Water-based self-suspension fracturing propping agent as well as preparation method and application thereof

Abstract

The invention provides a water-based self-suspension fracturing propping agent as well as a preparation method and application thereof, and relates to the technical field of oil exploitation. The water-based self-suspension fracturing propping agent comprises aggregate and polyacrylamide gel coated on the surface of the aggregate, wherein the aggregate is quartz sand or ceramsite; according to the invention, the polyacrylamide gel is coated on the surface of the quartz sand or the ceramsite, and by controlling the particle size of the aggregate, the dosage of the polyacrylamide gel and the like, the obtained propping agent overcomes the problems of high settling velocity, high fracturing construction pressure, poor flow conductivity after fracturing and great formation damage of the existing fracturing propping agent, and has the advantages of strong pressure bearing capacity and good self-suspension performance.

Description

Technical Field

[0001] This application relates to the technical field of oil extraction, and particularly relates to an aqueous self-suspending fracturing proppant, a preparation method thereof, and an application thereof. Background Art

[0002] Due to the poor permeability of low-permeability reservoir formations, it is impossible to establish an effective seepage channel relying solely on the formation itself, resulting in difficulties in establishing a reservoir displacement pressure system and low reservoir utilization. During the development process, it shows characteristics of low production, low liquid production, and low recovery degree. Fracturing technology, as an important and effective means to improve the production increase of low-permeability reservoirs, is widely used in the reservoir transformation of low-permeability oil reservoirs and plays an important role in improving the development effect of low-permeability oil reservoirs. During the fracturing process, using existing active water or guar gum as fracturing fluid can meet the requirements of fracturing construction. However, research has found that there are still many problems after the fracturing fluid is pumped into the ground, such as limited sand-carrying capacity, fast settlement speed, slow dissolution and dispersion in water, easy breakage of proppants, etc. In addition, after the fracturing is completed, the fracturing fluid does not break gel completely and remains in the formation, causing formation pollution and damage. Therefore, it is necessary to provide a new type of aqueous self-suspending fracturing proppant. Summary of the Invention

[0003] Aiming at the deficiencies of the prior art, this application provides an aqueous self-suspending fracturing proppant and a preparation method thereof, which solves at least some of the problems existing in the prior art.

[0004] To achieve the above object, the technical solutions adopted in this application are as follows: On the one hand, an aqueous self-suspending fracturing proppant includes aggregate and polyacrylamide gel coated on the surface of the aggregate; The aggregate is quartz sand or ceramsite; The viscosity of the polyacrylamide gel < 2000 mPa·s, and the dissolution time < 5 min; The mass ratio of the aggregate to the polyacrylamide gel is 10:(1 - 10); The bulk density of the aqueous self-suspending fracturing proppant is 1.40 - 1.60 g / cm³.

[0005] Further, the particle size of the aggregate is 20 - 80 mesh.

[0006] Preferably, the particle size of the quartz sand is 20 - 40 mesh, and the particle size of the ceramsite is 40 - 60 mesh.

[0007] Preferably, the viscosity of the polyacrylamide gel is 200 - 2000 mPa·s, and the dissolution time is 20 s - 5 min.

[0008] In this application, a polyacrylamide gel that simultaneously meets the range of viscosity < 2000 mPa·s and dissolution time < 5 min is used as a thickening agent to coat the surface of quartz sand or ceramsite to prepare a fracturing proppant. The aggregate and polyacrylamide gel are prepared into a fracturing proppant with a bulk density of 1.40 - 1.60 g / cm³ according to a certain ratio. When this fracturing proppant is put into clear water, the coated polyacrylamide gel can dissolve in water, increasing the relative density, so that the proppant can be suspended in the clear water, reducing the frictional resistance of the proppant and extending the conveying distance of the proppant. After the fracturing proppant breaks gel, there is almost no residue, and the polyacrylamide gel is a non-toxic substance, causing almost no damage to the formation.

[0009] It should be noted that as long as the polyacrylamide gel simultaneously meets the range of < 2000 mPa·s and dissolution time < 5 min, the above-mentioned effects can be achieved according to the material ratios and the like defined above, and a water-based self-suspending fracturing proppant can be obtained, reducing the frictional resistance of the proppant and extending the conveying distance of the proppant, without other special limitations. However, the strength of ordinary polyacrylamide gel is relatively poor, it is easy to break, and its anti-shearing performance and salt tolerance need to be improved, resulting in poor performance in a high-salt environment. Moreover, after the proppant enters the formation, under the action of high-speed fluid, the viscosity of the polyacrylamide gel drops rapidly, and the proppant cannot be transported deeper into the formation.

[0010] Therefore, in a further embodiment, the polyacrylamide gel comprises the following raw materials in parts by weight: 40 - 50 parts of acrylamide, 20 - 30 parts of acrylic acid, 15 - 25 parts of 4-methacrylamidosalicylic acid, 1 - 5 parts of carbamide, 5 - 15 parts of sodium hydroxide, 0.02 - 0.08 parts of EDTA-2Na, 5 - 15 parts of crosslinking agent, 1 - 10 parts of initiator, 0.01 - 0.1 parts of sodium formate, and 40 - 65 parts of water.

[0011] Optionally, the crosslinking agent is a crosslinking agent containing a bisacrylamide group, including but not limited to N,N-methylenebisacrylamide, N,N-propylenediacrylamide, N,N-tetramethylenediacrylamide, N,N-hexamethylenediacrylamide, or N,N-m-xylenediacrylamide, etc.

[0012] Optionally, the initiator is selected from at least one of peroxide initiators and azo initiators; the peroxide initiators include but not limited to benzoyl peroxide, lauroyl peroxide, cumene hydroperoxide, tert-butyl hydroperoxide, di-tert-butyl peroxide, diisopropylbenzene peroxide, tert-butyl perbenzoate, tert-butyl peroxypivalate, diisopropyl peroxydicarbonate, dicyclohexyl peroxydicarbonate, potassium persulfate, sodium persulfate, ammonium persulfate, etc.; the azo initiators include but not limited to azobisisobutyronitrile, azobisisoheptonitrile, azobis(2-methylpropionamidine) dihydrochloride, azobis(2-methyl-2-imidazoline) dihydrochloride, etc.

[0013] Furthermore, the polyacrylamide gel further comprises dipropionaldehyde pentaerythritol acetal, and the addition amount of dipropionaldehyde pentaerythritol acetal is 1.5 - 2 parts.

[0014] Preferably, the mass ratio of acrylamide, acrylic acid, 4 - methacrylamide salicylic acid, and dipropionaldehyde pentaerythritol acetal is (8 - 10):(4 - 6):(3 - 4):(0.3 - 0.4).

[0015] Furthermore, the polyacrylamide gel further comprises sodium carboxymethyl cellulose, and the degree of substitution DS of sodium carboxymethyl cellulose is 0.6 - 0.8; the addition amount of sodium carboxymethyl cellulose is 5% - 8% of the mass of acrylamide.

[0016] Further, the polyacrylamide gel is prepared by the following method: Add urea, EDTA - 2Na, acrylic acid, acrylamide, acrylic acid, 4 - methacrylamide salicylic acid, and dipropionaldehyde pentaerythritol acetal into water, add sodium hydroxide to adjust the pH, then add an initiator to react, and finally add sodium formate to stop the reaction, thus obtaining the polyacrylamide gel.

[0017] Furthermore, the temperature of the reaction is not lower than 70 °C, preferably 70 - 80 °C; the time is 3 - 5 h.

[0018] Furthermore, the reaction solution further comprises sodium carboxymethyl cellulose accounting for 5% - 8% of the mass of acrylamide.

[0019] Furthermore, the reaction solution further comprises 1.5 - 2 parts of dipropionaldehyde pentaerythritol acetal.

[0020] Furthermore, during the preparation of the polyacrylamide gel, it also includes drying the polyacrylamide gel until the water content ≤ 10% to make a polyacrylamide gel dry powder.

[0021] This application copolymerizes acrylamide, acrylic acid, and 4-methacrylamidosalicylic acid as monomers to prepare a polyacrylamide gel with a multiple cross-linked network structure. While ensuring rapid dissolution, enabling the proppant to be rapidly suspended in the water-based fracturing fluid and reducing frictional resistance, it also has high strength, enabling the proppant to have good anti-crushing ability. After testing, the crushing rate at 86 MPa is lower than 6%. The polyacrylamide also has good anti-shearing performance, can carry the proppant deeper into the formation, and can achieve the purpose that the proppant fully fills the fracturing cracks during the fracturing process. However, the phenolic hydroxyl group in 4-methacrylamidosalicylic acid will also affect the salt resistance of the gel. To solve this problem, a certain amount of diallyl aldehyde acetalized pentaerythritol is further introduced in this application. Acting synergistically with 4-methacrylamidosalicylic acid, it can balance hydration, control the degree of cross-linking, avoid excessive hydrophobicity, make up for the defect of poor salt resistance, and further improve the strength and anti-shearing performance of the gel. In addition, it is also found that adding sodium carboxymethyl cellulose with a certain degree of substitution can increase the degree of cross-linking to a certain extent, enhance the strength and anti-shearing performance of the gel, and also reduce the salting-out effect of the gel under high-salt or high-salinity conditions, improving the stability of the gel under high-salt and high-salinity conditions.

[0022] The fracturing proppant prepared by coating the above polyacrylamide gel on quartz sand or ceramsite can be rapidly suspended in water, has good drag reduction effect, low crushing rate, excellent anti-shearing performance, can be rapidly restored under shear when the formation fluid flows at high speed, and enables the formation fluid to maintain a certain viscosity. Carrying the proppant, it can enter deeper into the formation. As it contacts with oil and gas, the proppant continuously spreads in the cracks, the proppant settles and evenly spreads in the fracturing cracks, effectively increasing the volume of the fracturing cracks, thereby better improving the formation conductivity.

[0023] Furthermore, the surface of the aggregate is also loaded with isocyanate compounds, and the loading amount is 2-5% (by mass).

[0024] Optionally, the isocyanate curing agent is selected from hexamethylene diisocyanate (HDI) and its dimers or trimers, diphenylmethane diisocyanate (MDI), 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (IPDI) and its dimers or trimers, toluene diisocyanate (TDI), dimer fatty acid isocyanate (DDI) and its dimers or trimers; preferably hexamethylene diisocyanate (HDI) and its dimers or trimers, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (IPDI) and its dimers or trimers, dimer fatty acid isocyanate (DDI) and its dimers or trimers; more preferably hexamethylene diisocyanate (HDI) and its dimers or trimers, dimer fatty acid isocyanate (DDI) and its dimers or trimers.

[0025] On the other hand, the preparation method of the water-based self-suspending fracturing proppant described above is characterized by including the following steps: mixing quartz sand or ceramsite with polyacrylamide gel, stirring, drying, and cooling to obtain the water-based self-suspending fracturing proppant.

[0026] The water-based self-suspending fracturing proppant provided by this application, when used in injection, does not require pre-preparing active water-based fracturing fluids. It can directly use clear water or seawater as the fracturing fluid. Just stir the proppant evenly with clear water according to the fracturing operation technical standard and it can be used. After the proppant is pumped into the formation, as the temperature and pressure increase, the molecular micelles on the surface of the proppant undergo molecular thermal motion dissociation and hydrophobic association under high temperature and high pressure, the molecular weight ester bonds are hydrolyzed and broken, the gel-forming system is destroyed, the network-like micelle system decomposes, and the bulk viscosity decreases, greatly reducing the backflow cost and the chemical injection cost.

[0027] Furthermore, before mixing quartz sand or ceramsite with polyacrylamide gel, it also includes surface loading treatment of quartz sand or ceramsite with isocyanate compounds, and the loading amount is 2 - 5%.

[0028] Optionally, the loading treatment method includes: cleaning and dehydrating the quartz sand, then putting it into an aqueous solution containing isocyanate compounds and stirring, and taking it out and drying.

[0029] On the other hand, the application of the water-based self-suspending fracturing proppant or the water-based self-suspending fracturing proppant prepared by the above preparation method in fracturing.

[0030] Compared with the prior art, this application has the following beneficial effects: 1. The water-based self-suspending fracturing proppant provided by this application can be quickly and stably suspended in water for a long time, with a slow sedimentation rate and good self-suspending performance. Its unique molecular structure on the surface makes the proppant have good lubricity, greatly reducing the frictional resistance during the migration of the proppant, effectively reducing the loss of the proppant and the loss of the proppant to the pipe string and injection equipment.

[0031] 2. This application coats the surface of the bone particles with polyacrylamide gel with a viscosity < 2000 mPa·s and a dissolution time < 5 min to obtain a fracturing proppant with an apparent viscosity in the range of 1.40 - 1.60 g / cm³. The proppant can be suspended in clear water, reducing the frictional resistance of the proppant and extending the transportation distance; after the fracturing proppant is broken, there is almost no residue, and polyacrylamide gel is a non-toxic substance, causing almost no damage to the formation.

[0032] 3. The present application copolymerizes acrylamide, acrylic acid, and 4-methacrylamidosalicylic acid as monomers to prepare a polyacrylamide gel with a multiple cross-linked network structure, enabling the proppant to be stably suspended rapidly and for a long time in water, having good salt resistance, providing the proppant with good lubricity, greatly reducing the frictional resistance during its migration, and also having excellent shear resistance. It can carry the proppant deeper into the formation and continuously spread in the fractures, effectively increasing the volume of the fracture created by hydraulic fracturing, thereby better improving the formation conductivity. A certain amount of diallyl aldehyde acetal of pentaerythritol is added to the polyacrylamide gel, which synergistically acts with 4-methacrylamidosalicylic acid to balance hydration, control the degree of cross-linking, and avoid excessive hydrophobicity, thereby further enhancing the strength, salt resistance, and shear resistance of the gel. Adding sodium carboxymethyl cellulose with a certain degree of substitution can not only increase the degree of cross-linking to a certain extent, enhance the strength and shear resistance of the gel, but also reduce the salting-out effect of the gel under high-salt or high-salinity conditions, improving the stability of the gel under high-salt and high-salinity conditions.

[0033] 4. For the water-based self-suspending fracturing proppant provided by the present application, the quartz sand or ceramic proppant is also treated with an isocyanate compound before being coated with the polyacrylamide gel. The surface of the treated quartz sand or ceramic proppant contains a certain amount of isocyanate compound, which can react with amino groups, hydroxyl groups, etc. in the gel, so that the gel is coated more uniformly on the surface of the aggregate, thereby improving the comprehensive performance of the proppant.

[0034] 5. For the water-based self-suspending fracturing proppant provided by the present application, when it is used in the injection process, there is no need to pre-prepare active water-based fracturing fluids. It can directly use fresh water, river water, seawater, formation water, and fracturing flowback water as fracturing fluids, and also has the advantages of being easy to break gel and having a low residue content after gel breaking.

[0035] 6. The water-based self-suspending fracturing proppant provided by the present application can be used together with other fracturing aids such as other flowback aids, clay stabilizers, and oil displacement agents in fracturing operations. It has good compatibility and good effects, and has good application prospects. Detailed Embodiments

[0036] The following non-limiting examples can enable those of ordinary skill in the art to more comprehensively understand the present application, but do not limit the present application in any way. The following content is only an exemplary illustration of the scope claimed in the present application. Those skilled in the art can make various changes and modifications to the invention of the present application based on the disclosed content, and it should also fall within the scope claimed in the present application.

[0037] In the embodiments of the present application, various chemical reagents are obtained through conventional commercial channels without special instructions. Among them, 4-methylacrylamidosalicylic acid (CAS No. 50512-48-6) was purchased from Shanghai Youhe Biotechnology Co., Ltd., and diallylaldehyde pentaerythritol acetal (CAS No. 78-19-3) was purchased from Suzhou Qihang Biotechnology Co., Ltd.

[0038] In the present application, the polyacrylamide gel is prepared by the following method: Add urea, EDTA-2Na, acrylic acid, acrylamide, acrylic acid, 4-methylacrylamidosalicylic acid, and diallylaldehyde pentaerythritol acetal into water, add sodium hydroxide to adjust the pH, and then add an initiator to react; after the reaction is completed, add sodium formate to stop the reaction, and the polyacrylamide gel is obtained. Among them, there is no specific order limit for the addition sequence of the raw materials urea, EDTA-2Na, acrylic acid, acrylamide, acrylic acid, 4-methylacrylamidosalicylic acid, and diallylaldehyde pentaerythritol acetal. In the following specific examples, the preparation method of the polyacrylamide gel is as follows: (1) Mix sodium hydroxide, urea, EDTA-2Na, and acrylic acid with water to obtain Solution I; (2) Dissolve acrylamide in water, add 4-methylacrylamidosalicylic acid, diallylaldehyde pentaerythritol acetal, and a cross-linking agent and mix evenly to obtain Solution II. Mix Solution II with Solution I to obtain a reaction solution; (3) Add an initiator to the reaction solution, react at 70-80 °C for 3-5 h, and then add sodium formate to stop the reaction to obtain the polyacrylamide gel. Although the above preparation steps list the specific addition sequence of the raw materials, the preparation sequences of Solution I and Solution II in steps (1) and (2) can be changed, which has no influence on the preparation of the polyacrylamide gel and does not constitute a limitation to the application. It can be understood that changing the addition sequence of one or several of these raw materials can still exhibit the advantages described above, and a polyacrylamide gel with a fast dissolution rate, high drag reduction, good salt tolerance, and good mechanical shear stability can be obtained. Those skilled in the art can easily change the addition sequence of these raw materials without creative labor.

[0039] In the following specific Examples 1-4, the polyacrylamide gel used is a laboratory self-made product, which is prepared by reacting acrylamide and acrylic acid as reaction monomers with N,N'-methylenebisacrylamide as a cross-linking agent. The specific formulation dosage and preparation method can be adjusted according to the required apparent viscosity and swelling degree. This polyacrylamide gel can also be directly a commercially available product or prepared by a well-known preparation method in the art, as long as the requirements for viscosity and dissolution time are met, and it does not constitute a limitation to the present application.

[0040] In this application, the particle size of "20 - 80 mesh" refers to the average particle size. For example, the quartz sand with a particle size of "20 mesh" means that the average particle size of the ceramsite is 40 mesh. In this application, the quartz sand or ceramsite is not limited to the direct use of commercially available products, and can also be used after grinding to the required particle size.

[0041] The following further illustrates this application by means of specific examples.

[0042] Example 1 A polyacrylamide gel was prepared by the following method: (1) Mix 6 parts of sodium hydroxide, 3 parts of urea, 0.05 part of EDTA - 2Na, 30 parts of acrylic acid and 15 parts of water to obtain Solution I; (2) Dissolve 40 parts of acrylamide in 45 parts of water, add 15 parts of N,N - methylenebisacrylamide to obtain Solution II, and mix Solution II with Solution I to obtain a reaction solution; (3) Add 8 parts of tert - butyl hydroperoxide to the reaction solution, react at 80 °C for 3 h, and then add 0.05 part of sodium formate to stop the reaction to obtain a polyacrylamide gel, denoted as Gel 1#.

[0043] Example 2 A polyacrylamide gel was prepared by the following method: (1) Dissolve 15 parts of sodium hydroxide, 5 parts of urea, 0.08 part of EDTA - 2Na, 50 parts of acrylic acid and 20 parts of water, and fully dissolve to obtain Solution I; (2) Dissolve 55 parts of acrylamide in 45 parts of water, add 20 parts of N,N - methylenebisacrylamide to obtain Solution II, and mix Solution II with Solution I to obtain a reaction solution; (3) Add 10 parts of tert - butyl hydroperoxide to the reaction solution, react at 80 °C for 5 h, and then add 0.1 part of sodium formate to stop the reaction to obtain a polyacrylamide gel, denoted as Gel 2#.

[0044] Example 3 A polyacrylamide gel was prepared by the following method: (1) Mix 15 parts of sodium hydroxide, 5 parts of urea, 0.08 part of EDTA - 2Na, 50 parts of acrylic acid and 20 parts of water to obtain Solution I; (2) Dissolve 60 parts of acrylamide in 50 parts of water, add 25 parts of N,N - methylenebisacrylamide to obtain Solution II, and mix Solution II with Solution I to obtain a reaction solution; (3) Add 10 parts of tert - butyl hydroperoxide to the reaction solution, react at 80 °C for 5 h, and then add 0.1 part of sodium formate to stop the reaction to obtain a polyacrylamide gel, denoted as Gel 3#.

[0045] Example 4 A method for preparing polyacrylamide gel, comprising the following steps: (1) Mix 5 parts of sodium hydroxide, 1 part of carbamide, 0.02 part of EDTA-2Na, 20 parts of acrylic acid and 10 parts of water to obtain Solution I; (2) Dissolve 40 parts of acrylamide in 30 parts of water, add 15 parts of 4-methacrylamidosalicylic acid and 5 parts of N,N-tetramethylenediacrylamide and mix well to obtain Solution II. Mix Solution II with Solution I to obtain a reaction solution; (3) Add 1 part of tert-butyl hydroperoxide to the reaction solution, control the reaction temperature at 70 °C, add 0.01 part of sodium formate after 3 h to stop the reaction, and obtain polyacrylamide gel, denoted as Gel 4#.

[0046] Example 5 A method for preparing polyacrylamide gel, comprising the following steps: (1) Mix 8 parts of sodium hydroxide, 3 parts of carbamide, 0.05 part of EDTA-2Na, 25 parts of acrylic acid and 15 parts of water to obtain Solution I; (2) Dissolve 45 parts of acrylamide in 45 parts of water, add 20 parts of 4-methacrylamidosalicylic acid and 10 parts of N,N-methylenebisacrylamide and mix well to obtain Solution II. Mix Solution II with Solution I to obtain a reaction solution; (3) Add 8 parts of tert-butyl hydroperoxide to the reaction solution, react at 80 °C for 3 h, then add 0.05 part of sodium formate to stop the reaction, and obtain polyacrylamide gel, denoted as Gel 5#.

[0047] Example 6 A method for preparing polyacrylamide gel, comprising the following steps: (1) Mix 15 parts of sodium hydroxide, 5 parts of carbamide, 0.08 part of EDTA-2Na, 30 parts of acrylic acid and 20 parts of water to obtain Solution I with a mass concentration of 50%; (2) Dissolve 50 parts of acrylamide in 45 parts of water, add 25 parts of 4-methacrylamidosalicylic acid and 15 parts of methylenebisacrylamide and mix well to obtain Solution II. Mix Solution II with Solution I to obtain a reaction solution; (3) Add 10 parts of tert-butyl hydroperoxide to the reaction solution, react at 80 °C for 5 h, then add 0.1 part of sodium formate to stop the reaction, and obtain polyacrylamide gel, denoted as Gel 6#.

[0048] Example 7 The difference from Example 5 is that the addition amount of 4-methylacrylamidosalicylic acid is 25 parts, that is, the mass ratio of acrylamide, acrylic acid and 4-methylacrylamidosalicylic acid is 9:5:5, and the obtained polyacrylamide gel is denoted as Gel 7#.

[0049] Example 8 The difference from Example 5 is that the addition amount of 4-methylacrylamidosalicylic acid is 10 parts, that is, the mass ratio of acrylamide, acrylic acid and 4-methylacrylamidosalicylic acid is 9:5:2, and the obtained polyacrylamide gel is denoted as Gel 8#.

[0050] Example 9 The difference from Example 5 is that it further includes 1.5 parts of dipropenal acetal pentaerythritol, that is, the mass ratio of acrylamide, acrylic acid, 4-methylacrylamidosalicylic acid and dipropenal acetal pentaerythritol is 9:5:4:0.3, and the obtained polyacrylamide gel is denoted as Gel 9#.

[0051] Example 10 The difference from Example 5 is that it further includes 2 parts of dipropenal acetal pentaerythritol, that is, the mass ratio of acrylamide, acrylic acid, 4-methylacrylamidosalicylic acid and dipropenal acetal pentaerythritol is 9:5:4:0.4, and the obtained polyacrylamide gel is denoted as Gel 10#.

[0052] Example 11 The difference from Example 5 is that it further includes 3 parts of dipropenal acetal pentaerythritol, that is, the mass ratio of acrylamide, acrylic acid, 4-methylacrylamidosalicylic acid and dipropenal acetal pentaerythritol is 9:5:4:0.6, and the obtained polyacrylamide gel is denoted as Gel 11#.

[0053] Example 12 The difference from Example 10 is that in step (2), the dipropenal acetal pentaerythritol is replaced with an equal amount of dipropenyl amine, and the obtained polyacrylamide gel is denoted as Gel 12#.

[0054] Example 13 The difference from Example 5 is that it further includes 3.6 parts of sodium carboxymethyl cellulose (degree of substitution 0.6), and the obtained polyacrylamide gel is denoted as Gel 13#.

[0055] Example 14 The difference from Example 10 is that it further includes 2.25 parts of sodium carboxymethyl cellulose (degree of substitution 0.8), and the obtained polyacrylamide gel is denoted as Gel 14#.

[0056] Example 15 The difference from Example 14 is that the degree of substitution of sodium carboxymethyl cellulose is 0.5, and the obtained polyacrylamide gel is denoted as Gel 15#.

[0057] Example 16 The difference from Example 14 is that the degree of substitution of sodium carboxymethyl cellulose is 1.0, and the obtained polyacrylamide gel is denoted as Gel 16#.

[0058] Example 17 The difference from Example 5 is that 4-methacrylamidosalicylic acid in step (2) is replaced with an equal amount of 2-acrylamido-2-methylpropanesulfonic acid, and the obtained polyacrylamide gel is denoted as Gel 17#.

[0059] Test Example 1 Test the viscosity, dissolution time in water, shear resistance performance, and drag reduction rates in fresh water and salt water of Gels 1# - 17# prepared in the above examples; among them, the drag reduction rate is tested according to the technical indicators of SY / T 5107 - 2016 using a JZLI type drag reduction rate tester. The polyacrylamide gel is added to fresh water at 0.05% (volume percentage) and to salt water (sodium chloride mass fraction 8% and calcium chloride 2% in seawater) at 0.25% (volume percentage) respectively; the viscosity is tested using a rheometer.

[0060] Table 1 shows the test results of viscosity, dissolution time in water, and drag reduction rate. As shown in the table, the viscosities and dissolution times of Gels 1# and 2# are within 5 minutes, and the dissolution speed is fast; the drag reduction rate in fresh water is above 68%, and the drag reduction rate in seawater is below 64%, indicating good drag reduction effect in fresh water. Compared with Gels 1# - 3#, the drag reduction rates of Gels 4# - 16# in fresh water have increased. Among them, the drag reduction rates of Gels 4# - 6# / 9# / 10# / 13# / 14# in fresh water reach above 73%, and the drag reduction rates in seawater are above 62%. Especially for Gels 9# / 10# / 13# / 14#, the drag reduction rates in seawater are above 70%, and the drag reduction effect and salt tolerance have been improved.

[0061] Table 1

[0062] The shear resistance performance is tested according to the technical indicators of SY / T 5107 - 2016. During the test, the polyacrylamide gel is prepared into a 1% mass fraction solution, the shear rate is 170 s -1 , the temperature is 25 °C, and the apparent viscosity of the test solution at different shear times is tested to evaluate its shear resistance performance. Table 2 shows the test results of shear resistance performance. As shown in the table, the apparent viscosities of the 1% solutions of Gels 1# / 2# at a shear rate of 170 s -1 are in the range of 410 - 470 mPa·s, and the viscosity is below 90 mPa·s after 12 hours of long-term shear, indicating relatively poor shear resistance performance. The apparent viscosities of the 1% solutions of Gels 5# - 7# / 10# / 11# / 14# / 15# at a shear rate of 170 s -1The apparent viscosity is in the range of 410 - 470 mPa·s, and after 12 hours of long-term shearing, the viscosity is in the range of 165 - 200 mPa·s, with good shear resistance, making up for the defect of poor shear stability of the existing polyacrylamide gel.

[0063] Table 2

[0064] Example 18 A water-based self-suspending fracturing proppant, comprising aggregate and polyacrylamide gel; wherein, Aggregate: quartz sand or ceramsite, the particle size of quartz sand is 20 - 40 mesh, and the particle size of ceramsite is 40 - 60 mesh; The mass ratio of aggregate to polyacrylamide gel is 10:(1 - 10).

[0065] Its preparation method includes the following steps: Put quartz sand into a container with stirring, start stirring, add the polyacrylamide gel obtained in Example 1, control the temperature at 95 ± 5 °C, stir and coat and evaporate the water; stop heating after 90 minutes and ventilate and cool to room temperature to obtain an anti-settling and fully spread fracturing proppant.

[0066] The following proppants are prepared according to the above preparation method, specifically as follows: Proppant 1# Put 1 kg of quartz sand (particle size 40 mesh) into a container with stirring, start stirring, add 200 g of Gel 1# obtained in Example 1, stir and coat and evaporate the water, and cool to obtain Proppant 1#.

[0067] Proppant 2# The difference from Proppant 1# is that the polyacrylamide gel is Gel 2#.

[0068] Proppant 3# The difference from Proppant 1# is that the polyacrylamide gel is Gel 3#.

[0069] Proppant 4# The difference from Proppant 1# is that the polyacrylamide gel is Gel 4#.

[0070] Proppant 5# The difference from Proppant 1# is that the polyacrylamide gel is Gel 5#.

[0071] Proppant 6# The difference from Proppant 1# is that the polyacrylamide gel is Gel 6#.

[0072] Proppant 7# The difference from proppant 1# is that the polyacrylamide gel is gel 7#.

[0073] Proppant 8# The difference from proppant 1# is that the polyacrylamide gel is gel 8#.

[0074] Proppant 9# The difference from proppant 1# is that the polyacrylamide gel is gel 9#.

[0075] Proppant 10# The difference from proppant 1# is that the polyacrylamide gel is gel 10#.

[0076] Proppant 11# The difference from proppant 1# is that the polyacrylamide gel is gel 11#.

[0077] Proppant 12# The difference from proppant 1# is that the polyacrylamide gel is gel 12#.

[0078] Proppant 13# The difference from proppant 1# is that the polyacrylamide gel is gel 13#.

[0079] Proppant 14# The difference from proppant 1# is that the polyacrylamide gel is gel 14#.

[0080] Proppant 15# The difference from proppant 1# is that the polyacrylamide gel is gel 15#.

[0081] Proppant 16# The difference from proppant 1# is that the polyacrylamide gel is gel 16#.

[0082] Proppant 17# The difference from proppant 1# is that the polyacrylamide gel is gel 17#.

[0083] Proppant 18# The difference from proppant 5# is that the aggregate is ceramsite with a particle size of 60 mesh.

[0084] Proppant 19# The difference from proppant 5# is that the dosage of gel 5# is 50 g.

[0085] Proppant 20# The difference from proppant 5# is that the dosage of gel 5# is 100 g.

[0086] Proppant 21# The difference from proppant 5# is that the dosage of gel 5# is 1000 g.

[0087] Proppant 22# The difference from proppant 5# is that MDI accounting for 2% of the mass of quartz sand is further added. The MDI is first mixed with gel 5# and then used to coat the quartz sand.

[0088] Proppant 23# The difference from proppant 5# is that the surface of the quartz sand is also treated with MDI. The steps are as follows: the quartz sand is cleaned and dehydrated, then put into an aqueous solution containing sufficient MDI (mass fraction 5%) and stirred, taken out and dried. The loading amount of the isocyanate compound MDI on the surface of the quartz sand is 2%.

[0089] Proppant 24# The difference from proppant 23# is that MDI is replaced with isophorone diamine and the loading amount remains unchanged.

[0090] Test Example 2 According to "SY / T5108-2006 Performance Index and Test Recommended Method for Fracturing Proppants", the volume density, pressure-bearing capacity, suspension time, etc. of the proppants 1# - 24# prepared above are tested. The results are shown in Table 3 below.

[0091] The results show that the volume density of the proppants provided by this application is in the range of 1.40 - 1.60 g / cm 3 range, the breakage rate under 86 MPa is lower than 6%, and can reach as low as 1.4%. They have high strength, low breakage rate, strong pressure-bearing capacity; the suspension time is greater than 6 h, which can fully meet the fracturing requirements of deep wells. The proppants 1# - 3# have a relatively high breakage rate and a relatively short suspension time. Compared with the proppants 1# - 3#, the breakage rates of the proppants 4# - 6# / 9# / 10# / 13# / 14# are significantly decreased, the strength is improved, and the suspension time is extended, making up for the defects of ordinary polyacrylamide gels. It can also be seen that adding a certain amount of diallyl aldehyde acetal pentaerythritol and / or carboxymethyl cellulose sodium with a specific molecular weight to the polyacrylamide gel can further improve the strength of the gel, reduce the breakage rate of the proppant, and extend the suspension time. In addition, the ratio of polyacrylamide gel to bone particles and the treatment of the bone particle surface also have a certain impact on the performance of the proppant; if too little polyacrylamide gel is added, the resulting proppant has a high volume density, high breakage rate, and short suspension time; treating the bone particle surface with an isocyanate compound can improve the loading uniformity of the polyacrylamide gel, thereby improving the performance of the proppant.

[0092] Table 3

[0093] The proppants #1-24 are added into water at a mass fraction of 0.3%, and 1‰ ammonium persulfate is added. After gel formation, it is broken at 60°C, and the viscosity and residue content after gel breaking are tested. The results are shown in Table 4 below. It can be seen that the viscosity of the water-based self-suspending fracturing proppant provided by this application is lower than 5 mPa·s and the residue content is not higher than 10 mg / L after gel breaking, having the advantages of easy gel breaking, complete gel breaking, and low residue content after gel breaking.

[0094] Table 4

[0095] The above description of the embodiments is to enable those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative efforts. Therefore, this application is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of this application according to the disclosure of this application should be within the protection scope of this application.

Claims

1. A water-based self-suspending fracturing proppant, characterized in that: It comprises aggregate and polyacrylamide gel coated on the surface of the aggregate; The aggregate is quartz sand or ceramsite; The viscosity of the polyacrylamide gel is less than 2000 mPa·s and the dissolution time is less than 5 min; The mass ratio of the aggregate to the polyacrylamide gel is 10:(1-10); The bulk density of the water-based self-suspending fracturing proppant is 1.40-1.60 g / cm 3 ; The polyacrylamide gel comprises the following raw materials in parts by weight: 40-50 parts of acrylamide, 20-30 parts of acrylic acid, 15-25 parts of 4-methylacrylamidosalicylic acid, 1-5 parts of carbonamide, 5-15 parts of sodium hydroxide, 0.02-0.08 parts of EDTA-2Na, 5-15 parts of a crosslinking agent, 1-10 parts of an initiator, 0.01-0.1 parts of sodium formate, and 40-65 parts of water.

2. The water-based self-suspending fracturing proppant according to claim 1, characterized in that: The particle size of the aggregate is 20-80 mesh.

3. The water-based self-suspending fracturing proppant according to claim 2, characterized in that: The polyacrylamide gel also contains diacryl pentaerythritol acetal, and the added amount of diacryl pentaerythritol acetal is 1.5-2 parts.

4. The water-based self-suspending fracturing proppant according to claim 3, characterized in that: The polyacrylamide gel also contains sodium carboxymethyl cellulose, and the substitution degree of the sodium carboxymethyl cellulose is 0.6-0.

8.

5. The water-based self-suspending fracturing proppant according to claim 3 or 4, characterized in that: The aggregate surface is also loaded with isocyanate compounds; the loading amount of the isocyanate compounds on the aggregate surface is 2-5%.

6. The water-based self-suspending fracturing proppant according to claim 5, characterized in that: The isocyanate compound is selected from any one of hexamethylene diisocyanate and its dimer or trimer, diphenylmethylene diisocyanate, 3-isocyanate methylene-3,5,5-trimethylcyclohexyl isocyanate and its dimer or trimer, toluene diisocyanate, dimer fatty acid isocyanate and its dimer or trimer.

7. The method for preparing the water-based self-suspending fracturing proppant according to any one of claims 1 to 6, characterized in that: The following steps are involved: The quartz sand or ceramsite is mixed and stirred with the polyacrylamide gel, dried, cooled, crushed and sieved to obtain a water-based self-suspended fracturing proppant.

8. The method for preparing a water-based self-suspending fracturing proppant according to claim 7, characterized in that: Before the quartz sand or ceramsite is mixed with the polyacrylamide gel, the surface of the quartz sand or ceramsite is treated with an isocyanate compound, and the loading amount is 2-5%.

9. Use of the water-based self-suspending fracturing proppant according to any one of claims 1 to 6, or the water-based self-suspending fracturing proppant prepared by the preparation method according to claim 7 or 8 in fracturing.

Images