Delayed-gelation plugging gel for well cementation, and preparation method therefor and use thereof

Abstract

The present invention relates to a delayed-gelation plugging gel for well cementation, and a preparation method therefor and the use thereof. The delayed-gelation plugging gel for well cementation comprises 2-3 parts of anionic polyacrylamide, 3-4 parts of cationic acrylamide, 1 part of a stabilizer, 1 part of a cross-linking agent, and 6 parts of distilled water, wherein the stabilizer is obtained by reacting citric acid with disodium ethylenediaminetetraacetate under the action of an initiator; and the cross-linking agent is obtained by reacting chromium lactate with chromium nicotinate under the action of azodiisobutylamidine hydrochloride and tetramethylethylenediamine. For the purpose of well cementation, a delayed-gelation plugging gel is provided. The plugging gel is pH-sensitive. By prolonging the gelation time of the gel that originally gelates fast at a certain temperature, a preflush system to which the delayed-gelation plugging gel is added can effectively plug a lost circulation zone when arriving at a destination formation, thereby laying a foundation for the subsequent operation of cement injection.

Description

Delayed gelling plugging gel for cementing, preparation method and application thereof Technical Field

[0001] The present invention belongs to the field of oilfield plugging materials, and relates to a delayed gelling plugging gel for cementing, a preparation method and application thereof Background Art

[0002] Reservoir heterogeneity, large leakage paths, and fluidity dictate that leakage pathways are often composed of large, multi-sized fractures or pores. The uncertainty of leakage pathways during reservoir leakage not only significantly impacts drilling efficiency but can also lead to problems such as large-scale drilling fluid losses. Currently, the main plugging materials used to address reservoir leakage include cement slurry, bridging plugging materials, and flexible plugging materials. However, the success rate of current plugging methods is relatively low, especially for fracture-type leakage. Conventional wellbore management measures are even less than ideal due to the uncertainty of leakage pathways. Currently, cement slurry is the most commonly used plugging material for addressing malignant leakage, such as fracture-type and porosity-type leakage. However, cement slurry easily mixes with formation water upon contact, resulting in erosion and dilution, making it difficult to retain in the leakage zone near the wellbore. Consequently, cement slurry plugging agents struggle to form a sufficiently strong, tight seal around the wellbore, resulting in suboptimal plugging results.

[0003] Cementing and plugging are done to achieve better oilfield drilling results. The cementing and plugging process usually involves first sending the drill bit into the leaking layer where the well is leaking, and then pulling out the drill bit after injecting cement slurry. Unlike large-particle plugging in drilling fluid, in order to prevent large particles from clogging the pressure transmission holes and check valves of the tail pipe hanger, the plugging materials in cementing slurry often use materials that are not easy to clog tools or accessories. Polymer gel-based plugging materials are also one of the commonly used plugging materials. Considering that as long as the gelling time of the gel can be accurately controlled and it solidifies quickly after reaching the target layer, the problem of difficulty in staying in the formation can be overcome. Therefore, it is planned to develop a delayed gelling gel for use in the pre-fluid system, which can be precisely solidified after reaching the target layer and is suitable for plugging work in the cementing process. Summary of the Invention

[0004] In response to the problems existing in the prior art, the present invention proposes a delayed gelling plugging gel for cementing, its preparation method and application, and adds the delayed gelling gel to the pre-fluid system during the construction process, so that the pre-fluid system with the added gel can be controllably sealed after reaching the target layer, thereby achieving a good plugging effect and reducing the construction process, laying the foundation for future cementing processes.

[0005] The present invention adopts the following technical solutions:

[0006] The delayed gelling plugging gel for well cementing of the present invention comprises 2-3 parts of anionic polyacrylamide, 3-4 parts of cationic acrylamide, 1 part of a stabilizer, 1 part of a cross-linking agent, and 6 parts of distilled water; the stabilizer is obtained by reacting citric acid and disodium ethylenediaminetetraacetic acid under the action of an initiator; and the cross-linking agent is obtained by reacting chromium lactate and chromium nicotinate under the action of azobisisobutylamidine hydrochloride and TMEDA (tetramethylethylenediamine).

[0007] The initiator is sodium persulfate; the mass ratio is citric acid: disodium ethylenediaminetetraacetic acid: initiator = 2:1:1.

[0008] Calculated by mass ratio, chromium lactate: chromium nicotinate: azobisisobutylamidine hydrochloride: tetramethylethylenediamine = 3:2:1:1.

[0009] The preparation method of the delayed gelling plugging gel for cementing comprises the following specific steps:

[0010] (2-1) Dissolve anionic polyacrylamide in distilled water and stir evenly, then slowly add cationic acrylamide and stir evenly to obtain slurry II;

[0011] (2-2) Slowly add stabilizer and crosslinker to slurry II and stir until uniform. The inventors discovered during their experiments that adding the stabilizer first can prevent acrylamide monomers from agglomerating. If the crosslinker is added first, the viscosity of the acrylamide increases upon addition of water, and the crosslinker tends to only partially react with the acrylamide, resulting in agglomeration.

[0012] The stabilizer is prepared by dissolving citric acid, disodium ethylenediaminetetraacetic acid, and an initiator in water, stirring evenly, and heating at 70° C. for 4 hours. The stabilizer of the present invention is used to maintain the stability of the gel and increase the gel strength.

[0013] The preparation method of the cross-linking agent is:

[0014] (1-1) Chromium lactate and chromium nicotinate are added to distilled water and stirred uniformly to obtain slurry I;

[0015] (1-2) Azobisisobutylamidine hydrochloride and tetramethylethylenediamine were added to slurry I, stirred and mixed uniformly, and heated at 50°C for 4 hours to obtain a crosslinking agent.

[0016] In this invention, citric acid and disodium EDTA react with potassium persulfate to form a new compound for use as a stabilizer, rather than using conventional citric acid or disodium EDTA alone. This is primarily because EDTA is a commonly used chelating agent. Using EDTA-based substances (such as EDTA, EDTA-2Na, and EDTA-4Na) alone as a stabilizer can cause Cr 3+ in the organic chromium crosslinker to be chelated by EDTA, forming a new compound. This prevents subsequent hydroxyl bridge reactions, preventing the Cr 3+ from being dissociated and reacting with acrylamide to form a gel. The chemical reaction formula for EDTA chelating Cr 3+ is as follows:

[0017] .

[0018] Chromium lactate and chromium nicotinate react in the presence of azobisisobutylamidine hydrochloride and tetramethylethylenediamine to produce a crosslinker. Cr 3+ reacts with HPAM, CPAM, and other materials to form gels. Experimental studies have shown that the crosslinker obtained using this invention is pH-sensitive, allowing the release of Cr 3+ to be controlled by controlling the pH. The delay mechanism is that the dissociation of the crosslinking center ion Cr 3+ is controlled, thereby slowing the rate of Cr 3+ hydroxyl bridge reaction, achieving delayed gelation.

[0019] The delayed gelling plugging gel of the present invention can be applied in cementing work and used in the pre-pad fluid system of cementing work, so as to facilitate controlling the gelling time of the gel according to different situations.

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

[0021] (1) Based on the purpose of cementing, the present invention proposes a delayed gelling plugging gel, which prolongs the gelling time of the gel that originally gelled quickly at a certain temperature, so that after adding it into the pre-fluid system, it can effectively plug the lost reservoir when it reaches the target layer, laying the foundation for subsequent cementing work.

[0022] (2) The plugging gel of the present invention is pH-sensitive. The present invention delays gelation by controlling the release rate of Cr 3+ in the cross-linking agent. The pre-pad system is a weakly acidic environment. When the plugging gel is in the pre-pad system, it has not yet gelled. When cement slurry is added later, the weakly acidic environment becomes alkaline, allowing gelation to occur, thereby achieving the purpose of plugging the target formation. After gelation, the gel of the present invention has strong compressive resistance and relatively high strength, so mixing with cement slurry increases the strength of the cement paste.

[0023] (3) The present invention avoids the use of Cr 6+ , thus avoiding the problem of serious harm to the health of operators and easy environmental pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 shows the gelation time of gel F1 under different pH conditions;

[0025] Figure 2 shows the gelation time of gel F2 under different pH conditions;

[0026] Figure 3 shows the gelation time of gel F3 under different pH conditions. DETAILED DESCRIPTION

[0027] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0028] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations and / or combinations thereof.

[0029] In order to enable those skilled in the art to more clearly 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.

[0030] Example 1

[0031] The preparation steps of the cross-linking agent are:

[0032] The organic chromium crosslinking agent is pH sensitive. Within a certain pH range, the Cr 3+ at the center of the crosslinking agent can be dissociated. The raw material composition is as follows: 3 parts of chromium lactate, 2 parts of chromium nicotinate, 1 part of azobisisobutylamidine hydrochloride, 1 part of tetramethylethylenediamine, and 10 parts of distilled water.

[0033] (1-1) Add 3 parts of chromium lactate and 2 parts of chromium nicotinate to distilled water and stir evenly to obtain slurry I;

[0034] (1-2) Adding azobisisobutylamidine hydrochloride and tetramethylethylenediamine to slurry I, stirring and mixing uniformly, and heating in a 50°C water bath for 4 hours to obtain a crosslinking agent;

[0035] The inventors mixed the cross-linking agent with distilled water. Initially, the solution was basically colorless. After gradually adjusting the pH to a weakly acidic environment, Cr 3+ in the cross-linking agent dissociated to form a purple solution.

[0036] Example 2

[0037] The preparation steps of the stabilizer are as follows: dissolve 2 parts of citric acid, 1 part of disodium ethylenediaminetetraacetate, and 1 part of sodium persulfate in 10 parts of distilled water, stir evenly, and heat at 70° C. for 4 hours to obtain the stabilizer.

[0038] Example 3

[0039] The delayed gelling plugging gel for cementing is composed of the following raw materials in parts by weight: 2 parts of HPAM, 3 parts of CPAM, 1 part of cross-linking agent, 1 part of stabilizer, and 6 parts of distilled water; the cross-linking agent is the cross-linking agent obtained in Example 1, and the stabilizer is the temperature agent obtained in Example 2;

[0040] The specific preparation steps are:

[0041] (2-1) Weigh all the raw materials in proportion and set aside;

[0042] (2-2) Mix 2 parts of HPAM and 3 parts of CPAM, add 6 parts of distilled water, and stir evenly at a stirring speed of 550 r·min -1 to obtain slurry II;

[0043] (2-3) Mix 1 part of stabilizer with slurry II and stir evenly at a stirring speed of 550 r·min -1 to obtain slurry III;

[0044] (2-4) Slurry III was mixed with 1 part of a cross-linking agent and stirred evenly at a stirring speed of 550 r·min -1 to obtain gel F1.

[0045] Example 4

[0046] The delayed gelling plugging gel for cementing is composed of the following raw materials in parts by weight: 3 parts of HPAM, 3 parts of CPAM, 1 part of crosslinking agent, 1 part of stabilizer, and 6 parts of distilled water; the crosslinking agent is the crosslinking agent obtained in Example 1, and the stabilizer is the temperature agent obtained in Example 2;

[0047] The specific preparation steps are:

[0048] (2-1) Weigh all the raw materials in proportion and set aside;

[0049] (2-2) 3 parts of HPAM and 3 parts of CPAM were mixed evenly, 6 parts of distilled water were added, and the mixture was stirred evenly at a stirring speed of 550 r·min -1 to obtain slurry II;

[0050] (2-3) Mix 1 part of stabilizer with slurry II and stir evenly at a stirring speed of 550 r·min -1 to obtain slurry III;

[0051] (2-4) Slurry III was mixed with 1 part of type A organic chromium crosslinker and stirred evenly at a stirring speed of 550 r·min -1 to obtain gel F2.

[0052] Example 5

[0053] The delayed gelling plugging gel for cementing is composed of the following raw materials in parts by weight: 2 parts of HPAM, 4 parts of CPAM, 1 part of a crosslinking agent, 1 part of a stabilizer, and 6 parts of distilled water; the crosslinking agent is the crosslinking agent obtained in Example 1, and the stabilizer is the temperature agent obtained in Example 2;

[0054] The specific preparation steps are:

[0055] (4-1) Weigh all the raw materials in proportion and set aside;

[0056] (4-2) Mix 2 parts of HPAM and 4 parts of CPAM, add 6 parts of distilled water, and stir evenly at a stirring speed of 550 r·min -1 to obtain slurry II;

[0057] (4-3) Mix 1 part of stabilizer with slurry II and stir evenly at a stirring speed of 550 r·min -1 to obtain slurry III;

[0058] (4-4) Slurry III was mixed with 1 part of type A organic chromium crosslinker and stirred evenly at a stirring speed of 550 r·min -1 to obtain gel F3.

[0059] Comparative Example 1

[0060] The delayed gelling plugging gel for cementing is composed of the following raw materials in parts by weight: 2 parts of HPAM, 4 parts of CPAM, 1 part of a cross-linking agent, 1 part of a stabilizer, and 6 parts of distilled water; the stabilizer is EDTA-2NA; the cross-linking agent is the cross-linking agent obtained in Example 1;

[0061] The specific preparation steps are:

[0062] (4-1) Weigh all the raw materials in proportion and set aside;

[0063] (4-2) Mix 2 parts of HPAM and 4 parts of CPAM, add 6 parts of distilled water, and stir evenly at a stirring speed of 550 r·min -1 to obtain slurry II;

[0064] (4-3) Mix 1 part of stabilizer with slurry II and stir evenly at a stirring speed of 550 r·min -1 to obtain slurry III;

[0065] (4-4) Slurry III was mixed with a cross-linking agent and stirred evenly at a stirring speed of 550 r·min -1 to obtain product F4;

[0066] EDTA is a commonly used chelating agent. Using EDTA-based substances (such as EDTA, EDTA-2Na, and EDTA-4Na) alone as a stabilizer will cause the Cr 3+ in the crosslinker to be chelated by EDTA, forming new compounds. This prevents the subsequent hydroxyl bridge reaction and prevents the Cr 3+ from being dissociated and reacting with acrylamide-based substances to form a gel. The chemical reaction formula for EDTA chelating Cr 3+ is as follows:

[0067] .

[0068] Comparative Example 2

[0069] The delayed gelling plugging gel for cementing is composed of the following raw materials, in parts by weight: 2 parts HPAM, 4 parts CPAM, 1 part crosslinking agent, 1 part stabilizer, and 6 parts distilled water; the crosslinking agent is single chromium lactate. The stabilizer is the stabilizer obtained in Example 2;

[0070] (5-1) Weigh all the raw materials in proportion and set aside;

[0071] (5-2) Mix 2 parts of HPAM and 4 parts of CPAM, add 6 parts of distilled water, and stir evenly at a stirring speed of 550 r·min -1 to obtain slurry II;

[0072] (5-3) Mix 1 part of stabilizer with slurry II and stir evenly at a stirring speed of 550 r·min -1 to obtain slurry III;

[0073] (5-4) Slurry III was mixed with 1 part of chromium lactate and stirred evenly at a stirring speed of 550 r·min -1 to obtain product F5;

[0074] Because chromium lactate alone has extremely low solubility and is practically insoluble in water, it is difficult to form a usable crosslinking agent. Product F5, a gel formed using chromium lactate as a crosslinker, exhibits high viscosity and low strength. It is essentially a high-viscosity polymer formed by heating acrylamide monomers. Chromium lactate alone does not crosslink, and the resulting gel cannot be used normally.

[0075] Experimental Example 1

[0076] To simulate cementing formation conditions, the temperature was set at 80°C. The delay times of gels F1, F2, and F3 at different pH values ​​(pH = 4-8) were examined. The experimental results are shown in Figures 1-3. These results demonstrate that the delayed gelation effect of these gels is best under weakly acidic conditions. By controlling the pH environment to control the dissociation of Cr 3+ in the crosslinker, it was found that in weakly acidic environments, Cr 3+ dissociation is slower, resulting in better delayed gelation.

[0077] Experimental Example 2

[0078] Compressive strength is one of the most important properties of cement paste. To test whether the addition of the gel to the pre-pad system affects subsequent cementing work, the present invention uses a columnar core for compressive strength testing. The core column has a diameter of 25 mm and a height of 50 mm. The prepared cement slurry is introduced into each columnar core barrel, the end caps are tightened and sealed, and the core barrel is placed in a 50°C constant temperature curing box for one day. After demolding, the compressive strength of the cement blocks with and without the gel are tested. The test results are shown in Table 1:

[0079] .

[0080] As can be seen from Table 1 above, the compressive strength of the cement block is slightly increased after the addition of the gel, and it is preliminarily judged that the gel has a positive effect on the cementing work.

[0081] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. Delayed gelling plugging gel for cementing, characterized by: The invention comprises 2-3 parts of anionic polyacrylamide, 3-4 parts of cationic acrylamide, 1 part of a stabilizer, 1 part of a crosslinking agent, and 6 parts of distilled water; the stabilizer is obtained by reacting citric acid and disodium ethylenediaminetetraacetate in the presence of an initiator; the crosslinking agent is obtained by reacting chromium lactate and chromium nicotinate in the presence of azobisisobutyramidine hydrochloride and tetramethylethylenediamine; The initiator is sodium persulfate; By mass ratio, citric acid: disodium EDTA: initiator = 2:1:1; Chromium lactate: chromium nicotinate: azobisisobutylamidine hydrochloride: tetramethylethylenediamine = 3:2:1:

1.

2. The method for preparing the delayed gelling plugging gel for cementing according to claim 1, characterized in that: The specific steps are: (2-1) Dissolve anionic polyacrylamide in distilled water and stir evenly, then slowly add cationic acrylamide and stir evenly to obtain slurry II; (2-2) Slowly add stabilizer and cross-linking agent to slurry II and stir evenly to obtain.

3. The method for preparing the delayed gelling plugging gel for cementing according to claim 2, characterized in that: The preparation method of the stabilizer is as follows: dissolving citric acid, disodium ethylenediaminetetraacetic acid and an initiator in water, stirring evenly, and heating at 70° C. for 4 hours.

4. The method for preparing the delayed gelling plugging gel for cementing according to claim 2, characterized in that: The preparation method of the cross-linking agent is: (1-1) Chromium lactate and chromium nicotinate are added to distilled water and stirred uniformly to obtain slurry I; (1-2) Azobisisobutylamidine hydrochloride and tetramethylethylenediamine were added to slurry I, stirred and mixed uniformly, and heated at 50°C for 4 hours to obtain a crosslinking agent.

5. Use of the delayed gelling plugging gel for cementing according to claim 1 in cementing work.

6. Use of the delayed gelling plugging gel for cementing according to claim 5 in cementing work, characterized in that: The delayed gelling plugging gel for cementing is used in the pre-fluid system of cementing work.

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