Solid waste synergistically modified high-temperature-resistant oil well cement system and preparation method thereof

Abstract

This invention relates to a high-temperature resistant oil well cement slurry system and its preparation method based on solid waste synergistic modification, belonging to the field of oil and gas well cementing materials. This invention employs synergistic modification with steel slag micropowder and electrolytic manganese slag to increase the 3-day compressive strength to over 20 MPa; API filtration loss is reduced to <50 mL through saturated adsorption of a water-reducing agent by steel slag micropowder; and C2S is directionally converted into calcium silicate (XRD quantitative >75%) under high pressure by nano-silica sol and steel slag Fe2O3, achieving a 28-day strength retention rate of >90% at 150℃. This invention significantly reduces raw material costs and carbon emissions, solves the risk of annular flow in deep well cementing, and is suitable for oil well conditions at 150-180℃.

Description

Technical Field

[0001] This invention relates to the field of cement slurry materials for cementing operations in oil and gas engineering, specifically to a high-temperature resistant oil well cement system with solid waste synergistic modification and its preparation method. Background Technology

[0002] In deep and ultra-deep oil and gas resource development, cement slurry must withstand bottom-hole static temperatures (BHST) as high as 150℃-250℃. Conventional API G-grade silicate cement undergoes severe mineral phase transformation at these temperatures: its main hydration product, CSH gel, begins to transform into hard calcium silicate (C6S6H3) with a modified phosphogypsum structure when the temperature exceeds 110℃, and further forms layered white calcium zeolite (C6S6H2) when the temperature rises above 150℃. The compressive strength of these crystalline phases is only 30%-40% of that of CSH gel, resulting in a 30%-50% strength degradation rate in the cement stone after 28 days. To delay this phase transformation, the industry standard API SPEC 10A-2019 mandates the addition of 30-40% silica sand to reduce the calcium-silicon ratio (C / S < 1.0) of the system. However, high sand content (>35%) leads to an increase in the plastic viscosity of the slurry, a decrease in fluidity, and a significant increase in the risk of well leakage; the energy consumption of quartz sand mining reaches 1.2 tons of standard coal / ton, and the high sand content increases the cost of oil well cement slurry application; when the well temperature exceeds 180℃, the sandy system still experiences a 10-15% strength decline due to insufficient activity of the silica components.

[0003] In recent years, high belite cement (HBC), due to its main mineral component being dicalcium silicate (C2S content 40%-60%), has been used in the construction industry for crack prevention in large-volume concrete (e.g., CN 10307323A) due to its naturally low calcium-to-silicon ratio (C / S≈1.5-2.0) and low heat of hydration. It is worth noting that high belite cement (HBC), with dicalcium silicate (C2S content 40%-60%) as its main mineral, has a significantly lower natural calcium-to-silicon ratio (C / S≈1.5-2.0) than grade G cement. Theoretically, this avoids the phase transformation risk induced by a high calcium-to-silicon ratio, making it a potential material for addressing high-temperature strength degradation.

[0004] However, applying high-belite cement to oil wells faces insurmountable technical hurdles: First, oil well cementing requires a 3-day compressive strength ≥17.5MPa (API 10A), but due to the slow hydration characteristics of C2S, HBC's 3-day strength is only 12-14MPa, which cannot meet the strength aging requirements of annular seals; second, the high-pressure environment of oil wells further breaks down HBC fine particles (<10μm accounting for more than 40%), causing the specific surface area to soar to >500m². 2 / kg, triggering a strong adsorption effect on oil well additives—retarder failure leads to thickening time fluctuations >±30%, and saturated adsorption of water loss reducing agent results in API filtration loss >200mL (far exceeding the 50mL upper limit); most importantly, the application of HBC in the construction field only focuses on room temperature performance (GB / T 20472 maximum temperature 80℃), while the purpose of solid waste admixture is purely to reduce costs (such as fly ash admixture of 30-50%), and the regulation mechanism of the active components of solid waste (such as SiO2 / Al2O3) on the high-temperature phase composition has never been studied, let alone the lattice stabilizing effect of Fe2O3 under high pressure. This fundamental difference in cross-domain technical goals has led to a research gap in the synergistic stabilization mechanism of the existing "HBC-solid waste" system under extreme temperature and pressure, keeping HBC in the field of deep well cementing at the theoretical potential stage for a long time. Summary of the Invention

[0005] To address the shortcomings of existing high-belite cement in oil well applications, such as insufficient early strength, uncontrolled rheological properties, and lack of high-temperature phase transformation mechanisms, the present invention aims to provide a high-temperature resistant oil well cement system with solid waste synergistic modification and its preparation method. The core objective is to activate the C2S low-temperature hydration pathway to achieve a 3-day compressive strength ≥20MPa and to promote the formation of stable minerals such as calcareous siliceous stone (C5S6H5) in the system at 150℃.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A high-temperature resistant oil well cement system co-modified by solid waste, mainly composed of the following raw materials in parts by weight: High-Belit cement, 55-65 parts: C2S content 35-60%, ground to a specific surface area of ​​320-380 m² by vertical mill. 2 / kg, control the proportion of 3-35μm particles to ≥85%, and spray 0.3%-0.8% of triethanolamine by weight of high belite cement clinker during the grinding process to enhance the surface activity of C2S. 5-8 parts of electrolytic manganese slag: Electrolytic manganese slag is made by drying manganese slag at 100℃-120℃ until the moisture content is <1%, and then crushing it into powder with a median particle size of 3-8μm; 15-25 parts of quartz sand: SiO2 purity ≥ 98%, D 50 =15-20μm, 300 mesh screen residue ≤0.5%; Water loss reducer 0.8-1.8 parts: Depending on the situation, AMPS / IA / AM terpolymer or AMPS / NVP / AA terpolymer can be selected, etc. 0.2-0.6 parts of retarder: Select a high-temperature resistant organic retarder, such as AMPS / AADA macromolecular binary copolymer, etc. 40-50 parts water.

[0007] Preferably, the above-mentioned solid waste co-modification high-temperature oil well cement system further includes the following raw materials in parts by weight: 1-4 parts of nano-silica sol suspension (based on the total mass of the suspension), wherein the SiO2 solids in the suspension account for 0.25%-1.4% of the total dry powder mass of the system.

[0008] Preferably, the preparation method of the above-mentioned nano-silica sol suspension is as follows: silica sol with SiO2 content of 25-35% is mixed with polycarboxylic acid ether dispersant (PCE, molecular weight 8000) at a mass ratio of (8-12):1, and ultrasonic treatment (40kHz, 30min) is performed to form a stable suspension.

[0009] Preferably, the above-mentioned solid waste co-modification high-temperature oil well cement system further includes the following raw materials in parts by weight: 8-12 parts of steel slag powder, which is obtained by ball milling converter steel slag after magnetic separation to remove iron, to a D content. 90 The steel slag powder is obtained by using particles ≤20μm, and the active Fe2O3 content in the powder is ≥25%.

[0010] In this invention, the mass ratio of steel slag powder to electrolytic manganese slag is controlled at 1.0-2.0:1, and the Fe / Mn molar ratio is 2.5-3.5:1.

[0011] The second technical solution provided by this invention is: a method for preparing a high-temperature resistant oil well cement system with solid waste co-modification, which is achieved through the following steps: Step 1) Mix the high-belite cement, steel slag powder, electrolytic manganese slag, and quartz sand according to the formula. The mixing speed is 45-60 rpm and the mixing time is 8-15 min to obtain dry mix. Step 2) Add the formulated amount of nano silica sol suspension, water, water loss reducer, and organic retarder to the dry mixture obtained in Step 1), and shear and stir at 1800-2200 rpm for 4-8 minutes. Step 3) After pre-curing at 70℃-90℃ for 4-8 hours, demold and then cure at a high temperature of 150-180℃ / 21MPa at a rate of 2-5℃ / min for 28-90 days. During this period, a snow-silica calcium stone (C5S6H5, PDF#45-1480) crystal phase is formed at 150℃. ; Step 4) Determine the slurry properties at 150℃-180℃ according to API RP 10B-2013.

[0012] The cement system of this invention retains ≥90% of its strength after curing at a well temperature of 150-180℃ for 28 days. Furthermore, the amount of quartz sand used in this invention is reduced by more than 30% compared to traditional high-temperature oil well cement systems.

[0013] Compared with the prior art, the present invention has the following significant effects: 1. This invention utilizes the saturation effect of steel slag micropowder on the adsorption sites of water loss reducing agents to reduce API filtration loss in the HBC system; 2. This invention utilizes the soluble Mn in electrolytic manganese slag. 2+ With steel slag Fe 3+ The formed [FeMn]O4 2- The activated complex significantly accelerated the low-temperature hydration reaction of C2S and promoted C2S hydration in high-temperature application environments, increasing the 3-day compressive strength from 12-14 MPa of conventional high-belite cement to 21-23 MPa, breaking through the 17.5 MPa strength threshold specified by API 10A, and solving the risk of annular flow caused by insufficient early sealing strength. 3. This invention utilizes the synergistic effect of nano-silica sol and Fe2O3 steel slag powder under high pressure to directionally induce the transformation of C2S into the stable phase of calcareous silica (C5S6H5), thereby improving the 28-day strength retention rate. This represents an improvement over the traditional quartz sand system in terms of strength decay at the same temperature. 4. This invention replaces traditional quartz sand reinforcement materials with composite solid waste activators, which significantly reduces raw material costs while achieving simultaneous reduction of energy consumption and carbon emissions through the carbon fixation characteristics of steel slag / manganese slag, thus overcoming the challenge of synergistic high performance and greening in the field of deep well cementing. Detailed Implementation

[0014] The present invention will now be further described with reference to specific embodiments. The following are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any similar or equivalent substitutions without departing from the concept of the present invention should fall within the scope of protection of the present invention.

[0015] Example 1 (water-to-solid ratio 0.44) High-Belit Cement: 65 parts (C2S content 45%, ground to a specific surface area of ​​360m²) 2 / kg, D 50 =12μm), steel slag powder: 10 parts, quartz sand: 25 parts, nano silica sol suspension: 2 parts (containing 0.6 parts SiO2 (solids)), water loss reducer: 1.2 parts, retarder: 0.4 parts, water: 44 parts (including moisture in the sol and admixtures).

[0016] Preparation method: Dry mix high belite cement, steel slag powder, and quartz sand at 45 rpm for 10 min, then add nano silica sol suspension, water, water loss reducer, and retarder, and shear and stir at 1800-2200 rpm for 5 min; then demold after pre-curing at 70-90℃ for 4-8 h, and then cure at 150℃ and 21MPa.

[0017] Example 2 (water-to-solid ratio 0.44) High-Belit Cement: 60 parts (C2S content 45%, ground to a specific surface area of ​​360m²) 2 / kg, D 50 =12μm), steel slag powder: 10 parts, electrolytic manganese slag: 5 parts, quartz sand: 27 parts, water loss reducer: 1.2 parts, retarder: 0.4 parts, water: 44 parts (including water in the admixtures) (water-to-solid ratio 0.44).

[0018] Preparation method: Dry mix high belite cement, steel slag powder, electrolytic manganese slag, and quartz sand at 45 rpm for 10 min, then add water, water loss reducer, and retarder, and shear and stir at 1800-2200 rpm for 5 min; then demold after pre-curing at 70-90℃ for 4-8 h, and then cure at 150℃ and 21MPa.

[0019] Example 3 (water-to-solid ratio 0.44) High-Belit Cement: 60 parts (C2S content 45%, ground to a specific surface area of ​​360m²) 2 / kg, D 50 =12μm), steel slag powder: 10 parts, electrolytic manganese slag: 5 parts, quartz sand: 25 parts, nano silica sol suspension: 2 parts (containing 0.6 parts SiO2 (solids)), water loss reducer: 1.2 parts, retarder: 0.4 parts, water: 44 parts (including moisture in the sol and additives).

[0020] Preparation method: Dry mix high belite cement, steel slag powder, electrolytic manganese slag, and quartz sand at 45 rpm for 10 min, then add nano silica sol suspension, water, water loss reducer, and retarder, and shear and stir at 1800-2200 rpm for 5 min; then demold after pre-curing at 70-90℃ for 4-8 h, and then cure at 150℃ and 21MPa.

[0021] Comparative Example 1 (water-to-solid ratio 0.44) High-Belit Cement: 75 parts (C2S content 45%, ground to a specific surface area of ​​360m²) 2 / kg, D 50 =12μm), quartz sand: 35 parts, water loss reducing agent: 1.2 parts, retarder: 0.4 parts, water: 44 parts (including water in the admixtures).

[0022] Preparation method: Dry mix high belite cement and quartz sand at 45 rpm for 10 min, then add water, water loss reducer and retarder, and shear and stir at 1800-2200 rpm for 5 min; then demold after pre-curing at 70-90℃ for 4-8 h, and then high temperature curing at 150℃ and 21MPa.

[0023] Table 1 below shows the cement system mix proportions for Examples 1 to 3 and Comparative Example 1 of the present invention; Table 2 shows the cement slurry test results for Examples 1 to 3 and Comparative Example 1 of the present invention. Table 1 Cement grout mix proportions (by weight): .

[0024] Table 2 Cement grout test results .

Claims

1. A high temperature resistant oil well cement system synergistically modified with solid waste, characterized in that, It is mainly composed of the following raw materials in parts by weight: 55-65 parts of high belite cement, 8-12 parts of steel slag powder, 15-25 parts of quartz sand, 0.8-1.8 parts of water loss reducer, 0.2-0.6 parts of retarder, and 40-50 parts of water.

2. The solid waste synergistically modified high temperature resistant oil well cement system according to claim 1, characterized in that, It also includes the following raw materials in parts by weight: 1-4 parts of nano silica sol suspension.

3. The solid waste synergistically modified high temperature resistant oil well cement system according to claim 1 or 2, characterized in that, It also includes the following raw materials in parts by weight: 5-8 parts of electrolytic manganese slag.

4. The solid waste synergistically modified high temperature resistant oil well cement system according to claim 3, characterized in that, The C2S content in the above-mentioned high-belite cement is 35-60%, and it is ground to a specific surface area of ​​320-380 m² after being ground in a vertical mill. 2 / kg, with the particle size distribution controlled at ≥85% of particles with a size of 3-35μm, and 0.3%-0.8% of triethanolamine by weight of high belite cement sprayed in during the grinding process.

5. The solid waste synergistically modified high temperature resistant oil well cement system according to claim 4, characterized in that, The steel slag micro-powder is obtained by ball-milling the converter steel slag after removing iron by magnetic separation to D 90 ≤ 20 μm, and the active Fe2O3 content in the steel slag micro-powder is ≥ 25%.

6. The solid waste synergistically modified high temperature resistant oil well cement system according to claim 5, characterized in that, The above-mentioned nano-silica sol suspension is prepared by mixing silica sol with SiO2 content of 25-35% with polycarboxylic acid ether dispersant at a mass ratio of (8-12):1, and then treating it with ultrasound to form a stable suspension.

7. The high-temperature resistant oil well cement system with solid waste synergistic modification according to claim 6, characterized in that, The aforementioned electrolytic manganese slag is made by drying manganese slag at 100℃-120℃ until the moisture content is <1%, and then pulverizing it into powder with a median particle size of 3-8μm.

8. The solid waste synergistically modified high temperature resistant oil well cement system according to claim 7, characterized in that, The SiO2purity of the above quartz sand is ≥98%, D 50 = 15-20 μm, 300 mesh residue ≤0.5%.

9. The solid waste synergistically modified high temperature resistant oil well cement system according to claim 8, characterized in that, Its preparation method is achieved through the following steps: Step 1) Mix the high-belite cement, steel slag powder, electrolytic manganese slag, and quartz sand according to the formula to obtain a dry mix; Step 2) Add the formulated amount of nano silica sol suspension, water, water loss reducer, and retarder to the dry mixture obtained in Step 1), and shear and stir at 1800-2200 rpm for 4-8 minutes. Step 3) First, pre-cur at 70℃-90℃ for 4-8 hours, then demold, and then cure at 150-180℃ / 21MPa at a rate of 2-5℃ / min for 28-90 days.