Cementing breaker, its preparation method and application

Abstract

This invention belongs to the field of oilfield chemical cementing, and relates to a cementing breaker, its preparation method, and its application. The breaker, by weight percentage, comprises: 2-3 parts chitosan, 1 part liquid paraffin, 1 part ethanol, 2 parts sodium dodecyl sulfate, 1 part acrylic acid, 2 parts oxidant, and 120 parts water. The breaker uses an encapsulation structure to carry the oxidant as a carrier core, and can be directly applied to the pre-flush fluid system during the cementing process. Upon reaching the target formation, the coating senses and controls the release of the carrier core through the weakly acidic nature of the pre-flush fluid system, rapidly unblocking the blockage. This achieves both rapid and precise breaker release, avoiding the drawback of oxidative breakers being incompatible with the pre-flush fluid system, and plays an important role in reservoir protection and unblocking. The preparation method of the breaker is simple and reliable, which not only improves the development efficiency of oil and gas fields but also helps reduce development costs and protect the environment, possessing significant practical value and broad market prospects.

Description

Technical Field

[0001] This invention belongs to the field of oilfield chemical cementing, and relates to a cementing breaker, its preparation method, and its application. Background Technology

[0002] In oil and gas field development, HPAM (partially hydrolyzed polyacrylamide) gels are frequently used for temporary plugging to effectively control downhole pressure, improve cementing quality, and prevent formation water breakthrough. This material is widely used in cementing, fracturing, and other production enhancement operations due to its excellent viscoelasticity and adjustable viscosity. However, if the gel is not broken down in time, it may clog the pores and fractures of the oil and gas reservoir, affecting oil and gas flow, thereby reducing the production efficiency of the oil and gas well and impacting the long-term production potential of the reservoir. Therefore, these gels must be quickly and thoroughly destroyed once they have completed their plugging task.

[0003] Oxidative breaker agents, such as potassium persulfate and ammonium persulfate, are commonly used breaker agents. However, in cementing operations, if they are directly added to the pre-fracturing fluid, they will cause a rapid decrease in the viscosity of the fracturing fluid, weaken its sand-carrying capacity, increase filtrate, affect the fracturing fluid's ability to create fractures during operation, and may even cause premature sand removal, leading to operation failure. Moreover, oxidative breaker agents are non-specific reactants and can react with any reactants they encounter, such as pipe materials, formation matrix, and hydrocarbons, generating contaminants that are incompatible with the formation and causing formation damage.

[0004] Delayed-release breaker can effectively avoid the above problems and provide a more effective breaker. However, existing delayed-release breaker generally have some drawbacks, such as long breaker time, low efficiency, potential environmental hazards, and relatively high cost. Especially under complex geological conditions, such as high-temperature and high-salt environments, the effectiveness of traditional breaker is often greatly reduced, making it difficult to meet industrial needs.

[0005] Therefore, it is particularly important to develop a breaker that can efficiently break down adhesives in a short time, and is environmentally friendly and cost-effective. Summary of the Invention

[0006] The main objective of this invention is to develop a cementing breaker, its preparation method, and its application for easily leaking reservoirs. When added to the gel during construction, it enables the gel to break down rapidly, playing an important role in reservoir protection and unblocking.

[0007] During construction, it is added to the pre-fluid system to rapidly break down the gel in the target layer, which plays an important role in reservoir protection and unblocking.

[0008] The cementing breaker described in this invention, by weight percentage, comprises: 2-3 parts chitosan, 2 parts sodium dodecyl sulfate, 1 part acrylic acid, 1 part liquid paraffin, 1 part anhydrous ethanol, 2 parts oxidant, and 120 parts water.

[0009] The oxidant is ammonium persulfate or a mixture of ammonium persulfate and potassium persulfate. When a mixture of ammonium persulfate and potassium persulfate is used, the mass ratio of ammonium persulfate to potassium persulfate is 1:1.

[0010] The preparation method of the cementing breaker described above includes the following specific steps:

[0011] (1) Weigh each raw material according to the proportion;

[0012] (2) After adding acrylic acid and anhydrous ethanol to water and stirring evenly, chitosan is added and stirred evenly. Liquid paraffin is then added to obtain slurry I.

[0013] (3) Add sodium dodecyl sulfate to water and stir until homogeneous, then add oxidant to obtain slurry II;

[0014] (4) Drop slurry I into slurry II to obtain a desiccant.

[0015] The de-icing agent obtained by this invention is spherical with a diameter of millimeters. It is coated with sodium dodecyl sulfate and chitosan, and encapsulates ammonium persulfate solution or a solution of ammonium persulfate and potassium persulfate.

[0016] The stirring speed in steps (2) and (3) is 550 r·min. -1 Slurry I is dripped into slurry II at a rate of one drop every three seconds; otherwise, the number of broken balls will exceed 50% or the balls will not form.

[0017] In this invention, chitosan molecules and sodium dodecyl sulfate molecules form a mixed adsorption layer and a multilayer interfacial film, enhancing interfacial activity. Chitosan is an abundant cationic biopolyelectrolyte; when compounded with sodium dodecyl sulfate, electrostatic attraction enhances the binding between chitosan and sodium dodecyl sulfate molecules, constructing a film structure that allows it to support a core containing ammonium persulfate solution or a solution of ammonium persulfate and potassium persulfate. The liquid core facilitates faster gel breaking. In this invention, acrylic acid and anhydrous ethanol contribute to better water solubility of chitosan.

[0018] Chitosan, also known as deacetylated chitin, is a widely distributed natural polymer material, renowned for its rigid molecular structure and wide range of applications. The charge density of this material can be controlled by adjusting the degree of deacetylation and pH value. Changes in pH affect the protonation state of chitosan molecules, thereby altering the flexibility of the molecular chains and intermolecular interactions, which significantly impacts the stability of the emulsions formed. Therefore, chitosan exhibits a pronounced pH-responsive characteristic and shows great potential in the research of stimulus-responsive materials. However, the scarcity of hydrophobic groups in chitosan molecules, and the spatial barriers created by the random distribution of these groups, weakens its contact ability with the oil-water interface. The combination of surfactants with chitosan can enhance the strength of the interfacial film, reduce droplet aggregation, and thus improve the stability and temperature and salt resistance of the emulsion.

[0019] The gel-breaking agent described in this invention is added to the cementing pre-fluid system to break up the gel. In practical use, the pre-fluid system with the gel-breaking agent is directly pumped into the location blocked by HPAM gel to achieve rapid unblocking.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) The breaker described in this invention uses encapsulation technology to encapsulate the oxidant and is used in conjunction with cementing pre-fill fluid. Unlike conventional direct injection breaker, it can control the release of the core carrier after reaching the destination layer to achieve precise release.

[0022] (2) The gel breaking agent described in this invention rapidly breaks down the HPAM gel that was originally solidified in the formation, so that when it is added to the pre-filled liquid system, it can effectively seal the lost reservoir when it reaches the target layer, laying the foundation for subsequent cementing work.

[0023] (3) The preparation method of the breaker described in this invention is simple, reliable, easy to produce on a large scale and apply on site. It can not only improve the development efficiency of oil and gas fields, but also help reduce development costs and protect the environment. It has important practical value and broad market prospects. Attached Figure Description

[0024] Figure 1 The desiccant obtained in Example 1;

[0025] Figure 2 This is a debonding agent used after the core is released;

[0026] Figure 3 The desiccant obtained in Example 5;

[0027] Figure 4 Viscosity change curves under different amounts of breaker;

[0028] Figure 5 The desiccant obtained in Comparative Example 1;

[0029] Figure 6 The desiccant obtained in Comparative Example 2. Detailed Implementation

[0030] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0031] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms “comprising” and / or “including” are used herein, they indicate the presence of features, steps, operations, and / or combinations thereof.

[0032] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0033] Example 1

[0034] The cementing breaker, by weight, consists of the following raw materials: 2 parts chitosan, 2 parts sodium dodecyl sulfate, 1 part acrylic acid, 1 part liquid paraffin, 1 part anhydrous ethanol, 1 part ammonium persulfate, 1 part potassium persulfate, and 120 parts water.

[0035] The preparation steps are as follows:

[0036] (1-1) Weigh each raw material according to the proportion and set aside;

[0037] (1-2) Add 1 part acrylic acid and 1 part anhydrous ethanol to 80 parts water and stir evenly. Then add 2 parts chitosan and stir at 550 r·min. -1 Stir at high speed for 30 minutes. After stirring evenly, add 1 part of liquid paraffin and continue stirring for 1 minute to obtain slurry I.

[0038] (1-3) Add 2 parts sodium dodecyl sulfate to 40 parts water and stir well. Then add 1 part ammonium persulfate and 1 part potassium persulfate. Stir at 550 r·min. -1 , to obtain slurry II;

[0039] (1-4) Place slurry I in a separatory funnel and add it to slurry II at a rate of one drop every three seconds to obtain a core-carrying transparent sphere, i.e., a breaker. Figure 1 As shown.

[0040] Example 2

[0041] A weakly acidic environment was simulated in the pre-fluid system (the pre-fluid system formula was: 100g water + 8% HPAM aqueous solution + 0.1g sodium dodecyl sulfate + 0.1g Jiahua G-grade cement). The breaker prepared in Example 1 was placed in the pre-fluid system, and it was observed that the breaker automatically released the carrier core. After releasing the carrier core, as shown... Figure 2 As shown.

[0042] Example 3

[0043] Chitosan, sodium dodecyl sulfate (SDS), and liquid paraffin were prepared in different proportions. The breaker was prepared according to the synthesis method of Example 1. The prepared breaker was placed in the weakly acidic pretreatment liquid described in Example 2 to form mixed slurry III. The presence of ammonium persulfate and potassium persulfate in the core was detected by titration.

[0044] The oxidizing properties of ammonium persulfate and potassium persulfate were utilized, and titration was performed using potassium iodide as a reducing agent and starch solution. The specific steps were as follows: Potassium iodide and water were added to mixed slurry III, shaken well, and left in the dark for a certain period of time. At this point, the solution turned blue. Titration was then performed using a standard sodium thiosulfate solution, and the blue color of the solution disappeared. Records of the release time, defined as the complete disappearance of the blue color, are shown in the table below:

[0045] .

[0046] Example 4

[0047] The preparation steps for HPAM-type gels are as follows:

[0048] The gel, which is guaranteed to seal the target layer, has the following raw material composition by weight: 2 parts HPAM, 1 part organic chromium crosslinking agent, 1 part stabilizer, and 20 parts distilled water.

[0049] (1-1) Weigh each raw material according to the proportion and set aside;

[0050] (1-2) Add 2 parts HPAM to 20 parts distilled water, stir well, and stir at a speed of 550 r·min. -1 , thus obtaining slurry IV;

[0051] (1-3) Mix 1 part of stabilizer with slurry IV, stir evenly, and stir at a speed of 550 r·min. -1 , thus obtaining slurry V;

[0052] (1-4) Mix slurry V with 1 part of organic chromium crosslinking agent to form a homogeneous slurry, stir evenly, and stir at a speed of 550 r·min. -1 Placed in an 80℃ heating furnace for 6 hours, the pH was adjusted to obtain gel G1.

[0053] Example 5

[0054] The cementing breaker, by weight percentage, consists of: 2 parts chitosan, 2 parts sodium dodecyl sulfate, 1 part acrylic acid, 1 part anhydrous ethanol, 1 part liquid paraffin, 2 parts ammonium persulfate, and 120 parts water.

[0055] The preparation steps are as follows:

[0056] (1-1) Weigh each raw material according to the proportion and set aside;

[0057] (1-2) Add 1 part acrylic acid and 1 part anhydrous ethanol to 80 parts water and stir evenly. Then add 2 parts chitosan and stir at 550 r·min. -1 Stir at high speed for 30 minutes. After stirring evenly, add 1 part of liquid paraffin and continue stirring for 1 minute to obtain slurry VI.

[0058] (1-3) Add 2 parts sodium dodecyl sulfate to 40 parts water and stir until well mixed. Then add 2 parts ammonium persulfate and stir at a speed of 550 r·min. -1 , thus obtaining slurry VII;

[0059] (1-5) Place slurry VI in a separatory funnel and add it dropwise to slurry VII at a rate of one drop every three seconds to obtain a transparent spherical breaker, such as... Figure 3 As shown.

[0060] Example 6

[0061] To simulate the pre-treatment liquid system, the HPAM-type gel prepared in Example 4 was mixed with the breaker prepared in Example 1 at ratios of 1:10 (mass ratio) and 1:15 (mass ratio), and then mixed with the breaker prepared in Example 5 at a ratio of 1:10 (mass ratio). This mixture was then added to the pre-treatment liquid system and stirred until homogeneous at a stirring speed of 550 r·min. -1 The breaking temperature was set at 80℃. The breaking process was observed by testing the viscosity change, and the breaking time was recorded. The specific results are as follows:

[0062] This study uses a rotational viscometer to test liquid viscosity, primarily by calculating the viscosity value based on the resistance encountered by the rotating column as it rotates within the liquid. The formula for calculating viscosity using a rotational viscometer is as follows:

[0063] ;

[0064] in, N The rotational speed (rpm) of the rotating column. R Let be the radius (mm) of the rotating cylinder. VThe velocity (mm / s) of the liquid flowing on the rotating column is given by the viscosity, which is measured in centipoises (cP). The viscosity value calculated using a rotational viscometer can be used to determine the flow properties and mass of the liquid. A viscosity change curve is shown in the figure. Figure 4 As shown.

[0065] Comparative Example 1

[0066] A desiccant, by weight percentage, comprises: 2 parts chitosan, 1 part anhydrous ethanol, 1 part liquid paraffin, 1 part acrylic acid, 2 parts ammonium persulfate, and 120 parts water.

[0067] The preparation steps are as follows:

[0068] (1-1) Weigh each raw material according to the proportion and set aside;

[0069] (1-2) Add 1 part acrylic acid and 1 part anhydrous ethanol to 80 parts water and stir evenly. Then add 2 parts chitosan and stir at 550 r·min. -1 Stir at high speed for 30 minutes. After stirring evenly, add 1 part of liquid paraffin and continue stirring for 1 minute to obtain slurry VIII.

[0070] (1-3) Add 2 parts of ammonium persulfate to 40 parts of water and stir until homogeneous. The stirring speed is 550 r·min. -1 , thus obtaining slurry IX;

[0071] (1-4) Place slurry VIII in a separatory funnel and add it dropwise to slurry IX at a rate of one drop every three seconds. This will result in a mixed slurry, which cannot achieve encapsulation. Figure 5 As shown.

[0072] Comparative Example 2

[0073] A degumming agent, by weight percentage, comprises: 2 parts chitosan, 2 parts anionic surfactant salt-type fatty alcohol ether carboxylic acid ester, 1 part anhydrous ethanol, 1 part liquid paraffin, 1 part acrylic acid, 1 part ammonium persulfate, 1 part potassium persulfate, and 120 parts water.

[0074] The preparation steps are as follows:

[0075] (1-1) Weigh each raw material according to the proportion and set aside;

[0076] (1-2) Add 1 part acrylic acid and 1 part anhydrous ethanol to 80 parts water and stir evenly. Then add 2 parts chitosan and stir at 550 r·min. -1 Stir at high speed for 30 minutes. After stirring evenly, add 1 part of liquid paraffin and continue stirring for 1 minute to obtain slurry X.

[0077] (1-3) Add 2 parts of anionic surfactant salt-type fatty alcohol ether carboxylic acid ester to 40 parts of water and stir well. Then add 1 part each of ammonium persulfate and potassium persulfate and stir at 550 r·min. -1 , thus obtaining slurry XI;

[0078] (1-4) Placing slurry X in a separatory funnel and adding it dropwise to slurry XI at a rate of one drop every three seconds will result in a mixed, hard plastic substance that cannot achieve spherical encapsulation, such as... Figure 6 As shown.

[0079] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A spherical breaker for cementing used in pre-cementing fluid systems, characterized in that, By weight percentage, its raw material composition is: 2-3 parts chitosan, 2 parts sodium dodecyl sulfate, 1 part acrylic acid, 1 part liquid paraffin, 1 part anhydrous ethanol, 2 parts oxidant, and 120 parts water; the cementing breaker uses sodium dodecyl sulfate and chitosan to form a film, and the inside is a solution of oxidant. The specific preparation steps are as follows: (1) Weigh each raw material according to the proportion; (2) After adding acrylic acid and anhydrous ethanol to water and stirring evenly, chitosan is added and stirred evenly. Liquid paraffin is then added to obtain slurry I. (3) Add sodium dodecyl sulfate to water and stir until homogeneous, then add oxidant to obtain slurry II; (4) Drop slurry I into slurry II to obtain spherical desiccant.

2. The spherical breaker for cementing in a pre-cementing fluid system according to claim 1, characterized in that, The oxidant is ammonium persulfate or a mixture of ammonium persulfate and potassium persulfate.

3. The spherical breaker for cementing in a pre-cementing fluid system according to claim 1, characterized in that, By mass ratio, ammonium persulfate: potassium persulfate = 1:

1.

4. The spherical breaker for cementing in a pre-cementing fluid system according to claim 1, characterized in that, The stirring speed in steps (2) and (3) is 550 r·min. -1 .

5. The spherical breaker for cementing in a pre-cementing fluid system according to claim 1, characterized in that, Slurry I is dripped into slurry II at a rate of one drop every three seconds.

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