A foam composition, viscoelastic foam system for acid gas switch, and method and application for enhanced oil recovery using the same

Abstract

The application discloses a foaming agent composition, a viscoelastic foam system of an acid gas switch, and a method and application for improving recovery efficiency. The foaming agent composition comprises a pH switch surfactant and a hydrocarbon-based anion surfactant; the pH switch surfactant is at least one of long-chain hydrocarbon-based amines. When the viscoelastic foam system comprising the foaming agent composition of the application meets acid gas, the pH switch surfactant and the hydrocarbon-based anion surfactant interact to enhance, the viscosity increases, the formed foam has better stability and plugging performance, the apparent viscosity of the foam formed in a core when the viscoelastic foam system is injected at 1.0 pV is greater than or equal to 270 mPa.s, the recovery efficiency can be improved by more than 20%, and the long-chain hydrocarbon-based amines improve the salt tolerance of a single anion, so that the salinity application range of the system is increased to 10-200 g / L.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of enhanced oil recovery, in particular to a foaming agent composition, a viscoelastic foam system of acid gas switch and a method for improving recovery efficiency and application thereof. BACKGROUND

[0002] Foam is a dispersion system formed by insoluble or slightly soluble gas dispersed in liquid phase. The gas in the foam for enhanced oil recovery is usually steam, nitrogen, natural gas or CO2, and the liquid phase is usually aqueous solution. Foam belongs to a thermodynamically unstable system. After the formation of foam, the liquid is continuously separated due to gravity and capillary force, the liquid film is thinned, and the separation pressure and viscosity between liquid films delay the thinning of the liquid film. At the same time of thinning of the liquid film, the gas also diffuses through the liquid film from small bubbles to large bubbles, so that the small bubbles become smaller and smaller until disappear, and the large bubbles become larger and larger until break.

[0003] Foreign countries have carried out technical research on foam controlling gas mobility since the 1970s. Anionic surfactant sodium alpha-olefin sulfonate is most commonly used because of the repulsion between anions, which enhances the separation pressure of liquid film, so that the foam is not easy to thin and break. The disadvantage of sodium alpha-olefin sulfonate as a foaming agent is that the anion charge repulsion between molecules is low, the saturated adsorption amount is low, the CMC in aqueous solution is as high as several hundred to several thousand mg / L, the dilution resistance is poor, the ability to resist calcium, magnesium and other multivalent ions is insufficient, and the calcium ion concentration of 200 mg / L can easily precipitate, and the foaming and foam stability ability decreases sharply.

[0004] In order to improve the salt tolerance of the system, anionic surfactants such as alkyl polyether ammonium sulfate and alkyl polyether carboxylate are often used. However, when CO2 and other acid gases are used as gas sources, the dissolution in aqueous solution greatly reduces the pH, the carboxylate is easy to form carboxylic acid, which affects its solubility in aqueous solution, the ammonium sulfate salt hydrolyzes, and the structural stability is reduced under acidic conditions.

[0005] Therefore, there is a need for a foaming agent suitable for acid gas conditions. SUMMARY

[0006] To solve the problems in the prior art, the present application provides a foaming agent composition, a viscoelastic foam system of an acid gas switch and a method and application for enhancing oil recovery by using the same. The foaming agent composition of the present application comprises a pH switch surfactant and a hydrocarbon-based anionic surfactant; the pH switch surfactant is at least one of long-chain hydrocarbon-based amines. The viscoelastic foam system of the present application comprises the foaming agent composition and water. The present application designs a method for enhancing oil recovery by using a viscoelastic foam system of an acid gas switch, taking advantage of the pH adjustment characteristics of acid gas, and taking the disadvantageous factors as the dominant factors, so as to achieve the purpose of enhancing oil recovery. Acid gas can improve the interaction of surfactants, so that the injected surfactants have low viscosity under neutral conditions, and after meeting the acid gas, the interaction is enhanced and the viscosity is increased, and the formed foam has better stability and plugging performance.

[0007] One of the purposes of the present application is to provide a foaming agent composition comprising a pH switch surfactant and a hydrocarbon-based anionic surfactant; the pH switch surfactant is at least one of long-chain hydrocarbon-based amines.

[0008] In a preferred embodiment of the present application,

[0009] The pH switch surfactant is at least two of long-chain hydrocarbon-based amines; and / or,

[0010] The structure of the long-chain hydrocarbon-based amine is shown in formula (1):

[0011]

[0012] wherein R1 is selected from C 11 -C 24 fatty hydrocarbon groups, preferably from C 11 -C 20 fatty hydrocarbon groups; R2 is selected from C1-C5 fatty hydrocarbon groups, preferably from C1-C3 fatty hydrocarbon groups; R3, R4, R5 are each independently selected from H, C1-C3 fatty hydrocarbon groups or substituted fatty hydrocarbon groups, preferably from H, C1-C3 fatty hydrocarbon groups;

[0013] m+n+p is 0-30, preferably 0-6, wherein m, n, p are each independently any number from 0 to 10, preferably any number from 0 to 2; the any number is preferably any integer; q is 0-2.

[0014] When m, n or p is 0, the corresponding R3, R4 or R5 is directly connected to N.

[0015] In the present application, the term "long-chain hydrocarbon group" refers to a saturated or unsaturated aliphatic hydrocarbon group having 11 or more carbon atoms.

[0016] The long chain hydrocarbyl amine of formula (1) above can be a commercially available product from the prior art. It can also be prepared by reaction methods of the prior art. The method of preparation preferably comprises:

[0017] The fatty acid is reacted with thionyl chloride and N,N-dimethylformamide at 70-100°C for 2-5 hours, excess thionyl chloride is removed under reduced pressure to obtain a fatty acid chloride wherein R1 in the fatty acid is a C 11 -C 24 fatty hydrocarbyl group. The resulting fatty acid chloride is mixed with toluene and a mixture of the desired ratio of amine and pyridine is added dropwise at 60-90°C for 2-5 hours, and after work-up the product of formula (1) is obtained.

[0018] The molar ratio of the fatty acid, thionyl chloride and N,N-dimethylformamide above is 1:1.0-2.0:0.03-0.1, the volume ratio of the fatty acid chloride to toluene is 1:0.5-1.5, and the molar ratio of the fatty acid chloride to amine, pyridine is 1:1-1.5:1-2.5.

[0019] R1 in the fatty acid above is a C 11 -C 24 fatty hydrocarbyl group.

[0020] When there is only one amine group in the amine above, the structure of the amine is and / or,

[0021] When there are more than two amine groups in the amine, the structure of the amine is

[0022] wherein R2 is selected from a C1-C5 fatty hydrocarbyl group; R3, R4, R5 are each independently selected from H, a C1-C3 fatty hydrocarbyl group or a substituted fatty hydrocarbyl group.

[0023] The long chain hydrocarbyl amine obtained by the amidation reaction above:

[0024]

[0025] wherein R1 is selected from a C 11 -C 24 fatty hydrocarbyl group; R2 is selected from a C1-C5 fatty hydrocarbyl group; R3, R4, R5 are each independently selected from H, a C1-C3 fatty hydrocarbyl group or a substituted fatty hydrocarbyl group; m, n and p are each 0.

[0026] When there is only one amine group in the amine in the starting material above, q in formula (1) is 0; when there are more than two amine groups in the amine in the starting material, q in formula (1) is 1-2.

[0027] Further, a preferred embodiment of the long-chain hydrocarbyl amine according to the present application is as follows:

[0028] The product of the above amide reaction, as shown in formula (1), when at least one of R3, R4, R5 is H, can be subjected to an alkoxylation reaction with ethylene oxide (molar ratio of ethylene oxide to the product of formula (1) is 1-30:1) at a reaction temperature of 80-160°C and a pressure of less than 0.60 MPa gauge, to obtain a long-chain hydrocarbyl amine as shown in formula (1) below:

[0029]

[0030] wherein R1 is selected from a C1-C5 aliphatic hydrocarbyl group; R2 is selected from a C1-C5 aliphatic hydrocarbyl group; and R3, R4, R5 are each independently selected from H, a C1-C3 aliphatic hydrocarbyl group or a substituted aliphatic hydrocarbyl group, and at least one is H. 11 ~C 24

[0031] m+n+p is 1-30, and q is 0-2.

[0032] The long-chain hydrocarbyl amine product obtained from the amide reaction of the raw materials and conditions described above, or the long-chain hydrocarbyl amine product obtained from the amide reaction followed by alkoxylation reaction, can be directly used as the pH switch surfactant according to the present application, and applied to the viscoelastic foam system according to the present application.

[0033] In a preferred embodiment of the present application,

[0034] The hydrocarbyl anionic surfactant is at least one of an alkyl carboxylate, an alkyl sulfate, an alkyl sulfonate, and an olefin sulfonate; the number of carbon atoms in the alkyl group is preferably 1-20, more preferably 1-12; the number of carbon atoms in the olefin sulfonate is preferably 10-20; and the olefin sulfonate is preferably an alpha-olefin sulfonate.

[0035] In a preferred embodiment of the present application,

[0036] The mass ratio of the pH switch surfactant to the hydrocarbyl anionic surfactant is 1:0.05-15, preferably 1:0.1-3.

[0037] The second object of the present application is to provide a viscoelastic foam system for acid gas switch, comprising the foam composition according to the first object of the present application. The foam composition according to the present application, as a key component of the viscoelastic foam system, can form a viscoelastic foam under the action of acid gas.

[0038] In a preferred embodiment of the present application,

[0039] ​The viscoelastic foam system further comprises water; and / or,

[0040] The water is mineral-containing water, preferably at least one of tap water, oil and gas field formation injection water, and water oil and gas field injection water, more preferably brine with salinity ranging from 10 to 200 g / L.

[0041] In a preferred embodiment of the present application,

[0042] The pH switch surfactant in the foam composition accounts for 0.2 to 1 wt% of the viscoelastic foam system; preferably 0.3 to 0.6 wt%; and / or,

[0043] The hydrocarbon-based anionic surfactant in the foam composition accounts for 0.05 to 0.3 wt% of the viscoelastic foam system; preferably 0.1 to 0.2 wt%; and / or,

[0044] The foam system can form a solution viscosity of 3 to 30 mPa·s under the action of acid gas; and / or,

[0045] The foam system forms a foam with an apparent viscosity of ≥270 mPa·s in a high-permeability porous medium after injection of 1.0 pV.

[0046] A third object of the present application is to provide a method for preparing the viscoelastic foam system of the second object of the present application.

[0047] The preparation method comprises thoroughly mixing components including the foam composition and water.

[0048] A fourth object of the present application is to provide a method for enhancing oil recovery using the viscoelastic foam system of the second object of the present application or the viscoelastic foam system prepared by the method of the third object of the present application.

[0049] The method comprises:

[0050] The viscoelastic foam system is alternately or jointly injected with acid gas into a porous medium containing crude oil to form a foam in situ in the porous medium, thereby enhancing oil recovery.

[0051] The viscoelastic foam system of the present application forms a viscoelastic foam under the action of acid gas, thereby expanding the sweep efficiency of the displacement phase and further enhancing the recovery of the displaced phase, i.e., crude oil, which can be increased by more than 20%.

[0052] In a preferred embodiment of the present application,

[0053] The acid gas is at least one of CO2 and H2S.

[0054] In a preferred embodiment of the present application,

[0055] The volume ratio of the acid gas to the viscoelastic foam system is 1:0.1-2.

[0056] The fifth object of the present application is to provide an application of the viscoelastic foam system of the second object of the present application or the viscoelastic foam system prepared by the method of the third object of the present application in oil recovery of 10-200 g / L salinity reservoir.

[0057] The present application has the following advantages:

[0058] The present application takes full advantage of the pH improvement of acid gas. The long-chain hydrocarbon-based amine in the foam composition of the present application is converted into a quaternary ammonium with a positive charge under the action of acid gas. The quaternary ammonium and the anionic surfactant have electrostatic attraction, and are easy to form larger micelles, thereby increasing the viscosity of the system.

[0059] The thinning equation of the bubble film is:

[0060]

[0061] In the above equation, μ is the viscosity of the solution, RF is the surface radius of curvature, Cf is the correction factor, and ΔP is the pressure difference between the adjacent P region and the separation pressure.

[0062] As can be seen from the above equation, the increase in viscosity can delay the precipitation of foam from the liquid and stabilize the foam.

[0063] The increase in the viscosity of the liquid film can reduce the diffusion speed of the gas through the liquid film, making the foam more stable.

[0064] At the same time, the long-chain hydrocarbon-based amine in the foam composition improves the salt tolerance of the single anionic surfactant, and the salinity application range of the viscoelastic foam system is increased to 10-200 g / L. DETAILED DESCRIPTION

[0065] The present application will be described in detail below with reference to specific examples. It is necessary to point out here that the following examples are only used to further illustrate the present application and cannot be understood as limiting the protection scope of the present application. Some non-essential improvements and adjustments of the present application made by those skilled in the art based on the content of the present application still fall within the protection scope of the present application.

[0066] The raw materials used in the examples are all conventional commercially available raw materials.

[0067] Example 1

[0068] Preparation of the pH switch surfactant:

[0069] (1) Dodecanoic acid 200 g (1.0 mol), sulfurous dichloride 149 g (1.25 mol) and 3 g (0.04 mol) of N,N-dimethylformamide (DMF) were added into a four-necked flask equipped with a sealed mechanical stirrer, a thermometer and a condenser, and reacted at 90°C for 3 hours. The excess sulfurous dichloride was distilled off under reduced pressure to obtain fatty acid chloride (C 11 H 23 COCl). When the temperature dropped to 60°C, toluene 70 g was added, and after stirring, a mixture of propylenediamine 74 g (1.0 mol) and pyridine 99.0 g (1.25 mol) was slowly added dropwise while controlling the temperature to be less than 60°C. After the dropwise addition was completed, the temperature was raised to 85°C and reacted for 2 hours. After cooling, the crude product was recrystallized from ethanol, and then dried under vacuum to obtain a white powdery solid (the white powdery solid is C 11 H 23 CONHC3H6NH2) with a total yield of 90%.

[0070] (2) A reactor equipped with a condenser, a stirring device and a gas disperser was charged with 128 g (0.5 mol) of the above white powdery solid, heated to 80-90°C, and dehydrated under high vacuum for 1 hour. Then, the system was purged with nitrogen for 3-4 times to remove air in the system, and then the reaction temperature of the system was adjusted to 130°C, and 88 g (2 mol) of ethylene oxide was slowly introduced while controlling the pressure to be <0.60 MPa to perform alkoxylation reaction. After the reaction was completed, the system was purged with nitrogen to remove unreacted ethylene oxide, and then cooled, neutralized, decolorized, filtered, and dehydrated to obtain long-chain hydrocarbyl amine 1A with a yield of 93%.

[0071] Structure of long-chain hydrocarbyl amine 1A:

[0072]

[0073] R1 is C 11 H 23 ; R2 is C3H6; R3, R4 and R5 are H; m+n+p=4, and q=1.

[0074] Long-chain hydrocarbyl amines 1B, 1C and 1D were obtained by replacing the fatty acid raw material with myristic acid, palmitic acid and stearic acid, respectively, and performing reaction according to the above conditions.

[0075] In the structure of long-chain hydrocarbyl amines 1B, 1C and 1D, R1 is C 13 H 27 , C 15 H 31 and C 17 H 35 , respectively, and the other parts are the same as those of long-chain hydrocarbyl amine 1A.

[0076] The pH switch surfactant used in the viscoelastic foam system of Example 1 is a mixture of long-chain hydrocarbon-based amines 1A, 1B, 1C and 1D, with a molar ratio of 0.067:0.059:0.316:0.569.

[0077] Preparation of the viscoelastic foam system:

[0078] At room temperature and normal pressure, 0.5 g of the pH switch surfactant and 0.1 g of sodium decyl sulfonate (TCI) were weighed and added to 100 g of brine with a salinity of 50 g / L to obtain a viscoelastic foam system.

[0079] The viscoelastic foam system was saturated with 0.1 MPa CO2 at room temperature, and the viscosity was tested to be 5 mPa·s.

[0080] Oil displacement experiment of the viscoelastic foam system:

[0081] A simulated core with a permeability of 1 D was saturated with water and then with Shengli crude oil until no water was left. The aged core was then displaced with brine with a salinity of 50 g / L until no crude oil flowed out, and the water displacement recovery was recorded as 51%. Then, the viscoelastic foam system in Example 1 was injected together with CO2, with a volume ratio of CO2 to viscoelastic foam system of 1:2, and the total injection rate of the viscoelastic foam system and CO2 was 2 mL / min. The oil recovery rates of the viscoelastic foam system injected at 0.5 pV and 1.0 pV were 70% and 81%, respectively, with an enhanced oil recovery of 19% and 30%, respectively. The apparent viscosity of the foam formed in the core was 353 mPa·s when the viscoelastic foam system was injected at 1.0 pV.

[0082] Comparative Example 1

[0083] Preparation of the foam system:

[0084] At room temperature and normal pressure, 0.6 g of the pH switch surfactant in Example 1 was weighed and added to 100 g of brine with a salinity of 50 g / L to obtain a foam system.

[0085] The above foam system was saturated with 0.1 MPa CO2 at room temperature, and the viscosity was tested to be close to that of water, both being 1 mPa·s.

[0086] Oil displacement experiment of the foam system:

[0087] The simulated core with permeability of 1 D is saturated with water, then saturated with Shengli crude oil to leave no water, and then placed for 1 month to age the core. The aged core is displaced with brine with salinity of 50 g / L to no oil flow, and the water flooding recovery rate is recorded as 50%. Then, the 0.5% foam system in Comparative Example 1 is co-injected and displaced with CO2, the volume ratio of CO2 to the foam system is 1:2, and the total injection rate of the foam system and CO2 is 2 mL / min. The oil recovery rates displaced by the foam system with injection amount of 0.5 pV and 1.0 pV are 60% and 69% respectively, and the enhanced oil recovery rates are 10% and 19% respectively. When the foam system with injection amount of 1.0 pV is injected, the apparent viscosity of the foam in the core is 30 mPa·s.

[0088] Comparative Example 2

[0089] Preparation of the foam system:

[0090] At normal temperature and pressure, 0.6 g of sodium decyl sulfonate in Example 1 is added into brine with salinity of 50 g / L to obtain a total of 100 g of the foam system after mixing.

[0091] The above foam system is saturated with 0.1 MPa CO2 at normal temperature, and the viscosity is close to that of water, which is 1 mPa·s.

[0092] Foam system oil displacement experiment:

[0093] The simulated core with permeability of 1 D is saturated with water, then saturated with Shengli crude oil to leave no water, and then placed for 1 month to age the core. The aged core is displaced with brine with salinity of 50 g / L to no oil flow, and the water flooding recovery rate is recorded as 51%. Then, the 0.6% foam system in Comparative Example 1 is co-injected and displaced with CO2, the volume ratio of CO2 to the foam system is 1:2, and the total injection rate of the foam system and CO2 is 2 mL / min. The oil recovery rates displaced by the foam system with injection amount of 0.5 pV and 1.0 pV are 53% and 56% respectively, and the enhanced oil recovery rates are 2% and 5% respectively. When the foam system with injection amount of 1.0 pV is injected, the apparent viscosity of the foam in the core is 5 mPa·s.

[0094] Example 2

[0095] The pH switch surfactant structure and preparation process are the same as those in Example 1.

[0096] Preparation of the viscoelastic foam system:

[0097] At normal temperature and pressure, 0.3 g of the pH switch surfactant in Example 1, 0.3 g of sodium ethoxylated alkyl sulfate (Jitong Chemical, model: AES, alkyl carbon atom number C 12 -C 14)0.2g, added to 100g / L salinity brine to make 100g viscoelastic foam system.

[0098] The viscoelastic foam system was saturated with 0.1 MPa CO2 at room temperature, and the viscosity was tested to be 4 mPa-s.

[0099] Viscoelastic foam system oil displacement experiment:

[0100] The simulated core with a permeability of 1D was saturated with water and then with Shengli crude oil until no water was left. The core was then aged for one month. The aged core was displaced with 100g / L salinity brine until no crude oil flowed out, and the water displacement recovery rate was recorded as 47%. Then, the viscoelastic foam system in Example 2 was co-injected with CO2 to displace the crude oil, with a volume ratio of CO2 to viscoelastic foam system of 1:1, and the total injection rate of the viscoelastic foam system and CO2 was 2 mL / min. The oil recovery rates of the viscoelastic foam system injected at 0.5 pV and 1.0 pV were 64% and 75%, respectively, with an enhanced oil recovery rate of 17% and 28%, respectively. The apparent viscosity of the foam formed in the core was 301 mPa-s when the viscoelastic foam system was injected at 1.0 pV.

[0101] Comparative Example 3

[0102] Foam system preparation:

[0103] At room temperature and atmospheric pressure, 0.5g of the sodium ethoxylated alkyl sulfate in Example 2 was added to 100g / L salinity brine to make 100g of the foam system.

[0104] The above foam system was saturated with 0.1 MPa CO2 at room temperature, and the viscosity was tested to be close to that of water, i.e., 1 mPa-s.

[0105] Foam system oil displacement experiment:

[0106] The simulated core with a permeability of 1D was saturated with water and then with Shengli crude oil until no water was left. The core was then aged for one month. The aged core was displaced with 100g / L salinity brine until no crude oil flowed out, and the water displacement recovery rate was recorded as 47%. Then, the viscoelastic foam system in Example 2 was co-injected with CO2 to displace the crude oil, with a volume ratio of CO2 to viscoelastic foam system of 1:1, and the total injection rate of the viscoelastic foam system and CO2 was 2 mL / min. The oil recovery rates of the viscoelastic foam system injected at 0.5 pV and 1.0 pV were 64% and 75%, respectively, with an enhanced oil recovery rate of 17% and 28%, respectively. The apparent viscosity of the foam formed in the core was 301 mPa-s when the viscoelastic foam system was injected at 1.0 pV.

[0107] Example 3

[0108] Preparation of pH switch surfactant:

[0109] (1) Put 200 g (1.0 mol) of lauric acid, 149 g (1.25 mol) of sulfuryl chloride and 3 g (0.04 mol) of N, N-dimethylformamide (DMF) into a four-necked flask equipped with a sealed mechanical stirrer, a thermometer and a condenser, and react at 90°C for 3 hours. Then, evaporate the excess sulfuryl chloride under reduced pressure to obtain fatty acid chloride. When the temperature drops to 60°C, add 70 g of toluene, and then slowly drop a mixture of 144 g (1.0 mol) of N, N'-di-n-propylethylenediamine and 99.0 g (1.25 mol) of pyridine into the mixture while controlling the temperature to be less than 60°C. After the dropping is completed, raise the temperature to 85°C and react for 2 hours. Then, cool, filter, recrystallize the crude product with ethanol, and dry under vacuum to obtain white powdery solid (C 11 H 23 CONHC2H4N(C3H7)2) with a yield of 91%.

[0110] (2) Put 163 g (0.5 mol) of the above reactant into a reactor equipped with a condenser, a stirring device and a gas disperser, heat to 80-90°C, open the vacuum system, and dehydrate under high vacuum for 1 hour. Then, purge the system with nitrogen for 3-4 times to remove air in the system, and then adjust the reaction temperature of the system to 130°C, slowly pass 22 g (0.5 mol) of ethylene oxide, and control the pressure to be less than 0.60 MPa to perform alkoxylation reaction. After the reaction is completed, purge the system with nitrogen to remove unreacted ethylene oxide, and then cool, neutralize, decolorize, filter, and dehydrate to obtain the pH switch surfactant, i.e., long-chain hydrocarbon-based amine 2 (structure is described below) with a yield of 92%.

[0111] Structure of pH switch surfactant:

[0112]

[0113] R1 is C 11 H 23 ; R2 is C2H4; R3 and R4 are C3H7; R5 is H; m = 1, n = 0, p = 0, and q = 1.

[0114] Preparation of viscoelastic foam system:

[0115] At normal temperature and pressure, put 0.6 g of the pH switch surfactant in Example 3 and 0.15 g of sodium acetate into 100 g of salt water with a salinity of 10 g / L to obtain a viscoelastic foam system.

[0116] The viscoelastic foam system is saturated with 0.1 MPa CO2 at normal temperature, and the viscosity of the system can reach 10 mPa·s.

[0117] Viscoelastic foam system oil displacement experiment:

[0118] The simulated core with a permeability of 1 D was saturated with water and then saturated with Shengli crude oil until no water was left. The core was then aged for one month. The aged core was displaced with 10 g / L brine until no crude oil flowed out, and the water displacement recovery rate was recorded as 53%. Then, the viscoelastic foam system in Example 3 was co-injected with CO2 for displacement, the volume ratio of CO2 to the viscoelastic foam system was 1:0.5, and the total injection rate of the viscoelastic foam system and CO2 was 2 mL / min. The oil recovery rates of the viscoelastic foam system injected at 0.5 pV and 1.0 pV were recorded as 67% and 82%, respectively, and the enhanced oil recovery rates were 14% and 29%, respectively. The apparent viscosity of the foam formed in the core when the viscoelastic foam system was injected at 1.0 pV was 307 mPa·s.

[0119] Comparative Example 4

[0120] Preparation of the foam system:

[0121] At room temperature and normal pressure, 0.75 g of the pH switch surfactant in Example 3 was weighed and added to 10 g / L brine to obtain a total of 100 g of the foam system.

[0122] The foam system was saturated with 0.1 MPa CO2 at room temperature, and the viscosity was tested to be 2 mPa·s.

[0123] Foam system oil displacement experiment:

[0124] The simulated core with a permeability of 1 D was saturated with water and then saturated with Shengli crude oil until no water was left. The core was then aged for one month. The aged core was displaced with 10 g / L brine until no crude oil flowed out, and the water displacement recovery rate was recorded as 54%. Then, the foam system in Comparative Example 4 was co-injected with CO2 for displacement, the volume ratio of CO2 to the foam system was 1:0.5, and the total injection rate of the foam system and CO2 was 2 mL / min. The oil recovery rates of the foam system injected at 0.5 pV and 1.0 pV were recorded as 67% and 74%, respectively, and the enhanced oil recovery rates were 13% and 20%, respectively. The apparent viscosity of the foam formed in the core when the foam system was injected at 1.0 pV was 130 mPa·s.

[0125] Comparative Example 5

[0126] Preparation of the foam system:

[0127] At room temperature and normal pressure, 0.75 g of sodium acetate in Example 3 was weighed and added to 10 g / L brine to obtain a total of 100 g of the foam system.

[0128] The viscosity of the above foam system is close to that of water, which is 1 mPa s, after saturated with 0.1 MPa CO2 at room temperature.

[0129] Foam system oil displacement experiment:

[0130] The simulated core with a permeability of 1 D was saturated with water and then with Shengli crude oil until no water was left. The aged core was then displaced with brine with a salinity of 10 g / L until no crude oil was discharged. The water displacement recovery rate was recorded as 48%. Then, the foam system in Comparative Example 5 was co-injected with CO2 for displacement. The volume ratio of CO2 to the foam system was 1:0.5, and the total injection rate of the foam system and CO2 was 2 mL / min. The oil recovery rates of the foam system injection amounts of 0.5 pV and 1.0 pV were recorded as 50% and 52%, respectively, with the enhanced oil recovery rates being 2% and 4%, respectively. The apparent viscosity of the foam formed in the core was 2 mPa s when the foam system was injected at 1.0 pV.

[0131] Example 4

[0132] The pH switch surfactant structure and preparation process were the same as in Example 3.

[0133] Preparation of viscoelastic foam system:

[0134] At room temperature and normal pressure, 0.2 g of the pH switch surfactant in Example 3 and 0.1 g of sodium alpha-alkenyl sulfonate (Zhongqin Chemicals, model: AOS / 92) were weighed and added to 100 g of brine with a salinity of 10 g / L to obtain a viscoelastic foam system.

[0135] The viscosity of the viscoelastic foam system can reach 3 mPa s after saturated with 0.1 MPa CO2 at room temperature.

[0136] Viscoelastic foam system oil displacement experiment:

[0137] The simulated core with a permeability of 1 D was saturated with water and then with Shengli crude oil until no water was left. The aged core was then displaced with brine with a salinity of 10 g / L until no crude oil was discharged. The water displacement recovery rate was recorded as 48%. Then, the foam system in Comparative Example 5 was co-injected with CO2 for displacement. The volume ratio of CO2 to the foam system was 1:0.5, and the total injection rate of the foam system and CO2 was 2 mL / min. The oil recovery rates of the foam system injection amounts of 0.5 pV and 1.0 pV were recorded as 50% and 52%, respectively, with the enhanced oil recovery rates being 2% and 4%, respectively. The apparent viscosity of the foam formed in the core was 2 mPa s when the foam system was injected at 1.0 pV.

[0138] Comparative Example 6

[0139] Preparation of the foam system:

[0140] At room temperature and normal pressure, 0.3 g of the sodium olefin sulfonate in Example 4 was added into 10 g / L salinity brine to obtain a total of 100 g of the foam system after mixing.

[0141] The above foam system was saturated with 0.1 MPa CO2 at room temperature, and the viscosity was close to that of water, being 1 mPa-s.

[0142] Oil displacement experiment of the foam system:

[0143] A simulated core with a permeability of 1 D was saturated with water and then saturated with Shengli crude oil to leave no water, and then the core was aged for one month. The aged core was displaced with 10 g / L salinity brine until no crude oil flowed out, and the water displacement recovery was recorded as 49%. Then the foam system in Comparative Example 6 was co-injected with CO2 for displacement, the volume ratio of CO2 to the foam system was 1:1.5, the total injection rate of the foam system and CO2 was 2 mL / min, and the oil recovery rates of the foam system injection amounts of 0.5 pV and 1.0 pV were 59% and 65%, respectively, the enhanced oil recovery was 10% and 16%, respectively, and the apparent viscosity of the foam formed in the core was 100 mPa-s when the foam system was injected at 1.0 pV.

[0144] Example 5

[0145] Preparation of the pH switch surfactant:

[0146] (1) Eicosanoic acid 312 g (1.0 mol), thionyl chloride 149 g (1.25 mol) and 3 g (0.04 mol) of N,N-dimethylformamide (DMF) were added into a four-necked flask equipped with a sealed mechanical stirrer, a thermometer, and a condenser tube, and reacted at 90°C for 3 hours. The excess thionyl chloride was evaporated under reduced pressure to obtain fatty acid chloride. When the temperature dropped to 60°C, 70 g of toluene was added, and then a mixture of dipropylene triamine 131 g (1.0 mol) and pyridine 99.0 g (1.25 mol) was slowly added dropwise while controlling the temperature to be less than 60°C. After the dropwise addition was completed, the temperature was raised to 85°C and reacted for 2 hours. After cooling, filtration, and recrystallization of the crude product with ethanol, a white powdery solid (C 19 H 39 CO(NHC3H6)2NH2) was obtained in a yield of 89%.

[0147] (2) Into a reactor equipped with a condenser, stirring device and gas disperser, 213 g (0.5 mol) of the above reactant was added, heated to 80-90°C, vacuum system was opened, dehydrated under high vacuum for 1 hour, then purged with nitrogen for 3-4 times to remove air in the system, then the reaction temperature of the system was adjusted to 130°C, 132 g (3.0 mol) of ethylene oxide was slowly introduced, the pressure was controlled to be <0.60 MPa to carry out the alkoxylation reaction; after the reaction was completed, the system was purged with nitrogen to remove unreacted ethylene oxide, and after cooling, neutralization, decolorization, filtration and dehydration, a pH switch surfactant was obtained: that is, the long-chain hydrocarbon-based amine 3 (structure as follows), with a yield of 91%.

[0148] Structure of the pH switch surfactant:

[0149]

[0150] R1 is C 19 H 39 ; R2 is C3H6; R3, R4, R5 are H; m+n+p=6, q=2.

[0151] Preparation of the viscoelastic foam system:

[0152] At room temperature and normal pressure, 0.4 g of the pH switch surfactant in Example 5 and 0.1 g of sodium butyl sulfonate were weighed and added to 100 g of a brine with a salinity of 200 g / L to obtain a viscoelastic foam system.

[0153] The viscoelastic foam system was saturated with 0.1 MPa CO2 at room temperature, and the viscosity reached 23 mPa·s.

[0154] Oil displacement experiment of the viscoelastic foam system:

[0155] A simulated core with a permeability of 1 D was saturated with water, then saturated with Shengli crude oil until no water was left, and then the core was aged for 1 month. The aged core was displaced with a brine with a salinity of 200 g / L until no crude oil flowed out, and the water displacement recovery was recorded as 45%. Then the viscoelastic foam system in Example 5 was co-injected with CO2 for displacement, the volume ratio of CO2 to the viscoelastic foam system was 1:0.5, the total injection rate of the viscoelastic foam system and CO2 was 2 mL / min, and the oil recovery rates of the viscoelastic foam system injected at 0.5 pV and 1.0 pV were recorded as 59% and 74%, respectively, which increased the recovery by 14% and 29%, respectively. When the viscoelastic foam system was injected at 1.0 pV, the apparent viscosity of the foam formed in the core was 307 mPa·s.

[0156] Comparative Example 7

[0157] Preparation of the foam system:

[0158] At room temperature and normal pressure, 0.5 g of the pH switch surfactant in Example 5 was weighed and added into 200 g / L salinity brine to obtain a total of 100 g of the foam system after mixing.

[0159] The viscosity of the foam system saturated with 0.1 MPa CO2 at room temperature can reach 2 mPa s.

[0160] Foam system oil displacement experiment:

[0161] The simulated core with a permeability of 1 D was saturated with water and then saturated with Shengli crude oil until no water was left. The aged core was then placed for one month. The aged core was displaced with 200 g / L salinity brine until no crude oil flowed out, and the water displacement recovery was recorded as 44%. Then, the foam system in Comparative Example 7 was co-injected with CO2 for displacement, and the volume ratio of CO2 to the foam system was 1:0.5. The total injection rate of the foam system and CO2 was 2 mL / min. The oil recovery rates of the foam system injection amount of 0.5 pV and 1.0 pV were 53% and 62%, respectively, and the enhanced oil recovery rates were 9% and 18%, respectively. The apparent viscosity of the foam formed in the core was 140 mPa s when the foam system was injected at 1.0 pV.

[0162] Example 6

[0163] The pH switch surfactant structure and preparation process were the same as those in Example 5.

[0164] Preparation of viscoelastic foam system:

[0165] At room temperature and normal pressure, 0.7 g of the pH switch surfactant in Example 5 and 0.05 g of sodium butyl sulfonate were weighed and added into 200 g / L salinity brine to obtain a total of 100 g of the viscoelastic foam system after mixing.

[0166] The viscosity of the viscoelastic foam system saturated with 0.1 MPa CO2 at room temperature can reach 4 mPa s.

[0167] Viscoelastic foam system oil displacement experiment:

[0168] The simulated core with permeability of 1 D was saturated with water, then saturated with Shengli crude oil to leave no water, and then placed for 1 month to age the core. The aged core was displaced with brine with a salinity of 200 g / L until no crude oil flowed out, and the water flooding recovery rate was recorded as 46%. Then, the foam system in Example 5 was co-injected and displaced with CO2, the volume ratio of CO2 to the foam system was 1:1.5, and the total injection rate of the foam system and CO2 was 2 mL / min. The oil recovery rates displaced by the foam system injected in an amount of 0.5 pV and 1.0 pV were 60% and 69% respectively, and the enhanced oil recovery rates were 14% and 23% respectively. When the foam system was injected in an amount of 1.0 pV, the apparent viscosity of the foam formed in the core was 270 mPa s.

[0169] Comparative Example 8

[0170] Preparation of the foam system:

[0171] At room temperature and normal pressure, 0.75 g of the sodium butyl sulfonate in Example 5 was added to brine with a salinity of 200 g / L to obtain a total of 100 g of the foam system after mixing.

[0172] The above foam system was saturated with 0.1 MPa CO2 at room temperature, and then the viscosity was tested. The viscosity was close to the viscosity of water, which was 1 mPa s.

[0173] Foam system oil displacement experiment:

[0174] The simulated core with permeability of 1 D was saturated with water, then saturated with Shengli crude oil to leave no water, and then placed for 1 month to age the core. The aged core was displaced with brine with a salinity of 200 g / L until no crude oil flowed out, and the water flooding recovery rate was recorded as 46%. Then, the foam system in Comparative Example 8 was co-injected and displaced with CO2, the volume ratio of CO2 to the foam system was 1:1.5, and the total injection rate of the foam system and CO2 was 2 mL / min. The oil recovery rates displaced by the foam system injected in an amount of 0.5 pV and 1.0 pV were 49% and 54% respectively, and the enhanced oil recovery rates were 3% and 8% respectively. When the foam system was injected in an amount of 1.0 pV, the apparent viscosity of the foam formed in the core was 3 mPa s.

[0175] Example 7

[0176] The long-chain hydrocarbon-based amine 1A switchable surfactant prepared in Example 1 was used.

[0177] Preparation of the viscoelastic foam system:

[0178] At room temperature and normal pressure, 0.5 g of the long-chain hydrocarbon-based amine 1A pH switchable surfactant and 0.1 g of sodium decyl sulfonate (TCI) were added to brine with a salinity of 50 g / L to obtain a total of 100 g of the viscoelastic foam system after mixing.

[0179] The viscoelastic foam system has a viscosity of 3 mPa s after being saturated with 0.1 MPa CO2 at room temperature.

[0180] Viscoelastic foam system oil displacement experiment:

[0181] The simulated core with a permeability of 1 D was saturated with water and then saturated with Shengli crude oil until no water was left over, and then the core was left to age for one month. The aged core was displaced with brine with a salinity of 50 g / L until no crude oil flowed out, and the water displacement recovery was recorded as 50%. Then, the viscoelastic foam system in Example 1 was co-injected with CO2 for displacement, the volume ratio of CO2 to the viscoelastic foam system was 1:2, the total injection rate of the viscoelastic foam system and CO2 was 2 mL / min, and the oil recovery rates of the crude oil displaced by the viscoelastic foam system at injection amounts of 0.5 pV and 1.0 pV were 67% and 77%, respectively, which increased the recovery rate by 17% and 27%, respectively, and the apparent viscosity of the foam formed in the core at the injection amount of 1.0 pV was 301 mPa s.

[0182] As can be seen from Examples 1 and 7, mixing long-chain hydrocarbyl amines prepared from different fatty acids in the viscoelastic foam system has a better effect on increasing the oil recovery rate than long-chain hydrocarbyl amines prepared from a single fatty acid, and in the present application, mixing can increase the oil recovery rate by 10% compared to a single C 12 Fatty acid-prepared long-chain hydrocarbyl amines, the oil recovery rate can be increased by 10%.

[0183] As can be seen from Examples 1-7 and Comparative Examples 1-8, after the viscoelastic foam system of the present application meets the acid gas, the pH switch surfactant and the hydrocarbyl anion surfactant interact to increase the viscosity, the foam formed has better stability and plugging performance, the apparent viscosity of the foam formed in the core at an injection amount of 1.0 pV is ≥270 mPa s, the recovery rate can be increased by more than 20%, and the long-chain hydrocarbyl amine improves the salt tolerance of the single anion surfactant, so that the salinity application range of the system is increased to 10-200 g / L.

Claims

1. A foaming agent composition comprising a pH-switching surfactant and a hydrocarbon-based anionic surfactant; wherein the pH-switching surfactant is at least one of long-chain hydrocarbon amines; The structure of the long-chain hydrocarbon amine is shown in formula (1): in, R1 is selected from C 11 ~C 24 R2 is selected from C1 to C5 aliphatic hydrocarbon groups; R3, R4, and R5 are each independently selected from H, C1 to C3 aliphatic hydrocarbon groups or substituted aliphatic hydrocarbon groups, and at least one of R3, R4, and R5 is H. m+n+p is 1 to 30, and q is 0 to 2; The hydrocarbon-based anionic surfactant is at least one of alkyl carboxylates, alkyl sulfates, alkyl sulfonates, and olefin sulfonates; The alkyl group has 1 to 20 carbon atoms; The olefin sulfonate has 10 to 20 carbon atoms; The mass ratio of the pH-switching surfactant to the hydrocarbon-based anionic surfactant is 1:0.05–15.

2. The foaming agent composition according to claim 1, characterized in that: The pH-switching surfactant is at least two of long-chain hydrocarbon amines.

3. The foaming agent composition according to claim 2, characterized in that: R1 is selected from C 11 ~C 20 The aliphatic hydrocarbon group; R2 is selected from C1 to C3 aliphatic hydrocarbon groups.

4. The foaming agent composition according to claim 1, characterized in that: The alkyl group has 1 to 12 carbon atoms.

5. The foaming agent composition according to claim 1, characterized in that: The mass ratio of the pH-switching surfactant to the hydrocarbon-based anionic surfactant is 1:0.1 to 3.

6. A viscoelastic foam system for acidic gas switching, comprising the foaming agent composition according to any one of claims 1-5.

7. The viscoelastic foam system as described in claim 6, characterized in that: The viscoelastic foam system also contains water; the water is mineral-containing water, and the saline solution has a mineralization range of 10 to 200 g / L.

8. The viscoelastic foam system as described in claim 7, characterized in that: The water is at least one of tap water, oil and gas field formation water, and water-oil-gas field injection water.

9. The viscoelastic foam system as described in claim 6, characterized in that: The pH-switching surfactant in the foaming agent composition accounts for 0.2–1 wt% of the viscoelastic foam system; and / or, The hydrocarbon-based anionic surfactant in the foaming agent composition accounts for 0.05–0.3 wt% of the viscoelastic foam system; and / or, The foam system can form a solution viscosity of 3 to 30 mPa·s under the action of acidic gas.

10. The viscoelastic foam system as described in claim 9, characterized in that: The pH-switching surfactant in the foaming agent composition accounts for 0.3–0.6 wt% of the viscoelastic foam system; and / or, The hydrocarbon-based anionic surfactant in the foaming agent composition accounts for 0.1 to 0.2 wt% of the viscoelastic foam system.

11. A method for preparing a viscoelastic foam system as described in any one of claims 6-10, comprising thoroughly mixing components including the foaming agent composition and water.

12. A method for enhancing oil recovery using the viscoelastic foam system according to any one of claims 6-10 or the viscoelastic foam system prepared according to claim 11, comprising injecting the viscoelastic foam system and acid gas alternately or together into a porous medium containing crude oil, thereby forming foam in situ in the porous medium to enhance oil recovery.

13. The method as described in claim 12, characterized in that: The acidic gas is at least one of CO2 and H2S.

14. The method as described in claim 12, characterized in that: The volume ratio of the acidic gas to the viscoelastic foam system is 1:0.1 to 2.

15. The application of a viscoelastic foam system as described in any one of claims 6-10 or the viscoelastic foam system prepared according to claim 11 in oil production in reservoirs with a salinity of 10-200 g / L.

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