cyclone separator (4) is connected to the center of the top of the reaction chamber (1) via a connecting pipe.

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