阅读说明：本技术 一种超临界二氧化碳泡沫体系及其制备方法与起泡液 (Supercritical carbon dioxide foam system, preparation method thereof and foaming liquid ) 是由 李伟涛 魏发林 熊春明 邵黎明 戴明利 张松 于 2020-03-27 设计创作，主要内容包括：本发明提供一种超临界二氧化碳泡沫体系及其制备方法与起泡液。以超临界二氧化碳泡沫体系用起泡液的质量为100％计,该起泡液包括0.01-1wt％的发泡剂、0.1-3wt％稳泡剂,余量为盐水；其中所述发泡剂为两性表面活性剂、所述稳泡剂为亲水性硅溶胶。超临界二氧化碳泡沫体系包括超临界二氧化碳和上述起泡液。本发明提供的起泡液与超临界二氧化碳作用能够很好地形成超临界二氧化碳泡沫体系,形成的超临界二氧化碳泡沫体系抗盐性能好,发泡性好,在苛刻油藏条件下能够产生丰富的泡沫。(The invention provides a supercritical carbon dioxide foam system, a preparation method thereof and foaming liquid. The foaming liquid for the supercritical carbon dioxide foam system comprises 0.01-1 wt% of foaming agent, 0.1-3 wt% of foam stabilizer and the balance of saline water, wherein the mass of the foaming liquid is 100%; wherein the foaming agent is an amphoteric surfactant, and the foam stabilizer is hydrophilic silica sol. The supercritical carbon dioxide foam system comprises supercritical carbon dioxide and the foaming liquid. The foaming liquid provided by the invention can well form a supercritical carbon dioxide foam system under the action of supercritical carbon dioxide, the formed supercritical carbon dioxide foam system has good salt resistance and good foamability, and abundant foam can be generated under severe oil reservoir conditions.)

1. The foaming liquid for the supercritical carbon dioxide foam system comprises 0.01-1 wt% of foaming agent, 0.1-3 wt% of foam stabilizer and the balance of brine, wherein the mass of the foaming liquid is 100%; the foaming agent is an amphoteric surfactant, and the foam stabilizer is hydrophilic silica sol.

2. The foaming liquid of claim 1, wherein the amphoteric surfactant comprises at least one of tetradecyl hydroxysultaine and hexadecyl hydroxysultaine.

3. The foaming solution according to claim 1, wherein the mass fraction of the active ingredient of the hydrophilic silica sol is 10% to 50%, preferably 30%, based on 100% of the total mass of the hydrophilic silica sol.

4. A foaming liquid as claimed in claim 1 or 3, wherein the particle size of the silica particles in the hydrophilic silica sol is 5-30 μm.

5. Foaming liquid according to claim 1, wherein the brine has a degree of mineralization of 1 x 10⁴mg/L-25×10⁴mg/L。

6. Foaming liquid according to claim 1 or 5, wherein the brine comprises NaCl and CaCl₂。

7. Foaming liquid according to claim 6, wherein the NaCl and CaCl are₂The mass ratio is 5:1-10:1, preferably 9: 1.

8. Foaming liquid according to claim 6 or 7, wherein the foaming liquid comprises a foaming agent, a foam stabilizer, NaCl, CaCl₂The mass ratio of the water to the water is (0.1-1): 0.01-0.1): 1.8-22.5): 0.2-2.5): 100.

9. A supercritical carbon dioxide foam system, wherein the system comprises supercritical carbon dioxide and a foaming fluid as claimed in any one of claims 1 to 8.

10. A method of preparing the supercritical carbon dioxide foam system of claim 9, wherein the method comprises:

introducing carbon dioxide into the high-temperature high-pressure reactor filled with the bubble liquid, and stirring at 60-120 ℃ and 7.5-15MPa to obtain the supercritical carbon dioxide foam system;

preferably, stirring is carried out at 70 ℃ and under the condition of 8 MPa;

preferably, the stirring speed is 500-;

preferably, the stirring time is 3-10min, more preferably 5 min.

Technical Field

The invention belongs to the technical field of oil and gas field development and oil extraction, and particularly relates to a supercritical carbon dioxide foam system suitable for a high-salinity oil reservoir, a preparation method of the supercritical carbon dioxide foam system, and foaming liquid for the supercritical carbon dioxide foam system.

Background

In China, high-temperature high-salinity low-permeability oil reservoirs are gradually developed along with the continuous reduction of yield-increasing potential of old oil fields. Under the condition of an oil reservoir, the supercritical carbon dioxide has high-efficiency oil displacement effects of viscosity reduction, expansion and energy increase, interface tension reduction and the like, and gradually becomes an important technical means for low-permeability oil reservoir development. And CO₂The oil displacement also becomes CCUS (CO)₂Capture, utilization, and sequestration) technology, can realize CO recovery while underground₂And (7) burying.

However, in the supercritical carbon dioxide flooding process, due to the characteristics of small gas density, low viscosity, stratum heterogeneity and the like, problems of gas channeling, overlaying, viscous fingering and the like often occur, so that the gas flooding efficiency is low, and the effect of improving the recovery ratio is poor. Therefore, to expand the gas flooding spread, supercritical CO₂Foams have developed into an important technological means of reducing the fluidity of carbon dioxide. The conventional carbon dioxide foam has poor foaming performance and low stability under the condition of high salt, so that the foam flooding effect is reduced. For example, the commonly used anionic surfactant Sodium Dodecyl Sulfate (SDS) precipitates when it encounters inorganic salts, and the cationic surfactant cetyltrimethylammonium bromide (CTAB) has a high absorption loss in formation rock, which all contribute to poor foam properties. In order to improve the foam stability, a method of adding a polymer, inorganic particles, or the like to a foaming agent is generally employed. Although the methods can improve the foam stability, under the oil reservoir conditions of high temperature, high salinity and high pressure, the polymer is easy to degrade, the inorganic particles are easy to adsorb and settle, and finally the foam stabilizing effect is poor. For example, CN 102746841a discloses a composite bubble with added nanoparticles for oil and gas fieldA foam system and a method for preparing the same. The composite foam system consists of anionic surfactant and hydrophobically modified silica nanoparticles, and although the composite system improves foam stability under indoor conditions, the composite foam system is especially Ca-modified under high-salt reservoir conditions²⁺、Mg²⁺Under the condition of higher content, the anionic surfactant and the nano particles can be precipitated, so that the underground foaming effect is poor.

Disclosure of Invention

The invention aims to provide a foaming liquid for a supercritical carbon dioxide foam system, which is suitable for a high-salinity oil reservoir. The foaming liquid and the supercritical carbon dioxide act to form a supercritical carbon dioxide foam system. The formed supercritical carbon dioxide foam system has good salt resistance and good foamability, and can generate abundant foam under severe oil reservoir conditions.

In order to achieve the above object, the present invention provides a foaming liquid for a supercritical carbon dioxide foam system, wherein the foaming liquid comprises 0.01-1 wt% of a foaming agent, 0.1-3 wt% of a foam stabilizer, and the balance of brine, based on 100% of the mass of the foaming liquid; the foaming agent is an amphoteric surfactant, and the foam stabilizer is hydrophilic silica sol.

In the foaming liquid for the supercritical carbon dioxide foam system, the foam stabilizer hydrophilic silica sol is an aqueous solution of nano silica particles, can be well dispersed in an aqueous solution of the two-type surfactant, plays an excellent foam stabilizing role in the aqueous solution of the two-type surfactant, and forms the foaming liquid for the supercritical carbon dioxide foam system in a saline water system together with the amphoteric surfactant.

In the foaming liquid for a supercritical carbon dioxide foam system described above, preferably, the amphoteric surfactant includes at least one of tetradecyl hydroxysultaine and hexadecyl hydroxysultaine.

In the foaming liquid for a supercritical carbon dioxide foam system, the mass fraction of the active ingredient of the hydrophilic silica sol is preferably 10% to 50% based on 100% of the total mass of the hydrophilic silica sol, and more preferably the mass fraction of the active ingredient of the hydrophilic silica sol is 30% based on 100% of the total mass of the hydrophilic silica sol.

In the foaming liquid for a supercritical carbon dioxide foam system, preferably, the particle size of the silica particles in the hydrophilic silica sol is 5 to 30 μm.

In the foaming liquid for the supercritical carbon dioxide foam system, preferably, the salinity of the brine is 1 × 10⁴mg/L-25×10⁴mg/L。

In the above-mentioned foaming liquid for supercritical carbon dioxide foam system, preferably, the brine contains NaCl and CaCl₂(ii) a More preferably, the NaCl and CaCl₂The mass ratio is 5:1-10: 1; further preferably, the NaCl and CaCl are₂The mass ratio is 9: 1.

In a specific embodiment, the foaming liquid contains a foaming agent, a foam stabilizer, NaCl, CaCl₂The mass ratio of the water to the water is (0.1-1): 0.01-0.1): 1.8-22.5): 0.2-2.5): 100.

In a specific embodiment, the foaming liquid contains a foaming agent, a foam stabilizer, NaCl, CaCl₂The mass ratio of the water to the water is (0.1-1): 0.01-0.1):1.8:0.2: 100.

In a specific embodiment, the foaming liquid contains a foaming agent, a foam stabilizer, NaCl, CaCl₂The mass ratio of the water to the water is (0.1-1): 0.01-0.1):4.5:0.5: 100.

In a specific embodiment, the foaming liquid contains a foaming agent, a foam stabilizer, NaCl, CaCl₂The mass ratio of the water to the water is (0.1-1): 0.01-0.1):9:1: 100.

In a specific embodiment, the foaming liquid contains a foaming agent, a foam stabilizer, NaCl, CaCl₂The mass ratio of the water to the water is (0.1-1): 0.01-0.1):13.5:1.5: 100.

In a specific embodiment, the foaming liquid contains a foaming agent, a foam stabilizer, NaCl, CaCl₂The mass ratio of the water to the water is (0.1-1): 0.01-0.1):18:2: 100.

In a specific embodiment, the foaming liquid contains a foaming agent, a foam stabilizer, NaCl, CaCl₂The mass ratio of the water to the water is (0.1-1): (0.01-0.1):22.5:2.5: 100.

In a specific embodiment, the foaming liquid contains a foaming agent, a foam stabilizer, NaCl, CaCl₂The mass ratio of the water to the water is (0.1-1): 0.01-0.1):9:1: 100.

The invention also provides a preparation method of the foaming liquid for the supercritical carbon dioxide foam system, wherein the method comprises the following steps:

preparing saline water, adding a foaming agent and a foam stabilizer into the saline water, and mixing (which can be performed by adopting a magnetic stirring mode) to obtain the foaming liquid for the supercritical carbon dioxide foam system.

The invention also provides a supercritical carbon dioxide foam system, wherein the system comprises supercritical carbon dioxide and the foaming liquid.

The invention also provides a preparation method of the supercritical carbon dioxide foam system, wherein the preparation method comprises the following steps: introducing carbon dioxide into the high-temperature high-pressure reactor filled with the bubble liquid, and stirring at 60-120 ℃ and 7.5-15MPa (preferably 70 ℃ and 8MPa) to obtain the supercritical carbon dioxide foam system.

In the above method for preparing a supercritical carbon dioxide foam system, the stirring speed is preferably 500-3000r/min, and more preferably 2000 r/min.

In the above preparation method of the supercritical carbon dioxide foam system, preferably, the stirring time is 3-10 min; more preferably, the stirring time is 5 min.

The foaming agent adopted by the foaming liquid for the supercritical carbon dioxide foam system provided by the invention is an amphoteric surfactant, and CO is generated in a high-pressure environment₂The aqueous solution is acidic, and with the increase of the mineralization degree, the salt ions can shield the action repulsion force between the amphoteric surfactants and increase the adsorption of the surfactants on a gas-liquid interface, thereby enhancing the stability of the liquid film. The foam stabilizer is hydrophilic silica sol which is easily dispersed in water and has good compatibility with a surfactant, and nano particles in the silica sol can be directionally adsorbed on a gas-liquid interface to fill gaps left by the surfactant on the interface, so that the compactness and the foam stability of a liquid film are improved; and the silica sol is negatively chargedThe carbon dioxide-containing silica sol has the beneficial effects that the carbon dioxide-containing silica sol can generate repulsion with salt ions, and the adsorption of nano particles in the silica sol on a gas-liquid interface can be improved along with the increase of the mineralization degree, so that the carbon dioxide-containing silica sol and a foaming agent can play a synergistic effect, and the application effect of the supercritical carbon dioxide foam system under severe oil reservoir conditions is greatly improved.

According to the supercritical carbon dioxide foam system provided by the invention, the foaming liquid containing the amphoteric surfactant, the hydrophilic silica sol and the saline water and the supercritical carbon dioxide are adopted to form the supercritical carbon dioxide foam system, and under the coordination of the amphoteric surfactant and the hydrophilic silica sol, the formed supercritical carbon dioxide foam system can show excellent foaming capacity and foam stability (the stability shows good shear stability, longer half-life period and the like) under the condition of high mineralization degree, has good salt resistance, and can be suitable for high-mineralization-degree oil reservoirs.

Drawings

FIG. 1 shows an apparatus for preparing a high temperature and high pressure supercritical carbon dioxide foam system used in example 1.

Figure 2 is a graph of the viscosity versus the supercritical carbon dioxide foam system at different shear rates provided in examples 19-24.

Detailed Description

The technical solutions of the present invention will be described in detail below in order to clearly understand the technical features, objects, and advantages of the present invention, but the present invention is not limited to the practical scope of the present invention.

Description of terms:

supercritical carbon dioxide is carbon dioxide at an ambient temperature and pressure above the critical point (31 ℃, 7.38 MPa).

Example 1

The embodiment provides a foaming liquid for a supercritical carbon dioxide foam system, wherein the foaming liquid comprises 0.1g of tetradecyl dimethyl betaine, 0.01g of hydrophilic silica sol (the mass fraction of active ingredients of the hydrophilic silica sol is 30%, and the particle size of silica particles in the hydrophilic silica sol is 5-30 μm) and saline; wherein the brine comprises 1.8g NaCl, 0.2g CaCl₂The mass was 100mL of water.

The foaming liquid for the supercritical carbon dioxide foam system is prepared by the following preparation method:

adding NaC and CaCl₂Mixing with water to prepare saline, then adding tetradecyl dimethyl betaine and hydrophilic silica sol into the saline, and magnetically stirring for 10-15min to obtain the foaming liquid for the supercritical carbon dioxide foam system.

The embodiment also provides a supercritical carbon dioxide foam system, wherein the system comprises supercritical carbon dioxide and the foaming liquid provided by the embodiment.

The supercritical carbon dioxide foam system is prepared by a preparation method, wherein,

the preparation method adopts a device shown in figure 1 for preparation, the device comprises a carbon dioxide gas cylinder, an intermediate container and a visual reaction kettle which are connected in sequence, wherein the visual reaction kettle is a high-temperature high-pressure reaction kettle, the reaction kettle is provided with a liquid inlet for conveying foaming liquid and an exhaust port for exhausting, and the reaction kettle controls the stirring speed, the temperature and the pressure through a computer;

the preparation method comprises the following steps: 100mL of foaming liquid provided by the embodiment is input into a visual reaction kettle (with the volume of 600mL), then carbon dioxide is introduced into the visual reaction kettle to enable the pressure of the reaction kettle to reach 5MPa, the temperature is heated to 70 ℃, the pressure is regulated to 8MPa through a vent valve at constant temperature, and after the temperature and the pressure are constant, the supercritical carbon dioxide foam system is obtained by stirring at the speed of 2000r/min for 5 minutes.

The initial foam volume and the decant volume were recorded as a function of time. The lather volume and half-life are determined and are shown in Table 1.

Table 1 examples 1-6 properties of supercritical carbon dioxide foam systems

	Degree of mineralization/104mg·L-1	Bubbling volume/mL	Half life/min
				Example 1	2	560	8.9
Example 2	5	557	9.2
				Example 2	10	550	10.6
Example 4	15	542	12.8
				Example 5	20	540	13.7
Example 6	25	535	16.3

Example 2

This example provides a foaming liquid for a supercritical carbon dioxide foam system, which differs from example 1 only in that the brine of the foaming liquid has a NaCl mass of 4.5g and CaCl₂The mass was 0.5g, and the rest was the same as in example 1.

This example also provides a supercritical carbon dioxide foam system that differs from example 1 only in that the foaming fluid provided in this example was used as the foaming fluid.

The lather volume and half-life measured in this example are shown in Table 1.

Example 3

This example provides a foaming liquid for a supercritical carbon dioxide foam system, which differs from example 1 only in that the brine of the foaming liquid has a NaCl mass of 9g and CaCl₂The mass was 1g, and the rest was the same as in example 1.

This example also provides a supercritical carbon dioxide foam system that differs from example 1 only in that the foaming fluid provided in this example was used as the foaming fluid.

The lather volume and half-life measured in this example are shown in Table 1.

Example 4

This example provides a foaming liquid for a supercritical carbon dioxide foam system, which differs from example 1 only in that the brine of the foaming liquid has a NaCl mass of 13.5g and CaCl₂The mass was 1.5g, and the rest was the same as in example 1.

This example also provides a supercritical carbon dioxide foam system that differs from example 1 only in that the foaming fluid provided in this example was used as the foaming fluid.

The lather volume and half-life measured in this example are shown in Table 1.

Example 5

This example provides a foaming liquid for a supercritical carbon dioxide foam system, which differs from example 1 only in that the brine of the foaming liquid has a NaCl mass of 18g and CaCl₂Mass 2g, others are carried outExample 1 is the same.

This example also provides a supercritical carbon dioxide foam system that differs from example 1 only in that the foaming fluid provided in this example was used as the foaming fluid.

The lather volume and half-life measured in this example are shown in Table 1.

Example 6

This example provides a foaming liquid for a supercritical carbon dioxide foam system, which differs from example 1 only in that the brine of the foaming liquid has a NaCl mass of 22.5g and CaCl₂The mass was 2.5g, and the rest was the same as in example 1.

This example also provides a supercritical carbon dioxide foam system that differs from example 1 only in that the foaming fluid provided in this example was used as the foaming fluid.

The lather volume and half-life measured in this example are shown in Table 1.

As can be seen from Table 1, the foaming volume was substantially 530-560mL with increasing degree of mineralization, and the change was small. However, the half-life increases with increasing degree of mineralization, when the degree of mineralization is from 2X 10⁴The mg/L is increased to 25X 10⁴mg/L, the half-life increased from 8.9min to 16.3min, indicating that the mineralization increased the stability of the foam better.

Example 7

This example provides a foaming liquid for a supercritical carbon dioxide foam system, which is different from example 1 only in that the mass of tetradecyldimethyl betaine in the foaming liquid is 0.5g, the mass of hydrophilic silica sol is 0.05g, and the rest is the same as example 1.

This example also provides a supercritical carbon dioxide foam system that differs from example 1 only in that the foaming fluid provided in this example was used as the foaming fluid.

The lather volume and half-life measured in this example are shown in Table 2.

Table 2 examples 7-12 properties of supercritical carbon dioxide foam systems

Example 8

This example provides a foaming fluid for a supercritical carbon dioxide foam system which differs from example 7 only in that the brine of the foaming fluid has a NaCl mass of 4.5g and CaCl₂The mass was 0.5g, and the rest was the same as in example 7.

This example also provides a supercritical carbon dioxide foam system that differs from example 7 only in that the foaming fluid provided in this example was used as the foaming fluid.

The lather volume and half-life measured in this example are shown in Table 2.

Example 9

This example provides a foaming liquid for a supercritical carbon dioxide foam system, which differs from example 7 only in that the brine of the foaming liquid has a NaCl mass of 9g and CaCl₂The mass was 1g, and the rest was the same as in example 7.

This example also provides a supercritical carbon dioxide foam system that differs from example 7 only in that the foaming fluid provided in this example was used as the foaming fluid.

The lather volume and half-life measured in this example are shown in Table 2.

Example 10

This example provides a foaming liquid for a supercritical carbon dioxide foam system, which differs from example 7 only in that the brine of the foaming liquid has a NaCl mass of 13.5g and CaCl₂The mass was 1.5g, and the rest was the same as in example 7.

This example also provides a supercritical carbon dioxide foam system that differs from example 7 only in that the foaming fluid provided in this example was used as the foaming fluid.

The lather volume and half-life measured in this example are shown in Table 2.

Example 11

This embodiment provides a superFoaming liquid for critical carbon dioxide foam system, which is different from example 7 only in that the brine of the foaming liquid has NaCl mass of 18g and CaCl₂The mass was 2g, and the rest was the same as in example 7.

This example also provides a supercritical carbon dioxide foam system that differs from example 7 only in that the foaming fluid provided in this example was used as the foaming fluid.

The lather volume and half-life measured in this example are shown in Table 2.

Example 12

This example provides a foaming liquid for a supercritical carbon dioxide foam system, which differs from example 7 only in that the brine of the foaming liquid has a NaCl mass of 22.5g and CaCl₂The mass was 2.5g, and the rest was the same as in example 7.

This example also provides a supercritical carbon dioxide foam system that differs from example 7 only in that the foaming fluid provided in this example was used as the foaming fluid.

The lather volume and half-life measured in this example are shown in Table 2.

As can be seen from Table 2, the foaming volume was substantially 520-550mL with little change as the degree of mineralization increased. However, the half-life increases with increasing degree of mineralization, when the degree of mineralization is from 2X 10⁴The mg/L is increased to 25X 10⁴mg/L, half-life increased from 22.2min to 35.2min, indicating better stability of the mineralization increasing foam.

Example 13

This example provides a foaming liquid for a supercritical carbon dioxide foam system, which is different from example 1 only in that the mass of tetradecyldimethyl betaine in the foaming liquid is 1g, the mass of hydrophilic silica sol is 0.1g, and the other steps are the same as example 1.

This example also provides a supercritical carbon dioxide foam system that differs from example 1 only in that the foaming fluid provided in this example was used as the foaming fluid.

The lather volume and half-life measured in this example are shown in Table 3.

Table 3 examples 13-18 properties of supercritical carbon dioxide foam systems

	Degree of mineralization/104mg·L-1	Bubbling volume/mL	Half life/min
				Example 13	2	540	28.8
Example 14	5	536	29.3
				Example 15	10	531	30.8
Example 16	15	527	36.7
				Example 17	20	523	38.2
Example 18	25	510	40.5

Example 14

This example provides a foaming fluid for a supercritical carbon dioxide foam system which differs from example 13 only in that the brine of the foaming fluid has a NaCl mass of 4.5g and CaCl₂The mass was 0.5g, and the rest was the same as in example 13.

This example also provides a supercritical carbon dioxide foam system that differs from example 13 only in that the foaming fluid provided in this example was used as the foaming fluid.

The lather volume and half-life measured in this example are shown in Table 3.

Example 15

This example provides a foaming liquid for a supercritical carbon dioxide foam system, which differs from example 13 only in that the brine of the foaming liquid has a NaCl mass of 9g and CaCl₂The mass was 1g, and the rest was the same as in example 13.

This example also provides a supercritical carbon dioxide foam system that differs from example 13 only in that the foaming fluid provided in this example was used as the foaming fluid.

The lather volume and half-life measured in this example are shown in Table 3.

Example 16

This example provides a foaming liquid for a supercritical carbon dioxide foam system, which differs from example 13 only in that the brine of the foaming liquid has a NaCl mass of 13.5g and CaCl₂The mass was 1.5g, and the rest was the same as in example 13.

This example also provides a supercritical carbon dioxide foam system that differs from example 13 only in that the foaming fluid provided in this example was used as the foaming fluid.

The lather volume and half-life measured in this example are shown in Table 3.

Example 17

This example provides a foaming liquid for a supercritical carbon dioxide foam system, which differs from example 13 only in that the brine of the foaming liquid has a NaCl mass of 18g and CaCl₂The mass was 2g, and the rest was the same as in example 13.

This example also provides a supercritical carbon dioxide foam system that differs from example 13 only in that the foaming fluid provided in this example was used as the foaming fluid.

The lather volume and half-life measured in this example are shown in Table 3.

Example 18

This example provides a foaming liquid for a supercritical carbon dioxide foam system, which differs from example 13 only in that the brine of the foaming liquid has a NaCl mass of 22.5g and CaCl₂The mass was 2.5g, and the rest was the same as in example 13.

This example also provides a supercritical carbon dioxide foam system that differs from example 13 only in that the foaming fluid provided in this example was used as the foaming fluid.

The lather volume and half-life measured in this example are shown in Table 3.

As can be seen from Table 3, the foaming volume was substantially 520-550mL with little change as the degree of mineralization increased. However, the half-life increases with increasing degree of mineralization, when the degree of mineralization is from 2X 10⁴The mg/L is increased to 25X 10⁴mg/L, half-life increased from 28.8min to 40.5min, indicating better stability of the mineralization increasing foam.

Example 19

The embodiment provides a foaming liquid for a supercritical carbon dioxide foam system, wherein the foaming liquid comprises 0.5g of tetradecyl dimethyl betaine, 0.05g of hydrophilic silica sol (the mass fraction of active ingredients of the hydrophilic silica sol is 30%, and the particle size of silica particles in the hydrophilic silica sol is 5-30 μm) and saline; wherein the brine comprises 1.8g of NaCl and CaCl₂The mass was 0.2g, and the volume of water was 100 mL.

The foaming liquid for the supercritical carbon dioxide foam system is prepared by the following preparation method:

adding NaC and CaCl₂Mixing with water to prepare saline, then adding tetradecyl dimethyl betaine and hydrophilic silica sol into the saline, and magnetically stirring for 10-15min to obtain the foaming liquid for the supercritical carbon dioxide foam system.

The embodiment also provides a supercritical carbon dioxide foam system, wherein the system comprises supercritical carbon dioxide and the foaming liquid provided by the embodiment.

The supercritical carbon dioxide foam system is prepared by a preparation method, wherein,

the preparation method comprises the following steps: under the conditions of 70 ℃ and 8MPa, injecting the carbon dioxide and the foaming liquid gas-liquid ratio for the supercritical carbon dioxide foam system into a capillary (the length of the capillary is 8m, and the inner diameter is 0.5mm) at the total flow rate of 6mL/min, 10mL/min, 15mL/min and 20mL/min respectively according to the ratio of the carbon dioxide to the foaming liquid gas to the supercritical carbon dioxide foam system of 1:1, and obtaining the supercritical carbon dioxide foam system under the conditions of different shear rates.

The viscosity of the supercritical carbon dioxide foam system under different shear rate conditions is calculated by measuring the pressure difference at the two ends of the capillary, and the experimental result is shown in fig. 2.

The conversion relationship between the shear rate and the flow rate is shown in the following equations (1) to (5):

τ＝Kγⁿ (3)

γ_Nfor shear rate, S^-1；τ_NIs a shear stress Pa; n is a flow index and has no dimension; k is a consistency coefficient and has no dimension; v. of_fIs CO₂The section velocity of foam in the capillary tube flow, m/s, D capillary diameter, mm; pressure drop, Pa, across the Δ P capillary; l capillary length, mm; q is flow, mL/min; a is the cross-sectional area of the capillary tube, mm²。

Example 20

This example provides a foaming fluid for a supercritical carbon dioxide foam system which differs from example 19 only in that the brine of the foaming fluid has a NaCl mass of 4.5g and CaCl₂The mass was 0.5g, and the rest was the same as in example 19.

This example also provides a supercritical carbon dioxide foam system that differs from example 19 only in that the foaming fluid provided in this example was used as the foaming fluid.

The viscosities of the supercritical carbon dioxide foam systems at different shear rates measured in this example are shown in figure 2.

Example 21

This example provides a foaming liquid for a supercritical carbon dioxide foam system, which differs from example 19 only in that the brine of the foaming liquid has a NaCl mass of 9g and CaCl₂The mass was 1g, and the rest was the same as in example 19.

This example also provides a supercritical carbon dioxide foam system that differs from example 19 only in that the foaming fluid provided in this example was used as the foaming fluid.

The viscosities of the supercritical carbon dioxide foam systems at different shear rates measured in this example are shown in FIG. 2

Example 22

This example provides a foaming liquid for a supercritical carbon dioxide foam system, which differs from example 19 only in that the brine of the foaming liquid has a NaCl mass of 13.5g and CaCl₂1.5g in mass, the others being equal toExample 19 is the same.

This example also provides a supercritical carbon dioxide foam system that differs from example 19 only in that the foaming fluid provided in this example was used as the foaming fluid.

The viscosities of the supercritical carbon dioxide foam systems at different shear rates measured in this example are shown in figure 2.

Example 23

This example provides a foaming liquid for a supercritical carbon dioxide foam system, which differs from example 19 only in that the brine of the foaming liquid has a NaCl mass of 18g and CaCl₂The mass was 2g, and the rest was the same as in example 19.

This example also provides a supercritical carbon dioxide foam system that differs from example 19 only in that the foaming fluid provided in this example was used as the foaming fluid.

The viscosities of the supercritical carbon dioxide foam systems at different shear rates measured in this example are shown in figure 2.

Example 24

This example provides a foaming liquid for a supercritical carbon dioxide foam system, which differs from example 19 only in that the brine of the foaming liquid has a NaCl mass of 22.5g and CaCl₂The mass was 2.5g, and the rest was the same as in example 19.

This example also provides a supercritical carbon dioxide foam system that differs from example 19 only in that the foaming fluid provided in this example was used as the foaming fluid.

The viscosities of the supercritical carbon dioxide foam systems at different shear rates measured in this example are shown in figure 2.

As can be seen from FIG. 2, under the conditions of different shear rates, the higher the mineralization degree is, the higher the viscosity of the supercritical carbon dioxide foam system is, the more favorable the reduction of the fluidity of the supercritical carbon dioxide is, thereby enlarging the swept volume and improving the oil reservoir recovery ratio. The increase of the mineralization degree can enable the foam to be more stable, the salt ions can shield the action repulsion force between the surface active agents, and the adsorption of the surface active agents on a gas-liquid interface is increased, so that the stability of the liquid film is enhanced.

Example 25

This example provides a foaming liquid for a supercritical carbon dioxide foam system, which is different from example 1 only in that the mass of tetradecyldimethyl betaine in the foaming liquid is 0.5g, the mass of hydrophilic silica sol is 1g, and the other steps are the same as example 1.

This example also provides a supercritical carbon dioxide foam system that differs from example 1 only in that the foaming fluid provided in this example was used as the foaming fluid.

The lather volume and half-life measured in this example are shown in Table 4.

Table 4 examples 25-29 properties of supercritical carbon dioxide foam systems

	Content of hydrophilic silica sol/%)	Bubbling volume/mL	Half life/min
				Example 25	0.02	545	17.2
Example 26	0.04	550	20.3
				Example 27	0.06	540	24.8
Example 28	0.08	535	26.2
				Example 29	0.1	540	28.5

Example 26

This example provides a foaming liquid for a supercritical carbon dioxide foam system, which is different from example 25 only in that the mass of hydrophilic silica sol in the foaming liquid is 2g, and the rest is the same as example 25.

This example also provides a supercritical carbon dioxide foam system that differs from example 25 only in that the foaming fluid provided in this example was used as the foaming fluid.

The lather volume and half-life measured in this example are shown in Table 4.

Example 27

This example provides a foaming liquid for a supercritical carbon dioxide foam system, which is different from example 25 only in that the mass of hydrophilic silica sol in the foaming liquid is 3g, and the other steps are the same as example 25.

This example also provides a supercritical carbon dioxide foam system that differs from example 25 only in that the foaming fluid provided in this example was used as the foaming fluid.

The lather volume and half-life measured in this example are shown in Table 4.

Example 28

This example provides a foaming liquid for a supercritical carbon dioxide foam system, which is different from example 25 only in that the mass of hydrophilic silica sol in the foaming liquid is 4g, and the rest is the same as example 25.

This example also provides a supercritical carbon dioxide foam system that differs from example 25 only in that the foaming fluid provided in this example was used as the foaming fluid.

The lather volume and half-life measured in this example are shown in Table 4.

Example 29

This example provides a foaming liquid for a supercritical carbon dioxide foam system, which is different from example 25 only in that the mass of hydrophilic silica sol in the foaming liquid is 5g, and the other steps are the same as example 25.

This example also provides a supercritical carbon dioxide foam system that differs from example 25 only in that the foaming fluid provided in this example was used as the foaming fluid.

The lather volume and half-life measured in this example are shown in Table 4.

It can be seen from table 4 that the foam volume did not change much with increasing hydrophilic silica sol; when the hydrophilic silica sol is increased from 0.02% to 0.1%, the half-life is increased from 17.2min to 28.5min, which indicates that the hydrophilic silica sol can enhance the stability of the foam.

Although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that: modifications and equivalents may be made thereto without departing from the spirit and scope of the invention and it is intended to cover any modifications or equivalents as may fall within the scope of the invention.