A viscosity reducer, an oil displacement composition containing the same, and an oil displacement method.

Abstract

This invention provides a viscosity reducer, an oil displacement composition containing the same, and an oil displacement method. The monomer units of the viscosity reducer include acrylamide, sodium p-styrene sulfonate, and 4-allyl-2,6-dimethoxyphenol. The viscosity reducer, together with polyacrylamide with a weight-average molecular weight of 12 million to 15 million g / mol and soft particles with a particle size of 0.2 to 30 μm, constitutes an oil displacement composition. The oil displacement composition exhibits strong viscosity-reducing, oil-washing, and cross-flow control capabilities, achieving a viscosity reduction rate of up to 94.25% for heavy oil below 2000 mPa·s (50°C). The resulting low-viscosity emulsion obtained after mixing with heavy oil demonstrates good stability, with a minimum water separation rate of 17.00% within 1 hour. The oil displacement method involves sequentially injecting a sacrificial slug, an oil displacement slug, and a flow control slug into the reservoir. During implementation, the injection pressure significantly increases and stabilizes, resulting in an enhanced oil recovery rate of up to 38.72% in laboratory settings.

Description

Technical Field

[0001] This invention relates to the field of oilfield flooding, and more particularly to a viscosity reducer, an oil displacement composition containing the same, and an oil displacement method. Background Technology

[0002] China's heavy oil reserves are generally deep-buried and highly viscous, with most reservoirs concentrated in loose sandstone formations at depths of 1000 to 1500 meters. Crude oil viscosity is generally greater than 400 mPa·s (50℃), and steam injection is the primary method of thermal recovery. Annual production is approximately 15 million tons, with an average recovery rate of less than 20%, leaving abundant residual oil in the formation. However, after multiple rounds of steam injection, the thermal radius is difficult to increase, the oil-gas ratio continues to decline, and the water cut continues to rise, leading to a continuous deterioration in thermal recovery efficiency. Therefore, there is an urgent need for replacement technologies suitable for improving recovery rates in the later stages of heavy oil development.

[0003] Chemical composite flooding is a promising and feasible replacement technology proposed by Sinopec. However, a mature and effective chemical composite flooding composition for heavy oil has not yet been formed. Existing chemical composite systems mostly draw on binary and ternary composite flooding compositions for conventional light oil, which have problems such as unsatisfactory viscosity reduction effect and poor crossflow control effect, and cannot meet the requirements of chemical composite flooding after multiple rounds of steam huff and puff in heavy oil reservoirs. Summary of the Invention

[0004] One aspect of the present invention provides a viscosity reducer, the monomer units of which include acrylamide, sodium p-styrenesulfonate and 4-allyl-2,6-dimethoxyphenol.

[0005] In one specific embodiment, the mass ratio of acrylamide, sodium p-styrenesulfonate, and 4-allyl-2,6-dimethoxyphenol is (10 to 20):(2 to 4):(1 to 2).

[0006] The second aspect of the present invention provides a method for preparing the viscosity reducer described in the first aspect of the present invention, which includes the following steps:

[0007] A monomer and an initiator corresponding to the monomer unit are added to water to obtain a first reaction solution. After deoxygenation, the solution is reacted at a first temperature for a first time to obtain the viscosity reducer.

[0008] In one specific embodiment, the first reaction solution is taken as 100% by mass, and the first reaction solution comprises 20% to 30% of the monomer, 0.06% to 0.21% of the initiator, and the balance being water; and / or

[0009] In the monomer, the mass ratio of acrylamide, sodium p-styrenesulfonate and 4-allyl-2,6-dimethoxyphenol is (10 to 20):(2 to 4):(1 to 2);

[0010] Preferably, the mass of the first reaction solution is 100%, and the first reaction solution comprises 20% to 30% of the monomer, 0.1% to 0.15% of the initiator and the balance being water.

[0011] In one specific embodiment, the initiator is (NH4)2S2O8 and NaHSO3;

[0012] Preferably, the molar ratio of (NH4)2S2O8 to NaHSO3 is 1:1; and / or

[0013] The first temperature is 60 to 70°C; and / or

[0014] The first duration is 5 to 10 hours;

[0015] Preferably, the first temperature is 65°C;

[0016] Preferably, the first duration is 6 hours.

[0017] The third invention provides an oil displacement composition comprising the viscosity reducer described in the first invention, a first polyacrylamide, and soft particles.

[0018] In one specific embodiment, the oil displacement composition is 100% by mass, and the oil displacement composition comprises 0.2% to 1% of the viscosity reducer, 0.1% to 0.5% of the first polyacrylamide, 5% to 20% of the soft particles, and the balance being water;

[0019] Preferably, the oil displacement composition comprises 0.3% to 0.6% of the viscosity reducer, 0.1% to 0.2% of the first polyacrylamide, 5% to 10% of the soft particles, and the balance being water.

[0020] In one specific embodiment, the first polyacrylamide is anionic polyacrylamide and / or nonionic polyacrylamide; and / or

[0021] The first polyacrylamide has a weight-average molecular weight of 12 million to 15 million g / mol; and / or

[0022] The soft particles have a particle size of 0.2 to 30 μm;

[0023] Preferably, the degree of hydrolysis of the anionic polyacrylamide is 18% to 20%;

[0024] Preferably, the degree of hydrolysis of the nonionic polyacrylamide is 3% to 5%;

[0025] Preferably, the first polyacrylamide is anionic polyacrylamide.

[0026] The fourth invention provides an oil displacement method, which includes the following steps:

[0027] 1) Inject the first volume of sacrificial agent slug, the second volume of oil displacement slug, and the third volume of flow control slug into the reservoir in sequence;

[0028] 2) Continuously inject water into the reservoir;

[0029] The oil displacement slug is an oil displacement composition provided in the third part of the present invention.

[0030] In one specific embodiment, the sacrificial slug is an aqueous solution of an anionic surfactant; and / or

[0031] The flow control slug is an aqueous solution of a second polyacrylamide; and / or

[0032] In the flow control slug, the second polyacrylamide is anionic polyacrylamide and / or nonionic polyacrylamide;

[0033] Preferably, the second polyacrylamide is anionic polyacrylamide;

[0034] Preferably, the weight-average molecular weight of the second polyacrylamide is 12 million to 15 million g / mol;

[0035] Preferably, the degree of hydrolysis of the anionic polyacrylamide is 18% to 20%;

[0036] Preferably, the degree of hydrolysis of the nonionic polyacrylamide is 3% to 5%.

[0037] In one specific embodiment, the sacrificial slug is 100% by mass, and the sacrificial slug comprises 0.05% to 0.2% anionic surfactant and the balance being water; and / or

[0038] The mass of the flow control slug is taken as 100%, and the flow control slug comprises 0.1% to 0.3% of a second polyacrylamide and the balance is water.

[0039] In one specific embodiment, the anionic surfactant in the sacrificial septum is sodium dodecyl sulfonate;

[0040] and / or

[0041] The first volume is 2% to 5% of the target reservoir pore volume; and / or

[0042] The second volume is 40% to 60% of the target reservoir pore volume; and / or

[0043] The third volume is 5% to 10% of the target reservoir pore volume.

[0044] The application of at least one of the viscosity reducer described in one of the present inventions, the viscosity reducer prepared by the method described in the second of the present invention, the oil displacement composition described in the third of the present invention, and the oil displacement method described in the fourth of the present invention in oilfield oil displacement, especially in oil displacement after steam huff and puff in heavy oil reservoirs.

[0045] The fifth invention provides a soft particle, which is prepared by the following method:

[0046] 1) The crosslinking agent, nonionic polyacrylamide, reinforcing agent and water are mixed to obtain a second reaction solution, sealed and reacted at a second temperature for a second time to obtain the reaction product;

[0047] 2) The obtained reaction product is granulated to obtain the soft particles.

[0048] In one specific embodiment, the second reaction solution is 100% by mass, and the second reaction solution comprises 0.2% to 1.0% of the crosslinking agent, 0.3% to 0.8% of the nonionic polyacrylamide, 0.05% to 0.5% of the reinforcing agent, and the balance being water;

[0049] Preferably, the second reaction solution is 100% by mass, and the second reaction solution comprises 0.3% to 0.5% of the crosslinking agent, 0.3% to 0.5% of the nonionic polyacrylamide, 0.05% to 0.2% of the reinforcing agent, and the balance being water.

[0050] In one specific embodiment, the crosslinking agent is a mixture of hydroquinone and hexamethylenetetramine;

[0051] Preferably, the mass ratio of hydroquinone to hexamethylenetetramine is (1 to 2):(1 to 2); and / or

[0052] The reinforcing agent is lignin sulfonate and / or silicate;

[0053] Preferably, the nonionic polyacrylamide has a weight-average molecular weight of 8 million to 9.6 million g / mol and a degree of hydrolysis of 3% to 5%.

[0054] Preferably, the reinforcing agent is at least one selected from sodium lignosulfonate, calcium lignosulfonate, and sodium silicate.

[0055] In one specific embodiment, the second temperature is 95 to 105°C; and / or

[0056] The second duration is 24 to 48 hours; and / or

[0057] The granulation shear rate is 2000 to 3000 rpm; and / or

[0058] The granulation shear spacing is 5 to 50 μm; and / or

[0059] The granulation shearing time is 5 to 15 minutes.

[0060] The beneficial effects of this invention are:

[0061] This invention addresses the problems of existing chemical composite flooding compositions having unsatisfactory viscosity-reducing effects and poor cross-flow control in heavy oil reservoirs, failing to meet the requirements of chemical composite flooding after multiple rounds of steam huff and puff. It provides a viscosity reducer, a flooding composition containing the reducer, and a flooding method. The product and flooding method of this invention have the following advantages:

[0062] 1) The viscosity reducer provided by this invention can effectively reduce the viscosity of heavy oil and improve the stability of emulsion;

[0063] 2) In the oil displacement composition provided by the present invention, the viscosity reducer, polyacrylamide and soft particles have good compatibility, do not undergo chemical reaction, and do not produce flocculation or precipitation. They can enhance the viscosity reduction ability, oil washing ability, cross-flow control ability and improve emulsion stability of the oil displacement composition.

[0064] 3) In the oil displacement composition provided by the present invention, the viscosity reducer, polyacrylamide and soft particles have good synergistic effect. The viscosity of the oil displacement composition is 30 to 90 mPa·s, the viscosity reduction rate of heavy oil can reach more than 90%, the water separation rate of the emulsion after 1 hour can be less than 20%, the injection pressure increases significantly and is stable, the crossflow control ability is strong, the indoor enhanced oil recovery rate reaches 38.72%, which is more than 15% higher than the enhanced oil recovery rate of polyacrylamide under the same viscosity, and more than 20% higher than the enhanced oil recovery rate of the viscosity reducer alone. It can meet the needs of oil displacement after multiple rounds of heavy oil steam huff and puff at 2000 mPa·s (50℃).

[0065] 4) The raw materials for preparing the oil displacement composition of the present invention are cheap and readily available, and the oil displacement composition is simple to prepare;

[0066] 5) The oil displacement method provided by the present invention has a simple construction process. It uses the oil displacement sluice as the main sluice and the sacrificial agent sluice and the flow control sluice as two auxiliary sluices, which can effectively improve the oil recovery rate after multiple rounds of heavy oil steam huff and puff. Detailed Implementation

[0067] 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.

[0068] Preparation of viscosity reducers

[0069] Example 1

[0070] In a 100mL three-necked round-bottom flask equipped with a stirrer, thermometer, and nitrogen circulation system, 30g of ultrapure water was added. While stirring, 6.93g of acrylamide, 1.38g of sodium p-styrenesulfonate, and 0.69g of 4-allyl-2,6-dimethoxyphenol were added, and the mixture was heated to 65°C in a water bath. Nitrogen gas was continuously purged for 30min to remove oxygen. Then, 0.045g of a mixture of (NH4)2S2O8 and NaHSO3 in a 1:1 molar ratio was added. The reaction was carried out under nitrogen purging and stirred with a magnetic rotor for 6h. The resulting gel was then cut into small pieces, dried in an oven at 80°C for 12h, and finally ground and granulated to obtain viscosity reducer C1.

[0071] Example 2

[0072] In a 100mL three-necked round-bottom flask equipped with a stirrer, thermometer, and nitrogen circulation system, 30g of ultrapure water was added. While stirring, 5.63g of acrylamide, 2.25g of sodium p-styrenesulfonate, and 1.12g of 4-allyl-2,6-dimethoxyphenol were added, and the mixture was heated to 65°C in a water bath. Nitrogen gas was continuously purged for 30min to remove oxygen. Then, 0.045g of a mixture of (NH4)2S2O8 and NaHSO3 in a 1:1 molar ratio was added. The reaction was carried out under nitrogen purging and stirred with a magnetic rotor for 6h. The resulting gel was then cut into small pieces, dried in an oven at 80°C for 12h, and finally ground and granulated to obtain the viscosity reducer C2.

[0073] Example 3

[0074] In a 100mL three-necked round-bottom flask equipped with a stirrer, thermometer, and nitrogen circulation system, 30g of ultrapure water was added. While stirring, 7.83g of acrylamide, 0.78g of sodium p-styrenesulfonate, and 0.39g of 4-allyl-2,6-dimethoxyphenol were added, and the mixture was heated to 65°C in a water bath. Nitrogen gas was continuously purged for 30min to remove oxygen. Then, 0.045g of a mixture of (NH4)2S2O8 and NaHSO3 in a 1:1 molar ratio was added. The reaction was carried out under nitrogen purging and stirred with a magnetic rotor for 6h. The resulting gel was then cut into small pieces, dried in an oven at 80°C for 12h, and finally ground and granulated to obtain viscosity reducer C3.

[0075] Example 4

[0076] In a 100mL three-necked round-bottom flask equipped with a stirrer, thermometer, and nitrogen circulation system, 30g of ultrapure water was added. While stirring, 7.20g of acrylamide, 1.44g of sodium p-styrenesulfonate, and 0.36g of 4-allyl-2,6-dimethoxyphenol were added, and the mixture was heated to 65°C in a water bath. Nitrogen gas was continuously purged for 30min to remove oxygen. Then, 0.045g of a mixture of (NH4)2S2O8 and NaHSO3 in a 1:1 molar ratio was added. The reaction was carried out under nitrogen purging and stirred with a magnetic rotor for 6h. The resulting gel was then cut into small pieces, dried in an oven at 80°C for 12h, and finally ground and granulated to obtain the viscosity reducer C4.

[0077] Preparation of soft particles

[0078] Hydroquinone and hexamethylenetetramine: purchased from Shandong Shida Oilfield Service Technology Co., Ltd.

[0079] Nonionic polyacrylamide (weight average molecular weight of 9.6 million g / mol, degree of hydrolysis of 4.5%): purchased from Xinxing Chemical Co., Ltd.

[0080] Nonionic polyacrylamide (weight average molecular weight of 8 million g / mol, degree of hydrolysis of 3%): purchased from Xinxing Chemical Co., Ltd.

[0081] Nonionic polyacrylamide (weight-average molecular weight of 8.8 million g / mol, degree of hydrolysis of 5%): purchased from Xinxing Chemical Co., Ltd.

[0082] Sodium lignosulfonate: purchased from Binzhou Shuangfeng Chemical Co., Ltd.;

[0083] Calcium lignosulfonate: purchased from Shandong Jinan Shengteng Chemical Co., Ltd.

[0084] Example 5

[0085] 1) Add 0.3g of crosslinking agent (0.15g hydroquinone, 0.15g hexamethylenetetramine) to 99.35g of water and stir for 20min;

[0086] 2) While stirring, slowly add 0.3g of nonionic polyacrylamide (weight average molecular weight of 9.6 million g / mol, degree of hydrolysis of 4.5%), and continue stirring for 30 minutes;

[0087] 3) Add 0.05g of sodium lignosulfonate and stir for 5 minutes;

[0088] 4) After the solution is stirred, it is sealed and heated in a constant temperature oven at 100℃ for 48 hours to obtain the reaction product colloid;

[0089] 5) The obtained reaction product colloid was added to a colloid mill for shearing and crushing. The mill was sheared at a constant speed of 2000 rpm and a shearing interval of 50 μm for 5 min to obtain soft particles A1 with an average particle size of 28 μm.

[0090] Example 6

[0091] 1) Add 0.5g of crosslinking agent (0.25g hydroquinone, 0.25g hexamethylenetetramine) to 98.80g of water and stir for 20min;

[0092] 2) While stirring, slowly add 0.5g of nonionic polyacrylamide (weight average molecular weight of 9.6 million g / mol, degree of hydrolysis of 4.5%), and continue stirring for 30 minutes;

[0093] 3) Add 0.2g of sodium lignosulfonate and stir for 5 minutes;

[0094] 4) After the solution is stirred, it is sealed and heated in a constant temperature oven at 100℃ for 48 hours to obtain the reaction product colloid;

[0095] 5) The obtained reaction product colloid was added to a colloid mill for shearing and crushing. The mill was sheared at a constant speed of 3000 rpm and a shearing interval of 5 μm for 15 min to obtain soft particles A2 with an average particle size of 0.21 μm.

[0096] Example 7

[0097] Step 5) in Example 6 is changed to: constant shearing at 3000 rpm and a shearing gap of 10 μm for 5 min, with other steps being the same as in Example 6, thereby obtaining soft particles A3 with an average particle size of 3.1 μm.

[0098] Example 8

[0099] 1) Add 0.2g of crosslinking agent (0.07g hydroquinone, 0.13g hexamethylenetetramine) to 99.28g of water and stir for 20min;

[0100] 2) While stirring, slowly add 0.4g of nonionic polyacrylamide (weight average molecular weight of 8 million g / mol, degree of hydrolysis of 3%), and continue stirring for 30 minutes;

[0101] 3) Add 0.12g of calcium lignosulfonate and stir for 5 minutes;

[0102] 4) After the solution is stirred, it is sealed and heated in a constant temperature oven at 105℃ for 48 hours to obtain the reaction product colloid;

[0103] 5) The obtained reaction product colloid was added to a colloid mill for shearing and crushing. The mill was sheared at a constant speed of 2000 rpm and a shearing interval of 35 μm for 5 min to obtain soft particles A4 with an average particle size of 10 μm.

[0104] Example 9

[0105] 1) Add 1.0g of crosslinking agent (0.5g of hydroquinone and 0.5g of hexamethylenetetramine) to 97.70g of water and stir for 20min;

[0106] 2) While stirring, slowly add 0.8g of nonionic polyacrylamide (weight-average molecular weight of 8.8 million g / mol, degree of hydrolysis of 5%), and continue stirring for 30 minutes;

[0107] 3) Add 0.5g of calcium lignosulfonate and stir for 5 minutes;

[0108] 4) After the solution is stirred, it is sealed and heated in a 95℃ constant temperature oven for 48 hours to obtain the reaction product colloid;

[0109] 5) The obtained reaction product colloid was added to a colloid mill for shearing and crushing. The mill was sheared at a constant speed of 2000 rpm and a shearing interval of 50 μm for 5 min to obtain soft particles A5 with an average particle size of 28 μm.

[0110] Example 10

[0111] 1) Add 0.4g of crosslinking agent (0.26g of hydroquinone and 0.14g of hexamethylenetetramine) to 99.08g of water and stir for 20min;

[0112] 2) While stirring, slowly add 0.4g of nonionic polyacrylamide (weight-average molecular weight of 8.8 million g / mol, degree of hydrolysis of 5%), and continue stirring for 30 minutes;

[0113] 3) Add 0.12g of calcium lignosulfonate and stir for 5 minutes;

[0114] 4) After the solution is stirred, it is sealed and heated in a constant temperature oven at 105℃ for 48 hours to obtain the reaction product colloid;

[0115] 5) The obtained reaction product colloid was added to a colloid mill for shearing and crushing. The mill was sheared at a constant speed of 2000 rpm and a shearing interval of 15 μm for 10 min to obtain soft particles A6 with an average particle size of 5.3 μm.

[0116] Preparation of oil displacement composition

[0117] Anionic polyacrylamide (weight-average molecular weight of 13 million g / mol, degree of hydrolysis of 18.6%): purchased from Xinxing Chemical Co., Ltd.

[0118] Anionic polyacrylamide (weight-average molecular weight of 12 million g / mol, degree of hydrolysis of 18%): purchased from Xinxing Chemical Co., Ltd.

[0119] Anionic polyacrylamide (weight average molecular weight of 15 million g / mol, degree of hydrolysis of 20%): purchased from Xinxing Chemical Co., Ltd.

[0120] Example 11

[0121] 1) Add 0.4g of viscosity reducer C4 to 91.4g of water and stir for 2 minutes until fully dissolved;

[0122] 2) Add 8g of soft granules A3 and stir for 10 minutes to disperse them fully;

[0123] 3) While stirring, add 0.2g of anionic polyacrylamide (weight average molecular weight of 13 million g / mol, degree of hydrolysis of 18.6%) and continue stirring for 30 minutes until it is fully dissolved to obtain oil displacement composition B1.

[0124] Example 12

[0125] 1) Add 0.2g of viscosity reducer C1 to 91.7g of water and stir for 2 minutes until fully dissolved;

[0126] 2) Add 8g of soft granules A1 and stir for 10 minutes to disperse them fully;

[0127] 3) While stirring, add 0.1g of anionic polyacrylamide (weight average molecular weight of 12 million g / mol, degree of hydrolysis of 18%) and continue stirring for 30 minutes until it is fully dissolved to obtain oil displacement composition B2.

[0128] Example 13

[0129] 1) Add 0.3g of viscosity reducer C2 to 79.55g of water and stir for 2 minutes to dissolve completely;

[0130] 2) Add 20g of soft granules A2 and stir for 10 minutes to disperse them fully;

[0131] 3) While stirring, add 0.15g of anionic polyacrylamide (weight average molecular weight of 12 million g / mol, degree of hydrolysis of 18%) and continue stirring for 30 minutes until it is fully dissolved to obtain oil displacement composition B3.

[0132] Example 14

[0133] 1) Add 0.6g of viscosity reducer C2 to 88.90g of water and stir for 2 minutes to dissolve completely;

[0134] 2) Add 10g of soft granules A4 and stir for 10 minutes to disperse them fully;

[0135] 3) While stirring, add 0.5g of anionic polyacrylamide (weight average molecular weight of 12 million g / mol, degree of hydrolysis of 18%) and continue stirring for 30 minutes until it is fully dissolved to obtain oil displacement composition B4.

[0136] Example 15

[0137] 1) Add 1.0g of viscosity reducer C3 to 78.5g of water and stir for 2 minutes to dissolve completely;

[0138] 2) Add 20g of soft granules A5 and stir for 10 minutes to disperse them fully;

[0139] 3) While stirring, add 0.5g of anionic polyacrylamide (weight average molecular weight of 15 million g / mol, degree of hydrolysis of 20%) and continue stirring for 30 minutes until it is fully dissolved to obtain oil displacement composition B5.

[0140] Example 16

[0141] 1) Add 1.0g of viscosity reducer C3 to 93.5g of water and stir for 2 minutes to dissolve completely;

[0142] 2) Add 5g of soft granules A6 and stir for 10 minutes to disperse them fully;

[0143] 3) While stirring, add 0.5g of anionic polyacrylamide (weight average molecular weight of 15 million g / mol, degree of hydrolysis of 20%) and continue stirring for 30 minutes until it is fully dissolved to obtain oil displacement composition B6.

[0144] Implement oil displacement methods

[0145] Sodium dodecyl sulfonate: purchased from Shida Oilfield Service Co., Ltd.;

[0146] Anionic polyacrylamide (weight-average molecular weight of 13 million g / mol, degree of hydrolysis of 18.6%): purchased from Xinxing Chemical Co., Ltd.

[0147] Anionic polyacrylamide (weight-average molecular weight of 12 million g / mol, degree of hydrolysis of 18%): purchased from Xinxing Chemical Co., Ltd.

[0148] Anionic polyacrylamide (weight average molecular weight of 15 million g / mol, degree of hydrolysis of 20%): purchased from Xinxing Chemical Co., Ltd.

[0149] Establish a reservoir model after steam huff and puff:

[0150] 1) A heterogeneous oil reservoir was constructed using a parallel double-filled sand pipe method. The crude oil viscosity was 2000 mPa·s, the displacement rate was 0.5 mL / min, the pore volume was 134 mL, the permeability of the low-permeability layer was 1D, the permeability of the high-permeability layer was 3D, and the oil saturation was 84%. The heavy oil primary reservoir was established at 50℃.

[0151] 2) Water drive to a water cut of 95%, simulate steam flow after steam injection, and establish a reservoir model after steam injection.

[0152] Example 17

[0153] 1) Inject 4 ml of 0.2 wt% sodium dodecyl sulfate aqueous solution into the reservoir model;

[0154] 2) Inject 67 ml of oil displacement composition B1 into the reservoir model;

[0155] 3) Inject 10 ml of 0.2 wt% anionic polyacrylamide (weight average molecular weight of 13 million g / mol, degree of hydrolysis of 18.6%) aqueous solution into the reservoir model;

[0156] 4) Continuously inject water into the reservoir model.

[0157] Example 18

[0158] 1) Inject 2.68 ml of 0.05 wt% sodium dodecyl sulfate aqueous solution into the reservoir model;

[0159] 2) Inject 53.6 ml of oil displacement composition B2 into the reservoir model;

[0160] 3) Inject 6.7 ml of 0.1 wt% anionic polyacrylamide (weight average molecular weight of 15 million g / mol, degree of hydrolysis of 20%) aqueous solution into the reservoir model;

[0161] 4) Continuously inject water into the reservoir model.

[0162] Example 19

[0163] 1) Inject 2.68 ml of 0.1 wt% sodium dodecyl sulfate aqueous solution into the reservoir model;

[0164] 2) Inject 53.6 ml of oil displacement composition B3 into the reservoir model;

[0165] 3) Inject 6.7 ml of 0.1 wt% anionic polyacrylamide (weight average molecular weight of 13 million g / mol, degree of hydrolysis of 18.6%) aqueous solution into the reservoir model;

[0166] 4) Continuously inject water into the reservoir model.

[0167] Example 20

[0168] 1) Inject 6.7 ml of 0.2 wt% sodium dodecyl sulfate aqueous solution into the reservoir model;

[0169] 2) Inject 80.4 ml of oil displacement composition B4 into the reservoir model;

[0170] 3) Inject 13.4 ml of 0.3 wt% anionic polyacrylamide (weight average molecular weight of 15 million g / mol, degree of hydrolysis of 20%) aqueous solution into the reservoir model;

[0171] 4) Continuously inject water into the reservoir model.

[0172] Example 21

[0173] 1) Inject 6.7 ml of 0.2 wt% sodium dodecyl sulfate aqueous solution into the reservoir model;

[0174] 2) Inject 80.4 ml of oil displacement composition B5 into the reservoir model;

[0175] 3) Inject 13.4 ml of 0.3 wt% anionic polyacrylamide (weight average molecular weight of 12 million g / mol, degree of hydrolysis of 18%) aqueous solution into the reservoir model;

[0176] 4) Continuously inject water into the reservoir model.

[0177] Example 22

[0178] 1) Inject 6.7 ml of 0.2 wt% sodium dodecyl sulfate aqueous solution into the reservoir model;

[0179] 2) Inject 80.4 ml of oil displacement composition B6 into the reservoir model;

[0180] 3) Inject 13.4 ml of 0.3 wt% anionic polyacrylamide (weight average molecular weight of 13 million g / mol, degree of hydrolysis of 18.6%) aqueous solution into the reservoir model;

[0181] 4) Continuously inject water into the reservoir model.

[0182] Comparative Example 1

[0183] Preparation of viscosity reducers:

[0184] In a 100mL three-necked round-bottom flask equipped with a stirrer, thermometer, and nitrogen circulation system, 30g of ultrapure water was added. While stirring, 6.93g of acrylamide, 1.38g of sodium p-styrene sulfonate, and 0.69g of acrylic acid were added, and the mixture was heated to 65°C in a water bath. Nitrogen gas was continuously purged for 30min to remove oxygen. Then, 0.045g of a mixture of (NH4)2S2O8 and NaHSO3 in a 1:1 molar ratio was added. The reaction was carried out under nitrogen purging and stirred with a magnetic rotor for 6h. The resulting gel was then cut into small pieces, dried in an oven at 80°C for 12h, and finally ground and granulated to obtain the viscosity reducer C5.

[0185] Comparative Example 2

[0186] Preparation of oil displacement composition:

[0187] The viscosity reducer C4 in Example 11 was replaced with an equal mass of water, and everything else remained the same as in Example 11, to obtain an oil displacement composition.

[0188] Implement oil displacement methods:

[0189] The oil displacement composition B1 in Example 17 was replaced with an equal volume of the oil displacement composition obtained in this comparative example, and everything else was the same as in Example 17.

[0190] Comparative Example 3

[0191] Preparation of oil displacement composition:

[0192] The anionic polyacrylamide (weight-average molecular weight of 13 million g / mol and degree of hydrolysis of 18.6%) in Example 11 was replaced with an equal mass of water, and all other aspects were the same as in Example 11, to obtain the oil displacement composition.

[0193] Implement oil displacement methods:

[0194] The oil displacement composition B1 in Example 17 was replaced with an equal volume of the oil displacement composition obtained in this comparative example, and everything else was the same as in Example 17.

[0195] Comparative Example 4

[0196] Preparation of oil displacement composition:

[0197] The soft particles A3 in Example 11 were replaced with an equal mass of water, and everything else remained the same as in Example 11, to obtain an oil displacement composition.

[0198] Implement oil displacement methods:

[0199] Replace the oil displacement composition B1 in Example 17 with an equal volume of the oil displacement composition obtained in this example, otherwise remain the same as in Example 17.

[0200] Comparative Example 5

[0201] Preparation of oil displacement composition:

[0202] The viscosity reducer C4 in Example 11 was replaced with an equal mass of the viscosity reducer C5 prepared in Comparative Example 1, and the rest was the same as in Example 11, to obtain the oil displacement composition.

[0203] Implement oil displacement methods:

[0204] Replace the oil displacement composition B1 in Example 17 with an equal volume of the oil displacement composition obtained in this example, otherwise remain the same as in Example 17.

[0205] Comparative Example 6

[0206] Implement oil displacement methods:

[0207] The oil displacement composition B1 in Example 17 was replaced with an equal volume of water, and everything else was the same as in Example 17.

[0208] Comparative Example 7

[0209] Implement oil displacement methods:

[0210] The oil displacement composition B1 in Example 17 was replaced with an aqueous solution of anionic polyacrylamide (weight-average molecular weight of 13 million g / mol and degree of hydrolysis of 18.6%) of equal volume and viscosity, otherwise the same as in Example 17.

[0211] Comparative Example 8

[0212] Prepare the following formulations according to the mass fraction of each component in the oil displacement composition B1:

[0213] 1) Add 0.4g of viscosity reducer C4 to 99.6g of water, stir for 2 minutes to dissolve completely, and obtain F1;

[0214] 2) Add 8g of soft granules A3 to 92g of water and stir for 10 minutes to disperse them fully, thus obtaining F2;

[0215] 3) Add 0.2g of anionic polyacrylamide (weight average molecular weight of 13 million g / mol, degree of hydrolysis of 18.6%) to 99.8g of water and stir continuously for 30min until it is fully dissolved to obtain F3.

[0216] Implement oil displacement methods:

[0217] Replace step 2) of Example 17, “Inject 67 ml of oil displacement composition B1 into the reservoir model”, with the following: “Inject 67 ml of F1, 50 ml of water, 67 ml of F2, 50 ml of water and 67 ml of F3 into the reservoir model in sequence”, and the rest is the same as in Example 17.

[0218] Comparative Example 9

[0219] Implement oil displacement methods:

[0220] Replace step 2) of Example 17, “Inject 67 ml of oil displacement composition B1 into the reservoir model”, with “Inject 67 ml of F3, 50 ml of water, 67 ml of F2, 50 ml of water and 67 ml of F1 into the reservoir model in sequence”. The rest is the same as in Example 17. The F1, F2 and F3 used here are the same as F1, F2 and F3 in Comparative Example 8, respectively.

[0221] Experimental Evaluation

[0222] 1. Viscosity determination of the oil displacement composition

[0223] The viscosity of the oil displacement compositions obtained in Examples 11 to 16, Comparative Examples 2 to 5, and the anionic polyacrylamide aqueous solution used in Comparative Example 7 was measured using a rotational viscometer at room temperature and 6 r / min. The results are shown in Table 1.

[0224] Table 1. Viscosity of Oil Displacement Composition and Polyacrylamide Solution

[0225] Serial Number Example 11 Example 12 Example 13 Example 14 Example 15 Example 16 Viscosity / mPa·s 36 13 24 78 89 83 Serial Number Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 7 / Viscosity / mPa·s 34 11 31 36 36 /

[0226] 2. Determination of viscosity reduction rate of viscosity reducer and oil displacement composition

[0227] Heavy oil with a viscosity of 2000 mPa·s at 50°C from Shengli Oilfield was mixed sequentially with 0.4 wt% of aqueous solutions of viscosity reducers from Examples 1 to 4 and Comparative Example 1, as well as oil displacement compositions obtained from Examples 11 to 16 and Comparative Examples 2 to 5, at a volume ratio of 3:7, and stirred until homogeneous to obtain emulsions R1 to R15.

[0228] The viscosities of emulsions R1 to R15 were measured using a rotational viscometer at 50°C and 6 r / min. The viscosity reduction rates of the viscosity reducer and the oil displacement composition were calculated based on the heavy oil viscosity and the measured emulsion viscosity. The results are shown in Table 2.

[0229] Table 2. Emulsion viscosity and viscosity reduction rate

[0230] Serial Number lotion Emulsion viscosity / mPa·s Viscosity reduction rate / % Example 1 R1 112 94.4 Example 2 R2 125 93.75 Example 3 R3 156 92.2 Example 4 R4 108 94.6 Example 11 R5 115 94.25 Example 12 R6 428 90.6 Example 13 R7 156 92.2 Example 14 R8 177 91.15 Example 15 R9 196 90.2 Example 16 R10 183 90.85 Comparative Example 1 R11 915 54.25 Comparative Example 2 R12 1552 22.40 Comparative Example 3 R13 109 94.55 Comparative Example 4 R14 112 94.40 Comparative Example 5 R15 672 66.4

[0231] 3. Determination of water separation rate of emulsions obtained by mixing viscosity reducer and oil displacement composition with heavy oil respectively.

[0232] The water separation rate of emulsions obtained after mixing viscosity reducer and oil displacement composition with heavy oil was determined after 1 hour. The determination method was as follows:

[0233] 1) Heavy oil with a viscosity of 2000 mPa·s at 50°C from Shengli Oilfield was mixed sequentially with 0.4 wt% of aqueous solutions of viscosity reducers from Examples 1 to 4 and Comparative Example 1, as well as oil displacement compositions obtained from Examples 11 to 16 and Comparative Examples 2 to 5, at a volume ratio of 3:7, and stirred until homogeneous to obtain emulsions R1 to R15.

[0234] 2) Pour the well-stirred R1 to R15 into 50mL stoppered centrifuge tubes, keep the temperature constant at 50℃, observe the amount of precipitated liquid, and calculate the emulsion water separation rate.

[0235] The specific results are shown in Table 3:

[0236] Table 3. Emulsion water separation rate

[0237] Serial Number lotion 1h water separation rate / % Example 1 R1 44 Example 2 R2 45 Example 3 R3 48 Example 4 R4 43

[0238] (Continued from Table 3)

[0239] Serial Number lotion 1h water separation rate / % Example 11 R5 18 Example 12 R6 33 Example 13 R7 36 Example 14 R8 20 Example 15 R9 18 Example 16 R10 17 Comparative Example 1 R11 75 Comparative Example 2 R12 92 Comparative Example 3 R13 41 Comparative Example 4 R14 36 Comparative Example 5 R15 72

[0240] 4. Determination of the ability of the oil displacement composition to control cross-flow

[0241] Experimental methods:

[0242] 1) A heterogeneous reservoir was constructed using a parallel double-filled sand pipe method. The reservoir was saturated with water, with a pore volume of 134 mL, a permeability of 1 D in the low-permeability layer, and a permeability of 3 D in the high-permeability layer. The heterogeneous reservoir was established at 50 °C.

[0243] 2) Test according to the methods of Examples 17 to 22 and Comparative Examples 2 to 9, calculate the profile improvement rate, and evaluate the ability of the oil displacement composition to control crossflow in heterogeneous reservoirs.

[0244] f = (Q hb / Q lb -Q ha / Q la ) / (Q hb / Q lb )

[0245] Q hb Q ha — These represent the water absorption rates before and after the high-permeability layer treatment, in %;

[0246] Q lb Q la — These represent the water absorption rates before and after the low-permeability layer treatment, in percentages.

[0247] The specific results are shown in Table 4:

[0248] Table 4. Profile Improvement Rate

[0249] Serial Number Profile improvement rate / % Example 17 94.2 Example 18 84.5 Example 19 91.1 Example 20 85.7 Example 21 84.6 Example 22 93.3 Comparative Example 2 93.8

[0250] (Continued from Table 4)

[0251] Serial Number Profile improvement rate / % Comparative Example 3 89.5 Comparative Example 4 52.5 Comparative Example 5 77.9 Comparative Example 6 25.1 Comparative Example 7 63.4 Comparative Example 8 81.5 Comparative Example 9 82.3

[0252] 5. Measurement of injection pressure and recovery rate during the implementation of oil displacement methods.

[0253] During the implementation of Examples 17 to 22 and Comparative Examples 2 to 9, data such as injection pressure and recovery rate are shown in Table 5:

[0254] Table 5. Data related to injection pressure and recovery rate

[0255]

[0256] 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-assisted oil displacement 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 viscosity reducer, a first polyacrylamide, and soft particles; The first polyacrylamide has a weight-average molecular weight of 12 million to 15 million g / mol; the first polyacrylamide is anionic polyacrylamide; the degree of hydrolysis of the anionic polyacrylamide is 18% to 20%. The monomer unit of the viscosity reducer includes acrylamide, sodium p-styrene sulfonate and 4-allyl-2,6-dimethoxyphenol; the mass ratio of acrylamide, sodium p-styrene sulfonate and 4-allyl-2,6-dimethoxyphenol is (10 to 20):(2 to 4):(1 to 2). The soft particles are prepared by the following method: 1) a crosslinking agent, nonionic polyacrylamide, reinforcing agent and water are mixed to obtain a second reaction solution, sealed and reacted at a second temperature for a second time to obtain a reaction product; 2) the obtained reaction product is granulated to obtain the soft particles. in, The crosslinking agent is a mixture of hydroquinone and hexamethylenetetramine; the reinforcing agent is lignin sulfonate and / or silicate; The oil displacement composition is 100% by mass, comprising 0.2% to 1% of the viscosity reducer, 0.1% to 0.5% of the first polyacrylamide, 5% to 20% of the soft particles, and the balance being water.

2. The oil displacement composition according to claim 1, characterized in that, The oil displacement composition is 100% by mass, comprising 0.3% to 0.6% of the viscosity reducer, 0.1% to 0.2% of the first polyacrylamide, 5% to 10% of the soft particles, and the balance being water.

3. The oil displacement composition according to claim 1 or 2, characterized in that, The viscosity reducer is prepared according to the following steps: A monomer and an initiator corresponding to the monomer unit are added to water to obtain a first reaction solution. After deoxygenation, the solution is reacted at a first temperature for a first time to obtain the viscosity reducer.

4. The oil displacement composition according to claim 3, characterized in that, The mass of the first reaction solution is 100%, and the first reaction solution comprises 20% to 30% of the monomer, 0.06% to 0.21% of the initiator, and the balance being water.

5. The oil displacement composition according to claim 4, characterized in that, The mass of the first reaction solution is 100%, and the first reaction solution comprises 20% to 30% of the monomer, 0.1% to 0.15% of the initiator and the balance being water.

6. The oil displacement composition according to claim 3, characterized in that, The initiator is (NH4)2S2O8 and NaHSO3, with a molar ratio of (NH4)2S2O8 to NaHSO3 of 1:1; and / or The first temperature is 60 to 70°C; and / or The first duration is 5 to 10 hours.

7. The oil displacement composition according to claim 1 or 2, characterized in that, The particle size of the soft particles is 0.2 to 30 μm.

8. The oil displacement composition according to claim 1 or 2, characterized in that, The second reaction solution is 100% by mass, and the second reaction solution comprises 0.2% to 1.0% of the crosslinking agent, 0.3% to 0.8% of the nonionic polyacrylamide, 0.05% to 0.5% of the reinforcing agent, and the balance being water.

9. The oil displacement composition according to claim 8, characterized in that, The second reaction solution is 100% by mass, and the second reaction solution comprises 0.3% to 0.5% of the crosslinking agent, 0.3% to 0.5% of the nonionic polyacrylamide, 0.05% to 0.2% of the reinforcing agent, and the balance being water.

10. The oil displacement composition according to claim 1 or 2, characterized in that, The mass ratio of hydroquinone to hexamethylenetetramine is (1 to 2):(1 to 2); and / or The nonionic polyacrylamide has a weight-average molecular weight of 8 million to 9.6 million g / mol and a degree of hydrolysis of 3% to 5%. The reinforcing agent is at least one of sodium lignosulfonate, calcium lignosulfonate, and sodium silicate.

11. The oil displacement composition according to claim 1 or 2, characterized in that, The second temperature is 95 to 105°C; and / or The second duration is 24 to 48 hours; and / or The granulation shear rate is 2000 to 3000 rpm; and / or The granulation shear spacing is 5 to 50 μm; and / or The granulation shearing time is 5 to 15 minutes.

12. An oil displacement method, comprising the following steps: 1) Inject the first volume of sacrificial agent slug, the second volume of oil displacement slug, and the third volume of flow control slug into the reservoir in sequence; 2) Continuously inject water into the reservoir; The oil displacement slug is the oil displacement composition according to any one of claims 1 to 11.

13. The oil displacement method according to claim 12, characterized in that, The sacrificial slug is 100% by mass, and the sacrificial slug comprises 0.05% to 0.2% anionic surfactant and the balance being water; and / or The mass of the flow control slug is taken as 100%, and the flow control slug comprises 0.1% to 0.3% of a second polyacrylamide and the balance is water.

14. The oil displacement method according to claim 12, characterized in that, In the sacrificial slug, the anionic surfactant is sodium dodecyl sulfonate; and / or The first volume is 2% to 5% of the target reservoir pore volume; and / or The second volume is 40% to 60% of the target reservoir pore volume; and / or The third volume is 5% to 10% of the target reservoir pore volume.

15. The use of the oil displacement composition according to any one of claims 1 to 11 or the oil displacement method according to any one of claims 12 to 14 in oilfield oil displacement.

16. The application according to claim 15, characterized in that, The application refers to the use of the oil displacement composition or the oil displacement method in oil displacement after steam huff and puff in heavy oil reservoirs.

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