Screening method of surfactant

Abstract

The invention relates to the technical field of oil exploitation, in particular to a surfactant screening method which comprises the following steps: acquiring an oil-water interfacial tension index of each surfactant, and screening the surfactant meeting a first preset rule; obtaining a wetting reversibility index of the surfactant meeting a first preset rule, and screening the surfactant meeting a second preset rule; obtaining the anti-adsorption performance of the surfactant meeting a second preset rule, and screening the surfactant meeting a third preset rule; and obtaining an imbibition recovery rate index of a surfactant meeting a third preset rule, and screening a surfactant meeting a fourth preset rule as a target surfactant. According to the method, the oil-water interfacial tension, the wetting reversibility, the anti-adsorption performance and the imbibition recovery efficiency indexes of the surfactant are evaluated step by step by following the logic sequence of the action of the surfactant, the actual application process can be more accurately simulated, the surfactant with the optimal performance can be screened out, and the screening efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum exploitation, in particular to a method for screening a surfactant. Background Art

[0002] The exploitation of shale oil reservoirs faces a series of complex challenges, and fracturing technology, as an effective coping strategy, is widely adopted to promote the exploitation of oil reservoirs. In order to further improve the fracturing effect, it has become a common practice to add surfactants to the fracturing fluid. These surfactants can further improve the water injection capacity, achieve efficient reversal of rock surface wettability, reduce capillary forces, and improve imbibition efficiency, thereby optimizing the exploitation process at multiple levels.

[0003] However, despite the availability of a variety of surfactants on the market, the lack of a unified and scientific evaluation method often makes it difficult for researchers to determine which surfactant is most suitable for specific reservoir conditions. This situation has undoubtedly become a key factor restricting further improvement of oil recovery efficiency.

[0004] Therefore, it is particularly important to develop a comprehensive and accurate surfactant evaluation method. This evaluation method should cover multiple key performance indicators of surfactants in fracturing fluids, including but not limited to oil-water interfacial tension, wettability reversal, adsorption resistance, and imbibition recovery. By comprehensively considering these indicators, staff can more accurately screen out the surfactant that best suits their specific mining conditions, thereby ensuring the best crude oil recovery results. Summary of the invention

[0005] The purpose of the present invention is to provide a method for screening surfactants in order to solve at least one of the above-mentioned technical problems. This method can not only provide scientific guidance for workers and help them make more reasonable choices, but also maximize production and further optimize the entire mining process.

[0006] The present invention achieves the above-mentioned purpose through the following technical solutions:

[0007] A method for screening a surfactant comprises the following steps:

[0008] Obtaining the oil-water interfacial tension index of each surfactant, and screening the surfactant that meets the first preset rule;

[0009] Obtaining a wetting reversal index of a surfactant that meets a first preset rule, and screening a surfactant that meets a second preset rule;

[0010] Obtaining the anti-adsorption performance of the surfactant that meets the second preset rule, and screening the surfactant that meets the third preset rule;

[0011] The imbibition recovery index of the surfactant that meets the third preset rule is obtained, and the surfactant that meets the fourth preset rule is selected as the target surfactant.

[0012] Furthermore, the oil-water interfacial tension index of each surfactant is obtained, including:

[0013] The oil phase is simulated oil, and the liquid phase is formation water;

[0014] Prepare a preliminary surfactant solution with formation water; use a glass capillary to suck the surfactant solution or formation water, then drop oil droplets into it, ensuring that there are no bubbles and the measuring tube is airtight, to obtain the first solution;

[0015] Using kerosene as a control, repeat the above steps to obtain a comparative solution;

[0016] Testing the oil-water interfacial tension of the first solution and the comparative solution to obtain a first oil-water interfacial tension of the surfactant;

[0017] After the surfactant is aged at high temperature, the surfactant solution is prepared again, and the above steps are repeated to obtain the second oil-water interfacial tension of the surfactant.

[0018] Furthermore, the first preset rule is that the first oil-water interfacial tension and the second oil-water interfacial tension are both within the order of 10 -2 mN / m.

[0019] Furthermore, testing the oil-water interfacial tension includes:

[0020] Place the solution on a Texas-500 spinning drop interfacial tension meter and set the speed to 6000 rpm; turn it on. Under the action of centrifugal force, gravity and interfacial tension, the oil droplets in the solution form a cylindrical shape. First, record the width of the oil droplets at 1 min, 3 min, and 5 min, and then record the data every 6 min until the change amplitude of three consecutive readings is within 0.001 cm. Calculate the average value of the three tests.

[0021] Further, obtaining a wettability reversal index of a surfactant that satisfies a first preset rule includes:

[0022] The solid-liquid-oil three-phase determination method is adopted, wherein the core is the solid phase, the kerosene droplets are the oil phase, and the surfactant solution with a fixed concentration is the liquid phase;

[0023] After soaking the core slices in the surfactant solution for 24 hours, they were taken out and dried;

[0024] Oil droplets were placed on the surface of the core slice in contact with the surfactant;

[0025] Use a contact angle meter to measure the contact angle between the oil drop and the glass slide;

[0026] The wetting angle change value was calculated based on the initial value and the contact angle.

[0027] Furthermore, the second preset rule is: the change value of the wetting angle is greater than 50%.

[0028] Further, obtaining the anti-adsorption performance of the surfactant that meets the second preset rule includes:

[0029] The experimental liquid phase was formation water, and a sand-filled tube was used to simulate the formation rock surface;

[0030] Passing a surfactant solution of a fixed concentration through the sand-filled tube in batches, and recovering the solution after a certain amount of the solution passes through;

[0031] Measure the interfacial tension of the recovery liquid;

[0032] The change in interfacial tension of the surfactant solution passing through the sand-filled tube is analyzed.

[0033] Furthermore, the third preset rule is: after a predetermined number of experiments are completed, the interfacial tension of the surfactant solution is substantially restored to its original value.

[0034] Further, obtaining an imbibition recovery index of a surfactant that meets the third preset rule includes:

[0035] The experimental oil phase is simulated oil, the liquid phase is formation water; the experimental core is an artificial core;

[0036] Conduct imbibition experiments of surfactant types at different concentrations;

[0037] Obtain the imbibition recovery of the surfactant.

[0038] Furthermore, the fourth preset rule is: when the surfactant concentration is at an optimal concentration, the imbibition recovery rate of the surfactant is the highest; the optimal concentration is a concentration selected based on engineering cost-effectiveness under specific reservoir conditions.

[0039] The technical effects of the present invention are remarkable, mainly reflected in the following aspects:

[0040] First, the present invention provides a scientific basis and clear guidance for shale oil production. By introducing the limit elimination method, a set of strict and systematic surfactant optimization evaluation criteria is established. This standard can accurately identify and screen the surfactant combination that best suits specific shale reservoir conditions, thereby effectively improving the efficiency and output of shale oil production. The present invention targets the characteristics of shale oil reservoirs and meets the requirements of specific reservoir conditions.

[0041] Secondly, the screening process of the present invention is sequential, and the evaluation is carried out in the order of oil-water interfacial tension, wettability reversal, anti-adsorption performance and imbibition recovery. This sequentiality helps to gradually and deeply identify surfactants with excellent performance. There are clear screening criteria in each evaluation step, such as the maximum critical value of oil-water interfacial tension, which helps to quickly screen out surfactants that meet specific requirements.

[0042] In addition, the present invention provides detailed experimental steps and conditions in the experimental design, which helps to improve the accuracy and repeatability of the experiment, thereby ensuring the reliability of the evaluation results. The present invention evaluates the performance of the surfactant more comprehensively by comprehensively evaluating four key performance indicators, and the evaluation method is comprehensive and detailed.

[0043] Finally, the present invention also takes cost-effectiveness into consideration during the evaluation process, focusing not only on the performance of the surfactant but also on its economy in practical applications, thereby providing strong support for achieving sustainable development of shale oil extraction. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A flow chart of a method for screening a surfactant according to one embodiment of the present invention;

[0045] Figure 2 A schematic diagram of a method for screening a surfactant according to an embodiment of the present invention;

[0046] Figure 3 This is a comparison diagram of the oil-water interfacial tension changes caused by different surfactants in Example 3;

[0047] Figure 4 This is a comparison diagram of the effect of temperature on the oil-water interfacial tension of different surfactants in Example 3;

[0048] Figure 5 This is a comparison chart of the ability of different surfactants to change the wetting angle in Example 3;

[0049] Figure 6 is a graph showing the variation of the interfacial tension of different surfactants with the injection amount of the solution in Example 3;

[0050] Figure 7 This is a comparison result of static imbibition recovery at fixed concentrations of different surfactants in Example 3;

[0051] Figure 8 This is a curve diagram of the imbibition recovery rate changing with the surfactant concentration in Example 3. DETAILED DESCRIPTION

[0052] The content of the present invention will now be discussed with reference to exemplary embodiments. It should be understood that the embodiments discussed are only to enable those skilled in the art to better understand and thus implement the content of the present invention, rather than implying any limitation on the scope of the present invention.

[0053] As used herein, the term “including” and variations thereof are to be interpreted as open-ended terms meaning “including, but not limited to.” The term “based on” is to be interpreted as “based, at least in part, on.” The terms “one embodiment” and “an embodiment” are to be interpreted as “at least one embodiment.”

[0054] Embodiment 1

[0055] Figure 1 FIG. 1 is a flow chart of a method for screening a surfactant according to an embodiment of the present invention. Figure 1 As shown, according to one embodiment of the present invention, a method for screening a surfactant comprises the following steps:

[0056] Step S102, obtaining the oil-water interfacial tension index of each surfactant, and screening the surfactant that meets the first preset rule;

[0057] Step S104, obtaining the wetting reversal index of the surfactant that meets the first preset rule, and screening the surfactant that meets the second preset rule;

[0058] Step S106, obtaining the anti-adsorption performance of the surfactant that meets the second preset rule, and screening the surfactant that meets the third preset rule;

[0059] Step S108, obtaining the imbibition recovery index of the surfactant that meets the third preset rule, and selecting the surfactant that meets the fourth preset rule as the target surfactant.

[0060] Oil-water interfacial tension index: It is the basic parameter for evaluating the performance of surfactants. The reduction of oil-water interfacial tension helps to improve the injection capacity of water and is a prerequisite for the surfactant to play a role. Therefore, evaluating this index first can quickly screen out surfactants that perform poorly in reducing interfacial tension and avoid subsequent more complex tests. Wetting reversal index: The change in wettability directly affects the wetting state of the rock surface, thereby affecting the adsorption and distribution of the surfactant. After the oil-water interfacial tension index meets the requirements, further evaluating the wettability reversal can ensure that the surfactant can effectively change the wettability of the reservoir and create conditions for subsequent imbibition and oil displacement. Anti-adsorption performance: The anti-adsorption performance of the surfactant determines its effective concentration and action distance in the reservoir. After the wettability is improved, evaluating the anti-adsorption performance can ensure that the surfactant maintains an effective concentration in the reservoir and reduce the performance degradation caused by adsorption. Imbibition recovery rate index: The imbibition recovery rate is a key indicator for evaluating the final oil displacement effect of the surfactant. After the previous interfacial tension, wettability and anti-adsorption performance are optimized, the level of imbibition recovery rate directly reflects the actual oil displacement effect of the surfactant.

[0061] In this embodiment, a method for screening a surfactant is provided to accurately evaluate and screen out surfactants with excellent performance. First, we focus on the oil-water interfacial tension index of the surfactant, which is the basic and crucial parameter for evaluating its performance. By setting the first predetermined rule, those surfactants that perform poorly in reducing the oil-water interfacial tension are quickly identified and eliminated, thereby avoiding wasting resources on subsequent more complex tests. Then, on the basis that the oil-water interfacial tension index meets the requirements, the wettability reversal index of the surfactant is further investigated. The change in wettability directly affects the wetting state of the rock surface, and then affects the adsorption and distribution of the surfactant. By setting the second predetermined rule, it can be ensured that the selected surfactant can effectively change the wettability of the reservoir and create favorable conditions for subsequent imbibition and oil recovery processes. Then, the anti-adsorption performance of the surfactant is deeply evaluated. This performance determines the effective concentration and action distance of the surfactant in the reservoir. After the wettability is improved, by setting the third predetermined rule, those surfactants that can maintain an effective concentration in the reservoir and reduce the performance degradation caused by adsorption can be screened out. Finally, pay attention to the imbibition recovery index of the surfactant, which is the key to evaluating its final oil recovery effect. After the previous oil-water interfacial tension, wettability and anti-adsorption properties are optimized, the fourth predetermined rule is set to use the level of imbibition recovery as a basis for directly reflecting the actual oil displacement effect of the surfactant, thereby screening out the target surfactant with the best performance.

[0062] The present invention follows the logical order of surfactant action, gradually evaluates its oil-water interfacial tension, wettability reversal, anti-adsorption performance and imbibition recovery index, and ensures that each step is based on the previous step, so as to more accurately simulate the actual application process and screen out the surfactant with the best performance. The present invention not only improves the screening efficiency and can quickly exclude options with poor performance, but also realizes a comprehensive evaluation of the surfactant from physical and chemical properties to oil displacement effect, ensuring that the surfactant finally selected has excellent comprehensive performance.

[0063] According to one embodiment of the present invention, step S102 includes:

[0064] Step S1021, obtaining the oil-water interfacial tension index of the surfactant, specifically:

[0065] The oil phase is simulated oil, and the liquid phase is formation water;

[0066] Prepare a preliminary surfactant solution with formation water; use a glass capillary to suck the surfactant solution or formation water, then drop oil droplets into it, ensuring that there are no bubbles and the measuring tube is airtight, to obtain the first solution;

[0067] Using kerosene as a control, repeat the above steps to obtain a comparative solution;

[0068] Testing the oil-water interfacial tension of the first solution and the comparative solution to obtain the first oil-water interfacial tension of the surfactant;

[0069] After the surfactant is aged at high temperature, the surfactant solution is prepared again, and the above steps are repeated to obtain the second oil-water interfacial tension of the surfactant.

[0070] Preferably, testing the oil-water interfacial tension comprises the following steps:

[0071] The solution was placed on a Texas-500 spinning drop interfacial tension meter and the speed was set to 6000 rpm. The oil droplets in the solution were formed into a cylindrical shape under the action of centrifugal force, gravity and interfacial tension. The width of the oil droplets was first recorded at 1 min, 3 min and 5 min, and then the data was recorded every 6 min until the change amplitude of three consecutive readings was within 0.001 cm (the system was considered to have reached equilibrium at this time). The average value of the three tests was calculated.

[0072] Step S1022, determining whether the oil-water interfacial tension index of each surfactant meets the first preset rule; if not, screen it out.

[0073] Preferably, the first preset rule is: the order of magnitude of the first oil-water interfacial tension and the second oil-water interfacial tension is not more than 10 -2 mN / m.

[0074] In this embodiment, for the screening of surfactants, step S102 describes in detail how to obtain and evaluate its oil-water interfacial tension index. The specific steps include: first, using simulated oil as the oil phase and formation water as the liquid phase, use formation water to prepare the primary selected surfactant solution. Then, the surfactant solution or formation water is sucked in through a glass capillary, and then oil droplets are dropped in to ensure that there are no bubbles in the measuring tube and it is airtight, and the test solution is formed after the oil droplets are dropped in. Using kerosene as a control, repeat the above steps. Then, using a Texas-500 spinning drop interfacial tension meter, at a speed of 6000 rpm, observe and record the oil drop width until the system reaches a state of equilibrium (i.e., the change in the amplitude of three consecutive readings is less than 0.001 cm), and calculate the average value to obtain the first oil-water interfacial tension of the surfactant.

[0075] In order to evaluate the temperature resistance of the surfactant, it is necessary to re-prepare the solution after high-temperature aging and repeat the above test to obtain the second oil-water interfacial tension.

[0076] According to the first preset rule, the order of magnitude of the first oil-water interfacial tension and the second oil-water interfacial tension is not more than 10 -2 mN / m, screen out surfactants with strong ability to reduce interfacial tension and good temperature resistance. In this process, if the oil-water interfacial tension does not exceed the maximum critical value of 10 -2 mN / m, the oil-water interfacial tension index performance of the surfactant meets the fracturing requirements, and this part of the surfactant is retained; if the oil-water interfacial tension exceeds the maximum critical value of 10 -2 mN / m, the surfactant is eliminated. The retained surfactants are subjected to subsequent screening steps. This meticulous and scientific evaluation process ensures that the screened surfactants have excellent oil-water interfacial tension performance, laying a solid foundation for subsequent applications.

[0077] The present invention adopts a scientific and meticulous evaluation process, uses the Texas-500 spinning drop interfacial tension meter to test the oil-water interfacial tension of surfactants in a simulated oil and formation water system, and takes into account its temperature resistance, successfully screening out surfactants with strong interfacial tension reduction capabilities and good temperature resistance, providing a material foundation with excellent performance for subsequent applications.

[0078] According to one embodiment of the present invention, step S104 includes:

[0079] Step S1041, obtaining the wettability reversal index of the surfactant, specifically:

[0080] The solid-liquid-oil three-phase determination method is adopted, wherein the core is the solid phase, the kerosene droplets are the oil phase, and the surfactant solution with a fixed concentration is the liquid phase;

[0081] The core slices were immersed in the surfactant solution for 24 hours and then taken out and dried;

[0082] Oil droplets were placed on the surface of the core slice in contact with the surfactant;

[0083] Use a contact angle meter to measure the contact angle between the oil drop and the glass slide;

[0084] The wetting angle change value was calculated based on the initial value and the contact angle.

[0085] Step S1042, determining whether the wetting angle change value of each surfactant satisfies a second preset rule; if not, screening it out.

[0086] Preferably, the second preset rule is: the change value of the wetting angle is greater than 50%.

[0087] In this embodiment, for the screening of surfactants, step S104 describes in detail how to obtain and evaluate its wettability reversal index and screen surfactants that meet the requirements of fracturing operations. The specific steps include: first, a solid-liquid-oil three-phase determination method is used as an experimental method, in which the core of the well core is used as the solid phase, kerosene droplets are used as the oil phase, and various surfactant solutions of fixed concentrations are used as the liquid phase. During the experiment, the core slices are immersed in different surfactant solutions, taken out and dried after 24 hours. Then, kerosene droplets are added to the surface of the core slices in contact with the surfactant, and a contact angle meter is used to accurately measure the contact angle between these oil droplets and the core slices (or glass slides for comparison, depending on the experimental design). By comparing the changes in the contact angles before and after the treatment, the change in the wetting angle is calculated. This change value becomes a key indicator for evaluating the wetting reversal performance of the surfactant. If the wetting angle change value of a surfactant does not meet the second preset rule standard, that is, the wetting angle change value does not exceed 50%, it indicates that the surfactant has a poor flipping effect and its wetting reversal effect does not meet the fracturing requirements, so it will be screened out. When the fracturing requirements are not met, it indicates that the solid surface is hydrophobic, that is, the liquid does not wet the solid easily and moves easily on the surface.

[0088] The present invention can accurately screen out surfactants with excellent wettability reversal performance, ensure the effectiveness of the surfactants in fracturing operations, improve the wettability of the surfactants to solids, and thus optimize the fracturing effect.

[0089] According to one embodiment of the present invention, step S106 includes:

[0090] Step S1061, obtaining the anti-adsorption performance of the surfactant, specifically:

[0091] The experimental liquid phase was formation water, and a sand-filled tube was used to simulate the formation rock surface;

[0092] The surfactant solution with fixed concentration is passed through the sand-filled tube in batches and recovered after a certain amount has passed;

[0093] Measure the interfacial tension of the recovery liquid;

[0094] Analyze the change in interfacial tension of surfactant solution passing through a sand-filled tube.

[0095] Step S1062, determining whether the interfacial tension change of each surfactant solution satisfies the third preset rule; if not, screening it out.

[0096] Preferably, the third preset rule is: after a predetermined number of experiments are completed, the interfacial tension of the surfactant solution substantially returns to its original value.

[0097] In this embodiment, for the screening of surfactants, step S106 describes in detail how to obtain and evaluate its anti-adsorption performance. The specific steps include: first, the experimental liquid phase is set to formation water, and a sand-filled tube is used to simulate the surface of the formation rock, and the experiment is carried out based on this basic environment. Next, the surfactant solution of fixed concentration is passed through the sand-filled tube in batches, and these solutions are recovered after a certain amount of passing. The key step is to measure the interfacial tension of the recovered liquid and analyze the change in the interfacial tension of the surfactant solution passing through the sand-filled tube. According to the third preset rule, that is, after the predetermined number of experiments are completed, if the interfacial tension of the surfactant solution can be restored to its original size, it is considered that it meets the requirements of anti-adsorption performance. The predetermined number of times in the third preset rule is set by experts in this field according to actual operation requirements. For example, the recovery of the interfacial tension is observed through four experiments. In the first three experiments, the interfacial tension of multiple groups of surfactants is basically restored to its original size, that is, the interfacial tension recovers faster; and the remaining surfactants need to complete more experiments to basically recover to their original size, that is, the interfacial tension recovers slower. At this time, the predetermined number of times in the third preset rule is set to three times.

[0098] The present invention sets an experimental environment simulated by formation water and sand filling pipes, passes a surfactant solution of fixed concentration in batches and recovers and measures the change in interfacial tension to evaluate the anti-adsorption performance of the surfactant; through a predetermined number of experiments, a surfactant whose interfacial tension can be basically restored to its original size is screened out, which effectively improves the screening efficiency and accuracy, and ensures that the screened surfactant has excellent anti-adsorption performance and is suitable for practical applications in specific environments.

[0099] According to one embodiment of the present invention, step S108 includes:

[0100] Step S1081, obtaining the imbibition recovery index of the surfactant, specifically:

[0101] The experimental oil phase is simulated oil, the liquid phase is formation water; the experimental core is an artificial core;

[0102] Conduct imbibition experiments of surfactant types at different concentrations;

[0103] Obtain the imbibition recovery of the surfactant.

[0104] Step S1082, determining whether the imbibition recovery rate of each surfactant satisfies the fourth preset rule; if not, screen it out.

[0105] Preferably, the fourth preset rule is: when the surfactant concentration is at the optimal concentration, the imbibition recovery rate of the surfactant is the highest; the optimal concentration is the concentration selected according to the engineering cost-effectiveness under specific reservoir conditions.

[0106] In this embodiment, for the screening of surfactants, step S108 describes in detail how to obtain and evaluate its imbibition recovery index. The specific steps include: first, using simulated oil and formation water as the experimental oil phase and liquid phase, using artificial cores to simulate formation conditions, and conducting imbibition experiments under different surfactant types and concentration conditions. Then measure the imbibition recovery rate of each surfactant at different concentrations. Finally, according to the fourth preset rule, the surfactant with the highest imbibition efficiency is screened as the target surfactant; that is, when the surfactant concentration is at the optimal concentration, the imbibition recovery rate of the surfactant is the highest; the optimal concentration is the concentration selected according to the engineering cost-effectiveness under specific reservoir conditions. In this embodiment, the fourth preset rule is specifically set as: when the surfactant concentration is 0.3%, the imbibition recovery rate of the surfactant is the highest. This method ensures that the screened surfactant has the best imbibition recovery rate by systematically conducting experiments and data analysis, providing strong technical support for practical applications.

[0107] The present invention systematically conducts imbibition experiments of different surfactants, uses simulated oil and formation water as well as artificial cores to simulate formation conditions, and successfully screens out surfactants that meet the fourth preset rule, significantly improving the accuracy and efficiency of surfactant screening, providing an efficient and reliable surfactant selection scheme for practical applications.

[0108] The present invention provides a comprehensive and scientific standard for the performance evaluation of surfactants by systematically setting and evaluating four major indicators: oil-water interfacial tension, wettability reversal, anti-adsorption performance, and imbibition recovery rate. By gradually following the first to fourth preset rules, surfactants that can effectively reduce oil-water interfacial tension and have excellent wettability reversal, strong anti-adsorption ability, and high imbibition recovery rate are accurately screened out. The present invention not only significantly improves the screening efficiency and accuracy, but also ensures that the selected surfactants can perform at their best in practical applications, providing strong technical support and reliable selection solutions for optimizing oil and gas production effects and increasing oil and gas production.

[0109] Embodiment 2

[0110] Figure 2 Schematic diagram of a method for screening a surfactant according to an embodiment of the present invention. Figure 2 As shown, according to one embodiment of the present invention, a method for screening a surfactant comprises the following steps:

[0111] Step S202: Evaluate the oil-water interfacial tension index of the surfactant according to a first predetermined rule.

[0112] The quality of surfactants was evaluated by evaluating the oil-water interfacial tension index, and the types of surfactants with stronger ability to reduce interfacial tension were preliminarily screened out.

[0113] In the fracturing process of oil-wet crude oil reservoirs, that is, the process of surfactant entering the crude oil reservoir, the surface interfacial tension of crude oil is proportional to the capillary force. When the interfacial tension increases, the capillary force also increases. Because the capillary force is a resistance, if the interfacial tension is too large at this time, the capillary force as a resistance will also be large, which will hinder the surfactant pressure liquid from entering the reservoir. Therefore, the interfacial tension cannot be too high at this time.

[0114] When the surfactant enters the crude oil reservoir, the wettability of the reservoir changes from the original lipophilicity to hydrophilicity. At this time, the capillary force in the reservoir becomes a driving force, and the capillary force can spontaneously drive the fracturing fluid into the reservoir to displace the crude oil. At this time, since the surface interfacial tension of crude oil is proportional to the capillary force, if the interfacial tension is too low, the capillary force as the driving force for displacing crude oil will also be low, which is not conducive to displacing crude oil and will reduce oil recovery efficiency. Therefore, by evaluating the oil-water interface index, the oil recovery efficiency of the surfactant can be evaluated, thereby evaluating the performance of the surfactant.

[0115] Specifically, step S202 includes:

[0116] The oil phase is simulated oil, the liquid phase is formation water, the surfactant concentration is 0.3%, and an interfacial tension test is carried out, with kerosene as a control; simulated oil is dropped into the surfactant solution, and the oil-water interfacial tension at the interface of the mixed liquid is measured using an interfacial tension meter; the surfactant types with stronger ability to reduce interfacial tension are preliminarily screened out.

[0117] When the oil-water interfacial tension is lower than the maximum value, the oil-water interfacial tension index performance of this part of the surfactants is evaluated to meet the fracturing requirements, and this part of the surfactants is retained, and some surfactants with oil-water interfacial tension higher than the maximum value are eliminated, and the remaining surfactants are screened in the next step.

[0118] Preferably, the maximum critical value of the oil-water interfacial tension (i.e., the maximum value of the oil-water interfacial tension) is 10 - 2 mN / m.

[0119] The crude oil may be kerosene, diesel, etc., and the staff can select the required crude oil type according to actual needs. After the surfactant is mixed with the crude oil, the staff can use an interfacial tension meter to measure the oil-water interfacial tension of the mixed liquid.

[0120] The maximum critical value of the oil-water interfacial tension can be set according to the actual site conditions. In this embodiment, after many experiments, according to the experience of technical experts in this field, the maximum critical value of the oil-water interfacial tension is determined to be 10 - 2 mN / m. Therefore, after measuring the oil-water interfacial tension, when the measured oil-water interfacial tension is lower than 10 -2 When the surface tension is 0.0447mN / m, it can be evaluated that the performance of the surfactant in this part is relatively good. The staff can use the data measured by the surface tension meter as a predetermined rule to preliminarily screen out the type of surfactant with a stronger ability to reduce interfacial tension.

[0121] Step S204: Based on the first predetermined rule, the wettability reversal index of the surfactant is evaluated according to the second predetermined rule.

[0122] The quality of surfactants was evaluated by evaluating the wetting reversal index, and the surfactant types with better wetting reversal effect were further screened out.

[0123] Specifically, step S204 includes:

[0124] The experiment adopts a solid-liquid-oil three-phase determination method, in which the core (drilling core) is the solid phase, kerosene droplets are the oil phase, and 0.3% various surfactant solutions are the liquid phase; a glass piece treated to be oil-wet is placed in 0.3% various surfactants; after taking out the core slice, oil droplets are dripped on the surface of the core slice in contact with the surfactant; a contact angle meter measures the contact angle between the oil droplet and the core slice; the wetting reversal effect of each surfactant is analyzed. When the wetting angle changes slightly, it means that this part of the surfactant has a poor reversal effect. The wetting reversal index of the surfactant does not meet the fracturing requirements and is not selected. The remaining surfactants are screened in the next step.

[0125] Among them, the staff can use dimethylchlorosilane to process the core slices to be oil-wet. Of course, the core slices can also be processed to be oil-wet in other ways, and this application does not make the sole limitation. The oil-wet state means that the core slices are in an oil-wet state. If an oil drop is dropped on a glass sheet at this time, the contact angle between the oil drop and the glass sheet will be less than 90°.

[0126] When the wetting reversal contact angle is greater than or equal to 90°, it indicates that the solid surface is hydrophobic, that is, the liquid does not wet the solid easily and moves easily on the surface.

[0127] The staff can use the wettability reversal property of the surfactant to evaluate the performance of the surfactant. The staff can combine this predetermined rule with the oil-water interfacial tension index of step S202 to evaluate the performance of the surfactant.

[0128] Step S206: Based on the second predetermined rule, the anti-adsorption performance of the surfactant is evaluated according to the third predetermined rule.

[0129] The quality of surfactants was evaluated by evaluating their anti-adsorption properties, and the types of surfactants with better anti-adsorption properties were further screened.

[0130] Specifically, step S206 includes:

[0131] The experimental liquid phase is formation water, and a sand-filled tube is used to simulate the surface of the formation rock. A 0.3% concentration surfactant solution is passed through the sand-filled tube in batches. After a certain amount (selected according to the operational requirements, set to 50 ml in this embodiment) passes through, it is recovered, and the interfacial tension of the recovered liquid is measured. The changes in the interfacial tension of various types of surfactant solutions passing through the sand-filled tube are analyzed, and the types of surfactants with better anti-adsorption properties are further screened.

[0132] Among them, the sand filling tube is made: the sand filling tube is 30 cm long and 2.5 cm in inner diameter, and filled with 243 g of 20 / 40 mesh quartz sand;

[0133] For example, when evaluating the performance of three types of surfactants (represented by 1, 2, and 3), the interfacial tension of 1 and 2 recovers faster, while 3 recovers slower, indicating that 3 has a large adsorption capacity and a short action distance, so 1 and 2 are selected for the next screening. The staff can combine the three predetermined rules in step S202, step S204, and step S206 to comprehensively evaluate the performance of adding rock powder to the surfactant.

[0134] Step S208: Based on the third predetermined rule, the imbibition recovery index of the surfactant is evaluated according to the fourth predetermined rule.

[0135] The quality of surfactants is evaluated by evaluating the imbibition recovery index, and finally the best imbibition agent type and concentration are screened out.

[0136] Specifically, step S208 includes:

[0137] The experimental oil phase is simulated oil, and the liquid phase is formation water. Imbibition experiments are carried out under different surfactant types and fixed concentrations (such as 0.3%). The experimental cores are artificial cores with a permeability of about 0.1mD-10mD. The imbibition recovery rate is used as an indicator to finally screen out the best imbibition agent type and concentration.

[0138] When the static spontaneous imbibition efficiency of the surfactant is the highest, the imbibition recovery index of the surfactant is evaluated to meet the optimization requirements, and the final surfactant is selected.

[0139] Specifically, the staff can comprehensively evaluate the performance of the surfactant in combination with the multiple predetermined rules in steps S202 to S208.

[0140] The surfactant screening method provided by the present invention can provide the staff with a performance evaluation standard of the surfactant, so that a surfactant can be further selected from multiple surfactants to provide guidance for increasing oil and gas production. In each predetermined rule, the evaluation method includes: evaluating the oil-water interfacial tension index of the surfactant according to the first predetermined rule; evaluating the wettability reversal index of the surfactant according to the second predetermined rule; evaluating the anti-adsorption performance of the surfactant according to the third predetermined rule; and evaluating the imbibition recovery index of the surfactant according to the fourth predetermined rule. It should be noted that each step needs to be carried out step by step and can be executed according to each predetermined rule.

[0141] The surfactant screening method of the present invention selects four indicators of oil-water interfacial tension index, wettability reversal index, anti-adsorption performance and imbibition recovery rate index according to predetermined requirements and gradually evaluates; by evaluating the oil-water interfacial tension index of the surfactant according to the first predetermined rule; evaluating the wettability reversal index of the surfactant according to the second predetermined rule; evaluating the anti-adsorption performance of the surfactant according to the third predetermined rule; and evaluating the imbibition recovery rate index of the surfactant according to the fourth predetermined rule. The present invention uses the limit elimination method to evaluate the performance of surfactants, so as to further optimize a set of surfactant systems suitable for specific shale reservoirs and provide guidance for increasing oil and gas production. The surfactant screening method provided by the present invention can provide staff with performance evaluation standards for surfactants and select the most suitable surfactant for the formation.

[0142] Embodiment 3

[0143] In this embodiment, the performance evaluation and optimization process of ten types of surfactants is taken as an example to explain the method for screening surfactants.

[0144] The steps for staff to evaluate the performance of 1#, 2#, 3#, 4#, 5#, 6#, 7#, 8#, 9#, and 10# surfactants in tight oil reservoirs are as follows:

[0145] Step S302: The oil phase is simulated oil, the liquid phase is formation water, and the surfactant concentration is 0.3%. The interfacial tension test is carried out, and kerosene is used as a control to preliminarily screen out the surfactant type with a strong ability to reduce the interfacial tension. Add the surfactant solution and the oil droplets into the glass tube to form two liquid phases, and then rotate the glass tube at a certain angular velocity. Under the action of centrifugal force and interfacial tension, the oil droplets in the liquid change from spherical to ellipsoidal. The width of the upper and lower end surfaces is measured to calculate the interfacial tension. The calculation formula is:

[0146]

[0147] Among them, γ is the oil-water interfacial tension, Δd is the density difference, ω is the rotation angular velocity, and Y is the minor axis diameter of the droplet.

[0148]

[0149] Table 1 Oil-water interfacial tension test results of different surfactants

[0150] Table 1 is a data table of oil-water interfacial tension test results for different surfactants. Figure 3 This is a comparison chart of how different surfactants change the oil-water interfacial tension in Example 3. Figure 4 This is a comparison chart of the effect of temperature on the oil-water interfacial tension of different surfactants in Example 3. Figure 3 , Figure 4 As shown, the interfacial tension of kerosene, simulated oil 5#, and 8# is too large, greater than 10 -2 mN / m, which does not meet the requirements; after high temperature aging, 1# and 10# are greater than 10 -2 mN / m does not meet the requirements. Agents 2#, 3#, 4#, 6#, 7#, and 9# have better temperature resistance.

[0151] After screening in step S302, surfactants 2#, 3#, 4#, 6#, 7#, and 9# are selected for the next screening step.

[0152] Step S304: The experiment adopts a solid-liquid-oil three-phase determination method, in which the core (drilling coring) is the solid phase, kerosene droplets are the oil phase, and 0.3% solutions of various surfactants are the liquid phase. The wetting reversal effects of 2#, 3#, 4#, 6#, 7#, and 9# surfactants are analyzed to further screen out surfactant types with better wetting reversal effects.

[0153] When kerosene was used for testing, the wetting angle could not be captured due to the strong oil-wetting property of the core slice. Therefore, the wetting reversal effect of each surfactant was measured by dripping formation water.

[0154]

[0155] Table 2 Data table of wetting angle changes of different surfactants

[0156] Table 2 is a data table showing the change in wetting angle for different surfactants. Figure 5 This is a comparison chart of the ability of different surfactants to change the wetting angle in Example 3. Figure 5 As shown, all types of surfactants can change the wetting angle. Agents 2# and 9# change the wetting angle less, while other agents change the wetting angle by more than 50%, indicating that agents 2# and 9# have poor flipping effects and are not selected.

[0157] After screening in step S304, 3#, 4#, 6#, and 7# are selected for the next screening.

[0158] Step S306: The experimental liquid phase is formation water, and a sand-filled tube is used to simulate the formation rock surface. 1000 ml of 0.3% concentration 3#, 4#, 6#, and 7# surfactant solutions are passed through the sand-filled tube in batches, and 50 ml is recovered after passing through. The interfacial tension of the recovered liquid is measured, and the changes in the interfacial tension of various types of surfactant solutions passing through the sand-filled tube are analyzed to further screen the surfactant type with better anti-adsorption performance.

[0159] Prepare 1000 ml of surfactant solution at a ratio of 0.3%, measure and record the initial interfacial tension of the solution;

[0160] Make a sand-filled tube: The sand-filled tube is 30 cm long and 2.5 cm in inner diameter, and filled with 243 g of 20 / 40 mesh quartz sand;

[0161] The surfactant solution was passed through the sand-filled tube at a displacement of 10 ml / min, and recovered by 1 PV volume (50 ml), and the interfacial tension of the recovered liquid was measured;

[0162] Repeat the steps and continue to let the solution pass through the sand-filled tube. Each time 1PV volume (about 50 ml) of solution passes through, measure the interfacial tension after the liquid passes through, until the interfacial tension of the solution passing through the sand-filled tube no longer shows a significant change trend.

[0163]

[0164] Table 3 Data table of anti-adsorption test results of different surfactants

[0165] Table 3 is a data table of the anti-adsorption test results of different surfactants. Figure 6 The interfacial tension of different surfactants in Example 3 varies with the amount of solution injected. Figure 6 As shown in the figure, after the 3#, 4#, 6#, and 7# reagents pass through the sand filling tube, the interfacial tension first increases with the injection volume and then decreases and tends to the initial value.

[0166] A certain amount of surfactant is adsorbed on the rock surface, the concentration of the agent in the solution decreases, and the interfacial tension increases; after the agent adsorption on the rock is basically saturated, the amount of surfactant adsorbed in the later injected solution continues to decrease, so the interfacial tension finally returns to its original size; among them, the interfacial tension of 3#, 6#, and 7# recovers faster, while 4# recovers slower, indicating that 4# agent has a large adsorption capacity and a short action distance, so 3#, 6#, and 7# are selected for the next screening.

[0167] Step S308: The experimental oil phase is simulated oil, and the liquid phase is formation water. Imbibition experiments are carried out under different surfactant types (3#, 6#, 7#) and fixed concentration (0.3%). The experimental core is an artificial core with a permeability of about 0.1mD-10mD. The imbibition recovery rate is used as an indicator, and finally the type and concentration with the best effect are screened out.

[0168]

[0169] Table 4 Data table of static imbibition test results of different surfactants at fixed concentrations

[0170] Table 4 is a data table of static imbibition test results of fixed concentrations of different surfactants. Figure 7 The static imbibition recovery rate comparison results of different surfactants at fixed concentrations in Example 3 are shown in Table 4 and Figure 7As shown in the figure, the static spontaneous imbibition efficiency of agent 7# is the highest, and the static imbibition recovery rate of each surfactant is in the order of 7#>3#>6#. Therefore, 7# is finally selected as the imbibition surfactant.

[0171]

[0172]

[0173] Table 5 Static absorption test results of different concentrations of different surfactants

[0174] Table 5 is a data table of static imbibition test results of different concentrations of different surfactants. Figure 8 The imbibition recovery rate in Example 3 varies with the surfactant concentration. Figure 8 As shown in the figure, whether it is 3# or 7# surfactant, as the concentration of the agent increases, the imbibition recovery rate will increase. When the surfactant concentration is 0.3%, the recovery rate is the highest. If it continues to increase, the recovery rate increase effect is not obvious, and the cost is too high. Therefore, the reasonable concentration is 0.3%.

[0175] Through the above experiments, 7# was finally selected as the surfactant for imbibition with a concentration of 0.30%.

[0176] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the present application is not limited to the technical solution formed by a specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept. For example, the above features are replaced with (but not limited to) technical features with similar functions disclosed in the present application.

[0177] It should be understood that the size of the serial numbers of each step in the content of the invention and the embodiments of the present invention does not absolutely mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

Claims

1. A method for screening a surfactant, characterized in that: The following steps are involved: Obtaining the oil-water interfacial tension index of each surfactant, and screening the surfactant that meets the first preset rule; Obtaining a wetting reversal index of a surfactant that meets a first preset rule, and screening a surfactant that meets a second preset rule; Obtaining the anti-adsorption performance of the surfactant that meets the second preset rule, and screening the surfactant that meets the third preset rule; The imbibition recovery index of the surfactant that meets the third preset rule is obtained, and the surfactant that meets the fourth preset rule is selected as the target surfactant.

2. The method for screening a surfactant according to claim 1, characterized in that: Obtain the oil-water interfacial tension index of each surfactant, including: The oil phase is simulated oil, and the liquid phase is formation water; Prepare a preliminary surfactant solution with formation water; use a glass capillary to suck the surfactant solution or formation water, then drop oil droplets into it, ensuring that there are no bubbles and the measuring tube is airtight, to obtain the first solution; Using kerosene as a control, repeat the above steps to obtain a comparative solution; Testing the oil-water interfacial tension of the first solution and the comparative solution to obtain a first oil-water interfacial tension of the surfactant; After the surfactant is aged at high temperature, the surfactant solution is prepared again, and the above steps are repeated to obtain the second oil-water interfacial tension of the surfactant.

3. The method for screening a surfactant according to claim 2, characterized in that: The first preset rule is: the first oil-water interfacial tension and the second oil-water interfacial tension are both less than 10 -2 mN / m.

4. The method for screening a surfactant according to claim 2, characterized in that: Testing of oil-water interfacial tension includes: Place the solution on a Texas-500 spinning drop interfacial tension meter and set the speed to 6000 rpm; turn it on. Under the action of centrifugal force, gravity and interfacial tension, the oil droplets in the solution form a cylindrical shape. First, record the width of the oil droplets at 1 min, 3 min, and 5 min, and then record the data every 6 min until the change amplitude of three consecutive readings is within 0.001 cm. Calculate the average value of the three tests.

5. The method for screening surfactants according to claim 1, characterized in that: Obtaining a wettability reversal index of a surfactant that satisfies a first preset rule, including: The solid-liquid-oil three-phase determination method is adopted, wherein the core is the solid phase, the kerosene droplets are the oil phase, and the surfactant solution with a fixed concentration is the liquid phase; After soaking the core slices in the surfactant solution for 24 hours, they were taken out and dried; Oil droplets were placed on the surface of the core slice in contact with the surfactant; Use a contact angle meter to measure the contact angle between the oil drop and the glass slide; The wetting angle change value was calculated based on the initial value and the contact angle.

6. The method for screening a surfactant according to claim 5, characterized in that: The second preset rule is: the change value of the wetting angle is greater than 50%.

7. The method for screening a surfactant according to claim 1, characterized in that: Obtaining the anti-adsorption performance of the surfactant that meets the second preset rule, including: The experimental liquid phase was formation water, and a sand-filled tube was used to simulate the formation rock surface; Passing a surfactant solution of a fixed concentration through the sand-filled tube in batches, and recovering the solution after a certain amount of the solution passes through; Measure the interfacial tension of the recovery liquid; The change in interfacial tension of the surfactant solution passing through the sand-filled tube is analyzed.

8. The method for screening surfactants according to claim 7, characterized in that: The third preset rule is: after a predetermined number of experiments are completed, the interfacial tension of the surfactant solution is substantially restored to its original value.

9. The method for screening a surfactant according to claim 1, characterized in that: Obtaining an imbibition recovery index of a surfactant that meets the third preset rule, including: The experimental oil phase is simulated oil, the liquid phase is formation water; the experimental core is an artificial core; Conduct imbibition experiments of surfactant types at different concentrations; Obtain the imbibition recovery of the surfactant.

10. The method for screening surfactants according to claim 9, characterized in that: The fourth preset rule is: when the surfactant concentration is at the optimal concentration, the imbibition recovery rate of the surfactant is the highest; the optimal concentration is the concentration selected according to the engineering cost performance under specific reservoir conditions.

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