Well cementation cement repairing agent and preparation method of self-repairing cement-based material

Abstract

The invention discloses a well cementation cement repairing agent and a preparation method of a self-repairing cement-based material. The repairing agent is prepared from the following components in percentage by mass: microbial powder, nutrient substances, chitosan and a calcium source, the preparation method comprises the following steps: mixing the bacterial powder, the nutrient, the calcium source and the chitosan, and extruding and granulating; the particles are chemically cured through a sodium hydroxide solution and a sodium tripolyphosphate solution in sequence, and the high-strength chitosan-based repairing agent is formed; the repairing agent is doped into the cement-based material, and the doping amount is 1%-5% of the total mass of the cementing material. Through innovative design and preparation of the repairing agent, once the well cementation cement-based material cracks, a self-repairing mechanism is accurately triggered in a leaked CO2 environment, meanwhile, the mechanical strength of repairing agent particles is improved to 120 N through a chemical curing process, the strength, stability and durability of the repairing agent particles in the cement-based material are ensured, and the repairing agent is suitable for well cementation. Reliable guarantee is provided for long-term safe operation of carbon dioxide sealing wells and oil and gas wells.

Description

Technical Field

[0001] The present invention belongs to a cement-based material and a preparation method thereof, and particularly relates to a CO2-triggered crack self-healing cement-based material for a carbon dioxide sequestration well or an oil and gas well and a preparation method thereof, as well as a microbial repair agent for preparing the cement-based material. Background Art

[0002] In a carbon sequestration (CCS) project, the sealing performance of the wellbore cement sheath is the key to ensuring long-term CO2 sequestration. The rupture of the cement sheath will cause CO2 to leak along the cracks to non-target formations or the ground surface, destroying the integrity of the sequestration body, not only reducing the carbon sequestration efficiency, but also possibly causing secondary risks such as groundwater acidification and formation structure instability. At the same time, the leaked CO2 continuously reacts with the cement matrix, accelerating the crack propagation and corroding the wellbore casing, forming a "leakage-corrosion" vicious cycle, seriously threatening the safety and environmental benefits of the CCS project. Therefore, developing a self-healing cement-based material with CO2-triggered response ability is the key technical direction to solve the long-term sealing problem of the cement sheath.

[0003] Traditional repair technologies rely on manual intervention or passive repair, and have problems such as lagging response, poor environmental adaptability, and inability to implement repair due to the narrow space in the wellbore. In recent years, the microbial-induced mineralization repair technology has attracted attention due to its characteristics of environmental friendliness and high compatibility between the mineralization product and the matrix. The microbial-induced mineralization technology naturally generates mineralization products through microbial metabolism, and has both environmental friendliness and high-efficiency self-healing ability, providing a sustainable solution for green building materials and carbon sequestration projects.

[0004] Existing microbial repair agents mostly rely on moisture or mechanical stress triggering (such as the release of microorganisms due to crack propagation and fragmentation), and cannot achieve precise activation for the specific scenario of CO2 leakage. Conventional repair agents are prone to prematurely release microorganisms and calcium sources in a non-CO2 environment, resulting in loss of activity. Summary of the Invention

[0005] Technical Problem: The present invention provides a preparation method for a well cement repair agent and a self-healing cement-based material. The preparation method of the present invention is simple, reliable, green and natural, and has good application prospects. In addition, the preparation method of the present invention can be extended to the self-healing protection of other acidic gas (such as H2S, SO2) leakage scenarios through the acid-responsive characteristics of chitosan, providing a general solution for engineering sealing problems in similar gas environments.

[0006] Technical Solution: A well cement repair agent of the present invention is composed of the following components by mass percentage: the mass percentage of the microbial powder is 20%-30%, the mass percentage of the nutrient is 8%-12%, the mass percentage of the chitosan is 45%-55%, and the mass percentage of the calcium source is 12%-18%.

[0007] Among them,

[0008] the microbial bacterial powder is selected from one or more of Bacillus mucilaginosus, Bacillus pasteurii, Bacillus subtilis, Bacillus alkalophilus, Bacillus sp., Thiobacillus, Micrococcus; the calcium source is one or more of calcium lactate, calcium acetate, calcium nitrate, calcium chloride, calcium phosphate, calcium formate.

[0009] The nutrient substances include at least two of yeast extract, peptone, urea, and glucose.

[0010] The chitosan has a molecular weight of 50 - 200 kDa and a deacetylation degree of 75% - 95%, and the chitosan can dissolve in an acidic environment with pH ≤ 6.

[0011] The calcium source is a soluble calcium salt, which is used to generate calcium carbonate deposits under the induction of microbial metabolism.

[0012] The preparation method of the well cement repair agent described in the present invention includes the following steps:

[0013] Step 1. Mixing and stirring: Mix the microbial bacterial powder, nutrient substances, calcium source and chitosan powder evenly, and then add acetic acid solution and stir to form a wet material;

[0014] Step 2. Extrusion granulation: Place the wet material in an extrusion granulator for extrusion granulation;

[0015] Step 3. Chemical curing: Immerse the particles obtained in Step 2 in sodium hydroxide solution and sodium tripolyphosphate solution in sequence, and dry after curing to obtain high-strength repair agent particles;

[0016] Step 4. Screening and curing: Screen the cured repair agent particles, control the particle size to be 1 - 3 mm, and cure for 48 - 72 hours under the conditions of temperature 20 - 30 °C and relative humidity 60% - 80%.

[0017] Among them,

[0018] In Step 1, the volume concentration of acetic acid is 1% - 5%, and the mass ratio of acetic acid solution to chitosan is 0.4 - 0.8:1.

[0019] In Step 3, the mass concentration of the sodium hydroxide solution is 2% - 6%, the mass concentration of the sodium tripolyphosphate solution is 6% - 15%, the curing time is 6 h - 48 h, the curing temperature is 15 - 25 °C, and the strength after curing ≥ 60 N.

[0020] The well cement self-repairing cementitious material using the well cement repair agent described in the present invention is composed of the well cement repair agent and a cementitious material, and the dosage of the well cement repair agent is 0.5% - 5% of the mass of the cementitious material.

[0021] The gelling material is a hydraulic inorganic gelling material, including one or more of portland cement, ordinary portland cement or oil well cement.

[0022] The mechanism of the repair agent's response to CO2 is as follows: A large number of amino (-NH2) groups in the chitosan molecule can undergo a protonation reaction with hydrogen ions (H + ), generating positively charged ammonium ions (-NH3 + ). This process transforms the chitosan molecule into a cationic polymer, thus significantly increasing its solubility in acidic solutions. It is shown that chitosan can dissolve in aqueous solutions with a pH of 4 - 6, while the pH of a CO2-saturated solution is lower than 5.5. After cracks occur in the oil well cement, the chitosan in the crack area dissolves and releases microorganisms for mineralization reactions to carry out repairs.

[0023] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages:

[0024] (1) By utilizing the solubility characteristics of chitosan, the present invention can trigger the repair agent under CO2 conditions, release microorganisms and carry out mineralization in the crack area, realizing the self-repair of cement-based materials under CO2 response;

[0025] (2) The present invention uses a curing method of first sodium hydroxide and then sodium tripolyphosphate, which improves the single-particle strength of the repair agent, prevents breakage during stirring and reduces the strength of the cement-based material;

[0026] (3) The preparation method of the present invention is simple, reliable, green and natural, and has good application prospects. In addition, through the acid-responsive characteristics of chitosan, the preparation method of the present invention can be extended to self-repair protection for leakage scenarios of other acidic gases (such as H2S, SO2), providing a general solution for engineering sealing problems in similar gas environments. Description of the Drawings

[0027] Figure 1 It is a schematic diagram of the mechanism of the repair agent particles' response to CO2,

[0028] Figure 2 It is a comparison chart of the compressive strength of the cement-based material doped with repair agent particles in Example 3 after curing for 7 days, 14 days, and 28 days,

[0029] Figure 3 It is a single-particle strength result chart of the repair agent in Example 4,

[0030] Figure 4 It is the test result of the ultrasonic wave propagation speed after repair of the cracked cement-based material with and without the repair agent in Example 5. Detailed Embodiments

[0031] The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

[0032] Example 1

[0033] (1) Mix chitosan: Bacillus subtilis: yeast extract powder: calcium acetate in a mass ratio of 6:2:1:1 to form a powder for standby;

[0034] (2) Prepare an acetic acid solution with a mass concentration of 2%, and spray the acetic acid solution into the mixer while stirring the mixed powder. The spraying amount is 40% of the mass of chitosan. After the spraying is completed, continue to stir for 3 minutes;

[0035] (3) Place the obtained wet material in an extrusion granulator for extrusion granulation to obtain repair agent particles;

[0036] (4) Put the repair agent particles into a sodium hydroxide solution with a mass fraction of 4% and a sodium tripolyphosphate solution with a mass fraction of 10% for solidification for 12 hours each;

[0037] (5) Place the solidified repair agent particles in a constant temperature and aerated environment at 20 °C for curing for 48 hours, and then sieve to obtain particles with a particle size of 1 mm - 1.5 mm.

[0038] Example 2

[0039] (1) Mix chitosan: Bacillus: yeast extract powder: calcium lactate in a mass ratio of 7:2:0.5:0.5 to form a powder for standby

[0040] (2) Prepare an acetic acid solution with a mass concentration of 1.5%, and spray the acetic acid solution into the mixer while stirring the mixed powder. The spraying amount is 40% of the mass of chitosan. After the spraying is completed, continue to stir for 3 minutes;

[0041] (3) Place the obtained wet material in an extrusion granulator for extrusion granulation to obtain repair agent particles;

[0042] (4) Put the repair agent particles into a sodium hydroxide solution with a mass fraction of 4% and a sodium tripolyphosphate solution with a mass fraction of 10% for solidification for 12 hours each;

[0043] (5) Place the solidified repair agent particles in a constant temperature and aerated environment at 20 °C for curing for 48 hours, and then sieve to obtain particles with a particle size of 1.5 mm - 2 mm.

[0044] (6) Take two repair agent particles of the same size and put them into two beakers. Add 100 mL of deionized water to each beaker, and adjust the pH of the water to 5 and 13 respectively. Observe the changes of the particles after 7 days;

[0045] (7) Experimental results show that the repair agent particles in water with a pH of 5 have completely dissolved, while only a small part of the repair agent particles in water with a pH of 13 have dissolved. The realization mechanism is as Figure 1 .

[0046] Example 3

[0047] (1) Mix chitosan, Thiobacillus, yeast extract powder, and calcium lactate in a mass ratio of 6:2:1:1 to make a powder for later use.

[0048] (2) Prepare an acetic acid solution with a mass concentration of 2%. While stirring the mixed powder, spray the acetic acid solution into the blender. The spraying amount is 40% of the mass of chitosan. After the spraying is completed, continue to stir for 3 minutes.

[0049] (3) Place the obtained wet material in an extrusion granulator for extrusion granulation to obtain repair agent particles.

[0050] (4) Put the repair agent particles into a sodium hydroxide solution with a mass fraction of 4% and a sodium tripolyphosphate solution with a mass fraction of 10% for solidification for 12 hours each.

[0051] (5) Place the solidified repair agent particles in a constant temperature and aerated environment at 20°C for curing for 48 hours, and then screen to obtain particles with a particle size of 1.5 mm - 2 mm.

[0052] (6) Weigh 3 groups of neat pastes. Each group consists of: 99 g of P 042.5 grade ordinary Portland cement, 1 g of repair agent particles, and 54.5 g of water. Mix the neat paste. Place the neat paste specimens under standard conditions for curing for 7 days, 14 days, and 28 days respectively, and then test the compressive strength and compare it with the control. The composition of the control group is: 100 g of ordinary Portland cement and 54 g of water. Figure 2 The results show that the repair agent particles have a promoting effect on the early compressive strength of cement, and the negative impact in the later stage is limited.

[0053] Example 4

[0054] (1) Mix chitosan, Bacillus polymyxa, yeast extract powder, and calcium formate in a mass ratio of 6.5:2.5:0.5:0.5 to make a powder for later use;

[0055] (2) Prepare an acetic acid solution with a mass concentration of 2%. While stirring the mixed powder, spray the acetic acid solution into the blender. The spraying amount is 45% of the mass of chitosan. After the spraying is completed, continue to stir for 3 minutes.

[0056] (3) Place the obtained wet material in an extrusion granulator for extrusion granulation to obtain repair agent particles.

[0057] (4) The small repair agent particles are successively placed in a sodium hydroxide solution with a mass fraction of 6% and a sodium tripolyphosphate solution with a mass fraction of 12% for solidification for 12 h each;

[0058] (5) The solidified repair agent particles are placed in a constant temperature and aerated environment at 20 °C for curing for 48 h, and then sieved to obtain particles with a particle size of 1.5 mm - 2 mm.

[0059] (6) Randomly select 50 repair agent particles, and use a digital display push-pull force gauge with a measuring range of 500 N and an accuracy of ±1 N to conduct strength tests on the repair agent particles. The test process is as follows: Adjust the digital display push-pull force gauge to the peak hold mode, place the repair agent particle in the exact middle of the sensor of the digital display push-pull force gauge, manually control the loading rate to be 1 N / S until the particle breaks and stop loading, and record the data. Zero the reading of the digital display push-pull force gauge before each test. The test results are as Figure 3 , and the average particle strength is obtained at 122 N. This strength is 22% higher than that of traditional bottom substrate repair agents, and it can prevent the repair agent from cracking during the mixing process of cement paste.

[0060] Example 5

[0061] (1) Mix chitosan: Paenibacillus polymyxa: yeast extract powder: calcium formate in a mass ratio of 7:2:0.5:0.5 to make a powder for standby;

[0062] (2) Prepare an acetic acid solution with a mass concentration of 4%, and spray the acetic acid solution into the mixer while stirring the mixed powder. The spraying amount is 50% of the mass of chitosan. After the spraying is completed, continue stirring for 3 min;

[0063] (3) Place the obtained wet material in an extrusion granulator for extrusion granulation to obtain repair agent particles;

[0064] (4) The repair agent particles are successively placed in a sodium hydroxide solution with a mass fraction of 4% and a sodium tripolyphosphate solution with a mass fraction of 9% for solidification for 12 h each;

[0065] (5) The solidified repair agent particles are placed in a constant temperature and aerated environment at 20 °C for curing for 48 h, and then sieved to obtain particles with a particle size of 2 mm - 3 mm.

[0066] (6) Weigh 99 g of P·O 42.5 grade ordinary Portland cement, 1 g of repair agent particles, and 40 g of water, mix the neat cement paste sample, place the neat cement paste sample under standard conditions for curing for 28 d, then make cracks, and set the crack width to 0.3 mm;

[0067] (7) Cure the cracked neat cement specimen in a carbonation chamber with a temperature of 20 °C, a relative humidity of 80%, and a CO2 concentration of 20%. When the curing time is 7 d, 14 d, and 28 d, measure the ultrasonic propagation velocity across the cracks of the cracked cement-based material specimens. The variation of the ultrasonic propagation velocity with the repair time is as shown in Figure 4 . It can be seen that within the curing periods of 7 d, 14 d, and 28 d, the ultrasonic velocity of the cement-based material incorporated with chitosan repair agent is much higher than that of the specimen without the repair agent.

Claims

1. A cement repair agent, characterized in that: The repair agent consists of the following components by mass percentage: The mass percentage of microbial powder is: 20%-30%, The mass percentage of nutrients is: 8%-12%, The mass percentage of chitosan is: 45%-55%, The mass percentage of the calcium source is: 12%-18%.

2. The cement repair agent according to claim 1, characterized in that: The microbial powder is selected from one or more of Bacillus mucilaginosus, Bacillus pasteurianus, Bacillus subtilis, Bacillus alkaliphilus, Bacillus, Thiobacillus, and Micrococcus; the calcium source is one or more of calcium lactate, calcium acetate, calcium nitrate, calcium chloride, calcium phosphate, and calcium formate.

3. The cement repairing agent according to claim 1, characterized in that: The nutrients include at least two of yeast extract, peptone, urea and glucose.

4. The cement repair agent according to claim 1, characterized in that: The molecular weight of the chitosan is 50-200 kDa, the deacetylation degree is 75%-95%, and the chitosan can be dissolved in an acidic environment with a pH value of ≤6.

5. The cement repair agent according to claim 1, characterized in that: The calcium source is a soluble calcium salt, which is used to generate calcium carbonate deposits under the induction of microbial metabolism.

6. A method for preparing the cement repair agent according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1. Mixing and stirring: evenly mix the microbial powder, nutrients, calcium source and chitosan powder, add acetic acid solution and stir to form a wet material; Step 2. extrusion granulation: placing the wet material in an extrusion granulator for extrusion granulation; Step 3. Chemical curing: The particles obtained in step 2 are immersed in a sodium hydroxide solution and a sodium tripolyphosphate solution in sequence, and then dried after curing to obtain high-strength repair agent particles; Step 4. Screening and curing: Screen the cured repair agent particles to control the particle size to 1-3 mm, and cure at a temperature of 20-30° C. and a relative humidity of 60%-80% for 48-72 hours.

7. The method for preparing the cement repairing agent according to claim 6, characterized in that: In step 1, the volume concentration of acetic acid is 1%-5%, and the mass ratio of acetic acid solution to chitosan is 0.4-0.8:

1.

8. The method for preparing the cement repairing agent according to claim 6, characterized in that: In step 3, the mass concentration of the sodium hydroxide solution is 2%-6%, the mass concentration of the sodium tripolyphosphate solution is 6%-15%, the curing time is 6h-48h, the curing temperature is 15-25°C, and the strength after curing is ≥60N.

9. A self-repairing cement-based material using the cement repair agent according to any one of claims 1 to 5, characterized in that: The cementing self-repairing cement-based material is formed by mixing the cementing cement repairing agent and a gelling material, and the addition amount of the cementing cement repairing agent is 0.5%-5% of the mass of the gelling material.

10. The self-repairing cement-based material for well cementing according to claim 9, characterized in that: The cementitious material is a hydraulic inorganic cementitious material, including one or more of silicate cement, ordinary silicate cement or oil well cement.

Images