Acid-soluble cement slurry leak plugging agent for oil wells and preparation method thereof

Abstract

The invention discloses an acid-soluble cement slurry plugging agent for oil wells and a preparation method thereof, and belongs to the technical field of plugging agents. The acid-soluble cement slurry plugging agent for oil wells comprises the following components in parts by weight: 55-80 parts of G-grade oil well cement, 5-30 parts of calcium carbonate powder, 5-25 parts of lime powder, 5-15 parts of bentonite powder, 5-10 parts of modified acid-soluble gel, 5-10 parts of modified tricalcium phosphate, 5-10 parts of fluid loss reducer and 1-5 parts of accelerator. The preparation method of the acid-soluble cement slurry plugging agent for oil wells of the present invention comprises: mixing G-grade oil well cement, bentonite powder, lime powder, calcium carbonate powder, modified acid-soluble gel, modified tricalcium phosphate, fluid loss reducer and accelerator in two steps to obtain the acid-soluble cement slurry plugging agent for oil wells. The present invention significantly improves the compressive strength and acid dissolution effect of the acid-soluble cement slurry plugging agent for oil wells.

Description

Technical Field

[0001] The invention belongs to the technical field of plugging agents, and in particular relates to an acid-soluble cement slurry plugging agent for oil wells and a preparation method thereof. Background Art

[0002] In oil well operations, the stability and integrity of the well wall are the key to ensuring production safety and efficiency. However, under complex geological conditions, cracks and pores in the well wall often lead to leakage, which not only affects the normal operation of the oil well, but also may cause serious damage to the geological structure and environment. Therefore, the development of efficient and reliable plugging technology and materials has become an urgent task in the oil industry. Among the many plugging technologies, acid-soluble cement slurry plugging agents have gradually become a research hotspot due to their unique performance advantages.

[0003] Acid-soluble cement slurry plugging agent is a cement slurry system that can be dissolved in an acidic environment. It adds specific acid-soluble materials, such as acid-soluble quartz powder, calcium carbonate, etc., to the cement slurry, so that the cement slurry can be quickly dissolved under acidic conditions after solidification to form a dense plugging layer, thereby effectively plugging the leakage channel. Compared with traditional plugging materials, acid-soluble cement slurry plugging agents have significant advantages such as rapid solubility, strong environmental adaptability, simple operation, little impact on oil layers, strong adjustability and good economy. However, traditional oil well cement plugging agents have obvious deficiencies in acid solubility, which to a certain extent limits their application effect under complex formation conditions. Therefore, the development of new acid-soluble cement slurry plugging agents for oil wells is of great significance to solve the problem of low acid solubility of plugging agents. Summary of the invention

[0004] The purpose of the present invention is to provide an acid-soluble cement slurry plugging agent for oil wells and a preparation method thereof, so as to solve the technical problem of low acid solubility of plugging agents for oil well cement in the prior art.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The invention provides an acid-soluble cement slurry plugging agent for oil wells, comprising the following components in parts by weight: 55-80 parts of G-grade oil well cement, 5-30 parts of calcium carbonate powder, 5-25 parts of lime powder, 5-15 parts of bentonite powder, 5-10 parts of modified acid-soluble gel, 5-10 parts of modified tricalcium phosphate, 5-10 parts of fluid loss reducer and 1-5 parts of coagulant; the modified acid-soluble gel is prepared by using dead-burned magnesium oxide as a raw material and being modified by sodium dihydrogen phosphate, sodium silicate and oxalic acid in a magnesium chloride solution; the modified tricalcium phosphate is prepared by using tricalcium phosphate as a raw material and being modified by tricalcium tripolyphosphate.

[0007] Furthermore, the preparation of the modified acid-soluble gel comprises the following steps:

[0008] (1) Mixing: weigh the dead-burned magnesium oxide and the modifier 1 and mix them evenly to obtain a dry ash mixture;

[0009] (2) Preparation of solution: Weigh anhydrous magnesium chloride and dissolve it in water to prepare a magnesium chloride solution. Pour the magnesium chloride solution into a beaker and place it on the base of a constant speed stirrer. Start the motor and stir at a low speed. At the same time, quickly add the dry ash mixture, cover the slurry cup with a lid, and continue stirring at a high speed to obtain a modified acid-soluble gel.

[0010] Furthermore, in step (1), the modifier 1 is a mixture of sodium dihydrogen phosphate, sodium silicate and oxalic acid, and the mass ratio of sodium dihydrogen phosphate, sodium silicate and oxalic acid is 1: (1-1.5): (1-2), wherein sodium dihydrogen phosphate has the ability to adjust pH, and can neutralize part of the alkaline substances, making the reaction environment more suitable for the formation of gel. Sodium silicate can be hydrolyzed in water to form silicic acid and sodium hydroxide. Silicic acid is a weak acid, and its silica sol has good adhesion and stability. During the gel formation process, silicic acid can react with magnesium oxide in the system to form magnesium silicate compounds, which can significantly enhance the mechanical strength and water resistance of the gel. At the same time, the addition of sodium silicate can also improve the microstructure of the gel, making it more dense and uniform. Oxalic acid is a The organic dibasic acid has strong reducing and coordination abilities. During the gel formation process, oxalic acid can react with magnesium ions in the system to form a stable chelate. In addition, oxalic acid can also be used as a pH regulator to affect the gel formation process and performance by adjusting the pH of the system. The weight ratio of dead-burned magnesium oxide to modifier 1 is 1:0.05-0.2. In step (2), the concentration of the magnesium chloride solution is 25-35 w / v%, the mass ratio of anhydrous magnesium chloride to dead-burned magnesium oxide is 1:2-5, the constant speed agitator is set to stir at a low speed of 30-100 r / min, and the dry ash mixture is quickly added within 15-20 seconds, and stirred at a high speed of 300-500 r / min for 30-40 seconds.

[0011] The preparation of modified tricalcium phosphate comprises the following steps:

[0012] Q1. Prepare suspension: weigh tricalcium phosphate and place it in deionized water, and then ultrasonically vibrate to obtain tricalcium phosphate suspension;

[0013] Q2, adding modifier 2: adding modifier 2 to the tricalcium phosphate suspension, then adding NaOH to adjust the pH, stirring and then standing to obtain a modified mixed solution;

[0014] Q3. Washing and drying: Pour out the supernatant from the modified mixed solution, wash and place in a constant temperature drying oven to dry, and grind to obtain modified tricalcium phosphate.

[0015] Furthermore, the mass concentration of the tricalcium phosphate suspension in Q1 is 20~60w / v%, the frequency of ultrasonic oscillation is 100~300Hz, and the time is 20~60min; the modifier 2 in Q2 is sodium tripolyphosphate, the mass ratio of tricalcium phosphate to the modifier is 1:0.02~0.05, NaOH is added to adjust the pH to 8, stirred at a speed of 400~600r / min for 0.5~1 hour, and allowed to stand for 1~3 hours; Q3 is washed with water 2~3 times, and dried in a constant temperature drying oven at a temperature of 80~90℃ for 12~24 hours.

[0016] The fluid loss reducer is one or both of carboxymethyl cellulose and hydroxyethyl cellulose; the coagulant is one or more of calcium chloride, sodium sulfate, triethanolamine and calcium formate.

[0017] The present invention also provides a method for preparing an acid-soluble cement slurry plugging agent for oil wells, comprising the following steps:

[0018] M1. Primary mixing: weigh G-grade oil well cement, bentonite powder, lime powder and calcium carbonate powder, put them into a mixer and stir them evenly to obtain a primary mixture;

[0019] M2. Final mixing: Weigh the modified acid-soluble gel, modified tricalcium phosphate, fluid loss reducer and coagulant, add them into the primary mixture, stir them thoroughly, and obtain the acid-soluble cement slurry plugging agent for oil wells.

[0020] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0021] 1. The present invention significantly improves the compressive strength and acid dissolution effect of the acid-soluble cement slurry plugging agent for oil wells by proportioning G-grade oil well cement, bentonite powder, lime powder, calcium carbonate powder, modified acid-soluble gel, modified tricalcium phosphate, fluid loss reducer and coagulant. Among them, the introduction of modified acid-soluble gel and modified tricalcium phosphate not only enhances the acid solubility of cement slurry, but also improves the mechanical properties of cement slurry. The synergistic effect of fluid loss reducer and coagulant further optimizes the fluid properties of cement slurry, ensuring effective plugging and rapid solidification under high pressure and high temperature conditions. The acid-soluble cement slurry plugging agent for oil wells of the present invention uses a mixed solution of hydrochloric acid and hydrofluoric acid during the later dissolution, and controls the concentration of hydrochloric acid to be 3~37wt%, and the concentration of hydrofluoric acid to be 3~8wt%.

[0022] 2. The present invention forms a modified acid-soluble gel by mixing sodium dihydrogen phosphate, sodium silicate and oxalic acid with dead-burned magnesium oxide, and in the presence of a magnesium chloride solution. During the gel formation process, sodium dihydrogen phosphate can ionize hydrogen ions and dihydrogen phosphate ions in an aqueous solution, and these ions can react with magnesium ions in the system to form a stable compound or complex, thereby enhancing the chemical stability and structural strength of the gel; silicic acid is a weak acid, and its silica sol has good adhesion and stability; oxalic acid can react with magnesium ions in the system to form a stable chelate. Therefore, in the process of plugging oil wells, the use of modified acid-soluble gel not only improves the mechanical properties of the plugging agent and enhances the durability of the plugging effect, but also the gel can be gradually dissolved in the acidic environment of the oil well, avoiding adverse effects on subsequent production and maintenance of the oil well, ensuring that the oil well can quickly resume production after plugging, reducing the production interruption time caused by plugging operations, and greatly improving the efficiency of oil well exploitation.

[0023] 3. The present invention adds a modifier sodium tripolyphosphate to the tricalcium phosphate suspension, and uses NaOH to adjust the pH value of the solution. The appropriate pH value can improve the stability of the modified mixed solution, prevent particle aggregation and precipitation, and ensure the smooth progress of the modification process. The sodium polyphosphate molecule has multiple phosphate ions, which can react chemically or physically adsorb with calcium ions on the surface of tricalcium phosphate, thereby forming a modified layer composed of sodium tripolyphosphate molecules on the surface of tricalcium phosphate particles. The modified layer can not only change the surface charge and wettability of tricalcium phosphate particles, but also connect multiple tricalcium phosphate particles through cross-linking to form a tighter network structure, significantly improve the bonding performance of cement slurry, and enhance the integrity and strength of the plugging structure. In addition, when the modified tricalcium phosphate is added to the acid-soluble cement slurry as a plugging agent component, it can quickly dissolve and release the effective ingredients when encountering an acidic solution, thereby quickly responding to the acidic conditions in the oil well and significantly improving the solubility in an acidic environment. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] Embodiment 1:

[0026] The present embodiment provides an acid-soluble cement slurry plugging agent for oil wells, comprising the following components by weight: 80 kg of G-grade oil well cement, 26 kg of calcium carbonate powder, 23 kg of lime powder, 13 kg of bentonite powder, 5 kg of modified acid-soluble gel, 5 kg of modified tricalcium phosphate, 5 kg of fluid loss reducer and 1 kg of accelerator.

[0027] Specifically, the preparation of the modified acid-soluble gel comprises the following steps:

[0028] (1) Mixing: Weigh 1000 g of dead-burned magnesium oxide, 15 g of sodium dihydrogen phosphate, 15 g of sodium silicate and 20 g of oxalic acid and mix them evenly to obtain a dry ash mixture;

[0029] (2) Preparation of solution: Weigh 250 g of anhydrous magnesium chloride and put it into a beaker. Add water to the mark of 1000 mL and stir to dissolve. After preparing a magnesium chloride solution with a weight volume percentage concentration of 25 w / v%, pour the magnesium chloride solution into a beaker and place it on the base of a constant speed stirrer. Start the motor and stir at 30 r / min. At the same time, add the dry ash mixture within 15 seconds. Cover the slurry cup with a lid and continue stirring at 300 r / min for 30 seconds to obtain a modified acid-soluble gel.

[0030] Specifically, the preparation of modified tricalcium phosphate includes the following steps:

[0031] Q1. Preparation of suspension: weigh 200g tricalcium phosphate into a beaker and add deionized water to the 1000mL mark. The frequency of ultrasonic oscillation is 100Hz for 20min. After the end, a 20w / v% tricalcium phosphate suspension is obtained.

[0032] Q2, add modifier: add 4g sodium tripolyphosphate to the tricalcium phosphate suspension, then add NaOH to adjust the pH to 8, stir at a speed of 400r / min for 0.5 hours and then stand for 1 hour to obtain a modified mixed solution;

[0033] Q3. Washing and drying: Pour out the supernatant from the modified mixed liquid, wash it with water twice, and then place it in a constant temperature drying oven to dry. The temperature of the constant temperature drying oven is 80°C and the drying time is 24 hours. After grinding, modified tricalcium phosphate is obtained.

[0034] Among them, the fluid loss reducer is carboxymethyl cellulose; the coagulant is calcium chloride.

[0035] The preparation method of the acid-soluble cement slurry plugging agent for oil wells in this embodiment comprises the following steps:

[0036] M1. Primary mixing: weigh 80 kg of G-grade oil well cement, 13 kg of bentonite powder, 23 kg of lime powder, and 26 kg of calcium carbonate powder, put them into a mixer, and stir them evenly to obtain a primary mixture;

[0037] M2. Final mixing: Weigh 5 kg of modified acid-soluble gel, 5 kg of modified tricalcium phosphate, 5 kg of fluid loss reducer and 1 kg of accelerator, add them to the primary mixture, stir them thoroughly, and obtain an acid-soluble cement slurry plugging agent for oil wells.

[0038] Embodiment 2:

[0039] This embodiment provides an acid-soluble cement slurry plugging agent for oil wells, including the following ingredients by weight: 75 kg of G-grade oil well cement, 10 kg of bentonite powder, 8 kg of lime powder, 7 kg of calcium carbonate powder, 5 kg of modified acid-soluble gel, 5 kg of modified tricalcium phosphate, 5 kg of filtrate reducer and 1 kg of accelerator.

[0040] Specifically, the preparation of the modified acid-soluble gel comprises the following steps:

[0041] (1) Mixing: Weigh 1000 g of dead-burned magnesium oxide, 20 g of sodium dihydrogen phosphate, 30 g of sodium silicate and 20 g of oxalic acid and mix them evenly to obtain a dry ash mixture;

[0042] (2) Preparation of solution: Weigh 250 g of anhydrous magnesium chloride and put it into a beaker. Add water to the mark of 1000 mL and stir to dissolve. After preparing a magnesium chloride solution with a weight volume percentage concentration of 25 w / v%, pour the magnesium chloride solution into a beaker and place it on the base of a constant speed stirrer. Start the motor and stir at 50 r / min. At the same time, add the dry ash mixture within 15 seconds. Cover the slurry cup with a lid and continue stirring at 350 r / min for 30 seconds to obtain a modified acid-soluble gel.

[0043] Specifically, the preparation of modified tricalcium phosphate includes the following steps:

[0044] Q1. Preparation of suspension: weigh 250g tricalcium phosphate into a beaker and add deionized water to the 1000mL mark. The frequency of ultrasonic oscillation is 150Hz for 25min. After the end, a 25w / v% tricalcium phosphate suspension is obtained.

[0045] Q2, add modifier: add 5g sodium tripolyphosphate to the tricalcium phosphate suspension, then add NaOH to adjust the pH to 8, stir at a speed of 450r / min for 0.5 hour and then stand for 1 hour to obtain a modified mixed solution;

[0046] Q3. Washing and drying: Pour out the supernatant from the modified mixed liquid, wash it with water three times and place it in a constant temperature drying oven to dry. The temperature of the constant temperature drying oven is 82°C and the drying time is 22 hours. After grinding, modified tricalcium phosphate is obtained.

[0047] The fluid loss reducer is an equal mixture of carboxymethyl cellulose and hydroxyethyl cellulose; and the coagulant is an equal mixture of calcium chloride and triethanolamine.

[0048] The preparation method of the acid-soluble cement slurry plugging agent for oil wells in this embodiment comprises the following steps:

[0049] M1. Primary mixing: weigh 75 kg of G-grade oil well cement, 10 kg of bentonite powder, 8 kg of lime powder and 7 kg of calcium carbonate powder into a mixer and stir evenly to obtain a primary mixture;

[0050] M2. Final mixing: Weigh 5 kg of modified acid-soluble gel, 5 kg of modified tricalcium phosphate, 5 kg of fluid loss reducer and 1 kg of accelerator, add them to the primary mixture, stir them thoroughly, and obtain an acid-soluble cement slurry plugging agent for oil wells.

[0051] Embodiment 3:

[0052] This embodiment provides an acid-soluble cement slurry plugging agent for oil wells, including the following ingredients by weight: 75 kg of G-grade oil well cement, 10 kg of bentonite powder, 10 kg of lime powder, 15 kg of calcium carbonate powder, 7 kg of modified acid-soluble gel, 6 kg of modified tricalcium phosphate, 5 kg of filtration reducer and 1 kg of accelerator.

[0053] Specifically, the preparation of the modified acid-soluble gel comprises the following steps:

[0054] (1) Mixing: Weigh 1000 g of dead-burned magnesium oxide, 20 g of sodium dihydrogen phosphate, 20 g of sodium silicate and 20 g of oxalic acid and mix them evenly to obtain a dry ash mixture;

[0055] (2) Preparation of solution: Weigh 300 g of anhydrous magnesium chloride and put it into a beaker. Add water to the mark of 1000 mL and stir to dissolve. After preparing a magnesium chloride solution with a weight volume percentage concentration of 30 w / v%, pour the magnesium chloride solution into a beaker and place it on the base of a constant speed stirrer. Start the motor and stir at 60 r / min. At the same time, add the dry ash mixture within 18 seconds. Cover the slurry cup with a lid and continue stirring at 400 r / min for 30 seconds to obtain a modified acid-soluble gel.

[0056] Specifically, the preparation of modified tricalcium phosphate includes the following steps:

[0057] Q1. Preparation of suspension: weigh 300g of tricalcium phosphate into a beaker and add deionized water to the 1000mL mark. The frequency of ultrasonic oscillation is 100Hz for 30min. After the end, a 30w / v% tricalcium phosphate suspension is obtained.

[0058] Q2, add modifier: add 6g sodium tripolyphosphate to the tricalcium phosphate suspension, then add NaOH to adjust the pH to 8, stir at a speed of 450r / min for 0.5 hours and then stand for 2 hours to obtain a modified mixed solution;

[0059] Q3. Washing and drying: Pour out the supernatant from the modified mixed solution, wash it with water twice, and then place it in a constant temperature drying oven to dry. The temperature of the constant temperature drying oven is 85°C, and the drying time is 20 hours. After grinding, modified tricalcium phosphate is obtained.

[0060] The fluid loss reducer is an equal mixture of carboxymethyl cellulose and hydroxyethyl cellulose; and the coagulant is an equal mixture of calcium chloride and calcium formate.

[0061] The preparation method of the acid-soluble cement slurry plugging agent for oil wells in this embodiment comprises the following steps:

[0062] M1. Primary mixing: weigh 75 kg of G-grade oil well cement, 10 kg of bentonite powder, 10 kg of lime powder, and 15 kg of calcium carbonate powder, put them into a mixer, and stir evenly to obtain a primary mixture;

[0063] M2. Final mixing: Weigh 7 kg of modified acid-soluble gel, 6 kg of modified tricalcium phosphate, 5 kg of fluid loss reducer and 1 kg of accelerator, add to the primary mix, stir thoroughly, and obtain an acid-soluble cement slurry plugging agent for oil wells.

[0064] Embodiment 4:

[0065] This embodiment provides an acid-soluble cement slurry plugging agent for oil wells, including the following ingredients by weight: 70 kg of G-grade oil well cement, 12 kg of bentonite powder, 15 kg of lime powder, 15 kg of calcium carbonate powder, 8 kg of modified acid-soluble gel, 8 kg of modified tricalcium phosphate, 6 kg of filtration reducer and 3 kg of accelerator.

[0066] Specifically, the preparation of the modified acid-soluble gel comprises the following steps:

[0067] (1) Mixing: Weigh 1000 g of dead-burned magnesium oxide, 30 g of sodium dihydrogen phosphate, 30 g of sodium silicate and 60 g of oxalic acid and mix them evenly to obtain a dry ash mixture;

[0068] (2) Preparation of solution: Weigh 300 g of anhydrous magnesium chloride and put it into a beaker. Add water to the mark of 1000 mL and stir to dissolve. After preparing a magnesium chloride solution with a weight volume percentage concentration of 30 w / v%, pour the magnesium chloride solution into a beaker and place it on the base of a constant speed stirrer. Start the motor and stir at 65 r / min. At the same time, add the dry ash mixture within 15 to 20 seconds. Cover the slurry cup with a lid and continue stirring at 450 r / min for 30 to 40 seconds to obtain a modified acid-soluble gel.

[0069] Specifically, the preparation of modified tricalcium phosphate includes the following steps:

[0070] Q1. Preparation of suspension: weigh 350g tricalcium phosphate into a beaker and add deionized water to the 1000mL mark. The frequency of ultrasonic oscillation is 200Hz and the time is 40min. After the end, a 35w / v% tricalcium phosphate suspension is obtained;

[0071] Q2, add modifier: add 6g sodium tripolyphosphate to the tricalcium phosphate suspension, then add NaOH to adjust the pH to 8, stir at a speed of 500r / min for 1 hour and then stand for 3 hours to obtain a modified mixed solution;

[0072] Q3. Washing and drying: Pour out the supernatant from the modified mixed liquid, wash it with water three times and place it in a constant temperature drying oven to dry. The temperature of the constant temperature drying oven is 86°C and the drying time is 18 hours. After grinding, modified tricalcium phosphate is obtained.

[0073] The fluid loss reducer is an equal mixture of carboxymethyl cellulose and hydroxyethyl cellulose; and the coagulant is an equal mixture of calcium chloride, triethanolamine and calcium formate.

[0074] The preparation method of the acid-soluble cement slurry plugging agent for oil wells in this embodiment comprises the following steps:

[0075] M1. Primary mixing: weigh 70 kg of G-grade oil well cement, 12 kg of bentonite powder, 15 kg of lime powder and 15 kg of calcium carbonate powder into a mixer and stir evenly to obtain a primary mixture;

[0076] M2. Final mixing: Weigh 8 kg of modified acid-soluble gel, 8 kg of modified tricalcium phosphate, 6 kg of fluid loss reducer and 3 kg of accelerator, add to the primary mix, stir thoroughly, and obtain an acid-soluble cement slurry plugging agent for oil wells.

[0077] Embodiment 5:

[0078] This embodiment provides an acid-soluble cement slurry plugging agent for oil wells, including the following ingredients by weight: 60 kg of G-grade oil well cement, 15 kg of bentonite powder, 10 kg of lime powder, 15 kg of calcium carbonate powder, 7 kg of modified acid-soluble gel, 8 kg of modified tricalcium phosphate, 6 kg of filtrate reducer and 3 kg of accelerator.

[0079] Specifically, the preparation of the modified acid-soluble gel comprises the following steps:

[0080] (1) Mixing: Weigh 1000 g of dead-burned magnesium oxide, 50 g of sodium dihydrogen phosphate, 50 g of sodium silicate and 50 g of oxalic acid and mix them evenly to obtain a dry ash mixture;

[0081] (2) Preparation of solution: Weigh 310 g of anhydrous magnesium chloride and put it into a beaker. Add water to the mark of 1000 mL and stir to dissolve. After preparing a magnesium chloride solution with a weight volume percentage concentration of 31 w / v%, pour the magnesium chloride solution into a beaker and place it on the base of a constant speed stirrer. Start the motor and stir at 80 r / min. At the same time, add the dry ash mixture within 18 seconds. Cover the slurry cup with a lid and continue stirring at 450 r / min for 35 seconds to obtain a modified acid-soluble gel.

[0082] Specifically, the preparation of modified tricalcium phosphate includes the following steps:

[0083] Q1. Preparation of suspension: weigh 350g tricalcium phosphate into a beaker and add deionized water to the 1000mL mark. The frequency of ultrasonic oscillation is 200Hz and the time is 40min. After the end, a 35w / v% tricalcium phosphate suspension is obtained;

[0084] Q2, add modifier: add 8g sodium tripolyphosphate to the tricalcium phosphate suspension, then add NaOH to adjust the pH to 8, stir at a speed of 550r / min for 1 hour and then stand for 3 hours to obtain a modified mixed solution;

[0085] Q3. Washing and drying: Pour out the supernatant from the modified mixed liquid, wash it with water three times and place it in a constant temperature drying oven to dry. The temperature of the constant temperature drying oven is 90°C and the drying time is 16 hours. After grinding, modified tricalcium phosphate is obtained.

[0086] The fluid loss reducer is an equal mixture of carboxymethyl cellulose and hydroxyethyl cellulose; and the coagulant is an equal mixture of calcium chloride, triethanolamine and calcium formate.

[0087] The preparation method of the acid-soluble cement slurry plugging agent for oil wells in this embodiment comprises the following steps:

[0088] M1. Primary mixing: weigh 60 kg of G-grade oil well cement, 15 kg of bentonite powder, 10 kg of lime powder and 15 kg of calcium carbonate powder into a mixer and stir evenly to obtain a primary mixture;

[0089] M2. Final mixing: Weigh 7 kg of modified acid-soluble gel, 8 kg of modified tricalcium phosphate, 6 kg of fluid loss reducer and 3 kg of accelerator, add to the primary mix, stir thoroughly, and obtain an acid-soluble cement slurry plugging agent for oil wells.

[0090] Embodiment 6:

[0091] This embodiment provides an acid-soluble cement slurry plugging agent for oil wells, including the following ingredients by weight: 55 kg of G-grade oil well cement, 15 kg of bentonite powder, 15 kg of lime powder, 20 kg of calcium carbonate powder, 10 kg of modified acid-soluble gel, 10 kg of modified tricalcium phosphate, 8 kg of filtration reducer and 4 kg of accelerator.

[0092] Specifically, the preparation of the modified acid-soluble gel comprises the following steps:

[0093] (1) Mixing: Weigh 1000 g of dead-burned magnesium oxide, 50 g of sodium dihydrogen phosphate, 60 g of sodium silicate and 90 g of oxalic acid and mix them evenly to obtain a dry ash mixture;

[0094] (2) Preparation of solution: Weigh 350 g of anhydrous magnesium chloride and put it into a beaker. Add water to the mark of 1000 mL and stir to dissolve. After preparing a magnesium chloride solution with a weight volume percentage concentration of 35 w / v%, pour the magnesium chloride solution into a beaker and place it on the base of a constant speed stirrer. Start the motor and stir at 90 r / min. At the same time, add the dry ash mixture within 15 to 20 seconds. Cover the slurry cup with a lid and continue stirring at 500 r / min for 30 to 40 seconds to obtain a modified acid-soluble gel.

[0095] Specifically, the preparation of modified tricalcium phosphate includes the following steps:

[0096] Q1. Preparation of suspension: weigh 500g of tricalcium phosphate into a beaker and add deionized water to the 1000mL mark. The frequency of ultrasonic oscillation is 300Hz for 60min. After the end, a 50w / v% tricalcium phosphate suspension is obtained.

[0097] Q2, add modifier: add 10g sodium tripolyphosphate to the tricalcium phosphate suspension, then add NaOH to adjust the pH to 8, stir at a speed of 550r / min for 1 hour and then stand for 3 hours to obtain a modified mixed solution;

[0098] Q3. Washing and drying: Pour out the supernatant from the modified mixed liquid, wash it with water three times and place it in a constant temperature drying oven to dry. The temperature of the constant temperature drying oven is 90°C and the drying time is 18 hours. After grinding, modified tricalcium phosphate is obtained.

[0099] The fluid loss reducer is an equal mixture of carboxymethyl cellulose and hydroxyethyl cellulose; and the coagulant is an equal mixture of calcium chloride, sodium sulfate, triethanolamine and calcium formate.

[0100] The preparation method of the acid-soluble cement slurry plugging agent for oil wells in this embodiment comprises the following steps:

[0101] M1. Primary mixing: weigh 55 kg of G-grade oil well cement, 15 kg of bentonite powder, 15 kg of lime powder, and 20 kg of calcium carbonate powder, put them into a mixer, and stir evenly to obtain a primary mixture;

[0102] M2. Final mixing: Weigh 10 kg of modified acid-soluble gel, 10 kg of modified tricalcium phosphate, 8 kg of fluid loss reducer and 4 kg of accelerator, add to the primary mix, stir thoroughly, and obtain an acid-soluble cement slurry plugging agent for oil wells.

[0103] Embodiment 7:

[0104] This embodiment provides an acid-soluble cement slurry plugging agent for oil wells, including the following ingredients by weight: 55 kg of G-grade oil well cement, 15 kg of bentonite powder, 25 kg of lime powder, 20 kg of calcium carbonate powder, 10 kg of modified acid-soluble gel, 10 kg of modified tricalcium phosphate, 10 kg of filtrate reducer and 5 kg of accelerator.

[0105] Specifically, the preparation of the modified acid-soluble gel comprises the following steps:

[0106] (1) Mixing: Weigh 1000 g of dead-burned magnesium oxide, 40 g of sodium dihydrogen phosphate, 60 g of sodium silicate and 80 g of oxalic acid and mix them evenly to obtain a dry ash mixture;

[0107] (2) Preparation of solution: Weigh 350 g of anhydrous magnesium chloride and put it into a beaker. Add water to the mark of 1000 mL and stir to dissolve. After preparing a magnesium chloride solution with a weight volume percentage concentration of 35 w / v%, pour the magnesium chloride solution into a beaker and place it on the base of a constant speed stirrer. Start the motor and stir at 100 r / min. At the same time, add the dry ash mixture within 15 seconds. Cover the slurry cup with a lid and continue stirring at 500 r / min for 30 seconds to obtain a modified acid-soluble gel.

[0108] Specifically, the preparation of modified tricalcium phosphate includes the following steps:

[0109] Q1. Prepare suspension: weigh 600g tricalcium phosphate into a beaker and add deionized water to the 1000mL mark. The frequency of ultrasonic oscillation is 300Hz for 60min. After the end, a 60w / v% tricalcium phosphate suspension is obtained.

[0110] Q2, add modifier: add 10g sodium tripolyphosphate to the tricalcium phosphate suspension, then add NaOH to adjust the pH to 8, stir at a speed of 600r / min for 1 hour and then stand for 3 hours to obtain a modified mixed solution;

[0111] Q3. Washing and drying: Pour out the supernatant from the modified mixed liquid, wash it with water three times and place it in a constant temperature drying oven to dry. The temperature of the constant temperature drying oven is 90°C and the drying time is 12 hours. After grinding, modified tricalcium phosphate is obtained.

[0112] The fluid loss reducer is an equal mixture of carboxymethyl cellulose and hydroxyethyl cellulose; and the coagulant is an equal mixture of calcium chloride, sodium sulfate, triethanolamine and calcium formate.

[0113] The preparation method of the acid-soluble cement slurry plugging agent for oil wells in this embodiment comprises the following steps:

[0114] M1. Primary mixing: weigh 55 kg of G-grade oil well cement, 15 kg of bentonite powder, 25 kg of lime powder, and 20 kg of calcium carbonate powder, put them into a mixer, and stir evenly to obtain a primary mixture;

[0115] M2. Final mixing: Weigh 10 kg of modified acid-soluble gel, 10 kg of modified tricalcium phosphate, 10 kg of fluid loss reducer and 5 kg of accelerator, add to the primary mix, stir thoroughly, and obtain an acid-soluble cement slurry plugging agent for oil wells.

[0116] Comparative Example 1:

[0117] Comparative Example 1 Compared with Example 6, in Comparative Example 1, no modified acid-soluble gel is added to the acid-soluble cement slurry plugging agent for oil wells, and other conditions remain unchanged.

[0118] Comparative Example 2:

[0119] Comparative Example 2 Compared with Example 6, in Comparative Example 2, no modified tricalcium phosphate is added to the acid-soluble cement slurry plugging agent for oil wells, and other conditions remain unchanged.

[0120] Comparative Example 3:

[0121] Comparative Example 3 Compared with Example 6, in Comparative Example 3, no fluid loss reducer is added to the acid-soluble cement slurry plugging agent for oil wells, and other conditions remain unchanged.

[0122] Comparative Example 4:

[0123] Comparative Example 4 Compared with Example 6, in Comparative Example 4, no coagulant is added to the acid-soluble cement slurry plugging agent for oil wells, and other conditions remain unchanged.

[0124] Experimental example

[0125] The performance of the acid-soluble cement slurry plugging agents for oil wells of Examples 1 to 7 of the present invention and Comparative Examples 1 to 4 was measured.

[0126] 1. Determination of acid solubility

[0127] According to the determination method of acid insolubles in SY / T5559-1992 "General Test Methods for Drilling Fluid Treatment Agents", the acid solubility of the plugging agents of Examples 1 to 7 of the present invention and Comparative Examples 1 to 4 was determined. The test results are shown in Table 1.

[0128] Table 1

[0129]

[0130] According to the test results in Table 1, the acid-soluble cement slurry plugging agents for oil wells of Examples 1 to 7 of the present invention all have excellent acid solubility. By comparing Examples 1 to 7 with Comparative Examples 1 to 4, it can be seen that after adding the modified acid-soluble gel and modified tricalcium phosphate, the acid solubility of the plugging agent increases, indicating that the modified acid-soluble gel and modified tricalcium phosphate can quickly respond to the acidic conditions in the oil well and significantly improve the solubility in the acidic environment.

[0131] 2. Determination of compressive strength

[0132] Take 50 g of the acid-soluble cement slurry plugging agent for oil wells of Examples 1 to 7 of the present invention and Comparative Examples 1 to 4, add 100 mL of clean water and stir evenly, pour into a 5 cm × 5 cm × 5 cm sealed mold, place in an oil bath box, and after curing at 80 ° C for 12 h, use a compressive strength tester to measure the compressive strength after curing. The measurement results are shown in Table 2.

[0133] Table 2

[0134]

[0135] According to the test results in Table 2, the acid-soluble cement slurry plugging agents for oil wells of Examples 1 to 7 of the present invention all have excellent compressive strength. By comparing Examples 1 to 7 with Comparative Examples 1 to 4, it can be seen that after adding modified acid-soluble gel and modified tricalcium phosphate, the compressive strength of the plugging agent is significantly increased, indicating that modified acid-soluble gel and modified tricalcium phosphate can improve the compressive performance of the plugging agent. The acid-soluble cement slurry plugging agent for oil wells of the present invention uses a mixed solution of hydrochloric acid and hydrofluoric acid during dissolution in the later stage, and the concentration of hydrochloric acid is controlled to be 3 to 37wt%, and the concentration of hydrofluoric acid is 3 to 8wt%.

[0136] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

[0137] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only specific implementation methods. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. Acid-soluble cement slurry plugging agent for oil wells, characterized in that: The invention comprises the following ingredients in parts by weight: 55-80 parts of G-grade oil well cement, 5-30 parts of calcium carbonate powder, 5-25 parts of lime powder, 5-15 parts of bentonite powder, 5-10 parts of modified acid-soluble gel, 5-10 parts of modified tricalcium phosphate, 5-10 parts of fluid loss reducer and 1-5 parts of accelerator; The modified acid-soluble gel is prepared by using dead-burned magnesium oxide as a raw material and being modified by sodium dihydrogen phosphate, sodium silicate and oxalic acid in a magnesium chloride solution; the modified tricalcium phosphate is prepared by using tricalcium phosphate as a raw material and being modified by sodium tripolyphosphate.

2. The acid-soluble cement slurry plugging agent for oil wells according to claim 1, characterized in that: The preparation method of the modified acid-soluble gel comprises the following steps: (1) Mixing: weigh the dead-burned magnesium oxide and the modifier 1 and mix them evenly to obtain a dry ash mixture; (2) Preparation of solution: Weigh anhydrous magnesium chloride and dissolve it in water to prepare a magnesium chloride solution. Pour the magnesium chloride solution into a beaker and place it on the base of a constant speed stirrer. Start the motor and stir at a low speed. At the same time, quickly add the dry ash mixture, cover the slurry cup with a lid, and continue stirring at a high speed to obtain a modified acid-soluble gel.

3. The acid-soluble cement slurry plugging agent for oil wells according to claim 2, characterized in that: In step (1), the modifier 1 is a mixture of sodium dihydrogen phosphate, sodium silicate and oxalic acid, and the mass ratio of sodium dihydrogen phosphate, sodium silicate and oxalic acid is 1: (1-1.5): (1-2); the weight ratio of dead-burned magnesium oxide to modifier 1 is 1: 0.05-0.

2.

4. The acid-soluble cement slurry plugging agent for oil wells according to claim 2, characterized in that: In step (2), the concentration of the magnesium chloride solution is 25-35 w / v%, the mass ratio of anhydrous magnesium chloride to dead-burned magnesium oxide is 1:2-5, the constant speed agitator is set to stir at a low speed of 30-100 r / min, and the dry ash mixture is quickly added within 15-20 seconds, and stirred at a high speed of 300-500 r / min for 30-40 seconds.

5. The acid-soluble cement slurry plugging agent for oil wells according to claim 1, characterized in that: The preparation method of modified tricalcium phosphate comprises the following steps: Q1. Prepare suspension: weigh tricalcium phosphate and place it in deionized water, and then ultrasonically vibrate to obtain tricalcium phosphate suspension; Q2, adding modifier 2: adding modifier 2 to the tricalcium phosphate suspension, then adding NaOH to adjust the pH, stirring and then standing to obtain a modified mixed solution; Q3. Washing and drying: Pour out the supernatant from the modified mixed solution, wash and place in a constant temperature drying oven to dry, and grind to obtain modified tricalcium phosphate.

6. The acid-soluble cement slurry plugging agent for oil wells according to claim 5, characterized in that: The mass concentration of the tricalcium phosphate suspension in Q1 is 20~60wt%, the frequency of ultrasonic oscillation is 100~300Hz, and the time is 20~60min.

7. The acid-soluble cement slurry plugging agent for oil wells according to claim 5, characterized in that: Modifier 2 in Q2 is sodium tripolyphosphate, and the mass ratio of tricalcium phosphate to modifier is 1:0.02~0.

05. NaOH is added to adjust the pH to 8, and the mixture is stirred at a speed of 400~600r / min for 0.5~1 hour and allowed to stand for 1~3 hours. In Q3, the mixture is washed with water 2~3 times and dried in a constant temperature drying oven at 80~90℃ for 12~24 hours.

8. The acid-soluble cement slurry plugging agent for oil wells according to claim 1, characterized in that: The fluid loss reducer is one or both of carboxymethyl cellulose and hydroxyethyl cellulose; the coagulant is one or more of calcium chloride, sodium sulfate, triethanolamine and calcium formate.

9. The method for preparing the acid-soluble cement slurry plugging agent for oil wells according to claim 1, characterized in that: The following steps are involved: M1. Primary mixing: weigh G-grade oil well cement, bentonite powder, lime powder and calcium carbonate powder, put them into a mixer and stir them evenly to obtain a primary mixture; M2. Final mixing: Weigh the modified acid-soluble gel, modified tricalcium phosphate, fluid loss reducer and coagulant, add them into the primary mixture, stir them thoroughly, and obtain the acid-soluble cement slurry plugging agent for oil wells.

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