Step-by-step plugging agent as well as preparation method and application thereof

Abstract

The invention discloses a step-by-step blocking agent as well as a preparation method and application thereof. The step-by-step plugging agent comprises the following raw materials: a thickening agent, a low-temperature cross-linking agent, lignin, an in-situ catalyst, a high-temperature cross-linking agent and water. The step-by-step plugging agent is prepared by uniformly mixing raw materials including a thickening agent, a low-temperature cross-linking agent, lignin, an in-situ catalyst, a high-temperature cross-linking agent and water. The plugging system is divided into the first-stage weak crosslinking low-temperature gel and the second-stage strong crosslinking high-temperature gel, the temperature use range of the system is expanded, stratums can be plugged at different temperature sections, the plugging system has the advantages of being high in strength, large in plugging strength, wide in application range, high in plugging efficiency and the like, a steam channeling channel can be effectively plugged for a long time, and the plugging effect is good. And meanwhile, the production cost of the plugging agent is reduced, the performance and economical efficiency requirements of site construction are met, and the practicability is relatively high.

Description

Technical Field

[0001] The present invention relates to the technical field of plugging agents for crude oil production. Further, it relates to a step-by-step plugging agent, its preparation method and application. Background Art

[0002] Among the remaining world's petroleum resources, about 70% are heavy oil. Continuous, effective and economical heavy oil development has become the main focus of oil production increase in various countries. Currently, thermal recovery technologies such as steam stimulation and steam flooding are the main methods used in heavy oil development. In the later stage of development, due to limitations such as poor development of formation interlayers, permeability differences between layers and development conditions, problems such as low injection-production ratio, low formation pressure, serious steam channeling, sand production, edge water flooding, and great difficulty in stable production have emerged. The plugging agents used for sealing steam channeling and suppressing edge water invasion in heavy oil mainly include steam foam, inorganic particles, high-temperature gel, etc. Among them, the on-site construction process of injecting foam is complex, and inorganic particles often remain in the near-wellbore area. High-temperature gel still has problems such as short plugging validity period and easy loss of plugging effect under high temperature and high salinity. In view of the increasingly serious problems of steam channeling and edge water invasion, there is an urgent need to develop a chemical plugging system that can plug step by step at different temperature ranges, is resistant to high temperature, has high strength, and is suitable for deep plugging.

[0003] Lignin is the second largest natural organic matter. Using lignin as a raw material for preparing plugging agents can turn waste into treasure and reduce the cost of preparing plugging agents. With the rising price of petrochemical raw materials and the increasing environmental protection requirements, green chemicals using low-cost natural renewable resources such as lignin as raw materials have become an international hot research and development direction. However, the main connection methods between the main structures of natural lignin are ether bonds and carbon-carbon bonds, with low hydroxyl content, large steric hindrance on the benzene ring, and significantly insufficient reaction activity. For commercially available industrial by-product lignin, due to the condensation reaction after chemical treatment, its reaction sites are even fewer. Therefore, in the process of oilfield application, the existing lignin-based plugging systems cannot achieve low-temperature plugging, the gel formation is uncontrollable, and the gel formation strength is generally low, with high costs. Summary of the Invention

[0004] To solve the problems in the prior art, the present invention provides a step-by-step plugging agent, its preparation method and application. The plugging agent in the present invention is pumped into and migrates to the deep formation. Under the formation temperature conditions, the thickener and the low-temperature crosslinking agent undergo a first-stage weak crosslinking to form a low-temperature gel, which can fix lignin and other components of the plugging system in the low-temperature gel. With the injection of steam, the formation temperature gradually increases, the low-temperature gel slowly breaks, and part of the lignin is in-situ liquefied under the action of the in-situ catalyst to obtain phenolic substances such as guaiacol and 2,6-dimethoxyphenol. The phenolic substances act as co-crosslinking agents under high-temperature conditions, and the undegraded lignin, high-temperature crosslinking agent and phenolic substances undergo a second-stage strong crosslinking to obtain a high-temperature gel. The experimental results of the present invention show that the prepared high-temperature gel does not break gel at 300 °C for 30 days, and the plugging rate is higher than 98.6%. In summary, the plugging system of the present invention is divided into a first-stage weak crosslinking low-temperature gel and a second-stage strong crosslinking high-temperature gel. This system expands the temperature application range, can plug the formation in different temperature sections, and has high strength. It has the characteristics of large plugging strength, wide application range, high plugging efficiency, etc., can effectively plug the steam channel for a long time, realize the efficient development of heavy oil reservoirs, and at the same time reduce the production cost of the plugging agent, meet the performance and economic requirements of on-site construction, and has high practicability.

[0005] One object of the present invention is to provide a step-by-step plugging agent, which comprises a thickener, a low-temperature crosslinking agent, lignin, an in-situ catalyst, a high-temperature crosslinking agent and water;

[0006] Based on the total weight of the thickener, the low-temperature crosslinking agent, lignin, the in-situ catalyst, the high-temperature crosslinking agent and water being 100%,

[0007] the content of the thickener is 0.05 - 0.3 wt%;

[0008] the content of the low-temperature crosslinking agent is 0.03 - 0.2 wt%;

[0009] the content of lignin is 1 - 5 wt%;

[0010] the content of the in-situ catalyst is 0.5 - 3 wt%;

[0011] the content of the high-temperature crosslinking agent is 0.5 - 2 wt%;

[0012] the balance is water.

[0013] In the step-by-step plugging agent of the present invention, preferably,

[0014] the content of the thickener is 0.1 - 0.25 wt%; and / or,

[0015] the content of the low-temperature crosslinking agent is 0.05 - 0.15 wt%; and / or,

[0016] The content of the lignin is 2-4 wt%; and / or,

[0017] The content of the in-situ catalyst is 1-2 wt%; and / or,

[0018] The content of the high-temperature crosslinking agent is 0.8-1.5 wt%.

[0019] In the present invention, those skilled in the art can also add other commonly used substances in the art according to the common knowledge in the art, and the addition amount of the substance is the ordinary addition amount in the art.

[0020] In the stepwise plugging agent described in the present invention, preferably,

[0021] The thickener is selected from amide thickeners, preferably at least one selected from acrylamide polymers;

[0022] Further preferably, the thickener is selected from at least one of acrylamide / 2-acrylamido-2-methylpropanesulfonic acid copolymer (AM / AMPS); that is, at least one of AM / AMPS copolymers with different AM / AMPS ratios or different molecular weights;

[0023] Still further preferably, the molecular weight of the thickener is 10 million to 20 million.

[0024] In the stepwise plugging agent described in the present invention, preferably,

[0025] The low-temperature crosslinking agent is selected from at least one of aluminum crosslinking agents;

[0026] Preferably, the low-temperature crosslinking agent is selected from at least one of aluminum citrate and aluminum tartrate.

[0027] In the stepwise plugging agent described in the present invention, preferably,

[0028] The lignin is selected from at least one of alkali lignin and enzymatically hydrolyzed lignin;

[0029] More preferably, the particle size of the lignin is less than 100 mesh, and more preferably, the particle size of the lignin is 100-300 mesh.

[0030] In the stepwise plugging agent described in the present invention, preferably,

[0031] The in-situ catalyst is selected from formates, and preferably, the in-situ catalyst is selected from at least one of sodium formate and potassium formate.

[0032] In the stepwise plugging agent described in the present invention, preferably,

[0033] The high-temperature crosslinking agent is selected from at least one of formaldehyde, paraformaldehyde, and hexamethylenetetramine; and / or,

[0034] In the present invention, the water is not specifically limited and may be river water, lake water, atmospheric water, seawater, groundwater, artificially produced water, produced water from oil fields, etc.; preferably, the water has a salinity of not more than 50,000 mg / L, and more preferably, the salinity of the water is 0 to 20,000 mg / L.

[0035] The second object of the present invention is to provide a preparation method of a step-by-step plugging agent, comprising the following steps:

[0036] Mix the raw materials including a thickening agent, a low-temperature crosslinking agent, lignin, an in-situ catalyst, a high-temperature crosslinking agent, and water evenly to obtain the step-by-step plugging agent;

[0037] Preferably, it is used to prepare the step-by-step plugging agent according to any one of the first objects of the present invention.

[0038] In the preparation method of the step-by-step plugging agent of the present invention, preferably, the following steps:

[0039] (1) Dissolve the thickening agent in water until completely dissolved;

[0040] (2) Add the low-temperature crosslinking agent, the in-situ catalyst, and the high-temperature crosslinking agent, mix evenly, and optionally adjust the pH value;

[0041] (3) Add lignin and disperse evenly to obtain the step-by-step plugging agent;

[0042] Preferably, adjust the pH value to 6.5 - 8.5.

[0043] In the preparation method of the step-by-step plugging agent of the present invention, preferably,

[0044] Based on the total weight of the thickening agent, the low-temperature crosslinking agent, lignin, the in-situ catalyst, the high-temperature crosslinking agent, and water being 100%,

[0045] the content of the thickening agent is 0.05 - 0.3 wt%;

[0046] the content of the low-temperature crosslinking agent is 0.03 - 0.2 wt%;

[0047] the content of lignin is 1 - 5 wt%;

[0048] the content of the in-situ catalyst is 0.5 - 3 wt%;

[0049] the content of the high-temperature crosslinking agent is 0.5 - 2 wt%.

[0050] In the preparation method of the step-by-step plugging agent of the present invention, preferably,

[0051] The content of the thickener is 0.1-0.25 wt%; and / or,

[0052] The content of the low-temperature crosslinking agent is 0.05-0.15 wt%; and / or,

[0053] The content of the lignin is 2-4 wt%; and / or,

[0054] The content of the in-situ catalyst is 1-2 wt%; and / or,

[0055] The content of the high-temperature crosslinking agent is 0.8-1.5 wt%.

[0056] In the present invention, those skilled in the art can also add other commonly used substances in the art according to the common knowledge in the art, and the substance can be added in the ordinary addition amount in the art.

[0057] In the preparation method of the step-by-step plugging agent described in the present invention, preferably,

[0058] The thickener is selected from amide thickeners, preferably at least one selected from acrylamide polymers;

[0059] Further preferably, the thickener is selected from at least one of acrylamide / 2-acrylamide-2-methylpropanesulfonic acid copolymers (AM / AMPS); that is, at least one of AM / AMPS copolymers with different AM / AMPS ratios or different molecular weights;

[0060] Still further preferably, the molecular weight of the thickener is 10 million to 20 million.

[0061] In the preparation method of the step-by-step plugging agent described in the present invention, preferably,

[0062] The low-temperature crosslinking agent is selected from at least one of aluminum crosslinking agents;

[0063] Preferably, the low-temperature crosslinking agent is selected from at least one of aluminum citrate and aluminum tartrate.

[0064] In the preparation method of the step-by-step plugging agent described in the present invention, preferably,

[0065] The lignin is selected from at least one of alkali lignin and enzymatically hydrolyzed lignin;

[0066] More preferably, the particle size of the lignin is less than 100 mesh, and more preferably, the particle size of the lignin is 100-300 mesh.

[0067] In the preparation method of the step-by-step plugging agent described in the present invention, preferably,

[0068] The in-situ catalyst is selected from formates. Preferably, the in-situ catalyst is selected from at least one of sodium formate and potassium formate.

[0069] In the preparation method of the step-by-step plugging agent described in the present invention, preferably,

[0070] The high-temperature crosslinking agent is selected from at least one of formaldehyde, paraformaldehyde, and hexamethylenetetramine; and / or,

[0071] In the present invention, the water is not specifically limited and can be river water, lake water, atmospheric water, seawater, groundwater, artificial water, produced water from oil fields, etc.; preferably, the water has a salinity not higher than 50000 mg / L, and more preferably, the salinity of the water is 0 - 20000 mg / L.

[0072] The third object of the present invention is to provide an application of the step-by-step plugging agent described in any one of the first objects of the present invention or the step-by-step plugging agent prepared by the preparation method described in any one of the second objects of the present invention in the operation of plugging steam channeling in oil production, preferably in the operation of plugging steam channeling during the thermal recovery of heavy oil.

[0073] In the application of the step-by-step plugging agent described in the present invention, preferably,

[0074] Pump the step-by-step plugging agent into the ground and migrate it to the target formation; inject steam to preheat the formation to the required reaction temperature to cause the step-by-step plugging agent to react and plug the steam channeling pores;

[0075] Preferably, the reaction temperature is 150°C - 300°C.

[0076] In the application method of the present invention, pump the above-mentioned plugging agent stock solution into the ground and migrate it to the target formation to generate a first-stage weakly crosslinked gel; inject steam to preheat the formation to the required reaction temperature, and lignin is liquefied under the action of an in-situ catalyst to obtain a phenolic co-crosslinking agent; the phenolic co-crosslinking agent and the high-temperature crosslinking agent react with lignin together to obtain a high-temperature resistant plugging agent to plug the steam channeling pores.

[0077] In summary, the present invention provides a step-by-step plugging system based on in-situ liquefaction of lignin, its preparation method and application. In this patent, the plugging system is divided into a first-stage weak cross-linked low-temperature gel and a second-stage strong cross-linked high-temperature gel, specifically including a thickener, a low-temperature cross-linking agent, lignin, an in-situ catalyst, a high-temperature cross-linking agent and water. The above plugging agent is pumped into and transported to the deep formation. Under the formation temperature condition, the thickener and the low-temperature cross-linking agent undergo a first-stage weak cross-linking to form a low-temperature gel; with the injection of steam, the low-temperature gel slowly breaks, and lignin is in-situ liquefied to obtain phenolic substances such as guaiacol and 2,6-dimethoxyphenol. The phenolic substances act as co-cross-linking agents under high-temperature conditions, and lignin + high-temperature cross-linking agent + phenolic substances undergo a second-stage strong cross-linking to obtain a high-temperature gel, which does not break gel at 300°C for 30 days, and the plugging rate is higher than 98.6%. This system expands the temperature range of use, can plug the formation at different temperature segments, and has high strength. It has the characteristics of large plugging strength, wide application range, high plugging efficiency, etc., can effectively plug the steam channel for a long time, realize the efficient development of heavy oil reservoirs, and at the same time reduce the production cost of the plugging agent, meet the performance and economic requirements of on-site construction, and has high practicability. The present invention solves the problems that the existing lignin-based plugging system cannot achieve low-temperature plugging, the gel formation is uncontrollable, the gel formation strength is generally low, and the cost is high during the application process in oilfields through a step-by-step plugging method.

[0078] In the present invention, the endpoints and any values within the disclosed ranges are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in this article. In the following text, in principle, various technical solutions can be combined with each other to obtain new technical solutions, which should also be regarded as specifically disclosed in this article.

[0079] Compared with the prior art, the present invention has at least the following advantages:

[0080] In the prior art, lignin cannot form a gel at low temperatures below 100°C. When high-pressure steam is injected, the system is easily diluted and washed away, resulting in poor gel formation or even inability to form a gel. The present invention solves the problem that lignin is easily diluted and washed away when injecting steam through a first-stage weak cross-linking, which is beneficial to the temperature rise in the near-wellbore area;

[0081] The in-situ catalyst of the present invention solves the problems of low activity and large dosage of lignin;

[0082] The lignin of the present invention is in-situ degraded underground to form phenolic cross-linking agents; in the two-stage cross-linking structure, the first-stage weak gel plugs the formation at low temperatures and keeps the system from being diluted, and forms a second-stage strong gel at high temperatures to solve the problems of poor gel formation effect and low plugging strength of the high-temperature plugging system. Detailed implementation manners

[0083] The present invention will be specifically described below in conjunction with specific embodiments. It is necessary to point out here that the following embodiments are only used for further illustration of the present invention, and cannot be understood as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention still fall within the protection scope of the present invention.

[0084] In addition, it should be noted that the various specific technical features described in the following specific implementation manners can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0085] Furthermore, any combination can be made between various different embodiments of the present invention, as long as it does not violate the idea of the present invention. The technical solutions formed thereby belong to a part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0086] Raw material sources:

[0087] Enzymatic lignin is purchased from Shandong Longli Biotechnology Co., Ltd., and the particle size is 100 - 300 mesh.

[0088] Alkali lignin is purchased from J&K Scientific Ltd., and the particle size is 100 - 300 mesh.

[0089] The amide thickener (AM / AMPS copolymer) is purchased from Shandong Baomo Biochemical Co., Ltd., with an effective content of about 88 wt%, and a weight average molecular weight of 15 million. The commonly used amide thickeners in the art are white particles with a water content of less than 12 wt% and an effective content greater than 88 wt%.

[0090] If there is no special limitation on other raw materials in the plugging system of the present invention, they are all disclosed in the prior art. For example, they can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0091] Testing methods:

[0092] Gel formation test:

[0093] Place the plugging agent in a high-temperature and high-pressure reactor, place it at the gel formation temperature, and observe the gel formation progress by taking samples from the reactor every 4 hours; after gel formation, observe the gel breaking situation by taking samples from the reactor every 2 days.

[0094] Strength test:

[0095] The gel strength was tested by the breakthrough vacuum degree method. The specific operation was as follows: The formed gel was loaded into the test bottle of the breakthrough vacuum degree experimental device. The tip of a 1 mL pipette was inserted 1 cm below the surface of the gel. The vacuum pump was started, and the knob was slowly adjusted to increase the system vacuum degree. When the air broke through the gel, the maximum reading of the vacuum degree on the vacuum gauge was the breakthrough vacuum degree of the gel. Each sample was measured 3 times, and the arithmetic mean was taken as its final strength value.

[0096] Blocking rate test:

[0097] A simulated core was prepared (core diameter was 25 mm and length was 600 mm), and it was evacuated and saturated with water. First, water was injected into the core at a certain flow rate to measure the permeability before plugging (k0) of the core; then, under the condition of a gas-liquid ratio of 1:1, different plugging agents were injected into the core at an injection rate of 2 mL / min. After stabilizing at 100 °C for 12 hours, the heating jacket was heated to 300 °C for subsequent steam displacement; finally, water was injected to measure the permeability after plugging (k') of the core. The blocking rate was used as a parameter to characterize the plugging effect of the plugging agent. The calculation formula for the blocking rate was where k0 was the permeability before plugging, μm 2 ; k' was the permeability after plugging, μm 2 .

[0098] Example 1

[0099] 0.2 g of an amide thickener (AM / AMPS copolymer) was dissolved in 80 g of prepared water with a salinity of 5000 mg / L and stirred until evenly dissolved at a rotation speed of 500 r / min; then, 0.12 g of aluminum citrate, 1.5 g of sodium formate, and 1.2 g of hexamine were added, and then sodium hydroxide was added to adjust the pH to 6.5; finally, 3.2 g of enzymatically hydrolyzed lignin was added and stirred until evenly dispersed, and the prepared water with a salinity of 5000 mg / L was quantitatively added to 100 g to obtain a step-by-step plugging system.

[0100] After the above plugging agent gelled at 100 °C, the strength reached 0.087 MPa; it was continuously heated to 300 °C and maintained for 42 days without gel breaking; the obtained plugging agent was subjected to a plugging test, and the blocking rate was 99.2%.

[0101] Example 2

[0102] 0.1 g of an amide thickener (AM / AMPS copolymer) was dissolved in 80 g of prepared water with a salinity of 50000 mg / L and stirred until evenly dissolved at a rotation speed of 500 r / min; then, 0.05 aluminum tartrate, 1 g of sodium formate, and 0.8 g of paraformaldehyde were added, and then sodium hydroxide was added to adjust the pH to 6.5; finally, 4 g of alkali lignin was added and stirred until evenly dispersed, and the prepared water with a salinity of 50000 mg / L was quantitatively added to 100 g to obtain a step-by-step plugging system.

[0103] The strength of the above plugging agent reaches 0.082 MPa after gelation at 100 °C; the temperature is continuously raised to 300 °C and maintained for 36 days without gel breaking; the obtained plugging agent is subjected to a plugging test, and the plugging rate is 98.6%.

[0104] Example 3

[0105] Dissolve 0.25 g of an amide thickener (AM / AMPS copolymer) in 80 g of prepared water with a salinity of 10,000 mg / L, and stir at a speed of 500 r / min until uniformly dissolved; then, add 0.15 aluminum citrate, 2 g of sodium formate, and 1.5 g of hexamine, and then add sodium hydroxide to adjust the pH to 6.5; finally, add 2 g of enzymatically hydrolyzed lignin and stir until uniformly dispersed, and quantitatively add prepared water with a salinity of 10,000 mg / L to 100 g to obtain a step-by-step plugging system.

[0106] The strength of the above plugging agent reaches 0.085 MPa after gelation at 100 °C; the temperature is continuously raised to 300 °C and maintained for 38 days without gel breaking; the obtained plugging agent is subjected to a plugging test, and the plugging rate is 99.1%.

[0107] Example 4

[0108] Conduct the experiment according to the method of Example 1, except that 1.5 g of sodium formate is replaced with 1.5 g of potassium formate to obtain a step-by-step plugging system. The strength of the above plugging agent reaches 0.081 MPa after gelation at 100 °C; the temperature is continuously raised to 300 °C and maintained for 38 days without gel breaking; the obtained plugging agent is subjected to a plugging test, and the plugging rate is 99.0%.

[0109] Example 5

[0110] Conduct the experiment according to the method of Example 1, except that 1.2 g of hexamine is replaced with 1.2 g of formaldehyde to obtain a step-by-step plugging system. The strength of the above plugging agent reaches 0.085 MPa after gelation at 100 °C; the temperature is continuously raised to 300 °C and maintained for 30 days without gel breaking; the obtained plugging agent is subjected to a plugging test, and the plugging rate is 98.8%.

[0111] Example 6

[0112] Conduct the experiment according to the method of Example 1, except that adjusting the pH to 6.5 is replaced with adjusting the pH to 8 to obtain a step-by-step plugging system. The strength of the above plugging agent reaches 0.082 MPa after gelation at 100 °C; the temperature is continuously raised to 300 °C and maintained for 32 days without gel breaking; the obtained plugging agent is subjected to a plugging test, and the plugging rate is 98.7%.

[0113] Comparative Example 1

[0114] The experiment was carried out according to the method of Example 1, except that the enzymatically hydrolyzed lignin was replaced with sodium lignosulfonate, and the lignin was completely dissolved. The strength of the obtained plugging agent after gelation at 100 °C was 0.032 MPa, and it had broken gel after being heated to 300 °C for 14 days. The obtained plugging agent was subjected to a plugging test, and the plugging rate was 65.6%.

[0115] From the results of Example 1 and Comparative Example 2, it can be seen that only when the plugging agent system of the present invention is combined with a specific lignin can the comprehensive performance of the secondary strong cross-linked high-temperature gel be better.

[0116] Comparative Example 2

[0117] The experiment was carried out according to the method of Example 1, except that 1.5 g of the in-situ catalyst sodium formate was replaced with an equal mass of sodium chloride. The strength of the obtained plugging agent after gelation at 100 °C was 0.085 MPa, and it had broken gel after being heated to 300 °C for 16 days. The obtained plugging agent was subjected to a plugging test, and the plugging rate was 56.9%.

[0118] From the results of Example 1 and Comparative Example 2, it can be seen that only when the plugging agent system of the present invention is combined with a specific in-situ catalyst can the comprehensive performance of the secondary strong cross-linked high-temperature gel be better.

[0119] Comparative Example 3

[0120] The experiment was carried out according to the method of Example 1, except that 0.12 g of the low-temperature cross-linking agent aluminum citrate was replaced with an equal mass of hexamethylenetetramine. The obtained plugging agent did not gel at 100 °C and had broken gel after being heated to 300 °C for 10 days. The obtained plugging agent was subjected to a plugging test, and the plugging rate was 43.1%.

[0121] From the results of Example 1 and Comparative Example 3, it can be seen that the plugging agent system of the present invention solves the problem that lignin is easily diluted and washed away during steam injection through primary weak cross-linking, which is beneficial to the temperature rise in the near-wellbore area.

[0122] The present invention has been described in detail above in combination with specific embodiments and exemplary examples, but these descriptions should not be construed as limiting the present invention. Those skilled in the art understand that without departing from the spirit and scope of the present invention, various equivalent substitutions, modifications or improvements can be made to the technical solutions of the present invention and their implementation manners, and all of these fall within the scope of the present invention. The protection scope of the present invention is subject to the appended claims.

[0123] All publications, patent applications, patents and other references mentioned in this specification are hereby incorporated by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0124] When this specification uses prefixes such as "known to those skilled in the art", "prior art", or similar terms to introduce materials, substances, methods, steps, devices, or components, etc., the objects introduced by such prefixes cover those commonly used in the art at the time when this application is filed, but also include those that are not commonly used at present but will become recognized in the art as suitable for similar purposes.

[0125] In the context of this specification, any matter or thing not mentioned, except for what is clearly stated, directly applies to those known in the art without any change.

Claims

1. A step-by-step plugging agent, characterized in that: The step-by-step plugging agent comprises a thickener, a low-temperature crosslinking agent, lignin, an in-situ catalyst, a high-temperature crosslinking agent and water; Based on the total weight of the thickener, low-temperature crosslinking agent, lignin, in-situ catalyst, high-temperature crosslinking agent and water being 100%, The content of the thickener is 0.05 - 0.3 wt%; The content of the low-temperature crosslinking agent is 0.03 - 0.2 wt%; The content of the lignin is 1 - 5 wt%; The content of the in-situ catalyst is 0.5 - 3 wt%; The content of the high-temperature crosslinking agent is 0.5 - 2 wt%.

2. The step-by-step plugging agent according to claim 1, characterized in that: Based on the total weight of the thickener, low-temperature crosslinking agent, lignin, in-situ catalyst, high-temperature crosslinking agent and water being 100%, The content of the thickener is 0.1 - 0.25 wt%; and / or, The content of the low-temperature crosslinking agent is 0.05 - 0.15 wt%; and / or, The content of the lignin is 2 - 4 wt%; and / or, The content of the in-situ catalyst is 1 - 2 wt%; and / or, The content of the high-temperature crosslinking agent is 0.8 - 1.5 wt%.

3. The step-by-step plugging agent according to claim 1, characterized in that: The thickener is selected from amide thickeners, preferably at least one selected from acrylamide polymers; Further preferably, the thickener is selected from at least one of acrylamide / 2-acrylamido-2-methylpropanesulfonic acid copolymers; Even more preferably, the molecular weight of the thickener is 10 million - 20 million.

4. The step-by-step plugging agent according to claim 1, characterized in that: The low-temperature crosslinking agent is selected from at least one of aluminum crosslinking agents; Preferably, the low-temperature crosslinking agent is selected from at least one of aluminum citrate and aluminum tartrate.

5. The step-by-step plugging agent according to claim 1, characterized in that: The lignin is selected from at least one of alkali lignin and enzymatically hydrolyzed lignin; More preferably, the particle size of the lignin is less than 100 mesh, and even more preferably, the particle size of the lignin is 100 - 300 mesh.

6. The step-by-step plugging agent according to claim 1, characterized in that: The in-situ catalyst is selected from formates, preferably at least one of sodium formate and potassium formate.

7. The step-by-step plugging agent according to claim 1, characterized in that: The high-temperature crosslinking agent is selected from at least one of formaldehyde, paraformaldehyde and hexamethylenetetramine; and / or, The water has a salinity of not more than 50000 mg / L, and preferably, the salinity of the water is 0 - 20000 mg / L.

8. A preparation method of a step-by-step plugging agent, characterized in that, Comprises the following steps: Mix the raw materials including the thickener, low-temperature crosslinking agent, lignin, in-situ catalyst, high-temperature crosslinking agent and water evenly to obtain the step-by-step plugging agent; Preferably used for preparing the step-by-step plugging agent according to any one of claims 1 - 7.

9. The preparation method of the step-by-step plugging agent according to claim 8, characterized in that, Comprises the following steps: (1) Dissolve the thickener in water until completely dissolved; (2) Add the low-temperature crosslinking agent, in-situ catalyst and high-temperature crosslinking agent, mix evenly, and optionally adjust the pH value; (3) After adding lignin, it is evenly dispersed to obtain the step-by-step plugging agent; Preferably, the pH value is adjusted to 6.5 - 8.

5.

10. Application of the step-by-step plugging agent according to any one of claims 1 - 7 or the step-by-step plugging agent prepared by the preparation method according to any one of claims 8 - 9 in the operation of plugging steam channeling in oil production, preferably in the operation of plugging steam channeling during the process of thermal recovery of heavy oil.

11. According to the application described in claim 10, characterized in that: Pump the step-by-step plugging agent into the ground and migrate it to the target formation; inject steam to preheat the formation to the required reaction temperature to cause the step-by-step plugging agent to react and plug the steam channeling pores; Preferably, the reaction temperature is 150°C - 300°C.