A CO2-responsive gel system suitable for crack regulation and its preparation method and application

Abstract

The present invention belongs to the field of CO2 anti-gas channeling technology, and specifically relates to a CO2 responsive gel system suitable for fracture control, its preparation method, and application. The system comprises the following components and their weight portions: 3-10 parts of a nonionic responsive surfactant, 1-5 parts of a rheology modifier, 0.1-1 parts of a suspending agent, 1-3 parts of an additive, and 80-100 parts of water. The responsive gel system of the present invention has excellent injection performance, gelling properties, and high-temperature stability, and its gel breaks when exposed to oil, causing little damage to the matrix of low-permeability reservoirs. This overcomes the problem that existing plugging materials have limited fracture control capabilities and are prone to damage to the reservoir matrix.

Description

Technical Field

[0001] The present invention belongs to the technical field of CO2 anti-gas channeling, and specifically relates to a CO2 responsive gel system suitable for crack regulation, and a preparation method and application thereof. Background Art

[0002] CO2 flooding technology is an effective way to achieve a win-win situation for both increasing oil production and sequestering carbon, with promising prospects for resourceful utilization of greenhouse gases and improved oil and gas recovery. Reservoir heterogeneity is a key factor affecting the swept volume and gas channeling during CO2 flooding. Gas channeling is the primary factor limiting CO2 flooding effectiveness during this process. The presence of cracks and high-permeability zones in low-permeability reservoirs after fracturing exacerbates reservoir heterogeneity and gas channeling, reducing the swept volume and significantly impacting development effectiveness.

[0003] To block CO2 channeling, currently developed technical means such as injection and production control, gas-water alternation, stratified gas injection, well pattern adjustment and chemical plugging are used to delay gas channeling and improve CO2 sweep efficiency. However, there is no effective control technology for the cracks and high permeability channels existing in low permeability oil reservoirs. CN113321769A discloses a low permeability oil reservoir carbon dioxide non-miscible flooding channeling blocking system and channeling blocking method, wherein the channeling blocking system is made of a gel formed by mixing modified starch, acrylamide, a retarder, a cross-linking agent and water. CN112342006A discloses a contact-responsive gel channeling blocking system for expanding the swept volume of carbon dioxide gas drive, as well as its preparation method and application. The contact-responsive gel channeling blocking system is composed of the following components by mass percentage: 0.3-8.0 wt% of anionic surfactant and 0.1-2.0 wt% of small molecule amine. Summary of the Invention

[0004] To address the aforementioned issues, the present invention provides a CO2-responsive gel system suitable for fracture control, as well as its preparation method and application. The responsive gel system exhibits excellent injection performance, gelling properties, and high-temperature stability. Furthermore, it exhibits minimal damage to the matrix of low-permeability reservoirs due to oil-induced gel breakage. This overcomes the limitations of existing plugging materials, which have limited fracture control capabilities and are susceptible to damage to the reservoir matrix.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a CO2 responsive gel system suitable for crack regulation, comprising the following components and their weight parts: 3-10 parts of nonionic responsive surfactant, 1-5 parts of rheology regulator, 0.1-1 part of suspending agent, 1-3 parts of auxiliary agent, and 80-100 parts of water.

[0007] Furthermore, the nonionic responsive surfactant is one or more of lauric acid diethanolamide, coconut acid diethanolamide, palmitic acid diethanolamide, and oleic acid diethanolamide.

[0008] Furthermore, the rheology regulator is one or both of sodium montmorillonite and calcium montmorillonite.

[0009] Furthermore, the suspending agent is one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, and cellulose acetate butyrate.

[0010] Furthermore, the auxiliary agent is one or more of sodium carbonate, sodium oxalate and sodium sulfate.

[0011] The present invention also provides a method for preparing the CO2-responsive gel system suitable for crack regulation, the method comprising the following steps:

[0012] (I) adding a nonionic responsive surfactant and a rheology modifier to water and stirring until uniformly dispersed to obtain the mixed solution a;

[0013] (II) adding the suspending agent to the mixed solution a and stirring until completely dissolved to obtain the mixed solution b;

[0014] (III) Add the additive to the mixed solution b and stir until it is completely dissolved to obtain a CO2-responsive gel system suitable for crack regulation.

[0015] Furthermore, in step (I), a high-speed emulsifier is used to stir at 10,000 to 20,000 rpm until uniformly dispersed; in step (II), a magnetic stirrer is used to stir at 500 to 1,000 rpm until completely dissolved; and in step (III), a magnetic stirrer is used to stir at 300 to 500 rpm until completely dissolved.

[0016] The present invention also provides the above-mentioned CO2 responsive gel system suitable for crack regulation or the use of the CO2 responsive gel system prepared by the method in plugging cracks and preventing CO2 gas channeling.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] The CO2-responsive gel sealing system provided by the present invention has very low viscosity before encountering CO2 and is easily injected into low-permeability reservoirs, thus having good injection characteristics. After the system is injected into the reservoir, it preferentially enters the reservoir fractures. After the injection is completed, CO2 is then injected. The CO2 reacts with the responsive gel system to increase viscosity and form a gel, sealing the fractures and forcing the CO2 to enter the low-permeability matrix, thereby expanding the CO2 sweep system and improving the recovery rate.

[0019] The present invention uses a nonionic responsive surfactant, which can form worm-like micelles after being protonated by CO2, and is entangled together to form a three-dimensional network structure through mutual cross-linking. At the same time, because the surfactant is positively charged after protonation, it undergoes electrostatic complexation with the negatively charged clay, playing a cross-linking role, further increasing the viscosity of the system. The CO2 responsive gel system of the present invention has the response characteristics of increasing viscosity when encountering CO2 and reducing viscosity when encountering oil. After the system is thickened, the viscosity of the gel is reduced when encountering crude oil, and the cracks provide oil flow channels for the crude oil. Therefore, the CO2 responsive gel system has low damage characteristics to the reservoir.

[0020] Compared to other CO2-responsive gel systems, the gel sealing system provided by the present invention is composed of organic active substances and inorganic particles. After gelation, it has higher strength and toughness, and has a better crack sealing effect. Furthermore, the CO2-responsive gel system provided by the present invention exhibits shear-responsive properties. Under low shear rates, the viscosity of the gel system increases, while under high shear rates, the viscosity decreases. When the shear rate returns to low, the viscosity of the gel system decreases further.

[0021] The preparation method of the CO2 responsive gel system provided by the present invention is simple and easy to operate, and can be prepared and injected online. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The apparent viscosity of CO2-responsive gel crack sealing system A1 changes with shear rate;

[0023] Figure 2 The apparent viscosity of CO2-responsive gel crack sealing system A2 changes with shear rate;

[0024] Figure 3 The apparent viscosity of CO2-responsive gel crack sealing system A3 changes with shear rate;

[0025] Figure 4 The apparent viscosity of CO2-responsive gel crack sealing system D1 changes with shear rate;

[0026] Figure 5 The apparent viscosity of the CO2-responsive gel crack sealing system D2 changes with shear rate. DETAILED DESCRIPTION

[0027] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0028] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and "include" are used in this specification, they indicate the presence of features, steps, operations and combinations thereof.

[0029] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0030] Apparent viscosity of the responsive gel sealing system: The apparent viscosity of the responsive gel system was tested under different shear rate conditions using an Anton Paar rotational rheometer. The greater the apparent viscosity, the better the crack sealing effect of the responsive gel system. Specifically, the shear rate of the Anton Paar rotational rheometer was 0.01s -1 ~100S -1 .

[0031] Channel blocking effect of CO2 responsive gel system: A high-temperature and high-pressure core displacement device was used to test the channel blocking effect of CO2 responsive gel system. The core length used was 10 cm and the crack width was 500 μm.

[0032] Specific testing method: First, use an ISCO pump to inject CO2 into the fractured core to test the pressure; then pour the prepared 500mL CO2-responsive gel system into the intermediate container, inject a certain amount into the fractured core through the ISCO pump, and then inject a certain amount of CO2, and close the valves at both ends of the core; solidify at 50°C, use the ISCO pump to inject CO2 into the fractured core again and test the pressure, and compare the CO2 injection pressure before and after.

[0033] Low-damage characteristics of CO2-responsive gel: First, crude oil is injected into the low-permeability core to test the pressure; then 500 mL of the prepared CO2-responsive gel system is poured into the intermediate container, and a certain amount is injected into the fractured core using an ISCO pump. Then, a certain amount of CO2 is injected, and the valves at both ends of the core are closed; solidification is carried out at 50°C, and crude oil is injected into the low-permeability core again using an ISCO pump to test the pressure.

[0034] Example 1

[0035] A CO2-responsive gel system suitable for crack regulation includes: 3 parts of cocoyl diethanolamide, 1 part of sodium montmorillonite, 0.1 part of carboxymethyl cellulose, 1 part of sodium carbonate, and 100 parts of water.

[0036] The preparation method of the CO2-responsive gel system suitable for crack regulation comprises the following steps:

[0037] (I) adding cocodiethanolamide and sodium montmorillonite to water, and stirring with a high-speed emulsifier at 10,000 rpm until the mixture is uniformly dispersed to obtain the mixed solution a;

[0038] (II) adding carboxymethyl cellulose to the mixed solution a, and stirring with a magnetic stirrer at 500 rpm until completely dissolved to obtain the mixed solution b;

[0039] (III) Sodium carbonate was added to the mixed solution b, and stirred at 300 rpm using a magnetic stirrer until it was completely dissolved to obtain a CO2-responsive gel system A1 suitable for crack regulation.

[0040] First, the effect of shear rate on apparent viscosity was tested before CO2 was introduced into the system, and then the change of apparent viscosity of the system with shear rate was tested after CO2 was introduced into the system. Figure 1 shown.

[0041] Depend on Figure 1 As can be seen, before CO2 was introduced, the system's apparent viscosity was very low, only 1 mPa·s, and as the shear rate increased, the system's viscosity remained essentially unchanged. After CO2 was introduced, when the shear rate was zero (static state), the system responded and the viscosity reached over 800 mPa·s. As the shear rate increased, the apparent viscosity initially remained constant and then gradually decreased, indicating that the system exhibits shear-thinning properties. This property enables deep flooding of CO2-responsive gel systems. The relatively high shear rate near the wellbore reduces the system's viscosity and increases its mobility, allowing the system to migrate deeper into the formation. Far from the wellbore, the shear rate is relatively low, and the system's viscosity increases, meeting the needs of deep CO2 fracture control.

[0042] The sealing ability of the CO2 responsive gel system A1 was tested using a fracture core displacement experiment. Before the injection of the CO2 responsive gel solution, the injection pressure of CO2 in the fracture core was 0.5 kPa. After the injection of the CO2 responsive gel solution, the injection pressure of CO2 in the fracture core was 20 kPa, which was 40 times that before injection. This was mainly because the CO2 responsive gel solution reacted with CO2 to form a higher-strength CO2 responsive gel, which sealed the fracture core.

[0043] The low-damage characteristics of the CO2-responsive gel system A1 were tested using core flooding experiments. The core permeability measured with crude oil before the injection of the CO2-responsive gel system was 200 mD. After the injection of the CO2-responsive gel solution, the core permeability measured with crude oil was 175 mD, and the core damage rate was 12.5%.

[0044] Example 2

[0045] A CO2-responsive gel system suitable for crack regulation includes: 10 parts of lauric acid diethanolamide, 5 parts of sodium montmorillonite, 1 part of hydroxypropyl methylcellulose, 3 parts of sodium oxalate, and 80 parts of water.

[0046] The preparation method of the CO2-responsive gel system suitable for crack regulation comprises the following steps:

[0047] (I) adding lauric acid diethanolamide and sodium montmorillonite to water, and stirring with a high-speed emulsifier at 20,000 rpm until the mixture is uniformly dispersed to obtain the mixed solution a;

[0048] (II) adding hydroxypropyl methylcellulose to the mixed solution a, and stirring with a magnetic stirrer at 1000 rpm until completely dissolved to obtain the mixed solution b;

[0049] (III) Sodium oxalate was added to the mixed solution b, and stirred at 500 rpm using a magnetic stirrer until it was completely dissolved to obtain a CO2-responsive gel system A2 suitable for crack regulation.

[0050] First, the effect of shear rate on apparent viscosity was tested before CO2 was introduced into the system, and then the change of apparent viscosity of the system with shear rate was tested after CO2 was introduced into the system. Figure 2 shown.

[0051] Depend on Figure 2 As can be seen, before CO2 was introduced, the system's apparent viscosity was very low, only 3 (appropriate) mPa·s, and the system's viscosity remained essentially unchanged as the shear rate increased. After CO2 was introduced, when the shear rate was zero (static state), the system responded and the viscosity reached over 700 mPa·s. As the shear rate increased, the apparent viscosity initially remained constant and then gradually decreased, indicating that the system exhibits shear-thinning properties. This property enables deep flooding of CO2-responsive gel systems. The relatively high shear rate near the wellbore reduces the system's viscosity and increases its mobility, allowing the system to migrate deeper into the formation. Far from the wellbore, the shear rate is relatively low, and the system's viscosity increases, meeting the needs of CO2 fracture control deep within the formation.

[0052] The sealing ability of the CO2 responsive gel system A2 was tested using a fracture core displacement experiment. Before the injection of the CO2 responsive gel solution, the injection pressure of CO2 in the fracture core was 0.5 kPa. After the injection of the CO2 responsive gel solution, the injection pressure of CO2 in the fracture core was 15 kPa, which was 30 times that before injection. This was mainly because the CO2 responsive gel solution reacted with CO2 to form a higher-strength CO2 responsive gel, which sealed the fracture core.

[0053] The low-damage characteristics of the CO2-responsive gel system A2 were tested using core displacement experiments. The core permeability measured with crude oil before the injection of the CO2-responsive gel system was 232 mD. After the injection of the CO2-responsive gel solution, the core permeability measured with crude oil was 206 mD, and the core damage rate was 11.2%.

[0054] Example 3

[0055] A CO2 responsive gel system suitable for crack regulation includes: 5 parts of oleic acid diethanolamide, 3 parts of calcium montmorillonite, 0.5 parts of hydroxypropyl methylcellulose, 2 parts of sodium sulfate, and 89.5 parts of water.

[0056] The preparation method of the CO2-responsive gel system suitable for crack regulation comprises the following steps:

[0057] (I) adding oleic acid diethanolamide and calcium montmorillonite to water, and stirring with a high-speed emulsifier at 15,000 rpm until the mixture is uniformly dispersed to obtain the mixed solution a;

[0058] (II) adding hydroxypropyl methylcellulose to the mixed solution a, and stirring with a magnetic stirrer at 800 rpm until completely dissolved to obtain the mixed solution b;

[0059] (III) Sodium sulfate was added to the mixed solution b, and stirred at 400 rpm using a magnetic stirrer until it was completely dissolved to obtain a CO2-responsive gel system A3 suitable for crack regulation.

[0060] First, the effect of shear rate on apparent viscosity was tested before CO2 was introduced into the system, and then the change of apparent viscosity of the system with shear rate was tested after CO2 was introduced into the system. Figure 3 shown.

[0061] Depend on Figure 3 As can be seen, before CO2 was introduced into the system, the apparent viscosity was very low, only 5 (appropriate) mPa·s, and the viscosity remained essentially unchanged as the shear rate increased. After CO2 was introduced, when the shear rate was zero (static state), the system responded and the viscosity reached over 1000 mPa·s. As the shear rate increased, the apparent viscosity initially remained constant and then gradually decreased, indicating that the system exhibits shear-thinning properties. This property enables deep flooding of CO2-responsive gel systems. The relatively high shear rate near the wellbore reduces the system viscosity and increases its mobility, allowing the system to migrate deeper into the formation. Far from the wellbore, the shear rate is relatively low, and the system viscosity increases, meeting the needs of CO2 fracture control deep in the formation.

[0062] The sealing ability of the CO2 responsive gel system A3 was tested using a fracture core displacement experiment. Before the injection of the CO2 responsive gel solution, the injection pressure of CO2 in the fracture core was 0.5 kPa. After the injection of the CO2 responsive gel solution, the injection pressure of CO2 in the fracture core was 25 kPa, which was 50 times that before injection. This was mainly because the CO2 responsive gel solution reacted with CO2 to form a higher-strength CO2 responsive gel, which sealed the fracture core.

[0063] The low-damage characteristics of the CO2-responsive gel system A3 were tested using core flooding experiments. The core permeability measured with crude oil before the injection of the CO2-responsive gel system was 224 mD. After the injection of the CO2-responsive gel solution, the core permeability measured with crude oil was 193 mD, and the core damage rate was 13.8%.

[0064] Comparative Example 1

[0065] A CO2-responsive gel system was prepared using the same formulation and method as in Example 3, except that no rheology modifier was present. The CO2-responsive gel system D1 was prepared, and its apparent viscosity was tested as a function of shear rate.

[0066] Depend on Figure 4 It can be seen that the CO2-responsive gel system without a rheology modifier still responds to CO2 and becomes viscous, and system D1 still exhibits shear-thinning properties, but the system viscosity decreases. After the introduction of CO2, when the shear rate is zero (static state), the system viscosity after the response is only 600 mPa·s. The reduced system viscosity deteriorates the sealing strength of the crack.

[0067] Comparative Example 2

[0068] A CO2-responsive gel system was prepared using the same formulation and method as in Example 3. However, after the system thickened, 5% kerosene was added and the container was inverted to mix the system. This yielded CO2-responsive gel system D2, and its apparent viscosity was then tested for changes in shear rate.

[0069] Depend on Figure 5 The viscosity of the CO2-responsive gel solution significantly decreased with the addition of 5% kerosene, to only about 10 mPa·s. Furthermore, system D2 no longer exhibited shear-thinning properties, with the viscosity of the system showing little change with shear rate. This property of viscosity reduction upon contact with oil could allow cracks to function as oil flow channels again.

[0070] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A CO2-responsive gel system suitable for crack control, characterized in that: The invention comprises the following components and their weight parts: 3 to 10 parts of nonionic responsive surfactant, 1 to 5 parts of rheology regulator, 0.1 to 1 part of suspending agent, 1 to 3 parts of auxiliary agent, and 80 to 100 parts of water; The nonionic responsive surfactant is one or more of lauric acid diethanolamide, coconut acid diethanolamide, palmitic acid diethanolamide, and oleic acid diethanolamide; The rheology regulator is one or both of sodium montmorillonite and calcium montmorillonite; The suspending agent is one or both of carboxymethyl cellulose and hydroxypropyl methyl cellulose; The auxiliary agent is one or more of sodium carbonate, sodium oxalate and sodium sulfate.

2. The method for preparing the CO2-responsive gel system suitable for crack regulation according to claim 1, characterized in that: The following steps are involved: (I) adding a nonionic responsive surfactant and a rheology modifier to water and stirring until uniformly dispersed to obtain a mixed solution a; (II) adding the suspending agent to the mixed solution a and stirring until completely dissolved to obtain the mixed solution b; (III) Add the additive to the mixed solution b and stir until it is completely dissolved to obtain a CO2-responsive gel system suitable for crack control.

3. The method for preparing the CO2-responsive gel system suitable for crack control according to claim 2, characterized in that: In step (I), a high-speed emulsifier is used to stir at 10,000 to 20,000 rpm until the mixture is uniformly dispersed; in step (II), a magnetic stirrer is used to stir at 500 to 1,000 rpm until the mixture is completely dissolved; and in step (III), a magnetic stirrer is used to stir at 300 to 500 rpm until the mixture is completely dissolved.

4. Use of the CO2 responsive gel system suitable for crack regulation according to claim 1 or the CO2 responsive gel system prepared by the method according to any one of claims 2-3 in plugging cracks to prevent CO2 gas channeling.

Images