CN113237795B - Method for evaluating expansion viscoelastic salt effect of foam liquid film - Google Patents

Abstract

The invention discloses a method for evaluating the expanding viscoelastic salt effect of a foam liquid film, which comprises the following steps: step S10, determining the dynamic surface tension curve of the foam system according to the conventional dynamic surface tension measuring method; step S20, determining the diffusion coefficient of the foam system at the initial adsorption stage according to the dynamic surface tension curve of the foam system; s30, repeating the steps S10-S20 to obtain diffusion coefficients of the foam system at the initial adsorption stage under different salinity; and step S40, evaluating the expanding viscoelastic salt effect of the foam liquid film according to the diffusion coefficient of the foam system at the initial adsorption stage under different salinity. Based on the generation reason of surface expansion viscoelasticity, the method utilizes dynamic surface tension test to replace expansion modulus test to evaluate the influence of salinity on the viscoelasticity of the foam liquid film, greatly reduces the threshold of a test instrument, reduces the experiment cost, and is quick, accurate and reliable.

Description

A method for evaluating the viscoelastic salt effect of foam liquid film expansion

technical field

The invention relates to a method for evaluating the viscoelastic salt effect of foam liquid film expansion, and belongs to the technical field of oil and gas field development.

Background technique

After more than half a century of continuous large-scale development of domestic oil fields, high-quality reserves are scarce. The reserves of heterogeneous and high-salt oil reservoirs widely distributed across the country are increasingly becoming the focus of increasing reserves and production. How to improve their recovery has become our focus. formidable challenges ahead. Foam flooding has the characteristics of gas and liquid double displacement medium, not only has good mobility control ability and certain oil washing ability, but also has higher temperature resistance and salt resistance than ordinary chemical flooding. Therefore, foam flooding is suitable for heterogeneous high-salt oil reservoirs. It has significant technical advantages in development. Numerous studies have shown that the enhanced oil recovery effect of foam flooding is closely related to the stability of foam in the reservoir, which is largely controlled by its liquid film expansion viscoelasticity. Therefore, in order to give full play to the oil displacement potential of foam flooding in high-salt reservoirs, it is necessary to clearly grasp the salt effect of foam liquid film expansion viscoelasticity.

The expansion viscoelasticity of foam liquid films is usually quantitatively characterized by the surface expansion modulus. The surface expansion modulus is the ratio of the change in surface tension to the change in surface area when the surface is subjected to periodic compression and expansion. When the foam liquid film expands, if the surface tension gradient on the nascent surface disappears rapidly, the surface expansion modulus will be small, and the liquid film expansion viscoelasticity will be correspondingly weak. The measurement of surface expansion modulus is divided into Langmuir groove method and droplet (bubble) expansion method. The Langmuir trough method is based on the Langmuir trough, and the compression or expansion of the surface is achieved by the movement of the sliding barrier. The Langmuir groove method can be divided into surface wave method, steady-state method and interfacial tension relaxation method according to the different sliding modes. The droplet (bubble) expansion method is usually performed with a droplet profile analyzer, and the compression or expansion of the surface is achieved by periodically changing the size of the droplet (bubble). The Langmuir cell method and the droplet (bubble) expansion method have their own technical advantages, but both require expensive testing instruments such as interface expansion rheometers, which undoubtedly raises the threshold for researchers to understand the viscoelasticity of foam liquid film expansion. , which seriously restricts the application and development of foam flooding.

SUMMARY OF THE INVENTION

In order to overcome the problems in the prior art, the present invention provides a method for evaluating the viscoelastic salt effect of foam liquid film expansion. The magnitude of the surface tension gradient on the membrane is controlled by the rate of adsorption of the foam system from the bulk to the surface. Since the initial adsorption rate is an order of magnitude higher than the late adsorption rate, it has an absolute control on the magnitude of the surface tension gradient. Therefore, by analyzing the effect of salinity on the initial adsorption rate of the foam system, its effect on the expansion viscoelasticity of the foam liquid film can be obtained, and the initial adsorption rate of the foam system can be obtained by using the dynamic surface tension curve.

The technical scheme provided by the present invention to solve the above-mentioned technical problems is: a method for evaluating the viscoelastic salt effect of foam liquid film expansion, comprising:

Step S10, determine the dynamic surface tension curve of the foam system according to the conventional dynamic surface tension measurement method;

Step S20, determining the diffusion coefficient in the initial stage of adsorption of the foam system according to the dynamic surface tension curve of the foam system;

Step S30, repeating steps S10-S20, to obtain the diffusion coefficient in the initial stage of adsorption of the foam system under different salinities;

Step S40, evaluating the viscoelastic salt effect of foam liquid film expansion according to the diffusion coefficient in the initial stage of adsorption of the foam system under different salinities.

A further technical solution is that the conventional dynamic surface tension decay measurement method is one of a pendant drop method, a drop volume method, and a maximum bubble pressure method.

A further technical solution is that the specific steps of the step S20 are:

Step S21, drawing the relationship curve between the surface tension of the foam system and the square root of time according to the dynamic surface tension curve of the foam system;

Step S22, fitting and calculating the slope of the left straight line segment of the relationship curve between the surface tension of the foam system and the square root of time;

Step S23: Calculate the diffusion coefficient in the initial stage of adsorption of the foam system according to the slope of the straight line segment on the left side of the relationship curve.

A further technical solution is that the calculation formula in the step S23 is:

where c ₀ is the bulk concentration of the surfactant, mol/L; R is the gas constant, 8.314J/(mol·K); T is the absolute temperature, K.

A further technical solution is that, in the step S30, at least two diffusion coefficients at the initial stage of adsorption of the foam system under different salinities are obtained.

A further technical solution is that the evaluation criteria in the step S40 are:

If the diffusion coefficient increases with the increase of salinity, the salt detracts from the expansion viscoelasticity of the foam liquid film;

If the diffusion coefficient decreases with increasing salinity, the salt enhances the expansion viscoelasticity of the foam liquid film.

The present invention has the following beneficial effects:

1. Based on the causes of surface expansion viscoelasticity, the present invention uses dynamic surface tension test instead of expansion modulus test to evaluate the influence of salinity on the viscoelasticity of foam liquid film, which is scientific and reliable;

2. The present invention lowers the instrument threshold of the expansion viscoelasticity evaluation, reduces the experiment cost, and is fast, accurate and reliable;

3. The dynamic surface tension curve involved in the present invention can be completed by using various dynamic surface tension testing instruments, and has the advantages of being simple and easy to popularize.

Description of drawings

Fig. 1 is a graph showing the effect of salinity on the dynamic surface tension of 0.2% AB in Example 1;

Figure 2 is the surface expansion viscoelasticity diagram of 0.2% AB under different salinities in Example 1;

Figure 3 is a graph of the effect of salinity on the dynamic surface tension of 0.2% HH in Example 2;

4 is a graph of the surface expansion viscoelasticity of 0.2% HH at different salinities in Example 2. FIG.

Detailed ways

The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

A method for evaluating the viscoelastic salt effect of foam liquid film expansion of the present invention comprises the following steps:

Step S10, testing the dynamic surface tension curve γ(t)-t of the foam system using conventional dynamic surface tension measurement methods such as the pendant drop method, the drop volume method, and the maximum bubble pressure method;

Step S20, determining the diffusion coefficient in the initial stage of adsorption of the foam system according to the dynamic surface tension curve of the foam system;

Step S21, draw the relationship curve γ(t)-t ^0.5 between the surface tension of the foam system and the square root of time according to the dynamic surface tension curve of the foam system;

Step S22, fitting and calculating the slope of the left straight line segment of the relationship curve γ(t)-t ^0.5 between the surface tension of the foam system and the square root of time;

Step S23, calculating the diffusion coefficient of the foam system in the initial stage of adsorption according to the slope of the left straight line segment of the relationship curve (that is, the straight line segment in the initial stage of adsorption);

where c ₀ is the bulk concentration of the surfactant, mol/L; R is the gas constant, 8.314J/(mol K); T is the absolute temperature, K;

Step S30, repeating steps S10-S20, to obtain the diffusion coefficient in the initial stage of adsorption of the foam system under different salinities;

Step S40, evaluating the influence of salinity on the viscoelasticity of foam liquid film expansion according to the characteristic frequency with the largest value in the bulk-surface diffusion exchange relaxation process of the foam system under different salinities;

If the diffusion coefficient increases with the increase of salinity, the salt detracts from the expansion viscoelasticity of the foam liquid film;

If the diffusion coefficient decreases with increasing salinity, the salt enhances the expansion viscoelasticity of the foam liquid film.

Example 1

A method for evaluating the viscoelastic salt effect of foam liquid film expansion of the present invention comprises the following steps:

Step 1. Measure the dynamic surface tension curve γ(t)-t of the foam system 0.2% AB under 1.2mol/L NaCl, as shown in Figure 1;

Step 2. Draw the γ(t)-t ^0.5 curve of 0.2% AB at two salinities, and fit the slope of the straight line segment in the initial stage of adsorption; calculate the diffusion coefficient D in the early stage of adsorption according to formula (1), and the results are shown in Table 1 shown;

Step 3. Repeat steps 1-2 to obtain the diffusion coefficient D at the initial stage of adsorption of the foam system under 2.4mol/L NaCl, and the results are shown in Table 1;

Table 1

NaCl concentration (mol/L) 1.2 2.4 D(10^-12m²/s) 2.32 3.69

Step 4. According to Table 1, the diffusion coefficient increases with the increase of salinity, which means that the expansion viscoelasticity of the foam liquid film is degraded by the salt.

The surface expansion viscoelasticity of 0.2% AB under 1.2 mol/L and 2.4 mol/L NaCl was measured by the shaking drop method, and the results are shown in Fig. 2 . The figure shows that as salinity increases, the expansion viscoelasticity of the foam liquid film decreases. This conclusion is consistent with that obtained using the test method of the present invention.

Example 2

A method for evaluating the viscoelastic salt effect of foam liquid film expansion of the present invention comprises the following steps:

Step 1. Measure the dynamic surface tension curve γ(t)-t of the foam system 0.2% HH under 2.4mol/L NaCl, as shown in Figure 3;

Step 2. Draw the γ(t)-t ^0.5 curve of 0.2% HH at two salinities, and fit and calculate the slope of the straight line segment in the initial stage of adsorption; calculate the diffusion coefficient D in the early stage of adsorption according to formula (1), and the results are shown in Table 2 shown;

Step 3. Repeat steps 1-2 to obtain the diffusion coefficient D at the initial stage of adsorption of the foam system under 3.6mol/L NaCl, and the results are shown in Table 2;

Table 2

NaCl concentration (mol/L) 2.4 3.6 D(10^-12m²/s) 7.49 4.07

Step 4. According to Table 2, the diffusion coefficient decreases with the increase of salinity, which means that the expansion viscoelasticity of the foam liquid film is enhanced by the salt.

The surface expansion viscoelasticity of 0.2% HH under 2.4mol/L and 3.6mol/L NaCl was measured by the shaking drop method, and the results are shown in Fig. 4 .

The figure shows that as salinity increases, the expansion viscoelasticity of the foam liquid film increases. This conclusion is consistent with that obtained using the test method of the present invention.

The above is not intended to limit the present invention in any form. Although the present invention has been disclosed through the above-mentioned embodiments, it is not intended to limit the present invention. Any person skilled in the art, within the scope of the technical solution of the present invention, The technical content disclosed above can be used to make some changes or modifications to equivalent embodiments of equivalent changes, but any simple modifications and equivalent changes made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention and modification, all still belong to the scope of the technical solution of the present invention.

Claims (2)

1. A method for evaluating the viscoelastic salt effect of foam liquid film expansion is characterized in that, comprising: Step S10, determine the dynamic surface tension curve of the foam system according to the conventional dynamic surface tension measurement method; Step S20, determining the diffusion coefficient in the initial stage of adsorption of the foam system according to the dynamic surface tension curve of the foam system; Step S21, drawing the relationship curve between the surface tension of the foam system and the square root of time according to the dynamic surface tension curve of the foam system; Step S22, fitting and calculating the slope of the left straight line segment of the relationship curve between the surface tension of the foam system and the square root of time; Step S23, calculating the diffusion coefficient in the initial stage of adsorption of the foam system according to the slope of the straight line segment on the left side of the relationship curve;

where c ₀ is the bulk concentration of the surfactant, mol/L; R is the gas constant, 8.314J/(mol K); T is the absolute temperature, K; Step S30, repeating steps S10-S20, to obtain the diffusion coefficient in the initial stage of adsorption of the foam system under different salinities; In the step S30, at least two diffusion coefficients at the initial stage of adsorption of the foam system under different salinities are obtained; Step S40, evaluating the viscoelastic salt effect of foam liquid film expansion according to the diffusion coefficient in the initial stage of adsorption of the foam system under different salinities; If the diffusion coefficient increases with the increase of salinity, the salt detracts from the expansion viscoelasticity of the foam liquid film; If the diffusion coefficient decreases with increasing salinity, the salt enhances the expansion viscoelasticity of the foam liquid film. 2. a kind of method of evaluating foam liquid film expansion viscoelastic salt effect according to claim 1, is characterized in that, described conventional dynamic surface tension decay measuring method is in pendant drop method, drop volume method, maximum bubble pressure method. a kind of.

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