Micro-support fracturing micro-powder material, preparation method and application thereof

Abstract

The application belongs to the technical field of oil and gas reservoir fracturing, and particularly discloses a micro-supporting fracturing micro-powder material, a preparation method and application thereof.The micro-supporting fracturing micro-powder material provided by the application takes light calcium carbonate, quartz, resin and a curing agent as raw materials, has a small bulk density, is more easily carried by a preflush to micro-fractures, is not prone to sedimentation, and has an improved filling efficiency; in addition, the surface of the micro-supporting fracturing micro-powder material is crosslinked by resin curing and uniformly adheres to nanoscale silicon dioxide, and the acid and alkali resistance is better than that of conventional carbonated rock powder and conventional proppants; meanwhile, the nanoscale silicon dioxide can be used as an oil-repellent material to reduce the oil absorption of the micro-powder, and oil and gas molecules in the micro-fractures can be reduced in adsorption by the micro-supporting fracturing micro-powder material.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas reservoir fracturing technology, specifically relating to a micro-supported fracturing powder material, its preparation method, and its application. Background Technology

[0002] Shale, tight sandstone, and tight conglomerate reservoirs share the common characteristic of being low-permeability or ultra-low-permeability reservoirs. Shale permeability is generally below 0.001 millidarcy, and tight sandstone permeability is generally below 0.1 millidarcy. Conventional development methods cannot effectively develop these reservoirs. Currently, hydraulic fracturing is generally used for extraction. The purpose of large-scale hydraulic fracturing is to create artificial fractures in low-permeability reservoirs, thereby connecting oil and gas storage areas, releasing oil and gas production potential, and improving the permeability of the stirred-up formations.

[0003] Generally, artificially constructed fractures, without connecting to other non-target formations, need to maximize fracture volume to form a complex fracture network system, ensuring the migration of oil and gas. This complex fracture network system consists of primary fractures, secondary fractures, and microfractures. Artificial fractures are opened by the fracturing fluid generated by the surface fracturing unit, exceeding the fracturing pressure at the initiation point. Simultaneously, proppant is added to support the artificial fractures to prevent closure after the surface equipment is removed. Considering the size of the primary fractures and some secondary fractures, both artificial microfractures and existing reservoir microfractures are crucial for overall reservoir connectivity. Artificial microfractures connect with natural fractures, making the fracture network system more complete and effective. Fractures with an aperture less than 50 μm are generally defined as microfractures. However, current conventional proppant particle sizes are typically 140-200 mesh (106 μm to 850 μm), which cannot penetrate microfractures. Conventional proppants are generally quartz sand and ceramsite; however, quartz sand has low sphericity and low compressive strength, while ceramsite proppant is more expensive. Meanwhile, the fracturing fluid used in fracturing is a high-viscosity liquid, and particles with low mesh size are prone to agglomeration and cannot be dispersed during fracturing. Therefore, there is an urgent need to develop a microcrack filling technology.

[0004] For example, Chinese patent CN110573592A discloses a fracturing sand composition with nanoparticles and resin coating. The fracturing sand composition with nanoparticles and resin coating includes silica sand, epoxy resin, methanol, curing agent and nanoparticles. However, the fracturing sand components have large particle sizes and cannot be applied to microcracks. Moreover, the preparation process is complicated and the cost of silica sand is high. Summary of the Invention

[0005] The purpose of this invention is to provide a micro-support fracturing powder material for filling micro-cracks with an aperture of less than 200 μm after fracturing, its preparation method, and its application.

[0006] A micro-supported fracturing powder material includes: lightweight calcium carbonate, quartz, epoxy resin and curing agent as raw materials.

[0007] The light calcium carbonate has an oil absorption value of 60-90 ml / 100 mg and a bulk density of 0.5-0.7 g / cm³. 3 .

[0008] The epoxy resin has an epoxy value of 0.48 to 0.56 and a curing shrinkage rate of 1 to 3%.

[0009] The mass ratio of epoxy resin to curing agent is (1-4):1; the mass ratio of light calcium carbonate to quartz is (2-1):1; and the mass ratio of epoxy resin to light calcium carbonate is 1:(1-4).

[0010] The preparation process of the micro-supported fracturing powder material involves curing nano-sized silica onto the surface of lightweight calcium carbonate microspheres using epoxy resin and a curing agent to form a powder resistant to acid and alkali environments and high temperature and pressure.

[0011] The lightweight calcium carbonate microspheres are not acid-resistant. The acidity and alkalinity of the geological environment are unstable. Calcium carbonate is easily corroded by acid in acidic environments. The surface is protected from acid and alkali corrosion by attaching silica.

[0012] The epoxy resin is preferably epoxy resin E51, which has high adhesive strength and bonding strength. The epoxy resin structure contains aliphatic hydroxyl groups, ether groups, and highly reactive epoxy groups; it also has low shrinkage and dimensional stability. The curing agent added to epoxy resin E51 cures through a direct addition reaction, therefore no byproducts are generated during curing, and no bubbles are produced, resulting in very low shrinkage. In contrast, other thermosetting resins have high shrinkage, produce bubbles during curing, and are prone to shrinkage and deformation under high pressure.

[0013] The curing agent is one of methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, triethylamine, and maleic anhydride.

[0014] Specifically, the preparation process of the micro-supported fracturing powder material is as follows:

[0015] (1) Grinding: Grind the light calcium carbonate to a particle size of 200-2000 mesh and the quartz to a particle size of 10nm-30nm for later use;

[0016] (2) Preparation of resin-curing agent mixture: First, mix epoxy resin with reactive diluent at a mass ratio of (2-4):1 to obtain mixed resin diluent. Then, add curing agent and stir the mixed resin diluent and curing agent to obtain resin-curing agent mixture.

[0017] (3) Add the ground light calcium carbonate to the resin-curing agent mixture and stir to obtain light calcium carbonate-based balls with epoxy resin and curing agent attached; filter out excess liquid with a filter screen.

[0018] (4) Add the ground quartz to the light calcium carbonate-based balls with epoxy resin and curing agent attached, stir, filter out the excess quartz powder with a filter screen, and obtain light calcium carbonate with quartz powder (nano-sized silica) attached.

[0019] (5) The light calcium carbonate with attached quartz powder is heated and washed to obtain micro-supported fracturing powder material.

[0020] The preparation method of light calcium carbonate in step (1) is as follows: limestone is calcined to produce lime (the main component is calcium oxide) and carbon dioxide, then water is added to digest the lime to produce lime milk (the main component is calcium hydroxide), then carbon dioxide is introduced to carbonize the lime milk to produce calcium carbonate precipitate, and finally light calcium carbonate is obtained by dehydration, drying and pulverization.

[0021] The main component of the limestone is calcium carbonate, and the main component of the quartz is silicon dioxide.

[0022] The light calcium carbonate is ground using a ball mill or an ultrafine mill; the quartz is ground using an air jet mill.

[0023] Light calcium carbonate has better impact strength and rigidity, while heavy calcium carbonate has better tensile strength. Given the high-pressure environment of the formation, light calcium carbonate with better rigidity is chosen. Light calcium carbonate has an oil absorption value of 60-90 ml / 100 mg, significantly higher than the 40-60 ml / 100 mg of heavy calcium carbonate. To ensure uniform resin adhesion to the calcium carbonate-based spheres, light calcium carbonate with better oil absorption is selected. The most significant difference between heavy and light calcium carbonate lies in their bulk density; heavy calcium carbonate has a higher bulk density, typically 0.8-1.3 g / cm³. 3 Light calcium carbonate products have a lower bulk density, typically ranging from 0.5 to 0.7 g / cm³. 3 Its lower density makes it easier for fracturing fluid (which can be water or slippery water) to carry it into the microfractures of the formation.

[0024] The lightweight calcium carbonate is an oleophilic and hydrophobic material. When calcium carbonate is added directly to clean water or slickwater in excessive amounts without treatment, agglomeration occurs between calcium carbonate particles. After the surface is cured with resin-cured nano-silica, the silica has excellent hydrophilic and oleophobic properties, and the micro powder exhibits hydrophilicity. In applications, it can be uniformly dispersed in low-viscosity carrier fluids such as clean water or slickwater. It can be used in pre-fracturing fluid (pre-fracturing fluid is the liquid used to create fractures in the fracturing process. Due to its low viscosity, it originally does not contain supporting materials). While maintaining the fracture-creating function of the pre-fracturing fluid, the micro-support fracturing powder material can be used to fill the micro-fractures at the very end, thus increasing the function of the pre-fracturing fluid.

[0025] In step (2), the active diluent is n-butyl glycidyl ether, o-cresol glycidyl ether, or trimethylolpropane triglycidyl ether.

[0026] The light calcium carbonate is a porous material with many tiny pores and voids on its surface. This porous structure gives light calcium carbonate strong adsorption properties. Epoxy resin, being an oily material, can penetrate into the tiny pores and voids of light calcium carbonate, filling the micropores. After the resin that has entered the pores of light calcium carbonate cures, it increases the rigidity of the light calcium carbonate, strengthens the lightweight structure, and further enhances its compressive strength. Light calcium carbonate has a large specific surface area, and the viscous nature of the resin allows it to adhere evenly to the light calcium carbonate.

[0027] In step (2), the stirring speed is 500-1000 r / min and the stirring time is 30-45 min.

[0028] In step (3), the stirring speed is 500-1000 r / min and the stirring time is 60-120 min, so that the mixture of epoxy resin and curing agent is uniformly attached to the surface of the lightweight calcium carbonate-based balls.

[0029] In step (4), the stirring method is as follows: add the light calcium carbonate-based balls with epoxy resin and the ground quartz into a solid particle mixer and stir at a speed of 500-1000 r / min for 50-100 min. Relying on the adhesive force of the resin, the nano-sized silica will be uniformly bonded to the surface of the light calcium carbonate, but the bonding is not stable at this time.

[0030] In step (5), the heating temperature is 140-160℃ and the heating time is 2h-4h;

[0031] In step (5), the washing reagent is one or more of ethanol, acetone, toluene, and xylene.

[0032] In this invention, the resin-curing agent mixture is first stirred with light calcium carbonate to adhere to the light calcium carbonate, and then stirred with an excess of nano-silica powder, so that the silica powder adheres to the calcium carbonate surface more evenly and compactly.

[0033] This invention also provides the application of the above-mentioned micro-supported fracturing powder material, and the specific application process is as follows:

[0034] (1) Calculate the amount of micro-supported fracturing powder material to be used based on the fracturing design scheme:

[0035] The amount of the micro-supported fracturing powder material used is X×Y×a×b;

[0036] Where X is the pre-fluid volume / m³ 3 Y represents the fracture-forming efficiency of the pre-flush fluid; a represents the effective connectivity rate of the fracture; b represents the volume ratio of the micro-supported fracturing powder material in the fracture.

[0037] (2) Mix the micro-supported fracturing powder material and the pre-fluid evenly in the micro-supported fracturing powder material conveying equipment;

[0038] (3) The mixture in (2) is transported to the sand mixing truck according to the designed displacement. During the pre-flush stage, the mixture is lowered into the target reservoir through the operation of the sand mixing truck and the fracturing truck group.

[0039] The fracture formation efficiency Y of the pre-filled fluid is generally 25-50%; the modified volume (SRV) = X × Y; the effective fracture connectivity a is generally 5-20%; the effective modified volume: ESRV = X * Y * a; using distributed filling (point support), it is recommended to fill 15-30% of the fracture volume, i.e., b = 15-30%.

[0040] The aforementioned micro-supported fracturing powder materials are used in various fracturing reservoir stimulation applications, especially in the development of tight, low-permeability reservoirs, including fracturing stimulation of unconventional oil and gas reservoirs such as shale, tight sandstone, and tight conglomerate.

[0041] Beneficial effects:

[0042] 1. This invention is the first to propose that different calcium carbonate-based spheres have a significant impact on micro-supported fracturing powder materials. This invention uses light calcium carbonate as the base sphere for micro-supported fracturing powder materials. Light calcium carbonate not only has excellent impact strength and rigidity, but also has a low bulk density, making it easy to be carried into micro-cracks. Furthermore, due to its excellent oil absorption properties, it can work together with resin to make silica uniformly adhere to the surface of the calcium carbonate-based spheres. Moreover, due to its large specific surface area, it can adsorb resin to fill the pores of light calcium carbonate, thereby enhancing the compressive strength of the micro-supported fracturing powder materials.

[0043] 2. The surface of the micro-supported fracturing powder material is cross-linked by resin curing, and nano-sized silica is uniformly attached. It has better acid and alkali resistance than conventional carbonate rock powder and conventional proppant. At the same time, nano-silica can be used as an oleophobic material to reduce the oil absorption of the micro-supported fracturing powder material. Oil and gas molecules in micro-fractures can be reduced by the adsorption of the micro-supported fracturing powder material.

[0044] 3. Micro-supported fracturing powder material is introduced into the micro-fractures during fracturing operations. It can first fill the micro-fractures themselves, fully opening up the oil and gas migration channels in the reservoir, increasing the drainage area, and improving the well's production. Subsequently, after temporary plugging and diversion fracturing, a large number of micro-fractures will be formed, which conventional proppant cannot enter, causing the micro-fractures to close rapidly. The effect of temporary plugging and diversion fracturing will be greatly reduced. By applying micro-supported fracturing filling technology during temporary plugging and diversion, micro-supported fracturing powder material is injected after adding temporary plugging agent. The micro-fractures are quickly filled, which can greatly improve the support effect of micro-fractures after temporary plugging.

[0045] 4. Currently, oilfield blocks often adopt the well factory fracturing operation mode, forming a fracture network through simultaneous fracturing of multiple wells. Due to the mutual interference of stress, a more complex fracture network system is formed. The complex fracture network system relies on the interconnection of microfractures to achieve the ideal production enhancement effect. However, the application technology of micro-supported fracturing powder material provided by this invention can effectively fill the microfractures in each well, and at the same time realize the overall interconnection of the reservoir fracture network system. This truly achieves the overall fracturing transformation of the reservoir, promotes the migration of oil and gas throughout the block, and allows the effect of fracturing transformation to be reflected in the entire oilfield block, not just a single well, thereby significantly improving the block's production capacity. Detailed Implementation

[0046] Implementation 1:

[0047] Taking the preparation of 500g of micro-supported fracturing powder material (particle size of 400 mesh) as an example:

[0048] (1) Take 1500g of limestone and calcine it at 1000℃ to produce light calcium carbonate. After cooling, grind the light calcium carbonate into 400 mesh particles using an ultrafine mill. Take 750g for later use.

[0049] (2) Grind 750g of quartz to a particle size of 15 nanometers using an air jet mill, and set aside;

[0050] (3) Take 500g of epoxy resin E51, add 125g of trimethylolpropane triglycidyl ether, stir at room temperature at a speed of 800r / min, and reduce the stirring time by 40min to completely dilute the epoxy resin E51 to obtain a mixed resin dilution; add 125g of methylhexahydrophthalic anhydride to the mixed resin dilution, stir at a speed of 1000r / min, and reduce the stirring time by 100min to obtain a resin-curing agent mixture;

[0051] (4) Add 750g of light calcium carbonate to the resin-curing agent mixture, stir at 800r / min at room temperature, reduce the stirring time to 60min, and filter out the light calcium carbonate-based balls with epoxy resin E51 attached using a filter screen.

[0052] (5) Add 750g of quartz powder to (4), add the resulting mixture to a solid particle mixer, and stir at 1000r / min for 60min; use a filter screen to filter out excess quartz powder.

[0053] (6) The material formed in (5) is placed in an oil bath at 150°C and heated for 3 hours. After cooling, the cooled material is cleaned with acetone to obtain the micro-supported fracturing powder material.

[0054] The light calcium carbonate described above has an oil absorption value of 87 ml / 100 mg and a bulk density of 0.58 g / cm³. 3 The epoxy value of the epoxy resin is 0.50; the curing shrinkage rate is 1.35%.

[0055] Acid etching tests were performed on the micro-supported fracturing powder material: 50g of light calcium carbonate powder and 50g of micro-supported fracturing powder material were added to 50g of a 1wt% hydrochloric acid solution, respectively. Bubbles appeared in the beaker containing the light calcium carbonate powder, while no change was observed in the beaker containing the micro-supported fracturing powder material. The mass of the micro-supported fracturing powder material was measured; 50g showed no change. The mass of the light calcium carbonate was measured; 49.32g was measured.

[0056] Example 2:

[0057] In this embodiment, the oil absorption value of light calcium carbonate is 81 ml / 100 mg; the bulk density is 0.63 g / cm³. 3 The remaining components and processes are the same as in Example 1.

[0058] Example 3:

[0059] The epoxy value of the epoxy resin described in this embodiment is 0.52; the curing shrinkage rate is 1.15%; the remaining components and processes are the same as in Example 1.

[0060] Example 4:

[0061] In this embodiment, the amount of light calcium carbonate used is 800g; the remaining components and processes are the same as in Example 1.

[0062] Comparative Example 1:

[0063] In this comparative example, the light calcium carbonate in Example 1 is replaced with heavy calcium carbonate, while the remaining components and processes are the same as in Example 1.

[0064] The heavy calcium carbonate has an oil absorption value of 42 ml / 100 mg and a bulk density of 1.21 g / cm³. 3 .

[0065] After the heavy calcium carbonate is bonded to epoxy resin E51, the mass of the remaining resin is tested. The mass of epoxy resin E51 on the light calcium carbonate-based spheres with attached epoxy resin E51 and curing agent is 70% greater than the mass of epoxy resin E51 on the heavy calcium carbonate-based spheres with attached epoxy resin E51 and curing agent.

[0066] Furthermore, the resin adhering to the surface of the micro-supported fracturing powder material prepared in Comparative Example 1 was uneven, which in turn led to uneven bonding with nano-silica.

[0067] The compressive strength of the micro-supported fracturing powder material was tested using a compression test method, and the compressive strength was compared based on displacement deformation. 100 ml of the micro-supported fracturing powder material prepared in Example 1 was added to the proppant fracture chamber. Using a compression testing machine, a pressure of 70 MPa was applied to the micro-supported fracturing powder material according to the fracture chamber size, and the displacement deformation was measured to be 0.05 mm. 100 ml of the micro-supported fracturing powder material prepared in Comparative Example 1 was added to the proppant fracture chamber. Using a compression testing machine, a pressure of 70 MPa was applied to the micro-supported fracturing powder material according to the fracture chamber size, and the displacement deformation was measured to be 2 mm. The experiment showed that the powder material prepared using lightweight calcium carbonate as the base sphere is less prone to deformation under high pressure and can provide better support.

[0068] Application Example 1:

[0069] In this application example, the microcrack opening is 100 μm, and 400 mesh micro-supported fracturing powder material is suitable, which has a particle size of 38 μm.

[0070] (1) Calculate the design dosage of micro-supported fracturing powder material: X = 300 m³ of pre-fracturing fluid for a certain well. 3 The pre-filled fluid has a crack-forming efficiency of Y = 30% and an effective crack connectivity rate of a = 10%.

[0071] Therefore, the modified volume SRV = 300 × 30% = 90m 3 Effective modification volume ESRV: 90 × 10% = 9m 3 ;

[0072] Filling to 20% is sufficient; it is recommended to fill the fracture volume b = 20%. The dosage of micro-supported fracturing powder material is 9m³. 3 ×20%=1.8m 3 .

[0073] (2) Mix the micro-supported fracturing powder material and the pre-fluid evenly in the micro-supported fracturing powder material conveying equipment.

[0074] (3) The mixture in (2) is transported to the sand mixing truck according to the designed displacement. During the pre-flush stage, the mixture is lowered into the target reservoir through the operation of the sand mixing truck and the fracturing truck group.

[0075] The use of micro-supported fracturing powder in this well significantly increased production. Before micro-supported fracturing, the well's daily oil production was 1.2 t / d; after using the micro-supported fracturing powder, the daily oil production increased to 8.9 t / d. Micro-supported fracturing technology using micro-supported fracturing powder can substantially improve the production of fracturing wells.

[0076] The micro-supported fracturing powder materials prepared in Examples 1 to 4 and Comparative Example 1 were applied to fracturing wells using the above application methods, and the oil production results are shown in the table below.

[0077] Table 1. Oil production before and after application of micro-supported fracturing powder materials

[0078]

[0079]

Claims

1. A method for preparing a micro-supported fracturing powder material, characterized in that, The preparation process of the micro-supported fracturing powder material is as follows: (1) Grinding: Grind the light calcium carbonate to a particle size of 200~2000 mesh and the quartz to a particle size of 10 nm for later use; (2) Preparation of resin-curing agent mixture: First, mix epoxy resin with reactive diluent in a volume ratio of (2~4):1 to obtain mixed resin diluent. Then, add curing agent and stir the mixed resin diluent and curing agent to obtain resin-curing agent mixture. (3) Add the ground light calcium carbonate to the resin-curing agent mixture and stir to obtain light calcium carbonate-based spheres with epoxy resin and curing agent attached. (4) Add the ground quartz to the light calcium carbonate-based balls with epoxy resin and curing agent attached, stir, filter out the excess quartz powder with a filter screen, and obtain light calcium carbonate with quartz powder attached. (5) Light calcium carbonate with attached quartz powder is heated and washed to obtain micro-supported fracturing powder material; The light calcium carbonate has an oil absorption value of 60-90 ml / 100 mg and a bulk density of 0.5-0.7 g / cm³. 3 ; The mass ratio of epoxy resin to curing agent is (1~4):1; the mass ratio of light calcium carbonate to quartz is (2~1):1; the mass ratio of epoxy resin to light calcium carbonate is 1:(1~4). The curing agent is one of methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, triethylamine, or maleic anhydride; The epoxy resin has an epoxy value of 0.48 to 0.56 and a curing shrinkage rate of 1 to 3%.

2. The method for preparing a micro-supported fracturing powder material according to claim 1, characterized in that, The epoxy resin is epoxy resin E51.

3. The method for preparing micro-supported fracturing powder material according to claim 1, characterized in that, The method for preparing light calcium carbonate in step (1) is as follows: limestone is calcined to produce lime and carbon dioxide, then water is added to digest the lime to produce lime milk, then carbon dioxide is introduced to carbonize the lime milk to produce calcium carbonate precipitate, and finally light calcium carbonate is obtained by dehydration, drying and pulverization.

4. The method for preparing the micro-supported fracturing powder material according to claim 3, characterized in that, The light calcium carbonate is ground using a ball mill or an ultrafine mill; the quartz is ground using an air jet mill.

5. The method for preparing micro-supported fracturing powder material according to claim 1, characterized in that, In step (2), the active diluent is one of n-butyl glycidyl ether, o-cresol glycidyl ether, or trimethylolpropane triglycidyl ether.

6. The method for preparing micro-supported fracturing powder material according to claim 1, characterized in that, In step (2), the stirring speed is 500~1000 r / min and the stirring time is 30min~45min.

7. The method for preparing micro-supported fracturing powder material according to claim 1, characterized in that, In step (3), the stirring speed is 500~1000 r / min and the stirring time is 60~120 min.

8. The method for preparing micro-supported fracturing powder material according to claim 1, characterized in that, In step (4), the stirring method is as follows: add the light calcium carbonate-based balls with epoxy resin and curing agent attached and the ground quartz into a solid particle mixer and stir at a speed of 500~1000r / min for 50~100min.

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