Construction method adopting water-based self-suspension fracturing propping agent

Abstract

The invention provides a construction method adopting a water-based self-suspension fracturing propping agent, and relates to the technical field of oil exploitation. The construction method comprises a liquid presetting stage, a sand adding and shot hole polishing stage, a prepad liquid stage, a main sand adding stage and a replacement stage. In the main sand adding stage, sand-carrying fluid prepared from fracturing fluid and a water-based self-suspension fracturing propping agent is used for sand adding construction, the sand-fluid ratio of the sand-carrying fluid is in a stepped rising mode, the initial sand-fluid ratio is 3-5%, 1-5% of the sand-fluid ratio is increased each time, and the maximum sand-fluid ratio is 60% until the designed sand amount is added; the particle size of the water-based self-suspension fracturing propping agent is 20-140 meshes, and the volume density is smaller than 1.60 g / cm < 3 >. According to the construction method, the traditional mode that the fracturing propping agent is laid through a viscosity suspension propping agent is changed, full-size filling of main fractures, natural fractures and micro fractures is achieved, the fracturing propping agent is laid farther and more evenly, the effective supporting volume of fracturing is greatly increased, and therefore the low-permeability oil reservoir development effect is improved.

Description

Technical Field

[0001] This application relates to the technical field of oil extraction, and particularly to a construction method using a water-based self-suspending fracturing proppant. Background Art

[0002] With the continuous extraction of oil, the reserves of ordinary oil reservoirs are decreasing, and the development of unconventional oil and gas fields such as low-permeability and tight shale oil and gas fields is increasing. For the development of low-permeability oil and gas fields and tight shale oil and gas fields, using fracturing proppants for fracturing and supporting to improve the fracture conductivity is an effective means to achieve production increase. The fracturing technology uses a ground high-pressure pump unit to inject a liquid with a certain viscosity into the reservoir through the wellbore. Due to the huge pressure generated by the fluid, artificial fractures are formed in the reservoir; further inject a fracturing fluid (also known as a sand-carrying fluid) carrying the proppant for oil and gas fracturing, and use the mechanical action of the proppant to form connected fractures with a certain size and high conductivity, so that oil and gas can flow into the well smoothly through the fractures, achieving the purpose of increasing production and efficiency.

[0003] In traditional fracturing processes, usually, guar gum and the like are added as thickeners to the sand-carrying fluid to increase the viscosity of the sand-carrying fluid, and the proppant is suspended by the viscosity to lay the fracturing proppant. However, the current sand-carrying fluid has many problems, such as a fast settlement speed, poor dissolution and dispersion in water, abrasion of solid proppants, damage to the fracturing fracture channels, and some insoluble substances in the thickener are not easily discharged back, remaining in the formation, causing formation pollution and damage; in addition, in the traditional proppant laying method of the fracturing process, after the sand-carrying fluid enters the formation, the viscosity decreases rapidly after being rapidly sheared, resulting in a decline in the sand suspension ability, so that the laying radius is very limited, the effective support radius is small, and different-scale fractures cannot be effectively supported. Summary of the Invention

[0004] The purpose of this application is to provide a construction method using a water-based self-suspending fracturing proppant in view of the deficiencies of the prior art.

[0005] To achieve the above purpose, the technical solutions adopted in this application are as follows: A construction method using a water-based self-suspending fracturing proppant includes a preflush stage, a sand-adding and wellbore grinding stage, a preflush fluid stage, a main sand-adding stage, and a displacement stage; In the main sand-adding stage, sand-adding construction is carried out using a sand-carrying fluid prepared from a fracturing fluid and a water-based self-suspending fracturing proppant. The sand-to-fluid ratio of the sand-carrying fluid adopts a stepped-up mode, with an initial sand-to-fluid ratio of 3 - 5%, increasing by 1 - 5% each time, and the maximum sand-to-fluid ratio being 60%, until all the designed sand volume is added; The particle size of the water-based self-suspending fracturing proppant is 20 - 140 mesh, and the bulk density < 1.60 g / cm³.

[0006] Further, in the preflush stage, the displacement rate of the preflush fluid is 3 - 8 m3 / min, the liquid volume is 6 - 60 m 3 。

[0007] Furthermore, in the stage of adding sand and grinding the perforation holes, a grinding fluid prepared by mixing a fracturing fluid base fluid with quartz sand or ceramic proppant is squeezed in; the sand - to - liquid ratio of the grinding fluid is 2 - 7%, the displacement is not less than 3 m 3 / min, the sand volume is 2 - 5 m 3 ; the particle size of the quartz sand or ceramic proppant is 40 - 140 mesh.

[0008] During the fracturing construction process, before squeezing in the pre - flush fluid, steps of squeezing in a pre - placed fluid and adding sand to grind the perforation holes are added. Squeezing in the pre - placed fluid can reduce filtration loss and improve the fluidity of the fracturing fluid in the formation, creating good conditions for the subsequent sand - adding fracturing operation; adding sand to grind the perforation holes can trim the perforation holes formed by perforating, improve the flow - through capacity of the perforation holes, reduce the flow resistance during fracturing, enable the fracturing fluid and the proppant to enter the formation more smoothly, improve the placement effect of the proppant in the fracture, and enhance the conductivity of the fracture.

[0009] Furthermore, in the pre - flush fluid stage, the displacement of the pre - flush fluid is 4 - 26 m 3 / min, and the liquid volume is 15 - 50% of the total liquid volume of the fracturing fluid.

[0010] Furthermore, in the main sand - adding stage, the displacement of the sand - carrying fluid is 4 - 26 m 3 / min, and the total liquid volume and the total sand - adding volume are designed according to the required fracture geometry size based on reservoir parameters. The reservoir parameters include reservoir porosity, permeability, reservoir burial depth, and reservoir thickness.

[0011] Furthermore, the main sand - adding stage includes three stages; The first stage: the initial sand - to - liquid ratio is 3 - 5%, increasing step by step by 1 - 3% as a sand - adding step, divided into 2 - 3 steps for sand - adding, and the highest sand - to - liquid ratio is 9 - 12%; the sand volume is 10 - 20% of the total sand - adding volume in the main sand - adding stage; The second stage: the initial sand - to - liquid ratio is 9 - 12%, increasing step by step by 2 - 3% as a sand - adding step, and the highest sand - to - liquid ratio is 30 - 50%, and the sand volume is 50 - 75% of the total sand - adding volume in the main sand - adding stage; The third stage: the initial sand - to - liquid ratio is 30 - 50%, increasing step by step by 2 - 5% as a sand - adding step, and the highest sand - to - liquid ratio is 40 - 60%, and the sand volume is 15 - 30% of the total sand - adding volume in the main sand - adding stage.

[0012] Furthermore, the displacement in each stage of the main sand - adding stage can be the same or different.

[0013] Furthermore, in the main proppant addition stage, water-based self-suspending fracturing proppants with different particle sizes are used for proppant addition construction; the particle sizes of the water-based self-suspending fracturing proppants are added in the order from small to large; the dosages of various water-based self-suspending fracturing proppants with different particle sizes are confirmed according to specific reservoir parameters, fracture fluid conductivity, etc.

[0014] Further, the fracturing fluid, fracturing fluid base fluid, preflush fluid, and pad fluid are each selected from any one or more of fresh water, river water, seawater, formation water, and fracturing flowback water.

[0015] Further, the water-based self-suspending fracturing proppant includes aggregate and polyacrylamide gel coated on the surface of the aggregate; The aggregate is quartz sand or ceramsite; the particle size of the quartz sand or ceramsite is 20 - 140 mesh; The mass ratio of the aggregate to the polyacrylamide gel is 10:(1 - 10).

[0016] Furthermore, the particle size of the quartz sand is preferably 20 - 40 mesh, and the particle size of the ceramsite is preferably 40 - 60 mesh.

[0017] Furthermore, the viscosity of the polyacrylamide gel is 200 - 2000 mPa·s, and the dissolution time is 20 s - 5 min.

[0018] 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 thickener 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 the 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 clear water, reducing the frictional resistance of the proppant and extending the transportation distance of the proppant; after the fracturing proppant breaks, there is almost no residue, and the polyacrylamide gel is a non-toxic substance, causing almost no damage to the formation.

[0019] 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 effects can be achieved according to the material ratios and other limitations described above, obtaining a water-based self-suspending fracturing proppant, reducing the frictional resistance of the proppant and extending the transportation 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 high-salt environments. 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.

[0020] The polyacrylamide gel contains raw materials in the following 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 urea, 5 - 15 parts of sodium hydroxide, 0.02 - 0.08 parts of EDTA - 2Na, 5 - 15 parts of cross - linker, 1 - 10 parts of initiator, 0.01 - 0.1 parts of sodium formate, and 40 - 65 parts of water.

[0021] Optionally, the cross - linker is a cross - linker containing bisacrylamide groups, including but not limited to N,N - methylenebisacrylamide, N,N - propylenediacrylamide, N,N - tetramethylenediacrylamide, N,N - hexamethylenediacrylamide, or N,N - m - xylylenediacrylamide, etc.

[0022] 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.

[0023] Furthermore, the polyacrylamide gel further contains dipropionaldehyde - pentaerythritol acetal, and the addition amount of dipropionaldehyde - pentaerythritol acetal is 1.5 - 2 parts.

[0024] Preferably, the mass ratio of acrylamide, acrylic acid, 4 - methacrylamidosalicylic acid, and dipropionaldehyde - pentaerythritol acetal is (8 - 10):(4 - 6):(3 - 4):(0.3 - 0.4).

[0025] Furthermore, the polyacrylamide gel further contains sodium carboxymethylcellulose, the degree of substitution DS of sodium carboxymethylcellulose is 0.6 - 0.8; the addition amount of sodium carboxymethylcellulose is 5% - 8% of the mass of acrylamide.

[0026] Further, the polyacrylamide gel is prepared by the following method: Add urea, EDTA - 2Na, acrylic acid, acrylamide, acrylic acid, 4 - methacrylamidosalicylic acid, and dipropionaldehyde - pentaerythritol acetal into water, add sodium hydroxide to adjust the pH, then add the initiator to react, and finally add sodium formate to stop the reaction, thus obtaining the polyacrylamide gel.

[0027] Furthermore, the temperature of the reaction is not lower than 70 °C, preferably 70 - 80 °C; the time is 3 - 5 h.

[0028] Furthermore, the reaction solution further comprises sodium carboxymethyl cellulose accounting for 5%-8% of the mass of acrylamide.

[0029] Furthermore, the reaction solution further comprises 1.5-2 parts of dipropenal acetal pentaerythritol.

[0030] Furthermore, during the preparation of the polyacrylamide gel, the polyacrylamide gel is further dried to a moisture content of ≤10% to form a polyacrylamide gel dry powder.

[0031] In this application, acrylamide, acrylic acid, and 4-methacrylamidosalicylic acid are used as monomers to copolymerize to prepare a polyacrylamide gel with a multi-crosslinked 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 less than 6%; the polyacrylamide also has good anti-shearing performance and can carry the proppant deeper into the formation, achieving the purpose that the proppant can fully fill 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 dipropenal acetal pentaerythritol is further introduced in this application. Acting synergistically with 4-methacrylamidosalicylic acid, it can balance hydration, control the degree of crosslinking, 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, to a certain extent, increase the degree of crosslinking, 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-mineralization conditions, improving the stability of the gel under high-salt and high-mineralization conditions.

[0032] The fracturing proppant prepared by coating the above polyacrylamide gel on quartz sand or ceramsite in this application 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 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.

[0033] Furthermore, the surface of the aggregate is further loaded with an isocyanate compound, and the loading amount is 2-5% (by mass).

[0034] 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.

[0035] The preparation method of the water-based self-suspending fracturing proppant described above is characterized by including the following steps: including the following steps: mixing and stirring quartz sand or ceramsite with polyacrylamide gel, drying and cooling to obtain the water-based self-suspending fracturing proppant. Before mixing quartz sand or ceramsite with polyacrylamide gel, it also includes surface loading treatment of quartz sand or ceramsite with an isocyanate compound, and the loading amount is 2-5%; the loading treatment method includes: cleaning and dehydrating quartz sand, then putting it into an aqueous solution containing an isocyanate compound and stirring, and drying it after taking it out.

[0036] Furthermore, in the displacement stage, the fracturing fluid base fluid or clear water is used for displacement, and the displacement volume is equal to the volume of the construction string.

[0037] Furthermore, before the stage of the fracturing fluid base fluid, steps such as pipe lifting, well flushing, pipe scraping, well washing, wellhead installation, and wellbore pressure testing can be carried out as required, and a well shut-in operation can be carried out as required after the displacement stage.

[0038] Compared with the prior art, the present application has the following beneficial effects: 1. The construction method of the water-based self-suspending fracturing proppant adopted in the present application changes the traditional laying method of the fracturing proppant by relying on the viscosity to suspend the proppant, makes up for the defects of the existing fracturing methods with a small laying radius and inability to effectively support fractures of different scales, realizes the full-size filling of the main fracture, natural fracture and microfracture, makes the fracturing proppant lay farther and more evenly, greatly increases the effective support volume of fracturing, and thus improves the development effect of low-permeability reservoirs.

[0039] 2. The construction method of the water-based self-suspending fracturing proppant adopted in the present application adds steps of squeezing in a pre-set fluid and sandblasting the perforations before squeezing in the preflush fluid, which can improve the fluidity of the fracturing fluid in the formation, enable the fracturing fluid and the proppant to enter the formation more smoothly, improve the placement effect of the proppant in the fracture, enhance the conductivity of the fracture, and improve the fracturing construction effect.

[0040] 3. In the proppant section of this application, by coordinating the stepwise change of the particle size and sand-fluid ratio of the self-suspending fracturing proppant, gradually transitioning from a low sand ratio to a high sand ratio, while increasing the comprehensive sand-fluid ratio, the problem of sand plugging caused by using high-concentration proppant at the beginning is avoided. This enables the proppant to better enter the fracture and be evenly distributed, and also enables the fracture to be reasonably supported at different stages, achieving the filling of fractures of different sizes and improving the fracturing construction effect.

[0041] 4. The self-suspending fracturing proppant of this application can be directly configured with fracturing fluids such as fresh water and seawater to form a sand-carrying fluid. The self-suspending fracturing proppant can quickly suspend in water, has good self-suspending performance, a slow settling speed, good drag reduction effect, is easy to break gel, has a low residue content after gel breaking, and is easy to flow back, thereby reducing the damage to the reservoir during fracturing construction. Specific Embodiments

[0042] The following non-limiting embodiments can enable those of ordinary skill in the art to more comprehensively understand this application, but do not limit this application in any way. The following content is merely an exemplary illustration of the scope claimed in this application. Those skilled in the art can make various changes and modifications to the invention of this application based on the disclosed content, and these should also fall within the scope claimed in this application.

[0043] All kinds of chemical reagents used in the embodiments of this application are obtained through conventional commercial channels without special instructions. Among them, 4-methacrylamidosalicylic acid (CAS No. 50512-48-6) was purchased from Shanghai Youhe Biotechnology Co., Ltd., and diallylaldehyde pentaerythritol (CAS No. 78-19-3) was purchased from Hubei Xinjing New Materials Co., Ltd.

[0044] In this application, the polyacrylamide gel is prepared by the following method: Add urea, EDTA-2Na, acrylic acid, acrylamide, acrylic acid, 4-methacrylamidosalicylic acid, and dipropenal pentaerythritol into water, adjust the pH with sodium hydroxide, 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-methacrylamidosalicylic acid, and dipropenal pentaerythritol. In the following specific examples, the preparation method of the polyacrylamide gel is as follows: (1) Mix sodium hydroxide, urea, EDTA-2Na, acrylic acid with water to obtain Solution I; (2) Dissolve acrylamide in water, add 4-methacrylamidosalicylic acid, dipropenal pentaerythritol, and a crosslinking 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 impact 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.

[0045] In the following specific Examples 1-4, the polyacrylamide gel used is a self-made product in the laboratory, prepared by reacting acrylamide and acrylic acid as reaction monomers with N,N-methylenebisacrylamide as a crosslinking 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 directly use commercially available products or be prepared by well-known preparation methods in the art, as long as the requirements for viscosity and dissolution time are met, which does not constitute a limitation to this application.

[0046] In this application, the statement that the sand-liquid ratio "increases by 1-3% each time" means that the sand-liquid ratio gradually increases in increments of 1-3%, and the difference in the sand-liquid ratio before and after is 1-3%; for example, if the initial sand-liquid ratio is 3% and it increases by 2% each time, it means that the sand-liquid ratio in the next stage increases to 5%. In this application, the particle size "20-140 mesh" refers to the average particle size. For example, "40-mesh" ceramsite means that the average particle size of the ceramsite is 40 mesh. In this application, quartz sand or ceramsite is not limited to direct use of commercially available products and can also be used after grinding to the required particle size.

[0047] In this application, the "water-based self-suspending fracturing proppant" refers to a fracturing proppant that can achieve good suspension in water. It does not require the preparation of active water-based fracturing fluids and can directly use fresh water, river water, seawater, formation water, fracturing return water, etc. as fracturing fluids. The "water-based self-suspending fracturing proppant" of this application is mainly prepared by coating polyacrylamide gel on the surface of quartz sand or ceramsite. By improving the polyacrylamide gel, after the water-based self-suspending fracturing proppant encounters water, the polyacrylamide gel can be used as a thickening agent to increase the density, viscosity, viscoelasticity, etc. of water, so that the proppant can be in a suspended state in water.

[0048] The following further illustrates this application in the form of specific examples.

[0049] 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#.

[0050] 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#.

[0051] 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, then add 0.1 part of sodium formate to stop the reaction, and obtain a polyacrylamide gel, denoted as Gel 3#.

[0052] Example 4 A method for preparing a polyacrylamide gel, comprising the following steps: (1) Mix 5 parts of sodium hydroxide, 1 part of urea, 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 a polyacrylamide gel, denoted as Gel 4#.

[0053] Example 5 A method for preparing a polyacrylamide gel, comprising the following steps: (1) Mix 8 parts of sodium hydroxide, 3 parts of urea, 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 a polyacrylamide gel, denoted as Gel 5#.

[0054] Example 6 A method for preparing a polyacrylamide gel, comprising the following steps: (1) Mix 15 parts of sodium hydroxide, 5 parts of urea, 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#.

[0055] 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#.

[0056] 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#.

[0057] Example 9 The difference from Example 5 is that it further includes 1.5 parts of diallyl aldehyde acetal pentaerythritol, that is, the mass ratio of acrylamide, acrylic acid, 4-methylacrylamidosalicylic acid and diallyl aldehyde acetal pentaerythritol is 9:5:4:0.3, and the obtained polyacrylamide gel is denoted as Gel 9#.

[0058] Example 10 The difference from Example 5 is that it further includes 2 parts of diallyl aldehyde acetal pentaerythritol, that is, the mass ratio of acrylamide, acrylic acid, 4-methylacrylamidosalicylic acid and diallyl aldehyde acetal pentaerythritol is 9:5:4:0.4, and the obtained polyacrylamide gel is denoted as Gel 10#.

[0059] Example 11 The difference from Example 5 is that it further includes 3 parts of diallyl aldehyde acetal pentaerythritol, that is, the mass ratio of acrylamide, acrylic acid, 4-methylacrylamidosalicylic acid and diallyl aldehyde acetal pentaerythritol is 9:5:4:0.6, and the obtained polyacrylamide gel is denoted as Gel 11#.

[0060] Example 12 The difference from Example 10 is that in step (2), the diallyl aldehyde acetal pentaerythritol is replaced with an equal amount of diallyl oxanilide, and the obtained polyacrylamide gel is denoted as Gel 12#.

[0061] 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#.

[0062] Example 14 The difference from Example 10 is that it further includes 2.25 parts of sodium carboxymethylcellulose (degree of substitution 0.8), and the obtained polyacrylamide gel is denoted as Gel 14#.

[0063] Example 15 The difference from Example 14 is that the degree of substitution of sodium carboxymethylcellulose is 0.5, and the obtained polyacrylamide gel is denoted as Gel 15#.

[0064] Example 16 The difference from Example 14 is that the degree of substitution of sodium carboxymethylcellulose is 1.0, and the obtained polyacrylamide gel is denoted as Gel 16#.

[0065] Example 17 The difference from Example 5 is that in step (2), 4-methacrylamidosalicylic acid is replaced with an equal amount of 2-acrylamido-2-methylpropanesulfonic acid, and the obtained polyacrylamide gel is denoted as Gel 17#.

[0066] Test Example 1 Test the viscosity, dissolution time in water, shear resistance performance, and drag reduction rates in fresh water and salt water of the 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 (8% sodium chloride and 2% calcium chloride in seawater) at 0.25% (volume percentage) respectively; the viscosity is tested using a rheometer.

[0067] 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%, and the drag reduction effect in fresh water is good. 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.

[0068] Table 1

[0069] The shear resistance performance is tested according to the technical indicators of SY / T 5107 - 2016. During the test, the polyacrylamide gel is configured into a solution with a mass fraction of 1%, and the shear rate is 170 s -1, at a temperature of 25 °C, the apparent viscosity of the test solution at different shear times was measured to evaluate its shear resistance. Table 2 shows the test results of shear resistance. As shown in the table, the apparent viscosity of the 1% solution of Gel 1# / 2# ranges from 410 to 470 mPa·s at a shear rate of 170 s -1 and is lower than 90 mPa·s after 12 h of long-term shear, indicating relatively poor shear resistance. The apparent viscosity of the 1% solution of Gels 5#~7# / 10# / 11# / 14# / 15# ranges from 410 to 470 mPa·s at a shear rate of 170 s -1 and is in the range of 165 - 200 mPa·s after 12 h of long-term shear, showing good shear resistance and making up for the defect of poor shear stability of existing polyacrylamide gels.

[0070] Table 2

[0071] Example 18 A water-based self-suspending fracturing proppant, comprising an aggregate and a 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 the aggregate to the polyacrylamide gel is 10:(1 - 10).

[0072] 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 to evaporate the water; stop heating after 90 min and ventilate and cool to room temperature to obtain an anti-settling and fully spread fracturing proppant.

[0073] The following proppants were 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 to evaporate the water, and cool to obtain Proppant 1#.

[0074] Proppant 2# The difference from Proppant 1# is that the polyacrylamide gel is Gel 2#.

[0075] Proppant 3# The difference from Proppant 1# is that the polyacrylamide gel is Gel 3#.

[0076] Proppant 4# The difference from Proppant 1# is that the polyacrylamide gel is Gel 4#.

[0077] Proppant 5# The difference from Proppant 1# is that the polyacrylamide gel is Gel 5#.

[0078] Proppant 6# The difference from Proppant 1# is that the polyacrylamide gel is Gel 6#.

[0079] Proppant 7# The difference from Proppant 1# is that the polyacrylamide gel is Gel 7#.

[0080] Proppant 8# The difference from Proppant 1# is that the polyacrylamide gel is Gel 8#.

[0081] Proppant 9# The difference from Proppant 1# is that the polyacrylamide gel is Gel 9#.

[0082] Proppant 10# The difference from Proppant 1# is that the polyacrylamide gel is Gel 10#.

[0083] Proppant 11# The difference from Proppant 1# is that the polyacrylamide gel is Gel 11#.

[0084] Proppant 12# The difference from Proppant 1# is that the polyacrylamide gel is Gel 12#.

[0085] Proppant 13# The difference from Proppant 1# is that the polyacrylamide gel is Gel 13#.

[0086] Proppant 14# The difference from Proppant 1# is that the polyacrylamide gel is Gel 14#.

[0087] Proppant 15# The difference from Proppant 1# is that the polyacrylamide gel is Gel 15#.

[0088] Proppant 16# The difference from Proppant 1# is that the polyacrylamide gel is Gel 16#.

[0089] Proppant 17# The difference from Proppant 1# is that the polyacrylamide gel is Gel 17#.

[0090] Proppant 18# The difference from Proppant 5# is that the aggregate is ceramsite with a particle size of 60 mesh.

[0091] Proppant 19# The difference from Proppant 5# is that the dosage of Gel 5# is 50 g.

[0092] Proppant 20# The difference from Proppant 5# is that the dosage of Gel 5# is 100 g.

[0093] Proppant 21# The difference from Proppant 5# is that the dosage of Gel 5# is 1000 g.

[0094] Proppant 22# The difference from Proppant 5# is that MDI accounting for 2% of the mass of quartz sand is also added. The MDI is first mixed evenly with Gel 5# and then used to coat the quartz sand.

[0095] 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 isocyanate compound MDI on the surface of the quartz sand is 2%.

[0096] Proppant 24# The difference from Proppant 23# is that MDI is replaced with isophorone diamine and the loading amount remains unchanged.

[0097] Test Example 2 According to "SY / T5108-2006 Performance Indexes and Test Recommended Methods for Fracturing Proppants", the volume density, pressure-bearing capacity, suspension time, etc. of the prepared Proppants 1# - 24# are tested. The results are shown in Table 3 below.

[0098] The results show that the volume density of the proppants provided by this application is in the range of 1.40 - 160 g / cm 3The range is such that the breakage rate under 86 MPa is lower than 6%, and can reach as low as 1.4%. It has high strength, low breakage rate, and strong pressure-bearing capacity. The suspension time is greater than 6 h, which can fully meet the fracturing requirements of deep wells. The breakage rate of proppants 1 - 3# is relatively high and the suspension time is relatively short. Compared with proppants 1 - 3#, the breakage rate of proppants 4# - 6# / 9# / 10# / 13# / 14# is significantly decreased, the strength is increased, 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 of pentaerythritol and / or sodium carboxymethylcellulose with a specific molecular weight to the polyacrylamide gel can further enhance 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 bulk density, high breakage rate, and short suspension time; treating the bone particle surface with an isocyanate compound can improve the load uniformity of the polyacrylamide gel, thereby improving the performance of the proppant.

[0099] Table 3

[0100] Add proppants 1# - 24# into water at a mass fraction of 0.3%, add 1‰ ammonium persulfate, and break the gel at 60℃ after gel formation. Test the viscosity and residue content after gel breaking. The results are shown in Table 4 below. It can be seen that the water-based self-suspending fracturing proppant provided by this application has a viscosity lower than 5 mPa·s and a residue content not higher than 10 mg / L after gel breaking, and has the advantages of easy gel breaking, complete gel breaking, and low residue content after gel breaking.

[0101] Table 4

[0102] Taking several adjacent wells in Xianhezhuang Oilfield as examples, the construction is carried out according to the construction method provided by this application, specifically as follows: Example 19 This example takes Well 1# (with a reservoir porosity of 12.7%, a permeability of 2.5 mD, an original formation pressure of 36.75 MPa, and an oil reservoir burial depth of 3659.3 - 3672.8 m, which is a low-permeability tight oil reservoir) as an example, and makes a specific description according to the following method for construction.

[0103] The fracturing construction steps of this example include: Prepad fluid stage: The prepad fluid is fresh water; Sand-adding and wellbore grinding stage: Inject a grinding fluid prepared by mixing the base fluid of the fracturing fluid (fresh water) and 70-mesh quartz sand; Pad fluid stage: The pad fluid is fresh water; Main proppant addition stage: Use a sand-carrying fluid prepared from a fracturing fluid and a water-based self-suspending fracturing proppant (Proppant 2# prepared in Example 18, with a particle size of 40 mesh and a bulk density of 1.58 g / cm 3 ). Carry out sand addition construction with the sand-carrying fluid. The sand-to-fluid ratio of the sand-carrying fluid adopts a stepped-up mode. The initial sand-to-fluid ratio is 3%, increasing by 1 - 5% each time, and the maximum sand-to-fluid ratio is 60% until all the designed sand volume is added; The main proppant addition stage includes first-stage sand addition, second-stage sand addition, and third-stage sand addition; First stage: The initial sand-to-fluid ratio is 3%, increasing step by step with a 2% sand addition step, and the maximum sand-to-fluid ratio is 9%; The sand volume is 10% of the total sand addition volume in the main proppant addition stage; Second stage: The initial sand-to-fluid ratio is 9%, increasing step by step with a 3% sand addition step, and the maximum sand-to-fluid ratio is 50%; The sand volume is 68% of the total sand addition volume in the main proppant addition stage; Third stage: The initial sand-to-fluid ratio is 50%, increasing step by step with a 5% sand addition step, and the maximum sand-to-fluid ratio is 60%; The sand volume is 22% of the total sand addition volume in the main proppant addition stage.

[0104] Displacement stage: Use clear water for displacement, and the displacement volume is equal to or the volume of the construction string.

[0105] The specific steps of the fracturing construction process are shown in Table 5 below: Table 5

[0106] The initial daily oil production after construction is 18.7 t, the annual cumulative oil production is 2620 t, and the average daily oil production is 7.18 t.

[0107] Example 20 In this example, well 2# (with a reservoir porosity of 15.5%, a permeability of 8.6 mD, an original formation pressure of 34.68 MPa, and a reservoir burial depth of 3451.6 - 3476.3 m, being a low-permeability tight oil reservoir) is used for construction. The difference in the construction method from Example 19 is that the self-suspending fracturing proppant in the fracturing fluid is Proppant 6#. After construction, it flows by itself for 225 days, with an initial daily oil production of 21.3 t, an annual cumulative oil production of 2865 t, and an average daily oil production of 7.85 t.

[0108] Example 21 In this example, well 3# (with a reservoir porosity of 14.7%, a permeability of 4.7 mD, an original formation pressure of 40.55 MPa, and a reservoir burial depth of 4047.2 - 4060.6 m, being a low-permeability tight oil reservoir) is used for construction. The difference in the construction method from Example 19 is that the self-suspending fracturing proppants used in the three stages of the main proppant addition stage are Proppant 18#, Proppant 5#, and Proppant 5# in sequence. After construction, the initial daily oil production is 24.2 t, the annual cumulative oil production is 2997 t, and the average daily oil production is 8.21 t.

[0109] Example 22 This example is applied to Well 4# (with reservoir porosity of 15.0%, permeability of 7.1 mD, original formation pressure of 39.75 MPa, and reservoir burial depth of 3970.2 - 3993.7 m, being a low-permeability tight oil reservoir). The difference in the construction method from Example 19 is that during the process of injecting fracturing fluid, the initial sand-fluid ratio is 3%, and the sand-fluid ratio increases stepwise by 5% each time until the maximum sand-fluid ratio reaches 50%. After construction, the initial daily oil production is 16.2 t, the annual cumulative oil production is 2383 t, and the average daily oil production is 6.53 t.

[0110] Example 23 This example is applied to Well 5# (with reservoir porosity of 14.9%, permeability of 3.5 mD, original formation pressure of 40.22 MPa, and reservoir burial depth of 4013.4 - 4038.5 m, being a low-permeability tight oil reservoir). The difference in the construction method from Example 19 is that during the fracturing construction process, the pre-fracturing fluid base fluid stage and the sand addition for hole grinding stage are not carried out. After construction, the initial daily oil production is 12.8 t, the annual cumulative oil production is 2089 t, and the average daily oil production is 5.72 t.

[0111] The above description of the examples is for the convenience of 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 examples and apply the general principles described herein to other examples without creative efforts. Therefore, this application is not limited to the above examples, 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 construction method using a water-based self-suspending fracturing proppant, characterized in that: It includes the pre-filling stage, sand adding and grinding the blasthole stage, the pre-filling stage, the main sand adding stage and the displacement stage; In the main sand adding stage, a sand-carrying fluid composed of fracturing fluid and water-based self-suspended fracturing proppant is used for sand adding construction. The sand-to-liquid ratio of the sand-carrying fluid adopts a step-by-step increase mode, with an initial sand-to-liquid ratio of 3-5%, which increases by 1-5% each time, and the maximum sand-to-liquid ratio is 60%, until all the designed sand volume is added; The water-based self-suspending fracturing proppant has a particle size of 20-140 mesh and a bulk density of <1.60 g / cm³; The water-based self-suspending fracturing proppant comprises aggregate and polyacrylamide gel coated on the surface of the aggregate; The aggregate is quartz sand or ceramsite; The mass ratio of the aggregate to the polyacrylamide gel is 10:(1-10); The viscosity of the polyacrylamide gel is 200-2000 mPa·s, and the dissolution time is 20s-5min.

2. A construction method using a water-based self-suspending fracturing proppant according to claim 1, characterized in that: During the pre-filling stage, the displacement of the pre-filling liquid is 3-8m 3 / min, liquid volume is 6-60m 3 .

3. A construction method using a water-based self-suspending fracturing proppant according to claim 1, characterized in that: During the sanding and polishing stage of the blasthole, a polishing liquid made of fracturing fluid base fluid and quartz sand or ceramsite is squeezed in; the sand-to-liquid ratio of the polishing liquid is 2-7%, and the displacement is not less than 3m 3 / min, sand volume is 2-5m 3 ; The particle size of quartz sand or expanded clay is 40-140 mesh.

4. A construction method using a water-based self-suspending fracturing proppant according to claim 1, characterized in that: In the pre-fluid stage, the displacement of the pre-fluid is 4-26m 3 / min, and the liquid volume is 15-50% of the total liquid volume of the fracturing fluid.

5. A construction method using a water-based self-suspending fracturing proppant according to claim 1, characterized in that: The main sanding stage consists of three phases; The first stage: the initial sand-liquid ratio is 3-5%, and the sand adding step is increased step by step by 1-3%, and the sand adding is divided into 2-3 steps. The highest sand-liquid ratio is 9-12%; the sand volume is mainly 10-20% of the total sand added in the sand adding stage; The second stage: the initial sand-liquid ratio is 9-12%, and the sand-adding step is increased step by step by 2-3%. The highest sand-liquid ratio is 30-50%, and the sand volume is mainly 50-75% of the total amount of sand added in the sand-adding stage; The third stage: the initial sand-to-liquid ratio is 30-50%, which increases step by step with 2-5% as a sand adding step. The highest sand-to-liquid ratio is 40-60%. The amount of sand is mainly 15-30% of the total amount of sand added in the sand adding stage.

6. A construction method using a water-based self-suspending fracturing proppant according to claim 1, characterized in that: In the main sand adding stage, water-based self-suspending fracturing proppants with different particle sizes are used for sand adding construction, and the particle sizes of the water-based self-suspending fracturing proppants are added in a mode of increasing from small to large.

7. A construction method using a water-based self-suspending fracturing proppant according to claim 1, characterized in that: 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.

8. A construction method using a water-based self-suspending fracturing proppant according to claim 7, characterized in that: The polyacrylamide gel further comprises diacryl pentaerythritol acetal and / or sodium carboxymethyl cellulose; the addition amount of the diacryl pentaerythritol acetal is 1.5-2 parts, and the substitution degree of the sodium carboxymethyl cellulose is 0.6-0.8; and / or The aggregate surface is also loaded with 2-5% isocyanate compounds.

9. A construction method using a water-based self-suspending fracturing proppant according to claim 1, characterized in that: During the displacement stage, fracturing fluid base fluid or clean water is used for displacement, and the displacement volume is equal to the volume of the construction string.

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