Seawater-based nano synergistic pressure flooding liquid system as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of fracturing fluids, and particularly relates to a seawater-based nano synergistic pressure flooding fluid system as well as a preparation method and application thereof. The seawater-based nano synergistic pressure flooding liquid system comprises modified nano SiO2 particles, a drag reducer, a bactericide, an anti-swelling agent, a scale inhibitor and water. According to the seawater-based nano synergistic pressure driving liquid system, seawater resources are reasonably utilized during offshore pressure driving, the demand of an offshore platform for fresh water resources is relieved, and the construction cost of the pressure driving liquid is greatly reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of pressure-displacing fluids, and in particular relates to a seawater-based nano-synergistic pressure-displacing fluid system and a preparation method and application thereof. Background Art

[0002] With the development of high-quality oil and gas reserves, the recoverable and easily recoverable reserves are constantly decreasing, and the focus of oil and gas development has gradually shifted from high permeability to low permeability. Due to the characteristics of low porosity, low permeability and strong heterogeneity, low permeability reservoirs have low efficiency in conventional water injection development / chemical flooding development, and face many challenges such as rapid production decline and low recovery. Pressure drive technology is a new technology to solve the problem of effective injection and production in low permeability reservoirs. Pressure drive adopts a combination of "oil drive + fracturing" to achieve reservoir transformation and improve recovery by supplementing formation energy, connecting micro-cracks, and imbibition replacement.

[0003] At present, the injection volume of a single well in an onshore oil field exceeds 10,000 cubic meters, which is mainly prepared with fresh water. Due to the particularity of the platform carrier, the pressure drive operation in offshore oil fields cannot meet the demand for large amounts of fresh water to prepare the pressure drive fluid. Although the use of seawater can save water resources and reduce costs, the mineralization of seawater is as high as about 35,000 mg / L. In addition to containing a large amount of Na + and K + In addition, it is rich in Ca 2+ Mg 2+ High mineralization and high divalent ions will cause the performance of conventional pressure-driven agents to decline due to salt sensitivity and fail to meet operational requirements. Patents such as CN 113201321 B and CN114774096 B all disclose salt-resistant nano-infiltrating agents.

[0004] Although the nano-imbibition agent in the published patent application has good salt tolerance and is mainly used as a functional additive for imbibition oil recovery, a single agent for offshore pressure drive operation cannot meet the construction and reservoir production requirements. Therefore, the research on the pressure drive fluid system suitable for seawater preparation is the key to solving the technical problems of offshore pressure drive and reducing the construction cost of offshore pressure drive. Summary of the invention

[0005] In view of the defects of the prior art, the present invention provides a seawater-based nano-synergistic pressure-displacing fluid system and a preparation method and application thereof.

[0006] Specifically, the present invention is achieved through the following technical solutions:

[0007] A seawater-based nano-synergistic pressure-driven fluid system comprises: modified nano-SiO2 particles, drag reducer, bactericide, anti-swelling agent, anti-scaling agent and water.

[0008] The above-mentioned seawater-based nano-synergistic pressure-driven fluid system includes, by weight percentage: 0.05-0.2% modified nano-SiO2 particles, 0.1-0.3% drag reducer, 0.01%-0.2% bactericide, 0.01%-0.15% anti-swelling agent, 0.02%-0.2% scale inhibitor and the balance water.

[0009] The above-mentioned seawater-based nano-synergistic pressure-driven fluid system comprises, by weight percentage: 0.1% of modified nano-SiO2 particles, 0.1% of drag reducer, 0.1% of bactericide, 0.1% of anti-swelling agent, 0.1% of scale inhibitor and the balance of seawater.

[0010] In the above-mentioned seawater-based nano-synergistic pressure-displacing fluid system, the modified nano-SiO2 particles are SiO2 particles modified by silane having a long-chain alkyl structure.

[0011] In the above-mentioned seawater-based nano-synergistic pressure-driven fluid system, the silane with a long-chain alkyl structure includes one or more of dodecyltriethoxysilane, hexadecyltriethoxysilane, octadecyltriethoxysilane, dodecyltrimethoxysilane, hexadecyltrimethoxysilane, and octadecyltrimethoxysilane.

[0012] In the above-mentioned seawater-based nano-synergistic pressure-driven fluid system, the drag reducer is a polymer of AM, AMPS and DtC18.

[0013] In the above-mentioned seawater-based nano-synergistic pressure-displacing fluid system, the bactericide is selected from one or more of sodium salicylate and tetrakis(hydroxymethyl)phosphonium sulfate.

[0014] In the above-mentioned seawater-based nano-synergistic pressure-displacing fluid system, the anti-swelling agent is one or more of potassium chloride, tetramethylammonium chloride, and dodecyltrimethylammonium chloride.

[0015] In the above-mentioned seawater-based nano-synergistic pressure-displacing fluid system, the scale inhibitor is diethylenetriaminepentamethylenephosphonic acid.

[0016] The above-mentioned seawater-based nano-synergistic pressure-displacing fluid system has a salinity of water of 30,000 mg / L-70,000 mg / L.

[0017] On the other hand, the present invention also provides a method for preparing the above-mentioned seawater-based nano-synergistic pressure-displacing fluid system, comprising:

[0018] S1: adding modified nano-SiO2 particles and drag reducer into water according to the proportion, stirring to obtain a uniform solution;

[0019] S2: adding bactericide, anti-swelling agent and anti-scaling agent into the solution, stirring, and fully mixing to obtain a seawater-based nano-synergistic pressure-displacing fluid system.

[0020] The preparation method of the above-mentioned seawater-based nano-synergistic pressure-displacing fluid system, the modified nano-SiO2 particles are prepared by the following method:

[0021] S11: adding silane having a long-chain alkyl structure into ethanol, adding acid to adjust the pH, and ultrasonicating to obtain hydrolyzed silane having a long-chain alkyl structure;

[0022] S12: dispersing nano-SiO2 into anhydrous ethanol, adding dropwise the hydrolyzed silane having a long-chain alkyl structure, and heating for reaction;

[0023] After the reaction in S13 is completed, centrifugal separation is performed to obtain a paste, which is then dried and ground to obtain modified nano-SiO2 particles.

[0024] In the preparation method of the above-mentioned seawater-based nano-synergistic pressure-displacing fluid system, the mass ratio of the silane with a long-chain alkyl structure to the nano-SiO2 is (1-2):5.

[0025] In the preparation method of the above-mentioned seawater-based nano-synergistic pressure-displacing fluid system, the temperature of the heating reaction is 40-60° C., and the reaction time is 12-24 hours.

[0026] The preparation method of the above-mentioned seawater-based nano-synergistic pressure-displacing fluid system, the drag reducer is prepared by the following method:

[0027] S21: Dissolve Span-80 and Tween-80 in solvent oil according to the ratio, and stir evenly to obtain an oil phase;

[0028] S22: dissolve AM in water, add alkali to neutralize AM, add AMPS and DtC18 according to the ratio, and stir evenly to obtain the aqueous phase;

[0029] S23 After adding alkali to the aqueous phase to adjust the pH, the aqueous phase is added dropwise to the oil phase under the protection of protective gas;

[0030] S24 adds an initiator, and after the reaction is completed, purifies and dries the polymer to obtain a drag reducer.

[0031] In the preparation method of the above-mentioned seawater-based nano-synergistic pressure-displacing fluid system, the mass ratio of the Span-80 to the Tween-80 is 1:0.02-1:0.25.

[0032] In the preparation method of the above-mentioned seawater-based nano-synergistic pressure-displacing fluid system, the mass ratio of the AM to the AMPS and the DtC18 is 0.70-0.89: 0.1-0.23: 0.003-0.07.

[0033] In the preparation method of the seawater-based nano-synergistic pressure-displacing fluid system, the volume ratio of the oil phase to the water phase is 0.5:1-0.9:1; the concentration of Span-80 and Tween-80 in the oil phase is 1%-9%.

[0034] In the preparation method of the above-mentioned seawater-based nano-synergistic pressure-displacing fluid system, the initiator is azobisisobutyramidine hydrochloride; the mass of the initiator is 0.08%-0.12% of the total mass of AM, AMPS and DtC18.

[0035] In another aspect, the present invention further provides a seawater-based nano-synergistic pressure-displacing fluid system, which is prepared by the above-mentioned preparation method.

[0036] The above-mentioned seawater-based nano-enhanced pressure-displacement fluid system is used in the development of offshore low-permeability oil fields.

[0037] The technical solution of the present invention has the following beneficial effects:

[0038] (1) The seawater-based nano-synergistic pressure-displacement fluid system of the present invention has a simple configuration process, a high drag reduction rate, salt resistance and shear resistance, and can have both fracturing sand carrying performance and oil displacement performance. It does not require flowback, and realizes the merging of fracturing and oil displacement operations into one operation, thereby improving the reservoir transformation effect;

[0039] (2) The seawater-based nano-synergistic fracturing fluid system of the present invention rationally utilizes seawater resources during offshore fracturing, which not only alleviates the demand for fresh water resources on offshore platforms, but also significantly reduces the construction cost of fracturing fluid. DETAILED DESCRIPTION

[0040] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail through the following specific embodiments. Except for the following contents, the process method of the present invention adopts conventional methods or devices in the art. Unless otherwise specified, the following terms have the meanings commonly understood by those skilled in the art.

[0041] When a numerical range is disclosed herein, the above range is considered to be continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0042] Specifically, the present invention provides a seawater-based nano-synergistic pressure-displacing fluid system, comprising: modified nano-SiO2 particles, a drag reducer, a bactericide, an anti-swelling agent, a scale inhibitor and water.

[0043] In the seawater-based nano-synergistic pressure-driven fluid system of the present invention, there is interaction between nanoparticles and drag reducers (i.e., amphiphilic polymers). Amphiphilic polymers have hydrophobic groups and hydrophilic main chains, and when the concentration of their solutions increases, polymer clusters are formed. When the concentration continues to increase and reaches the critical association concentration (CAC), the polymer forms a spatial network structure. Since the structure is composed of a large number of polymer clusters, the mutual repulsion of hydrophilic groups at the polymer aggregation makes the spatial structure unstable. In addition, the polymer molecules in the free state in the solution reduce the utilization rate of the polymer in the spatial network structure. After adding nano-silicon dioxide, its surface electronegativity attracts the positive charge of the hydrophobic group of the polymer through electrostatic action, adsorbs the free polymer molecules in the solution, and forms a molecular brush. After the polymer-nano-silicon dioxide molecular brush is formed, due to the molecular thermal motion and hydrogen bonding, the molecular brush is easily adsorbed at the connection of the polymer cluster, effectively improving the connection strength between the polymer structures, so that the rheological properties of the composite material solution are changed from viscosity to elasticity. At the same time, the adsorption effect improves the utilization rate of the polymer and enhances the structural strength of the polymer spatial network. Moreover, nano-silica, as an inorganic nanomaterial, can support the polymer network, thereby improving the salt tolerance of the polymer. In summary, the addition of nano-silica can improve the structural stability of the amphiphilic polymer solution, so that it still has good solution performance under high salt conditions.

[0044] The components of the seawater-based nano-synergistic pressure-displacing fluid system of the present invention are introduced in detail below:

[0045] Modified Nano-SiO2 Particles

[0046] In some preferred embodiments, the modified nano-SiO2 particles used in the present invention are SiO2 particles modified by silane having a long-chain alkyl structure.

[0047] Further preferably, the silane having a long-chain alkyl structure includes one or more of dodecyltriethoxysilane, hexadecyltriethoxysilane, octadecyltriethoxysilane, dodecyltrimethoxysilane, hexadecyltrimethoxysilane, and octadecyltrimethoxysilane.

[0048] More preferably, the silane having a long-chain alkyl structure is dodecyltriethoxysilane.

[0049] In some preferred embodiments, the modified nano-SiO2 particles are prepared by the following method:

[0050] S11: adding silane with a long-chain alkyl structure into ethanol, adding acid to adjust the pH, and ultrasonicating to obtain hydrolyzed silane with a long-chain alkyl structure; S12: dispersing nano-SiO2 into anhydrous ethanol, dropping the hydrolyzed silane with a long-chain alkyl structure, and heating for reaction; S13: after the reaction is completed, centrifugation is performed to obtain a paste, and modified nano-SiO2 particles are obtained by drying and grinding.

[0051] In step S11, glacial acetic acid (AcOH) with a mass concentration of 15%-30% is used to adjust the pH value of the system to 5-6, preferably 5.5.

[0052] In step S12, the heating reaction temperature is 40-60°C, and the reaction time is 12-24h; preferably, the reaction temperature is 60°C, and the reaction time is 24h.

[0053] In step S12, the mass concentration of nano-SiO2 in anhydrous ethanol is 0.1%-0.3%, preferably 0.2%.

[0054] In step S12, the mass ratio of the silane having a long-chain alkyl structure to the nano-SiO2 is 1-2:5.

[0055] Taking the silane with a long-chain alkyl structure as dodecyltriethoxysilane as an example, the reaction equation for preparing the modified nano-SiO2 particles of the present invention is as follows:

[0056]

[0057] The number of long-chain alkyl groups on the modified nano-SiO2 particles is related to the mass ratio of silicon dioxide to the silane having a long-chain alkyl structure. In a preferred embodiment, the molecular structure of the modified nano-SiO2 particles of the present invention is:

[0058]

[0059] From the above structure, it can be seen that the SiO2 particles of the present invention are grafted with long carbon chains, and therefore have strong hydrophobicity, which enables them to better maintain stability in a salt water environment and are not easily affected by salt.

[0060] In some preferred embodiments, in the seawater-based nano-synergistic pressure-displacing fluid system of the present invention, the weight percentage of the modified nano-SiO2 particles is 0.05-0.2%.

[0061] When the modified nano-SiO2 particle ratio is too small, on the one hand, there will not be enough nano-SiO2 to support the polymer, reducing stability; on the other hand, it will lead to a decrease in adsorbed free polymer molecules, reduce the molecular brush structure, reduce the connection strength of the polymer, reduce elasticity, and increase the free polymer molecules, weakening the spatial network structure of the polymer. When the modified nano-SiO2 particle ratio is too large, the modified nano-SiO2 will agglomerate together to form agglomerates larger than the SiO2 particle size, thereby blocking the large pores of the low permeability reservoir, causing damage to the reservoir, and is not conducive to the migration of fluids in the pores of the low permeability reservoir.

[0062] Further preferably, in the seawater-based nano-synergistic pressure-displacing fluid system of the present invention, the weight percentage of the modified nano-SiO2 particles is 0.1%.

[0063] Drag reducer

[0064] In some preferred embodiments, the drag reducer is a polymer of AM, AMPS and DtC18.

[0065] Among them, AM is acrylamide, ZMPS is 2-acrylamide-2-methyl-1-propanesulfonic acid, DtC18 is a double-tailed hydrophobic monomer, its chemical name is bis(octadecyldimethyl)-2-butenylammonium chloride, and the molecular structure is shown below.

[0066]

[0067] The drag reducer of the present invention is an emulsion drag reducer, which is an amphiphilic polymer with a salt thickening mechanism. The addition of strong electrolytes NaCl, CaCl2 and MgCl2 leads to an increase in the polarity of the solution, thereby leading to stronger association between non-polar hydrophobic groups. In deionized water, the molecular configuration of the polymer is highly stretched, resulting in the highest solution viscosity. Under low salinity, as the salinity increases, the electrostatic shielding effect of metal ions on anions is greater than the hydrophobic association effect, so the viscosity decreases with increasing salinity. The molecular configuration of the polymer becomes curled. Under high salinity, the shielding effect of metal ions on anions reaches a peak. As the salt ion concentration increases, the hydrophobic association effect is enhanced, and the polymer network becomes denser and more complex, resulting in salt thickening in the solution.

[0068] In some preferred embodiments, the drag reducer is prepared by the following method: S21 Span-80 and Tween-80 are dissolved in solvent oil according to a ratio, and stirred to obtain an oil phase; S22 AM is dissolved in water, and after adding alkali to neutralize AM, AMPS and DtC18 are added according to a ratio, and stirred to obtain an aqueous phase; S23 alkali is added to the aqueous phase to adjust the pH, and then the aqueous phase is added dropwise to the oil phase under the protection of a protective gas; S24 an initiator is added, and after the reaction is completed, the polymer is purified and dried to obtain a drag reducer.

[0069] Among them, the chemical reaction equation involved in the preparation process of the drag reducer is as follows:

[0070]

[0071] The value range and ratio range of x, y, and z are related to the added amounts of AM, AMPS, and DtC18, and the present invention does not make any specific limitations thereon.

[0072] In step S21, the mass ratio of the Span-80 to the Tween-80 is 1:0.02-1:0.25, preferably 1:0.09.

[0073] In step S22, the mass ratio of the AM to the AMPS and the DtC18 is 0.70-0.89:0.1-0.23:0.003-0.07, and more preferably 0.7:0.23:0.07.

[0074] In step S22, the total monomer concentration of AM, AMPS and DtC18 is 15%-25%, preferably 20%.

[0075] In step S23, the volume ratio of the oil phase to the water phase is 0.5:1-0.9:1 (more preferably 0.72:1); the concentration of Span-80 and Tween-80 in the oil phase is 1%-9% (more preferably 5%). The dripping rate of the water phase is 1-5 drops per second, and the dripping is carried out under stirring conditions and protective gas protection. More preferably, the protective gas is nitrogen or argon.

[0076] In step S22 and step S23, a sodium hydroxide aqueous solution with a mass concentration of 15%-30% is used to adjust the pH value of the system to 7.

[0077] In step S24, the initiator is selected from azobisisobutylamidine hydrochloride (AIBA); the mass of the initiator is 0.08%-0.12% of the total mass of AM, AMPS and DtC18, preferably 0.1%.

[0078] In step S24, the reaction temperature is 25-50°C, and the reaction time is 2-6 hours, preferably the reaction temperature is 50°C, and the reaction time is 5 hours.

[0079] In step S24, the drying process is performed in an oven at a drying temperature of 40°C.

[0080] In some preferred embodiments, in the seawater-based nano-synergistic pressure-displacing fluid system of the present invention, the weight percentage of the drag reducer is 0.1-0.3%.

[0081] When using high molecular weight polymer drag reducers to reduce drag, if the ratio of the drag reducer is too small, a satisfactory drag reduction effect cannot be achieved. If the ratio is too large, the stability of the fracturing fluid will be reduced, and the drag reduction effect will also be reduced, and the cost will be increased.

[0082] Further preferably, in the seawater-based nano-synergistic pressure-displacing fluid system of the present invention, the weight percentage of the drag reducer is 0.1%.

[0083] Other additives

[0084] In some preferred embodiments, the seawater-based nano-synergistic pressure-displacing fluid system of the present invention further includes a bactericide, an anti-swelling agent, and an anti-scaling agent.

[0085] Among them, the role of bactericide, anti-swelling agent and anti-scaling agent in the present invention is the same as that in the prior art, and the present invention will not make a detailed introduction to this.

[0086] In some preferred embodiments, the bactericide is selected from one or more of sodium salicylate and tetrakis(hydroxymethyl)phosphonium sulfate.

[0087] In some preferred embodiments, the anti-swelling agent is one or more of potassium chloride, tetramethylammonium chloride, and dodecyltrimethylammonium chloride.

[0088] In some preferred embodiments, the scale inhibitor is diethylenetriaminepentamethylenephosphonic acid.

[0089] In some preferred embodiments, the seawater-based nano-synergistic pressure-displacing fluid system of the present invention comprises, by weight percentage: 0.01%-0.2% bactericide, 0.01%-0.15% anti-swelling agent, and 0.02%-0.2% anti-scaling agent.

[0090] Further preferably, the seawater-based nano-synergistic pressure-displacing fluid system of the present invention comprises, by weight percentage: 0.1% bactericide, 0.1% anti-swelling agent, and 0.1% anti-scaling agent.

[0091] water

[0092] In some preferred embodiments, the water used in the present invention is simulated seawater.

[0093] Further preferably, the mineralization of the simulated seawater is 30000 mg / L-70000 mg / L.

[0094] On the other hand, the present invention also provides a method for preparing the above-mentioned seawater-based nano-synergistic pressure-displacing fluid system, comprising:

[0095] S1: adding modified nano-SiO2 particles and drag reducer into water according to the proportion, stirring to obtain a uniform solution;

[0096] S2: adding bactericide, anti-swelling agent and anti-scaling agent into the solution, stirring, and fully mixing to obtain a seawater-based nano-synergistic pressure-displacing fluid system.

[0097] Among them, the chemical composition, proportion and preparation method of modified nano-SiO2 particles, drag reducers, bactericides, anti-swelling agents and scale inhibitors are the same as those in the seawater-based nano-synergistic pressure-driven fluid system provided in the first aspect of the present invention, and the present invention will not repeat them here.

[0098] In another aspect, the present invention also provides the use of the above-mentioned seawater-based nano-synergistic pressure-displacing fluid system in the development of offshore low-permeability oil fields.

[0099] The present invention adopts a specific method to prepare modified nano-SiO2 and drag reducer, and then prepares them with bactericide, scale inhibitor, anti-swelling agent and simulated seawater into a nano-synergistic pressure-displacement fluid system with a specific formula. The system configuration process of the present invention is simple, the drag reduction rate is high, the salt resistance and shear resistance are strong, and the fracturing sand carrying performance and oil displacement performance can be combined. No backflow is required, and the two operations of fracturing and oil displacement are combined into one operation, which effectively improves the reservoir transformation effect.

[0100] Example

[0101] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions. The raw materials used in the following examples are all conventionally purchased.

[0102] Example 1

[0103] A seawater-based nano-synergistic pressure-displacing fluid system and a preparation method thereof, comprising the steps of:

[0104] (1) Synthesis of modified nano-SiO2

[0105] Take a certain amount of dodecyl triethoxysilane, dilute it with ethanol to a concentration of 2%, add glacial acetic acid AcOH to adjust the pH value to 5.5, and ultrasonically disperse it for 10 minutes for standby use. Weigh 1g of nano-SiO2 and disperse it in 50ml of anhydrous ethanol in a three-necked flask. Take 10ml of hydrolyzed dodecyl triethoxysilane and place it in a dropping funnel and drop it into the three-necked flask. React at 60℃ for 24h. After the reaction is completed, centrifuge at high speed, pour off the supernatant, wash the paste several times with deionized water and anhydrous ethanol respectively, and finally vacuum dry and grind to obtain white fluffy nano-SiO2 powder.

[0106] (2) Synthesis of emulsion drag reducer

[0107] Weigh 36g of white oil, 1.65g of Span80, and 0.15g of Tween80, add them into a four-necked flask equipped with a thermometer, a stirrer, and a condensation reflux device, stir and mix evenly at a speed of 1000r / min, and pass nitrogen for more than 30min to remove dissolved oxygen in the system.

[0108] Weigh 7 g of acrylamide (AM) into a beaker, then weigh 50 g of distilled water and add it dropwise into the beaker, use a magnetic stirrer to promote the dissolution of acrylamide (AM), add NaOH solution to neutralize AM to neutrality, then weigh 2.3 g of 2-acrylamide-2-methyl-1-propanesulfonic acid (AMPS) and 0.7 g of the double-tailed hydrophobic monomer DtC18 monomer in turn and dissolve them in the aqueous phase system, wait for the monomer to be completely dissolved, add NaOH and continue to adjust the pH value of the aqueous phase.

[0109] After the oil phase is stirred for 10 minutes, the water phase is added dropwise at a rate of 1-2 drops per second under the stirring condition of 1000 r / min and nitrogen protection. The water phase is added dropwise to the oil phase. After nitrogen is passed through the system to drive out oxygen for half an hour, the rotation speed is reduced to 350 r / min, and a 0.1% mass concentration of 2,2′-azobis(2-methylpropionamidine) dihydrochloride (AIBA) solution (the mass of AIBA is 0.1 g) is added to the microemulsion at a rate of 1-2 drops per second. After the addition is completed, the reaction is continued with stirring at 50°C under nitrogen protection for 5 hours.

[0110] After the reaction is completed, the mixture is cooled and allowed to stand at room temperature, the reaction product is removed from the reactor, the polymer product is purified with ethanol and acetone, and the purified product is placed in a 40° C. oven for drying to obtain a solid powder product.

[0111] (3) Preparation of Nano-Enhanced Pressure-Drive Fluid System

[0112] Add simulated seawater for liquid preparation into the stirrer, turn on the stirrer, adjust the stirrer speed, add 0.1% modified nano-SiO2 particles and 0.1% emulsion drag reducer into the solution and stir evenly. After a uniform solution is formed, add 0.1% sodium salicylate, 0.1% potassium chloride and 0.1% diethylenetriamine penta-methylenephosphonic acid, mix well and evenly to obtain a nano-synergistic pressure-driven liquid system.

[0113] Example 2

[0114] A seawater-based nano-enhanced pressure-displacing fluid system and a preparation method thereof are as described in Example 1, except that the concentration of the modified nano-SiO2 particles in step (3) is 0.08%; the other steps and conditions are the same as in Example 1.

[0115] Example 3

[0116] A seawater-based nano-synergistic pressure-displacing fluid system and a preparation method thereof are as described in Example 1, except that the concentration of the emulsion drag reducer in step (3) is 0.05%; the other steps and conditions are the same as in Example 1.

[0117] Comparative Example 1

[0118] A seawater-based nano-synergistic pressure-displacing fluid system and a preparation method thereof, as described in Example 1, except that: the double-tailed hydrophobic monomer DtC18 monomer is not added in step (2); the details are as follows:

[0119] Step (2) is as follows:

[0120] Weigh 36g of white oil, 1.65g of Span80, and 0.15g of Tween80, add them into a four-necked flask equipped with a thermometer, a stirrer, and a condensation reflux device, stir and mix evenly at a speed of 1000r / min, and pass nitrogen for more than 30min to remove dissolved oxygen in the system.

[0121] Weigh 7 g of acrylamide (AM) into a beaker, then weigh 50 g of distilled water and add it dropwise into the beaker, use a magnetic stirrer to promote the dissolution of acrylamide (AM), add NaOH solution to neutralize AM to neutrality, then weigh 2.3 g of 2-acrylamide-2-methyl-1-propanesulfonic acid (AMPS) monomer and dissolve it in the aqueous phase system, wait until the monomer is completely dissolved, add NaOH and continue to adjust the pH value of the aqueous phase.

[0122] After the oil phase is stirred for 10 minutes, the water phase is added dropwise at a rate of 1-2 drops per second under the stirring condition of 1000 r / min and nitrogen protection. The water phase is added dropwise to the oil phase. After nitrogen is passed through the system to drive out oxygen for half an hour, the rotation speed is reduced to 350 r / min, and a 0.1% mass concentration of 2,2′-azobis(2-methylpropionamidine) dihydrochloride (AIBA) solution (the mass of AIBA is 0.1 g) is added to the microemulsion at a rate of 1-2 drops per second. After the addition is completed, the reaction is continued with stirring at 50°C under nitrogen protection for 5 hours.

[0123] After the reaction is completed, the mixture is cooled and allowed to stand at room temperature, the reaction product is removed from the reactor, the polymer product is purified with ethanol and acetone, and the purified product is placed in a 40° C. oven for drying to obtain a solid powder product.

[0124] The other steps and conditions are the same as in Example 1.

[0125] Comparative Example 2

[0126] A seawater-based nano-synergistic pressure-displacing fluid system and a preparation method thereof, as described in Example 1, except that: modified nano-SiO2 particles are not added; specifically as follows:

[0127] Omit step (1);

[0128] The preparation of the emulsion drag reducer is the same as step (2);

[0129] Step (3) is as follows:

[0130] Add simulated seawater for liquid preparation into the stirrer, turn on the stirrer, adjust the stirrer speed, add 0.1% emulsion drag reducer, stir evenly, and after a uniform solution is formed, add 0.1% sodium salicylate, 0.1% TOS-1, and 0.1% YTZY-3, and mix well to obtain a nano-synergistic pressure-driven liquid system.

[0131] Comparative Example 3

[0132] A seawater-based nano-synergistic pressure-displacing fluid system and a preparation method thereof, as described in Example 1, except that no emulsion drag reducer is added; the details are as follows:

[0133] The preparation of modified nano-SiO2 particles is the same as step (1);

[0134] Omit step (2);

[0135] Step (3) is as follows:

[0136] Add simulated seawater for liquid preparation into the stirrer, turn on the stirrer, adjust the stirrer speed, add 0.1% modified nano-SiO2 particles, stir evenly, and after a uniform solution is formed, add 0.1% sodium salicylate, 0.1% TOS-1, and 0.1% YTZY-3, and mix well to obtain a nano-synergistic pressure-driven liquid system.

[0137] Test Example 1: Drag Reduction Rate Test

[0138] The drag reduction and temperature and shear resistance of slick water fracturing fluid were tested in a 10mm circulating pipeline test system. The experimental temperature was set to 75°C, the fracturing fluid flow rate was 500m / min, and the pressure difference of fracturing fluid and clean water in the pipeline was tested respectively: ① Fill the test sample (clean water or fracturing fluid) in the liquid distribution tank, and open the friction test software; ② Start the circulation pump and set the pump displacement value; ③ After the sample flow in the pipeline is stable, open the valves on both sides of the differential pressure sensor and record the pipeline pressure difference data. The test results are shown in Table 1.

[0139] The drag reduction of slick water is the core indicator for evaluating the flow of fracturing fluid. The drag reduction rate is:

[0140]

[0141] Where:

[0142] K——drag reduction rate, %

[0143] ΔP1——pressure difference of clean water passing through the pipeline, MPa;

[0144] ΔP2——pressure difference of fracturing fluid through pipeline, MPa.

[0145] Table 1 Drag reduction rate experimental data

[0146]

[0147]

[0148] Test Example 2: Shear resistance test

[0149] The Austrian MCR 301 rotational rheometer was used to test the nano-enhanced pressure-displacement fluid system samples at 75°C for 160 seconds. 1 The viscosity after shearing for 1 hour, the test results are shown in Table 2.

[0150] Table 2 Fracturing fluid viscosity data

[0151] system Viscosity / mPa·s Example 1 4.8 Example 2 3.7 Example 3 3.1 Comparative Example 1 2.7 Comparative Example 2 2.6 Comparative Example 3 2.2

[0152] Test Example 3: Core Damage Test

[0153] The core damage evaluation was carried out according to the petroleum and natural gas industry standard SY / T5107-2016. The specific experimental steps are as follows, and the test results are shown in Table 3:

[0154] (1) Measure the length, diameter and porosity of the core;

[0155] (2) reverse displacement using simulated formation water until the permeability is stable;

[0156] (3) Use of a fracturing fluid system for forward displacement;

[0157] (4) Use simulated formation water reverse displacement to measure the permeability after damage.

[0158] The calculation formula of core damage rate is:

[0159]

[0160] Where:

[0161] η d ——core damage rate, %;

[0162] K0——matrix permeability before fracturing fluid damage, μm 2 ;

[0163] K1——Matrix permeability after fracturing fluid damage, μm 2 .

[0164] Table 3 Core damage experimental data

[0165] system Core damage rate / % Example 1 3.2 Example 2 4.8 Example 3 5.9 Comparative Example 1 8.2 Comparative Example 2 15.2 Comparative Example 3 13.1

[0166] Test Example 4: Oil absorption and drainage performance test

[0167] Spontaneous imbibition was used to evaluate the oil-discharging capacity of the nano-enhanced pressure displacement fluid. The test steps are as follows. The results are shown in Table 4:

[0168] (1) Take the core and weigh its dry weight, recorded as m0;

[0169] (2) The core is vacuumed and saturated with simulated seawater, and the wet weight after saturation is measured and recorded as m1;

[0170] (3) Using high pressure displacement method to saturate simulated oil to a certain oil saturation and keep it in reserve;

[0171] (4) Place the core saturated with good crude oil into a customized infiltration bottle and add the nano-enhanced pressure-displacement fluid system;

[0172] (5) After aging at 75°C for 10 days, the imbibition experiment was stopped, the volume of crude oil produced by imbibition was measured, and the imbibition recovery factor was calculated.

[0173] The calculation method of imbibition recovery is as follows:

[0174]

[0175] Where:

[0176] E R ——core imbibition recovery rate, %;

[0177] V o ——Simulated oil volume, mL;

[0178] ρ o ——Simulated formation oil density, g / cm 3 ;

[0179] m0——core dry weight;

[0180] m1——wet weight of core.

[0181] Table 4 Nano-enhanced pressure-displacement fluid absorption and oil drainage performance

[0182] system Recovery rate / % Example 1 38.7 Example 2 36.4 Example 3 33.1 Comparative Example 1 31.6 Comparative Example 2 24.6 Comparative Example 3 28.8

[0183] The present invention has been disclosed above with preferred embodiments, but those skilled in the art should understand that these embodiments are only used to describe the present invention and should not be understood as limiting the scope of the present invention. It should be noted that all changes and substitutions equivalent to these embodiments should be deemed to be included in the scope of the claims of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined in the claims.

Claims

1. A seawater-based nano-synergistic pressure-displacing fluid system, characterized in that: include: Modified nano-SiO2 particles, drag reducer, bactericide, anti-swelling agent, anti-scaling agent and water.

2. The seawater-based nano-synergistic pressure-displacing fluid system according to claim 1, characterized in that: Calculated by weight percentage, the invention comprises: 0.05-0.2% of modified nano-SiO2 particles, 0.1-0.3% of drag reducer, 0.01%-0.2% of bactericide, 0.01%-0.15% of anti-swelling agent, 0.02%-0.2% of anti-scaling agent and the balance of water.

3. The seawater-based nano-synergistic pressure-displacing fluid system according to claim 1, characterized in that: Calculated by weight percentage, the invention comprises: 0.1% of modified nano-SiO2 particles, 0.1% of drag reducer, 0.1% of bactericide, 0.1% of anti-swelling agent, 0.1% of anti-scaling agent and the balance of sea water.

4. The seawater-based nano-synergistic pressure-displacing fluid system according to claim 1, characterized in that: The modified nano-SiO2 particles are SiO2 particles modified by silane with a long-chain alkyl structure.

5. The seawater-based nano-synergistic pressure-displacing fluid system according to claim 4, characterized in that: The silane having a long-chain alkyl structure includes one or more of dodecyltriethoxysilane, hexadecyltriethoxysilane, octadecyltriethoxysilane, dodecyltrimethoxysilane, hexadecyltrimethoxysilane, and octadecyltrimethoxysilane.

6. The seawater-based nano-synergistic pressure-displacing fluid system according to claim 1, characterized in that: The drag reducer is a polymer of AM, AMPS and DtC18.

7. The seawater-based nano-synergistic pressure-displacing fluid system according to claim 1, characterized in that: The bactericide is selected from one or more of sodium salicylate and tetrakis(hydroxymethyl)phosphonium sulfate.

8. The seawater-based nano-synergistic pressure-displacing fluid system according to claim 1, characterized in that: The anti-swelling agent is one or more of potassium chloride, tetramethylammonium chloride, and dodecyltrimethylammonium chloride.

9. The seawater-based nano-synergistic pressure-displacing fluid system according to claim 1, characterized in that: The scale inhibitor is diethylenetriaminepentamethylenephosphonic acid.

10. The seawater-based nano-synergistic pressure-displacing fluid system according to claim 1, characterized in that: The mineralization of the water is 30000mg / L-70000mg / L.

11. The method for preparing the seawater-based nano-synergistic pressure-displacing fluid system according to any one of claims 1 to 10, characterized in that: include: S1: adding modified nano-SiO2 particles and drag reducer into water according to the proportion, stirring to obtain a uniform solution; S2: adding bactericide, anti-swelling agent and anti-scaling agent into the solution, stirring, and fully mixing to obtain a seawater-based nano-synergistic pressure-displacing fluid system.

12. The method for preparing the seawater-based nano-synergistic pressure-displacing fluid system according to claim 11, characterized in that: The modified nano-SiO2 particles are prepared by the following method: S11: adding silane having a long-chain alkyl structure into ethanol, adding acid to adjust the pH, and ultrasonicating to obtain hydrolyzed silane having a long-chain alkyl structure; S12: dispersing nano-SiO2 into anhydrous ethanol, adding dropwise the hydrolyzed silane having a long-chain alkyl structure, and heating for reaction; After the reaction in S13 is completed, centrifugal separation is performed to obtain a paste, which is then dried and ground to obtain modified nano-SiO2 particles.

13. The method for preparing the seawater-based nano-synergistic pressure-displacing fluid system according to claim 12, characterized in that: The mass ratio of the silane having a long-chain alkyl structure to the nano-SiO2 is (1-2):

5.

14. The method for preparing the seawater-based nano-synergistic pressure-displacing fluid system according to claim 12, characterized in that: The temperature of the heating reaction is 40-60°C, and the reaction time is 12-24h.

15. The method for preparing the seawater-based nano-synergistic pressure-displacing fluid system according to claim 11, characterized in that: The drag reducer is prepared by the following method: S21: Dissolve Span-80 and Tween-80 in solvent oil according to the ratio, and stir evenly to obtain an oil phase; S22: dissolve AM in water, add alkali to neutralize AM, add AMPS and DtC18 according to the ratio, and stir evenly to obtain the aqueous phase; S23 After adding alkali to the aqueous phase to adjust the pH, the aqueous phase is added dropwise to the oil phase under the protection of protective gas; S24 adds an initiator, and after the reaction is completed, purifies and dries the polymer to obtain a drag reducer.

16. The method for preparing the seawater-based nano-synergistic pressure-displacing fluid system according to claim 15, characterized in that: The mass ratio of the Span-80 to the Tween-80 is 1:(0.02-0.25).

17. The method for preparing the seawater-based nano-synergistic pressure-displacing fluid system according to claim 15, characterized in that: The mass ratio of the AM to the AMPS and the DtC18 is 0.70-0.89: 0.1-0.23: 0.003-0.

07.

18. The method for preparing the seawater-based nano-synergistic pressure-displacing fluid system according to claim 15, characterized in that: The volume ratio of the oil phase to the water phase is 0.5:1-0.9:1; the concentration of Span-80 and Tween-80 in the oil phase is 1%-9%.

19. The method for preparing the seawater-based nano-synergistic pressure-displacing fluid system according to claim 15, characterized in that: The initiator is azobisisobutyramidine hydrochloride; the mass of the initiator is 0.08%-0.12% of the total mass of AM, AMPS and DtC18.

20. A seawater-based nano-synergistic pressure-displacing fluid system, characterized in that The preparation method is described in any one of claims 11 to 19.

21. Use of the seawater-based nano-synergistic pressure-displacing fluid system according to any one of claims 1 to 10 and 20 in developing offshore low-permeability oil fields.

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