A multiple emulsion with high-precision gas-sensitive fracturing tracing capability, and a preparation method and application thereof

Abstract

The application relates to a multiple emulsion with high-precision gas-sensitive fracturing tracing capability and a preparation method and application thereof, and belongs to the technical field of functional materials. In view of the fact that, in the prior art, there are few reports on the gas-phase tracer in unconventional reservoir fracturing effect evaluation, and there is no W / O / W emulsion with sensitive response characteristics of hydrocarbon gas in a formation reservoir to realize efficient monitoring of the three-phase output of oil, gas and water in a well, a W / O / W type multiple emulsion is prepared by taking a solution with small-molecule gaseous hydrocarbon sensitivity as an oil phase and using modified starch particles to replace traditional small-molecule surfactants as stabilizers to stabilize Pickering emulsion. The multiple emulsion can realize the release of small-molecule rare earth tracing materials in fracturing flowback fluid and underground oil and gas, and further realize efficient monitoring of the three-phase output of oil, gas and water in a well, analysis of the fracture network shape formed by fracturing construction and an oil and gas production layer profile.

Description

Technical Field

[0001] This invention belongs to the field of functional materials technology, specifically relating to a multi-emulsion with high-precision gas-sensitive fracturing tracing capability, its preparation method, and its application. Background Technology

[0002] Currently, the proven reserves of unconventional oil and gas resources such as shale oil and gas and tight oil and gas in China are increasing year by year, and the development demand for natural gas and shale gas is huge. Multi-stage hydraulic fracturing has gradually become a common technical means for the development of such oil fields. Characterizing the fracturing fractures is an important part of the horizontal well fracturing development process. At present, the methods for evaluating the fracturing effect are mostly based on geological data, numerical simulation, and changes in the concentration of a certain ion in the flowback fluid. These methods are mostly empirical or semi-empirical, with poor universality and certain limitations. Fracturing tracer technology, as a fracturing effect evaluation method, can indirectly obtain and analyze the flowback of fracturing fluid in each fracturing segment, the production status of each reservoir at different times, the production profile in the early stage of production, and the production contribution rate of each segment by monitoring the changes in the concentration of tracers in the flowback fluid of each fracturing segment. At the same time, it can quickly and effectively evaluate the effect of fracturing measures, which makes it play an important role in the development of unconventional oil and gas and has great application potential.

[0003] In fracturing tracer technology, tracers mainly include aqueous tracers, oil-phase tracers, and gas-phase tracers. However, there are currently few reports on the evaluation of the fracturing effect of gas-phase tracers in unconventional reservoirs. W / O / W emulsions, as a good carrier for controlled release, have an outermost aqueous phase that not only has good compatibility with the cement slurry system but also acts as a protective layer for the aqueous and oil-phase tracers encapsulated within the inner phase. Therefore, developing a W / O / W emulsion with sensitive response characteristics to hydrocarbon gases in the formation reservoir would increase the polymer network, thereby increasing the tracer release rate and achieving the purpose of information transmission. This would be of great significance for efficient monitoring of downhole oil, gas, and water production, as well as for analyzing the fracture network shape and oil and gas production layer profile formed during fracturing operations. Summary of the Invention

[0004] To address the limited reports on the evaluation of gaseous tracers in unconventional reservoir fracturing in existing technologies, and the lack of W / O / W emulsions with sensitive response characteristics to hydrocarbon gases in formation reservoirs, thereby enabling efficient monitoring of downhole oil, gas, and water production, this invention provides a W / O / W type multi-phase emulsion prepared by using a material sensitive to small-molecule gaseous hydrocarbons as the oil phase and modified starch particles to replace traditional small-molecule surfactants as stabilizers to stabilize the Pickering emulsion. This emulsion enables the release of small-molecule rare earth tracers in fracturing flowback fluid and downhole oil and gas, facilitating efficient monitoring of downhole oil, gas, and water production, as well as analysis of fracture network shape and oil and gas production layer profiles formed during fracturing operations.

[0005] To achieve the above-mentioned technical effects, the present invention provides the following technical solution:

[0006] The first objective of this invention is to provide a multiple emulsion with gas-sensitive fracturing tracer capability. The multiple emulsion is a W / O / W emulsion, comprising 70-90% oil phase and 10-30% aqueous phase, based on 100% by weight of the W / O / W emulsion. The oil phase is a stable water-in-oil emulsion, and the aqueous phase is prepared by dispersing solid particle surfactants in water. The water-in-oil emulsion, based on 100% by weight of the water-in-oil emulsion, comprises 40-60% oil phase and 40-60% aqueous phase. The oil phase of the water-in-oil emulsion is made from an oil phase solvent, an oil phase tracer, a rubber-grafted gas-sensitive material, and a nonionic surfactant. The aqueous phase of the water-in-oil emulsion is made from an aqueous phase tracer and water.

[0007] In one embodiment of the present invention, the solid particle surfactant is any one of modified SiO2, modified cellulose, and modified starch.

[0008] In one embodiment of the present invention, the oil phase of the water-in-oil emulsion contains 25% by mass of oil phase tracer, 30% by mass of rubber-grafted gas-sensitive material, and 3%-10% by mass of nonionic surfactant.

[0009] In one embodiment of the present invention, the preparation method of the rubber-grafted gas-sensitive material includes the following steps:

[0010] ① Mix one or more of the following monomers: acrylate monomer, alkyl acrylate monomer, and styrene monomer with a solvent to obtain a monomer solution;

[0011] ②The non-polar or weakly polar rubber particles are swollen in the monomer solution described in step ① to obtain a prepolymer;

[0012] ③ After mixing the prepolymer described in step ② with the release agent, a graft polymerization reaction is carried out under initiation polymerization conditions. The product is dried and pulverized to obtain a rubber-grafted gas-sensitive material.

[0013] In one embodiment of the present invention, the total mass fraction of monomers in the monomer solution in step ① is 20%-40%, and the solvent is any one of benzene, toluene, or xylene.

[0014] In one embodiment of the present invention, the acrylate monomer in step ① may be hexadecyl methacrylate, octadecyl methacrylate, methyl methacrylate, etc.

[0015] In one embodiment of the present invention, the alkyl olefin monomer in step ① may be undecenoic acid or the like.

[0016] In one embodiment of the present invention, the rubber particles in step ② are ethylene propylene rubber particles with a median particle size of 5 mm or isoprene rubber particles with a median particle size of 5 mm, and the swelling time is 6 h.

[0017] In one embodiment of the present invention, after the non-polar or weakly polar rubber particles in step ② are mixed with the monomer solution, the mass fraction of the non-polar or weakly polar rubber particles is 30%.

[0018] In one embodiment of the present invention, the mass ratio of the prepolymer to the release agent in step ③ is 1:1.

[0019] In one embodiment of the present invention, the separating agent in step ③ is silica.

[0020] In one embodiment of the present invention, the polymerization initiation method in step ③ is to perform high-energy electron irradiation at room temperature with an irradiation intensity of 120 kGy.

[0021] In one embodiment of the present invention, the drying conditions in step ③ are vacuum drying at 50°C for 12 hours.

[0022] In one embodiment of the present invention, the oil phase tracer is one or a combination of two or more liquid hydrocarbon compounds.

[0023] In one embodiment of the present invention, the nonionic surfactant is Span 20 or Span 80, or a combination of Span 20 and Span 80.

[0024] In one embodiment of the present invention, the mass fraction of the aqueous tracer in the aqueous phase of the water-in-oil emulsion is 25%; the aqueous tracer is one or a combination of two or more rare earth salt compounds.

[0025] A second objective of this invention is to provide a method for preparing the above-mentioned multiple emulsions, the method comprising the following steps:

[0026] (1) Preparation of water-in-oil emulsion:

[0027] A) The rubber-grafted gas-sensitive material, oil phase tracer, and surfactant are dispersed in toluene as the oil phase;

[0028] B) Dissolve the aqueous tracer in water to form the aqueous phase;

[0029] C) The oil phase described in step A) and the aqueous phase described in step B) are mixed and then homogenized and emulsified to obtain a water-in-oil emulsion;

[0030] (2) Preparation of water-in-oil-in-water emulsions:

[0031] a) Use the water-in-oil emulsion obtained in step (1) as the oil phase;

[0032] b) Solid particles with a water contact angle between 15 and 80° are dispersed in water as surfactants, forming the aqueous phase;

[0033] c) Mix the oil phase described in step a) with the aqueous phase described in step b), and then homogenize and emulsify to obtain a water-in-oil-in-water emulsion.

[0034] In one embodiment of the present invention, the oil phase tracer in step A) has a mass fraction of 25%, the rubber-grafted gas-sensitive material has a mass fraction of 30%, and the surfactant has a mass fraction of 3%-10%.

[0035] In one embodiment of the present invention, the oil phase tracer in step A) is a liquid hydrocarbon compound, specifically a C5 to C16 hydrocarbon compound.

[0036] In one embodiment of the present invention, the surfactant in step A) is Span 20 or Span 80.

[0037] In one embodiment of the present invention, the mass fraction of the aqueous tracer in the aqueous phase in step B) is 25%.

[0038] In one embodiment of the present invention, the aqueous tracer in step B) is a rare earth salt compound, specifically cerium chloride, lanthanum chloride, praseodymium chloride, neodymium chloride, yttrium chloride, samarium chloride, europium chloride, gadolinium chloride, dysprosium chloride, ytterbium chloride, holmium chloride, erbium chloride, or terbium chloride.

[0039] In one embodiment of the present invention, the volume ratio of the oil phase to the water phase in step C) is (4:6)-(6:4).

[0040] In one embodiment of the present invention, the homogenization speed in step C) is 15krpm-20krpm, and the emulsification time is 2min.

[0041] In one embodiment of the present invention, the solid particles in step b) are any one of modified SiO2, modified cellulose, and modified starch.

[0042] In one embodiment of the present invention, the oil phase and the water phase in step c) are mixed at a volume ratio of (9:1) to (7:3).

[0043] The third objective of this invention is to provide the application of the above-mentioned multiple emulsions or the above-mentioned preparation methods in achieving efficient monitoring of downhole oil, gas and water three-phase production, and in analyzing the fracture network shape and oil and gas producing layer profile formed by fracturing operations.

[0044] The beneficial effects of this invention are:

[0045] This invention provides a W / O / W type multiple emulsion prepared by using a solution sensitive to small molecule gaseous hydrocarbons as the oil phase and using modified starch particles to replace traditional small molecule surfactants as surfactants to stabilize Pickering multiple emulsions. The emulsion-type gas-phase fracturing tracer material provided by this invention has good stability. The outermost aqueous phase not only has good compatibility with the cement slurry system, but also acts as a protective layer to protect the aqueous and oil phase tracers encapsulated in the inner phase. When the W / O / W emulsion is transported to a specific location downhole, the polymer network increases based on the responsiveness of the gas-sensitive material to hydrocarbon gases in the formation reservoir, thereby increasing the tracer release rate to achieve the purpose of transmitting information. The inner W / O emulsion has a wide particle size distribution range and exhibits excellent and adjustable tracer release efficiency under this wide particle size distribution. During well construction and shale gas extraction, the tracer particles are transported to the wellhead with the produced fluid, and can be quickly and efficiently monitored for downhole oil, gas and water production using testing instruments, as well as evaluated for fracture network shape in unconventional reservoir fracturing, which can truly and effectively reflect the downhole situation. The emulsion-type gas phase fracturing tracer material provided by this invention can realize the release of small molecule rare earth tracer materials in fracturing flowback fluid and downhole oil and gas, enabling efficient monitoring of downhole oil, gas and water three-phase production, analysis of fracture network shape and oil and gas producing layer profile formed by fracturing construction. Attached Figure Description

[0046] Figure 1 The graph shows the detection results of tracer release efficiency in the emulsions prepared in Examples 1, 4, and 5; where, Figure 1 (a) in the figure shows the detection results of the tracer release efficiency in the emulsion prepared in Example 1. Figure 1 (b) in the figure shows the detection results of the tracer release efficiency in the emulsion prepared in Example 1. Figure 1 (c) in the figure is the detection result of the tracer release efficiency in the emulsion prepared in Example 1. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. It should be understood that the following drawings only illustrate certain embodiments of the invention and should not be considered as limiting the scope. Those skilled in the art can obtain other related drawings based on these drawings without any creative effort.

[0048] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Where specific conditions are not specified in the examples, they should be performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, all materials, reagents, methods, and instruments used are conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0049] Example 1:

[0050] Hexadecyl methacrylate, undecenoic acid, and styrene were dissolved in xylene to prepare a monomer solution with a total monomer concentration of 30 wt%, wherein the mass fraction of hexadecyl methacrylate was 20.0%, the mass fraction of undecenoic acid was 7.0%, the mass fraction of styrene was 3.0%, and the remainder was xylene. Ethylene-propylene rubber particles with a median particle size of 5 mm were subjected to diffusion-controlled swelling in the monomer solution for 6 hours to obtain a prepolymer, wherein the mass fraction of ethylene-propylene rubber particles was 30%. 50 wt% silica was added to the obtained prepolymer, and high-energy electron irradiation (120 kGy) was applied at room temperature to initiate graft polymerization of the monomers inside and on the surface of the rubber particles. The product was then vacuum-dried at 50 °C for 12 hours and pulverized to obtain the rubber-grafted gas-sensitive material. Weigh 25g of the aqueous tracer (neodymium chloride), dissolve it in 75mL of water to obtain the aqueous phase, and use 100mL of toluene solution (containing 25mL of oil tracer (pentane), 30mL of the rubber-grafted gas-sensitive material prepared above, and 5mL of Span 80) as the oil phase. Take 5mL of the aqueous phase and 5mL of the oil phase, mix them, and emulsify them using an IKU Ultra Turrax T18 homogenizer at 15krpm for 120s to obtain a W / O emulsion. Take 8mL of the obtained O / W emulsion as the oil phase, and 2mL of 5wt% modified starch (HBPS) aqueous solution as the aqueous phase. Mix them, and emulsify them using an IKU Ultra Turrax T18 homogenizer at 10krpm for 120s to obtain a W / O / W emulsion.

[0051] Example 2:

[0052] The difference from Example 1 is that, in the process of preparing the rubber-grafted gas-sensitive material, hexadecyl methacrylate, undecenoic acid, and styrene are dissolved in xylene to prepare a monomer solution with a total monomer mass concentration of 20 wt%, wherein the mass fraction of hexadecyl methacrylate is 14.0%, the mass fraction of undecenoic acid is 4.0%, the mass fraction of styrene is 2.0%, and the balance is xylene.

[0053] Example 3:

[0054] The difference from Example 1 is that, in the process of preparing the rubber-grafted gas-sensitive material, hexadecyl methacrylate, undecenoic acid, and styrene are dissolved in xylene to prepare a monomer solution with a total monomer mass concentration of 40 wt%, wherein the mass fraction of hexadecyl methacrylate is 28.0%, the mass fraction of undecenoic acid is 8.0%, the mass fraction of styrene is 4.0%, and the balance is xylene.

[0055] Example 4:

[0056] The difference from Example 1 is that, in the process of preparing the water-in-oil (W / O) emulsion, 4 mL of the aqueous phase and 6 mL of the oil phase were taken, mixed together, and emulsified for 120 s at 15 k rpm using an IKAUltra Turrax T18 homogenizer to obtain the W / O emulsion.

[0057] Example 5:

[0058] The difference from Example 1 is that, in the process of preparing the water-in-oil (W / O) emulsion, 6 mL of the aqueous phase and 4 mL of the oil phase were taken, mixed together, and emulsified for 120 s at 15 k rpm using an IKAUltra Turrax T18 homogenizer to obtain the W / O emulsion.

[0059] Example 6:

[0060] The difference from Example 1 is that, in the preparation of the water-in-oil (W / O) emulsion, 25g of aqueous tracer was weighed, dissolved in 75mL of water to form the aqueous phase, and 100mL of toluene solution (containing 25mL of oil tracer, 30mL of rubber-grafted gas-sensitive material, and 3mL of Span 80) was used as the oil phase. 5mL of the aqueous phase and 5mL of the oil phase were mixed and emulsified for 120s at 15krpm using an IKU Ultra Turrax T18 homogenizer to obtain the W / O emulsion.

[0061] Example 7:

[0062] The difference from Example 1 is that, in the preparation of the water-in-oil (W / O) emulsion, 25g of aqueous tracer was weighed, dissolved in 75mL of water to form the aqueous phase, and 100mL of toluene solution (containing 25mL of oil tracer, 30mL of rubber-grafted gas-sensitive material, and 10mL of Span 80) was used as the oil phase. 5mL of the aqueous phase and 5mL of the oil phase were mixed and emulsified for 120s at 15krpm using an IKU Ultra Turrax T18 homogenizer to obtain the W / O emulsion.

[0063] Example 8:

[0064] The difference from Example 1 is that, in the preparation of the water-in-oil (W / O) emulsion, 25g of aqueous tracer was weighed, dissolved in 75mL of water to form the aqueous phase, and 100mL of toluene solution (containing 25mL of oil tracer, 30mL of rubber-grafted gas-sensitive material, and 5mL of Span 80) was used as the oil phase. 5mL of the aqueous phase and 5mL of the oil phase were mixed and emulsified for 120s at 18krpm using an IKU Ultra Turrax T18 homogenizer to obtain the W / O emulsion.

[0065] Example 9:

[0066] The difference from Example 1 is that, in the preparation of the water-in-oil (W / O) emulsion, 25g of aqueous tracer was weighed, dissolved in 75mL of water to form the aqueous phase, and 100mL of toluene solution (containing 25mL of oil tracer, 30mL of rubber-grafted gas-sensitive material, and 5mL of Span 80) was used as the oil phase. 5mL of the aqueous phase and 5mL of the oil phase were mixed and emulsified for 120s at 20krpm using an IKU Ultra Turrax T18 homogenizer to obtain the W / O emulsion.

[0067] Example 10:

[0068] The difference from Example 1 is that isoprene rubber particles with a median particle size of 5 mm were selected in the process of preparing the rubber-grafted gas-sensitive material.

[0069] Example 11:

[0070] The difference from Example 1 is that, in the process of preparing the rubber-grafted gas-sensitive material, octadecyl acrylate, methyl methacrylate, and styrene are dissolved in xylene to prepare a monomer solution with a total monomer mass concentration of 30 wt%, wherein the mass fraction of octadecyl acrylate is 20.0%, the mass fraction of methyl methacrylate is 7.0%, the mass fraction of styrene is 3.0%, and the remainder is xylene.

[0071] Performance testing:

[0072] (1) Stability test: The multiple emulsions prepared in Examples 1-11 were centrifuged at 4000 rpm for 5 min. The separation height of the multiple emulsions prepared in Examples 1-11 was recorded after centrifugation, and the results are shown in Table 1. As can be seen from Table 1, the emulsions prepared in Examples 1-11 did not separate after centrifugation, indicating that the multiple emulsions prepared in Examples 1-11 all have good stability and can be stored at room temperature for at least one month.

[0073] (2) Particle size test: The droplet size of the W / O emulsions prepared in Examples 1-11 was tested using the light scattering method, and the results are shown in Table 1. As can be seen from Table 1, the droplet size of the W / O emulsion decreased with increasing Span 80 dosage and emulsification rate, demonstrating the adjustability of the emulsion droplets. Different droplet sizes also play a certain auxiliary role in regulating the release rate of the tracer.

[0074] Table 1 shows the stability of the multiple emulsions prepared in Examples 1-11 and the droplet size of the W / O emulsions.

[0075]

[0076] (3) Gas sensitivity test: Take 1.0 g (denoted as M0) of the W / O emulsion prepared in Examples 1-3 above and put it into a sealed container. After sealing, natural gas is added into the container and pressurized for 72 hours. After depressurization, the sample is taken out and weighed (denoted as Me). The swelling ratio of the sample in natural gas is Qq = (Me-M0) / M0 × 100%; the test results are shown in Table 2.

[0077] Table 2. Results of swelling ratio test of W / O emulsions prepared in Examples 1-3 in natural gas.

[0078]

[0079] As shown in Table 2, the W / O emulsions prepared in Examples 1-3 swelled after contact with gas. The larger the swelling ratio, the better the sensitivity to gas response.

[0080] (4) Tracer Release Test: Centrifuge at 10000 rpm for 10 min to break the W / O emulsion (taking Examples 1-3 as examples). Use ICP to test the tracer concentration in the upper and lower oil phases and the aqueous phase, respectively. This concentration is the maximum adsorption capacity of the tracer, C0. Place the above W / O emulsion sample into a sealed container, seal it, add natural gas into the container, maintain the pressurization state for a period of time (record in hours), and use ICP to test the tracer concentration Ce in the upper oil phase and the lower aqueous phase, respectively. Tracer release efficiency = (C0 - C e ) / C0×100%, the test results are as follows Figure 1As shown in Table 3.

[0081] Table 3. Results of tracer release efficiency testing of the W / O emulsions prepared in Examples 1-11

[0082]

[0083] As shown in Table 3, the tracer release efficiency in both the aqueous and oil phases of the W / O emulsions prepared in Examples 1-11 can achieve a relatively ideal effect.

[0084] The test results above show that the emulsion-type gas-phase fracturing tracer material provided by this invention has good stability. The outermost aqueous phase not only has good compatibility with the cement slurry system, but also acts as a protective layer to protect the aqueous and oil phase tracers encapsulated in the inner phase. The inner W / O emulsion has a wide particle size distribution range, and under this wide particle size distribution, it also exhibits excellent and adjustable tracer release efficiency, which can truly and effectively reflect the downhole conditions.

[0085] The embodiments described above are some, but not all, embodiments of the present invention. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A multi-emulsion with gas-sensitive fracturing tracer capability, characterized in that, The multiple emulsions are W / O / W emulsions. Based on 100% by weight, the W / O / W emulsion consists of 70-90% oil phase and 10-30% aqueous phase. The oil phase is a stable water-in-oil emulsion, and the aqueous phase is prepared by dispersing solid particle surfactants in water. The water-in-oil emulsions, based on 100% by weight, consist of 40-60% oil phase and 40-60% aqueous phase. The oil phase of the water-in-oil emulsion is made from an oil phase solvent, an oil phase tracer, a rubber-grafted gas-sensitive material, and a nonionic surfactant. The aqueous phase of the water-in-oil emulsion is made from an aqueous phase tracer and water. The solid particle surfactant is any one of modified SiO2, modified cellulose, or modified starch. The preparation method of the rubber-grafted gas-sensitive material includes the following steps: ① Mix one or more of the following monomers: acrylate monomer, alkyl acrylate monomer, and styrene monomer with a solvent to obtain a monomer solution with a total monomer mass concentration of 20%-40%. ②The non-polar or weakly polar rubber particles are swollen in the monomer solution obtained in step ① to obtain a prepolymer; ③ After mixing the prepolymer obtained in step ② with the release agent, a graft polymerization reaction is carried out under the initiation polymerization conditions. The product is dried and pulverized to obtain the rubber graft gas-sensitive material.

2. The multiple emulsion according to claim 1, characterized in that, In the water-in-oil emulsion, the oil phase tracer has a mass fraction of 25%, the rubber-grafted gas-sensitive material has a mass fraction of 30%, and the nonionic surfactant has a mass fraction of 3%-10%.

3. The multiple emulsion according to claim 1, characterized in that, In the preparation method of the rubber-grafted gas-sensitive material, the solvent in step ① is any one of benzene, toluene, or xylene; and in step ③, the mass ratio of the prepolymer to the release agent is 1:

1.

4. The multiple emulsion according to claim 2, characterized in that, Oil phase tracers are one or more combinations of liquid hydrocarbon compounds.

5. The multiple emulsion according to claim 2, characterized in that, The nonionic surfactant is Span 20 or Span 80, or a combination of Span 20 and Span 80.

6. The multiple emulsion according to claim 1, characterized in that, The mass fraction of the aqueous tracer in the aqueous phase of the water-in-oil emulsion is 25%; the aqueous tracer is one or more rare earth salt compounds.

7. A method for preparing the multiple emulsion according to any one of claims 1-6, characterized in that, The preparation method includes the following steps: (1) Preparation of water-in-oil emulsion: A) The rubber-grafted gas-sensitive material, oil phase tracer, and surfactant are dispersed in toluene as the oil phase; B) Dissolve the aqueous tracer in water to form the aqueous phase; C) The oil phase in step A) and the aqueous phase in step B) are mixed and then homogenized and emulsified to obtain a water-in-oil emulsion; (2) Preparation of water-in-oil-in-water emulsions: a) Use the water-in-oil emulsion obtained in step (1) as the oil phase; b) Solid particles with a water contact angle between 15 and 80° are dispersed in water as surfactants, forming the aqueous phase; c) Mix the oil phase from step a) with the aqueous phase from step b), and then homogenize and emulsify to obtain a water-in-oil-in-water emulsion.

8. The application of the multiple emulsions described in any one of claims 1-6 in achieving efficient monitoring of downhole oil, gas and water three-phase production, and in analyzing the fracture network shape and oil and gas producing layer profile formed during fracturing operations.

Images