Method for improving carbon dioxide oil displacement effect

Abstract

The invention relates to the technical field of oilfield development, and discloses a method for improving carbon dioxide oil displacement effect, which comprises the following steps: (1) injecting a first composition into an oil reservoir, and then injecting carbon dioxide; wherein the first composition comprises xanthan gum, silicate and an optional first solvent; (2) injecting a second composition into the oil reservoir, and then injecting carbon dioxide; wherein the second composition comprises fatty alcohol polyoxyethylene ether sulfate, alkyl hydroxypropyl phosphate betaine, alkyl glycoside, coconut oil diethanolamide and an optional second solvent. By means of the method, the problem that the oil extraction rate is reduced due to gas channeling in an oil field can be effectively solved. According to the method, the fluidity of carbon dioxide gas in a reservoir high-permeability area or a crack can be effectively reduced, and the gas flooding sweep range is expanded, so that the carbon dioxide oil flooding effect is improved.

Description

Technical Field

[0001] This invention relates to the field of oilfield development technology, and specifically to a method for improving the effect of carbon dioxide flooding. Background Technology

[0002] With the increasing global emphasis on CO2 emission reduction in recent years, more and more CO2 is being injected or is about to be injected underground, hoping to improve oil recovery while achieving emission reduction. A drawback of CO2 flooding is the significant difference in density and viscosity between CO2 and crude oil, leading to an excessively high CO2-to-crude oil mobility ratio. This easily causes viscosity fingering and gravity differentiation, thus affecting the gas sweep volume and reducing displacement efficiency. Currently, the main methods to improve CO2 flooding effectiveness are water-gas alternating injection (WAG), foam injection, and gel injection. Domestic and international practices have proven that foam is one of the effective methods to delay gas channeling, and foaming agents are key to the success of foaming measures. Therefore, extensive research and practice have been conducted on CO2 foaming agents both domestically and internationally, especially in the United States and Canada, such as lignin sulfonates described in USP4086964, α-olefin sulfonates described in USP4393937, Lathanol LAL70 from Stepan Chemical Co., and CD1045 from Chevrn. However, for reservoirs containing fractures and large pores, the effectiveness of foam is greatly reduced. Summary of the Invention

[0003] The purpose of this invention is to overcome the problem that in the existing technology, after carbon dioxide is injected for a certain period of time, the high-permeability areas or fractures of the reservoir are filled with carbon dioxide, and the mobility of carbon dioxide in them is very high, which cannot displace crude oil over a larger area, resulting in a decrease in oil recovery rate.

[0004] To achieve the above objectives, the first aspect of the present invention provides a method for carbon dioxide flooding, the method comprising the following steps:

[0005] (1) Injecting a first composition into the reservoir, followed by the injection of carbon dioxide; wherein the first composition comprises xanthan gum, silicate and optional first solvent;

[0006] (2) A second composition is injected into the reservoir, followed by the injection of carbon dioxide; wherein the second composition comprises fatty alcohol polyoxyethylene ether sulfate, alkyl hydroxypropyl phosphate betaine, alkyl glycoside, coconut oil diethanolamide and an optional second solvent.

[0007] The second aspect of this invention provides the application of the montmorillonite-modified rubber described above in carbon dioxide flooding.

[0008] The beneficial effects of this invention are as follows: The method of this invention can effectively solve the problem of gas channeling in oilfields, which leads to a decrease in oil recovery rate. This invention can effectively improve the oil recovery rate of low-permeability reservoirs by sequentially injecting a first composition and a second composition into the reservoir. Preferably, this invention can effectively solve the gas channeling problem in reservoirs containing fractures and large pores by sequentially injecting montmorillonite-modified rubber, the first composition, and the second composition into the reservoir, thereby improving the oil recovery rate. The preferred embodiment of this invention can increase the oil recovery rate by more than 16%.

[0009] The method of the present invention can effectively reduce the mobility of carbon dioxide gas in high-permeability areas or fractures of reservoirs, expand the gas drive sweep range, and thus improve the carbon dioxide flooding effect. Detailed Implementation

[0010] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0011] The first aspect of this invention provides a method for carbon dioxide flooding, the method comprising the following steps:

[0012] (1) Injecting a first composition into the reservoir, followed by the injection of carbon dioxide; wherein the first composition comprises xanthan gum, silicate and optional first solvent;

[0013] (2) A second composition is injected into the reservoir, followed by the injection of carbon dioxide; wherein the second composition comprises fatty alcohol polyoxyethylene ether sulfate, alkyl hydroxypropyl phosphate betaine, alkyl glycoside, coconut oil diethanolamide and an optional second solvent.

[0014] According to the present invention, preferably, the weight ratio of xanthan gum to silicate is 1:30-300, more preferably 1:33-100, and even more preferably 1:45-55. In the present invention, the weight ratio of xanthan gum to silicate can be 1:30, 1:50, 1:52, 1:53, 1:55, 1:60, 1:65, 1:70, 1:100, 1:200, or any two of the above ratios.

[0015] According to the present invention, preferably, the first solvent is water, wherein, based on the total weight of the first composition, the xanthan gum content is 0.01-0.3 wt%, more preferably 0.05-0.25 wt%, and even more preferably 0.1-0.23 wt%, and the silicate content is 2-15 wt%, more preferably 4-12 wt%, and even more preferably 6-11.6 wt%. In the present invention, the xanthan gum content can be 0.01 wt%, 0.1 wt%, 0.12 wt%, 0.13 wt%, 0.14 wt%, 0.15 wt%, 0.2 wt%, 0.22 wt%, 0.25 wt%, 0.3 wt%, and any two of the above ranges. The silicate content can be 2 wt%, 4 wt%, 6 wt%, 8 wt%, 10 wt%, 12 wt%, 15 wt%, and any two of the above ranges.

[0016] According to the present invention, the silicate can be any substance containing silicic acid groups, such as an alkali metal silicate. Preferably, the silicate includes at least one of sodium silicate, lithium silicate, and potassium silicate; more preferably, the silicate is lithium silicate. The inventors of the present invention have further discovered that when lithium silicate is used to prepare the first composition, not only can the rupture pressure of the first composition gel be increased, but the oil recovery rate can also be further improved.

[0017] According to a preferred embodiment of the present invention, the preparation method of the first composition includes: adding 100g of distilled water to a container, adding 0.15-0.3g of xanthan gum while stirring, and after the xanthan gum is completely dissolved, adding 20-30g of an aqueous solution of sodium silicate with a concentration of 45-50% by weight (e.g., 48-50% by weight), and stirring evenly.

[0018] According to the present invention, preferably, relative to 1cm 3 The reservoir porosity is determined by the dosage of the first composition at 0.05-0.3 cm³. 3 The amount of carbon dioxide used is 0.05-0.2 cm³. 3 .

[0019] According to the present invention, preferably, the weight ratio of fatty alcohol polyoxyethylene ether sulfate, alkyl hydroxypropyl phosphate betaine, alkyl glycoside and coconut oil diethanolamide is 1:0.01-60:0.01-60:0.008-20, more preferably 1:0.01-0.6:0.01-60:0.008-0.01.

[0020] According to the present invention, preferably, the second solvent is water, wherein, based on the total weight of the second composition, the content of the fatty alcohol polyoxyethylene ether sulfate is 0.005-0.5 wt%, more preferably 0.4-0.5 wt%, and even more preferably 0.48-0.5 wt%, the content of the alkyl hydroxypropyl phosphate betaine is 0.005-0.5 wt%, more preferably 0.1-0.3 wt%, and even more preferably 0.25-0.3 wt%, the content of the alkyl glycoside is 0.005-0.3 wt%, more preferably 0.005-0.008 wt%, and the content of the coconut oil diethanolamide is 0.004-0.1 wt%, more preferably 0.004-0.008 wt%.

[0021] According to the present invention, the type of cation in the fatty alcohol polyoxyethylene ether sulfate is not particularly limited, and can be a common cation, such as sodium ion, potassium ion, etc.; preferably, the anionic structure of the fatty alcohol polyoxyethylene ether sulfate is RO(CH2CH2O). n SO3 - Where n is 2-3, and R is a C8-C18 alkyl group, more preferably a C12-C14 alkyl group.

[0022] According to the present invention, preferably, the alkyl group in the alkyl hydroxypropyl phosphate betaine is a C8-C16 alkyl group, more preferably a C12-C14 alkyl group. In the present invention, the alkyl group in the alkyl hydroxypropyl phosphate betaine can be, for example, a C8-C16 alkyl group, a C12-C14 alkyl group, or a C12-C16 alkyl group.

[0023] According to the present invention, preferably, the alkyl group in the alkyl glycoside is a C8-C16 alkyl group, more preferably a C8-C14 alkyl group. In the present invention, the alkyl group in the alkyl glycoside can be a C8-C16 alkyl group, a C8-C14 alkyl group, a C12-C16 alkyl group, or a C8-C12 alkyl group.

[0024] According to a preferred embodiment of the present invention, the preparation method of the second composition includes: adding 100g of distilled water to a container; adding 0.45-0.55g of fatty alcohol polyoxyethylene ether sulfate while stirring, wherein the fatty alcohol polyoxyethylene ether sulfate has 2-3 ethylene oxides and the alkyl group R is a C8-C18 alkyl group; adding 0.005-0.3g of alkyl hydroxypropyl phosphate betaine (e.g., 0.005-0.01g, 0.25-0.3g), wherein the alkyl group of alkyl hydroxypropyl phosphate betaine is a C12-C16 alkyl group; adding 0.005-0.008g of alkyl glycoside, wherein the alkyl group of alkyl glycoside is a C12-C16 alkyl group; adding 0.004-0.006g of coconut oil diethanolamide; and stirring until completely dissolved.

[0025] According to the present invention, preferably, relative to 1cm 3 The reservoir porosity is determined by the amount of the second composition used, which is 0.05-0.3 cm³. 3 .

[0026] According to the present invention, preferably, in step (2), the volume ratio of the second composition to the injected carbon dioxide is 1:0.02-1, more preferably 1:0.5-0.8. After the injection in step (2) is completed, carbon dioxide is injected again until no more oil is extracted.

[0027] According to the present invention, preferably, the method further includes: performing step (1-A) before step (1), injecting montmorillonite-modified rubber into the reservoir, and then injecting carbon dioxide.

[0028] According to the present invention, preferably, the method for preparing the montmorillonite-modified rubber includes the following steps:

[0029] (a) Hydrate and peel the montmorillonite, then add latex and mix, and then dry;

[0030] (b) The dried product is crushed, then mixed with crosslinking agent, accelerator, activator and anti-aging agent, and then plasticized and / or compounded, and then vulcanized.

[0031] According to the present invention, preferably, the montmorillonite-modified rubber is injected into the reservoir in the form of an aqueous suspension, wherein the concentration of the montmorillonite-modified rubber aqueous suspension is 0.01-10% by weight, more preferably 0.5-1% by weight.

[0032] According to the present invention, preferably, relative to 1cm 3 The reservoir porosity was determined by the amount of montmorillonite-modified rubber aqueous suspension used, which was 0.05-0.3 cm³. 3 The amount of carbon dioxide used is 0.05-0.2 cm³. 3 .

[0033] According to the present invention, preferably, the particle size of the montmorillonite is 100-500 mesh, more preferably 200-300 mesh.

[0034] According to the present invention, preferably, the solid content of the latex is 50-80% by weight.

[0035] According to the present invention, preferably, the amount of montmorillonite used is 1-50g per 100g of latex, more preferably 5-40g, and even more preferably 5-10g.

[0036] According to the present invention, preferably, during the hydration stripping process, the ratio of water to montmorillonite is 1-10:1, more preferably 9-10:1.

[0037] According to the present invention, preferably, the hydration stripping is carried out under alkaline conditions, which are provided by an alkaline substance (e.g., an alkali metal hydroxide and / or a weak acid salt of an alkali metal). The alkali metal hydroxide may be sodium hydroxide or potassium hydroxide. The weak acid salt of the alkali metal may be sodium bicarbonate, sodium carbonate, potassium bicarbonate, or potassium carbonate. The amount of the alkaline substance used is 0.01-2 g relative to 100 g of montmorillonite.

[0038] In this invention, the hydration stripping can also be carried out under non-alkaline conditions, that is, the alkaline substances mentioned above are not added during the hydration stripping process.

[0039] According to the present invention, preferably, the crushing conditions result in a particle size of 20-500 mesh, more preferably 50-200 mesh. In this invention, "mesh" refers to the number of sieve openings per inch of area.

[0040] According to the present invention, preferably, the crosslinking agent is sulfur; the amount of the crosslinking agent is 1-5g per 100g of latex, more preferably 1-3g, and even more preferably 1-1.5g.

[0041] According to the present invention, preferably, the accelerator is N-cyclohexyl-2-benzothiazole sulfenamide; the amount of the accelerator relative to 100g of latex is 0.2-3g, more preferably 0.2-2g, and even more preferably 0.2-0.3g.

[0042] According to the present invention, preferably, the activator includes a first activator and a second activator, wherein the first activator is stearic acid and the second activator is ZnO.

[0043] According to the present invention, preferably, the amount of the first activator is 1-3g per 100g of latex, more preferably 0.1-2g, and even more preferably 0.1-0.2g.

[0044] According to the present invention, preferably, the amount of the second activator is 1-8g per 100g of latex, more preferably 1-6g, and even more preferably 1-2g.

[0045] According to the present invention, preferably, the anti-aging agent is a 2,2,4-trimethyl-1,2-dihydroquinoline polymer.

[0046] According to the present invention, preferably, the amount of the anti-aging agent is 0.2-3g per 100g of latex, more preferably 0.2-2.5g, and even more preferably 0.2-0.3g.

[0047] According to the present invention, preferably, the vulcanization conditions include: a temperature of 120-155°C, more preferably 135-150°C; and a pressure of 12-18 MPa, more preferably 14-16 MPa.

[0048] According to the present invention, preferably, when the width of the fracture in the reservoir is greater than 100 μm, the carbon dioxide flooding method includes steps (1-A), (1) and (2);

[0049] According to the present invention, preferably, when the width of the fractures in the reservoir is ≤100μm or there are no fractures, the carbon dioxide flooding method includes steps (1) and (2).

[0050] The second aspect of this invention provides the application of the montmorillonite-modified rubber described above in carbon dioxide flooding.

[0051] The present invention will be described in detail below through embodiments. In the following embodiments,

[0052] Preparation Example 1-1

[0053] (a) Dissolve 0.005g of sodium bicarbonate in 50g of distilled water, add 30g of montmorillonite with a particle size of 200 mesh and stir to hydrate and exfoliate it in the reaction system, then add 100g of natural rubber latex with a solid content of 70% by weight, stir evenly, spread it on a heating plate to dry, and then crush the dried solid product with a universal pulverizer.

[0054] (b) The solid particles crushed in step (a) are mixed with a crosslinking agent (sulfur), an accelerator (N-cyclohexyl-2-benzothiazole sulfenamide), a first activator (stearic acid), a second activator (ZnO), and an anti-aging agent (2,2,4-trimethyl-1,2-dihydroquinoline polymer) and then compounded. The mixture is then vulcanized to obtain montmorillonite-intercalated vulcanized rubber, which is then crushed to 20-500 mesh. The amounts of crosslinking agent, accelerator, first activator, second activator, and anti-aging agent per 100g of natural rubber latex are 2.5g, 1.2g, 0.8g, 4g, and 2g, respectively. The vulcanization conditions include a temperature of 145°C and a pressure of 14MPa.

[0055] Preparation Examples 1-2 to 1-9

[0056] The preparation method was carried out according to Example 1-1, except that the amounts of each component and the vulcanization conditions are shown in Table 1.

[0057] Table 1

[0058]

[0059] Note: In preparation examples 1-5, 1-6, 1-8, and 1-9, sodium bicarbonate was replaced with sodium carbonate.

[0060] Test Example 1

[0061] The swelling effect of montmorillonite-intercalated vulcanized rubbers prepared in Preparation Examples 1-1 to 1-9 in carbon dioxide gas was tested. The test method was as follows: A high-temperature, high-pressure, and visible reactor was used. The sample was fixed inside the reactor, making its main body visible from the outside. The reactor was placed in a constant-temperature oven, and the gas injection line and back pressure valve were connected. A camera was installed outside the oven to record the size of the sample inside the reactor. First, a vacuum was drawn to remove air from the lines and reactor. CO2 gas was then slowly injected into the reactor, and the oven temperature was set to the experimental temperature. During the injection process, the back pressure was gradually increased until the preset experimental pressure was reached. Gas was continued to be injected into the reactor using a high-pressure injection pump until the experimental design pressure was reached. The sample height was measured continuously using the camera to calculate the sample expansion ratio. The test results are shown in Table 2.

[0062] The formula for calculating the expansion factor is: (V1-V2) / V2; where V1 represents the volume of the sample under the set temperature and pressure, and V2 represents the initial volume of the sample.

[0063] Table 2

[0064]

[0065]

[0066] Preparation Example 2-1

[0067] Add 100g of distilled water to a container, then add 0.01g of xanthan gum while stirring. After the xanthan gum has completely dissolved, add 6g of a 50% by weight sodium silicate aqueous solution and stir well.

[0068] Preparation Examples 2-2 to 2-7

[0069] The preparation method was carried out in accordance with that of Example 2-1, except that the amounts of each component were as shown in Table 3.

[0070] Table 3

[0071] Preparation Example 2-2 Preparation Examples 2-3 Preparation Examples 2-4 Preparation Examples 2-5 Preparation Examples 2-6 Preparation Examples 2-7 Distilled water / g 100 100 100 100 100 100 xanthan gum / g 0.3 0.15 0.15 0.15 0.15 0.15 Silicate aqueous solution / g 30 16 16 16 20 10 Types of silicates Sodium silicate Sodium silicate Lithium silicate Potassium silicate Sodium silicate Sodium silicate

[0072] Test Example 2

[0073] The gelation properties of the first compositions prepared in Preparation Examples 2-1 to 2-7 were tested in the presence of carbon dioxide. The test method was as follows: carbon dioxide gas was passed into the composition solution until the solution changed from clear and transparent to dark. The composition solution was then placed in a constant temperature oven to allow it to solidify.

[0074] The obtained gel was subjected to strength testing: the strength of the gel was tested using a texture analyzer (model CT3, probe TA10, φ=12.7mm, area 1.266cm²). 2 The gel was placed in the instrument, and then pressure was applied to the gel downwards using the probe. The texture analyzer was set to Bloom mode, trigger speed 4g, velocity 0.5mm / s, and temperature 70℃. 1g of pressure was applied to a 1cm layer. 2 The cross-section is equivalent to a pressure of 98 Pa. The test results are shown in Table 4.

[0075] Table 4

[0076] Reaction time / h Temperature / °C Rupture pressure / Pa Preparation Example 2-1 20 70 19780 Preparation Example 2-2 20 70 56300 Preparation Examples 2-3 20 70 33100 Preparation Examples 2-4 20 70 72500 Preparation Examples 2-5 20 70 20500 Preparation Examples 2-6 20 70 38900 Preparation Examples 2-7 20 70 25400 Preparation Examples 2-3 20 50 30890 Preparation Examples 2-3 20 60 31500

[0077] Preparation Example 3-1

[0078] Add 100g of distilled water to a container. While stirring, add 0.005g of fatty alcohol polyoxyethylene ether sulfate (the fatty alcohol polyoxyethylene ether sulfate has 2-3 ethylene oxides and the alkyl group R is a C8-C18 alkyl group); add 0.005g of alkyl hydroxypropyl phosphate betaine (the alkyl group of alkyl hydroxypropyl phosphate betaine is a C12-C14 alkyl group); add 0.3g of alkyl glycoside (the alkyl group of alkyl glycoside is a C12-C16 alkyl group); add 0.1g of coconut oil diethanolamide; stir until completely dissolved.

[0079] Preparation Examples 3-2 to 3-7

[0080] The preparation was carried out according to the method of Preparation Example 3-1, except that the amounts of each component were as shown in Table 5.

[0081] Table 5

[0082]

[0083]

[0084] Test Example 3

[0085] The volume and half-life of foam generated by the second compositions prepared in Preparation Examples 3-1 to 3-7 in a carbon dioxide environment were measured using a Roche foam analyzer. The test procedure was in accordance with the national standard GB / T 7462. The test temperature and test results are shown in Table 6. The water used had a mineralization of 14550 ppm (of which the calcium and magnesium content was 55 ppm).

[0086] Table 6

[0087] foaming volume / mL Half-life / s Temperature / °C Preparation Example 3-1 300 1154 80 Preparation Example 3-2 350 1539 80 Preparation Example 3-3 360 1535 80 Preparation Examples 3-4 380 1290 80 Preparation Examples 3-5 330 1178 80 Preparation Examples 3-6 340 1309 80 Preparation Examples 3-7 355 1487 80 Preparation Example 3-3 340 1790 70 Preparation Example 3-3 310 1144 90

[0088] The following examples illustrate the carbon dioxide flooding method of the present invention, wherein,

[0089] The process of preparing a simulated fractured reservoir: A cylindrical core with a length of 30 cm and a diameter of 2.5 cm was taken. The core had a permeability of 1200 mD. Fractures were then created in the core, which was filled with 40-mesh quartz sand. Water and saturated oil with a viscosity of 17 cp (70℃) were then injected sequentially to obtain the simulated fractured reservoir. The reservoir water salinity of the simulated fractured reservoir was 7000 ppm (calcium and magnesium content 200 ppm), and the fracture width was greater than 100 μm.

[0090] The process for preparing a low-permeability reservoir: A cylindrical core with a length of 30 cm and a diameter of 2.5 cm was taken. The core had a permeability of 50 mD. Water was then injected sequentially, followed by saturated oil with a viscosity of 5 cp (70℃) to obtain the low-permeability reservoir. The reservoir water salinity of the low-permeability reservoir was 10,000 ppm (calcium and magnesium content 50 ppm).

[0091] Example 1

[0092] (1-A) An oil displacement experiment was conducted at 70℃. First, water flooding was performed to a water cut of 95%, followed by CO2 flooding (back pressure 8 MPa), resulting in gas channeling. An aqueous suspension (1% by weight) of montmorillonite-intercalated vulcanized rubber prepared in Examples 1-9 was injected into the simulated fractured reservoir after gas channeling, followed by carbon dioxide injection. The montmorillonite-intercalated vulcanized rubber had a particle size of 300 mesh relative to 1 cm. 3 The reservoir porosity was determined by using an aqueous suspension of montmorillonite-modified rubber at a concentration of 0.2 cm³. 3 The carbon dioxide injection volume was 0.1 cm. 3 .

[0093] (1) The first composition prepared in Preparation Example 2-3 was re-injected, followed by the injection of carbon dioxide; wherein, relative to 1 cm 3 The reservoir porosity was determined by using 0.2 cm³ of the first composition. 3 The carbon dioxide injection volume was 0.1 cm. 3 .

[0094] (2) Re-injection of the second composition prepared in Example 3-2, wherein, relative to 1 cm 3 The reservoir porosity was determined by the amount of the second composition used, which was 0.2 cm³. 3 Then continue injecting CO2 to drive out oil until no oil is produced.

[0095] Example 2

[0096] The procedure was carried out according to Example 1, except that "preparation of montmorillonite intercalated vulcanized rubber of Examples 1-9" was replaced with an equal amount of "preparation of montmorillonite intercalated vulcanized rubber of Examples 1-8"; "preparation of the first composition of Examples 2-3" was replaced with an equal amount of "preparation of the first composition of Example 2-1"; and "preparation of the second composition of Example 3-2" was replaced with an equal amount of "preparation of the second composition of Example 3-5".

[0097] Example 3

[0098] The procedure was carried out according to Example 1, except that “preparation of montmorillonite intercalated vulcanized rubber of Examples 1-9” was replaced with an equal amount of “preparation of montmorillonite intercalated vulcanized rubber of Examples 1-7”; and “preparation of the first composition of Examples 2-3” was replaced with an equal amount of “preparation of the first composition of Examples 2-6”.

[0099] Example 4

[0100] The procedure was carried out according to Example 1, except that "preparation of montmorillonite intercalated vulcanized rubber of Examples 1-9" was replaced with an equal amount of "preparation of montmorillonite intercalated vulcanized rubber of Examples 1-7"; "preparation of the first composition of Examples 2-3" was replaced with an equal amount of "preparation of the first composition of Examples 2-6"; and "preparation of the second composition of Examples 3-2" was replaced with an equal amount of "preparation of the second composition of Examples 3-4".

[0101] Example 5

[0102] (1) An oil displacement experiment was conducted at 70℃. First, water was used to drive the oil to a water cut of 95%, followed by CO2 injection (back pressure 8 MPa), which caused gas channeling. The first composition prepared in Preparation Examples 2-6 was injected into the low-permeability reservoir after gas channeling, and then carbon dioxide was injected. 3 The reservoir porosity was determined by using 0.2 cm³ of the first composition. 3 The carbon dioxide injection volume was 0.1 cm. 3 .

[0103] (2) Re-injection of the second composition prepared in Example 3-2, wherein, relative to 1 cm 3 The reservoir void volume is determined by the amount of the second composition used, which is 0.3 cm³. 3 Then continue injecting CO2 to drive out oil until no oil is produced.

[0104] Example 6

[0105] The procedure was carried out according to Example 5, except that “the first composition of Preparation Example 2-6” was replaced with an equal amount of “the first composition of Preparation Example 2-1”; and “the second composition of Preparation Example 3-2” was replaced with an equal amount of “the second composition of Preparation Example 3-1”.

[0106] Example 7

[0107] The procedure was carried out according to Example 5, except that “the first composition of Preparation Examples 2-6” was replaced with an equal amount of “the first composition of Preparation Examples 2-7”; and “the second composition of Preparation Examples 3-2” was replaced with an equal amount of “the second composition of Preparation Examples 3-6”.

[0108] Example 8

[0109] The procedure was carried out according to Example 5, except that “the first composition of Preparation Example 2-6” was replaced with an equal amount of “the first composition of Preparation Example 2-2”.

[0110] The percentage increase in oil recovery rate for Examples 1-8 is shown in Table 7. The formula for calculating the percentage increase in oil recovery rate is: η1-η2, where η1 is the oil recovery rate at the end of step (2), and η2 is the oil recovery rate when gas channeling begins; the formula for calculating the oil recovery rate is: amount of oil produced ÷ amount of saturated oil × 100%.

[0111] Table 7

[0112] Oil recovery rate increased by a certain percentage (%) Example 1 13.2 Example 2 4.4 Example 3 16.5 Example 4 13.5 Example 5 14.3 Example 6 5.7 Example 7 8.9 Example 8 16.8

[0113] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for carbon dioxide flooding, characterized in that, The method includes the following steps: (1) Injecting a first composition into the reservoir, followed by the injection of carbon dioxide; wherein the first composition comprises xanthan gum, silicate and optional first solvent; (2) The second composition is injected into the reservoir, followed by the injection of carbon dioxide; wherein the second composition comprises fatty alcohol polyoxyethylene ether sulfate, alkyl hydroxypropyl phosphate betaine, alkyl glycoside, coconut oil diethanolamide and optional second solvent.

2. The method according to claim 1, wherein, The weight ratio of xanthan gum to silicate is 1:30-300, preferably 1:33-100; And / or, the first solvent is water, wherein, based on the total weight of the first composition, the xanthan gum content is 0.01-0.3% by weight, preferably 0.05-0.25% by weight, and the silicate content is 2-15% by weight, preferably 4-12% by weight; And / or, the silicate includes at least one of sodium silicate, lithium silicate, and potassium silicate.

3. The method according to claim 2, wherein, Compared to 1cm 3 The reservoir porosity is determined by the dosage of the first composition at 0.05-0.3 cm³. 3 The amount of carbon dioxide used is 0.05-0.2 cm³. 3 .

4. The method according to claim 1, wherein, The weight ratio of the fatty alcohol polyoxyethylene ether sulfate, alkyl hydroxypropyl phosphate betaine, alkyl glycoside and coconut oil diethanolamide is 1:0.01-60:0.01-60:0.008-20, more preferably 1:0.01-0.6:0.01-60:0.008-0.01; And / or, the second solvent is water, wherein, based on the total weight of the second composition, the content of the fatty alcohol polyoxyethylene ether sulfate is 0.005-0.5 wt%, preferably 0.4-0.5 wt%, the content of the alkyl hydroxypropyl phosphate betaine is 0.005-0.5 wt%, preferably 0.1-0.3 wt%, the content of the alkyl glycoside is 0.005-0.3 wt%, preferably 0.005-0.008 wt%, and the content of the coconut oil diethanolamide is 0.004-0.1 wt%, preferably 0.004-0.008 wt%.

5. The method according to claim 4, wherein, The anionic structure of the fatty alcohol polyoxyethylene ether sulfate is RO(CH2CH2O). n SO3 - Where n is 2-3, and R is a C8-C18 alkyl group, preferably a C12-C14 alkyl group; And / or, the alkyl group in the alkyl hydroxypropyl phosphate betaine is a C8-C16 alkyl group, preferably a C12-C14 alkyl group; And / or, the alkyl group in the alkyl glycoside is a C8-C16 alkyl group, preferably a C8-C14 alkyl group.

6. The method according to claim 4 or 5, wherein, Compared to 1cm 3 The reservoir porosity is determined by the amount of the second composition used, which is 0.05-0.3 cm³. 3 .

7. The method according to claim 1, wherein, The method further includes: performing step (1-A) before step (1), injecting montmorillonite-modified rubber into the reservoir, and then injecting carbon dioxide; Preferably, the preparation method of the montmorillonite-modified rubber includes the following steps: (a) Hydrate and peel the montmorillonite, then add latex and mix, and then dry; (b) The dried product is crushed, then mixed with crosslinking agent, accelerator, activator, and anti-aging agent, and then plasticized and / or compounded, and then vulcanized. Preferably, the montmorillonite-modified rubber is injected into the reservoir in the form of an aqueous suspension, and the concentration of the montmorillonite-modified rubber aqueous suspension is 0.01-10% by weight. More preferably, relative to 1cm 3 The reservoir porosity was determined by the amount of montmorillonite-modified rubber aqueous suspension used, which was 0.05-0.3 cm³. 3 The amount of carbon dioxide used is 0.05-0.2 cm³. 3 .

8. The method according to claim 7, wherein, The particle size of the montmorillonite is 100-500 mesh, preferably 200-300 mesh; And / or, the solid content of the latex is 50-80% by weight; And / or, the amount of montmorillonite used is 1-50g, preferably 5-40g, relative to 100g of latex; And / or, the hydration stripping is carried out under alkaline conditions provided by alkali metal hydroxides and / or weak acid salts of alkali metals.

9. The method according to claim 7 or 8, wherein, The crushing conditions result in a particle size of 20-500 mesh, preferably 50-200 mesh; And / or, the crosslinking agent is sulfur; the amount of the crosslinking agent is 1-5g, preferably 1-3g, relative to 100g of latex; And / or, the accelerator is N-cyclohexyl-2-benzothiazole sulfenamide; the amount of the accelerator is 0.2-3g, preferably 0.2-2g, relative to 100g of latex; And / or, the activator includes a first activator and a second activator, wherein the first activator is stearic acid, and the amount of the first activator is 1-3g, preferably 0.1-2g, relative to 100g of latex; and the second activator is ZnO, and the amount of the second activator is 1-8g, preferably 1-6g, relative to 100g of latex. And / or, the anti-aging agent is a 2,2,4-trimethyl-1,2-dihydroquinoline polymer, and the amount of the anti-aging agent is 0.2-3g, preferably 0.2-2.5g, relative to 100g of latex; And / or, the vulcanization conditions include: a temperature of 120-155°C, preferably 135-150°C; and a pressure of 12-18 MPa, preferably 14-16 MPa.

10. The method according to claim 1, wherein, When the width of the fractures in the reservoir is greater than 100 μm, the carbon dioxide flooding method includes steps (1-A), (1) and (2); And / or, when the width of the fractures in the reservoir is ≤100μm or there are no fractures, the carbon dioxide flooding method includes steps (1) and (2).

11. The application of the montmorillonite-modified rubber according to any one of claims 7-9 in carbon dioxide flooding.

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