A suspended early strength agent for low density cement slurry

Abstract

This invention discloses a suspension early-strength agent for low-density cement slurry, comprising modified nanoporous molecular sieve powder, nano-mesoporous clay, modified biopolysaccharide copolymer, and ultrafine silica powder. The modified nanoporous molecular sieve is prepared by exchanging metal cations in a mixed solution of lithium nitrate, lithium chloride, and calcium formate with cations in MCM-48 mesoporous molecular sieve using a template agent exchange method, followed by adsorption modification with a mixture of triethanolamine and triisoethanolamine. The modified biopolysaccharide copolymer is prepared by graft copolymerization of p-styrene sulfonic acid and acrylonitrile with styrene-based rubber. This suspension early-strength agent for low-density cement slurry exhibits stable performance at high temperatures, with a temperature resistance up to 150℃. Its cement stone compressive strength is ≥17MPa / 24h / 150℃, and its cement stone top compressive strength is ≥7MPa / 48h / 50℃. In practical applications, this early-strength agent requires significantly less dosage compared to conventionally used suspending agents, and the system exhibits excellent suspension stability and rheological properties, as well as good compatibility with other admixtures.

Description

Technical Field

[0001] This invention relates to the field of oilfield cement slurry technology, and in particular to a suspension early-strength agent for low-density cement slurry. Background Technology

[0002] With the deepening of exploration and development, there is an increasing number of well cementing operations in formations prone to leakage and full-well sealing, leading to higher requirements for the settling stability and top strength development of low-density cement slurries at high temperatures. Low-density cement slurries often require the addition of weight-reducing materials to partially replace oil well cement or increase the liquid / solid ratio to lower the slurry density. These materials are mostly inert and lack reactivity, resulting in lower cement stone strength and increased porosity after curing, especially for long cementing sections where top strength development is slow. Simply reducing the water-cement ratio to increase cement stone strength deteriorates the slurry's rheological properties, making construction difficult. Schlumberger pioneered the introduction of particle size distribution theory into the design of unconventional density cement slurries. By grading materials of different particle sizes to achieve close packing, they reduced free water content while maintaining the slurry's rheological properties, developing LiteCREAT cement slurry. This results in low-density cement slurries achieving performance comparable to conventional density cement slurries in many aspects, including compressive strength, stability, and corrosion resistance. Major domestic oilfield service companies have also conducted related research. For example, CNPC Bohang Company has developed the BXE-600S and BXE-680S series of light-reducing and reinforcing materials based on the close packing theory. Ningxia Yiyun Company has developed the NXYN series of light-reducing agents. In addition, China Steel Maanshan and Shenglait have developed a series of high-strength glass microspheres as light-reducing agents. However, in the process of using these materials, common problems such as slow low-temperature strength development and poor high-temperature sedimentation stability have not been completely solved. Summary of the Invention

[0003] The purpose of this invention is to provide a suspension early strength agent for low-density cement slurry that overcomes the problems of slow low-temperature strength development and poor high-temperature settling stability of current low-density cement slurry.

[0004] Therefore, the technical solution of the present invention is as follows:

[0005] A low-density cement slurry suspension early-strength agent comprises, by weight, 30-60 parts of modified nanoporous molecular sieve powder, 10-20 parts of nano-mesoporous clay, 10-20 parts of modified biopolysaccharide copolymer, and 20-30 parts of ultrafine silica powder; wherein the modified nanoporous molecular sieve is prepared by template agent exchange, in which metal cations in a mixed solution of lithium nitrate, lithium chloride, and calcium formate are exchanged with cationic surfactants in MCM-48 mesoporous molecular sieve, and then adsorbed and modified by a mixture of triethanolamine and triisoethanolamine; the modified biopolysaccharide copolymer is prepared by graft copolymerization of p-styrene sulfonic acid and acrylonitrile with styrene-based rubber.

[0006] Preferably, in the preparation process of the modified nanoporous molecular sieve, the weight ratio of lithium nitrate, lithium chloride and calcium formate is 1:1:0.5; and the weight ratio of triethanolamine and triisoethanolamine is 1:1.

[0007] Preferably, the particle size of the modified nanoporous molecular sieve powder is 0.05–0.3 μm.

[0008] Preferably, the modified nanoporous molecular sieve is prepared by the following method:

[0009] Exchange modification: Lithium nitrate, lithium chloride, and calcium formate in a weight ratio of 1:1:0.5 were dissolved in water to prepare a 0.5 wt.% mixed salt solution; a mixing system was prepared by adding 10 parts by weight of MCM-48 mesoporous molecular sieve powder to every 100 parts by weight of the mixed salt solution. After stirring for 2-4 hours, the mixture was filtered, and the molecular sieve powder was calcined at 550℃ for 8 hours to obtain exchange-modified molecular sieve powder.

[0010] Adsorption modification: 50 parts by weight of exchange-modified molecular sieve powder were added to 1000 parts by weight of ethanol. Under stirring conditions, 0.5 parts by weight of a mixture of triethanolamine and triisoethanol in a weight ratio of 1:1 were added, and stirring was continued for at least 2 hours. After filtration and drying, modified nanoporous molecular sieve powder was obtained.

[0011] In low-density cement paste suspension early strength agents, modified nano-mesoporous MCM-48 can increase the viscosity of the system by utilizing its suspension effect; at the same time, calcium, lithium ions and triethanolamine are uniformly dispersed on the surface of the mesoporous nanomaterial pores, increasing its active sites and improving the early strength of cement paste.

[0012] Preferably, the particle size of nano-metakaolin is 80–150 nm. Nano-metakaolin is a highly reactive artificial volcanic ash material that can react with Ca(OH)₂ and water to produce hydration products similar to those in cement. In low-density cement paste, it can not only enhance the compressive, flexural, and splitting tensile strength of cement stone, but also increase its toughness.

[0013] Preferably, the particle size of the ultrafine silica is 0.1–2 μm. The role of ultrafine silica powder in the suspending early-strength agent for low-density cement paste is to fill the tiny gaps in the cement paste. Furthermore, its small particle size can play a role in secondary activating hydration.

[0014] Preferably, in the modified biopolysaccharide copolymer, the weight ratio of styrene sulfonic acid and acrylonitrile is (5-10):(1-2):(2-3).

[0015] Preferably, the modified biopolysaccharide is prepared by the following method:

[0016] S1. Under stirring conditions of 300-500 r / min, slowly add the warm wheel glue to 200-400 parts by weight of water to fully hydrate the warm wheel glue;

[0017] S2. When the styrene-based gel is in a colloidal state in water, add styrene-sulfonic acid and acrylonitrile, and stir until completely dissolved. Then, add 20-25 wt.% NaOH aqueous solution dropwise to adjust the pH of the mixed solution to 5-5.5.

[0018] S3. Add ammonium persulfate as an initiator to the mixed solution to initiate a free radical polymerization reaction. After reacting at room temperature for 2 hours, dry the resulting polymer, grind it into powder, and set it aside for later use.

[0019] The modified biopolysaccharide further enhances the suspension stability of cement slurry at high temperatures in low-density cement slurry, thereby reducing the thermal dilution effect of cement stone at high temperatures.

[0020] The low-density cement slurry suspension early strength agent is characterized by being composed of a variety of modified nano-mesoporous MCM-48, nano-meta-kaolin, modified biopolysaccharide copolymer, and ultrafine silica powder, which have a suspension effect. This gives it the advantages of good suspension performance at high temperatures and rapid early strength development at low temperatures. At the same time, the components are added in the form of nano- to micron-sized particles to form a particle size distribution, which can further improve the non-permeability of the cement slurry.

[0021] Compared with existing technologies, this low-density cement slurry suspension early-strength agent is prepared using a variety of hydrophilic materials, resulting in good dispersibility in the aqueous phase and a system density of 1.10–1.60 g / cm³. 3 The internal adjustment is verified. Experiments have shown that this early strength agent has stable performance at high temperatures, with a temperature resistance of up to 150℃. The compressive strength of its cement stone at 150℃ for 24 hours is ≥17MPa, and the top compressive strength of the cement stone at 50℃ for 48 hours is ≥7MPa / 48h. In practical applications, the dosage of this early strength agent is greatly reduced compared to conventionally used suspending agents. The suspension stability and rheological properties of the system are excellent, and it has good compatibility with other admixtures. Detailed Implementation

[0022] The present invention will be further described below with reference to specific embodiments, but the following embodiments are not intended to limit the present invention in any way. In the following embodiments and comparative examples, the amount of each component added is specifically in parts by weight.

[0023] Example 1

[0024] A low-density cement paste suspension early-strength agent is prepared by the following method:

[0025] Add 30 parts of modified nano-mesoporous molecular sieve powder to a mixer, turn on the agitator, and then slowly add 20 parts of nano-kaolin, 20 parts of modified biopolysaccharide copolymer, and 30 parts by weight of ultrafine silica powder in sequence. Then seal the mixing chamber, continue mixing for 1 hour, and collect the material to obtain a suspension early strength agent for low-density cement slurry.

[0026] Example 2

[0027] A low-density cement paste suspension early-strength agent is prepared by the following method:

[0028] 40 parts of modified nano-mesoporous molecular sieve powder were added to a mixer, the agitator was turned on, and then 20 parts of nano-kaolin, 15 parts of modified biopolysaccharide copolymer and 25 parts of ultrafine silica powder were added slowly in sequence. The mixing chamber was then closed, and the mixture was stirred for 1 hour before being collected to obtain a suspension early strength agent for low-density cement slurry.

[0029] Example 3

[0030] A low-density cement paste suspension early-strength agent is prepared by the following method:

[0031] Add 50 parts of modified nano-mesoporous molecular sieve powder to a mixer, turn on the agitator, and then slowly add 15 parts of nano-kaolin, 15 parts of modified biopolysaccharide copolymer, and 20 parts by weight of ultrafine silica powder in sequence. Then close the mixing chamber, continue mixing for 1 hour, and collect the material to obtain a suspension early strength agent for low-density cement slurry.

[0032] Example 4

[0033] A low-density cement paste suspension early-strength agent is prepared by the following method:

[0034] Add 60 parts of modified nano-mesoporous molecular sieve powder to a mixer, turn on the agitator, and then slowly add 10 parts of nano-kaolin, 10 parts of modified biopolysaccharide copolymer, and 20 parts by weight of ultrafine silica powder in sequence. Then seal the mixing chamber, continue mixing for 1 hour, and collect the material to obtain a suspension early strength agent for low-density cement slurry.

[0035] Comparative Example 1

[0036] A suspending agent prepared by the following method:

[0037] Add 30 parts of microsilica powder to the mixer, turn on the agitator, and then slowly add 10 parts of nano-kaolin, 10 parts of modified biopolysaccharide copolymer, and 20 parts by weight of ultrafine silica powder in sequence. Then close the mixing chamber, continue stirring for 1 hour, and collect the material to obtain the suspension.

[0038] The difference between Comparative Example 1 and Example 1 is that the modified nanoporous molecular sieve powder was replaced with microsilica powder having the same particle size range.

[0039] Comparative Example 2

[0040] A low-density cement slurry suspending agent is prepared by the following method:

[0041] Add 30 parts of modified nano-mesoporous molecular sieve powder to a mixer, turn on the agitator, and then slowly add 20 parts of nano-meta-kaolin and 30 parts by weight of ultrafine silica powder in sequence. Then close the mixing chamber, continue stirring for 1 hour, and collect the material to obtain a suspension.

[0042] The difference between Comparative Example 2 and Example 1 is that no modified biopolysaccharides were added.

[0043] In Examples 1-4 and Comparative Examples 1-2 above, nano-metakaolin, ultrafine silica powder, and microsilica powder were all purchased from commercially available products. The nano-metakaolin had a particle size of 80-150 nm; the ultrafine silica had a particle size of 0.1-2 μm; and the modified nanoporous molecular sieve powder had a particle size of 0.05-0.3 μm. The modified nanoporous MCM-48 powder and modified biopolysaccharide were prepared in the laboratory, and the raw materials used to prepare the modified nanoporous MCM-48 powder and modified biopolysaccharide were all purchased directly from commercially available products.

[0044] Specifically, the modified nanoporous MCM-48 is prepared using the following method:

[0045] Step 1: At 25–30°C, mix 10 parts by weight of 28 wt.% ammonia, 35 parts by weight of ethanol, and 100 parts by weight of deionized water until homogeneous, then add 0.5 parts by weight of cetyl ammonium bromide (CTA). + Add 3.5 parts by weight of surfactant F127, and after it is fully dissolved, add 2 parts by weight of tetraethyl orthosilicate, stir at 1000 r / min for at least 20 min, let stand for 24 h, and then filter, wash and dry to obtain MCM-48 mesoporous molecular sieve.

[0046] Step 2: Dissolve lithium nitrate, lithium chloride, and calcium formate in water at a weight ratio of 1:1:0.5 to prepare a 0.5 wt.% mixed salt solution; add 10 parts by weight of MCM-48 mesoporous molecular sieve powder to 100 parts by weight of the mixed salt solution and stir for at least 2 hours. Using a template exchange method, the metal cations in the mixed salt solution exchange with CTA+ and are adsorbed into the molecular sieve pores; after filtration, calcine the molecular sieve powder at 550℃ for 8 hours to obtain exchange-modified molecular sieve powder M-MCM-48 (M represents metal ion);

[0047] Step 3: Add 50 parts by weight of M-MCM-48 to 1000 parts by weight of ethanol solution, then add 0.5 parts by weight of a mixture of triethanolamine and triisoethanol in a weight ratio of 1:1 and stir for 2 hours; after filtration and drying, modified nanoporous molecular sieve powder is obtained.

[0048] Specifically, the modified biopolysaccharide is prepared using the following method:

[0049] Step 1: Under stirring conditions of 300-500 r / min, slowly add 5-10 parts by weight of warm wheel glue to 200-400 parts by weight of water;

[0050] Step 2: When the styrene sulfonic acid is fully hydrated and becomes colloidal, add 1-2 parts by weight of styrene sulfonic acid and 2-3 parts by weight of acrylonitrile. Continue stirring until they are completely dissolved, then add 20-25 wt.% NaOH solution to adjust the pH of the mixed solution to 5-5.5.

[0051] Step 3: Add 0.2 to 0.5 parts by weight of ammonium persulfate to the mixed solution as an initiator to initiate the free radical polymerization reaction, and react at room temperature for 2 hours. Dry the resulting polymer, grind it into powder, and set it aside for later use.

[0052] Performance testing:

[0053] The suspending agents prepared in Examples 1-4 and Comparative Examples 1 and 2 were added to low-density cement slurry to test their various performance characteristics. The performance tests were conducted in accordance with GB / T 19139-2012 Test Methods for Oil Well Cement.

[0054] In the test, the specific formula of the low-density cement slurry was: 100 parts by weight of Grade G high sulfur-resistant silicate oil well cement, 20 parts by weight of suspending agent, 25 parts by weight of silica powder, 40 parts by weight of hollow glass microspheres Y12000, and 3... The mixture contains, by weight, an expanding agent, 5 parts by weight, a water loss reducing agent, 0.5 parts by weight, a dispersant, 0.03 parts by weight, an antifoaming agent, 2 parts by weight, a retarder, and 100 parts by weight of distilled water; wherein, the suspending agent is the suspending agent prepared in Examples 1-4 and Comparative Examples 1-2 in sequence; the hollow glass microspheres Y12000 are hollow glass microspheres produced by Sinosteel Group Maanshan Mining Institute New Material Technology Co., Ltd., with an average density of 0.60±0.03 g / cm3 and an average particle size D50 of 45 μm; the expanding agent is the lattice expanding agent BH-P801S produced by China National Petroleum Corporation Bohai Drilling Company, the water loss reducing agent is the AMPS-type water loss reducing agent BH-F202S produced by China National Petroleum Corporation Bohai Drilling Company, the antifoaming agent is the phosphate ester BZXP-1 produced by China National Petroleum Corporation Bohai Drilling Company, and the retarder is the AMPS-type retarder BH-R101L produced by China National Petroleum Corporation Bohai Drilling Company. The density of the low-density cement slurry prepared using the above formula is 1.3 g / cm³. 3 .

[0055] The specific test results are shown in Table 1 below.

[0056] Table 1:

[0057]

[0058] As shown in Table 1 above, the low-density cement slurries prepared using the suspending early-strength agents in Examples 1-4 all exhibited a flowability >20 cm, a settling stability with a density difference ≤0.02 g / cm³, almost 0% free liquid, and a water loss control performance below 50 mL. These characteristics indicate good rheological properties of the cement, resulting in a stable slurry with minimal water loss. The cement stone formed by the solidification of this cement slurry showed a compressive strength higher than 16 MPa after 24 hours, and a top strength ≥7 MPa after 48 hours at 50°C, demonstrating excellent compressive strength. Furthermore, the permeability of the cement stone was <0.02 mD. Example 2 is the preferred embodiment of this application, and the low-density cement slurry prepared using Example 2 exhibits the best overall performance.

[0059] In Comparative Example 1, the replacement of modified nanoporous MCM-48 with a common suspending agent resulted in a deterioration in the suspension stability of the prepared low-density cement slurry at high temperatures. Specifically, the density difference after standing exceeded six times, the water loss of the cement slurry was >50mL, and the free liquid content was not zero. The compressive strength of the cement stone formed after solidification also decreased significantly. Similarly, Comparative Example 2, by not adding modified biopolysaccharides, also experienced a deterioration in its suspension stability at high temperatures. Specifically, the density difference after standing exceeded four times, the water loss of the cement slurry was >50mL, and the free liquid index was even worse. The compressive strength of the cement stone formed after solidification also decreased further.

Claims

1. A suspension accelerator for low-density cement slurry, characterized in that, The product comprises 30-60 parts by weight of modified nanoporous molecular sieve powder, 10-20 parts of nano-mesoporous clay, 10-20 parts of modified biopolysaccharide copolymer, and 20-30 parts of ultrafine silica powder. The modified nanoporous molecular sieve is prepared by exchanging metal cations in a mixed solution of lithium nitrate, lithium chloride, and calcium formate with cationic surfactants in MCM-48 mesoporous molecular sieve using a template agent exchange method, followed by adsorption modification with a mixture of triethanolamine and triisoethanolamine. The modified biopolysaccharide copolymer is prepared by graft copolymerization of p-styrene sulfonic acid and acrylonitrile with styrene-based ...

2. The suspending early-strength agent for low-density cement slurry according to claim 1, characterized in that, In the preparation of modified nanoporous molecular sieves, the weight ratio of lithium nitrate, lithium chloride and calcium formate is 1:1:0.5; the weight ratio of triethanolamine and triisoethanolamine is 1:

1.

3. The suspending early-strength agent for low-density cement slurry according to claim 1, characterized in that, The particle size of the modified nanoporous molecular sieve powder is 0.05–0.3 μm.

4. The suspending early-strength agent for low-density cement slurry according to claim 1, characterized in that, Modified nanoporous molecular sieves were prepared using the following method: Exchange modification: Lithium nitrate, lithium chloride and calcium formate in a weight ratio of 1:1:0.5 were dissolved in water to prepare a 0.5 wt.% mixed salt solution; a mixing system was prepared by adding 10 parts by weight of MCM-48 mesoporous molecular sieve powder to every 100 parts by weight of the mixed salt solution. After stirring for 2-4 hours, the mixture was filtered and the molecular sieve powder was calcined at 550℃ for 8 hours to obtain exchange-modified molecular sieve powder. Adsorption modification: 50 parts by weight of exchange-modified molecular sieve powder were added to 1000 parts by weight of ethanol. Under stirring conditions, 0.5 parts by weight of a mixture of triethanolamine and triisoethanol in a weight ratio of 1:1 were added, and stirring was continued for at least 2 hours. After filtration and drying, modified nanoporous molecular sieve powder was obtained.

5. The suspending early-strength agent for low-density cement slurry according to claim 1, characterized in that, The particle size of nano-metakaolin is 80–150 nm.

6. The suspending early-strength agent for low-density cement slurry according to claim 1, characterized in that, The particle size of ultrafine silica is 0.1–2 μm.

7. The suspending early-strength agent for low-density cement slurry according to claim 1, characterized in that, The weight ratio of warm rubber, styrene sulfonic acid and acrylonitrile is (5-10):(1-2):(2-3).

8. The suspending early-strength agent for low-density cement slurry according to claim 1, characterized in that, Modified biopolysaccharides were prepared using the following method: S1. Under stirring conditions of 300-500 r / min, slowly add the warm wheel glue to 200-400 parts by weight of water to fully hydrate the warm wheel glue; S2. When the styrene-based gel is in a colloidal state in water, add styrene-sulfonic acid and acrylonitrile, and stir until completely dissolved. Then, add 20-25 wt.% NaOH aqueous solution dropwise to adjust the pH of the mixed solution to 5-5.

5. S3. Add ammonium persulfate as an initiator to the mixed solution to initiate a free radical polymerization reaction. After reacting at room temperature for 2 hours, dry the resulting polymer, grind it into powder, and set it aside for later use.

Images