A screening method for the phase behavior of middle-phase microemulsion under high temperature and high pressure conditions

Abstract

The present invention relates to the field of oil and gas field development, and in particular to a method for screening the phase behavior of a middle-phase microemulsion under high-temperature and high-pressure conditions. The present invention simplifies the operating procedures of experimental research on the equilibrium behavior of microemulsion phases, and the experimental pressure is controllable and can predict the optimal point composition under other temperature and pressure conditions; the method connects multiple pressure vessels in series through a rotating steel shaft, and injects pre-screened surfactant solutions and experimental oils of different salinities into each pressure vessel at the formation temperature, and through a preset pressurization process, the internal pressure of the device is increased to the formation pressure, and the volumes of the surfactant solution and the oil are adjusted to meet the requirements of the phase behavior research, and the rotating shaft is rotated to stir the mixed liquid, and the microemulsion phase behavior after equilibrium is observed and the optimal microemulsion salinity formula is screened out, and the pressure and temperature are used as random variables, and the experimental observation data are combined through linear regression analysis to obtain a prediction model for the optimal middle-phase microemulsion salinity formula, and the optimal point composition under other temperature and pressure conditions is predicted.

Description

Technical Field

[0001] The invention belongs to the field of oil and gas field development engineering, and in particular relates to a method for screening a medium-phase microemulsion under high temperature and high pressure conditions. Background Art

[0002] In the microemulsion-related chemical flooding and enhanced oil recovery technology, the middle phase microemulsion has both ultra-low interfacial tension and strong volume expansion characteristics, and has great technical potential. Understanding the phase behavior characteristics of microemulsions is the core work of microemulsion research. Existing microemulsion phase behavior research mainly focuses on experiments at room temperature and pressure. For example, in the invention patent "A method for preparing a microemulsion" (CN107913641A), different proportions of surfactants, activators, oil and water are added to a beaker to screen out a transparent and stable reverse microemulsion. However, since the phase behavior of microemulsions is affected by temperature and pressure, the results of room temperature and pressure experiments are not representative in high temperature and high pressure applications. Therefore, before a microemulsion salinity formula is applied to an actual reservoir, it is necessary to study the microemulsion phase behavior under reservoir conditions to screen out the optimal microemulsion salinity formula.

[0003] At present, the method for studying the phase behavior of microemulsions under high temperature and high pressure conditions is mainly to inject the surfactant solution and oil into a sealed device with an observation window in turn, restore the high temperature and high pressure conditions, stir, stand, balance, and finally observe. Some scholars used a sapphire observation chamber with good light transmittance and high temperature and high pressure resistance to conduct phase behavior experiments on microemulsions, and measured parameters such as the volume of each phase, equilibrium time, and oil-water solubilization rate (Sara Bülow Sandersen, Erling H, Nicolas von Solms, et al. Stenby. The effect of pressure on the phase behavior of surfactant systems: An experimental study [J]. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2012, 415: 159-166); Existing methods of this type all use similar sapphire containers, but all have defects: for a single closed container that is not connected to other containers, the pressure during the heating process cannot be controlled; for a non-closed container, if a fixed amount of oil and surfactant solution is filled in the sapphire container in advance and the pressure is controlled by a piston, the liquid volume cannot be fixed during the pressurization process due to the different compression coefficients and temperature expansion coefficients of the two phases; if the piston is removed, the system requires multiple intermediate containers to hold surfactant solutions of different salinities, and the pressure cannot be controlled by simple operations. In addition, since the time required for the microemulsion to equilibrate once is long and the device is inconvenient to clean, the entire microemulsion screening process takes too long. When the experimental conditions are obstructed from sampling, the optimal point composition of the microemulsion under other temperature and pressure conditions cannot be predicted; therefore, it is necessary to invent a method for screening microemulsions under high temperature and high pressure conditions that is both time-saving and cost-controlled. Summary of the invention

[0004] The purpose of the present invention is to provide a method for screening microemulsions under high temperature and high pressure conditions to solve the technical problems raised by the above-mentioned background technology. The method connects multiple piston-free pressure vessels with sapphire observation windows in series through a rotating steel shaft, injects pre-screened surfactant solutions and experimental oils of different salinities into each pressure vessel at formation temperature, raises the internal pressure of the device to the formation pressure through a preset pressurization process, and adjusts the volumes of the surfactant solution and the oil to meet the requirements of the phase behavior study, rotates the rotating shaft to stir the mixed liquid, observes and studies the microemulsion phase behavior after equilibrium, and finally screens out the most suitable microemulsion salinity formula, and according to the conditional mean of pressure and temperature as random variables and the best middle phase microemulsion salinity formula as explanatory variables, the experimental observation data are combined through linear regression analysis to form a prediction model for the best middle phase microemulsion salinity formula, and the best point composition under other temperature and pressure conditions is predicted.

[0005] To achieve the above objectives, the present invention adopts the following technical solutions.

[0006] The steps include:

[0007] Step S1: prepare six piston-free pressure vessels with sapphire observation windows. The six pressure vessels are welded by a steel shaft. The connected steel shafts are kept in the same straight line and penetrate the oven 38. The six pressure vessels can be driven to swing back and forth by rotating the steel shaft. The pipelines connected to the pressure vessels should have sufficient movable length to ensure that the connected pipelines will not be entangled with the pressure vessels during swinging. The upper inlet 7 of the pressure vessel 8 is connected to the sample dispenser 3 filled with live oil, and the lower end is provided with a lower outlet 9 and a lower outlet 10. The lower outlet 9 is connected to a section of the sample injection pipeline 13 and the three-way valve 14 port of the three-way valve in turn. The three-way valve is also provided with a three-way valve 15 and a three-way valve 16. The two ports are connected to the injection pipeline 17 and the pressure regulating pipeline 18 respectively.

[0008] Step S2: connecting the pressure regulating line 18 to the fluorinated liquid intermediate container 21 containing the fluorinated liquid; if only the three-way valve 14 and the three-way valve 15 are opened, the injection line 17 and the sampling line 13 are connected, and the surfactant solution is injected into the injection line 17 through a syringe, the sampling line 13 and the pressure vessel 8 can be filled with the pre-screened surfactant solution. If only the three-way valve 14 and the three-way valve 16 are opened, the sampling line 13 and the pressure regulating line 18 are connected, the fluorinated liquid in the fluorinated liquid intermediate container 21 can be used as a displacement medium to adjust the volume of the surfactant solution entering the pressure vessel 8. Since sufficient volume is reserved in the sampling line 13, the volume of the fluorinated liquid emulsified by the surfactant after contact can be ignored;

[0009] Step S3: evacuate the pressure vessel 8 and the pipeline connected to the upper inlet 7, and fill the pre-screened surfactant solution and the fluoride liquid into the sampling pipeline 13 and the pressure regulating pipeline 18 respectively. After connecting the entire device, continue to inject the surfactant solution into the sampling pipeline 13 to fill the volume of the container, and then pressurize the fluoride liquid to increase the pressure in the container to the formation pressure; repeat this step to fill the remaining pressure vessels 41 to 45 with the pre-screened surfactant solution and reach the formation pressure;

[0010] Step S4: After the entire device is heated to the formation temperature by the oven 38, the oil sample is injected from the upper inlet 7 of the pressure vessel 8 at a constant speed, and the excess surfactant solution exits the pressure vessel 8 from the lower outlet 9 at a constant speed. When the volume of the oil in the pressure vessel is equal to the volume of the surfactant solution, the injection is stopped, and this step is repeated in the remaining pressure vessels 41 to 45;

[0011] Step S5: The steel shaft drives the pressure vessel to swing back and forth, and the pressure vessel is left to stand for a certain period of time. The volume of each phase is observed and recorded through the scale of the sapphire observation window. When the phase interface does not move for a long time, it is in equilibrium. If the microemulsion observed for the first time is a lower phase microemulsion, it is necessary to increase the salinity of the surfactant after cleaning the device and repeat the steps S2 to S4; if it is an upper phase microemulsion, it is necessary to reduce the salinity of the surfactant solution after cleaning the device and repeat the steps S2 to S4; if lower phase microemulsion and upper phase microemulsion appear in different pressure vessels respectively, it is necessary to reduce the concentration gradient within the salinity window where the two types of microemulsion appear after cleaning the device and repeat the steps S2 to S4; if a middle phase microemulsion appears, but the volume of the excess water phase below and the excess oil phase above are not equal, it is necessary to increase or reduce the salinity of the surfactant after cleaning the device and repeat the steps S2 to S4 until the volume of the excess water phase is equal to that of the excess oil phase;

[0012] Step S6: injecting dichloromethane from the upper inlet 7 of the pressure vessel 8 to clean the oil phase in the mixed solution, and connecting the waste liquid barrel 40 from the lower outlet 10, then injecting deionized water into the pressure vessel 8 to remove salt, and then injecting anhydrous ethanol to remove the water phase, and finally passing nitrogen to blow away the anhydrous ethanol and dichloromethane, removing the pressure regulating pipeline 18, the injection pipeline 17 and the sampling pipeline 13 and cleaning them, and repeating this step to clean the remaining pressure vessels 41 to 45;

[0013] Step S7: Repeat steps S4 to S6 near the optimal salinity, record the volume of each phase, and the microemulsion sample with the middle phase having the same volume of excess water phase and excess oil phase is the optimal point, and the salinity corresponding to the optimal point is the screened optimal middle phase microemulsion salinity formula;

[0014] Step S8: predicting the optimal salinity formula of the middle phase microemulsion under different pressure and temperature conditions.

[0015] As a further description of the above technical solution:

[0016] The pipelines connected to the pressure vessel in step S1 are all metal hoses resistant to high temperature and high pressure.

[0017] As a further description of the above technical solution:

[0018] The live oil in step S1 is obtained by mixing dead oil and associated gas, heating and pressurizing them to formation conditions, and stirring and configuring them.

[0019] As a further description of the above technical solution:

[0020] The fluorination liquid in step S2 can be selected from Fluorinert FC-40 electronic fluorination liquid with a relative density of 1.90, Fluorinert FC-3283 electronic fluorination liquid with a relative density of 1.82, or FomblinYLVAC25 / 6 electronic fluorination liquid with a relative density of 1.90.

[0021] As a further description of the above technical solution:

[0022] In step S5, after the pressure vessel is filled with oil and surfactant solution, the steel shaft drives the pressure vessel to rotate 120° clockwise, and then rotates counterclockwise to reset, reciprocating and swinging twenty times, and the static time is 24h-48h.

[0023] As a further description of the above technical solution:

[0024] In step S6, the upper inlet 7 of the pressure container 8 is connected to the cleaning device, and the waste liquid is discharged into the waste liquid bucket through the lower outlet 10.

[0025] As a further description of the above technical solution:

[0026] The cleaning device includes a dichloromethane intermediate container 33 filled with dichloromethane, a deionized water intermediate container 34 filled with deionized water, an anhydrous ethanol intermediate container 35 filled with anhydrous ethanol, a nitrogen intermediate container 36 filled with nitrogen, and a displacement pump 37.

[0027] As a further description of the above technical solution:

[0028] The purity of the nitrogen, anhydrous ethanol, dichloromethane and deionized water is greater than 99.5%.

[0029] As a further description of the above technical solution:

[0030] The prediction method in step S8 specifically includes the following steps:

[0031] Step S8.1: Based on the conditional means of pressure and temperature as random variables and the optimal middle phase microemulsion salinity formula as the explanatory variable, the experimental observation data are integrated through linear regression analysis to obtain a prediction model for the optimal middle phase microemulsion salinity formula, namely the HLD equation:

[0032] HLD=LnS – k ·EACN – α (T – T ref ) – β (P – P ref ) + C C (1),

[0033] Where: HLD is the hydrophilicity-lipophilicity deviation; S is the salinity of the optimal middle phase microemulsion salinity formula, g / 100ml; k is the slope of the logarithmic function of the optimal salinity and EACN, C C is the characteristic parameter of surfactant; EACN is the equivalent alkane carbon number of oil component; T is the salinity formulation temperature, ℃; T ref is the reference temperature, 20℃; P is the salinity formula pressure, MPa; P ref is the reference pressure, 0.101MPa; α is the temperature coefficient; β is the pressure coefficient;

[0034] When the salinity formula is at the optimal point mentioned above, the HLD value is 0, and equation (1) becomes:

[0035] 0 = LnS 0 * – k ·EACN – α (T 0 – T ref ) – β (P 0 – P ref ) + C C (2),

[0036] Where: S 0 * is the salinity corresponding to the optimal point, g / 100ml; T 0 is the formation temperature, °C; P 0 is the formation pressure, MPa;

[0037] Step S8.2: When only the pressure changes, equation (2) becomes:

[0038] 0 = LnS1 * – k ·EACN – α (T 0 – T ref ) – β (P 1 – P ref ) + C C (3),

[0039] Where: S 1 * is the salinity corresponding to the optimal point after pressure change, g / 100ml; P 1 is the changed pressure, MPa;

[0040] According to equation (2)-equation (3), we can get:

[0041] Ln(S 0 * / S 1 * ) = β ΔP (4),

[0042] Where: ΔP is the difference between the formation pressure and the changed pressure;

[0043] Repeat steps S8.1 to S8.2 three times to plot ΔP and Ln(S 0 * / S 1 * ) relationship curve, its slope is β The value of

[0044] Step S8.3: When only the temperature changes, equation (2) becomes:

[0045] 0 = LnS 2 * – k ·EACN – α (T 1 – T ref ) – β (P 0 – P ref ) + C C (5),

[0046] Where: S 2 * is the salinity corresponding to the optimal point after temperature change, g / 100ml; T 1 is the temperature after change, ℃;

[0047] According to equation (2)-equation (5), we can get:

[0048] Ln(S 0 * / S 2 * ) = α ΔT (6),

[0049] Where: ΔT is the difference between the formation temperature and the changed temperature, °C;

[0050] Step S8.4: Repeat steps S8.1 to S8.3 three times to plot ΔT and Ln(S 0 * / S 2 * ) relationship curve, its slope is α The temperature and pressure parameters in the HLD equation are known. When the surfactant parameters ( k and C C ) and the equivalent alkane carbon number (EACN) of the oil, the optimal salinity S of the middle phase microemulsion at different pressures and temperatures can be calculated according to the HLD equation. * .

[0051] Compared with the existing method, the present invention uses a fluorinated liquid with a large density difference between the two phases and a surfactant solution to achieve small interface area contact pressure control through a pipeline connection, and has the following beneficial effects: microemulsion research requires the preparation of a variety of salinities or surfactant compositions, and the connection method avoids the use of multiple displacement pumps and intermediate containers, simplifying the operation process; multiple microemulsion salinity formulas can be scanned at one time, saving a lot of time for the entire screening process; the use of pistons is abandoned, avoiding frequent disassembly and cleaning of the device, and controlling the cost to a certain extent; the use of multiple intermediate containers is avoided during the injection of oil and water phases, the operation is simpler, and the cost of high-temperature and high-pressure microemulsion research is further controlled; and according to the conditional mean of pressure and temperature as random variables and the optimal middle phase microemulsion salinity formula as an explanatory variable, the experimental observation data can be integrated through linear regression analysis to obtain a prediction model for the optimal middle phase microemulsion salinity formula, and the optimal point composition under other temperature and pressure conditions can be predicted. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is the experimental flow chart;

[0053] Figure 2 It is a system diagram of the microemulsion screening device under high temperature and high pressure conditions;

[0054] Figure 3 Schematic diagram of the lower phase microemulsion (Winsor Ⅰ type);

[0055] Figure 4 Schematic diagram of the upper phase microemulsion (Winsor II type);

[0056] Figure 5 Schematic diagram of a middle phase microemulsion (Winsor III type) with unequal excess water phase and excess oil phase;

[0057] Figure 6 Schematic diagram of the best point;

[0058] Figure 7 is ΔP and Ln(S 0 * / S 1 * ) relationship curve diagram;

[0059] Figure 8 is ΔT and Ln(S 0 * / S 2 * ) relationship curve diagram;

[0060] In the figure: 1, 23, 37 - displacement pumps; 2, 4-6, 11, 12, 19, 20, 22, 24-31 - valves; 3 - sample dispenser; 7 - upper inlet; 8, 41-45 - pressure vessels; 9, 10 - lower outlet; 13 - sample inlet line; 14-16 - three-way valves; 17 - injection line; 18 - pressure regulating line; 21 - intermediate container for fluorinated liquid; 32, 46 - pressure gauges; 33 - intermediate container for dichloromethane; 34 - intermediate container for deionized water; 35 - intermediate container for anhydrous ethanol; 36 - intermediate container for nitrogen; 38 - oven; 39 - steel shaft; 40 - waste liquid barrel. DETAILED DESCRIPTION

[0061] In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with preferred embodiments and accompanying drawings. For clarity and ease of understanding of the device, the various parts in the accompanying drawings are not drawn to scale. Similar components in the accompanying drawings are represented by the same reference numerals. Those skilled in the art should understand that the content specifically described below is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0062] Microemulsion screening device system under high temperature and high pressure conditions Figure 2 As shown, a method for screening microemulsions under high temperature and high pressure conditions specifically comprises the following steps:

[0063] Step S1: prepare six piston-free pressure vessels with sapphire observation windows. The six pressure vessels are welded by a steel shaft. The connected steel shafts are kept in the same straight line and penetrate the oven 38. The six pressure vessels can be driven to swing back and forth by rotating the steel shaft. The high-temperature and high-pressure resistant metal hoses connected to the pressure vessels should have sufficient movable length to ensure that the connected pipelines will not be entangled with the pressure vessels during swinging; the upper inlet 7 of the pressure vessel 8 is connected to the sample dispenser 3 filled with live oil, wherein the live oil is obtained by mixing dead oil and associated gas, heating and pressurizing to formation conditions and stirring and configuring. The lower end of the pressure vessel is provided with a lower outlet 9 and a lower outlet 10, and the lower outlet 9 is connected to a section of the sampling pipeline 13 and the three-way valve 14 port of the three-way valve in sequence. The three-way valve is also provided with a three-way valve 15 port and a three-way valve 16 port, which are respectively connected to the injection pipeline 17 and the pressure regulating pipeline 18;

[0064] Step S2: Connect the pressure regulating pipeline 18 to the fluorinated liquid intermediate container 21 containing the fluorinated liquid, wherein the fluorinated liquid can be selected from Fluorinert FC-40 electronic fluorinated liquid with a relative density of 1.90, Fluorinert FC-3283 electronic fluorinated liquid with a relative density of 1.82, or Fomblin YLVAC25 / 6 electronic fluorinated liquid; if only the three-way valve 14 port and the three-way valve 15 port are opened, the injection line 17 and the sampling line 13 are connected, and the surfactant solution is injected into the injection line 17 through a syringe, the sampling line 13 and the pressure vessel 8 can be filled with the pre-screened surfactant solution. If only the three-way valve 14 port and the three-way valve 16 port are opened, the sampling line 13 and the pressure regulating line 18 are connected, and the fluorinated liquid in the fluorinated liquid intermediate container 21 can be used as a displacement medium to adjust the volume of the surfactant solution entering the pressure vessel 8. Since sufficient volume is reserved in the sampling line 13, the volume of the fluorinated liquid emulsified by the surfactant after contact can be ignored;

[0065] Step S3: evacuate the pressure vessel 8 and the pipeline connected to the upper inlet 7, and fill the pre-screened surfactant solution and the fluoride liquid into the sampling pipeline 13 and the pressure regulating pipeline 18 respectively. After connecting the entire device, continue to inject the surfactant solution into the sampling pipeline 13 to fill the volume of the container, and then pressurize the fluoride liquid to increase the pressure in the container to the formation pressure; repeat this step to fill the remaining pressure vessels 41 to 45 with the pre-screened surfactant solution and reach the formation pressure;

[0066] Step S4: After the entire device is heated to the formation temperature by the oven 38, the oil sample is injected from the upper inlet 7 of the pressure vessel 8 at a constant speed, and the excess surfactant solution exits the pressure vessel 8 from the lower outlet 9 at a constant speed. When the volume of the oil in the pressure vessel is equal to the volume of the surfactant solution, the injection is stopped, and this step is repeated in the remaining pressure vessels 41 to 45;

[0067] Step S5: After the pressure vessel is filled with oil and surfactant solution, the steel shaft drives the pressure vessel to rotate 120° clockwise, and then rotates counterclockwise to reset, and swings back and forth twenty times. The static time is 24h-48h. The volume of each phase is observed and recorded through the scale of the sapphire observation window. When the phase interface does not move for a long time, it is balanced. If the microemulsion observed for the first time is the lower phase microemulsion, it is necessary to increase the salinity of the surfactant after cleaning the device and repeat steps S2 to S4; if it is the upper phase microemulsion, it is necessary to reduce the salinity of the surfactant after cleaning the device. Repeat steps S2 to S4 according to the salinity of the surfactant solution; if lower phase microemulsion and upper phase microemulsion appear in different pressure vessels respectively, it is necessary to reduce the concentration gradient within the salinity window where the two types of microemulsions appear after the device is cleaned and repeat steps S2 to S4; if a middle phase microemulsion appears, but the volume of the excess water phase below and the excess oil phase above are not equal, it is necessary to increase or decrease the surfactant salinity after the device is cleaned and repeat steps S2 to S4 until the volume of the excess water phase is equal to that of the excess oil phase;

[0068] Step S6: the upper inlet 7 of the pressure vessel 8 is connected to a cleaning device, which includes a dichloromethane intermediate container 33 filled with dichloromethane, a deionized water intermediate container 34 filled with deionized water, an anhydrous ethanol intermediate container 35 filled with anhydrous ethanol, and a nitrogen intermediate container 36 filled with nitrogen and a displacement pump 37; the purity of the nitrogen, anhydrous ethanol, dichloromethane and deionized water is greater than 99.5%; dichloromethane is injected from the upper inlet 7 of the pressure vessel 8 to clean the oil phase in the mixed solution, and the lower outlet 10 thereof is connected to a waste liquid barrel 40, and then deionized water is injected into the pressure vessel 8 to remove salt, and then anhydrous ethanol is injected to remove the water phase, and finally hot nitrogen is introduced to blow off the anhydrous ethanol and dichloromethane, and the pressure regulating pipeline 18, the injection pipeline 17 and the sampling pipeline 13 are removed and cleaned, and the steps are repeated to clean the remaining pressure vessels 41 to 45;

[0069] Step S7: Repeat steps S4 to S6 near the optimal salinity, record the volume of each phase, and the microemulsion sample with the middle phase having the same volume of excess water phase and excess oil phase is the optimal point, and the salinity corresponding to the optimal point is the screened optimal middle phase microemulsion salinity formula;

[0070] Step S8: predicting the optimal salinity formula of the middle phase microemulsion under different pressure and temperature conditions; the prediction method specifically comprises the following steps:

[0071] Step S8.1: Based on the conditional means of pressure and temperature as random variables and the optimal middle phase microemulsion salinity formula as the explanatory variable, the experimental observation data are integrated through linear regression analysis to obtain a prediction model for the optimal middle phase microemulsion salinity formula, namely the HLD equation:

[0072] HLD=LnS – k ·EACN – α (T – T ref ) – β (P – P ref ) + C C (1),

[0073] Where: HLD is the hydrophilicity-lipophilicity deviation; S is the salinity of the optimal middle phase microemulsion salinity formula, g / 100ml; k is the slope of the logarithmic function of the optimal salinity and EACN, C C is the characteristic parameter of surfactant; EACN is the equivalent alkane carbon number of oil component; T is the salinity formulation temperature, ℃; T ref is the reference temperature, 20℃; P is the salinity formula pressure, MPa; P ref is the reference pressure, 0.101MPa; α is the temperature coefficient; β is the pressure coefficient;

[0074] When the salinity formula is at the optimal point mentioned above, the HLD value is 0, and equation (1) becomes:

[0075] 0 = LnS 0 * – k ·EACN – α (T 0 – T ref ) – β (P 0 – P ref ) + C C (2),

[0076] Where: S 0 * is the salinity corresponding to the optimal point, g / 100ml; T 0 is the formation temperature, °C; P 0 is the formation pressure, MPa;

[0077] Step S8.2: When only the pressure changes, equation (2) becomes:

[0078] 0 = LnS 1 * – k ·EACN – α (T 0 – T ref ) – β (P 1 – P ref ) + C C (3),

[0079] Where: S 1 * is the salinity corresponding to the optimal point after pressure change, g / 100ml; P 1 is the changed pressure, MPa;

[0080] According to equation (2)-equation (3), we can get:

[0081] Ln(S 0 * / S 1 * ) = β ΔP (4),

[0082] Where: ΔP is the difference between the formation pressure and the changed pressure;

[0083] Repeat steps S8.1 to S8.2 three times to plot ΔP and Ln(S 0 * / S 1 * ) relationship curve, its slope is β The value of

[0084] Step S8.3: When only the temperature changes, equation (2) becomes:

[0085] 0 = LnS 2 * – k ·EACN – α (T 1 – T ref ) – β (P 0 – P ref ) + C C (5),

[0086] Where: S 2 *is the salinity corresponding to the optimal point after temperature change, g / 100ml; T 1 is the temperature after change, ℃;

[0087] According to equation (2)-equation (5), we can get:

[0088] Ln(S 0 * / S 2 * ) = α ΔT (6),

[0089] Where: ΔT is the difference between the formation temperature and the changed temperature, °C;

[0090] Step S8.4: Repeat steps S8.1 to S8.3 three times to plot ΔT and Ln(S 0 * / S 2 * ) relationship curve, its slope is α The temperature and pressure parameters in the HLD equation are known. When the surfactant parameters ( k and C C ) and the equivalent alkane carbon number (EACN) of the oil, the optimal salinity S of the middle phase microemulsion at different pressures and temperatures can be calculated according to the HLD equation. * .

[0091] The following takes the various physical parameters of a tight oil and gas reservoir in an oil field as the implementation object:

[0092] (1) Six piston-free pressure vessels with sapphire observation windows are connected in series through a steel shaft, and the volume of each vessel is 10 ml;

[0093] (2) In the sample preparation device 3, the dead oil and the associated gas are mixed, heated and pressurized to the formation conditions (temperature 70°C, pressure 30 MPa) and stirred to prepare the live oil;

[0094] (3) Connect the sample dispenser 3 and the pressure vessel 8, evacuate the vessel and pipeline, and close valves 4 and 6;

[0095] (4) With a concentration gradient of 2 wt%, 6 pre-screened surfactant solutions with NaCl concentrations ranging from 2 wt% to 12 wt% were prepared; specifically, the surfactant was Alfoterra 123-4S anionic surfactant, and its mass concentration in the solution was 1%;

[0096] (5) Taking the pressure vessel 8 as an example, open the three-way valve 14 and the three-way valve 15 to connect the sample injection line 13 with the injection line 17. Specifically, the volume of the sample injection line 13 is 5 ml, and the volume of the injection line 17 is 0.5 ml. Inject the prepared surfactant solution from the injection line 17 through a syringe. After the sample injection line 13 is filled, close the three-way valve 14 and the three-way valve 15, connect the sample injection line 13 with the pressure vessel 8 and keep the valve 11 closed. Then open the three-way valve 15, the three-way valve 14, and the valve 11, and continue to inject the surfactant solution until the container 8 is full of the surfactant solution. Repeat this step to fill the remaining containers with the pre-screened surfactant solution.

[0097] (6) Close valve 11, three-way valve 14, and three-way valve 15, open valve 19, valve 20, valve 22, and displacement pump 23, inject FC-40 electronic fluorine liquid in the fluorine liquid intermediate container 21 into the pressure regulating pipeline 18 until it is full, connect the pressure regulating pipeline 18 and the three-way valve 16, open valve 11 and the three-way valve 14, pressurize the pressure vessel 8 to the formation pressure of 30MPa through the fluorine liquid, close valve 19, isolate the pressure vessel 8 from the system, and repeat this step to raise the surfactant solution in all other containers to the formation pressure. Open valve 19 again, turn on the constant pressure mode of the displacement pump to keep the pressure constant, open the oven under the premise of formation conditions, raise the temperature to 70°C under formation conditions, then close valve 19, and repeat this step to raise the surfactant solution in all other containers to the formation temperature;

[0098] (7) Taking pressure vessel 8 as an example, open valve 2, valve 4, valve 6, valve 11, three-way valve 14, three-way valve 16, valve 19 and start displacement pump 1 and displacement pump 23. Live oil is injected into pressure vessel 8 from upper inlet 7 at a constant speed of 0.5 ml / min, and the surfactant solution exits the container from lower outlet 9 at the same speed. Observe through the observation window, when the oil-water interface is in the middle of the scale (that is, the oil and water phases are 5 mL each), stop the displacement pump and close all valves, and repeat this step in the remaining pressure vessels 41-pressure vessel 45 until all containers have 5 mL of oil and water phases each;

[0099] (8) By rotating the steel shaft 39, all the pressure vessels are driven to swing back and forth so that the mixed liquid in the container is fully stirred, and then all the pressure vessels are left to stand for 36 hours to wait for the mixed liquid to be balanced;

[0100] (9) Observe the phase behavior of the mixed liquid through the observation window. When the phase interface does not move for a long time, it can be considered to have reached equilibrium. Select the microemulsion with obvious middle phase or close to forming middle phase, and record its NaCl concentration;

[0101] (10) Taking the pressure vessel 8 as an example, open valve 12 to release the pressure to the waste liquid barrel 40, close valve 4, then open valve 5, valve 6, valve 24, valve 28 and displacement pump 37, inject dichloromethane into the outlet 7 through the dichloromethane intermediate container 33 to remove the oil phase of the microemulsion, close valve 24 and valve 28; open valve 25 and valve 29, inject deionized water through the deionized water intermediate container 34 to remove NaCl and surfactant, close valve 25 and valve 29; open valve 26 and valve 28. Door 30, inject anhydrous ethanol through the anhydrous ethanol intermediate container 35 to remove the remaining water, close valve 26 and valve 30, and finally open valve 27 and valve 31, inject hot nitrogen through the nitrogen intermediate container 36 to blow out the anhydrous ethanol and dichloromethane, close all valves and displacement pumps, remove the pressure regulating pipeline 18, the sampling pipeline 13 and the injection pipeline 17, and then inject dichloromethane, anhydrous ethanol and deionized water through a syringe to clean them, then connect the nitrogen bottle to blow them out, and repeat the cleaning steps in the remaining pressure vessels;

[0102] (11) After the entire device is cleaned, the NaCl concentration gradient is reduced to 0.2 wt% or 0.1 wt% near the concentration value recorded in step (9) and steps (3) to (10) are repeated; the volume of each phase after equilibrium is recorded, and the microemulsion sample with the same volume of excess water phase and excess oil phase is called the optimal point; the composition corresponding to the optimal point - 1 wt% 123-4S and 3.6 wt% NaCl, is the best microemulsion formula screened out;

[0103] The experimental pressure was changed to 15 MPa, 20 MPa, and 25 MPa, and the above experimental steps (1) to (11) were repeated three times. The experimental observation data were combined through linear regression analysis to obtain a prediction model for the optimal middle phase microemulsion salinity formula, namely the HLD equation:

[0104] HLD=LnS – k ·EACN – α (T – T ref ) – β (P – P ref ) + C C (1),

[0105] Where: HLD is the hydrophilicity-lipophilicity deviation; S is the salinity of the optimal middle phase microemulsion salinity formula, g / 100ml; k is the slope of the logarithmic function of the optimal salinity and EACN, C C is the characteristic parameter of surfactant; EACN is the equivalent alkane carbon number of oil component; T is the salinity formulation temperature, ℃; T ref is the reference temperature, 20℃; P is the salinity formula pressure, MPa; P refis the reference pressure, 0.101MPa; α is the temperature coefficient; β is the pressure coefficient;

[0106] When the salinity formula is at the optimal point mentioned above, the HLD value is 0, and equation (1) becomes:

[0107] 0 = LnS 0 * – k ·EACN – α (T 0 – T ref ) – β (P 0 – P ref ) + C C (2),

[0108] Where: S 0 * is the salinity corresponding to the optimal point, g / 100ml; T 0 is the formation temperature, °C; P 0 is the formation pressure, MPa;

[0109] When only the pressure changes, equation (2) becomes:

[0110] 0 = LnS 1 * – k ·EACN – α (T 0 – T ref ) – β (P 1 – P ref ) + C C (3),

[0111] Where: S 1 * is the salinity corresponding to the optimal point after pressure change, g / 100ml; P 1 is the changed pressure, MPa;

[0112] According to equation (2)-equation (3), we can get:

[0113] Ln(S 0 * / S 1 * ) = β ΔP (4),

[0114] Plot ΔP and Ln(S 0* / S 1 * ) relationship curve, such as Figure 7 As shown ( Figure 7 where x is ΔP in equation (4) and y is Ln(S 0 * / S 1 *), R 2 is the coefficient of determination. The closer its value is to 1, the stronger the correlation between the independent variable and the dependent variable. Its slope is -0.0194. β The experimental temperature was changed to 40℃, 50℃, and 60℃, and the above experimental steps (1) to (11) were repeated three times. Equation (2) becomes:

[0115] 0 = LnS 2 * – k ·EACN – α (T 1 – T ref ) – β (P 0 – P ref ) + C C (5),

[0116] Where: S 2 * is the salinity corresponding to the optimal point after temperature change, g / 100ml; T 1 is the temperature after change, ℃;

[0117] According to equation (2)-equation (5), we can get:

[0118] Ln(S 0 * / S 2 * ) = α ΔT (6),

[0119] ΔT and Ln(S 0 * / S 2 * ) relationship curve, such as Figure 8 As shown ( Figure 8 where x is ΔT in equation (6) and y is Ln(S 0 * / S 2 *), R 2 is the coefficient of determination. The closer its value is to 1, the stronger the correlation between the independent variable and the dependent variable. Its slope is -0.0008. α Value of; known surfactant parameters k is 0.049,C C is -1.55, and the equivalent alkane carbon number EACN of the oil is 7.3. According to the HLD equation, the optimal composition of the middle phase microemulsion at different pressures and temperatures can be predicted;

[0120] (12) Verification experiment: Set the temperature and pressure to 45°C and 18 MPa, substitute into equation (2), and calculate the optimal salinity S 0 * is 4.7 g / 100 ml; by repeating steps (1) to (11), at 45 °C, 18 MPa, and the same oil and surfactant, the optimal salinity of the screened microemulsion is 4.9 g / 100 ml, which is very close to the predicted value.

[0121] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for screening the phase behavior of a medium-phase microemulsion under high temperature and high pressure conditions, characterized in that: The steps include: Step S1: prepare six piston-free pressure vessels with sapphire observation windows. The six pressure vessels are welded to each other through a steel shaft. The connected steel shafts are kept in the same straight line and penetrate the oven (38). The six pressure vessels can be driven to swing back and forth by rotating the steel shaft. The pipelines connected to the pressure vessels should have sufficient movable length to ensure that the connected pipelines will not be entangled with the pressure vessels during swinging. The upper inlet (7) of the pressure vessel (8) is connected to a sample dispenser (3) filled with live oil. The lower end of the pressure vessel (8) is provided with a lower outlet (9) and a lower outlet (10). The lower outlet (9) is connected to a section of the sample injection pipeline (13) and a port of a three-way valve (14) in sequence. The three-way valve is also provided with a three-way valve (15) and a three-way valve (16). The ports of the two are respectively connected to an injection pipeline (17) and a pressure regulating pipeline (18). Step S2: connecting the pressure regulating pipeline (18) to the fluorinated liquid intermediate container (21) containing the fluorinated liquid; If only the three-way valve (14) port and the three-way valve (15) port are opened, the injection line (17) and the sample injection line (13) are connected, and the surfactant solution is injected into the injection line (17) through a syringe, the sample injection line (13) and the pressure vessel (8) can be filled with the pre-screened surfactant solution. If only the three-way valve (14) port and the three-way valve (16) port are opened, the sample injection line (13) and the pressure regulating line (18) are connected, the fluorinated liquid in the fluorinated liquid intermediate container (21) can be used as a displacement medium to adjust the volume of the surfactant solution entering the pressure vessel (8). Since sufficient volume is reserved in the sample injection line (13), the volume of the fluorinated liquid emulsified by the surfactant after contact can be ignored. Step S3: evacuate the pressure vessel (8) and the pipeline connected to the upper inlet (7), and fill the pre-screened surfactant solution and fluoride liquid into the sampling pipeline (13) and the pressure regulating pipeline (18) respectively. After connecting the entire device, continue to inject the surfactant solution into the sampling pipeline (13) to fill the volume of the container, and then pressurize the fluoride liquid to increase the pressure in the container to the formation pressure; repeat this step to fill the remaining pressure vessels (41) to the pressure vessel (45) with the pre-screened surfactant solution and reach the formation pressure; Step S4: After the entire device is heated to the formation temperature by the oven (38), the oil sample is injected from the upper inlet (7) of the pressure vessel (8) at a constant speed, and at the same time, the excess surfactant solution exits the pressure vessel (8) from the lower outlet (9) at a constant speed. When the volume of the oil in the pressure vessel is equal to the volume of the surfactant solution, the injection is stopped, and this step is repeated in the remaining pressure vessels (41) to the pressure vessel (45); Step S5: The steel shaft drives the pressure vessel to swing back and forth, and the pressure vessel is left to stand for a certain period of time. The volume of each phase is observed and recorded through the scale of the sapphire observation window. When the phase interface does not move for a long time, it is in equilibrium. If the microemulsion observed for the first time is a lower phase microemulsion, it is necessary to increase the salinity of the surfactant after cleaning the device and repeat the steps S2 to S4; if it is an upper phase microemulsion, it is necessary to reduce the salinity of the surfactant solution after cleaning the device and repeat the steps S2 to S4; if lower phase microemulsion and upper phase microemulsion appear in different pressure vessels respectively, it is necessary to reduce the concentration gradient within the salinity window where the two types of microemulsion appear after cleaning the device and repeat the steps S2 to S4; if a middle phase microemulsion appears, but the volume of the excess water phase below and the excess oil phase above are not equal, it is necessary to increase or reduce the salinity of the surfactant after cleaning the device and repeat the steps S2 to S4 until the volume of the excess water phase is equal to that of the excess oil phase; Step S6: injecting dichloromethane from the upper inlet (7) of the pressure vessel (8) to clean the oil phase in the mixed solution, and connecting the lower outlet (10) to the waste liquid barrel (40), then injecting deionized water into the pressure vessel (8) to remove salt, and then injecting anhydrous ethanol to remove the water phase, and finally passing nitrogen to blow away the anhydrous ethanol and dichloromethane, removing the pressure regulating pipeline (18), the injection pipeline (17) and the sampling pipeline (13) and cleaning them, and repeating this step to clean the remaining pressure vessels (41) to the pressure vessel (45); Step S7: Repeat steps S4 to S6 near the optimal salinity, record the volume of each phase, and the microemulsion sample with the middle phase having the same volume of excess water phase and excess oil phase is the optimal point, and the salinity corresponding to the optimal point is the screened optimal middle phase microemulsion salinity formula; Step S8: predicting the optimal salinity formula of the middle phase microemulsion under different pressure and temperature conditions; specifically comprising the following steps: Step S8.1: Based on the conditional means of pressure and temperature as random variables and the optimal middle phase microemulsion salinity formula as the explanatory variable, the experimental observation data are integrated through linear regression analysis to obtain a prediction model for the optimal middle phase microemulsion salinity formula, namely the HLD equation: HLD=LnS – k ·EACN – α (T – T ref ) – β (P – P ref ) + C C (1), Where: HLD is the hydrophilicity-lipophilicity deviation; S is the salinity of the optimal middle phase microemulsion salinity formula, g / 100ml; k is the slope of the logarithmic function of the optimal salinity and EACN, C C is the characteristic parameter of surfactant; EACN is the equivalent alkane carbon number of the oil component; T is the salinity formulation temperature, ℃; T ref is the reference temperature, 20°C; P is the salinity formula pressure, MPa; P ref is the reference pressure, 0.101MPa; α is the temperature coefficient; β is the pressure coefficient; When the salinity formula is at the optimal point mentioned above, the HLD value is 0, and equation (1) becomes: 0 = LnS0 * – k ·EACN – α (T0 – T ref ) – β (P0 – P ref ) + C C (2), Where: S0 * is the salinity corresponding to the optimal point, g / 100ml; T0 is the formation temperature, °C; P0 is the formation pressure, MPa; Step S8.2: When only the pressure changes, equation (2) becomes: 0 = LnS1 * – k ·EACN – α (T0 – T ref ) – β (P1 – P ref ) + C C (3), Where: S1 * is the salinity corresponding to the optimal point after the pressure change, g / 100ml; P1 is the pressure after the change, MPa; According to equation (2)-equation (3), we can get: Ln(S0 * / S1 * ) = β ·ΔP (4), Where: ΔP is the difference between the formation pressure and the changed pressure; Repeat steps S8.1 to S8.2 three times to plot ΔP and Ln(S0 * / S1 * ) relationship curve, its slope is β The value of Step S8.3: When only the temperature changes, equation (2) becomes: 0 = LnS2 * – k ·EACN – α (T1 – T ref ) – β (P0 – P ref ) + C C (5), Where: S2 * is the salinity corresponding to the optimal point after the temperature change, g / 100ml; T1 is the temperature after the change, ℃; According to equation (2)-equation (5), we can get: Ln(S0 * / S2 * ) = α ·ΔT (6), Where: ΔT is the difference between the formation temperature and the changed temperature, °C; Step S8.4: Repeat steps S8.1 to S8.3 three times to plot ΔT and Ln(S0 * / S2 * ) relationship curve, its slope is α The value of, the temperature and pressure parameters in the HLD equation are known, the slope k of the logarithmic function of the known optimal salinity and EACN, the surfactant characteristic parameters C C After calculating the equivalent alkane carbon number EACN of the oil component, the optimal salinity S of the middle phase microemulsion at different pressures and temperatures can be calculated according to the HLD equation. * .

2. The method for screening the phase behavior of a medium-phase microemulsion under high temperature and high pressure conditions according to claim 1, characterized in that: The pipelines connected to the pressure vessel in step S1 are all metal hoses resistant to high temperature and high pressure.

3. The method for screening the phase behavior of a medium-phase microemulsion under high temperature and high pressure conditions according to claim 1, characterized in that: The live oil in step S1 is obtained by mixing dead oil and associated gas, heating and pressurizing them to formation conditions, and stirring and configuring them.

4. The method for screening the phase behavior of a medium-phase microemulsion under high temperature and high pressure conditions according to claim 1, characterized in that: The fluorination liquid in step S2 is selected from Fluorinert FC-40 electronic fluorination liquid with a relative density of 1.90, Fluorinert FC-3283 electronic fluorination liquid with a relative density of 1.82, or Fomblin YLVAC25 / 6 electronic fluorination liquid with a relative density of 1.

90.

5. The method for screening the phase behavior of a medium-phase microemulsion under high temperature and high pressure conditions according to claim 1, characterized in that: In step S5, after the pressure vessel is filled with oil and surfactant solution, the steel shaft drives the pressure vessel to rotate 120° clockwise, and then rotates counterclockwise to reset, reciprocating and swinging twenty times, and the static time is 24h-48h.

6. The method for screening the phase behavior of a medium-phase microemulsion under high temperature and high pressure conditions according to claim 1, characterized in that: In step S6, the upper inlet (7) of the pressure container (8) is connected to the cleaning device, and the waste liquid is discharged into the waste liquid bucket through the lower outlet (10).

7. The method for screening the phase behavior of a medium-phase microemulsion under high temperature and high pressure conditions according to claim 6, characterized in that: The cleaning device comprises a nitrogen intermediate container (36) filled with nitrogen, an anhydrous ethanol intermediate container (35) filled with anhydrous ethanol, a dichloromethane intermediate container (33) filled with dichloromethane, a deionized water intermediate container (34) filled with deionized water, and a displacement pump (37).

8. The method for screening the phase behavior of a medium-phase microemulsion under high temperature and high pressure conditions according to claim 7, characterized in that: The purity of the nitrogen, anhydrous ethanol, dichloromethane and deionized water is greater than 99.5%.

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