Hydrothermal geothermal composite salt cement slurry system and preparation method

Abstract

The application provides a hydrothermal geothermal composite salt cement slurry system and a preparation method, and solves the problems of poor corrosion resistance, insufficient heat preservation and weak permeability resistance of a traditional cement slurry in a geothermal well. The system is composed of 40%-60% of base material cement, 4%-8% of metakaolin, 12%-18% of microsilica, 0.1%-0.3% of nanometer SiO 2 1%-3%, 0.5%-1.5% of foam stabilizer, 1.2%-1.8% of fluid loss additive, 0.2%-0.5% of drag reducing agent and 0.1%-0.3% of corrosion inhibitor. The corrosion inhibitor is a nanometer silicon shell slow-release unit. The preparation method comprises the following steps: multi-scale synergistic modification (three-stage treatment to construct a dense gel network), mechanical aeration foaming, functional treatment (step-by-step addition of the fluid loss additive / corrosion inhibitor), gradient heat preservation regulation (closed porosity≥85%). The system performance is as follows: permeability≤0.0028mD, thermal conductivity≤0.07W / (m·K), strength decay rate after 28-day CO2 corrosion≤5%, and the geothermal well cementing service life is significantly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of geothermal composite salt, in particular to a hydrothermal geothermal composite salt cement slurry system. BACKGROUND

[0002] As a clean and renewable energy, hydrothermal resources are becoming increasingly important in the global energy structure. However, well cementing operations in geothermal wells face many severe challenges.

[0003] High temperature and strong corrosive environment: Geothermal tail water usually contains CO2, H2S and other corrosive gases, which are prone to chemical reaction with cement hydration products such as Ca (OH)2. The reaction will cause the cement stone porosity to increase, the strength to decline, and seriously affect the cementing quality and the service life of geothermal wells. For example, in the case of Hebei Xiongxian medium-low temperature geothermal well, the permeability of ordinary cement slurry increases to 0.088mD under the action of CO2 corrosion, greatly reducing the impermeability of the cement stone.

[0004] High heat preservation requirement: The depth of geothermal well is generally 200-3000 meters, and there is a significant temperature difference between underground and surface. In order to reduce the loss of heat energy during transportation, strict requirements are put forward for the heat preservation performance of cement slurry. The heat preservation performance of traditional cement slurry is insufficient, which is difficult to meet the demand of efficient development of geothermal resources.

[0005] Complex geological conditions: The geological conditions of geothermal wells are complex, often accompanied by mudstone interlayer and fracture development. This requires cement slurry to have high impermeability and stability to effectively prevent formation fluid channeling and ensure the success of well cementing operations.

[0006] In the prior art, traditional cement slurry has obvious defects in dealing with the above challenges. It has poor corrosion resistance and cannot effectively resist the corrosion of corrosive gases in geothermal tail water; the heat preservation performance is not ideal, resulting in a large amount of heat loss; in complex geological conditions, it is difficult to guarantee good impermeability and stability. Therefore, it is urgent to develop a composite salt cement slurry system with excellent corrosion resistance, heat preservation and mechanical properties. SUMMARY

[0007] The present application aims to provide a preparation method of a hydrothermal geothermal composite salt cement slurry system, comprising the following steps:

[0008] Modification step: A modifier capable of achieving multi-scale synergistic modification is applied to the mixture containing base cement and functional additives, which is used to promote the construction of a densified gel network from microsilica, metakaolin and nanosilica from micro to nanoscale;

[0009] Foaming and liquid adding step: 40%-60% of water and a drag reduction agent by mass of the system are added, and the slurry density is 1.1-1.5g / cm3 ;

[0010] functional treatment step: sequentially adding a fluid loss additive and an inhibitor, stirring until the slurry is uniform, and making the system modified by the multi-scale synergy sequentially contact the fluid loss additive and the inhibitor to improve the stability and corrosion resistance of the slurry, wherein the fluid loss additive and the inhibitor are added, first adding the fluid loss additive and stirring for 5-8 min, then adding the inhibitor and stirring for 10-15 min;

[0011] performance control step: injecting a foam stabilizer into the functionalized slurry by mechanical aeration method to ensure the formation of a foam structure with a closed cell rate of ≥85% and realize gradient insulation design;

[0012] performance verification step: testing and analyzing the thermal conductivity, permeability and corrosion resistance of the slurry.

[0013] Further, the multi-scale synergistic modification comprises:

[0014] First level processing, reacting metakaolin with cement hydration product Ca(OH)2 to generate C-S-H gel, improving the density of cement stone;

[0015] Second level processing, using nano-silica to optimize the cement hydration reaction activity at high temperature;

[0016] Third level processing, using micro-silicon to fill the gap between cement particles, making the system permeability ≤0.0028 mD.

[0017] Further, the first level processing and / or second level processing is performed using a solution containing a hydration reaction accelerator, the hydration reaction accelerator containing a silicate activator or a nanocrystalline core material.

[0018] Further, after the third level processing, a gel network with dynamic barrier effect is formed, effectively blocking the penetration path of corrosion media such as CO2 and H2S.

[0019] Further, the inhibitor is a nano-silicon shell slow-release unit, which is composed of an inhibitor core and a nano-silica coating layer.

[0020] Further, the particle size of the nano-silicon shell slow-release unit is 1-10 μm, and the thickness of the coating layer accounts for 30%-50% of the total mass of the unit.

[0021] Further, the preparation method of the nano-silicon shell slow-release unit comprises:

[0022] (i) Ball milling the inhibitor and nano-silica at a mass ratio of 1:2-1:5;

[0023] (ii) Add silica sol binder and press it into shape at 150 MPa, wherein the concentration of the silica sol binder is 10%-15% and the amount added is 20%-40% of the mass of the corrosion inhibitor;

[0024] (iii) Crush and screen to obtain particles with a diameter of 1-10 μm.

[0025] Furthermore, in the performance regulation step, the mechanical inflation process applies a 150MPa micropore gradient homogenization treatment to make the average pore size of the foam ≤100μm.

[0026] Furthermore, the functionalization process maintains the slurry pH at ≥12.5 by adding calcium hydroxide buffer.

[0027] This invention also provides a hydrothermal geothermal composite salt cement slurry system, comprising the following components by weight percentage: base cement 40%-60%, metakaolin 4%-8%, microsilica 12%-18%, nano silica 1%-3%, foam stabilizer (mechanically aerated foaming method) 0.5%-1.5%, water loss reducer 1.2%-1.8%, drag reducer 0.2%-0.5%, and corrosion inhibitor 0.1%-0.3%;

[0028] The corrosion inhibitor is a nano-silicon shell slow-release unit, which consists of a corrosion inhibitor core and a nano-silica coating layer.

[0029] The hydrothermal geothermal composite salt cement slurry system of this application possesses a multi-scale corrosion resistance mechanism. Specifically, it is achieved through three-level synergistic modification: ① metakaolin reacts with Ca(OH)2 to generate CSH gel; ② nano-SiO2 optimizes high-temperature hydration activity; ③ microsilica fills the interparticle gaps. This forms a nano- to micron-scale gel network, and the corrosion inhibitor core is released slowly through a nano-SiO2 coating layer (particle size 1-10 μm, coating layer ratio 30%-50%), thereby achieving a dynamic barrier effect.

[0030] Specifically, the corrosive medium's penetration pathway is blocked by both physical and chemical methods; microsilica filling reduces the matrix permeability to 0.0028 mD (a 97% reduction compared to traditional slurries); the nano-SiO2 coating layer delays the release of the corrosive agent, and the CO2 / H2S permeation flux is ≤1.0×10⁻⁶ after 28 days. -5 mol / (m 2 •h). The stability of the gel network is improved at high temperature (110℃). The β-elimination method test shows that the erosion rate is ≤5% in an acidic environment with pH=4.0, and the free additive residue rate is <5%. The nano-silicon shell unit remains intact under fracturing stress, and 150MPa high-pressure molding ensures the uniformity of the coating layer, improving the corrosion inhibition efficiency by more than 40%. Attached Figure Description

[0031] Figure 1This is a flowchart of a method provided in an embodiment of the present invention. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1

[0034] This invention aims to provide a method for preparing a hydrothermal geothermal composite salt cement slurry system, comprising the following steps: a modification step: applying a modifier capable of multi-scale synergistic modification to a mixture containing base cement and functional additives, wherein the modifier is used to promote the construction of a dense gel network of microsilica, metakaolin, and nano silica from the micro to the nano scale; a foaming and liquid addition step: adding water and drag-reducing agent accounting for 40%-60% of the system mass, and mechanically aerating until the slurry density is 1.1-1.5 g / cm³. 3 Functionalization step: Add the water loss reducing agent and corrosion inhibitor sequentially, stir until the slurry is uniform, and allow the system that has undergone the multi-scale synergistic modification to come into contact with the water loss reducing agent and corrosion inhibitor sequentially to improve the stability and corrosion resistance of the slurry. Specifically, when adding the water loss reducing agent and corrosion inhibitor, add the water loss reducing agent first and stir for 5-8 minutes, then add the corrosion inhibitor and stir for 10-15 minutes. Performance control step: Inject the functionalized slurry with a foam stabilizer that has been foamed by mechanical aeration to ensure the formation of a foam structure with a closed-cell rate of ≥85% to achieve a gradient insulation design. Performance verification step: Test and analyze the thermal conductivity, permeability and corrosion resistance of the slurry.

[0035] In some embodiments, the multi-scale synergistic modification includes: a first-level treatment, in which metakaolin reacts with cement hydration product Ca(OH)2 to generate CSH gel, thereby increasing the density of cement stone; a second-level treatment, in which nano-silica is used to optimize the activity of cement hydration reaction at high temperature; and a third-level treatment, in which microsilica is used to fill the gaps between cement particles, thereby making the system permeability ≤0.0028mD.

[0036] In some embodiments, the first-stage treatment and / or the second-stage treatment are performed using a solution containing a hydration reaction promoter, wherein the hydration reaction promoter comprises a silicate activator or a nanocrystalline nucleus material.

[0037] In some embodiments, after the third-stage treatment, a gel network with a dynamic barrier effect is formed, effectively blocking the penetration pathways of corrosive media such as CO2 and H2S. Furthermore, the dynamic barrier effect is manifested as follows: the increase in permeability ≤ 0.0005 mD after 28 days of corrosion, and the strength degradation rate ≤ 5%.

[0038] In some embodiments, the three-level processing mechanism is illustrated in the table below.

[0039]

[0040] In some embodiments, the functionalization process may be preceded by a premixing step: mixing G-grade oil well cement, metakaolin, microsilica and nano silica evenly.

[0041] In some embodiments, the corrosion inhibitor is a nano-silica shell slow-release unit, which consists of a corrosion inhibitor core and a nano-silica coating layer. Further, the particle size of the nano-silica shell slow-release unit is 1-10 μm, and the coating layer thickness accounts for 30%-50% of the total mass of the unit. Further, the preparation method of the nano-silica shell slow-release unit includes: (i) ball milling and mixing the corrosion inhibitor and nano-silica at a mass ratio of 1:2-1:5; (ii) adding a silica sol binder and pressing the mixture at 150 MPa, wherein the concentration of the silica sol binder is 10%-15%, and the amount added is 20%-40% of the mass of the corrosion inhibitor; (iii) crushing and sieving to obtain particles with a particle size of 1-10 μm.

[0042] In some embodiments, during the performance regulation step, the mechanical inflation process applies a 150 MPa micropore gradient homogenization treatment to make the average pore size of the foam ≤100 μm.

[0043] In some embodiments, during the performance regulation step, the closed-cell foam structure is combined with low thermal conductivity additives to achieve a system thermal conductivity ≤0.07W / (m·K), thereby dynamically suppressing heat conduction.

[0044] In some embodiments, the functionalization process stage maintains the slurry pH ≥ 12.5 by adding calcium hydroxide buffer.

[0045] In some embodiments, the performance verification step includes: pore stability testing: evaluating the stability of the gel network under pH ≤ 11.0 conditions by simulating a high-temperature corrosion environment using the β-elimination method; and thermal insulation performance testing: measuring the density at 1.2 g / cm³. 3 Thermal conductivity of the system; Corrosion resistance test: CO2 corrosion test was conducted according to NB / T 11158-2023 standard.

[0046] In some embodiments, during the pore stability test, the peeling reaction rate is <10%, and the residual rate of unreacted free additives is <5%.

[0047] In some embodiments, the environmental adaptability verification step involves applying the slurry to a sandstone or carbonate rock thermal reservoir environment and monitoring its heat preservation efficiency and resistance to formation fluid crossflow at well depths with temperature differences of 200-3000 meters.

[0048] The present invention also provides a hydrothermal geothermal composite salt cement slurry system, comprising the following components by mass percentage: base cement 40%-60%, metakaolin 4%-8%, microsilica 12%-18%, nano silica 1%-3%, foam stabilizer by mechanical aeration 0.5%-1.5%, water loss reducer 1.2%-1.8%, drag reducer 0.2%-0.5%, and corrosion inhibitor 0.1%-0.3%; wherein the corrosion inhibitor is a nano silica shell slow-release unit, which is composed of a corrosion inhibitor core and a nano silica coating layer.

[0049] In some embodiments, the main functions of each component are as follows:

[0050]

[0051] In some embodiments, nano-calcium carbonate, a nucleating material, is added during the stability regulation stage at an amount of 0.1%-0.5% of the cement mass to promote hydration reaction in low-temperature well sections (<80°C).

[0052] In some embodiments, the hydrothermal geothermal composite salt cement slurry system satisfies: (a) density 1.1-1.5 g / cm³ 3 (b) Thermal conductivity ≤ 0.07 W / (m·K); (c) Permeability ≤ 0.0028 mD.

[0053] In some embodiments, the present invention also provides a performance verification method, comprising: dynamic corrosion flux testing: placing the cured cement stone in an environment with a CO2 partial pressure of 2 MPa, and monitoring the H2S / CO2 permeation flux over 28 days, requiring ≤1.0 × 10⁻⁶. -5 mol / (m 2 •h); Pore stability test: The gel network erosion rate was evaluated using the β-elimination method in an acidic environment at pH 4.0, with a requirement of ≤5%; Thermal conductivity test: The density was measured at 1.2 g / cm³. 3 Thermal conductivity of the slurry at 110℃.

[0054] The test results for this application are as follows:

[0055]

[0056] The hydrothermal geothermal composite salt cement slurry system of this application possesses a multi-scale corrosion resistance mechanism. Specifically, it is achieved through three-level synergistic modification: ① metakaolin reacts with Ca(OH)2 to generate CSH gel; ② nano-SiO2 optimizes high-temperature hydration activity; ③ microsilica fills the interparticle gaps. This forms a nano- to micron-scale gel network, and the corrosion inhibitor core is released slowly through a nano-SiO2 coating layer (particle size 1-10 μm, coating layer ratio 30%-50%), thereby achieving a dynamic barrier effect.

[0057] Specifically, the corrosive medium's penetration pathway is blocked by both physical and chemical methods; microsilica filling reduces the matrix permeability to 0.0028 mD (a 97% reduction compared to traditional slurries); the nano-SiO2 coating layer delays the release of the corrosive agent, and the CO2 / H2S permeation flux is ≤1.0×10⁻⁶ after 28 days. -5 mol / (m 2 •h). The stability of the gel network is improved at high temperature (110℃). The β-elimination method test shows that the erosion rate is ≤5% in an acidic environment with pH=4.0, and the free additive residue rate is <5%. The nano-silicon shell unit remains intact under fracturing stress, and 150MPa high-pressure molding ensures the uniformity of the coating layer, improving the corrosion inhibition efficiency by more than 40%.

[0058] The hydrothermal geothermal composite salt cement slurry system of this application features a gradient insulation design. Specifically, it is foamed using a mechanical aeration method and homogenized under a microporous gradient at 150 MPa, resulting in an average foam pore size ≤100 μm and a closed-cell rate ≥85%. The closed-cell foam forms a gas-solid dual-phase insulation layer with a thermal conductivity ≤0.07 W / (m·K) (65% lower than traditional slurries). The gradient pore size design (20-100 μm) effectively blocks heat convection, with a heat loss rate of <8% at a simulated well depth of 3000 meters (ΔT=120℃). The foam structure has been verified by the β-elimination method, showing pore stability >95% at high temperatures and a peeling reaction rate <10%, significantly extending geothermal transport efficiency.

[0059] This application provides a permeability control system, which mainly uses microsilica (12%-18%) to fill the gaps between cement particles, followed by CSH gel densification, resulting in a final product with a "nano-filled - micron-densified - macro-barrier" structure after three levels of modification. The permeability is ≤0.0028mD (reaching dense rock level), a 31-fold improvement compared to the 0.088mD of the prior art. The microsilica particle size (0.1-1μm) precisely matches the cement pore size, and the permeability increase after 28 days of CO2 corrosion is ≤0.0005mD. It enhances resistance to crossflow in fractured strata (such as mudstone interlayers), with a fluid breakthrough pressure ≥18MPa.

[0060] This application utilizes calcium hydroxide buffer to maintain an alkaline environment, avoiding competitive adsorption of additives, thus increasing the film-forming rate of the water loss reducing agent by 35% and achieving a filtration loss of <50mL / 30min. The high pH environment inhibits H2S ionization, reducing the corrosion rate to 0.02mm / year. The nucleation material, nano-CaCO3 (addition amount 0.1%-0.5%), promotes hydration in low-temperature well sections (<80℃), shortening the initial setting time by 20%.

[0061] This application features enhanced environmental adaptability and verification of sandstone / carbonate rock thermal reservoirs: monitoring thermal insulation efficiency at temperature differences of 200-3000 meters. In carbonate rock formations (high CO2 partial pressure 2MPa), the 28-day strength retention rate is ≥95%, exceeding the industry standard by 30%. Resistance to formation fluid cross-flow is demonstrated: 100% sealing rate when fracture width >200μm. Under a temperature difference of 3000 meters, the thermal insulation efficiency decay rate is <3% / year.

[0062] In the foregoing description, examples have been described with reference to specific exemplary embodiments. However, it will be apparent that various modifications and changes can be made to the specific examples without departing from the scope set forth in the appended claims, and the claims are not limited to the specific examples described above.

Claims

1. A method for preparing a hydrothermal geothermal composite salt cement slurry system, characterized in that, Includes the following steps: Modification step: Apply a modifier that enables multi-scale synergistic modification to a mixture comprising base cement and microsilica, metakaolin and nano silica, wherein the modifier is used to promote the construction of a dense gel network of microsilica, metakaolin and nano silica from the micro to the nano scale. Foaming and liquid addition steps: Add water and drag-reducing agent, accounting for 40%-60% of the system mass, and mechanically aerate until the slurry density is 1.1-1.5 g / cm³. 3 ; Functionalization process: Add the water loss reducer and corrosion inhibitor in sequence, stir until the slurry is uniform, and bring the system that has undergone the multi-scale synergistic modification into contact with the water loss reducer and corrosion inhibitor in sequence. When adding the water loss reducer and corrosion inhibitor, first add the water loss reducer and stir for 5-8 minutes, then add the corrosion inhibitor and stir for 10-15 minutes. Performance control steps: Inject a foam stabilizer that has been mechanically aerated into the functionalized slurry to ensure the formation of a foam structure with a closed-cell rate of ≥85% and to achieve a gradient insulation design. Performance verification steps: The thermal conductivity, permeability, and corrosion resistance of the slurry are tested and analyzed; The hydrothermal geothermal composite salt cement grout system comprises the following components by mass percentage: The base material consists of 40%-60% cement, 4%-8% metakaolin, 12%-18% microsilica, 1%-3% nano silica, 0.5%-1.5% foam stabilizer (mechanically aerated foaming), 1.2%-1.8% water loss reducer, 0.2%-0.5% drag reducer, and 0.1%-0.3% corrosion inhibitor. The corrosion inhibitor is a nano-silicon shell slow-release unit, which consists of a corrosion inhibitor core and a nano-silica coating layer; The multi-scale synergistic modification includes: The first stage of treatment involves reacting metakaolin with Ca(OH)2, a cement hydration product, to generate CSH gel, thereby increasing the density of the cement stone. The second stage of treatment involves optimizing the cement hydration reaction activity at high temperatures using nano-silica. The third stage of treatment involves filling the gaps between cement particles with microsilica to reduce the system permeability to ≤0.0028mD.

2. The preparation method of the hydrothermal geothermal composite salt cement slurry system according to claim 1, characterized in that, The first and / or second treatments are performed using a solution containing a hydration reaction promoter, wherein the hydration reaction promoter comprises a silicate activator or a nanocrystalline nucleus material.

3. The preparation method of the hydrothermal geothermal composite salt cement slurry system according to claim 1, characterized in that, After the third stage of treatment, a gel network with a dynamic barrier effect is formed, which effectively blocks the penetration path of CO2 and H2S corrosive media.

4. The preparation method of the hydrothermal geothermal composite salt cement slurry system according to claim 1, characterized in that, The particle size of the nano-silicon shell sustained-release unit is 1-10 μm, and the coating layer accounts for 30%-50% of the total mass of the unit.

5. The preparation method of the hydrothermal geothermal composite salt cement slurry system according to claim 4, characterized in that, The preparation method of the nano-silicon shell sustained-release unit includes: (i) The corrosion inhibitor and nano-silica are ball-milled and mixed at a mass ratio of 1:2 to 1:5; (ii) Add silica sol binder and press it into shape at 150 MPa, wherein the concentration of the silica sol binder is 10%-15% and the amount added is 20%-40% of the mass of the corrosion inhibitor; (iii) Crush and screen to obtain particles with a diameter of 1-10 μm.

6. The preparation method of the hydrothermal geothermal composite salt cement slurry system according to claim 1, characterized in that, In the performance regulation step, the mechanical inflation process applies a 150MPa micropore gradient homogenization treatment to make the average pore size of the foam ≤100μm.

7. The preparation method of the hydrothermal geothermal composite salt cement slurry system according to claim 1, characterized in that, The functionalization process maintains the slurry pH at ≥12.5 by adding calcium hydroxide buffer.

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