Fiber for oilfield fracturing and synthesis method thereof

Abstract

The present invention belongs to the field of oil extraction technology, and in particular to a fiber for oilfield fracturing and a synthesis method thereof. The synthesis method is as follows: 2,2,2-trifluoroethyl acrylate, p-styrene sulfonate, benzyl methacrylate, and water are sequentially added to a reactor equipped with a condenser, stirred, and the pH is adjusted to 6-7 with a sodium hydroxide solution, and stirring is continued to form an emulsion; a sodium persulfate solution is slowly added dropwise, the solution gradually thickens, and the stirring reaction is continued after the dropwise addition is completed, and a sodium sulfite solution is continued to be added dropwise, and stirring is continued after the dropwise addition is completed to obtain a viscous polymer; the above-mentioned polymer is subjected to jetting, winding, drawing, and shearing operations to obtain a fiber, i.e., a product oilfield fracturing fiber. The fiber for oilfield fracturing of the present invention has a high sand carrying capacity, and the static settling velocity reduction rate of ceramsite is greater than 25%; it has good flow conductivity, and the flow conductivity reduction rate is less than 2.5%.

Description

Technical Field

[0001] The invention belongs to the technical field of oil extraction, and in particular relates to a fiber for oilfield fracturing and a synthesis method thereof. Background Art

[0002] Fracturing technology has been widely used as a means of increasing the production of oil and gas wells. It uses a ground high-pressure pump group to pump fracturing fluid into the formation at a displacement rate that far exceeds the absorption capacity of the formation, forming cracks in the formation, increasing the seepage area of ​​the reservoir, and improving the conductivity of the oil and gas layer, thereby achieving the purpose of increasing production.

[0003] However, conventional hydraulic fracturing processes tend to form single, symmetrical fractures in the reservoir, preventing the effective utilization of reservoir reserves and limiting the effectiveness of fracturing. As a new fracturing construction measure, biodegradable fiber temporary plugging and diversion fracturing technology has received increasing attention in recent years. Its construction principle is to inject biodegradable fibers as temporary plugging agents into reservoir fractures along with fracturing fluid, effectively plugging the main fractures. Subsequent pumping of fracturing fluid generates a certain temporary plugging pressure, inducing the fractures to divert and form branch fractures. Ceramic sand proppants then enter these new fractures, improving the effectiveness of the fracturing operation.

[0004] After construction measures, the fiber gradually degrades at the formation temperature. As the fracturing flowback fluid is discharged from the reservoir, it will not affect the fracture conductivity after fracturing. Degradable fiber is different from other types of temporary plugging agents. In addition to having strong plugging ability, the addition of fiber can also improve the sand carrying performance of the fracturing fluid and effectively prevent the backflow of fracturing proppants.

[0005] Currently, the fiber materials used for fracturing are of varying quality, and there are still deficiencies in terms of sand-carrying performance and conductivity reduction, making it difficult to meet the sand-carrying needs of oil and gas reservoir fracturing. Furthermore, they are difficult to degrade in a short period of time, and are likely to cause a certain degree of pollution to the reservoir, thus failing to meet the requirements of environmentally friendly production.

[0006] CN106479475A discloses a process for preparing a low-temperature hydrolyzable fiber fracturing fluid. The prepared fiber fracturing fluid can be hydrolyzed at low temperatures without requiring flowback, has minimal reservoir damage, and exhibits excellent sand-carrying properties. The linear fiber fracturing fluid comprises, by weight, 0.5% guar gum; 2% KCl; 1% fiber; and the remainder water. The fiber is polyvinyl alcohol fiber. The polyvinyl alcohol (PVA) fibers used in this process can hydrolyze at low temperatures, achieving a degradation rate of over 85% within 20 hours at 70-75°C and over 90% within 4 hours at 90-95°C. Based on sand-carrying properties, the preferred PVA fibers are 20 μm in diameter, 8 mm in length, and contain 1% PVA by mass. The addition order is 0.5% guar gum, followed by 1% fiber, and finally proppant. The ceramsite settling velocity is 0.90 mm / min, resulting in excellent sand-carrying properties. The linear PVA fracturing fluid has a permeability damage rate of 24.55% on coal rock, which is less than 30%, indicating weak damage. The fibers cannot be fully degraded, and remaining in the formation can exacerbate damage to low-permeability reservoirs. Summary of the Invention

[0007] The present invention addresses the deficiencies of the prior art and provides a fiber for oilfield fracturing and a synthesis method thereof. The fiber for fracturing of the present invention has the characteristics of automatic degradation with adjustable temperature, strong sand carrying capacity, and low conductivity reduction rate.

[0008] One of the purposes of the present invention is to disclose a fiber for oilfield fracturing. The molecular structure of the fiber for oilfield fracturing is as follows:

[0009]

[0010] in:

[0011] x=1000-20000;

[0012] y = 200-4000;

[0013] z=500-10000.

[0014] The molecular weight of the fiber for oilfield fracturing is 400,000-4,000,000.

[0015] Another object of the present invention is to disclose a method for synthesizing the above-mentioned oilfield fracturing fiber, the specific steps of which are as follows:

[0016] (1) 2,2,2-trifluoroethyl acrylate, styrene p-sulfonate, benzyl methacrylate, and water were sequentially added to a reactor equipped with a condenser, stirred for 10-30 minutes, and the pH was adjusted to 6-7 with a 1 mol / L sodium hydroxide solution. Stirring was continued for 10-20 minutes to form an emulsion;

[0017] (2) Slowly dropwise adding sodium persulfate solution into the above emulsion until the solution gradually thickens. After the addition is complete, continue stirring and reacting for 1-2 hours. Continue to dropwise add sodium sulfite solution. After the addition is complete, continue stirring for 20-30 minutes to obtain a viscous polymer.

[0018] (3) The polymer is subjected to jetting, winding, drawing and shearing operations to obtain fibers, i.e., fibers for oilfield fracturing.

[0019] In the present invention, preferably, the weight ratio of the 2,2,2-trifluoroethyl acrylate, styrene p-sulfonate, and benzyl methacrylate is 1:0.2-0.4:0.5-1.

[0020] Preferably, in step (1), the mass of the water is 3-4 times the weight of 2,2,2-trifluoroethyl acrylate.

[0021] Preferably, in step (1), the stirring speed is 500-800 rpm.

[0022] In the present invention, preferably, in step (2), the mass concentrations of the sodium persulfate solution and the sodium sulfite solution are 3-5 wt% and 3-5 wt%, respectively.

[0023] Preferably, in step (2), the weight ratio of the sodium persulfate solution, the sodium sulfite solution and the 2,2,2-trifluoroethyl acrylate is 0.1-0.2:0.02-0.03:1.

[0024] Preferably, in step (2), the sodium persulfate solution and the sodium sulfite solution are added dropwise for 30-40 minutes and 10-20 minutes, respectively.

[0025] Preferably, in step (2), the stirring speed is 300-500 rpm.

[0026] In the present invention, preferably, in step (3), the fiber length is 3-8 mm.

[0027] In the present invention, the processes of jetting, winding, drawing, etc. performed on the polymer are all conventional techniques in the art, and their specific processes can be adjusted conventionally by those skilled in the art.

[0028] The reaction equation for the synthesis of the fiber for oilfield fracturing of the present invention is as follows:

[0029]

[0030]

[0031] in:

[0032] x=1000-20000;

[0033] y = 200-4000;

[0034] z=500-10000.

[0035] The molecular weight of the fiber for oilfield fracturing is 400,000-4,000,000.

[0036] The oilfield fracturing fiber of the present invention is a surface-active polymer composed of 2,2,2-trifluoroethyl acrylate, styrene p-sulfonate, and benzyl methacrylate as monomers. The 2,2,2-trifluoroethyl acrylate molecule contains fluorine, which can significantly reduce the frictional resistance between the product and the aqueous phase, and only slightly reduces the flow conductivity of the aqueous phase. styrene p-sulfonate is a surfactant that can enhance the emulsification of the entire system during the synthesis process, facilitating the stable polymerization reaction. The sulfonic acid group in the molecule is a hydrophilic group that can enhance the wetting of the product with the aqueous fracturing fluid, minimizing the reduction in flow conductivity. The benzene ring contained in the molecule is a rigid structure that can improve sand carrying capacity. Benzyl methacrylate also contains a benzene ring that can increase the strength of the molecule and facilitate sand carrying. 2,2,2-trifluoroethyl acrylate and benzyl methacrylate contain ester groups that are unstable at high temperatures, facilitating automatic degradation after fracturing. The sand carrying capacity, flow conductivity, and degradation time of the product can be adjusted by adjusting the ratio of the different monomers.

[0037] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0038] (1) The raw materials of the oilfield fracturing fiber of the present invention are widely available, the synthesis process is simple, the synthesis process is a one-pot method, and the yield is 100%;

[0039] (2) The oilfield fracturing fiber of the present invention can be automatically degraded and does not damage the formation after construction is completed. The dissolution temperature can be controlled according to different monomer ratios, thereby expanding the application range of the product;

[0040] (3) The fiber for oilfield fracturing of the present invention has a high sand carrying capacity, and the static settling velocity reduction rate of ceramsite is greater than 25%; it has good flow conductivity, and the flow conductivity reduction rate is less than 2.5%. DETAILED DESCRIPTION

[0041] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0042] Example 1:

[0043] (1) 1.5 kg of 2,2,2-trifluoroethyl acrylate, 0.3 kg of styrene p-sulfonate, 1.5 kg of benzyl methacrylate, and 4.5 kg of water were added to a reactor equipped with a condenser in sequence, and stirred for 10 minutes at a stirring speed of 500 rpm. The pH was adjusted to 6-7 with a 1 mol / L sodium hydroxide solution, and stirring was continued for 10 minutes at a stirring speed of 500 rpm to form an emulsion;

[0044] (2) Slowly dropwise add 0.15 kg of 3 wt% sodium persulfate solution into the above emulsion, and the solution gradually thickens. After 30 minutes of dropwise addition, continue stirring and reacting for 1 hour at a stirring speed of 500 rpm. Continue to dropwise add 0.03 kg of 3 wt% sodium sulfite solution. After 10 minutes of dropwise addition, continue stirring for 20 minutes at a stirring speed of 500 rpm to obtain a viscous polymer;

[0045] (3) The polymer is subjected to jetting, winding, drawing, and shearing operations to obtain fibers with a length of 3-8 mm, namely, the product fiber Y1 for oilfield fracturing.

[0046] Example 2:

[0047] (1) 1.5 kg of 2,2,2-trifluoroethyl acrylate, 0.4 kg of styrene p-sulfonate, 1.3 kg of benzyl methacrylate, and 4.8 kg of water were added to a reactor equipped with a condenser in sequence, and stirred for 20 min at a stirring speed of 600 rpm. The pH was adjusted to 6-7 with a 1 mol / L sodium hydroxide solution, and stirring was continued for 20 min at a stirring speed of 800 rpm to form an emulsion;

[0048] (2) Slowly dropwise add 0.18 kg of 5 wt% sodium persulfate solution into the above emulsion, and the solution gradually thickens. After 32 minutes of dropwise addition, continue stirring and reacting for 2 hours at a stirring speed of 300 rpm. Continue to dropwise add 0.033 kg of 5 wt% sodium sulfite solution. After 12 minutes of dropwise addition, continue stirring for 30 minutes at a stirring speed of 300 rpm to obtain a viscous polymer.

[0049] (3) The polymer is subjected to jetting, winding, drawing, and shearing operations to obtain fibers with a length of 3-8 mm, namely, the product fiber Y2 for oilfield fracturing.

[0050] Example 3:

[0051] (1) 1.5 kg of 2,2,2-trifluoroethyl acrylate, 0.5 kg of styrene p-sulfonate, 1.1 kg of benzyl methacrylate, and 5.0 kg of water were added to a reactor equipped with a condenser in sequence, and stirred for 30 min at a stirring speed of 800 rpm. The pH was adjusted to 6-7 with a 1 mol / L sodium hydroxide solution, and stirring was continued for 15 min at a stirring speed of 500 rpm to form an emulsion;

[0052] (2) Slowly dropwise add 0.2 kg of 4 wt% sodium persulfate solution into the above emulsion, and the solution gradually thickens. After 40 minutes of dropwise addition, continue stirring and reacting for 1.5 hours at a stirring speed of 400 rpm. Continue to dropwise add 0.036 kg of 4 wt% sodium sulfite solution. After 18 minutes of dropwise addition, continue stirring for 25 minutes at a stirring speed of 500 rpm to obtain a viscous polymer;

[0053] (3) The polymer is subjected to jetting, winding, drawing, and shearing operations to obtain fibers with a length of 3-8 mm, namely, the product fiber Y3 for oilfield fracturing.

[0054] Example 4:

[0055] (1) 1.5 kg of 2,2,2-trifluoroethyl acrylate, 0.55 kg of styrene p-sulfonate, 0.9 kg of benzyl methacrylate, and 5.5 kg of water were added to a reactor equipped with a condenser in sequence, and stirred for 15 minutes at a stirring speed of 700 rpm. The pH was adjusted to 6-7 with a 1 mol / L sodium hydroxide solution, and stirring was continued for 12 minutes at a stirring speed of 600 rpm to form an emulsion;

[0056] (2) Slowly dropwise add 0.25 kg of 5 wt% sodium persulfate solution into the above emulsion, and the solution gradually thickens. After 37 minutes of dropwise addition, continue stirring and reacting for 1.2 hours at a stirring speed of 500 rpm. Continue to dropwise add 0.04 kg of 3 wt% sodium sulfite solution. After 20 minutes of dropwise addition, continue stirring for 22 minutes at a stirring speed of 300 rpm to obtain a viscous polymer.

[0057] (3) The polymer is subjected to jetting, winding, drawing, and shearing operations to obtain fibers with a length of 3-8 mm, namely, the product fiber Y4 for oilfield fracturing.

[0058] Example 5:

[0059] (1) 1.5 kg of 2,2,2-trifluoroethyl acrylate, 0.6 kg of styrene p-sulfonate, 0.75 kg of benzyl methacrylate, and 6 kg of water were added to a reactor equipped with a condenser in sequence, and stirred for 25 minutes at a stirring speed of 600 rpm. The pH was adjusted to 6-7 with a 1 mol / L sodium hydroxide solution, and stirring was continued for 18 minutes at a stirring speed of 600 rpm to form an emulsion;

[0060] (2) Slowly dropwise add 0.3 kg of 4 wt% sodium persulfate solution into the above emulsion, and the solution gradually thickens. After 35 minutes of dropwise addition, continue stirring and reacting for 1.8 hours at a stirring speed of 400 rpm. Continue to dropwise add 0.045 kg of 3 wt% sodium sulfite solution. After 15 minutes of dropwise addition, continue stirring for 27 minutes at a stirring speed of 300 rpm to obtain a viscous polymer.

[0061] (3) The polymer is subjected to jetting, winding, drawing, and shearing operations to obtain fibers with a length of 3-8 mm, namely, the product fiber Y5 for oilfield fracturing.

[0062] Example 6 Sand Carrying Capacity Evaluation

[0063] In accordance with the requirements of Q / SH10202676-2018 "Technical Requirements for Fibers for Fracturing", the static settling velocity reduction rate of ceramsite was tested. The results are shown in Table 1.

[0064] Example 7 Evaluation of flow conductivity

[0065] According to the requirements of Q / SH10202676-2018 “Technical Requirements for Fracturing Fibers”, the conductivity reduction rate was tested. The results are shown in Table 1.

[0066] Table 1 Test results of sand carrying capacity and flow conductivity

[0067] goods Grain static descending speed reduction rate, % Current capacity reduction rate, % <![CDATA[Y1]]> 25 2.5 <![CDATA[Y2]]> 25 2.4 <![CDATA[Y3]]> 26 2.4 <![CDATA[Y4]]> 26 2.3 <![CDATA[Y5]]> 27 2.2

[0068] As can be seen from Table 1, the static settling velocity reduction rate of the fiber ceramsite for oil field fracturing of the present invention is greater than 25%, far exceeding the standard requirement of greater than 10%; the conductivity reduction rate is less than 2.5%, far below the standard requirement of less than 10%.

[0069] Example 8 High Temperature Solubility Evaluation

[0070] Tap water and the above products were added to a pressure vessel, placed in an oven at different temperatures, and left to stand for 24 hours. The vessel was opened and the dissolution was observed. The results are shown in Table 2.

[0071] Table 2 Solubility test results

[0072] goods 50℃ 60℃ 70℃ 80℃ 90℃ 100℃ 110℃ <![CDATA[Y1]]> Insoluble Insoluble Slightly soluble Slightly soluble Dissolution Dissolution Dissolution <![CDATA[Y2]]> Insoluble Insoluble Insoluble Slightly soluble Slightly soluble Dissolution Dissolution <![CDATA[Y3]]> Insoluble Insoluble Insoluble Slightly soluble Slightly soluble Dissolution Dissolution <![CDATA[Y4]]> Insoluble Insoluble Insoluble Insoluble Slightly soluble Dissolution Dissolution <![CDATA[Y5]]> Insoluble Insoluble Insoluble Insoluble Slightly soluble Slightly soluble Dissolution

[0073] In a high-temperature environment, the ester group in the molecule can decompose into carboxylic acid and alcohol. As can be seen from Table 2, the higher the proportion of ester groups in the oilfield fracturing fiber of the present invention, the lower the dissolution temperature. Therefore, the dissolution temperature can be controlled according to different monomer ratios to meet construction requirements.

[0074] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for synthesizing fiber for oilfield fracturing, characterized in that: The synthetic method is as follows: (1) Add 2,2,2-trifluoroethyl acrylate, styrene p-sulfonate, benzyl methacrylate, and water in sequence to a reactor equipped with a condenser, stir for 10-30 minutes, adjust the pH to 6-7 with a 1 mol / L sodium hydroxide solution, and continue stirring for 10-20 minutes to form an emulsion. The weight ratio of the 2,2,2-trifluoroethyl acrylate, styrene p-sulfonate, and benzyl methacrylate is 1:0.2-0.4:0.5-1; (2) slowly dripping sodium persulfate solution into the above emulsion until the solution gradually thickens. After the dripping is complete, stirring is continued for 1-2 hours. Then, sodium sulfite solution is continuously dripped. After the dripping is complete, stirring is continued for 20-30 minutes to obtain a viscous polymer. The weight ratio of the sodium persulfate solution, sodium sulfite solution and 2,2,2-trifluoroethyl acrylate is 0.1-0.2:0.02-0.03:

1. (3) The polymer is subjected to jetting, winding, drawing, and shearing operations to produce fibers, i.e., fibers for oilfield fracturing.

2. The synthesis method according to claim 1, wherein In step (1), the mass of the water is 3-4 times the weight of 2,2,2-trifluoroethyl acrylate.

3. The synthesis method according to claim 1, wherein In step (1), the stirring speed is 500-800 rpm.

4. The synthesis method according to claim 1, characterized in that In step (2), the mass concentrations of the sodium persulfate solution and the sodium sulfite solution are 3-5wt% and 3-5wt%, respectively.

5. The synthesis method according to claim 1, characterized in that In step (2), the sodium persulfate solution and the sodium sulfite solution are added dropwise for 30-40 minutes and 10-20 minutes, respectively.

6. The synthesis method according to claim 1, characterized in that In step (3), the fiber length is 3-8 mm.

7. The fiber for oilfield fracturing prepared by the synthesis method according to any one of claims 1 to 6, characterized in that: The molecular structure of the oilfield fracturing fiber is as follows: ， in: x=1000-20000； y=200-4000； z=500-10000。 8. The fiber for oilfield fracturing according to claim 7, characterized in that: The molecular weight of the fiber for oilfield fracturing is 400,000-4,000,000.

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