A method for determining the content of crude oil in an emulsion system

Abstract

This invention relates to a method for determining the crude oil content in an emulsion system, belonging to the field of oil and gas field development engineering. The method includes the following steps: (1) obtaining T2 spectra of formation crude oil with volumes of 1 ml, 2 ml, 3 ml, 4 ml, and 5 ml respectively, representing the signal intensity with the signal peak area, and plotting the relationship curve between oil phase volume and signal peak area; (2) taking a certain volume of the test phase from the emulsion system, transferring it to a special test tube, placing it in a nuclear magnetic resonance (NMR) device to test its T2 spectrum, substituting the signal peak area into the relationship formula between oil phase volume and signal peak area to obtain the oil phase volume of the test phase, thereby calculating the dispersed oil phase content in the emulsion system. This invention is reliable in principle, simple to operate, accurate in test results, and widely applicable. It can calculate the oil phase content in any emulsion system without damaging the emulsion system.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field development engineering, and specifically relates to a method for determining the crude oil content in an emulsion system. Background Technology

[0002] Both laboratory and field experiments have demonstrated that emulsification is highly beneficial for improving the oil displacement efficiency of chemical flooding. However, to apply numerical simulations of emulsification behavior to the reservoir scale, it is necessary to predict the emulsion phase behavior. Recent prediction models proposed by international scholars all require measuring the volumes of oil and water in the emulsion. Furthermore, directly measuring the amount of dissolved oil in the emulsion can replace experiments involving complex phase behavior.

[0003] Currently, the main methods for determining the oil content in oil-water emulsions require separating the oil-water mixture, a process that must include at least two steps: demulsification and oil-water separation. Traditional methods, such as centrifugation and high-temperature, high-pressure demulsification, suffer from drawbacks including unsatisfactory demulsification effects and high equipment requirements. Furthermore, these methods are difficult to implement when the volume of the emulsion to be tested is small. More novel methods include membrane filtration and chemical demulsification. Membrane filtration, as described in the invention patent "A Membrane for Oil-Water Emulsion Separation and its Preparation Method and Application" (CN104548667A), involves loading a metal oxide layer with a micron-nano composite structure onto the mesh openings and lines of a metal mesh to form a composite membrane. This membrane is superhydrophobic in oil and superoleophobic underwater, enabling rapid oil-water separation. However, the adsorbed oil is difficult to remove from the oil-absorbing material, leading to large measurement errors. Chemical demulsification methods, such as the invention patent "A method for separating oil-water emulsions" (CN108434788B), separate oil-water emulsions by gravity after the macroporous polymer has swelled and reached equilibrium with water. However, this method requires a relatively large percentage of chemical reagents, which can introduce non-negligible errors into the final test results. Since oil-water demulsification significantly impacts both the accuracy of test results and practical operational limitations, it is crucial to develop an in-situ method for testing the crude oil content in emulsion systems that bypasses the oil-water demulsification step. Summary of the Invention

[0004] The purpose of this invention is to provide a method for determining the crude oil content in an emulsion system. This method is reliable in principle, simple to operate, accurate in test results, and has a wide range of applications. For different types of emulsion systems, the T2 spectrum of the test phase is scanned by nuclear magnetic resonance (NMR) technology, and the oil phase content in any emulsion system can be calculated based on its signal peak area without destroying the emulsion system.

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

[0006] A method for determining the crude oil content in an emulsion system, comprising the following steps:

[0007] (1) T2 spectra of formation crude oil with volumes of 1 ml, 2 ml, 3 ml, 4 ml and 5 ml were obtained respectively. The signal intensity was represented by the signal peak area. The relationship curve between oil phase volume V and signal peak area A was plotted. The data points were fitted to a straight line to obtain the following relationship:

[0008] A = kV (1)

[0009] In the formula: V is the volume of the oil phase;

[0010] A represents the peak area of ​​the T2 spectrum;

[0011] k is the calibration curve coefficient;

[0012] (2) For different types of emulsion systems, the T2 spectrum of the test phase is scanned using nuclear magnetic resonance technology. The oil phase content of the emulsion system is calculated by the signal peak area. The specific process is as follows: a certain volume of the test phase is taken from the emulsion system and transferred into a special test tube. The test phase is placed in the nuclear magnetic resonance equipment to test its T2 spectrum. The signal peak area is substituted into formula (1) to obtain the oil phase volume of the test phase, thereby calculating the dispersed oil phase content in the emulsion system.

[0013] 1) Emulsion:

[0014] Stir the emulsion thoroughly until homogeneous. Measure the inner diameter of the test tube and the height of the emulsion column. Calculate the total volume V1 of the emulsion using the volume formula, and take the volume as V. i The emulsion was transferred into a special test tube and placed in a nuclear magnetic resonance (NMR) instrument to test its T2 spectrum. The signal peak area A1 was substituted into equation (1) to calculate the oil phase volume V′1 = A1 / k corresponding to A1. The dispersed oil phase volume V in the emulsion was then calculated using the following formula. O1 :

[0015]

[0016] In the formula: V i This represents the volume of emulsion taken during the measurement.

[0017] V′1 is the volume of the oil phase dispersed in the emulsion taken during the measurement;

[0018] V1 is the total volume of the emulsion.

[0019] 2) Lower phase microemulsion (O / W type):

[0020] After the microemulsion has been in equilibrium for a period of time, the inner diameter of the test tube and the height of the liquid column of the lower phase are measured. The total volume V2 of the lower phase is calculated according to the volume formula. The excess oil phase (upper phase) is removed, and the volume is taken as V. lThe lower phase of the microemulsion was transferred into a special test tube and placed in a nuclear magnetic resonance (NMR) instrument to test its T2 spectrum. The signal peak area A2 was substituted into equation (1) to calculate the oil phase volume V′2=A2 / k corresponding to A2. The volume V of the oil phase dispersed in the lower phase microemulsion was then calculated using the following formula. O2 :

[0021]

[0022] In the formula: V l This refers to the volume of the lower phase taken during the measurement.

[0023] V′2 is the volume of the oil phase dispersed in the lower phase taken during the measurement;

[0024] V2 is the total volume of the lower phase.

[0025] 3) Upper phase microemulsion (W / O type):

[0026] After the microemulsion has been in equilibrium for a period of time, the inner diameter of the test tube and the height of the upper phase liquid column are measured. The total volume of the upper phase, V3, is calculated according to the volume formula, and the volume is taken as V. u The upper phase of the microemulsion was transferred into a special test tube and placed in a nuclear magnetic resonance (NMR) instrument to test its T2 spectrum. The signal peak area A3 was substituted into equation (1) to calculate the oil phase volume V′3=A3 / k corresponding to A3. The oil phase volume V contained in the upper phase microemulsion was then calculated using the following formula. O3 :

[0027]

[0028] In the formula: V u This refers to the volume of the upper phase taken during the measurement.

[0029] V′3 is the volume of oil phase contained in the upper phase taken during the measurement;

[0030] V3 is the total volume of the upper phase.

[0031] 4) Middle-phase microemulsion:

[0032] After the microemulsion has been in equilibrium for a period of time, the inner diameter of the test tube and the height of the liquid column in the middle phase are measured. The total volume of the middle phase, V4, is calculated according to the volume formula. Excess oil phase is removed, and the volume is taken as V. m The middle phase of the microemulsion was transferred into a special test tube and placed in a nuclear magnetic resonance device to test its T2 spectrum. The signal peak area A4 was substituted into equation (1) to calculate the oil phase volume V′4=A4 / k corresponding to A4. The oil phase volume V contained in the middle phase microemulsion was then calculated using the following formula. O4 :

[0033]

[0034] In the formula: V m This represents the volume of the middle phase taken during the measurement.

[0035] V′4 is the volume of dispersed oil phase in the middle phase sample taken during the measurement;

[0036] V4 represents the total volume of the mesophase.

[0037] It should be noted that this invention is for different types of emulsion systems, in which the aqueous phase is heavy water, the mass fraction of surfactant is generally very small, and its T2 relaxation signal intensity is negligible.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The present invention can determine the oil content in small volume emulsions, which makes up for the shortcomings of conventional methods in dealing with small volume emulsions.

[0040] (2) The measurement process does not require demulsification and oil-water separation steps, making the operation simpler and the measurement results more accurate compared to other methods;

[0041] (3) It has a wide range of applications and can accurately measure microemulsions or emulsions. Attached Figure Description

[0042] Figure 1 The T2 relaxation spectrum of 1 ml crude oil.

[0043] Figure 2 This is a curve showing the relationship between crude oil volume and signal peak area.

[0044] Figure 3 The T2 relaxation spectrum of the middle phase. Detailed Implementation

[0045] The present invention will be further described below with reference to the accompanying drawings and specific examples. However, the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, any variations that fall within the spirit and scope of the present invention as defined and determined by the appended claims are all within the scope of protection.

[0046] Example

[0047] For an existing medium-phase microemulsion with heavy water as the aqueous phase, a method for determining the crude oil content in the emulsion system is as follows:

[0048] (1) T2 relaxation spectra of 1 ml, 2 ml, 3 ml, 4 ml, and 5 ml of formation crude oil, which are identical to the oil phase in the microemulsion, were tested in a nuclear magnetic resonance (NMR) instrument. The T2 spectrum of 1 ml of formation crude oil is shown below. Figure 1 As shown. Using the total area of ​​the signal peak to represent the signal intensity, a curve showing the relationship between crude oil volume V and signal peak area A is plotted, as follows. Figure 2 As shown, fitting the data points to a straight line yields the following relationship:

[0049] A = 1088V (6)

[0050] In the formula: V is the volume of the formation crude oil;

[0051] A represents the peak area of ​​the T2 spectrum of the formation crude oil.

[0052] (2) The microemulsion was equilibrated in a 50℃ oven for 24 hours. The inner diameter of the test tube was measured to be 1.20 cm, and the height of the middle phase column was measured to be 1.08 cm. The total volume of the middle phase was calculated to be 1.221 ml. Excess oil phase was removed, and 1 ml of the middle phase of the microemulsion was transferred to a special test tube and placed in an NMR spectroscopy apparatus to test the T2 relaxation spectrum. Figure 3 As shown. The total peak area is 857.677. Substituting it into equation (6), we can calculate that the oil volume contained in 1 ml of the phase is 0.788 ml. Therefore, the total oil volume contained in 1.221 ml of the phase is 0.963 ml.

Claims

1. A method for determining the crude oil content in an emulsion system, comprising the following steps: (1) T2 spectra of formation crude oil with volumes of 1 ml, 2 ml, 3 ml, 4 ml and 5 ml were obtained respectively. The signal intensity was represented by the signal peak area, and the oil phase volume was plotted. and signal peak area From the relationship curve, we obtain the following relationship formula: (1) In the formula: This represents the volume of the oil phase. The peak area of ​​the T2 spectrum; k is the calibration curve coefficient; (2) For different types of emulsion systems, the T2 spectrum of the test phase is scanned using nuclear magnetic resonance technology. The oil phase content of the emulsion system is calculated by the signal peak area. The specific process is as follows: a certain volume of the test phase in the emulsion system is transferred into a special test tube and placed in the nuclear magnetic resonance equipment to test its T2 spectrum. The signal peak area is substituted into formula (1) to obtain the oil phase volume of the test phase, thereby calculating the dispersed oil phase content in the emulsion system. The aqueous phase of the emulsion system is heavy water, and the T2 relaxation signal intensity of the surfactant is negligible.

2. The method for determining the crude oil content in an emulsion system as described in claim 1, characterized in that, The emulsion system is an emulsion: Stir the emulsion thoroughly until homogeneous, measure the inner diameter of the test tube and the height of the emulsion column, and calculate the total volume of the emulsion. Take the volume as The emulsion was transferred into a special test tube and placed in an NMR device to test its T2 spectrum. The signal peak area was then measured. Substitute into equation (1) and calculate. Corresponding oil phase volume The volume of the oil phase dispersed in the emulsion can be calculated using the following formula. : ； In the formula: This represents the volume of emulsion taken during the measurement. This represents the volume of the oil phase dispersed in the emulsion taken during the measurement. This represents the total volume of the emulsion.

3. The method for determining the crude oil content in an emulsion system as described in claim 1, characterized in that, The emulsion system is a lower-phase microemulsion: After the microemulsion has been in equilibrium for a period of time, measure the inner diameter of the test tube and the height of the lower phase liquid column, and calculate the total volume of the lower phase. Remove excess oil phase and take a volume of The lower phase of the microemulsion was transferred into a special test tube and placed in a nuclear magnetic resonance (NMR) instrument to test its T2 spectrum, and the signal peak area was measured. Substitute into equation (1) and calculate. Corresponding oil phase volume The volume of the oil phase dispersed in the lower phase microemulsion is calculated using the following formula. : ； In the formula: This refers to the volume of the lower phase taken during the measurement. This represents the volume of the dispersed oil phase taken during the measurement. This represents the total volume of the lower phase.

4. The method for determining the crude oil content in an emulsion system as described in claim 1, characterized in that, The emulsion system is an upper-phase microemulsion: After the microemulsion has been in equilibrium for a period of time, the inner diameter of the test tube and the height of the upper phase liquid column are measured, and the total volume of the upper phase is calculated. Take the volume as The microemulsion phase was transferred to a special test tube and placed in a nuclear magnetic resonance (NMR) instrument to test its T2 spectrum, and the signal peak area, Substitute into equation (1) and calculate. Corresponding oil phase volume The volume of the oil phase contained in the upper phase microemulsion is calculated using the following formula. : ； In the formula: This refers to the volume of the upper phase taken during the measurement. This represents the volume of oil phase contained in the upper phase sample taken during the measurement. This represents the total volume of the upper phase.

5. The method for determining the crude oil content in an emulsion system as described in claim 1, characterized in that, The emulsion system is a medium-phase microemulsion: After the microemulsion has been in equilibrium for a period of time, the inner diameter of the test tube and the height of the liquid column in the middle phase are measured, and the total volume of the middle phase is calculated. Remove excess oil phase and take a volume of The phase transfer in the microemulsion was transferred into a special test tube, and its T2 spectrum was measured in a nuclear magnetic resonance (NMR) instrument. The signal peak area was then recorded. Substitute into equation (1) and calculate. Corresponding oil phase volume The volume of the oil phase contained in the mid-phase microemulsion is calculated using the following formula. : ； In the formula: This represents the volume of the middle phase taken during the measurement. This represents the volume of dispersed oil phase contained in the middle phase sample taken during the measurement. This represents the total volume of the intermediate phase.

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