A method for preparing sustained-release acid microcapsules and an oil displacement composition containing the same.

Abstract

This invention provides a method for preparing sustained-release acid microcapsules and an oil displacement composition containing the same. The method for preparing the sustained-release acid microcapsules includes the following steps: 1) dispersing paraformaldehyde in an organic solvent to obtain a paraformaldehyde suspension; 2) dissolving ethyl cellulose in the paraformaldehyde suspension, then adding polydimethylsiloxane and stirring to obtain a reaction suspension containing the sustained-release acid microcapsules; 3) centrifuging the suspension containing the sustained-release acid microcapsules to obtain a precipitate; 4) washing and drying the precipitate to obtain the sustained-release acid microcapsules. The oil displacement composition includes a heat-generating agent, sustained-release acid microcapsules, a surfactant, water, and optionally a thickener.

Description

Technical Field

[0001] This invention relates to the field of reservoir flooding, and particularly to a slow-release acid microcapsule composition for oil displacement. Background Technology

[0002] As oilfield development deepens, traditional light oil reservoirs are gradually entering the later stages of high-extraction, high-water-cut development. The development of high-viscosity crude oil (e.g., heavy oil / high-pour-point oil) is increasingly becoming a crucial guarantee for maintaining crude oil production. Heavy oil and low-temperature high-pour-point oil reservoirs have high underground crude oil viscosity. During traditional water injection development, the high water-oil mobility ratio and reservoir heterogeneity make the water phase prone to cross-flow, resulting in poor development performance and waterflood recovery rates of only around 5% to 10%. Furthermore, injecting large amounts of cold water will cause a decrease in reservoir temperature and a further increase in formation crude oil viscosity, affecting development effectiveness. For example, temperature monitoring in exploration wells of the Shen 84-An 12 oil reservoir revealed that the temperature drop in cold water-injected reservoirs reached a maximum of 16.2℃.

[0003] Thermal recovery (such as steam injection, steam drive, and hot water drive) is a method of displacing oil by injecting hot fluids into the formation to heat and reduce the viscosity of crude oil. It has achieved good results in the high recovery rate of heavy oil / high pour point oil. However, due to factors such as large heat loss from steam injection and steam crosstalk, the effectiveness of thermal recovery has deteriorated year by year; moreover, the practice of consuming a large amount of fuel to prepare hot fluids has become less adaptable. Summary of the Invention

[0004] One aspect of the present invention provides a method for preparing sustained-release acid microcapsules, comprising the following steps:

[0005] 1) Disperse paraformaldehyde in an organic solvent to obtain a paraformaldehyde suspension;

[0006] 2) Ethyl cellulose is dissolved in the paraformaldehyde suspension, and then polydimethylsiloxane is added and stirred to react, so as to obtain a suspension containing the sustained-release acid microcapsules;

[0007] 3) Centrifuge the suspension containing the sustained-release acid microcapsules to obtain the precipitate after centrifugation;

[0008] 4) The precipitate is washed and dried to obtain sustained-release acid microcapsules.

[0009] In one specific embodiment, the amount of paraformaldehyde is 1 part by mass, the amount of ethyl cellulose is 1 to 3 parts by mass, and the amount of polydimethylsiloxane is 30 to 40 parts by mass.

[0010] In one specific embodiment, the organic solvent is dichloromethane or the like.

[0011] In one specific embodiment, in step 3), the washing is first performed with petroleum ether, and then with water.

[0012] In one specific embodiment, in step 2), the stirring reaction lasts for 30 to 60 minutes.

[0013] In one specific embodiment, the particle size of the sustained-release acid microcapsules is 10 to 50 μm.

[0014] The second invention provides an oil displacement composition comprising a heat-generating agent, sustained-release acid microcapsules prepared by the method as described in any one of the first inventions, a surfactant, water, and optionally a thickener.

[0015] In one specific embodiment, the heat-generating agent is ammonium chloride and sodium nitrite.

[0016] In one specific embodiment, the mass ratio of the ammonium chloride to the sodium nitrite is 4:5.

[0017] In one specific embodiment, the surfactant is sodium dodecyl sulfate and sodium fatty alcohol polyoxyethylene ether sulfate.

[0018] In one specific embodiment, the mass ratio of sodium dodecyl sulfate to sodium fatty alcohol polyoxyethylene ether sulfate is 1:3 to 1.5:1.

[0019] In one specific embodiment, the thickener is an associative polyacrylamide.

[0020] In one specific embodiment, the thickener is AP-P5.

[0021] In one specific embodiment, based on the total mass of the oil displacement composition as 100%, the content of the heat-generating agent is 20% to 40%, the content of the slow-release acid microcapsules is 0.3% to 0.6%, the content of the surfactant is 0.3% to 0.5%, and the content of the thickener is 0.0% to 0.6%.

[0022] In one specific embodiment, the content of the thickener is 0.3% to 0.6%.

[0023] The third invention provides the application of sustained-release acid microcapsules prepared by the method described in any one of the first inventions, or the oil displacement composition described in any one of the second inventions, in oil displacement in high-viscosity crude oil reservoirs. The viscosity of the high-viscosity crude oil can be above 610 mPa·s.

[0024] The beneficial effects of this invention are:

[0025] This invention utilizes slow-release acid microcapsules to achieve slow acid generation, thereby delaying the reaction time and effectively expanding the affected reservoir area to improve oil recovery. It can also be used in combination with associative polyacrylamide for synergistic effects, further enhancing oil recovery. Furthermore, the combined use of SDS and AES also has a synergistic effect, effectively improving the recovery rate of controlled-flow oil recovery. Attached Figure Description

[0026] Figure 1 The curves showing the pH value of the oil displacement compositions of Examples 4 to 11 and Comparative Examples 1 to 4 at 70°C over time are displayed.

[0027] Figure 2 The curves showing the pH value of the oil displacement compositions of Examples 4 to 11 as a function of time are displayed.

[0028] Figure 3 The curves showing the pH value of the oil displacement compositions of Comparative Examples 1 to 4 as a function of time are displayed. Detailed Implementation

[0029] The present invention will be further described below with reference to the embodiments. However, the embodiments of the present invention are merely illustrative examples and should not be construed as limiting the present invention under any circumstances.

[0030] Paraformaldehyde was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0031] Preparation of sustained-release acid microcapsules

[0032] Example 1

[0033] One part by mass of paraformaldehyde was ground and uniformly dispersed in dichloromethane to obtain a paraformaldehyde suspension. Two parts by mass of ethyl cellulose were dissolved in the paraformaldehyde suspension under stirring. Then, 35 parts by mass of polydimethylsiloxane were added and stirred for 45 minutes to initiate a gelation reaction, resulting in a suspension containing sustained-release acid microcapsules. The suspension containing sustained-release acid microcapsules was centrifuged, and the precipitate after centrifugation was washed three times with petroleum ether and then three times with water. The precipitate was then vacuum dried to obtain sustained-release acid microcapsules with a particle size of 20 to 30 μm.

[0034] Example 2

[0035] One part by mass of paraformaldehyde was ground evenly and dispersed in dichloromethane to obtain a paraformaldehyde suspension. One part by mass of ethyl cellulose was dissolved in the paraformaldehyde suspension under stirring. Then, 30 parts by mass of polydimethylsiloxane were added and stirred for 30 minutes to initiate a gelation reaction, resulting in a suspension containing sustained-release acid microcapsules. The suspension containing sustained-release acid microcapsules was centrifuged, and the precipitate after centrifugation was washed three times with petroleum ether and then three times with water. The precipitate was then vacuum dried to obtain sustained-release acid microcapsules with a particle size of 10 to 25 μm.

[0036] Example 3

[0037] One part by mass of paraformaldehyde was ground and uniformly dispersed in dichloromethane to obtain a paraformaldehyde suspension. Three parts by mass of ethyl cellulose were dissolved in the paraformaldehyde suspension under stirring. Then, 40 parts by mass of polydimethylsiloxane were added and stirred for 60 min to initiate a gelation reaction, resulting in a suspension containing sustained-release acid microcapsules. The suspension containing sustained-release acid microcapsules was centrifuged, and the precipitate after centrifugation was washed three times with petroleum ether and then three times with water. The precipitate was then vacuum dried to obtain sustained-release acid microcapsules with a particle size of 28 to 50 μm.

[0038] Preparation of oil displacement composition

[0039] Example 4

[0040] 8.90g ammonium chloride, 11.10g sodium nitrite, 0.30g slow-release acid microcapsules prepared in Example 1, 0.15g sodium dodecyl sulfate (SDS) and 0.15g sodium fatty alcohol polyoxyethylene ether sulfate (AES) were added to 79.4g water and mixed evenly to obtain the oil displacement composition.

[0041] Example 5

[0042] 13.35g ammonium chloride, 16.65g sodium nitrite, 0.45g slow-release acid microcapsules prepared in Example 1, 0.2g sodium dodecyl sulfate (SDS), and 0.2g sodium fatty alcohol polyoxyethylene ether sulfate (AES) were added to 69.15g water and mixed evenly to obtain an oil displacement composition.

[0043] Example 6

[0044] 17.80g ammonium chloride, 22.20g sodium nitrite, 0.60g slow-release acid microcapsules prepared in Example 1, 0.25g sodium dodecyl sulfate (SDS) and 0.25g sodium fatty alcohol polyoxyethylene ether sulfate (AES) were added to 58.90g water and mixed evenly to obtain the oil displacement composition.

[0045] Example 7

[0046] 1) Add 8.90g ammonium chloride, 11.10g sodium nitrite, 0.30g sustained-release acid microcapsules prepared in Example 1, 0.15g sodium dodecyl sulfate (SDS) and 0.15g sodium fatty alcohol polyoxyethylene ether sulfate (AES) to 79.10g water and mix well to obtain the first aqueous solution;

[0047] 2) While stirring, slowly add 0.3g of associative polyacrylamide (AP-P5, Sichuan Guangya Polymer Chemical Co., Ltd.) to the first aqueous solution and stir until fully dissolved to obtain the oil displacement composition.

[0048] Example 8

[0049] 1) Add 13.35g ammonium chloride, 16.65g sodium nitrite, 0.45g sustained-release acid microcapsules prepared in Example 1, 0.2g sodium dodecyl sulfate (SDS), and 0.2g sodium fatty alcohol polyoxyethylene ether sulfate (AES) to 68.70g water and mix well to obtain the first aqueous solution;

[0050] 2) While stirring, slowly add 0.45g of associative polyacrylamide (AP-P5, Sichuan Guangya Polymer Chemical Co., Ltd.) to the first aqueous solution and stir until fully dissolved to obtain the oil displacement composition.

[0051] Example 9

[0052] 1) Add 17.80g ammonium chloride, 22.20g sodium nitrite, 0.60g sustained-release acid microcapsules prepared in Example 1, 0.25g sodium dodecyl sulfate (SDS), and 0.25g sodium fatty alcohol polyoxyethylene ether sulfate (AES) to 58.3g water and mix well to obtain the first aqueous solution;

[0053] 2) While stirring, slowly add 0.6g of associative polyacrylamide (AP-P5, Sichuan Guangya Polymer Chemical Co., Ltd.) to the first aqueous solution and stir until fully dissolved to obtain the oil displacement composition.

[0054] Example 10

[0055] The sustained-release acid microcapsules prepared in Example 1 were used as a replacement for the sustained-release acid microcapsules prepared in Example 2, and the rest was the same as in Example 8.

[0056] 1) Add 13.35g ammonium chloride, 16.65g sodium nitrite, 0.45g sustained-release acid microcapsules prepared in Example 2, 0.2g sodium dodecyl sulfate (SDS), and 0.2g sodium fatty alcohol polyoxyethylene ether sulfate (AES) to 68.70g water and mix well to obtain the first aqueous solution;

[0057] 2) While stirring, slowly add 0.45g of associative polyacrylamide (AP-P5, Sichuan Guangya Polymer Chemical Co., Ltd.) to the first aqueous solution and stir until fully dissolved to obtain the oil displacement composition.

[0058] Example 11

[0059] The sustained-release acid microcapsules prepared in Example 1 were used as a replacement for the sustained-release acid microcapsules prepared in Example 3, and the rest was the same as in Example 8.

[0060] 1) Add 13.35g ammonium chloride, 16.65g sodium nitrite, 0.45g sustained-release acid microcapsules prepared in Example 3, 0.2g sodium dodecyl sulfate (SDS), and 0.2g sodium fatty alcohol polyoxyethylene ether sulfate (AES) to 68.70g water and mix well to obtain the first aqueous solution;

[0061] 2) While stirring, slowly add 0.45g of associative polyacrylamide (AP-P5, Sichuan Guangya Polymer Chemical Co., Ltd.) to the first aqueous solution and stir until fully dissolved to obtain the oil displacement composition.

[0062] Comparative Example 1

[0063] 13.35g ammonium chloride, 16.65g sodium nitrite, 0.45g paraformaldehyde, 0.2g sodium dodecyl sulfate (SDS) and 0.2g sodium fatty alcohol polyoxyethylene ether sulfate (AES) were added to 68.70g water and mixed evenly to obtain the oil displacement composition.

[0064] Comparative Example 2

[0065] 13.35g ammonium chloride, 16.65g sodium nitrite, 0.45g paraformaldehyde, and 0.4g sodium dodecyl sulfate (SDS) were added to 68.70g water and mixed evenly to obtain an oil displacement composition.

[0066] Comparative Example 3

[0067] 1) Add 13.35g ammonium chloride, 16.65g sodium nitrite, 0.45g paraformaldehyde, and 0.4g sodium fatty alcohol polyoxyethylene ether sulfate (AES) to 68.70g water and mix well to obtain an oil displacement composition.

[0068] Comparative Example 4

[0069] 1) Add 13.35g ammonium chloride, 16.65g sodium nitrite, 1.5g 30% hydrochloric acid aqueous solution (with an effective hydrogen chloride content of 0.45g), 0.2g sodium dodecyl sulfate (SDS), and 0.2g sodium fatty alcohol polyoxyethylene ether sulfate (AES) to water to make a total mass of 100g. Mix well to obtain an oil displacement composition.

[0070] Comparative Example 5

[0071] 1) Add 13.35g ammonium chloride, 16.65g sodium nitrite, 0.2g sodium dodecyl sulfate (SDS) and 0.2g sodium fatty alcohol polyoxyethylene ether sulfate (AES) to 69.15g water and mix well to obtain the first aqueous solution;

[0072] 2) While stirring, slowly add 0.45g of associative polyacrylamide (AP-P5, Sichuan Guangya Polymer Chemical Co., Ltd.) to the first aqueous solution and stir until fully dissolved to obtain the oil displacement composition.

[0073] Performance testing

[0074] 1. pH measurement

[0075] The oil displacement compositions of Examples 4 to 11 and Comparative Examples 1 to 4 were placed in a water bath at 70°C, and the pH value was measured every 1 hour using a Mettler Toledo pH meter for 10 hours. Based on the test results, a curve of pH value change over time was plotted. Figure 1 Since the data from Examples 4 to 11 are quite similar, the pH values ​​of the oil displacement compositions from Examples 4 to 11 were plotted separately over time. (See attached figures.) Figure 2 Since the data from Comparative Examples 1 to 3 are quite similar, the pH values ​​of the oil displacement compositions from Comparative Examples 1 to 4 were plotted separately over time. (See attached figures.) Figure 3 .

[0076] according to Figure 1 The results show that the oil displacement compositions of Examples 4 to 11 exhibit a significantly slower acid generation rate at a high temperature of 70°C compared to Comparative Examples 1 to 3. Among them, Comparative Example 4 does not have a slow-release effect. Therefore, the oil displacement compositions of Examples 4 to 11 will help to delay the reaction time, thereby effectively expanding the affected reservoir range and improving the recovery rate.

[0077] 2. Bubble capacity measurement

[0078] The foaming properties of the oil displacement compositions of Examples 4 to 11, Comparative Examples 2 and 3 were evaluated using a stirring method. The evaluation method is as follows: 100g of the oil displacement composition was taken and stirred with a Waring Blender at 7000 rpm for 1 min, and immediately poured into a 500mL graduated cylinder. The foam volume was recorded. The results are shown in Table 1.

[0079] Table 1

[0080]

[0081] According to Table 1, comparing Comparative Example 1 with Comparative Example 2 and Comparative Example 3, it can be seen that the combined use of SDS and AES can effectively improve the foam volume, indicating that SDS and AES have a synergistic effect. Furthermore, according to the experimental results, the oil displacement compositions of Examples 4 to 11 can all produce excellent foam volume.

[0082] 3. Simulated recovery rate determination

[0083] 1) Fill with 100 to 120 mesh quartz sand Sand-filled pipe a is used to simulate a heavy oil reservoir. The dry weight of the sand-filled pipe filled with quartz sand is weighed, then vacuumed, saturated with water, and the wet weight is weighed. The porosity is calculated based on the dry and wet weights.

[0084] 2) Place the sand-filled tube a, which is saturated with water, in a 70℃ constant temperature chamber for 15 hours. At 70℃, inject clean water into the sand-filled tube a at a rate of 1 mL / min. When the metering is stable, calculate the water permeability.

[0085] 3) Place the sand-filled pipe a horizontally and perform oil-drive water treatment until no water is visible at the core outlet. Calculate the original oil saturation and bound water saturation. The viscosity of crude oil at 70℃ is 610 mPa·s.

[0086] 4) At 70℃, water flooding was carried out at a displacement rate of 1 mL / min until the water content at the core outlet reached 95%, and the water flooding recovery rate was calculated.

[0087] 5) At 70°C, inject the oil displacement compositions of Examples 4 to 11 and Comparative Examples 1 to 4 at the same rate as water flooding, with a volume of 0.3 times the pore volume. Then, perform subsequent water flooding until the water cut reaches 98% or more. Calculate the controlled-up recovery rate and final recovery rate using the oil displacement compositions.

[0088] The results are shown in Table 2.

[0089] Table 2

[0090] Example 4 <![CDATA[0.81μm 2 ]]> 48.6％ 30.5％ 79.1％ Example 5 <![CDATA[0.83μm 2 ]]> 48.9％ 35.2％ 84.1％ Example 6 <![CDATA[0.81μm 2 ]]> 48.7％ 39.5％ 88.2％ Example 7 <![CDATA[0.81μm 2 ]]> 48.7％ 35.1％ 83.8％ Example 8 <![CDATA[0.82μm 2 ]]> 48.8％ 39.7％ 88.3％ Example 9 <![CDATA[0.81μm 2 ]]> 48.9％ 42.6％ 91.5％ Example 10 <![CDATA[0.81μm 2 ]]> 48.7％ 38.9％ 87.6％ Example 11 <![CDATA[0.83μm 2 ]]> 48.8％ 39.2％ 88.0％ Comparative Example 1 <![CDATA[0.84μm 2 ]]> 48.6％ 27.7％ 76.3％ Comparative Example 2 <![CDATA[0.83μm 2 ]]> 48.9％ 25.1％ 74.0％ Comparative Example 3 <![CDATA[0.82μm 2 ]]> 48.7％ 25.8％ 74.5％ Comparative Example 4 <![CDATA[0.81μm 2 ]]> 48.9％ 24.5％ 73.4％ Comparative Example 5 <![CDATA[0.82μm 2 ]]> 48.8％ 25.3％ 74.1％

[0091] According to Table 2, comparing the results of Example 5 with Comparative Example 1, it can be seen that replacing paraformaldehyde with slow-release acid microcapsules (i.e., paraformaldehyde microcapsules) can significantly improve the recovery rate of high-viscosity crude oil, thereby increasing the final recovery rate. Comparing the results of Example 5 with Comparative Example 4, it can be seen that replacing hydrochloric acid with slow-release acid microcapsules (i.e., paraformaldehyde microcapsules) can significantly improve the recovery rate of high-viscosity crude oil. Comparing the results of Example 5, Example 8, and Comparative Example 5, it can be seen that the combined use of slow-release acid microcapsules and AP-P5 can effectively improve the recovery rate of high-viscosity crude oil, indicating that slow-release acid microcapsules and AP-P5 have a synergistic effect. Comparing the results of Comparative Example 1 with Comparative Examples 2 and 3, it can be seen that the combined use of SDS and AES can effectively improve the recovery rate of high-viscosity crude oil, indicating that SDS and AES have a synergistic effect.

[0092] In summary, Examples 4 to 11 of the present invention significantly improved the oil recovery rate by using sustained-release acid microcapsules, SDS and AES composite surfactants, and AP-P5.

[0093] While the present invention has been described with reference to specific embodiments, those skilled in the art will understand that various changes can be made without departing from the true spirit and scope of the invention. Furthermore, numerous modifications can be made to the subject, spirit, and scope of the invention to suit specific situations, materials, material compositions, and methods. All such modifications are included within the scope of the claims of the present invention.

Claims

1. An oil displacement composition comprising a heat-generating agent, slow-release acid microcapsules, a surfactant, water, and a thickener; in, The sustained-release acid microcapsules were prepared according to the following steps: 1) Paraformaldehyde is dispersed in an organic solvent to obtain a paraformaldehyde suspension; 2) Ethyl cellulose is dissolved in the paraformaldehyde suspension, and then polydimethylsiloxane is added and stirred to react, so as to obtain a suspension containing the sustained-release acid microcapsules; 3) Centrifuge the suspension containing the sustained-release acid microcapsules to obtain the precipitate after centrifugation; 4) The precipitate is washed and dried to obtain sustained-release acid microcapsules; The surfactant is sodium dodecyl sulfate and sodium fatty alcohol polyoxyethylene ether sulfate; the mass ratio of sodium dodecyl sulfate to sodium fatty alcohol polyoxyethylene ether sulfate is 1:3 to 1.5:1; The thickener is an associative polyacrylamide; The total mass of the oil displacement composition is 100%, the content of the heat-generating agent is 20% to 40%, the content of the slow-release acid microcapsules is 0.3% to 0.6%, the content of the surfactant is 0.3% to 0.5%, and the content of the thickener is 0.3% to 0.6%.

2. The oil displacement composition according to claim 1, characterized in that, The amount of paraformaldehyde is considered as 1 part by mass, the amount of ethyl cellulose is 1 to 3 parts by mass, and the amount of polydimethylsiloxane is 30 to 40 parts by mass.

3. The oil displacement composition according to claim 1, characterized in that, The organic solvent is dichloromethane; and / or In step 4), the product is first washed with petroleum ether and then with water.

4. The oil displacement composition according to claim 1, characterized in that, In step 2), the stirring reaction lasts for 30 to 60 minutes.

5. The oil displacement composition according to claim 1, characterized in that, The heat-generating agent is ammonium chloride and sodium nitrite.

6. The oil displacement composition according to claim 5, characterized in that, The mass ratio of ammonium chloride to sodium nitrite is 4:

5.

7. The oil displacement composition according to claim 1, characterized in that, The thickener is AP-P5.

8. The use of the oil displacement composition according to any one of claims 1 to 7 in oil displacement of high viscosity crude oil reservoirs.

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