A kind of temperature-resistant thixotropic agent and its preparation method and application

Abstract

The present invention relates to the technical field of oil and gas well development, and specifically to a heat-resistant thixotropic agent, a preparation method thereof, and an application thereof. The present invention adopts acrylic acid and N-vinyl pyrrolidone to graft-modify diutan gum to obtain modified diutan gum; the modified diutan gum is compounded with magnesium aluminum silicate to prepare a heat-resistant thixotropic agent. The heat-resistant thixotropic agent prepared by the present invention can significantly improve the thixotropic properties of magnesium oxychloride cement in the high-temperature environment of oil and gas wells, effectively improve the rheological properties of cement slurry, enhance its retention capacity in cracks, and improve the sealing stability, etc., showing broad application prospects in oil and gas well engineering, and providing strong support for solving the problem of well leakage in fractured formations during oil and gas well drilling.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas well development, and in particular to a temperature-resistant thixotropic agent and a preparation method and application thereof. Background Art

[0002] When drilling oil and gas wells, the problem of well leakage is becoming increasingly prominent, especially in fractured formations. Due to the large number of natural and induced fractures, large leakage channels and fast leakage rates, plugging operations are difficult. Traditional plugging materials, such as walnut shells, rubber and other bridge plug materials and conventional plugging cement slurry, all have obvious shortcomings. Bridge plug materials are difficult to adapt to the fracture opening, have low plugging efficiency, and are prone to damage to the reservoir; although conventional plugging cement slurry has high pressure bearing capacity, it is very harmful to the reservoir and has poor acid solubility, and the reservoir flow capacity is slow to recover in the later stage.

[0003] Magnesium oxychloride cement has certain advantages in reservoir plugging due to its fast solidification and good acid solubility. However, when plugging fractured reservoirs, it is necessary to solve the problem of magnesium oxychloride cement being retained in the fractures, so magnesium oxychloride cement needs to have strong thixotropy. In addition, as oil and gas exploration and development expands to deeper layers, high temperature has also become one of the main problems faced by drilling plugging. At present, there are few studies on thixotropic agents suitable for high-temperature oil and gas well conditions, and most of them are only applicable to silicate cements, and there are very few studies on thixotropic agents suitable for magnesium oxychloride cement. Summary of the invention

[0004] In view of the above problems, the present invention proposes a temperature-resistant thixotropic agent and a preparation method and application thereof, wherein the thixotropic agent can significantly improve the thixotropic properties of magnesium oxychloride cement in a high-temperature environment of oil and gas wells.

[0005] The temperature-resistant thixotropic agent of the invention is prepared by compounding modified diutan gum and magnesium aluminum silicate; the modified diutan gum is prepared by grafting and modifying diutan gum with acrylic acid and N-vinyl pyrrolidone.

[0006] The specific steps are:

[0007] (1) Mix diutanol and deionized water and stir until diutanol is completely dissolved to obtain solution I.

[0008] In this step, high-speed stirring is performed at a rotation speed of 1000 rpm to 2000 rpm until the diutan gum is completely dissolved to form a uniform solution system, thereby ensuring that the starting materials for subsequent reactions are evenly dispersed and providing good basic conditions for the grafting modification reaction.

[0009] (2) Neutralize acrylic acid to a neutralization degree of 80-85%, add N-vinyl pyrrolidone and an initiator thereto, and stir to dissolve to obtain a solution II.

[0010] In this step, 17-19 parts of acrylic acid are neutralized to a neutralization degree of 80-85% using a sodium hydroxide solution having a concentration of 5 mol / L. The reaction conditions must be strictly controlled during the neutralization process to ensure the accuracy and stability of the neutralization reaction. After the reaction solution is cooled to room temperature, 1-3 parts of N-vinyl pyrrolidone and 0.10-0.12 parts of an initiator are added thereto, wherein the initiator is one or more of potassium persulfate, ammonium persulfate, and sodium persulfate, and the solution II is obtained after sufficient stirring and dissolution.

[0011] (3) Add solution II dropwise to solution I. After the addition is complete, raise the temperature to 65-75°C and stir to react. After the reaction is complete, perform post-treatment to obtain modified dimethoate powder.

[0012] In this step, the dripping method is used to control the reaction rate, so that the reaction proceeds more smoothly and avoids the occurrence of side reactions or uneven product performance due to excessively violent reactions. Subsequently, the system is heated to 65-75°C, maintained at this temperature and stirred for 3 hours. During this process, a graft polymerization reaction occurs in the system to generate a modified polymer with a specific structure and performance, thereby obtaining a crude product.

[0013] After the reaction is completed, the crude product is washed repeatedly with distilled water and ethanol solution for 3-5 times, and distilled water is used to remove water-soluble impurities, and ethanol solution is used to remove organic impurities, so as to thoroughly purify the product and ensure the purity and performance stability of the product. After that, it is dried to constant weight at 50-60°C to remove moisture, and then the dried sample is crushed into powder. It should be sieved through a 100-300 mesh standard sieve to obtain a modified dimethoate powder with a particle size in the range of 48μm~150μm. The appropriate particle size helps it to be better mixed with magnesium aluminum silicate in the subsequent composite process to play a synergistic role.

[0014] (4) The modified dimethoate powder is uniformly mixed with magnesium aluminum silicate to obtain a temperature-resistant thixotropic agent.

[0015] In this step, the mass ratio of modified dimethoate powder to magnesium aluminum silicate is 1: (1-2). The mixing process adopts a sieving mixing method, specifically, the two are placed in a 100-mesh sieving device, and the sieve is reciprocated by a mechanical device. The sieving operation is continued for 5-8 times to ensure that the modified dimethoate powder and magnesium aluminum silicate can be evenly and fully mixed to obtain a temperature-resistant thixotropic agent.

[0016] In the present invention, acrylic acid and N-vinyl pyrrolidone are used to graft and modify diutan gum to improve the heat and salt resistance of diutan gum. The carboxylic acid group of acrylic acid interacts with the components of magnesium oxychloride cement to improve compatibility and stability, form hydrogen bonds and cross-linked structures, enhance heat resistance and colloid strength, and prevent high-temperature degradation of cement slurry. N-vinyl pyrrolidone has good thermal stability, and its five-membered ring structure can improve the heat and salt resistance of the grafted copolymer, and its polar group can construct a complex three-dimensional network structure with acrylic acid and diutan gum, thereby enhancing the thixotropic properties and temperature resistance of magnesium oxychloride cement. Magnesium aluminum silicate, with its unique layered crystal structure and large specific surface area, can, on the one hand, further optimize the dispersion state of modified cement paste in cement slurry and enhance the stability of the system; on the other hand, its own good adsorption performance can help the modified cement paste to better adhere to the surface of the fracture, forming a more stable and dense sealing structure, thereby significantly improving the efficiency of the entire system in fractured reservoir plugging operations, ensuring the smooth progress of fractured reservoir plugging, and providing strong support for the safe and efficient exploitation of oil and gas wells.

[0017] The thixotropic agent obtained by the invention can be applied to plugging agents for drilling, and can be used in combination with magnesium oxychloride cement to achieve stable plugging.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The thixotropic agent of the present invention has good solubility and temperature and salt resistance, effectively enhances the thixotropy of cement slurry, has good adaptability to magnesium oxychloride cement, can play a stable role in the high temperature environment of oil and gas wells, enhances the retention capacity of plugging cement slurry in cracks, and forms a stable plug. In addition, the preparation method is simple and efficient, the raw materials are easy to obtain, and it has good prospects for industrial production and promotion. It is expected to effectively solve the problem of well leakage in fractured reservoirs of oil and gas wells and promote the development of oil and gas extraction technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Infrared spectrum analysis of modified diutan gum;

[0021] Figure 2 This is the TGA curve of modified ditopra. DETAILED DESCRIPTION

[0022] To make the technical advantages of the present invention more clear, the embodiments of the present invention are further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0023] Comparative Example 1

[0024] Only diutan gum was used as thixotropic agent.

[0025] Comparative Example 2

[0026] Only magnesium aluminum silicate was used as thixotropic agent.

[0027] Comparative Example 3

[0028] Only commercially available bentonite was used as thixotropic agent.

[0029] Example 1

[0030] The preparation method of the temperature-resistant thixotropic agent comprises the following specific steps:

[0031] To a three-necked flask equipped with a stirring device, 3 g of diutan gum and 150 mL of water were added, and the mixture was stirred at high speed until the diutan gum was completely dissolved to obtain solution I.

[0032] 18.18 g of acrylic acid was neutralized with a 5 mol / L NaOH solution to achieve a neutralization degree of 82%. After the reaction solution was cooled to room temperature, 1.82 g of N-vinyl pyrrolidone and 0.115 g of potassium persulfate were added thereto and stirred to dissolve, thereby obtaining a solution II.

[0033] Solution II was slowly and uniformly added to solution I through a constant pressure dropping funnel. After the dropping was completed, the temperature was raised to 69°C, the temperature was maintained and stirred for 3 hours to obtain a crude product. After the reaction was completed, the crude product was repeatedly washed 3 times with sufficient distilled water and ethanol solution in turn to completely remove impurities. Finally, it was dried to constant weight at 60°C, crushed to powder and sieved through a 100-mesh standard sieve to obtain a modified dimethoate powder that met the particle size requirements, marked as DG-1.

[0034] 10g of DG-1 and 10g of aluminum magnesium silicate powder were placed in a plastic bag and manually shaken to make the powders preliminarily mixed. The preliminarily mixed powders were transferred to a sieve shaker and sieved for 5 times to achieve uniform and sufficient mixing, and a finished product of a temperature-resistant thixotropic agent was obtained, which was marked as T-1.

[0035] A portion of DG-1 was scanned by Fourier infrared spectroscopy to obtain Figure 1 The results showed that the monomers were successfully grafted onto the diutan gum side chains.

[0036] Specifically, it can be seen from the infrared spectrum of the product that 3331.71cm -1 The stretching vibration absorption peak of OH is at 2932.89 cm -1 The asymmetric stretching vibration absorption peak of CH is at 1667.78 cm -1 The stretching vibration absorption peak of carbonyl C=O is at 1454.15cm -1 The bending vibration absorption peak of -CH2- is at 1403.21 cm -11289.70 cm is the stretching vibration absorption peak of the amide group CN on N-vinyl pyrrolidone, which is the characteristic absorption peak of the lactam structure in N-vinyl pyrrolidone; -1 The peak at 1042.07 cm is the stretching vibration absorption peak of COC, indicating that the monomer was successfully grafted onto diutanol; -1 The stretching vibration absorption peak of CO is at 1650-1590 cm -1 There is no N-H bending vibration absorption peak, which indicates that the vinyl group in N-vinyl pyrrolidone undergoes addition polymerization, but no ring-opening reaction occurs. In summary, the monomers of acrylic acid and N-vinyl pyrrolidone are successfully grafted onto diutan gum.

[0037] A portion of DG-1 was subjected to thermogravimetric analysis and the Figure 2 The TGA curve of the modified dimethoate shows that the temperature resistance of the modified dimethoate is good.

[0038] Specifically, the modified diutan gum undergoes significant mass loss after 400°C, and the thermal weight loss is mainly divided into two stages. The first stage is mainly the endothermic evaporation of free water and bound water in the molecule, and the second stage is mainly the cleavage and decomposition of the modified diutan gum polysaccharide main chain and branch chain and the thermal decomposition of the grafted group.

[0039] Example 2

[0040] The operation steps are basically the same as the preparation process of the modified diutan gum powder in Example 1, except that: 17.4 g of acrylic acid is neutralized to a degree of neutralization of 85%; 2.6 g of N-vinyl pyrrolidone is added and the reaction temperature is controlled at 75°C, and finally modified diutan gum powder DG-2 is obtained for standby use.

[0041] 10 g of DG-2 and 15 g of magnesium aluminum silicate powder were weighed at a weight ratio of 1:1.5, and mixed using the same sieving and mixing method as the preparation of the heat-resistant thixotropic agent in Example 1 to obtain a heat-resistant thixotropic agent finished product T-2.

[0042] Example 3

[0043] The operation steps are basically the same as the preparation process of the modified diutan gum powder in Example 1, except that: 19g of acrylic acid is neutralized to a neutralization degree of 80%; 1g of N-vinyl pyrrolidone is added and the reaction temperature is controlled at 70°C, and finally modified diutan gum powder DG-3 is obtained for standby use.

[0044] 10 g of DG-2 and 20 g of aluminum magnesium silicate powder were weighed in a weight ratio of 1:2, and mixed using the same sieving and mixing method as that used in the preparation of the heat-resistant thixotropic agent in Example 1 to obtain a finished heat-resistant thixotropic agent T-3.

[0045] Test Example 1

[0046] The application effects of the thixotropic agent provided in Comparative Examples 1-3 and the temperature-resistant thixotropic agent prepared in Example 1-3 in magnesium oxychloride cement were tested using Test Example 1. The specific operation is as follows:

[0047] Cement slurry was prepared according to the preparation method of oil well cement slurry in GB / T 19139-2012: 335 parts of light-burned magnesium oxide, 243 parts of magnesium chloride hexahydrate, 173 parts of water, 10 parts of retarder, 1.625 parts of the thixotropic agent provided in Comparative Example 1 were added to the cement-based slurry to prepare cement slurry C1, 6.5 parts of the thixotropic agent provided in Comparative Example 2 and Comparative Example 3 were added to the cement-based slurry to prepare cement slurries C2 and C3, and 6.5 parts of the temperature-resistant thixotropic agent prepared in Examples 1-3 were added to the cement-based slurry to prepare cement slurries C4-C6.

[0048] The thixotropic property of cement slurry is characterized by the increase in consistency after the thickener is turned on and off. The greater the increase in consistency, the better the thixotropic property of cement slurry. The cement slurries C1-C6 at 90°C were tested using the consistency increase method, and the measurement results are shown in Table 1.

[0049] Table 1 Thixotropic properties of magnesium oxychloride cement slurry containing thixotropic agent at 90℃

[0050] .

[0051] From the data in Table 1, it can be seen that the thixotropic agent provided in Comparative Example 1 can greatly enhance the thixotropy of cement slurry, but the thickening ability is too strong, so that the initial consistency of cement slurry reaches more than 30Bc, which is not conducive to pumping. In addition, the cost of Comparative Example 1 is relatively high and does not conform to the economic principle. The thixotropic agents provided in Comparative Examples 2 and 3 have limited application effects in magnesium oxychloride cement, and the thixotropy of cement slurry is average.

[0052] The temperature-resistant thixotropic agent prepared in the embodiment of the present invention can not only enhance the thixotropic performance of cement slurry to a good level, but also make the initial consistency of cement slurry meet the construction requirements, indicating that the temperature-resistant thixotropic agent of the present invention has a better application effect in magnesium oxychloride cement.

[0053] Test Example 2

[0054] The solubility properties of the thixotropic agent provided in Comparative Example 1 and the temperature-resistant thixotropic agent prepared in Examples 1-3 were tested using Test Example 2, and the specific operation was as follows:

[0055] Weigh 2g of sample and 100mL of ionized water, put them into a 200mL beaker, place them on a magnetic stirrer, set the stirring speed to 300r / min, and record the time required for the sample to be completely dissolved. The test results are shown in Table 2.

[0056] Table 2 Dissolution time of various thixotropic agent samples

[0057] .

[0058] It can be seen from the data in Table 2 that the thixotropic agent in Comparative Example 1 has extremely poor solubility. Not only is it not completely dissolved during the stirring time of 240 minutes, but it also undergoes agglomeration, which indicates that the thixotropic agent has poor affinity with water and is difficult to be evenly dispersed in the solution.

[0059] In contrast, the dissolution time of the heat-resistant thixotropic agent prepared in Examples 1-3 is between 14 and 17 minutes, and relatively sufficient dissolution and uniform dispersion can be achieved within a reasonable time. This indicates that the heat-resistant thixotropic agent prepared in the present invention not only ensures good compatibility with magnesium oxychloride cement, but also takes into account good solubility performance, and can more stably exert its advantages of improving the thixotropic properties of cement slurry and enhancing crack retention capacity in practical applications.

[0060] In summary, the thixotropic agent prepared by the preparation method of the temperature-resistant thixotropic agent of magnesium oxychloride cement provided in the embodiment of the present invention has good solubility and temperature resistance, effectively solves the multiple requirements for the thixotropic agent when plugging fractured formations during oil and gas well drilling, and reflects the innovation and practicality of the present invention in the research and development of magnesium oxychloride cement thixotropic agent.

[0061] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for preparing a temperature-resistant thixotropic agent, characterized in that: The modified diutan gum is grafted and modified by acrylic acid and N-vinyl pyrrolidone to obtain the modified diutan gum; the modified diutan gum is compounded with magnesium aluminum silicate to prepare a temperature-resistant thixotropic agent; In terms of mass ratio, dimethoate: acrylic acid: N-vinyl pyrrolidone = (2-4): (17-19): (1-3), modified dimethoate powder: magnesium aluminum silicate = 1: (1-2).

2. The method for preparing a temperature-resistant thixotropic agent according to claim 1, characterized in that: The specific steps are: (1) Mixing diutanol and deionized water and stirring until diutanol is completely dissolved to obtain solution I; (2) neutralizing acrylic acid to a neutralization degree of 80-85%, adding N-vinyl pyrrolidone and an initiator thereto, stirring and dissolving, to obtain a solution II; (3) Add solution II dropwise to solution I, raise the temperature to 65-75°C, keep the temperature and stir to react, and after the reaction is complete, perform post-treatment to obtain modified dimethoate powder; (4) The modified dimethoate powder is uniformly mixed with magnesium aluminum silicate to obtain a temperature-resistant thixotropic agent.

3. The method for preparing a temperature-resistant thixotropic agent according to claim 2, characterized in that: In terms of mass ratio, dimethoate: deionized water: initiator = (2-4): (150-200): (0.10-0.12).

4. The method for preparing a temperature-resistant thixotropic agent according to claim 2, characterized in that: The stirring speed in step (1) is in the range of 1000 rpm to 2000 rpm.

5. The method for preparing a temperature-resistant thixotropic agent according to claim 2, characterized in that: In step (2), acrylic acid is neutralized with a sodium hydroxide solution having a concentration of 5 mol / L.

6. The method for preparing the temperature-resistant thixotropic agent according to claim 2, characterized in that: The reaction time in step (3) is 3 h.

7. The method for preparing a temperature-resistant thixotropic agent according to claim 2, characterized in that: The particle size of the modified dimethoate powder in step (3) is 48 μm to 150 μm.

8. The method for preparing a temperature-resistant thixotropic agent according to claim 2, characterized in that: The mixing process in step (4) adopts the sieving mixing method.

9. A temperature-resistant thixotropic agent, characterized in that: The method is prepared by the method according to any one of claims 1 to 8.

10. Use of the temperature-resistant thixotropic agent according to claim 9 in plugging leaks in drilling.

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