Degradation control agent, refracturing controllable degradation plugging agent and preparation method

Abstract

The invention discloses a degradation control agent, a refracturing controllable degradation plugging agent and a preparation method. The degradation control agent is an inclusion compound of cyclodextrin and benzoyl peroxide; the controllable degradation plugging agent for refracturing comprises the degradation control agent; the cyclodextrin molecule has an annular cavity structure, an internal cavity is non-polar, and benzoyl peroxide serving as an organic gel breaker can enter the cavity to form an inclusion compound; when a liquid rubber plug formed by the refracturing controllable degradation plugging agent is in a release medium, benzoyl peroxide molecules are released, inclusion balance is destroyed, deinclusion is carried out to carry out gel breaking degradation, and then the purpose of controllable degradation of the refracturing plugging agent is achieved by controlling the dosage of the degradation control agent.

Description

Technical Field

[0001] The present invention relates to the technical field of oilfield chemistry, and in particular to a plugging agent for repeated fracturing and a preparation method thereof. Background Art

[0002] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0003] As an effective measure to increase production, fracturing technology is widely used in oil field production. However, as the development progresses, the water content of the oil field gradually increases, and the artificial fractures created by fracturing are more likely to become water channels, seriously affecting the effect and benefits of development. In recent years, many researchers have tackled the problem of repeated fracturing technology, temporarily blocking high-permeability areas, transforming low-permeability areas, and improving the development potential of reservoirs.

[0004] Temporary plugging agents are key agents in repeated fracturing technology. They form a dense and uniform temporary plugging layer in old fractures and high-permeability matrix, prompting the fracturing fluid to turn to open new fractures and tap the potential of remaining oil in low-permeability areas. At the same time, the plugging agent can be degraded when necessary without affecting the production of old fractures.

[0005] There are many patent documents reporting on temporary plugging agents for repeated fracturing. For example, Chinese patent CN112745819A discloses a degradable temporary plugging agent and its preparation method, which has the characteristics of strong plugging ability, rapid unblocking, and no environmental pollution. However, the temporary plugging agent is a granular temporary plugging agent, and the particle size needs to be considered during construction. At the same time, since it is a rigid material of a non-continuous phase, it is difficult to achieve uniform bridging in cracks with larger openings, which easily leads to filtration loss of fracturing fluid.

[0006] For example, Chinese patent CN109777387B discloses a temporary plugging agent for repeated fracturing and a preparation method thereof, which has the characteristics of high-strength plugging and dissolution in the formation. However, the temporary plugging agent dissolves in the reservoir environment by controlling the molecular weight, and the dissolution performance is unstable.

[0007] Another example: Chinese patent CN102344788B discloses a temporary plugging agent for horizontal well staged fracturing with controllable gel breaking and a preparation method thereof, which has the characteristic of withstanding a pressure difference of more than 30 MPa. However, the temporary plugging agent uses a capsule micro-breaker to achieve gel breaking, and the capsule breaker has the problems of uneven wrapping and unstable gel breaking performance.

[0008] Although there are many types of temporary plugging agents for repeated fracturing currently in use, few of them have both high plugging strength and controllable degradation. Therefore, it is of great significance to develop a controllable degradable plugging agent suitable for repeated fracturing to plug old fractures and press new fractures.

[0009] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may contain information that does not constitute prior art. Summary of the invention

[0010] In view of this, the present disclosure provides a degradation control agent and a re-fracturing controllable degradation plugging agent to solve the problem that the degradation performance of the existing re-fracturing plugging agent cannot be stably controlled.

[0011] In addition, the present disclosure also provides a preparation method of the degradation control agent and the repeated fracturing controllable degradation plugging agent.

[0012] In the first aspect, the degradation control agent is:

[0013] Inclusion complex of cyclodextrin and benzoyl peroxide.

[0014] In the present disclosure and possible embodiments, the cyclodextrin is allyl-β-cyclodextrin.

[0015] In a second aspect, the method for preparing the degradation control agent comprises:

[0016] The saturated aqueous solution method is adopted to add excess benzoyl peroxide into a saturated aqueous solution of cyclodextrin to form an inclusion compound, and the inclusion compound is precipitated and washed to obtain the degradation control agent.

[0017] In the present disclosure and possible embodiments, the molar ratio of the allyl-β-cyclodextrin to the benzamide peroxide is 1:10.

[0018] In a third aspect, the repeated fracturing controllably degradable plugging agent comprises:

[0019] The degradation controlling agent described in the first aspect.

[0020] In the present disclosure and possible embodiments, the composition also includes:

[0021] Enhancer;

[0022] The reinforcing agent is one or two of organic bentonite, carboxymethyl starch and polyester fiber.

[0023] In the present disclosure and possible embodiments, the composition also includes:

[0024] Acrylic acid, acrylamide, crosslinking agent and initiator.

[0025] In the present disclosure and possible embodiments, the cross-linking agent is N,N'-methylenebisacrylamide;

[0026] The initiator is selected from ammonium persulfate, potassium persulfate and cerium ammonium nitrate.

[0027] In the present disclosure and possible embodiments, the contents of the components in the composition are calculated by mass percentage: acrylic acid 1% to 3%, acrylamide 7% to 10%, cross-linking agent 0.05% to 0.5%, initiator 0.05% to 0.2%, degradation controller 0.05% to 0.15%, enhancer 0.05% to 0.2%, and the balance is water.

[0028] In a fourth aspect, the method for preparing the repeated fracturing controllably degradable plugging agent comprises:

[0029] Dissolving the acrylic acid and the acrylamide in water, adjusting the pH of the system to between 6 and 7, adding the degradation control agent and the enhancer to the system and mixing them evenly to form a main agent;

[0030] The main agent, the cross-linking agent and the initiator are mixed evenly to obtain the controllable degradation plugging agent.

[0031] When in use, the main agent, the cross-linking agent and the initiator are mixed evenly on site to obtain the controllable degradation plugging agent and directly injected.

[0032] The present disclosure has the following beneficial effects:

[0033] The degradation control agent of the present invention is conceived to apply cyclodextrin, a starch-based material with good biocompatibility and biodegradability, to the field of oilfield chemistry from the perspective of using polymer materials as drug controlled release system carriers in the field of biomedicine. The present invention specifically uses a cyclodextrin and benzoyl peroxide inclusion compound as a degradation control agent, and adds the degradation control agent to a repeated fracturing plugging agent.

[0034] During repeated fracturing, the mixed solution containing acrylic acid, acrylamide, crosslinking agent, initiator, cyclodextrin and degradation control agent of the present disclosure injected into the formation will preferentially enter the old fractures or the high permeability matrix. At a certain formation temperature, the initiator causes a polymerization reaction to form a liquid plug containing the inclusion compound of cyclodextrin and benzoyl peroxide, forming a dense and uniform temporary plugging layer at the high permeability part, so that the injected fracturing fluid is diverted, new fractures are opened, and the residual oil in the low permeability area is tapped.

[0035] After the new fracture is opened, in order not to affect the production of the old fracture, the controllable degradation of the plugging agent needs to be achieved. The degradation process of the disclosed repeated fracturing controllable degradable liquid rubber plug plugging agent system is composed of decomposition and oxidation reaction. The cyclodextrin molecule has an annular cavity structure, and the internal cavity is non-polar. Benzoyl peroxide as an organic breaker can enter the cavity to form an inclusion complex, and cyclodextrin isolates benzoyl peroxide (organic breaker) and the liquid rubber plug polymer.

[0036] On site, the liquid plugging agent system injected into the ground forms a liquid plug at the old cracks or high permeability base, and the inclusion complex of cyclodextrin and benzoyl peroxide is in equilibrium with the entire liquid plug mixture.

[0037] As the production progresses, the liquid rubber plug is in the crude oil, and the crude oil serves as the release medium of the liquid rubber plug. When the liquid rubber plug is in the release medium, the benzoyl peroxide molecules as the organic breaker are released, and the inclusion balance is destroyed. At this time, the de-inclusion process is carried out. Specifically, the oil molecules displace the benzoyl peroxide included in the annular cavity of the cyclodextrin in the liquid rubber plug, and the continuously released benzoyl peroxide releases oxygen free radicals after being heated and decomposed by underground temperature. The oxygen free radicals can attack the chain links of the polymer, destroy the structure of the liquid rubber plug, and play a role in breaking and degrading, thereby restoring the conductivity of the old seam and achieving the purpose of controllable degradation of the repeated fracturing plugging agent.

[0038] The purpose of controlling the gel breaking time can be achieved by controlling the amount of the inclusion complex of cyclodextrin and benzoyl peroxide added to the liquid rubber plug. Obviously, when the inclusion complex content is higher, more breaker molecules are released at the same time, and the gel breaking time is faster. DETAILED DESCRIPTION

[0039] The present disclosure is described below based on embodiments, but it is worth noting that the present disclosure is not limited to these embodiments. In the detailed description of the present disclosure below, some specific details are described in detail. However, for the parts that are not described in detail, those skilled in the art can also fully understand the present disclosure.

[0040] At the same time, unless the context clearly requires otherwise, the words "include", "comprises" and similar words throughout the specification and claims should be interpreted as inclusive rather than exclusive or exhaustive; that is, the meaning is "including but not limited to".

[0041] In the following embodiments of the present disclosure, the molecular formula of acrylic acid is: C3H4O2; the molecular formula of acrylamide is: C3H5NO; the molecular formula of N,N'-methylenebisacrylamide in the cross-linking agent is:

[0042] C7H 10 N2O2; the molecular formulas of ammonium persulfate, potassium persulfate and cerium ammonium nitrate in the initiator are: (NH4)2S2O8, K2S2O8, Ce(NH4)2(NO3)6; the molecular formulas of allyl-β-cyclodextrin and benzoyl peroxide in the degradation control agent are: C 42 H 70 O 35 (C3H4) n , C 14 H 10O4; the molecular formula of organic bentonite in the enhancer is: Al2O3·4(SiO2)·H2O, and the molecular formula of carboxymethyl starch is: [C6H7O2(OH)2OCH2COONa] n , The molecular formula of polyester fiber is: [(CH2)4OOCC6H4COO] n .

[0043] The raw materials used in the following examples of the present disclosure were purchased from the following manufacturers:

[0044] Acrylic acid and acrylamide were purchased from Dongying Jiangyuan Chemical Co., Ltd.;

[0045] N,N'-Methylenebisacrylamide was purchased from Daqing Ruidefeng Materials Trading Co., Ltd.;

[0046] Ammonium persulfate, potassium persulfate, and cerium ammonium nitrate were purchased from Daqing Jinpenghui Technology Co., Ltd.;

[0047] Benzoyl peroxide was purchased from Wuxi Jingke Chemical Co., Ltd.;

[0048] Allyl-β-cyclodextrin was purchased from Xi’an Qiyue Biotechnology Co., Ltd.;

[0049] Organic bentonite was purchased from Jianping County Wanxing Bentonite Co., Ltd.;

[0050] Carboxymethyl starch was purchased from Linyi Lvsen Chemical Co., Ltd. (specification 20);

[0051] Polyester fibers were purchased from Tai'an Anfeng New Material Technology Co., Ltd. (fiber length specifications were 3 mm and / or 6 mm).

[0052] The present invention discloses a method for preparing a re-fracture controllably degradable plugging agent and a re-fracture controllably degradable liquid rubber plug according to the following embodiments, which adopts the following steps:

[0053] (1) first dissolving allyl-β-cyclodextrin in distilled water, heating to completely dissolve it, then dissolving benzoyl peroxide in anhydrous ethanol, wherein the initial molar ratio of allyl-β-cyclodextrin to benzamide peroxide is 1:10; adding the benzoyl peroxide solution to the cooled allyl-β-cyclodextrin solution, stirring at room temperature for 3 to 5 hours, repeatedly washing the reactants with distilled water and anhydrous ethanol to remove unreacted allyl-β-cyclodextrin and benzoyl peroxide, and vacuum drying to obtain an allyl-β-cyclodextrin and benzoyl peroxide inclusion complex degradation control agent;

[0054] (2) dissolving acrylic acid and acrylamide in water according to the designed ratio, adjusting the pH to between 6 and 7 with NaOH solution, adding a cross-linking agent, a degradation control agent, an enhancer, and an initiator in sequence, mixing and stirring evenly, and preparing a re-fracturing controllable degradation plugging agent;

[0055] (3) The repeated fracturing controllable degradation plugging agent is placed in a 45°C oven for cross-linking reaction to obtain a repeated fracturing controllable degradation liquid rubber plug.

[0056] Example 1

[0057] (1) Dissolve 1 g of allyl-β-cyclodextrin in 99 g of distilled water, heat to 50° C. to dissolve it completely, then dissolve 2 g of benzoyl peroxide in 98 g of anhydrous ethanol, add the 2% benzoyl peroxide solution to the cooled 1% allyl-β-cyclodextrin solution, stir at room temperature for 4 h, wash the reactants repeatedly with distilled water and anhydrous ethanol, and vacuum dry to obtain an allyl-β-cyclodextrin and benzoyl peroxide inclusion complex degradation control agent.

[0058] (2) 1 g of acrylic acid and 9 g of acrylamide were dissolved in 89.5 g of water, the pH was adjusted to between 6 and 7 with a NaOH solution, 0.1 g of N,N'-methylenebisacrylamide, 0.05 g of allyl-β-cyclodextrin and benzoyl peroxide inclusion complex, 0.25 g of organic bentonite, and 0.1 g of ammonium persulfate were added in sequence, and the mixture was mixed and stirred to obtain a re-fracturing controllable degradation plugging agent;

[0059] (3) The repeated fracturing controllable degradation plugging agent is placed in a 45°C oven for cross-linking reaction to obtain a repeated fracturing controllable degradation liquid rubber plug.

[0060] Example 2

[0061] (1) The preparation process of the inclusion complex of allyl-β-cyclodextrin and benzoyl peroxide is the same as that in Example 1.

[0062] (2) 0.5 g of acrylic acid and 9.5 g of acrylamide were dissolved in 89.25 g of water, the pH was adjusted to between 6 and 7 with a NaOH solution, 0.2 g of N,N'-methylenebisacrylamide, 0.1 g of allyl-β-cyclodextrin and benzoyl peroxide inclusion complex, 0.1 g of polyester fiber, and 0.15 g of potassium persulfate were added in sequence, and the mixture was mixed and stirred to obtain a re-fracturing controllable degradation plugging agent;

[0063] (3) The repeated fracturing controllable degradation plugging agent is placed in a 50° C. oven for cross-linking reaction to obtain a repeated fracturing controllable degradation liquid rubber plug.

[0064] Example 3

[0065] (1) The preparation process of the inclusion complex of allyl-β-cyclodextrin and benzoyl peroxide is the same as that in Example 1.

[0066] (2) 2 g of acrylic acid and 10 g of acrylamide were dissolved in 87.15 g of water, the pH was adjusted to between 6 and 7 with a NaOH solution, 0.4 g of N,N'-methylenebisacrylamide, 0.15 g of allyl-β-cyclodextrin and benzoyl peroxide inclusion complex, 0.1 g of carboxymethyl starch, and 0.2 g of ammonium persulfate were added in sequence, and the mixture was mixed and stirred to obtain a re-fracturing controllable degradation plugging agent;

[0067] (3) The re-fracture controllable degradation plugging agent is placed in a 60° C. oven for cross-linking reaction to obtain a re-fracture controllable degradation liquid rubber plug.

[0068] Comparative Example 1

[0069] (1) The preparation process of the inclusion complex of allyl-β-cyclodextrin and benzoyl peroxide is the same as that in Example 1.

[0070] (2) Dissolve 1 g of acrylic acid and 9 g of acrylamide in 89.75 g of water, adjust the pH to 6-7 with NaOH solution, add 0.1 g of N,N'-methylenebisacrylamide, 0.05 g of allyl-β-cyclodextrin and benzoyl peroxide inclusion complex, and 0.1 g of ammonium persulfate in sequence, mix and stir evenly, and place in an oven at 45°C for cross-linking reaction to prepare a sample of Comparative Example 1.

[0071] Comparative Example 2

[0072] 0.5 g of acrylic acid and 9.5 g of acrylamide were dissolved in 89.25 g of water, and the pH was adjusted to between 6 and 7 with NaOH solution. 0.2 g of N,N'-methylenebisacrylamide, 0.1 g of benzoyl peroxide, 0.1 g of polyester fiber, and 0.15 g of potassium persulfate were added in sequence. The mixture was stirred evenly and placed in an oven at 50°C for cross-linking reaction to prepare a comparative example 2 sample.

[0073] Comparative Example 3

[0074] 2 g of acrylic acid and 10 g of acrylamide were dissolved in 87 g of water, and the pH was adjusted to 6-7 with NaOH solution. 0.4 g of N, N'-methylenebisacrylamide, 0.2 g of allyl-β-cyclodextrin, 0.1 g of benzoyl peroxide, 0.1 g of carboxymethyl starch, and 0.2 g of ammonium persulfate were added in sequence. The mixture was mixed and stirred evenly, and placed in an oven at 60°C for cross-linking reaction to prepare a comparative example 3 sample.

[0075] Test example

[0076] The repeated fracturing controllably degradable liquid rubber plugs prepared in the above Experimental Examples 1 to 3 and Comparative Examples 1 to 3 were used to carry out an indoor core plugging experiment.

[0077] Experimental samples: the repeatedly-fractured controllably degradable liquid rubber plugs prepared in Examples 1 to 3 and Comparative Examples 1 to 3.

[0078] (1) Determination of core plugging pressure: At one end of the core containing the controlled degradable liquid plug for repeated fracturing, pressure is applied to the liquid plug in the core using liquid as the pressure transmission medium. When the pressure reaches a certain value and the shear stress on the liquid plug is greater than its resistance in the core, the liquid plug begins to flow. The pressure applied when the first drop of liquid flows out from the other end of the core is defined as the breakthrough pressure, i.e., the plugging pressure of the controlled degradable liquid plug for repeated fracturing on the core.

[0079] (2) Determination of plugging rate: The calculation formula of plugging rate is as follows:

[0080]

[0081] Where: K 前 ——Core permeability before plugging, mD;

[0082] K 后 ——Core permeability after plugging, mD;

[0083] E——Plugging rate, %.

[0084] (3) Breaking time: The time of injecting petroleum ether (simulated release medium) is t0, and the time when the rubber plug completely turns into liquid is t1. The breaking time is the stage when the breaker released by the inclusion complex in the release medium completely destroys the structure of the rubber plug, t1-t0.

[0085] (4) Determination of viscosity after degradation: At a certain temperature, petroleum ether (simulated release medium) was injected to allow the liquid rubber plug to gradually degrade. The viscosity of the liquid rubber plug after degradation was measured using a Brookfield rotational viscometer.

[0086] The above measurement results are shown in Table 1.

[0087] Table 1 Test results of various indicators of controlled degradation liquid rubber plugs for repeated fracturing

[0088]

[0089] It can be seen from Table 1 that the breaking time of the liquid plugs in Examples 1 to 3 is adjusted by the content of the inclusion compound. The inclusion compound content in Example 1 is relatively small, and the amount of the breaker released at the same time in the release medium is relatively small, resulting in a prolonged breaking time.

[0090] Compared with Examples 1 to 3, the core plugging strength of Comparative Example 1 is low and the plugging rate is small, indicating that no enhancer is used, resulting in low strength of the formed liquid plug, which cannot meet the requirements of repeated fracturing technology. However, due to the low strength of the liquid plug, the breaking time is relatively fast.

[0091] Compared with Examples 1 to 3, the strength of the liquid plug in Comparative Example 2 is significantly reduced, indicating that the system does not use allyl-β-cyclodextrin to encapsulate benzoyl peroxide, so that the organic oxidant directly contacts the liquid plug polymer, destroying the plug strength, causing the system to be degraded prematurely, and the core plugging pressure is greatly reduced.

[0092] Compared with Examples 1 to 3, the core plugging strength and plugging rate of Comparative Example 3 are both reduced, indicating that if the allyl-β-cyclodextrin and benzoyl peroxide inclusion complex is not prefabricated and is directly prepared in the liquid plug system, only a small amount of benzoyl peroxide can enter the allyl-β-cyclodextrin cavity, and most of the benzoyl peroxide is still free in the plug system, resulting in oxidative degradation of the system and reduced strength.

[0093] Comprehensive comparison shows that the plugging pressure of the controllable degradation plugging agent for repeated fracturing provided by the present invention after gelation is greater than 25 MPa, the plugging rate is more than 99%, the viscosity after degradation is less than 50 mPa·s, and the degradation liquid is conducive to discharge without affecting subsequent production.

[0094] Because the plugging pressure of the controllably degradable liquid rubber plug plugging agent for repeated fracturing provided by the present invention is above 25 MPa after gelling and the viscosity after degradation is less than 50 mPa·s, it is suitable for reservoirs at 45°C to 60°C and has certain development potential in temporary plugging during repeated fracturing.

[0095] The above-described embodiments are only embodiments of the present disclosure, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the present disclosure. It should be noted that, for a person of ordinary skill in the art, without departing from the concept of the present disclosure, several variations, equivalent substitutions, improvements, etc. may be made, all of which fall within the scope of protection of the present disclosure. Therefore, the scope of protection of the present disclosure shall be subject to the attached claims.

Claims

1. A degradation control agent, characterized in that: The control agent is: Inclusion complex of cyclodextrin and benzoyl peroxide.

2. The degradation control agent according to claim 1, characterized in that: The cyclodextrin is allyl-β-cyclodextrin.

3. The method for preparing the degradation control agent according to claim 1 or 2, characterized in that: include: The saturated aqueous solution method is adopted to add excess benzoyl peroxide into a saturated aqueous solution of cyclodextrin to form an inclusion compound, and the inclusion compound is precipitated and washed to obtain the degradation control agent.

4. The method for preparing the degradation control agent according to claim 3, characterized in that: The molar ratio of the allyl-β-cyclodextrin to the benzamide peroxide is 1:

10.

5. A controllable degradation plugging agent for repeated fracturing, characterized in that: Its composition includes: The degradation controlling agent according to claim 1 or 2.

6. The repeated fracturing controllably degradable plugging agent according to claim 5, characterized in that: Its composition also includes: Enhancer; The reinforcing agent is one or two of organic bentonite, carboxymethyl starch and polyester fiber.

7. The repeated fracturing controllably degradable plugging agent according to claim 6, characterized in that: Its composition also includes: Acrylic acid, acrylamide, crosslinking agent and initiator.

8. The re-fracturing controllably degradable plugging agent according to claim 7, characterized in that: The cross-linking agent is N,N'-methylenebisacrylamide; The initiator is selected from ammonium persulfate, potassium persulfate and cerium ammonium nitrate.

9. The re-fracturing controllably degradable plugging agent according to claim 8, characterized in that: Calculated by mass percentage, the contents of the components in the composition are: acrylic acid 1% to 3%, acrylamide 7% to 10%, cross-linking agent 0.05% to 0.5%, initiator 0.05% to 0.2%, degradation control agent 0.05% to 0.15%, enhancer 0.05% to 0.2%, and the balance is water.

10. The method for preparing the repeated fracturing controllably degradable plugging agent according to any one of claims 5 to 9, characterized in that: include: Dissolving the acrylic acid and the acrylamide in water, adjusting the pH of the system to between 6 and 7, adding the degradation control agent and the enhancer to the system and mixing them evenly to form a main agent; The main agent, the cross-linking agent and the initiator are uniformly mixed on site to obtain the controllable degradation plugging agent and directly injected.

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