Method for determining interfacial tension of microemulsion oil-water under high temperature and high pressure based on nuclear magnetic resonance

Abstract

The present application relates to a method for determining the oil-water interfacial tension of microemulsion under high temperature and high pressure based on nuclear magnetic resonance, comprising: placing a hollow ceramic tube into a holder and placing it in a nuclear magnetic resonance instrument; preparing a microemulsion with a formation oil and a surfactant salt solution; heating the holder to a desired temperature; pressurizing and saturating the ceramic tube with the formation oil, and testing the T2 spectrum of the formation oil in the ceramic tube; displacing the formation oil in the ceramic tube with the microemulsion, testing the T2 spectrum of the fluid in the ceramic tube once for every certain volume of microemulsion injected; making a curve of the oil-containing volume of the ceramic tube versus the injection volume of the microemulsion, identifying the type of the prepared microemulsion under high temperature and high pressure, changing the NaCl concentration in the surfactant salt solution until the Winsor III type of microemulsion under high temperature and high pressure is identified in the curve, and calculating the oil-water interfacial tension of the microemulsion. The present application has accurate and reliable test results, and can provide important support for the microemulsion enhanced oil recovery technology.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of oil and gas field development engineering, and particularly relates to a method for determining oil-water interfacial tension of microemulsion under high temperature and high pressure conditions based on nuclear magnetic resonance. BACKGROUND

[0002] In the process of microemulsion flooding enhanced oil recovery, oil-water interfacial tension is an important property, and the formation of ultra-low oil-water interfacial tension is one of the mechanisms by which microemulsion can greatly improve the recovery rate. Meanwhile, it is also an important indicator for measuring the hydrophilic-lipophilic property of the surfactant used. The lower the interfacial tension, the better the lipophilicity. Therefore, when screening a microemulsion system, it is necessary to determine the oil-water interfacial tension in the process of microemulsion flooding.

[0003] At present, the methods for testing oil-water interfacial tension mainly include the rotating drop method, the pendant drop method, the Du Noüy ring method, etc. The pendant drop method can test oil-water interfacial tension under high temperature and high pressure conditions. For example, the invention patent "Device and method for measuring oil-water interfacial tension variation in CO2 flooding process" (CN103048247B) presses crude oil into a pendant drop chamber, forms an oil drop at the probe, keeps it for a period of time, takes a photo of the oil drop by an enlarged camera system, and then calculates the equilibrium interfacial tension through the shape parameters of the oil drop and the corresponding formula. However, the pendant drop method cannot measure ultra-low oil-water interfacial tension in the process of surfactant flooding. The rotating drop method, which is suitable for measuring ultra-low interfacial tension, such as the utility model patent "Rotating drop method liquid interfacial tension tester" (CN2237848Y), can measure the size parameters of the elongated liquid drop by high-speed rotation of the rotating shaft, and then calculate the interfacial tension. However, this method is only suitable for normal temperature and pressure conditions. The rotating drop interfacial tension testing device capable of testing high temperature and high pressure conditions is expensive and complicated to operate, such as the invention patent "Rotating drop method ultra-low interfacial tension measuring device and measuring method" (CN102213668B).

[0004] The present application proposes a method that can measure ultra-low oil-water interfacial tension while adapting to high temperature and high pressure conditions, and is easy to operate and low in cost. SUMMARY

[0005] The application aims to provide a method for measuring oil-water interfacial tension of microemulsion under high temperature and high pressure conditions by using nuclear magnetic resonance technology, which comprises the following steps: making the microemulsion under high temperature and high pressure conditions through high-temperature circulation and pressure saturation, on-line monitoring T2 spectrum, obtaining oil-containing volume in the microemulsion, and then making characteristic identification curve of the oil-containing volume and injection volume to determine the type of the microemulsion under formation conditions, and after identifying the middle phase, substituting the parameters into Chun Huh formula (Chun Huh, Interfacial tensions and solubilizing ability of a microemulsion phase that coexists with oil and brine [J]. Journal of Colloid and Interface Science, 1979, 71(2): 408-426) to calculate the oil-water interfacial tension.

[0006] To achieve the above technical purposes, the application adopts the following technical scheme.

[0007] The method for measuring oil-water interfacial tension of microemulsion under high temperature and high pressure conditions based on nuclear magnetic resonance comprises the following steps in sequence:

[0008] (1) a hollow ceramic tube with a volume of V0 is placed in a holder, and the holder is placed in a nuclear magnetic resonance instrument, the inlet end of the holder is connected with a microemulsion intermediate container and a formation oil intermediate container respectively, the outlet end of the holder is connected with a back pressure valve and a measuring cylinder, the nuclear magnetic resonance instrument is connected with a data collector, and the holder is connected with a circulating heating system;

[0009] (2) a microemulsion is prepared by using formation oil and a surfactant salt solution, in the surfactant salt solution, the solvent is heavy water, the concentration of NaCl and the concentration of the surfactant are known, the total volume of the surfactant is V1, and the prepared microemulsion is transferred to the intermediate container and stirred and placed;

[0010] (3) the holder is heated to a required temperature through the circulating heating system;

[0011] (4) after the formation oil intermediate container is heated to a required temperature, the ceramic tube is pressurized and saturated by using formation oil through a displacement pump;

[0012] (5) the T2 spectrum of the formation oil in the ceramic tube is tested, and the total signal peak area A0 is used to represent the nuclear magnetic signal intensity;

[0013] (6) after the microemulsion intermediate container is heated to a required temperature and then increased to a required pressure, the formation oil in the ceramic tube is displaced by using the microemulsion, and the T2 spectrum of the fluid in the ceramic tube is tested once every time a certain volume of the microemulsion is injected, and the total signal peak area is A.i The oil-containing volume of the ceramic tube can be calculated by the following formula:

[0014]

[0015] In the formula:

[0016] A0——the nuclear magnetic signal intensity of the ceramic tube when saturated with formation oil;

[0017] A i ——the nuclear magnetic signal intensity of the fluid in the ceramic tube after injection of the microemulsion;

[0018] V0——the volume of the ceramic tube, ml;

[0019] ——the oil-containing volume of the ceramic tube, ml;

[0020] (7) a curve of the relationship between the oil-containing volume of the ceramic tube V x as the ordinate and the microemulsion injection volume V as the abscissa is plotted, and the type of the prepared microemulsion under high temperature and high pressure conditions is identified according to the curve:

[0021] If it is Winsor III type, directly enter step (8);

[0022] If it is not Winsor III type, repeat steps (2) to (7), change the concentration of NaCl in the surfactant salt solution, until the type of the prepared microemulsion under high temperature and high pressure conditions is identified as Winsor III type in the curve of the relationship between V

[0023] (8) the oil-water interfacial tension γ ow of the Winsor III type microemulsion is calculated, the process being as follows:

[0024] 1) when the middle phase volume is greater than the volume of the ceramic tube:

[0025] read the middle phase volume Vm and the oil-containing volume of the ceramic tube when saturated with the middle phase of the microemulsion from the curve According to the Chunhuh formula, the oil-water interfacial tension γ ow of the Winsor III type microemulsion is calculated by the following formula:

[0026]

[0027] In the formula:

[0028] γ ow ——the oil-water interfacial tension of the Winsor III type microemulsion, mN / m;

[0029] C = interfacial characteristic value of the middle phase, 0.3;

[0030] SPo = solubilization parameter of oil in the middle phase;

[0031] SP o is calculated by the formula:

[0032]

[0033] where:

[0034] V m = volume of the middle phase, ml;

[0035] = volume of oil in the middle phase when the ceramic tube is saturated with the middle phase of the microemulsion, ml;

[0036] V0 = volume of the ceramic tube, ml;

[0037] V1 = total volume of the surfactant, ml;

[0038] Substituting equation (3) into equation (2), the calculation formula of the oil-water interfacial tension γ ow is:

[0039]

[0040] 2) When the volume of the middle phase is less than the volume of the ceramic tube:

[0041] The oil volume in the upper phase when the ceramic tube is saturated with the microemulsion upper phase is read from the curve The oil volume when the middle phase enters the ceramic tube completely and the volume of the middle phase V m , then the volume of the upper phase V u is:

[0042] V u = V0-V m (5)

[0043] The oil volume fraction S uo of the upper phase is:

[0044]

[0045] The oil volume V uo of the upper phase is:

[0046] V uo = V u × S uo (7)

[0047] The oil volume V mo of the middle phase is:

[0048]

[0049] Solubilization parameter SP of middle phase middle oil o is:

[0050]

[0051] Substitute formula (5)-(8) into formula (9), the calculation formula of SP o is:

[0052]

[0053] In the formula:

[0054] V n Middle phase volume, ml;

[0055] Oil volume when all the middle phase of microemulsion enters the ceramic tube, ml;

[0056] Oil volume when the ceramic tube is saturated by the upper phase of microemulsion, ml;

[0057] Substitute formula (10) into formula (2), the calculation formula of oil-water interfacial tension γ ow is:

[0058]

[0059] Further, in the step (1), the wettability of the ceramic tube is water-wet.

[0060] Further, in the step (6), the nuclear magnetic signal of the surfactant is ignored.

[0061] Compared with the prior art, the present application has the following beneficial effects:

[0062] (1) The present application can measure the ultra-low oil-water interfacial tension of microemulsion under high temperature and high pressure conditions, so that the measurement range of the oil-water interfacial tension of microemulsion is wider;

[0063] (2) The present application is determined on the basis of existing nuclear magnetic equipment, the process is simple, and the cost is lower;

[0064] (3) The test result is accurate and reliable. BRIEF DESCRIPTION OF DRAWINGS

[0065] Figure 1 T2 spectrum when the ceramic tube is saturated with formation oil.

[0066] Figure 2 When the microemulsion is Winsor I type, the relationship curve between the oil volume in the ceramic tube and the microemulsion injection volume.

[0067] Figure 3 For the case that the microemulsion is Winsor III type and the middle phase volume is less than the ceramic tube volume, the relationship curve between the oil volume contained in the ceramic tube and the microemulsion injection volume.

[0068] Figure 4 For the case that the microemulsion is Winsor III type and the middle phase volume is greater than the ceramic tube volume, the relationship curve between the oil volume contained in the ceramic tube and the microemulsion injection volume.

[0069] Figure 5 For the case that the microemulsion is Winsor II type, the relationship curve between the oil volume contained in the ceramic tube and the microemulsion injection volume. DETAILED DESCRIPTION

[0070] The present application is further illustrated below with reference to the accompanying drawings and examples, so as to facilitate the understanding of the present application by those skilled in the art. However, it should be clear that the present application is not limited in the scope of the specific embodiments, and any changes within the spirit and scope of the present application as defined and determined by the appended claims are within the protection of the present application.

[0071] Example (formation temperature is 46.7°C, formation pressure is 27 MPa)

[0072] The method for determining the oil-water interfacial tension of a microemulsion under high temperature and high pressure conditions based on nuclear magnetic resonance specifically comprises the following steps:

[0073] (1) A ceramic tube with an inner diameter of 1.8 mm, a length of 10 cm (volume V0 is 1.018 ml), and a water-wet inner wall is placed in a holder, and then placed in a magnet box of a nuclear magnetic resonance instrument;

[0074] (2) A Winsor III type microemulsion is prepared with 10 ml of oil and 10 ml of a surfactant salt solution. In the surfactant salt solution, the solvent is heavy water, the NaCl concentration is 6.8 wt%, and the surfactant 123-4S (alkoxylated alcohol ether sulfate) concentration is 1 wt%. According to the density 1.38 g / cm 3 converted into the total volume V1 is 0.08 ml. After stirring and standing for 24 h, the upper phase volume is measured to be 8.68 ml, the lower phase volume is measured to be 8.62 ml, and the middle phase volume is measured to be 2.70 ml. The prepared microemulsion is transferred into an intermediate container;

[0075] (3) The circulating heating system is started, and the temperature of the holder is raised to 46.7°C;

[0076] (4) After the microemulsion intermediate container is also raised to 46.7°C, the pressure of the microemulsion intermediate container is raised to 27 MPa, and the microemulsion is allowed to stand for 24 h for equilibrium;

[0077] (5) The ceramic tube was pressurized and saturated with formation oil, and the pressure was increased to 27 MPa;

[0078] (6) When oil is stably flowing out of the outlet, the T2 spectrum of the fluid inside the ceramic tube is as follows: Figure 1 As shown, the total area of ​​the signal peaks is 952.

[0079] (7) Turn on the injection pump and use the microemulsion to displace the formation oil in the ceramic tube. The volume in the pipeline is 1.2 ml. When the injection volume is 1.2 ml, the microemulsion begins to enter the ceramic tube. After stopping the pump, test the T2 spectrum of the fluid in the ceramic tube. Then, test the T2 spectrum of the fluid in the ceramic tube once every 0.5 ml of microemulsion is injected. When the cumulative injection volume exceeds 9.2 ml, test the T2 spectrum once every 0.1 ml is injected. Record the area of ​​the signal peak each time. Calculate the oil-containing volume of the ceramic tube after each test according to formula (1).

[0080] (8) After all the microemulsion has been injected, turn off the injection pump, then turn the injection pump back on and reduce it to atmospheric pressure to displace the remaining microemulsion in the pipeline with heavy water.

[0081] (9) Plot the relationship curve between the oil-containing volume of the ceramic tube and the injection volume of the microemulsion. like Figure 2 As shown, it can be seen that under high temperature and high pressure conditions, the microemulsion changes from Winsor III type to Winsor I type. Inflection point 1 indicates that the oil sample is completely displaced by the upper phase of the microemulsion. Inflection point 2 indicates that the lower phase of the microemulsion begins to enter the ceramic tube, which occurs before half the volume (10 ml) of the microemulsion is injected. Inflection point 3 indicates that the upper phase of the microemulsion is completely displaced, and at this time only the lower phase remains in the ceramic tube.

[0082] (10) Change the NaCl concentration to obtain Winsor III type microemulsion under high temperature and high pressure conditions, that is, increase the NaCl concentration by 0.2wt% each time, keep the surfactant concentration unchanged, prepare a new microemulsion and place it in an intermediate container, repeat steps (2)-(9), the specific process is as follows:

[0083] 1) When the NaCl concentration was 7.6 wt%, the prepared microemulsion was of type Winsor II, with a lower phase volume of 9.10 ml and an upper phase volume of 10.90 ml. The relationship curve between the oil volume in the ceramic tube and the injected microemulsion volume under high temperature and high pressure conditions is shown below. Figure 3As shown in FIG. 2, the microemulsion prepared is Winsor III type at high temperature and high pressure, and the volume of the middle phase is less than the volume of the ceramic tube. The inflection point 1 indicates that the oil sample is completely displaced by the upper phase of the microemulsion, the inflection point 2 indicates that the middle phase of the microemulsion begins to enter the ceramic tube, the inflection point 3 indicates that the lower phase of the microemulsion begins to enter the ceramic tube, at this time the three phases coexist in the ceramic tube, the inflection point 4 indicates that the upper phase of the microemulsion is completely displaced, and the middle phase and the lower phase of the microemulsion remain in the ceramic tube, and the inflection point 5 indicates that the middle phase of the microemulsion is completely displaced, and only the lower phase of the microemulsion remains in the ceramic tube. From the figure, V m is 0.62 ml, is 0.63 ml, is 0.95 ml, and the oil-water interfacial tension γowof the microemulsion at this time is calculated by substituting into equation (11) to be 0.0322 mN / m. ow is 0.0896 mN / m:

[0084] 2) When the concentration of NaCl is 7.8 wt%, the microemulsion prepared is Winsor II type, the volume of the lower phase is 8.68 ml, and the volume of the upper phase is 11.32 ml. The relationship between the oil-containing volume in the ceramic tube and the injection volume of the microemulsion under high temperature and high pressure conditions is shown in FIG. 3. Figure 4 As shown in FIG. 3, the microemulsion prepared is Winsor III type at high temperature and high pressure, and the volume of the middle phase is greater than the volume of the ceramic tube. The inflection point 1 indicates that the oil sample is completely displaced by the upper phase of the microemulsion, the inflection point 2 indicates that the middle phase begins to enter the ceramic tube, the inflection point 3 indicates that at this time the ceramic tube is entirely filled with the middle phase of the microemulsion, the inflection point 4 indicates that the lower phase of the microemulsion begins to enter the ceramic tube, and the inflection point 5 indicates that at this time there is only the lower phase of the microemulsion in the ceramic tube. Compared with FIG. 2, Figure 3 because the volume of the middle phase of the microemulsion is greater than the volume of the ceramic tube, Figure 4 there is a "step" in the middle section of the curve. From the figure, V m is 1.20 ml, is 0.62 ml, and the oil-water interfacial tension γowof the microemulsion at this time is calculated by substituting into equation (4) to be 0.0322 mN / m.

[0085] 3) When the concentration of NaCl is 8.4 wt%, the microemulsion prepared is Winsor II type, the volume of the lower phase is 7.85 ml, and the volume of the upper phase is 12.15 ml. The relationship between the oil-containing volume in the ceramic tube and the injection volume of the microemulsion under high temperature and high pressure conditions is shown in FIG. 4. Figure 5 As shown in FIG. 4, the microemulsion prepared is Winsor II type at high temperature and high pressure. Similar to Figure 2 , but Figure 5 the inflection point 2 appears after half of the injection volume (10 ml) of the microemulsion.

Claims

1. A method for determining the interfacial tension of a microemulsion under high temperature and high pressure based on nuclear magnetic resonance, comprising the following steps in sequence: (1) Place a hollow ceramic tube with a volume of V0 into a holder, and place the holder in a nuclear magnetic resonance instrument, connect the inlet end of the holder to a microemulsion intermediate container and a formation oil intermediate container respectively, connect the outlet end of the holder to a back pressure valve and a graduated cylinder, connect the nuclear magnetic resonance instrument to a data collector, and connect the holder to a circulating heating system; (2) Prepare a microemulsion using formation oil and a surfactant salt solution, wherein the solvent in the surfactant salt solution is heavy water, the concentration of NaCl and the concentration of surfactant are known, the total volume of surfactant is V1, and the prepared microemulsion is transferred to the intermediate container and stirred and left to stand; (3) Heat the holder to the required temperature by the circulating heating system; (4) After heating the formation oil intermediate container to the required temperature, saturate the ceramic tube with formation oil by using a displacement pump; (5) Test the T2 spectrum of the formation oil in the ceramic tube, and use the total area A0 of the signal peaks to represent the nuclear magnetic signal intensity; (6) After the microemulsion intermediate container is heated to the required temperature, it is then raised to the required pressure. After standing for 24 h, the microemulsion is used to displace the formation oil in the ceramic tube. The T2 spectrum of the fluid in the ceramic tube is tested once for every certain volume of microemulsion injected, and the total signal peak area is A i The oil volume in the ceramic tube is calculated by the following formula: In the formula: A0 is the nuclear magnetic signal intensity when the ceramic tube is saturated with formation oil; A i - the intensity of the nuclear magnetic signal of the fluid in the ceramic tube after injection of the microemulsion; V0 is the volume of the ceramic tube, ml; - Ceramic tube oil containment volume, ml; (7) with the oil-containing volume of the ceramic tube as the ordinate with the microemulsion injection volume V as the abscissa x a relationship curve is drawn According to the curve, the type of the prepared microemulsion under high temperature and high pressure conditions is identified: If it is Winsor III type, directly proceed to step (8); If not Winsor III, repeat steps (2) to (7) with varying the concentration of NaCl in the surfactant salt solution until the microemulsion prepared is in If the type of the microemulsion prepared at high temperature and high pressure is identified as Winsor I or Winsor II in the relationship curve, go to step (8). (8) The oil-water interfacial tension γ of Winsor III microemulsions was calculated ow The procedure was as follows: 1) When the volume of the middle phase is greater than the volume of the ceramic tube, the volume of the middle phase Vm and the oil volume at which the ceramic tube is saturated with the middle phase of the microemulsion are read from the curve The oil-water interfacial tension γ of the Winsor III microemulsion is calculated by the following formula ow : In the formula: gamma ow - oil-water interfacial tension of Winsor III microemulsion, mN / m; C is the characteristic value of the phase interface, and the size is 0.3; V m - mid-phase volume, ml; - oil volume in ml when the ceramic tube is saturated with the phase of the microemulsion V0 is the volume of the ceramic tube, ml; V1 is the total volume of the surfactant, ml; 2) When the volume of the middle phase is less than the volume of the ceramic tube, read the oil volume at which the ceramic tube is saturated with the upper phase of the microemulsion from the curve Oil volume at which the middle phase enters the ceramic tube completely and the volume of the middle phase V m The oil-water interfacial tension γ of the Winsor Il type microemulsion is calculated by the following formula ow : In the formula: V m - mid-phase volume, ml; - oil volume contained in the microemulsion, ml, when all the phase enters the ceramic tube; - Oil volume in ml when the ceramic tube is saturated with the microemulsion top phase.

2. The method for determining the interfacial tension of a microemulsion at high temperature and high pressure using nuclear magnetic resonance as claimed in claim 1, wherein, In the step (1), the wettability of the ceramic tube is water-wet.

3. The method for determining the interfacial tension of a microemulsion at high temperature and high pressure using nuclear magnetic resonance as claimed in claim 1, wherein, In the step (6), the nuclear magnetic signal of the surfactant is ignored.

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