Viscous oil chemical oil-displacing agent evaluation method based on multi-element experiment

Abstract

The invention relates to a multi-element experiment-based heavy oil chemical oil-displacing agent evaluation method. The method comprises the following steps: S1, preparing an oil-displacing agent; s2, simulated formation water is prepared according to formation water components of the target oil reservoir; s3, mixing the crude oil and the kerosene according to the mass ratio of 1: 1 to obtain simulated oil; s4, preparing an oil sand sample, and aging the oil sand sample at a constant temperature of 60 DEG C; s5, respectively carrying out a static oil washing experiment on the to-be-tested oil displacement agent, screening out a qualified to-be-tested oil displacement agent according to an experiment result, and sequentially carrying out a core displacement experiment and an artificial core imbibition experiment on the qualified to-be-tested oil displacement agent; and S6, screening out an optimal oil-displacing agent concentration interval in the three experimental results, and selecting optimal data in an intersection part in the experimental results as a target oil-displacing agent. The method has the beneficial effects that the quaternary composite oil-displacing agent based on the modified nano SiO2 is introduced, and an evaluation experiment is improved, so that the oil-displacing effect of the oil-displacing agent under complex geological conditions is accurately quantified; not only is the oil displacement efficiency improved, but also the application range of the oil displacement agent is widened.

Description

Technical Field

[0001] The present invention relates to the technical field of oilfield development, and more particularly to a method for evaluating a heavy oil chemical flooding agent based on multivariate experiments. Background Art

[0002] In oil production, especially for heavy oil reservoirs with low permeability and high viscosity, traditional water flooding methods are difficult to effectively improve the recovery rate; in recent years, nanomaterials and composite oil flooding agents have gradually become an important means to improve the recovery rate.

[0003] However, existing technologies for evaluating the effectiveness of new oil-displacing agents primarily rely on static experiments or preliminary dynamic simulations, lacking a systematic and comprehensive evaluation system and unable to accurately reflect performance under actual operating conditions. Furthermore, the lack of customized evaluation indicators for different geological conditions and reservoir characteristics results in inaccurate evaluation results, making it difficult to guide field applications. Therefore, we propose a method for evaluating heavy oil chemical flooding agents based on multivariate experiments. Summary of the Invention

[0004] The present invention overcomes the deficiencies in the prior art and provides a method for evaluating a heavy oil chemical flooding agent based on multivariate experiments.

[0005] The purpose of the present invention is achieved through the following technical solutions.

[0006] A method for evaluating heavy oil chemical flooding agents based on multivariate experiments includes the following steps:

[0007] S1, preparing an oil-displacing agent;

[0008] S2. Prepare simulated formation water according to the formation water composition of the target reservoir;

[0009] S3, mixing crude oil and kerosene in a mass ratio of 1:1 to obtain simulated oil;

[0010] S4. After cleaning the quartz sand, mix it with simulated oil at an oil content of 14.9% to prepare an oil sand sample, and age the oil sand sample at a constant temperature of 60°C;

[0011] S5. Conducting static oil washing experiments on the oil-displacing agents to be tested, screening qualified oil-displacing agents to be tested based on the experimental results, and conducting core flooding experiments and artificial core imbibition experiments on the qualified oil-displacing agents to be tested in sequence;

[0012] S6. According to the experimental results of the static oil washing experiment, the core displacement experiment and the artificial core imbibition experiment, the optimal concentration range of each qualified oil displacing agent in the three experiments is obtained respectively, the optimal oil displacing agent concentration range of each qualified oil displacing agent in the three experimental results is screened out, the optimal data in the intersection of each qualified oil displacing agent in the experimental results is selected as the optimal concentration range of the oil displacing agent, the effects of each qualified oil displacing agent in the optimal concentration range are compared, the oil displacing agent with the best effect is used as the target oil displacing agent, and the optimal concentration range of the target oil displacing agent is obtained at the same time.

[0013] The oil displacement agent prepared in S1 is a quaternary composite oil displacement agent based on modified nano-SiO2, which includes polyacrylamide, alkali solution, surfactant and nano-SiO2 that has been subjected to liquid phase in-situ surface modification treatment.

[0014] The particle size of the modified nano-SiO2 is less than 10 nanometers.

[0015] The specific steps for preparing the oil displacement agent in S1 include:

[0016] S11. Preparation and modification of nano-SiO2,

[0017] Nano-SiO2 is dispersed in deionized water and subjected to hydrophilic modification and hydrophobic modification respectively to obtain modified nano-SiO2.

[0018] The modified nano-SiO2 is subjected to performance testing and judgment, and the modified nano-SiO2 that meets the judgment criteria is used as the raw material for preparing the composite oil displacement agent;

[0019] S12, preparation of composite oil displacement agent;

[0020] Slowly add the modified nano-SiO2 dispersion obtained in S11 to the polymer solution and stir thoroughly to make it evenly dispersed;

[0021] Add alkali solution and continue stirring until the system is uniform;

[0022] Add the surfactant solution and continue stirring until a stable composite oil displacement agent is formed;

[0023] S13. Evaluate the performance of the composite oil displacement agent;

[0024] Conduct stability tests on composite oil displacement agents and evaluate their dispersion stability through Zeta potential measurement to ensure their stability under different conditions.

[0025] Conduct interfacial tension tests on composite oil displacement agents. Use an interfacial tension meter to measure the interfacial tension between the composite oil displacement agent and simulated oil to verify the ability of the oil displacement agent to reduce interfacial tension.

[0026] A core displacement experiment was conducted on the composite oil-displacing agent. Sand-filled tubes were used as simulated cores to conduct core displacement experiments to detect the actual oil displacement effect of the composite oil-displacing agent.

[0027] The steps for testing and determining the performance of modified nano-SiO2 in S11 are as follows:

[0028] To verify the superhydrophobicity, the water contact angle of the solid surface treated with the modified nano-SiO2 dispersion was measured at 25°C using a contact angle meter to determine whether it met the judgment criteria, which were contact angle ≥175° and contact angle ≤180°.

[0029] To test pH tolerance, the nano-SiO2 dispersion was placed in buffer solutions with pH values ​​of 0, 7, and 14 and allowed to stand for 24 hours. The test was conducted to determine whether the dispersion met the criteria, which were a contact angle change of ≤5° and no significant sedimentation or agglomeration.

[0030] Conduct high-temperature stability testing by heating at 80°C and 100°C for 72 hours, measuring the zeta potential and particle size distribution; determine whether the product meets the criteria (zeta potential absolute value ≥ 30mV, particle size drift ≤ 10%);

[0031] To conduct a high-salt stability test, nano-SiO2 was mixed with a NaCl solution with a salt concentration of 15,000-20,000 mg / L and allowed to stand for 24 hours. The test was then conducted to determine whether the nano-SiO2 met the criteria, which were interfacial tension ≤ 0.02 mN / m, transmittance drop ≤ 15%, and no flocculation.

[0032] The specific steps of preparing and modifying nano-SiO2 in S11 include:

[0033] In the hydrophilic modification process of nano-SiO2, the nano-SiO2 dispersion is reacted with a hydrophilic modifier (silane coupling agent) at a temperature of 60-80°C for 2-4 hours, and the concentration of the hydrophilic modifier is 0.5-2wt%;

[0034] In the hydrophobic modification process of nano-SiO2, a hydrophobic modifier (hydroxy silicone oil) is added to the hydrophilically modified nano-SiO2 mixture, and the reaction is carried out at a temperature of 70-90°C for 3-5 hours, and the concentration of the hydrophobic modifier is 2.5-3wt%;

[0035] The molar ratio of the hydrophilic modifier to the hydrophobic modifier is adjusted to 1:2.5-1:3.

[0036] The specific steps of the static oil washing experiment in S5 include: taking 3 grams of the oil sand sample prepared in S4 and placing it in a screw-capped bottle, adding 7 grams of the oil displacement agent to be tested, expelling the air from the sample to be tested, and keeping the sample to be tested in an environment of 60°C for 36 hours. Using a fully automatic contact angle meter and an atomic force microscope to measure the water contact angle and surface micromorphology changes of the oil sand sample before and after the experiment, the degree of change of the oil displacement agent on the wettability and microstructure of the rock surface is obtained.

[0037] The specific steps of the core flooding experiment in S5 include:

[0038] A sand-filled tube with a diameter of 2.5 cm and a length of 20 cm was used as a simulated core. 183 g ± 3 g of oil sand sample prepared in S4 was placed in the tube and sealed and fixed, and then connected to the core flooding device.

[0039] Simulated brine was injected into the simulated core until saturated, and then simulated oil, oil displacement agent, and simulated brine were injected in sequence at a rate of 0.5 ml / min. The volume and oil content of the produced fluid were monitored during the experiment until the oil content of the produced fluid was less than 1 drop of oil in 20 drops of liquid.

[0040] A multi-parameter coupling model was constructed to calculate the displacement effect of the oil displacement agent. In the core displacement experiment, the pressure fluctuations, fluid saturation changes, and the adsorption amount of the oil displacement agent in the core were monitored in real time during the displacement process. A regression analysis method was used to establish an oil displacement effect prediction model using the pressure fluctuation frequency (ΔP / Δt), fluid saturation change rate (dS / dt), and adsorption amount (q) as input parameters:

[0041] Y=a·ΔP / Δt+b·dS / dt+c·q+d

[0042] Where Y is the predicted recovery factor, a, b, c, and d are regression coefficients;

[0043] The results output from the oil displacement effect prediction model were compared with the concentration-recovery rate curve drawn based on concentration and recovery rate in the core displacement experiment in S5 to determine the optimal oil displacement agent concentration range.

[0044] The oil displacement agent used in the indoor imbibition experiment in the artificial core in S5 was prepared by mixing the modified nano-SiO2 prepared in S11 with heavy water and an organic solvent to form a mixed solution. In the artificial core imbibition experiment, the crude oil content in the core was determined by nuclear magnetic resonance imaging technology, and the imbibition efficiency was calculated by comparing the changes in T2 spectra before and after imbibition.

[0045] The specific steps for drawing the concentration-recovery curve in the core flooding experiment in S5 include:

[0046] A1. Normalize the recovery factor and oil displacement agent concentration in the core flooding experiment, using the minimum and maximum experimental values ​​as the benchmark and eliminating abnormal data;

[0047] A2. Use linear or polynomial regression to determine the relationship between concentration and recovery factor;

[0048] A3. Draw the concentration-recovery rate curve to determine the optimal range of oil displacement agent concentration.

[0049] The beneficial effects of the present invention are:

[0050] 1. This multivariate experimental approach for evaluating heavy oil chemical flooding agents achieves precise quantification of the flooding effect of the flooding agent under complex geological conditions by introducing a quaternary composite flooding agent based on modified nano-SiO2 and employing a series of carefully designed experimental steps and technical parameter settings. Specifically, the modified nano-SiO2 not only maintains its super-hydrophobic properties within the pH range of 0-14, but also maintains a stable presence at the oil-water interface, effectively reducing the interfacial tension between oil and water, making it easier for oil droplets to deform and flow, and promoting the process of crude oil peeling from the rock surface. This not only improves the flooding efficiency, but also broadens the application range of the flooding agent.

[0051] 2. This multivariate experiment-based evaluation method for heavy oil chemical flooding agents places particular emphasis on simulating formation water properties, including the influence of key parameters such as salinity and chloride concentration. The selection of these parameters directly affects the performance of the flooding agent in actual applications, so the applicability under different water quality conditions is taken into account during the experimental design phase. By accurately simulating these properties, the actual performance of the flooding agent under field conditions can be more accurately predicted, thereby optimizing the flooding plan and improving the recovery efficiency. In addition, considering that different oil reservoirs may have different formation water properties, the present invention also provides flexibility, allowing appropriate adjustments based on specific circumstances to ensure the universal applicability and reliability of the evaluation results. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 Schematic diagram of the heavy oil chemical flooding agent evaluation method based on multivariate experiments of the present invention;

[0053] Figure 2 This is a schematic diagram of a static oil washing photograph of the modified nano-SiO2 composite oil-displacing agent of the present invention;

[0054] Figure 3 Schematic diagram of interfacial tension between the modified nano-SiO2 composite oil-displacing agent and simulated oil according to the present invention;

[0055] Figure 4 Schematic diagram of the wettability of the oil sand surface after displacement in the simulated sand filling oil displacement experiment of the present invention;

[0056] Figure 5 These are T2 spectra of the artificial core of the present invention before and after imbibition of different liquids. DETAILED DESCRIPTION

[0057] Example

[0058] like Figure 1 As shown, a method for evaluating heavy oil chemical flooding agents based on multivariate experiments includes the following steps:

[0059] S1, preparing an oil-displacing agent;

[0060] S2. Prepare simulated formation water according to the formation water composition of the target reservoir;

[0061] S3, mixing crude oil and kerosene in a mass ratio of 1:1 to obtain simulated oil;

[0062] S4. After cleaning the quartz sand, mix it with simulated oil at an oil content of 14.9% to prepare an oil sand sample, and age the oil sand sample at a constant temperature of 60°C;

[0063] S5. Conducting static oil washing experiments on the oil-displacing agents to be tested, screening qualified oil-displacing agents to be tested based on the experimental results, and conducting core flooding experiments and artificial core imbibition experiments on the qualified oil-displacing agents to be tested in sequence;

[0064] S6. According to the experimental results of the static oil washing experiment, the core displacement experiment and the artificial core imbibition experiment, the optimal concentration range of each qualified oil displacing agent in the three experiments is obtained respectively, the optimal oil displacing agent concentration range of each qualified oil displacing agent in the three experimental results is screened out, the optimal data in the intersection of each qualified oil displacing agent in the experimental results is selected as the optimal concentration range of the oil displacing agent, the effects of each qualified oil displacing agent in the optimal concentration range are compared, the oil displacing agent with the best effect is used as the target oil displacing agent, and the optimal concentration range of the target oil displacing agent is obtained at the same time.

[0065] Furthermore, the oil displacement agent prepared in S1 is a quaternary composite oil displacement agent based on modified nano-SiO2, comprising polyacrylamide, alkali solution, surfactant, and nano-SiO2 that has undergone liquid phase in-situ surface modification. The particle size of the modified nano-SiO2 is less than 10 nanometers.

[0066] The specific steps for preparing the oil displacement agent in S1 include:

[0067] S11. Preparation and modification of nano-SiO2,

[0068] Nano-SiO2 is dispersed in deionized water, and hydrophilic modification and hydrophobic modification are performed respectively to obtain modified nano-SiO2.

[0069] The modified nano-SiO2 is subjected to performance testing and judgment, and the modified nano-SiO2 that meets the judgment standard is used as a raw material for preparing a composite oil displacement agent.

[0070] S12, preparation of composite oil displacement agent;

[0071] Slowly add the modified nano-SiO2 dispersion obtained in S11 to the polymer solution and stir thoroughly to make it evenly dispersed;

[0072] Add alkali solution and continue stirring until the system is uniform;

[0073] Add the surfactant solution and continue stirring until a stable composite oil displacement agent is formed;

[0074] S13. Evaluate the performance of the composite oil displacement agent;

[0075] Conduct stability tests on composite oil displacement agents and evaluate their dispersion stability through Zeta potential measurement to ensure their stability under different conditions.

[0076] Conduct interfacial tension tests on composite oil displacement agents. Use an interfacial tension meter to measure the interfacial tension between the composite oil displacement agent and simulated oil to verify the ability of the oil displacement agent to reduce interfacial tension.

[0077] A core displacement experiment was conducted on the composite oil-displacing agent. Sand-filled tubes were used as simulated cores to conduct core displacement experiments to detect the actual oil displacement effect of the composite oil-displacing agent.

[0078] Furthermore, in the hydrophilic modification of S11, nano-SiO2 is dispersed in deionized water, and an appropriate amount of a hydrophilic modifier is added. In this embodiment, a silane coupling agent is used as the hydrophilic modifier. After stirring evenly, the mixture is reacted at a certain temperature for a period of time to perform the hydrophilic modification.

[0079] In the hydrophobic modification of S11, a hydrophobic modifier is added to the hydrophilic modified mixture. In this embodiment, hydroxy silicone oil is used. The reaction is continued by stirring until the ratio of the hydrophilic and hydrophobic modifiers is 1:2 to obtain the modified nano-SiO2.

[0080] Furthermore, in order to better optimize the ratio of hydrophilic and hydrophobic groups on the surface of modified nano-SiO2, this scheme provides the following specific steps for the preparation and modification of nano-SiO2 in S11:

[0081] In the hydrophilic modification process of nano-SiO2, the nano-SiO2 dispersion is reacted with a hydrophilic modifier, in this embodiment a silane coupling agent, at a temperature of 60-80°C for 2-4 hours, with a hydrophilic modifier concentration of 0.5-2 wt%.

[0082] During the hydrophobic modification of nano-SiO2, a hydrophobic modifier is added to the mixture of nano-SiO2 in the hydrophilic modification. In this embodiment, hydroxy silicone oil is used. The reaction is carried out at a temperature of 70-90°C for 3-5 hours, and the concentration of the hydrophobic modifier is 2.5-3wt%.

[0083] The molar ratio of the hydrophilic modifier to the hydrophobic modifier is adjusted to 1:2.5-1:3, so that the ratio of the hydrophilic group and the hydrophobic group on the surface of the modified nano-SiO2 reaches a balance, ensuring that the modified nano-SiO2 exists stably at the oil-water interface.

[0084] According to the above steps, the optimized modified nano-SiO2 can reduce the oil-water interfacial tension to 0.01-0.02 mN / m and remain stable under simulated Shengli reservoir conditions (salinity 15,000-20,000 mg / L, temperature 80-100°C), with the absolute value of Zeta potential ≥30 mV and the particle size distribution (D50) ≤10 nm.

[0085] Furthermore, the performance testing and determination steps for the modified nano-SiO2 in S11 are as follows:

[0086] To verify the superhydrophobicity, the water contact angle of the solid surface treated with the modified nano-SiO2 dispersion was measured at 25°C using a contact angle meter. The water contact angle was determined to be ≥175° and ≤180°, respectively. The allowable deviation in this step was ≤3°.

[0087] The pH tolerance test was conducted by placing the nano-SiO2 dispersion in buffer solutions of pH 0, 7, and 14 and letting it stand for 24 hours. The test was conducted to determine whether the dispersion met the criteria, which were that the contact angle change was ≤5° and there was no obvious sedimentation or agglomeration of the dispersion.

[0088] Conduct high-temperature stability testing by heating at 80°C and 100°C for 72 hours, measuring the zeta potential and particle size distribution; determine whether the product meets the criteria (zeta potential absolute value ≥ 30mV, particle size drift ≤ 10%);

[0089] To conduct a high-salt stability test, nano-SiO2 was mixed with a NaCl solution with a salt concentration of 15,000-20,000 mg / L and allowed to stand for 24 hours. The test was then conducted to determine whether the nano-SiO2 met the criteria, which were interfacial tension ≤ 0.02 mN / m, transmittance drop ≤ 15%, and no flocculation.

[0090] Preferably, in this embodiment S12, the polymer solution is prepared by dissolving polyacrylamide in deionized water. The alkali solution is sodium hydroxide solution.

[0091] In S2, the formation water composition of the target reservoir ranges from 5000 to 8000 mg / L of salinity and 300 to 600 mg / L of chloride.

[0092] Furthermore, the specific steps of the static oil washing experiment in S5 include: taking 3 grams of the oil sand sample prepared in S4 and placing it in a screw-capped bottle, adding 7 grams of the oil displacement agent to be tested, expelling the air from the sample to be tested, and then keeping the sample to be tested in a 60°C environment for 36 hours. Using a fully automatic contact angle meter and an atomic force microscope to measure the water contact angle and surface micromorphology changes of the oil sand sample before and after the experiment, the degree of change of the wettability and microstructure of the rock surface caused by the oil displacement agent was obtained.

[0093] Preferably, in this step, the water contact angle measurement range is set between 0 and 180 degrees, and the atomic force microscope resolution is set to nanometer level.

[0094] The specific steps of the core flooding experiment in S5 include:

[0095] A sand-filled tube with a diameter of 2.5 cm and a length of 20 cm was used as a simulated core. 183 g ± 3 g of oil sand sample prepared in S4 was placed in the tube and sealed and fixed, and then connected to the core flooding device.

[0096] Simulated brine was injected into the simulated core until saturated, and then simulated oil, oil displacement agent, and simulated brine were injected in sequence at a rate of 0.5 ml / min. The volume and oil content of the produced fluid were monitored during the experiment until the oil content of the produced fluid was less than 1 drop of oil in 20 drops of liquid.

[0097] A multi-parameter coupling model was constructed to calculate the displacement effect of the oil displacement agent. In the core displacement experiment, the pressure fluctuations, fluid saturation changes, and the adsorption amount of the oil displacement agent in the core were monitored in real time during the displacement process. A regression analysis method was used to establish an oil displacement effect prediction model using the pressure fluctuation frequency (ΔP / Δt), fluid saturation change rate (dS / dt), and adsorption amount (q) as input parameters:

[0098] Y=a·ΔP / Δt+b·dS / dt+c·q+d

[0099] Where Y is the predicted recovery factor, a, b, c, and d are regression coefficients;

[0100] The results output from the oil displacement effect prediction model were compared with the concentration-recovery rate curve drawn based on concentration and recovery rate in the core displacement experiment in S5 to determine the optimal oil displacement agent concentration range.

[0101] Furthermore, the specific steps for drawing the concentration-recovery curve in the core flooding experiment in S5 include:

[0102] A1. Normalize the recovery factor and oil displacement agent concentration in the core flooding experiment, using the minimum and maximum experimental values ​​as the benchmark and eliminating abnormal data;

[0103] A2. Use linear or polynomial regression to determine the relationship between concentration and recovery factor;

[0104] A3. Draw the concentration-recovery rate curve to determine the optimal range of oil displacement agent concentration.

[0105] In A1, the data collected in the core flooding experiment need to be standardized and regression analyzed using statistical software to draw a relationship curve between oil displacement agent concentration and recovery rate, so as to determine the optimal addition amount range.

[0106] In A3, the optimal range of oil displacement agent concentration was determined by selecting the concentration range near the recovery rate peak of the concentration-recovery rate curve, combining error control, error between the predicted value and the experimental value ≤5%, and multi-parameter model verification.

[0107] Furthermore, a concentration-recovery rate curve is obtained through imbibition experiments to derive an optimal oil displacement agent concentration range. The actual experimental results are compared and verified with the predicted data obtained from the oil displacement effect prediction model, and the intersection part is obtained as the result data.

[0108] Furthermore, the oil displacement agent used in the indoor imbibition experiment in the artificial core imbibition experiment in S5 was prepared into a mixed solution by mixing the modified nano-SiO2 prepared in S11 with heavy water and an organic solvent. In the artificial core imbibition experiment, the crude oil content in the core was determined by nuclear magnetic resonance imaging technology, and the imbibition efficiency was calculated by comparing the changes in T2 spectra before and after imbibition.

[0109] In this example, deuterated water was used as the heavy water, and dimethyl sulfoxide was used as the organic solvent. The organic solvent was added at a ratio of 5% to 10%. The heavy water concentration was 7500-8000 mg / L. This mixed solution was used in artificial core imbibition experiments to improve the diffusion rate and imbibition efficiency of the oil displacement agent within the core pores while preventing interference with the nuclear magnetic resonance (NMR) signal.

[0110] like Figure 2 As shown, this embodiment uses oil sand immersion experiments to study the effect of effective content on oil sand washing effect. Figure 2 Effects of nano-SiO2 composite flooding agents modified with different modifier ratios on oil sand immersion and oil washing at 60°C.

[0111] Figure 2(a) (b) are static oil washing diagrams of hydrophilic-first and then hydrophobic-modified nano-SiO2 composite oil-displacing agents. From left to right, the ratios of hydrophilic modifier: hydrophobic modifier are 2.0:1.0, 1.5:1.0, 1.0:1.0, 1.0:1.5, 1.5:2.0, and 0.5:2.5, respectively.

[0112] Figure 2 (c) (d) are static oil washing diagrams of the nano-SiO2 composite oil-displacing agent that was first hydrophobic and then hydrophilic modified. From left to right, the ratios of hydrophobic modifier: hydrophilic modifier are 2.0:1.0, 1.5:1.0, 1.0:1.0, 1.0:1.5, 1.5:2.0, and 0.5:2.5, respectively.

[0113] By observing the oil phase in the screw-cap bottle, it was found that the first to precipitate a small amount of oil was the composite oil-displacing agent with a modifier ratio of hydrophilic to hydrophobic of 1:2 in the nano-SiO2 quaternary composite oil-displacing agent modified first hydrophilically and then hydrophobically. When placed at 60°C for 3 hours, oil was precipitated from the composite oil-displacing agents of all modifier ratios, and the color of the oil-displacing agent between the upper oil precipitated and the lower oil sand became darker, and a small amount of simulated oil emulsified. After 6 hours, the amount of oil precipitated from the nano-SiO2 composite oil-displacing agents modified based on different modifier ratios increased, and a circle of oil appeared along the wall of the glass bottle. When the static oil washing time was extended to 12 hours, the amount of oil precipitated from the nano-SiO2 composite oil-displacing agents modified based on different modifier ratios continued to increase. The system was kept at 60°C for 36 hours, and the oil phase in the screw-cap bottle no longer changed, and the oil washing was completed.

[0114] After standing at a constant temperature for 36 hours, observe the changes in the oil phase in the screw-cap bottle. Figure 2 In (a) and (b), the oil-displacing agents with a ratio of hydrophilic modifier to hydrophobic modifier of 2:1 and 1.5:1 have poor oil-washing effects, while the oil-washing effects of other ratios are comparable. Figure 2 The oil washing results in (c) and (d) show that the oil washing effect of the modified nano-SiO2 composite oil-displacing agent with a ratio of 1:2 to hydrophilic modifier is poor, and there is less oil phase floating in the upper layer of the screw-mouth bottle; when the modified nano-SiO2 composite oil-displacing agent prepared by the two methods of first hydrophilic and then hydrophobic and first hydrophobic and then hydrophilic is statically washed, there are obvious oil droplets attached to the surface of the oil sand and oil droplets precipitated, and some oil droplets automatically peel off from the surface of the oil sand and float on the surface of the sample liquid. There may be a small amount of simulated oil dissolved or emulsified in the immersion liquid, and the color of the immersion liquid is also deepened. The results show that the modified nano-SiO2 quaternary composite oil-displacing agent has a larger amount of precipitated oil, the color of the immersion liquid is significantly deepened, and the stripping ability of the adsorbed oil is better, showing a good static oil washing effect; the static oil washing results are basically consistent with the core displacement results.

[0115] In this embodiment, oil sand was selected for core flooding experiment to investigate the oil displacement performance of modified nano-SiO2 composite oil-displacing agent; oil sand prepared by mixing crude oil and kerosene in a mass ratio of 1:1 was used to conduct core flooding experiment on different oil-displacing agents with the same concentration. The core flooding results are shown in Tables 1 and 2. Based on the nano-SiO2 composite oil-displacing agent modified by hydrophilic and then hydrophobic modification, the oil-displacing agent with the best oil-displacing performance was the oil-displacing agent with a modifier ratio of hydrophilic: hydrophobic of 1:2. On the basis of the primary water flooding recovery rate of 29.9%, the secondary water flooding recovery rate was 39.3%, and the oil-displacing agent with a modifier ratio of 1:1.5 was the secondary water flooding. The recovery rate is 30.9%. The composite oil-displacing agent with a modifier ratio of 0.5:2.5 has comparable oil-displacing performance, and the secondary water-displacing recovery rate is 29.2%. The oil-displacing performance of the nano-SiO2 composite oil-displacing agent modified first by hydrophobicity and then by hydrophilicity shows a trend of first increasing and then decreasing. The secondary water-displacing recovery rate is the highest at 30.9% when the hydrophobic:hydrophilic modifier ratio is 1:2. Under the conditions of using the same simulated oil sand, the oil-displacing performance of the modified nano-SiO2 composite oil-displacing agent is significantly improved compared with the secondary water-displacing recovery rate of 25.8% of the hydrophobic modified nano-SiO2 composite oil-displacing agent.

[0116] Table 1 Core flooding results based on modified nano-SiO2 (hydrophilic first and then hydrophobic) composite oil displacement agent

[0117]

[0118]

[0119] Table 2 Core flooding results based on modified nano-SiO2 (hydrophobic first and then hydrophilic) composite oil displacement agent

[0120]

[0121] The effect of oil displacement agent on water-oil interfacial tension is one of the important characteristics of analyzing its potential oil displacement mechanism. In this example, the interfacial tension of nano-SiO2 composite oil displacement agent modified with different modifier ratios and simulated oil (crude oil and kerosene mass ratio of 1:1) was measured. The results are as follows: Figure 3As shown in the figure, the nano-SiO2 composite oil-displacing agents modified with different modifier ratios all have a good ability to reduce the water-oil interfacial tension, and can quickly reduce the water-oil interfacial tension to below 0.1mN / m, but there are still certain differences in the ability to reduce the water-oil interfacial tension; it can be seen from the figure that among a series of modifier ratios of the nano-SiO2 composite oil-displacing agent based on first hydrophilic and then hydrophobic modification, the modifier ratio with the smallest final interfacial tension is hydrophilic: hydrophobic at 1:2, and the interfacial tension is reduced to 0.03165mN / m; among a series of modifier ratios of the SiO2 composite oil-displacing agent based on first hydrophobic and then hydrophilic modification, the modifier ratio with the smallest final interfacial tension is hydrophobic: hydrophilic at 1:2, and the interfacial tension is reduced to 0.04091mN / m; the test results of water-oil interfacial tension basically correspond to the core displacement results. The modified nano-SiO2 composite oil-displacing agent can reduce the interfacial tension, thereby reducing the residual oil saturation to improve the microscopic oil displacement efficiency.

[0122] After the core flooding is completed, the oil sands after being flooded by the nano-SiO2 composite flooding agent modified with a 1:2 ratio of first hydrophilic and then hydrophobic, surfactant and ternary composite flooding agent are dried. The dried oil sands are evenly spread on a glass slide in a pressed sample manner to measure the water contact angle. The results are as follows: Figure 4 As can be seen from the figure, the sandstone after displacement by surfactants and ternary composite oil-displacing agents still has good hydrophobicity. After the water droplet stays on the sandstone surface for 50 seconds, its water contact angle is still greater than 90°, showing hydrophobicity; after displacement by the quaternary composite oil-displacing agent, the water droplet can still be retained in the initial state, but the water droplet will quickly seep into the sandstone. After 50 seconds, there is no water droplet on the sandstone surface, indicating that the quaternary composite oil-displacing agent changes the wettability of the sandstone surface from hydrophobic to hydrophilic, thereby improving the ability of water phase seepage, increasing the number of water drive capillaries, and improving crude oil recovery.

[0123] Based on the significantly improved stability of the hydrophobically modified nano-SiO2 quaternary composite oil-displacing agent, a hydrophilic modifier was introduced and compounded with the hydrophobic modifier to regulate the hydrophilicity / lipophilicity of nano-SiO2, preparing a modified nano-SiO2 quaternary composite oil-displacing system and further improving the oil-displacing performance. By adjusting the addition order and ratio of the modifiers, a series of modified nano-SiO2 were prepared, which were dispersed in water to obtain nano-SiO2 dispersions and blended with polymers to obtain composite oil-displacing agents of the target concentration. The dispersion stability and oil-displacing performance of nano-SiO2 quaternary composite oil-displacing agents modified with different modifier ratios were investigated, and their potential oil-displacing mechanisms were analyzed. The results showed that:

[0124] (1) Under the synergistic effect of surfactant and alkali solution, hydrophobically modified nano-SiO2 with a particle size of less than 10nm is stably dispersed in water;

[0125] (2) The modified nano-SiO2 quaternary composite oil displacement agent has good dispersion stability, with an absolute value of zeta potential of 40-60mV; the quaternary composite oil displacement agent (simulating the salinity of Shengli oil reservoir) can be stably dispersed for 236 days at room temperature and for 21 days at 60°C;

[0126] (3) The oil displacement performance of the modified nano-SiO2 composite oil displacement agent was significantly improved. When the nano-SiO2 modified by the hydrophilic modifier was first added and the ratio of hydrophilic to hydrophobic modifier was 1:2, the composite oil displacement agent had a secondary water flooding recovery rate of 39.3% based on the primary water flooding recovery rate of 29.9%.

[0127] In order to verify the effect of different mass fractions of nano-displacement agents on crude oil recovery by imbibition, this example uses artificial cores to conduct spontaneous imbibition recovery experiments, and uses nuclear magnetic resonance equipment to characterize the degree of crude oil recovery in different pores of the cores.

[0128] (1) Experimental principle and method Nuclear magnetic resonance technology can characterize reservoir microscopic characteristics (reservoir physical properties, pore throat characteristics, etc.) and pore fluid parameters (mobile and bound fluid content and pore volume, etc.); when a core sample containing fluid (oil or water) is placed in the static magnetic field of the nuclear magnetic resonance device, the protons in the nuclei of the pore fluid are polarized. At this time, by adding a fixed frequency pulse in the direction perpendicular to the magnetic field, the rock fluid nuclear magnetic resonance signal can be collected; after mathematical inversion of the collected signal, the corresponding T2 relaxation time spectrum can be obtained; the relaxation time is proportional to the pore size; the envelope area under the relaxation image in the T2 spectrum represents the content of the fluid in the pore, and the peak area corresponding to different relaxation times corresponds to the volume of pores of different sizes. Therefore, the nuclear magnetic resonance technology can be used to intuitively and quantitatively characterize the amount of liquid in different pores, revealing the occurrence state of oil in the rock sample before and after imbibition in the microscopic pores; the imbibition recovery rate can be defined as:

[0129]

[0130] Where: R is imbibition recovery, %; S0 is the envelope area under the T2 spectrum before imbibition (i.e., under oil-saturated conditions), representing the pore oil volume; S n ——The envelope area under the T2 spectrum after imbibition characterizes the oil volume in the pores at that moment; heavy water (deuterated water, D2O) does not contain hydrogen nuclei and does not generate resonance signals under the action of magnetic field pulses. It will not interfere with the sample signal in the experiment. Therefore, heavy water can be used to prepare nano-oil displacement agents for imbibition experiments.

[0131] The low-permeability saturated artificial core was removed, and the T2 spectrum of the artificial core before the imbibition experiment was measured using a nuclear magnetic resonance device. Then, nano-displacement agent solutions with mass fractions of 1.0%, 1.5%, and 2.0% were prepared using heavy water (D2O). The solutions were stirred with a stirrer for 5 minutes. The saturated core was placed in the nano-displacement agent heavy water solution for spontaneous imbibition displacement experiment. The T2 spectrum of the core was measured after 72 hours of spontaneous imbibition.

[0132] (2) Experimental equipment and materials Experimental equipment: filtration bottle, nuclear magnetic resonance device and signal acquisition system; Experimental materials: saturated artificial core, YE-4B nano oil displacement agent, kerosene, heavy water.

[0133] The permeability of artificial cores is consistent with the characteristics of ultra-low permeability rocks.

[0134] (3) Experimental results and analysis

[0135] from Figure 5 It can be seen that after spontaneous imbibition of different liquids, the envelope area under the T2 spectrum of the core is different. The higher the dosage of nano-oil displacement agent, the greater the decrease in the spectrum peak and the smaller the envelope area under the peak, reflecting that the less remaining oil in the pores, the more spontaneous imbibition oil displacement in the core, and the higher the imbibition recovery rate.

[0136] The T2 image shows a clear bimodal structure, with the left peak corresponding to small pores in the core and the right peak corresponding to large pores in the core. It is obvious from the image that as the content of nano-displacement agent increases, the left peak decreases more, indicating that the nano-displacement agent has a higher degree of imbibition and recovery of crude oil in small pores, indicating that small pores play a major role in imbibition. This is because the pore throat diameter of small pores is smaller and the capillary force is stronger. When developing low permeability oil reservoirs, it is necessary to pay attention to the imbibition and oil recovery effect of small pores.

[0137] As shown in Table 3, the imbibition recovery degree was calculated based on the envelope area under the T2 spectrum collected by the equipment. The results show that the higher the amount of nano-displacement agent used, the higher the crude oil imbibition recovery degree. The recovery rate of artificial cores after spontaneous imbibition of a 2.0% nano-displacement agent by mass fraction can reach up to 51%. The crude oil recovery degree in different pores was calculated based on the envelope area under different peaks. The higher the amount of nano-displacement agent used, the greater the imbibition recovery degree of crude oil in small pores. The recovery rate of 2.0% nano-displacement agent for small pores is 2.73 times that of heavy water imbibition, and the recovery rate of crude oil in large pores is 2.53 times that of heavy water imbibition. Nano-displacement agent is more effective in improving the recovery rate of crude oil in small pores. It can recover crude oil from deep small pores where conventional liquids are difficult to enter, and displace crude oil through imbibition. It has broad application prospects in low-permeability reservoirs.

[0138] Table 3 T2 spectrum peak area and recovery rate before and after imbibition

[0139]

[0140]

[0141] In summary, this multivariate experimental-based evaluation method for heavy oil chemical flooding agents achieves accurate quantification of the oil recovery effect of flooding agents under complex geological conditions by introducing a quaternary composite flooding agent based on modified nano-SiO2 and adopting a series of carefully designed experimental steps and technical parameter settings. Specifically, modified nano-SiO2 can not only maintain its superhydrophobic properties within the pH range of 0-14, but can also stably exist at the oil-water interface, effectively reducing the interfacial tension between oil and water, making oil droplets easier to deform and flow, and promoting the process of crude oil peeling from the rock surface. This not only improves the oil recovery efficiency, but also broadens the application range of flooding agents.

[0142] Moreover, the evaluation method for chemical displacement agents for heavy oil based on multivariate experiments places particular emphasis on the consideration of simulated formation water properties, including the influence of key parameters such as salinity and chloride concentration. The selection of these parameters directly affects the performance of the displacement agent in actual applications, so the applicability under different water quality conditions is taken into account during the experimental design phase. By accurately simulating these properties, the actual performance of the displacement agent under field conditions can be more accurately predicted, thereby optimizing the displacement scheme and improving the recovery efficiency. Furthermore, considering that different oil reservoirs may have different formation water properties, the present invention also provides flexibility, allowing appropriate adjustments according to specific circumstances to ensure the universal applicability and reliability of the evaluation results, thus solving the problem that the existing technology for the evaluation of the effects of new displacement agents mainly relies on static experiments or preliminary dynamic simulations, lacks a systematic and comprehensive evaluation system, and cannot accurately reflect the performance under actual working conditions. In addition, there is a lack of the design of personalized evaluation indicators for different geological conditions and reservoir characteristics, resulting in inaccurate evaluation results and difficulty in guiding field applications.

[0143] The relevant modules involved in this system are all hardware system modules or functional modules that combine computer software programs or protocols with hardware in the existing technology. The computer software programs or protocols involved in the functional modules are themselves technologies that are well known to those skilled in the art and are not improvements to this system. The improvements to this system are the interaction or connection relationships between the modules, that is, improvements to the overall structure of the system to solve the corresponding technical problems to be solved by this system.

[0144] The embodiments of the present invention are described in detail above, but the contents described are only preferred embodiments of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A method for evaluating heavy oil chemical flooding agents based on multivariate experiments, characterized in that: The specific steps include: S1, preparing an oil-displacing agent; S2. Prepare simulated formation water according to the formation water composition of the target reservoir; S3, mixing crude oil and kerosene in a mass ratio of 1:1 to obtain simulated oil; S4. After cleaning the quartz sand, mix it with simulated oil at an oil content of 14.9% to prepare an oil sand sample, and age the oil sand sample at a constant temperature of 60°C; S5. Conducting static oil washing experiments on the oil-displacing agents to be tested, screening qualified oil-displacing agents to be tested based on the experimental results, and conducting core flooding experiments and artificial core imbibition experiments on the qualified oil-displacing agents to be tested in sequence; S6. According to the experimental results of the static oil washing experiment, the core displacement experiment and the artificial core imbibition experiment, the optimal concentration range of each qualified oil displacing agent in the three experiments is obtained respectively, the optimal oil displacing agent concentration range of each qualified oil displacing agent in the three experimental results is screened out, the optimal data in the intersection of each qualified oil displacing agent in the experimental results is selected as the optimal concentration range of the oil displacing agent, the effects of each qualified oil displacing agent in the optimal concentration range are compared, the oil displacing agent with the best effect is used as the target oil displacing agent, and the optimal concentration range of the target oil displacing agent is obtained at the same time.

2. The method for evaluating a heavy oil chemical flooding agent based on multivariate experiments according to claim 1, characterized in that: The oil displacement agent prepared in S1 is a quaternary composite oil displacement agent based on modified nano-SiO2, which includes polyacrylamide, alkali solution, surfactant and nano-SiO2 that has been subjected to liquid phase in-situ surface modification treatment.

3. The method for evaluating a heavy oil chemical flooding agent based on multivariate experiments according to claim 2, characterized in that: The particle size of the modified nano-SiO2 is less than 10 nanometers.

4. The method for evaluating heavy oil chemical flooding agents based on multivariate experiments according to claim 1, characterized in that: The specific steps for preparing the oil displacement agent in S1 include: S11. Preparation and modification of nano-SiO2, Nano-SiO2 is dispersed in deionized water and subjected to hydrophilic modification and hydrophobic modification respectively to obtain modified nano-SiO2. Performing performance testing on the modified nano-SiO2 and using the modified nano-SiO2 that meets the criteria as a raw material for preparing a composite oil displacement agent; S12, preparation of composite oil displacement agent; Slowly add the modified nano-SiO2 dispersion obtained in S11 to the polymer solution and stir thoroughly to make it evenly dispersed; Add alkali solution and continue stirring until the system is uniform; Add the surfactant solution and continue stirring until a stable composite oil displacement agent is formed; S13. Evaluate the performance of the composite oil displacement agent; Conduct stability tests on composite oil displacement agents and evaluate their dispersion stability through Zeta potential measurement to ensure their stability under different conditions. Conduct interfacial tension tests on composite oil displacement agents. Use an interfacial tension meter to measure the interfacial tension between the composite oil displacement agent and simulated oil to verify the ability of the oil displacement agent to reduce interfacial tension. A core displacement experiment was conducted on the composite oil-displacing agent. Sand-filled tubes were used as simulated cores to conduct core displacement experiments to detect the actual oil displacement effect of the composite oil-displacing agent.

5. The method for evaluating heavy oil chemical flooding agents based on multivariate experiments according to claim 4, characterized in that: The steps for testing and determining the performance of modified nano-SiO2 in S11 are as follows: To verify the superhydrophobicity, the water contact angle of the solid surface treated with the modified nano-SiO2 dispersion was measured at 25°C using a contact angle meter to determine whether it met the judgment criteria, which were contact angle ≥175° and contact angle ≤180°. To test pH tolerance, the nano-SiO2 dispersion was placed in buffer solutions with pH values ​​of 0, 7, and 14 and allowed to stand for 24 hours. The test was conducted to determine whether the dispersion met the criteria, which were a contact angle change of ≤5° and no significant sedimentation or agglomeration. Conduct high-temperature stability testing by heating at 80°C and 100°C for 72 hours, measuring the zeta potential and particle size distribution; determine whether the product meets the criteria (zeta potential absolute value ≥ 30mV, particle size drift ≤ 10%); To conduct a high-salt stability test, nano-SiO2 was mixed with a NaCl solution with a salt concentration of 15,000-20,000 mg / L and allowed to stand for 24 hours. The test was then conducted to determine whether the nano-SiO2 met the criteria, which were interfacial tension ≤ 0.02 mN / m, transmittance drop ≤ 15%, and no flocculation.

6. The method for evaluating heavy oil chemical flooding agents based on multivariate experiments according to claim 4, characterized in that: The specific steps of preparing and modifying nano-SiO2 in S11 include: In the hydrophilic modification process of nano-SiO2, the nano-SiO2 dispersion is reacted with a hydrophilic modifier at a temperature of 60-80°C for 2-4 hours, and the concentration of the hydrophilic modifier is 0.5-2wt%; In the hydrophobic modification process of nano-SiO2, a hydrophobic modifier is added to the mixture of hydrophilically modified nano-SiO2, and the reaction is carried out at a temperature of 70-90°C for 3-5 hours, and the concentration of the hydrophobic modifier is 2.5-3wt%; The molar ratio of the hydrophilic modifier to the hydrophobic modifier is adjusted to 1:2.5-1:

3.

7. The method for evaluating heavy oil chemical flooding agents based on multivariate experiments according to claim 1, characterized in that: The specific steps of the static oil washing experiment in S5 include: taking 3 grams of the oil sand sample prepared in S4 and placing it in a screw-capped bottle, adding 7 grams of the oil displacement agent to be tested, expelling the air from the sample to be tested, and keeping the sample to be tested in an environment of 60°C for 36 hours. Using a fully automatic contact angle meter and an atomic force microscope to measure the water contact angle and surface micromorphology changes of the oil sand sample before and after the experiment, the degree of change of the oil displacement agent on the wettability and microstructure of the rock surface is determined.

8. The method for evaluating heavy oil chemical flooding agents based on multivariate experiments according to claim 1, characterized in that: The specific steps of the core flooding experiment in S5 include: A sand-filled tube with a diameter of 2.5 cm and a length of 20 cm was used as a simulated core. 183 g ± 3 g of oil sand sample prepared in S4 was placed in the tube and sealed and fixed, and then connected to the core flooding device. Simulated brine was injected into the simulated core until saturated, and then simulated oil, oil displacement agent, and simulated brine were injected in sequence at a rate of 0.5 ml / min. The volume and oil content of the produced fluid were monitored during the experiment until the oil content of the produced fluid was less than 1 drop of oil in 20 drops of liquid. A multi-parameter coupling model was constructed to calculate the displacement effect of the oil displacement agent. In the core displacement experiment, the pressure fluctuations, fluid saturation changes, and the adsorption amount of the oil displacement agent in the core were monitored in real time during the displacement process. A regression analysis method was used to establish an oil displacement effect prediction model using the pressure fluctuation frequency (ΔP / Δt), fluid saturation change rate (dS / dt), and adsorption amount (q) as input parameters: Y=a·ΔP / Δt+b·dS / dt+c·q+d Where Y is the predicted recovery factor, a, b, c, and d are regression coefficients; The results output from the oil displacement effect prediction model were compared with the concentration-recovery rate curve drawn based on concentration and recovery rate in the core displacement experiment in S5 to determine the optimal oil displacement agent concentration range.

9. The method for evaluating a heavy oil chemical flooding agent based on multivariate experiments according to claim 4, characterized in that: The oil displacement agent used in the indoor imbibition experiment in the artificial core in S5 was prepared by mixing the modified nano-SiO2 prepared in S11 with heavy water and an organic solvent to form a mixed solution. In the artificial core imbibition experiment, the crude oil content in the core was determined by nuclear magnetic resonance imaging technology, and the imbibition efficiency was calculated by comparing the changes in T2 spectra before and after imbibition.

10. The method for evaluating heavy oil chemical flooding agents based on multivariate experiments according to claim 8, characterized in that: The specific steps for drawing the concentration-recovery curve in the core flooding experiment in S5 include: A1. Normalize the recovery factor and oil displacement agent concentration in the core flooding experiment, using the minimum and maximum experimental values ​​as the benchmark and eliminating abnormal data; A2. Use linear or polynomial regression to determine the relationship between concentration and recovery factor; A3. Draw the concentration-recovery rate curve to determine the optimal range of oil displacement agent concentration.

Images