A nitrogen surfactant composite throughput method and application

Abstract

The present invention provides a nitrogen surfactant composite injection method and application, and relates to the field of oil production technology. The method comprises sequentially injecting a composite surfactant front plug, a nitrogen main plug, a composite surfactant rear plug, and a nitrogen rear plug into the oil reservoir, shutting the well, and opening the well for production; wherein the composite surfactant in the composite surfactant front plug and the composite surfactant rear plug comprises: a main surfactant, an auxiliary surfactant, and water; the main surfactant comprises an oil-soluble surfactant and a fatty amide propyl dimethyl amine oxide; the auxiliary surfactant comprises a fatty alcohol polyoxyethylene polyoxypropylene block copolymer and a natural surfactant. The method can greatly reduce the oil-water interfacial tension, and can effectively inhibit the occurrence of gas cross-flow in the exploitation of low-permeability fault block oil reservoirs. The reagent enters a farther well area under the high pressure of nitrogen, thereby improving the oil washing efficiency and oil increase effect.

Description

Technical Field

[0001] The invention belongs to the technical field of oil production, and in particular relates to a nitrogen surfactant composite throughput method and application. Background Art

[0002] Tertiary oil recovery is a technology that relies on various physical and chemical methods to change the viscosity of crude oil and its adsorption to rocks, increase the fluidity of crude oil, and further improve the recovery rate of crude oil. The main methods of tertiary oil recovery include thermal oil recovery, chemical flooding (such as polymer flooding), gas flooding, miscible flooding, microbial flooding, etc.

[0003] The thickness, permeability and planar physical properties of low-permeability reservoirs vary greatly, and the formation energy decreases rapidly; fault-block reservoirs usually have a small oil-bearing area, many faults, narrow oil-bearing strips, complex oil-water relationships, and large differences in fluid density, viscosity and other physical properties in different blocks and different strata. For the above two types of reservoirs, gas injection production technology, especially nitrogen huff and puff production technology, has been used in recent years. However, due to the low viscosity and density of the gas during nitrogen huff and puff, the gas crossflow is serious and the huff and puff efficiency is low. In order to make up for the defects of gas crossflow during nitrogen huff and puff, people have developed nitrogen foam composite flooding, carbon dioxide foam composite flooding, air foam composite flooding and other technologies. Although the above methods are helpful to improve the problem of gas retention, they will also lead to some new problems, such as the poor stability of commonly used foaming agents. In addition, as the huff and puff process proceeds, the amount of movable oil within the effective range of the huff and puff becomes less and less, the crude oil production becomes lower and lower, the huff and puff effect decreases, and the production cycle is short. Summary of the invention

[0004] The purpose of the present invention is to provide a nitrogen surfactant composite huff-and-puff method and application in view of the deficiencies of the prior art. The nitrogen surfactant composite huff-and-puff method provided by the present invention can effectively inhibit the occurrence of gas cross-flow in the exploitation of low-permeability fault block oil reservoirs, increase the swept volume of nitrogen, and improve the exploitation efficiency.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A nitrogen surfactant composite huff-and-puff method comprises: sequentially injecting a composite surfactant front slug, a nitrogen main body slug, a composite surfactant rear slug, and a nitrogen rear slug into an oil reservoir, shutting the well, and opening the well for production; wherein:

[0007] The composite surfactant in the composite surfactant front slug and the composite surfactant rear slug both comprises: a main surfactant, a secondary surfactant and water;

[0008] The main surfactant comprises an oil-soluble surfactant and fatty amide propyl dimethyl amine oxide;

[0009] The auxiliary surfactant comprises a fatty alcohol polyoxyethylene polyoxypropylene block copolymer and a natural surfactant.

[0010] Furthermore, the oil-soluble surfactant is selected from at least one of AEO-3, AEO-5, Span 20, Span 40, Span 60 and Span 80.

[0011] Furthermore, the fatty amide propyl dimethyl amine oxide is a C12-C16 fatty amide propyl dimethyl amine oxide, specifically at least one selected from dodecyl amide propyl dimethyl amine oxide, tetradecyl amide propyl dimethyl amine oxide, hexadecyl amide propyl dimethyl amine oxide, and octadecyl amide propyl dimethyl amine oxide.

[0012] Furthermore, the mass ratio of the oil-soluble surfactant and the fatty amide propyl dimethyl amine oxide in the main surfactant is (55-80):(20-45), preferably (70-75):(25-30).

[0013] Furthermore, the structural formula of the fatty alcohol polyoxyethylene polyoxypropylene block copolymer is shown below (I):

[0014] (I);

[0015] Among them, R is a C12-C16 alkane, m=5-10, and n=2-4.

[0016] The structure of the fatty alcohol polyoxyethylene polyoxypropylene block copolymer of the present invention is an amphiphilic structure, in which R represents a non-polar alkyl chain, m represents the polymerization degree of polyoxyethylene, and n represents the polymerization degree of polyoxypropylene.

[0017] Furthermore, the natural surfactant is selected from tea saponin and / or alkyl glycoside.

[0018] Furthermore, the mass ratio of the fatty alcohol polyoxyethylene polyoxypropylene block copolymer to the natural surfactant in the auxiliary surfactant is (75-90):(10-25), preferably (80-85):(15-20).

[0019] Furthermore, the mass ratio of the main surfactant to the auxiliary surfactant is 100:(10-30), preferably 100:(20-25).

[0020] Furthermore, the mass concentration of the composite surfactant is 0.2% to 1.0%.

[0021] Furthermore, the pH value of the complex surfactant is 5.5-6.5.

[0022] Furthermore, the total injection volume of the composite surfactant is 30 to 70 m 3 The injection volume of the composite surfactant front segment plug is 20% to 50% of the total injection volume of the composite surfactant.

[0023] Furthermore, the total amount of nitrogen injected is 80000-500000m 3 ; The injection amount of the nitrogen main segment plug is 70% to 90% of the total nitrogen injection amount.

[0024] Furthermore, the nitrogen injection pressure of the nitrogen main segment plug and the nitrogen rear segment plug is 14-35 MPa.

[0025] The nitrogen surfactant composite huff-and-puff method is applied in heavy oil reservoirs, low permeability reservoirs or fault block reservoirs.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The nitrogen surfactant composite huff-and-puff method provided by the present invention can greatly reduce the oil-water interfacial tension and effectively inhibit the occurrence of gas crossflow in the exploitation of low-permeability fault block oil reservoirs; the reagent enters the farther well area under the high pressure of nitrogen, which can develop the oil reservoir farther from the well area and improve the oil washing efficiency and oil increase effect.

[0028] 2. The nitrogen surfactant composite throughput method of the present invention adopts an oil-soluble surfactant and fatty amide propyl dimethyl amine oxide as main surfactants, and an amphoteric surfactant fatty amide propyl dimethyl amine oxide. Compared with other amphoteric surfactants such as betaine, fatty amide propyl dimethyl amine oxide can be combined with an oil-soluble surfactant, which is more helpful to improve the foaming property and foam stability of the composite surfactant, so that it will not burst quickly after contacting crude oil, thereby improving the mining effect; it can improve the ability of the surfactant to reduce the oil-water interfacial tension, change the wettability of the oil-wet rock surface, form a water-in-oil emulsion with lower viscosity, and improve the oil washing efficiency; it can also help to enhance the shrinkage effect on rock cement, increase the seepage pores of reservoir rocks, and reduce the seepage resistance, thereby extending the production cycle of oil wells and improving the liquid production capacity of oil wells.

[0029] 3. The nitrogen surfactant composite throughput method of the present invention adopts fatty alcohol polyoxyethylene polyoxypropylene block copolymer and natural surfactant as auxiliary surfactants, and controls parameters such as the degree of polymerization of the fatty alcohol polyoxyethylene polyoxypropylene block copolymer, which helps to further improve the foam stability of the composite surfactant, improve the heat resistance, and expand the scope of application; the use of natural surfactants also helps to further improve the foaming properties of the composite surfactant; with the mutual cooperation of the two, the foaming properties and foam stability of the surfactant can be greatly improved, and its temperature resistance and salt resistance can be improved, thereby improving the oil recovery efficiency.

[0030] 4. In the nitrogen surfactant composite throughput method of the present invention, the main surfactant and the auxiliary surfactant cooperate with each other, which not only makes it have good temperature resistance and salt resistance, but also increases the foaming ability and stability, and maximizes the oil washing efficiency and oil increasing effect.

[0031] 5. The nitrogen surfactant composite huff-and-puff method of the present invention can be used for heavy oil and low permeability reservoirs. It also has excellent oil-increasing effects on small fault blocks and small reservoirs with complex lithology where interwell fluidity is poor and other methods for improving oil recovery are ineffective. DETAILED DESCRIPTION

[0032] The following non-limiting examples can enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way. The following content is only an exemplary description of the scope of the present invention, and those skilled in the art can make various changes and modifications to the invention of the present invention based on the disclosed content, and they should also fall within the scope of the present invention.

[0033] The present invention is further described below by way of specific examples. Unless otherwise specified, the various chemical reagents used in the examples of the present invention are obtained through conventional commercial channels.

[0034] Examples 1 to 16

[0035] A nitrogen surfactant composite throughput method, comprising:

[0036] S1, injection of composite surfactant pre-slug;

[0037] S2, nitrogen main slug;

[0038] S3, composite surfactant post-slug;

[0039] S4, nitrogen post-slug;

[0040] S5, stewing well;

[0041] S6. Start well production.

[0042] The specific composition of the composite surfactant in the above steps S1 and S3 is shown in Table 1 below. In Table 1, the fatty alcohol polyoxyethylene polyoxypropylene block copolymers all meet the following conditions: R is a C12 alkane, the degree of polymerization of polyoxyethylene m is 10, and the degree of polymerization of polyoxypropylene n is 4; the mass concentration of the composite surfactant is 0.6%, and the pH of the composite surfactant is 5.5.

[0043] Table 1. Composite surfactant raw material composition

[0044]

[0045] Embodiment 17

[0046] The difference from Example 4 is that the dodecyl acylamidopropyl dimethyl amine oxide is replaced by an equal amount of octadecyl acylamidopropyl dimethyl amine oxide.

[0047] Embodiment 18

[0048] The difference from Example 4 is that the alkyl glycoside is replaced by an equal amount of tea saponin.

[0049] Embodiments 19 to 20

[0050] The difference from Example 4 is that the specific parameters of the fatty alcohol polyoxyethylene polyoxypropylene block copolymer are different, as shown in Table 2 below.

[0051] Table 2. Structures of fatty alcohol polyoxyethylene polyoxypropylene block copolymers

[0052]

[0053] Examples 21-22

[0054] The difference from Example 4 is that the pH value of the composite surfactant is different, as shown in Table 3 below.

[0055] Table 3. pH of composite surfactants

[0056]

[0057] Comparative Examples 1 to 6

[0058] The difference from Example 4 is that the composition of the composite surfactant is different, as shown in Table 4 below.

[0059] Table 4. Composite surfactant composition

[0060]

[0061] Comparative Example 7

[0062] Another nitrogen surfactant composite throughput method includes:

[0063] S1, inject nitrogen;

[0064] S2, injecting a composite surfactant; the composition formula of the composite surfactant is the same as that of Example 4;

[0065] S3, stew well;

[0066] S4. Start well production.

[0067] Test Example 1

[0068] Stability of composite surfactants

[0069] 1. Foaming performance at room temperature

[0070] Use a measuring cylinder to measure 200 mL of the composite surfactant in the above embodiments and comparative examples in an automatic mixer. After high-speed stirring at 3000 r / min for 60 s, the foam is introduced into a 1000 mL measuring cylinder to read the foam volume. At the same time, the timing is started immediately after pouring into the measuring cylinder. The time when half of the foam volume disappears is recorded as the foam half-life.

[0071] 2. Foaming performance after high temperature treatment

[0072] The composite surfactants in the above examples and comparative examples were treated at a constant temperature of 120° C. for 24 hours, cooled to room temperature, and then tested for foaming volume and half-life according to the above foaming performance test method to evaluate their temperature resistance.

[0073] 2. Salt resistance

[0074] The water in the composite surfactant was replaced with an equal amount of simulated formation water (with Na + +K + Concentration: 5868mg / L, Ca 2 + Concentration: 475mg / L, Mg 2+ Concentration: 388 mg / L), using crude oil with a viscosity of about 2000 mPa·s as the oil sample, and referring to the provisions of SY / T5370-2018, the interfacial tension between the sample solution and the oil sample was measured at 50°C.

[0075] The results are shown in Tables 5 and 6 below.

[0076] Table 5. Foaming volume and half-life

[0077]

[0078] Table 6. Interfacial tension

[0079]

[0080] The results show that the composite surfactant provided by the present invention has a large foaming volume and a long half-life, and has good foaming performance and foam stability. After high-temperature treatment, its foaming volume decreases, but it still has a large foaming volume, and the half-life decreases slightly or even increases, indicating that it has excellent temperature resistance; and under high-salt conditions, the composite surfactant forms an ultra-low interfacial tension with crude oil, indicating that it has excellent salt resistance.

[0081] Test Example 2

[0082] Oil washing performance

[0083] Take oil sand from a block of Shengli Oilfield, age it at 80℃ for 7 days according to the oil-sand ratio of 1:4, mix the oil sand with the composite surfactant at a mass ratio of 1:10, age it at 70℃ for 48 hours, extract the crude oil in the solution with petroleum ether, make up the volume with a colorimetric tube, and perform colorimetric analysis with a spectrophotometer at a wavelength of 430nm. Calculate the oil washing rate of the composite surfactant using the standard curve.

[0084] The results are shown in Table 7 below.

[0085] Table 7. Oil washing rate

[0086]

[0087] The results show that the oil washing rate of the composite surfactant provided by the present invention can reach more than 80%, indicating that the composite surfactant of the present invention can form a water-in-oil emulsion with low viscosity with crude oil, thereby improving the oil washing efficiency.

[0088] Test Example 3

[0089] To simulate the production process of low permeability and fault block reservoirs, the specific steps are as follows:

[0090] (1) Use quartz sand to fill the core tube to simulate low permeability reservoirs and fault block reservoirs;

[0091] Simulated fault block reservoir: permeability is 1500×10 -3 μm 2 , porosity 23.8%, temperature 70°C, oil saturation 85%, core tube inclination setting 15°, and viscosity 400 mPa·s under reservoir conditions;

[0092] Simulated low permeability reservoir: permeability 20×10 -3 μm 2 , porosity 13.6%, temperature 70°C, viscosity 200 mPa·s under reservoir conditions;

[0093] (2) Taking measures using the method provided by the present invention:

[0094] S1, composite surfactant front slug; injection volume for low permeability reservoir is 20m 3 The injection volume of the fault block reservoir is 30m 3 ;

[0095] S2, nitrogen main segment plug: low permeability reservoir: nitrogen injection volume 150000m 3 , injection pressure is controlled at 14Mpa; fault block reservoir: nitrogen injection volume 200000m 3 , the injection pressure is controlled at 14Mpa;

[0096] S3, composite surfactant post-slug; injection volume for low permeability reservoir is 20m3 The injection volume of the fault block reservoir is 30m 3 ;

[0097] S4, nitrogen post-slug; low permeability reservoir: nitrogen injection volume 60000m 3 , injection pressure is controlled at 24Mpa; fault block reservoir: nitrogen injection volume 150000m 3 , the injection pressure is controlled at 20Mpa;

[0098] S5. Keep the well well sealed and start mining after the core pressure stabilizes.

[0099] (3) Comparative Example 7 was set up to conduct nitrogen huff-and-puff experiments in fault-block reservoirs:

[0100] Low permeability reservoir: First inject nitrogen 210000m 3 , the injection pressure is controlled at 24Mpa; then the composite surfactant is injected for 40m 3 ; Keep the well still and start mining after the core pressure stabilizes.

[0101] Fault-block reservoir: First inject nitrogen 350,000m 3 , the injection pressure is controlled at 20Mpa; then the composite surfactant is injected for 60m 3 ; Keep the well still and start mining after the core pressure stabilizes.

[0102] (4) A group of nitrogen injection experiments in fault-block reservoirs was set up as a control group: nitrogen was injected into the core tube through the production well at a rate of 1 mL / min. When the core tube pressure increased to 6 MPa, nitrogen injection was stopped and the well was shut down. Production was carried out after the core pressure stabilized.

[0103] (5) Monitor the daily oil production during the exploitation phase. When the daily oil production is less than 1 t / d, terminate the production cycle.

[0104] After one cycle of production is completed, steps (2) to (4) are repeated for three cycles of production. The degree of recovery in each cycle is recorded, and the total recovery of the three cycles is calculated relative to the increase in oil recovery in the control group with nitrogen injection.

[0105] The results are shown in Table 8 below.

[0106] Table 8. Oil recovery enhancement

[0107]

[0108] The results show that the nitrogen surfactant composite huff-and-puff method provided by the present invention can increase the total recovery rate of fault-block reservoirs by more than 18% after three production cycles compared with nitrogen huff-and-puff, and can increase the total recovery rate of low-permeability reservoirs by more than 14% after three production cycles compared with nitrogen huff-and-puff, with significant oil-increasing effects. In addition, in the simulation of low-permeability and fault-block reservoir tests, the crude oil is a heavy oil standard, indicating that the method provided by the present invention can be applied to heavy oil treatment.

[0109] Application Example 1

[0110] The present invention selects a typical low-permeability block of Shengli Oilfield for the test. The reservoir is buried at a depth of about 1800m, with an average effective thickness of 17.8m, an average porosity of 12.7%, and an average permeability of 4.6×10 -3 μm 2 The average formation pressure is 19MPa, the average oil layer temperature is 70℃, the crude oil viscosity is 1.65mPa·s, and the water content is 76%, which is a "low permeability" reservoir. Before the measures were taken, the well produced 6.5 cubic meters of liquid and 1.6 tons of oil per day, with a water content of 72%.

[0111] The method provided by the present invention is used to take measures on the well, and the specific steps are as follows:

[0112] S1, inject the composite surfactant pre-slug in Example 4, the injection amount is 20m 3 ;

[0113] S2, nitrogen main segment plug: nitrogen injection volume 160000m 3 , the injection pressure is controlled at about 18Mpa;

[0114] S3, composite surfactant post-slug;

[0115] S4, nitrogen post-slug; nitrogen injection volume 80000m 3 , the injection pressure is controlled at about 30Mpa;

[0116] S5, stewing well for 7 days;

[0117] S6. Start well production.

[0118] After the above measures were taken, the well reached a maximum daily oil production of 6.62 tons in 108 days, with a daily increase of 5.02 tons. After 8 months of production after the implementation of the plan, the measures continued to be effective. In 8 months (calculated as 245 days), the average daily oil production was 4.72 tons, the average daily liquid production was 4.8 cubic meters, the water content was 55%, the cumulative oil production increased by 764 tons, the average daily increase was 3.12 tons, and it is still effectively increased by more than 2.8 tons. It can be seen that the low permeability oil reservoir well is mined by the method provided by the present invention, and its oil production is greatly improved, indicating that the method provided by the present invention can be used for the exploitation of low permeability oil reservoirs and improve the oil recovery of low permeability oil reservoirs.

[0119] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A nitrogen surfactant composite throughput method, characterized in that: include: The composite surfactant front slug, nitrogen main slug, composite surfactant rear slug, and nitrogen rear slug are sequentially injected into the reservoir, the well is shut down, and the well is opened for production; wherein, The composite surfactant in the composite surfactant front slug and the composite surfactant rear slug both comprises: a main surfactant, a secondary surfactant and water; The mass ratio of the main surfactant to the auxiliary surfactant is 100:10-30; The main surfactant comprises an oil-soluble surfactant and a fatty amide propyl dimethyl amine oxide in a mass ratio of 55 to 80:20 to 45; The auxiliary surfactant comprises a fatty alcohol polyoxyethylene polyoxypropylene block copolymer and a natural surfactant in a mass ratio of 75 to 90:10 to 25; The natural surfactant is selected from tea saponin and / or alkyl glycoside; The oil-soluble surfactant is selected from at least one of AEO-3, AEO-5, Span 20, Span 40, Span 60 and Span 80.

2. The nitrogen surfactant composite throughput method according to claim 1, characterized in that: The fatty amide propyl dimethyl amine oxide is selected from at least one of dodecyl amide propyl dimethyl amine oxide, tetradecyl amide propyl dimethyl amine oxide, hexadecyl amide propyl dimethyl amine oxide, and octadecyl amide propyl dimethyl amine oxide.

3. The nitrogen surfactant composite throughput method according to claim 1, characterized in that: The mass ratio of the oil-soluble surfactant to the fatty amide propyl dimethyl amine oxide is 70-75:25-30.

4. The nitrogen surfactant composite throughput method according to claim 1, characterized in that: The structural formula of the fatty alcohol polyoxyethylene polyoxypropylene block copolymer is shown as (I): （I）； Among them, R is a C12-C16 alkane, m=5-10, and n=2-4.

5. The nitrogen surfactant composite throughput method according to claim 1, characterized in that: The mass ratio of the fatty alcohol polyoxyethylene polyoxypropylene block copolymer to the natural surfactant is 80-85:15-20.

6. The nitrogen surfactant composite throughput method according to claim 1, characterized in that: The mass ratio of the main surfactant to the auxiliary surfactant is 100:20-25.

7. The nitrogen surfactant composite throughput method according to claim 1, characterized in that: The total injection volume of the composite surfactant is 30 to 70 m 3 The injection volume of the composite surfactant front segment plug is 20% to 50% of the total injection volume of the composite surfactant.

8. The nitrogen surfactant composite throughput method according to claim 1, characterized in that: The total amount of nitrogen injected is 80000~500000m 3 ; The injection amount of the nitrogen main segment plug is 70% to 90% of the total nitrogen injection amount.

9. Application of the nitrogen surfactant composite huff-and-puff method according to any one of claims 1 to 8 in heavy oil reservoirs, low permeability reservoirs or fault-block reservoirs.

Images