Oil-displacing agent for chemical flooding of thickened oil and oil-displacing effect evaluation method

Abstract

The invention provides an oil-displacing agent for chemical flooding of thickened oil and an oil-displacing effect evaluation method, and belongs to the technical field of oilfield development. The oil-displacing agent for chemical flooding of thickened oil comprises a main surfactant, an auxiliary surfactant, low-carbon alcohol and the balance of water, wherein the main surface active agent is prepared from straight-chain fatty alcohol polyoxyethylene ether, isomeric fatty secondary alcohol polyoxyethylene ether and an anionic surface active agent; the auxiliary surfactant is a methyl glucoside derivative. The oil-displacing agent for chemical flooding of thickened oil is good in emulsification viscosity reduction, capable of effectively reducing interfacial tension, high in salt resistance, resistant to stratum adsorption and good in compatibility. According to the oil displacement effect evaluation method, comprehensive evaluation of the chemical oil displacement agent is achieved, the method is simple, the oil displacement agent with the better comprehensive oil displacement effect can be rapidly screened out, and the method has important practical significance on development of water-drive heavy oil reservoirs.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield development, and in particular to an oil displacement agent for heavy oil chemical flooding and an oil displacement effect evaluation method. Background Art

[0002] my country is rich in heavy oil and extra-heavy oil resources. Due to the high viscosity of heavy oil, its fluidity in the reservoir is poor, so reducing the viscosity of heavy oil is the key to improving the recovery rate of heavy oil. Cold recovery and viscosity reduction chemical flooding technology is a common mining technology for heavy oil reservoirs. This technology injects oil displacement agent solution into the formation to change the interface properties of crude oil, rock and water, thereby greatly increasing the oil displacement efficiency and improving the recovery rate. The development potential of cold recovery and viscosity reduction chemical flooding technology is huge.

[0003] With the continuous development of heavy oil reservoirs, cold recovery viscosity reduction chemical flooding technology has developed rapidly. At present, the research on viscosity reducers for heavy oil chemical flooding has made great progress. However, although the current viscosity reducers for heavy oil chemical flooding can reduce the oil-water interfacial tension and achieve emulsification and viscosity reduction of heavy oil, they may have problems such as poor resistance to formation adsorption and poor salt resistance, which affect the oil recovery rate; and due to the differences in the physical properties of crude oil in different blocks, a viscosity reducer cannot achieve good results in oil reservoirs in all blocks. Therefore, it is necessary to improve the existing oil displacement agent to adapt to the exploitation of complex oil reservoirs. Whether the oil displacement agent is suitable for the exploitation of oil reservoirs requires a pilot oil displacement test, and the appropriate viscosity reducer can be selected based on the evaluation of the oil displacement effect. However, most of the existing evaluation methods for chemical viscosity reducers still use the evaluation indicators and methods of water flooding. The oil displacement mechanisms of water flooding and chemical flooding are different. The oil displacement effect predicted by the water flooding evaluation method is quite different from the indoor measured and actual oil displacement effect. In addition, many evaluation methods only study a certain performance indicator of the oil displacement agent. The screened oil displacement agent cannot guarantee a favorable practical application effect when dealing with complex oil reservoirs. Therefore, it is necessary to provide a comprehensive oil displacement effect evaluation method for screening suitable viscosity reducers. Summary of the invention

[0004] In view of the shortcomings of the prior art, the first object of the present invention is to provide an oil-displacing agent for heavy oil chemical flooding, which has strong salt resistance and is resistant to formation adsorption.

[0005] The second object of the present invention is to provide an oil displacement effect evaluation method, which is simple and can quickly screen out oil displacement agents with better comprehensive oil displacement effects, and has important practical significance for the development of heavy oil reservoirs.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows: In one aspect, a heavy oil chemical flooding oil displacing agent comprises, by mass percentage, 35-50% of a main surfactant, 3.5-7.5% of a secondary surfactant, 10-15% of a low-carbon alcohol, and the remainder is water; Wherein, the main surfactant comprises straight-chain fatty alcohol polyoxyethylene ether, isomeric fatty secondary alcohol polyoxyethylene ether and anionic surfactant; The cosurfactant is a methyl glucoside derivative.

[0007] Furthermore, the mass ratio of the main surfactant to the auxiliary surfactant is 10:(1-1.5).

[0008] Furthermore, in the main surfactant, the mass ratio of the straight-chain fatty alcohol polyoxyethylene ether, the isomeric fatty secondary alcohol polyoxyethylene ether and the anionic surfactant is (40-55):(40-50):(5-10).

[0009] Furthermore, the carbon chain length of the linear fatty alcohol in the linear fatty alcohol polyoxyethylene ether is 18-25, and the polymerization degree of ethylene oxide in the linear fatty alcohol polyoxyethylene ether is 10-14.

[0010] Furthermore, the carbon chain length of the isomeric fatty secondary alcohol in the isomeric fatty secondary alcohol polyoxyethylene ether is 10-14, and the polymerization degree of ethylene oxide in the isomeric fatty secondary alcohol polyoxyethylene ether is 5-8.

[0011] Furthermore, the anionic surfactant is sodium dodecylbenzene sulfonate and / or sodium dodecyl sulfate.

[0012] Furthermore, the methyl glucoside derivative is selected from methyl glucose polyoxyethylene ether and / or methyl glucose polyoxyethylene ether benzoate, and the polymerization degree of ethylene oxide in the methyl glucose polyoxyethylene ether and methyl glucose polyoxyethylene ether benzoate is 20-25.

[0013] Furthermore, the low-carbon alcohol is selected from at least one of methanol, ethanol, propanol, isopropanol and butanol.

[0014] In a further embodiment, the heavy oil chemical flooding oil displacing agent further comprises 0.5-2% by mass of modified nano-calcium carbonate, wherein the modified nano-calcium carbonate is prepared by modifying the nano-calcium carbonate with epoxy linseed oil and fatty amine, and the carbon chain length of the fatty amine is 5-7. The addition of modified nano-calcium carbonate helps to further improve the resistance to formation adsorption and salt resistance of the oil displacing agent, improve viscosity reduction, and thus improve recovery.

[0015] Preferably, the mass ratio of the epoxy linseed oil, fatty amine and nano-calcium carbonate is (15-25):(5-10):100.

[0016] Preferably, the particle size of the nano calcium carbonate is 20 to 60 nm.

[0017] Specifically, the modified nano calcium carbonate is prepared by the following method: Nano calcium carbonate is dispersed in ether, ultrasonically treated, then heated to 50-70°C, sodium hydroxide solution is added to adjust to alkalinity, and epoxy linseed oil is added to react with fatty amine. After the reaction is completed, the modified nano calcium carbonate is taken out, washed with water, and dried to obtain the modified nano calcium carbonate.

[0018] Preferably, in the process of preparing modified nano-calcium carbonate, the mass fraction of the sodium hydroxide solution is 5-20%; the amount of the sodium hydroxide solution used is 2-8% of the mass of the nano-calcium carbonate.

[0019] Preferably, in the process of preparing modified nano-calcium carbonate, the power of the ultrasonic treatment is 200-300 W and the time is 10-30 min.

[0020] On the other hand, a method for preparing the above-mentioned heavy oil chemical flooding oil displacing agent comprises the following steps: The main surfactant is added to the low-carbon alcohol, mixed well, and then water is added to stir and react, and then the auxiliary surfactant is added, and the temperature is raised to 35-40° C. and kept warm for reaction to obtain the oil displacement agent for heavy oil chemical flooding.

[0021] Furthermore, the stirring reaction time at room temperature is 20 to 30 minutes.

[0022] Furthermore, the reaction time of the heat preservation reaction is 30 to 50 minutes.

[0023] Furthermore, the step of adding modified nano calcium carbonate is further included after adding the auxiliary surfactant.

[0024] In another aspect, a method for evaluating the oil displacement effect of the above-mentioned heavy oil chemical flooding oil displacement agent comprises the following steps: S1. Obtaining evaluation index parameters; the evaluation indexes include water content change rate, viscosity change rate, viscosity reduction rate change rate after adsorption, high salt interfacial tension change rate, and oil recovery change rate; S2, scoring the five evaluation indicators of step S1 respectively; S3. Classify the five evaluation indicators and determine the indicator weights; S4, obtaining data of five evaluation indicators of the oil displacement agent for heavy oil chemical flooding, substituting them into the following formula (I), and calculating the comprehensive evaluation value of the oil displacement effect; M=A*X1+B*X2+C*X3+D*X4+E*X5(I); In formula (I), A, B, C, D, and E represent the change rate of water content, the change rate of viscosity, the change rate of viscosity reduction after adsorption, the change rate of high-salinity interfacial tension, and the change rate of oil recovery, respectively; X1, X2, X3, X4, and X5 correspond to the weight values ​​of the change rate of water content, the change rate of viscosity, the change rate of viscosity reduction after adsorption, the change rate of high-salinity interfacial tension, and the change rate of oil recovery, respectively.

[0025] Furthermore, in step (1), the water content change rate refers to the change range between the water content A2 of the current month and the water content A1 of the previous month; the water content change rate A is calculated by the formula: A=|A2-A1|; The viscosity change rate B is calculated based on the viscosity of the crude oil after viscosity reduction B2 and the initial crude oil viscosity B1; the viscosity change rate B is calculated as follows: B=|B2-B1| / B1*100%; The viscosity reduction rate after adsorption C is calculated based on the viscosity reduction rate after adsorption C2 and the initial viscosity reduction rate C1. The viscosity reduction rate after adsorption C is used to evaluate its adsorption resistance to formations. The smaller the C value, the better the adsorption resistance to formations. The calculation formula of the viscosity reduction rate after adsorption C is: C=|C2-C1| / C1*100%; The high-salt interfacial tension change rate D is calculated based on the interfacial tension D2 and the initial interfacial tension D1 under high-salt conditions. The high-salt interfacial tension change rate D is used to evaluate salt tolerance. The smaller the D value, the better the salt tolerance. The high-salt interfacial tension change rate D is calculated as follows: D=|D2-D1| / D1*100%; The oil production change rate refers to the change in the current month's average daily oil production E2 and the previous month's average daily oil production E2; the calculation formula for the oil production change rate E is: E=|E2-E1|.

[0026] Compared with the prior art, the present invention has the following beneficial effects: 1. The oil displacing agent for heavy oil chemical flooding provided by the present invention has good emulsification and viscosity reduction properties, can effectively reduce interfacial tension, has strong salt resistance and is resistant to formation adsorption.

[0027] 2. The oil displacing agent for heavy oil chemical flooding of the present invention uses straight-chain fatty alcohol polyoxyethylene ether, isomerized fatty secondary alcohol polyoxyethylene ether and anionic surfactant as main surfactants. Compared with other surfactants, the addition of straight-chain fatty alcohol polyoxyethylene ether and isomerized fatty secondary alcohol polyoxyethylene ether, combined with anionic surfactant, makes the oil displacing agent have better emulsification and viscosity reduction properties, and the ability to reduce interfacial tension, thereby improving the salt resistance and formation adsorption resistance of the oil displacing agent and increasing the oil recovery rate.

[0028] 3. The methyl glucoside derivative is added as a co-surfactant to the heavy oil chemical flooding oil displacing agent of the present invention. The main and auxiliary surfactants cooperate with each other to help further improve the viscosity reduction of the oil displacing agent, enhance salt resistance and formation adsorption resistance, and increase oil recovery.

[0029] 4. The main and auxiliary surfactants of the present invention cooperate with each other and work together, which not only enables the heavy oil chemical flooding oil displacement agent to have excellent salt resistance and formation adsorption resistance, but also helps to improve its temperature resistance.

[0030] 5. The oil displacement effect evaluation method provided by the present invention realizes the comprehensive evaluation of chemical oil displacement agents. The method is simple and can quickly screen out oil displacement agents with better comprehensive oil displacement effects, which has important practical significance for the development of water-driven heavy oil reservoirs. DETAILED DESCRIPTION

[0031] 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.

[0032] In the following specific examples, the straight chain C 18 AEO 14 For example, the "C 18 " refers to the carbon chain length of the straight chain fatty alcohol in the straight chain fatty alcohol polyoxyethylene ether is 18, "AEO 14 " means that the degree of polymerization of ethylene oxide in the linear fatty alcohol polyoxyethylene ether is 14. This is an example, and other abbreviations are the same as the above unless otherwise specified.

[0033] In the following specific examples, "SDBS" means sodium dodecylbenzene sulfonate, and "SDS" means sodium dodecyl sulfate.

[0034] 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.

[0035] Examples 1 to 7 An oil displacement agent for heavy oil chemical flooding, comprising the following components in percentage by mass: The main surfactant is 35-50%, the auxiliary surfactant is 3.5-7.5%, the isopropanol is 12%, and the balance is water; wherein the specific composition of the main surfactant and the auxiliary surfactant is shown in Table 1 below: Table 1

[0036] The above-mentioned heavy oil chemical flooding oil displacing agent is prepared by the following method: The main surfactant was added to the low-carbon alcohol, mixed well, and then water was added and stirred for reaction for 30 minutes. Then the auxiliary surfactant was added, the temperature was raised to 40°C and kept for reaction for 50 minutes to obtain the oil displacement agent for heavy oil chemical flooding.

[0037] Embodiments 8 to 13 Another heavy oil chemical flooding agent is different from Example 2 in that 2% of modified nano calcium carbonate is added, and the modified nano calcium carbonate is prepared by the following method: Nano-calcium carbonate is dispersed in sufficient ether, ultrasonically treated at 300 W for 20 minutes, then heated to 70°C, and adjusted to alkalinity by adding 10% by mass sodium hydroxide solution, and epoxy linseed oil is added to react with fatty amine. After the reaction is completed, the mixture is taken out, washed with water, and dried to obtain modified nano-calcium carbonate; the carbon chain length of the above-mentioned fatty amine is 5 to 7, and the mass ratio of epoxy linseed oil, fatty amine and nano-calcium carbonate is (15 to 25):(5 to 10):100.

[0038] The specific dosage of the fatty amine and the modifier is shown in Table 2 below: Table 2

[0039] Comparative Examples 1 to 6 Another heavy oil chemical flooding agent is different from Example 2 in that the main surfactant and auxiliary surfactant components are shown in Table 3 below: Table 3

[0040] Embodiment 14 A method for evaluating oil displacement effect comprises the following steps: S1. Obtaining evaluation index parameters; the evaluation indexes include water content change rate, viscosity change rate, viscosity reduction rate change rate after adsorption, high salt interfacial tension change rate, and oil recovery change rate; S2, scoring the five evaluation indicators of step S1 respectively; The scoring criteria are as follows4: Table 4

[0041] S3. Classify the five evaluation indicators and determine the indicator weights; The weights of the above evaluation indicators are divided into the following table 5: Table 5

[0042] S4. Obtain data on five evaluation indicators of the oil displacement agent for heavy oil chemical flooding; wherein, the water content test method is: the oil displacement agent is prepared with simulated formation water with a salinity of 250,000 mg / L to prepare a 0.3% solution, and then the solution is measured in accordance with the petroleum industry standard SY / T0520-2008; The viscosity change rate B is calculated as: B=|B2-B1| / B1*100%; the test method is: the oil displacement agent is prepared with 0.3% solution of simulated formation water with a salinity of 250,000 mg / L, and then measured in accordance with the petroleum industry standard SY / T 0520-2008.

[0043] The calculation formula of viscosity reduction rate C after adsorption is: C=|C2-C1| / C1*100%; the test method is: first mix the chemical flooding agent with the simulated formation sand and adsorb it for 24 hours, then test the viscosity change rate C2 (i.e., viscosity reduction rate) at this time, and calculate it with the initial viscosity change rate C1.

[0044] The calculation formula of high-salinity interfacial tension change rate D is: D=|D2-D1| / D1*100%; the test method is: the oil displacement agent is prepared with a 0.3% solution of simulated formation water with a salinity of 250000 mg / L to prepare a sample, and the interfacial tension is measured as D1 according to SY / T 5370-2018, and Ca 2+ Concentration 2000mg / L, Mg 2+ The simulated formation water with a concentration of 2000 mg / L and a salinity of 250000 mg / L was used to prepare the oil displacement agent sample solution, and the interfacial tension was measured as D2.

[0045] The test methods for water content change rate and oil production change rate are as follows: Taking the test area of ​​Block B of Changqing Ansai Oilfield as an example, the oil layer thickness in the test area is 1500m, the underground viscosity of crude oil is 13.7mPa•s, the effective thickness is 18.0m, the porosity is 13.7%, the permeability is 2.29mdc, the water content is 97.7%, and the daily oil production is 1.7t.

[0046] The results are shown in Tables 6 and 7 below.

[0047] Table 6

[0048] Table 7

[0049] Substitute the above data into the following formula (I) to calculate the comprehensive evaluation value of oil displacement effect; M=A*0.25+B*0.25+C*0.125+D*0.125+E*0.25; The comprehensive evaluation values ​​of each group are shown in Table 8 below.

[0050] Table 8

[0051] In summary, the heavy oil chemical flooding oil displacing agent provided by the present invention has excellent emulsification and viscosity reduction properties through the mutual cooperation of the main and auxiliary surfactants, can significantly reduce the oil-water interfacial tension, has strong salt resistance, good formation adsorption resistance, and can greatly improve the oil recovery rate; and the oil displacement effect evaluation method of the heavy oil chemical flooding oil displacing agent provided by the present invention can quickly screen out the oil displacing agent with better comprehensive oil displacement effect, which has important practical significance for the development of water-driven heavy oil reservoirs.

[0052] 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 heavy oil chemical flooding oil displacing agent, characterized in that: Calculated by mass percentage, it contains 35-50% of a main surfactant, 3.5-7.5% of an auxiliary surfactant, 10-15% of a low-carbon alcohol, and the balance is water; The main surfactant comprises a linear fatty alcohol polyoxyethylene ether, an isomeric fatty secondary alcohol polyoxyethylene ether and an anionic surfactant in a mass ratio of (40-55):(40-50):(5-10); The cosurfactant is a methyl glucoside derivative.

2. The oil displacing agent for heavy oil chemical flooding according to claim 1, characterized in that: The mass ratio of the main surfactant to the auxiliary surfactant is 10:(1-1.5).

3. The oil displacing agent for heavy oil chemical flooding according to claim 1, characterized in that: The carbon chain length of the linear fatty alcohol in the linear fatty alcohol polyoxyethylene ether is 18 to 25, and the degree of polymerization of ethylene oxide in the linear fatty alcohol polyoxyethylene ether is 10 to 14; the carbon chain length of the isomeric fatty secondary alcohol in the isomeric fatty secondary alcohol polyoxyethylene ether is 10 to 14, and the degree of polymerization of ethylene oxide in the isomeric fatty secondary alcohol polyoxyethylene ether is 5 to 8.

4. The oil displacing agent for heavy oil chemical flooding according to claim 1, characterized in that: The methyl glucoside derivative is selected from methyl glucose polyoxyethylene ether and / or methyl glucose polyoxyethylene ether benzoate, and the polymerization degree of ethylene oxide in the methyl glucose polyoxyethylene ether and methyl glucose polyoxyethylene ether benzoate is 20-25.

5. The oil displacing agent for heavy oil chemical flooding according to claim 1, characterized in that: The heavy oil chemical flooding oil displacing agent also contains 0.5-2% by mass of modified nano-calcium carbonate, which is prepared by modifying the nano-calcium carbonate with epoxy linseed oil and fatty amine.

6. The oil displacing agent for heavy oil chemical flooding according to claim 5, characterized in that: The mass ratio of epoxy linseed oil, fatty amine and nano calcium carbonate in the modified nano calcium carbonate is (15-25):(5-10):

100.

7. A method for evaluating the oil displacement effect of the oil displacement agent for heavy oil chemical flooding according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. Obtaining evaluation index parameters; the evaluation indexes include water content change rate, viscosity change rate, viscosity reduction rate change rate after adsorption, high salt interfacial tension change rate, and oil recovery change rate; S2, scoring the five evaluation indicators of step S1 respectively; S3. Classify the five evaluation indicators and determine the indicator weights; S4. Testing the data of the five evaluation indicators of the heavy oil chemical flooding agent according to any one of claims 1 to 6, substituting the data into the following formula (I), and calculating the comprehensive evaluation value of the oil displacement effect; M=A*X1+B*X2+C*X3+D*X4+E*X5(I); In formula (I), A, B, C, D, and E represent the change rate of water content, the change rate of viscosity, the change rate of viscosity reduction after adsorption, the change rate of high-salinity interfacial tension, and the change rate of oil recovery, respectively; X1, X2, X3, X4, and X5 correspond to the weight values ​​of the change rate of water content, the change rate of viscosity, the change rate of viscosity reduction after adsorption, the change rate of high-salinity interfacial tension, and the change rate of oil recovery, respectively.

8. The method for evaluating oil displacement effect according to claim 7, characterized in that: In step S1, the moisture content change rate refers to the change range between the moisture content A2 of the current month and the moisture content A1 of the previous month; the moisture content change rate A is calculated as: A=|A2-A1|.

9. The oil displacement effect evaluation method according to claim 7, characterized in that: The viscosity reduction rate of change after adsorption C is calculated based on the viscosity reduction rate after adsorption C2 and the initial viscosity reduction rate C1. The viscosity reduction rate of change after adsorption C is used to evaluate its resistance to formation adsorption performance. The smaller the C value, the better the resistance to formation adsorption performance. The calculation formula of the viscosity reduction rate of change after adsorption C is: C=|C2-C1| / C1*100%.

10. The method for evaluating oil displacement effect according to claim 7, characterized in that: The high-salt interfacial tension change rate D is calculated based on the interfacial tension D2 and the initial interfacial tension D1 under high-salt conditions. The high-salt interfacial tension change rate D is used to evaluate salt resistance. The smaller the D value, the better the salt resistance. The calculation formula of the high-salt interfacial tension change rate D is: D=|D2-D1| / D1*100%.

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