Nanometer crystal nucleus oil well cement under low-temperature curing environment and preparation method thereof

Abstract

The invention discloses nano crystal nucleus oil well cement in a low-temperature curing environment and a preparation method. The nano crystal nucleus oil well cement is prepared from the following components in parts by weight: 90 to 110 parts of oil well cement, 42 to 46 parts of water, 0.8 to 1.2 parts of dispersing agent, 0.08 to 0.12 part of water reducing agent and 1 to 5 parts of C-S-H crystal nucleus type hydration accelerant, wherein the water-binder ratio is 0.41 to 0.47. The preparation method comprises the following steps: S1, pouring the cement, the water and the C-S-H hydration accelerant in percentage by weight into a planetary cement mortar stirrer; s2, after stirring is completed, forming is conducted immediately, a 40 * 40 * 160 mm mold is fixed to a compaction table, and a cementing material is put into the mold in two times; compacting and molding on a cement mortar vibrating table, slicking the surface, and covering the surface with a preservative film to prevent water from evaporating; and S3, putting into a standard curing chamber, standing for 24 hours, demolding, and putting into a corresponding curing chamber. Compared with the traditional oil well cement, the oil well cement provided by the invention has remarkable effects in rheological property, filtrate loss reduction performance, mechanical property and salt resistance of cured set cement and the like.

Description

Technical Field

[0001] The present invention relates to the field of oil well cement, and more specifically to a nanocrystalline core oil well cement and a preparation method for use in a low-temperature curing environment, particularly a technology for optimizing the proportion of oil well cement, which is used to improve the early strength, flow properties, and stability of cement in a low-temperature curing environment, thereby ensuring the high performance and reliability of cement in oil well engineering. Background Art

[0002] Oil well cementing is the process of injecting oil well cement slurry into the annulus between the casing and the rock formation exposed below the wellbore. The main functions of the cementing process include sealing to prevent fluid communication between different areas, providing structural support for the casing, and protecting the casing from corrosive fluids. During the cementing process, low formation temperatures limit the early strength development of the cement stone, increasing construction costs and making it difficult to ensure project quality and operational safety. High-performance admixtures are essential for improving the performance of oil well cement, increasing cementing efficiency, and thus maximizing the production potential of the oil well. Oil well cement slurry properties include rheology, free fluid, and water loss. The cement stone after solidification also has performance requirements such as mechanical strength and corrosion resistance.

[0003] Oil well cement, a crucial material in oil well construction, serves to isolate and prevent wellbore leakage, while also protecting oil and gas formations. While conventional oil well cement mixes meet basic requirements, they often suffer from insufficient early strength and high cracking rates when exposed to harsh environments such as high temperature, high pressure, and corrosive gases. Therefore, there is an urgent need to develop an optimized cement mix to meet the demands of complex oil well environments. Summary of the Invention

[0004] The present invention aims to provide an early-strength oil well cement with an optimized mix ratio and preparation method. By introducing a nano-CSH crystal nucleus-type hydration accelerator and optimizing the cement mix ratio, the cement can significantly improve its early strength, enhance its anti-permeability and fluidity under low-temperature curing conditions (8-20°C), and solve the problem of insufficient performance of traditional oil well cement in extreme downhole environments.

[0005] The technical solutions of the present invention are as follows:

[0006] On one hand, the present invention provides a nanocrystalline core oil well cement for low-temperature curing environment, which comprises the following components in parts by weight: 90-110 parts of oil well cement, 42-46 parts of water, 0.8-1.2 parts of a dispersant, 0.08-0.12 parts of a water reducer, 1-5 parts of a CSH crystal core type hydration accelerator, and a water-binder ratio of 0.41-0.47.

[0007] Furthermore, the composition is as follows: 100 parts of oil well cement, 44 parts of water, 1 part of dispersant, 0.1 part of water reducer, 1-5 parts of CSH crystal nucleus type hydration accelerator, and a water-binder ratio of 0.44, calculated by weight.

[0008] Furthermore, the CSH crystal nucleus type hydration accelerator serves as an auxiliary material for improving the early strength of concrete by accelerating the formation of early CSH gel.

[0009] Furthermore, the main chemical components of the oil well cement are: MgO 2.68%, SO3 2.01%, C3S 55.33%, C3A 2.02%, C4AF 14.58%, and Na2Oeq 0.66%.

[0010] Another aspect of the present invention provides a method for preparing nanocrystalline core oil well cement under a low temperature curing environment, comprising the following steps:

[0011] S1. Pour the above weight percentages of cement, water, and CSH hydration accelerator into a planetary cement mortar mixer, and set the motor stirring mode to low speed for 30 seconds, high speed for 30 seconds, stop for 90 seconds, and high speed for 60 seconds;

[0012] S2. Immediately after the mixing is completed, the mold is formed by fixing a 40×40×160 mm mold on a vibration table and loading the cementitious material into the mold in two batches; the mold is vibrated on a cement mortar vibration table to form the mold, the surface is scraped flat, and the surface is covered with plastic wrap to prevent moisture evaporation;

[0013] S3. Place it in a standard curing room and let it stand for 24 hours, then remove the mold and place it in the corresponding curing room.

[0014] The curing temperatures in the curing rooms are 8° C., 14° C., and 20° C., respectively, and the humidity is greater than 95%.

[0015] Technical effects and advantages of the present invention:

[0016] The crystal nucleus hydration accelerator designed and developed by this patent significantly improves the early strength performance of oil well cement under low temperature conditions. By compounding the crystal nucleus hydration accelerator with a dispersant and a water reducer and then applying it to oil well cement, and studying the various properties of oil well cement slurry with different contents of the crystal nucleus hydration accelerator, it was found that compared with traditional oil well cement, it has achieved significant results in rheological properties, fluid loss reduction performance, and mechanical properties and salt resistance of the cement stone after curing. Specifically:

[0017] 1) Improved Early Strength: The early-strength oil-well cement of this invention exhibits high early strength under low-temperature curing conditions. Under curing conditions of 8°C, 14°C, and 20°C, the 24-hour compressive strength of the cement incorporating 5 parts of a nucleus-type hydration accelerator reached 2.4 MPa, 6.2 MPa, and 15.2 MPa, respectively. Compared to the 24-hour compressive strengths of blank oil-well cement (0.1 MPa, 0.6 MPa, and 1.8 MPa), the early strength is significantly superior to that of conventional oil-well cement.

[0018] 2) Improved stability: The present invention significantly improves the stability of oil well cement in oil wells. Under environmental curing at 8°C, 14°C, and 20°C, the free liquid content of oil well cement added with 5 parts of crystal nucleus type hydration accelerator was 0, 0.1ml, and 0.2ml, respectively, and the API water loss was 17.2ml, 37.4ml, and 50ml, respectively; the free liquid content of the blank sample was 9.3ml, 10.4ml, and 14.8ml, respectively, and the API water loss was 286.2ml, 347ml, and 470ml, respectively. The early strength oil well cement of the present invention effectively reduces the free liquid content and water loss of the oil well cement slurry, which is lower than 5.90% of G-grade oil well cement, and meets the requirements of GB / T10238-2015 "Oil Well Cement Code Specification" for oil well cementing.

[0019] 3) Improved Workability: When constructing concrete in low-temperature environments, using early-strength oil-well cement mixed with a crystal nucleus-type hydration accelerator significantly enhances ease of construction. Compared to traditional oil-well cement, early-strength oil-well cement concrete is virtually identical in preparation, transportation, and placement, making it significantly easier to work with. Furthermore, it effectively addresses the issues of prolonged concrete setting time and slow strength growth in low-temperature conditions, significantly enhancing construction flexibility and efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The fluidity results of cement slurry added with crystal nucleus type hydration accelerator under low temperature curing environment in Examples 1 to 4 are shown;

[0021] Figure 2 The results of free liquid content in cement slurry added with crystal nucleus type hydration accelerator under low temperature curing environment in Examples 1 to 4 are shown;

[0022] Figure 3 The API water loss results of cement slurries added with crystal nucleus type hydration accelerators under low temperature curing conditions in Examples 1 to 4 are shown;

[0023] Figure 4 The graph shows the flexural strength results of cement slurry added with crystal nucleus type hydration accelerator under low temperature curing environment in Examples 1 to 4;

[0024] Figure 5This is a graph showing the compressive strength results of cement slurry added with a crystal nucleus type hydration accelerator under low temperature curing environment in Examples 1 to 4. DETAILED DESCRIPTION

[0025] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0026] Example 1: Take 800g of G-grade oil well cement, 8g of SD-600P-S dispersant, 0.8g of FA-367 water reducer, and the water-binder ratio is 0.44.

[0027] Preparation of the blank control group oil well cement comprises the following steps:

[0028] 1) Weigh the above ingredients in parts by weight and put them into a blender, stirring for 1 minute;

[0029] 2) Add sand and stone to the concrete mixer and continue stirring for about 2 minutes; thus, the early-strength oil well cement under low-temperature curing environment is prepared.

[0030] 3) After standing at room temperature for one day, demould and place in a low temperature environment (temperature 8, 14, 20 ° C, humidity > 95%) for curing for 24 hours and 48 hours respectively.

[0031] Example 2: 800 g of G-grade oil well cement, 8 g of SD-600P-S dispersant, 0.8 g of FA-367 water reducer, and 1% of a crystal nucleus type hydration accelerator (particle size 50-200 nm) were added, with a water-binder ratio of 0.44.

[0032] The preparation of oil well cement with optimized ratio includes the following steps:

[0033] 1) Weigh the above ingredients in parts by weight and put them into a blender, stirring for 1 minute;

[0034] 2) Continue adding sand and stone to the concrete mixer and continue mixing for about 2 minutes;

[0035] 3) Add water, water reducing agent and nano CSH crystal nuclei into the above mixture and stir evenly for 2 minutes to prepare early strength oil well cement under low temperature curing environment.

[0036] 4) After standing at room temperature for one day, remove the mold and place it in a low temperature environment (temperature 8, 14, 20℃, humidity > 95%) for curing for 24h and 48h respectively.

[0037] Example 3: 800 g of G-grade oil well cement, 8 g of SD-600P-S dispersant, 0.8 g of FA-367 water reducer, and 3% of a crystal nucleus type hydration accelerator (particle size 50-200 nm) were added, with a water-binder ratio of 0.44.

[0038] Preparation of early-strength oil well cement under low-temperature curing environment is the same as in Example 2.

[0039] Example 4: 800 g of G-grade oil well cement, 8 g of SD-600P-S dispersant, 0.8 g of FA-367 water reducer, and 5% of a crystal nucleus type hydration accelerator (particle size 50-200 nm) were added, with a water-binder ratio of 0.44.

[0040] Preparation of early-strength oil well cement under low-temperature curing environment is the same as in Example 2.

[0041] At 8°C, the fluidity of a blank oil-well cement slurry was 197 mm. The fluidities of slurries containing 1, 3, and 5 parts of a nucleus-type hydration accelerator were 202 mm, 211 mm, and 224 mm, respectively, representing increases of 5 mm, 14 mm, and 27 mm compared to the blank sample. The effects of hydration accelerators on the fluidity of oil-well cement also exhibited similar patterns at 14°C and 20°C.

[0042] At 8°C, 14°C, and 20°C, the free liquid content of the blank sample was 9.3ml, 10.4ml, and 14.8ml, respectively. When the crystal nucleus hydration accelerator was added at a dosage of 1 part, the free liquid content of the oil-well cement slurry was 5.7ml, 7.9ml, and 8.7ml, respectively. When added at a dosage of 3 parts, the free liquid content was 0.1ml, 0.2ml, and 0.3ml, respectively. When added at a dosage of 5 parts, the free liquid content was 0, 0.1ml, and 0.2ml, respectively. At low temperatures, the addition of the crystal nucleus hydration accelerator reduced the free liquid content of the oil-well cement slurry, and the effect became more pronounced with increasing dosage. Therefore, the crystal nucleus hydration accelerator can bind free water, effectively controlling the settling of cement particles and the precipitation of free liquid, thereby maintaining the stability of the oil-well cement slurry.

[0043] At 8°C, the API water loss of the blank sample was 286.2 ml. When the crystal nucleus hydration accelerator was added at 3 parts per million, the API water loss of the cement paste was 39.0 ml, an 86.4% decrease compared to the blank sample. When the hydration accelerator was added at 5 parts per million, the API water loss of the cement paste was only 17.2 ml, a 94.0% decrease compared to the blank sample. Similar patterns were observed in the effects of the crystal nucleus hydration accelerator on the API water loss of oil well cement at 14°C and 20°C.

[0044] At 20°C, the blank sample had a 24-hour flexural strength of 0.6 MPa and a 48-hour flexural strength of 2.0 MPa. When the temperature was lowered to 14°C, the blank sample's 24-hour flexural strength was 0.3 MPa and 1.2 MPa at 48 hours. At 8°C, the blank sample's 24-hour flexural strength was only 0.1 MPa and 1.1 MPa at 48 hours. After adding one part of a crystal nucleus-type hydration accelerator, the sample's 24-hour flexural strength increased by 1.5 times at 20°C, 1.0 times at 14°C, and 2.0 times at 8°C compared to the blank sample. The improvement in 48-hour flexural strength was less significant. After adding three parts of a hydration accelerator, the sample's 24-hour flexural strength at both 20°C and 14°C exceeded the blank sample's 48-hour flexural strength, and its 24-hour flexural strength at 8°C increased by 6.0 times compared to the blank sample. After adding 5 parts of hydration accelerator, the 24h and 48h flexural strengths of the sample at 8°C exceeded the flexural strength of the blank sample at the same age at 20°C. Therefore, the early flexural strength of oil well cement paste develops slowly at low temperatures, with almost no flexural strength after 24 hours. The addition of a crystal nucleus hydration accelerator is beneficial for improving its early flexural strength, and the effect is more significant at high dosages.

[0045] Under low-temperature curing at 8°C, 14°C, and 20°C, the 24h compressive strength of blank oil well cement was 0.1 MPa, 0.6 MPa, and 1.8 MPa, respectively, and the 48h compressive strength was 4.6 MPa, 9.5 MPa, and 22.0 MPa, respectively. At 8°C, when the nucleus-type hydration accelerator was added at 1 part, the 24h and 48h compressive strengths of the sample were 0.3 MPa and 7.0 MPa, respectively, with a 48h compressive strength ratio of 152%. When the hydration accelerator was added at 3 parts, the 24h and 48h compressive strengths of the sample were 1.4 MPa and 8.5 MPa, respectively, with a 48h compressive strength ratio of 185%. When the hydration accelerator was added at 5 parts, the 24h and 48h compressive strengths of the sample were 2.4 MPa and 9.5 MPa, respectively, with a 48h compressive strength ratio of 207%. At 14°C and 20°C, the crystal nucleus hydration accelerator also has a similar effect on improving the early compressive strength of oil well cement. At low temperatures, the crystal nucleus hydration accelerator has an excellent effect on improving the early strength of oil well cement, and the effect is more prominent when the dosage is high.

[0046] In summary, the early-strength oil well cement under low-temperature curing environment of the present invention can significantly improve the early strength of oil well cement under low-temperature environment, shorten the construction period, and reduce production costs through optimization of ratio design and preparation method.

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A nanocrystalline core oil well cement under low temperature curing environment, characterized in that: By weight: 90-110 parts of oil well cement, 42-46 parts of water, 0.8-1.2 parts of dispersant, 0.08-0.12 parts of water reducer, 1-5 parts of CSH crystal nucleus type hydration accelerator, and water-binder ratio of 0.41-0.

47.

2. The nanocrystalline oil well cement for low temperature curing according to claim 1, characterized in that: Calculated by weight: 100 parts of oil well cement, 44 parts of water, 1 part of dispersant, 0.1 part of water reducer, 1-5 parts of CSH crystal nucleus type hydration accelerator, and water-binder ratio of 0.

44.

3. The nanocrystalline core oil well cement for low temperature curing according to claim 1, characterized in that: The CSH crystal nucleus type hydration accelerator is used as an auxiliary material to improve the early strength of concrete by accelerating the formation of early CSH gel.

4. The nanocrystalline core oil well cement for low temperature curing according to claim 1, characterized in that: The main chemical components of the oil well cement are: MgO 2.68%, SO3 2.01%, C3S 55.33%, C3A 2.02%, C4AF 14.58%, and Na2Oeq 0.66%.

5. The method for preparing nanocrystalline core oil well cement under low temperature curing environment according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Pour the above-mentioned weight percentages of cement, water, and CSH hydration accelerator into a planetary cement mortar mixer and stir; S2. Immediately after the mixing is completed, the mold is fixed on a vibration table, and the cementitious material is loaded into the mold in two batches; the mold is vibrated on a cement mortar vibration table, the surface is smoothed, and the surface is covered with plastic wrap to prevent moisture evaporation; S3. Place it in a standard curing room and let it stand for 24 hours, then remove the mold and place it in the corresponding curing room.

6. The method for preparing nanocrystalline oil well cement under low temperature curing environment according to claim 5, characterized in that: The curing temperatures in the curing rooms are 8° C., 14° C., and 20° C., respectively, and the humidity is greater than 95%.

7. The method for preparing nanocrystalline core oil well cement under low temperature curing environment according to claim 5, characterized in that: In step S1, the stirring mode is low speed 30s, high speed 30s, stop 90s and high speed 60s.

8. The method for preparing nanocrystalline core oil well cement under low temperature curing environment according to claim 5, characterized in that: In step S2, the mold specifications are: 40×40×160 mm.

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