Hydrothermal terrestrial heat composite saltwater slurry system and preparation method thereof

Abstract

The invention provides a hydrothermal type geothermal composite salt cement slurry system and a preparation method thereof. The problems that traditional cement slurry is poor in corrosion resistance, insufficient in heat preservation and weak in impermeability in a geothermal well are solved. The system is composed of 40%-60% of base material cement, 4%-8% of metakaolin, 12%-18% of micro silicon, 1%-3% of nano SiO2, 0.5%-1.5% of a foam stabilizer, 1.2%-1.8% of a fluid loss agent, 0.2%-0.5% of a drag reducer and 0.1%-0.3% of a corrosion inhibitor. And the corrosion inhibitor is a nano silicon shell slow release unit. The preparation method comprises the following steps: multi-scale synergistic modification (three-stage treatment to construct a compact gel network), mechanical inflation foaming, functionalization treatment (step-by-step addition of a fluid loss agent / corrosion inhibitor), and gradient heat preservation regulation (the percentage of closed area is greater than or equal to 85%). According to the system performance, the permeability is smaller than or equal to 0.0028 mD, the heat conductivity coefficient is smaller than or equal to 0.07 W / (m.K), the strength recession rate after 28-day CO2 corrosion is smaller than or equal to 5%, and the well cementation service life of a geothermal well is remarkably prolonged.

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 the geothermal well. 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 corrosion of CO2, 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 the cement slurry to have high impermeability and stability to effectively prevent the channeling of formation fluid and ensure the success of well cementing operation.

[0006] In the prior art, the 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: 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 dense gel network from microsilica, metakaolin and nanosilica from micro to nanoscale; Foaming and liquid adding step: 40%-60% of water and drag reducing agent by mass of the system are added, and mechanical aeration is adopted to make the slurry density 1.1-1.5g / cm 3 ; The functional treatment step: sequentially add the fluid loss additive and the corrosion inhibitor, stir until the slurry is uniform, and make the system modified by the multi-scale synergy sequentially contact the fluid loss additive and the corrosion inhibitor to improve the stability and corrosion resistance of the slurry, wherein the fluid loss additive and the corrosion inhibitor are added, first add the fluid loss additive and stir for 5-8 min, then add the corrosion inhibitor and stir for 10-15 min; The performance control step: injecting the foam stabilizer of the mechanical aeration method into the slurry after the functional treatment to ensure the formation of a foam structure with a closed cell rate of ≥85% to realize gradient insulation design. The performance verification step: testing and analyzing the thermal conductivity, permeability and corrosion resistance of the slurry.

[0008] Further, the multi-scale synergistic modification comprises: The first level treatment to generate C-S-H gel by reacting metakaolin with cement hydration product Ca(OH)2 to improve the density of cement stone; The second level treatment to optimize the cement hydration reaction activity at high temperature by nano-silica; The third level treatment to fill the gap between cement particles with micro-silica to make the system permeability ≤0.0028 mD.

[0009] Further, the first level treatment and / or the second level treatment are performed using a solution containing a hydration reaction accelerator, and the hydration reaction accelerator contains a silicate activator or a nanocrystalline core material.

[0010] Further, after the third level treatment, a gel network with dynamic barrier effect is formed, effectively blocking the penetration path of corrosion media such as CO2 and H2S.

[0011] Further, the corrosion inhibitor is a nano-silicon shell slow-release unit, which is composed of a corrosion inhibitor core and a nano-silica coating layer.

[0012] 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.

[0013] Further, the preparation method of the nano-silicon shell slow-release unit comprises: (i) Ball milling the corrosion inhibitor and nano-silica at a mass ratio of 1:2-1:5; (ii) Adding a silica sol binder and pressing at 150 MPa, wherein the silica sol binder concentration is 10%-15%, and the addition amount 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.

[0014] Furthermore, in the performance control step, the mechanical inflation process applies a 150 MPa micropore gradient homogenization treatment to make the average pore diameter of the foam ≤100 μm.

[0015] Furthermore, the pH of the slurry is maintained at ≥12.5 during the functionalization treatment step, which is achieved by adding a calcium hydroxide buffer.

[0016] The present invention also provides a hydrothermal geothermal composite salt water slurry system, comprising the following components in percentage by mass: 40%-60% base cement, 4%-8% metakaolin, 12%-18% microsilica, 1%-3% nano-silicon dioxide, 0.5%-1.5% mechanical aeration foam stabilizer, 1.2%-1.8% fluid loss additive, 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 is composed of a corrosion inhibitor core and a nano-silicon dioxide coating layer.

[0017] The hydrothermal geothermal composite brine slurry system described in this application exhibits a multi-scale corrosion resistance mechanism. Specifically, it utilizes three synergistic modification steps: ① Metakaolin reacts with Ca(OH)2 to form CSH gel; ② Nano-SiO2 optimizes high-temperature hydration activity; and ③ Micro-SiO2 fills the intergranular spaces. This forms a nano-micrometer-scale gel network, allowing the corrosion inhibitor core to be slowly released through the nano-SiO2 coating (particle size 1-10μm, coating layer comprising 30%-50%), thus achieving a dynamic barrier effect.

[0018] The penetration path of the corrosive medium is blocked by both physical and chemical means. Micro-silicon filling reduces the matrix permeability to 0.0028 mD (97% lower than that of traditional slurry). The nano-SiO2 coating delays the release of corrosive agents, and the CO2 / H2S permeation flux is ≤1.0×10 -5 mol / (m 2 h). Gel network stability is enhanced at high temperatures (110°C). Beta-elimination testing shows a corrosion rate of ≤5% in an acidic environment of pH 4.0, and a residual free additive rate of <5%. The nano-silicon shell units remain intact under fracturing stress. High-pressure molding at 150 MPa ensures uniform coating, improving corrosion inhibition efficiency by over 40%. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A flow chart of a method provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0020] With reference to the accompanying drawings, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of the present application.

[0021] Embodiment 1 The present application aims to provide a preparation method of a hydrothermal type geothermal composite salt cement slurry system, comprising the following steps: a modification step: a modifier capable of achieving multi-scale synergistic modification is applied to a mixture containing base material cement and functional additives, the modifier being used to promote microsilica, metakaolin and nanosilica to construct a densification gel network from microscale to nanoscale; a foaming and liquid adding step: water and a drag reducing agent are added, the water accounting for 40%-60% of the mass of the system, and the system being mechanically aerated to a slurry density of 1.1-1.5 g / cm 3 ; a functional treatment step: a fluid loss additive and an inhibitor are sequentially added, the slurry is stirred until it is uniform, and the system subjected to the multi-scale synergistic modification is sequentially contacted with the fluid loss additive and the inhibitor, so as to improve the stability and corrosion resistance of the slurry, wherein the fluid loss additive and the inhibitor are added in the following order: the fluid loss additive is added first and stirred for 5-8 min, and then the inhibitor is added and stirred for 10-15 min; a performance control step: a foam stabilizer is added to the slurry after functional treatment by mechanical aeration, so as to ensure that a foam structure with a closed cell rate of ≥85% is formed, and a gradient heat preservation design is achieved; and a performance verification step: the thermal conductivity, permeability and corrosion resistance of the slurry are tested and analyzed.

[0022] In some embodiments, the multi-scale synergistic modification comprises: a first level treatment to react metakaolin with cement hydration product Ca(OH)2 to generate C-S-H gel, so as to improve the density of cement stone; a second level treatment to optimize the cement hydration reaction activity at high temperature by using nanosilica; and a third level treatment to fill the gap between cement particles by using microsilica, so that the permeability of the system is ≤0.0028 mD.

[0023] In some embodiments, the first level treatment and / or the second level treatment are performed using a solution containing a hydration reaction promoter, the hydration reaction promoter containing a silicate activator or a nanocrystalline core material.

[0024] In some embodiments, after the third level treatment, a gel network with a dynamic barrier effect is formed, which effectively blocks the penetration path of corrosion media such as CO2 and H2S. Further, the dynamic barrier effect is manifested in that the increase in permeability after 28 days of corrosion is ≤0.0005 mD, and the strength decay rate is ≤5%.

[0025] In some embodiments, the three-level treatment mechanism is illustrated by the following table.

[0026]

[0027] In some embodiments, the functionalization treatment step is preceded by a premixing step of uniformly dry mixing G-class oil well cement, metakaolin, microsilica, and nanosilica.

[0028] In some embodiments, the corrosion inhibitor is a nanosilica shell slow-release unit composed of a corrosion inhibitor core and a nanosilica coating layer. Further, the nanosilica shell slow-release unit has a particle size of 1-10 μm, and the coating layer has a thickness of 30%-50% of the total mass of the unit. Further, the preparation method of the nanosilica shell slow-release unit comprises: (i) ball-milling the corrosion inhibitor and nanosilica at a mass ratio of 1:2-1:5; (ii) adding a silica sol binder and pressing into a shape under 150 MPa, wherein the silica sol binder has a concentration of 10%-15% and an addition amount of 20%-40% of the mass of the corrosion inhibitor; and (iii) crushing and sieving to obtain particles with a particle size of 1-10 μm.

[0029] In some embodiments, in the performance regulation step, the mechanical aeration process applies a 150 MPa micro-pore gradient homogenization treatment to make the average pore size of the foam ≤100 μm.

[0030] In some embodiments, in the performance regulation step, the closed-cell foam structure is combined with a low thermal conductivity additive to make the thermal conductivity coefficient of the system ≤0.07 W / (m·K), achieving dynamic inhibition of heat conduction.

[0031] In some embodiments, the functionalization treatment step maintains the pH of the slurry ≥12.5, which is achieved by adding calcium hydroxide buffer.

[0032] In some embodiments, the performance verification step comprises: a pore stability test, which simulates a high-temperature corrosion environment by a β elimination method to evaluate the stability of the gel network under the condition of pH ≤11.0; a heat preservation performance test, which measures the thermal conductivity coefficient of the system with a density of 1.2 g / cm 3 ; and a corrosion resistance test, which performs a CO2 corrosion test according to the standard NB / T 11158-2023.

[0033] In some embodiments, in the pore stability test, the peeling reaction ratio is <10%, and the residual rate of free additives not involved in the reaction is <5%.

[0034] In some embodiments, the environmental adaptability verification step applies the slurry to a sandstone or carbonate rock thermal reservoir environment and monitors its heat preservation efficiency and anti-formation fluid channeling capacity at a temperature difference of 200-3000 meters of well depth.

[0035] The application further provides a hydrothermal geothermal composite salt cement slurry system, which comprises the following components in percentage by mass: base material cement 40-60%, metakaolin 4-8%, microsilica 12-18%, nano-silicon dioxide 1-3%, foam stabilizer for mechanical foaming 0.5-1.5%, fluid loss additive 1.2-1.8%, drag reducing agent 0.2-0.5%, corrosion inhibitor 0.1-0.3%; the corrosion inhibitor is a nano-silicon shell slow-release unit, which is composed of a corrosion inhibitor core and a nano-silicon dioxide coating layer.

[0036] In some embodiments, the main functions of each component are as follows:

[0037] In some embodiments, the stability regulation stage adds a crystal nucleus material nano-calcium carbonate, and the addition amount is 0.1-0.5% of the mass of the cement, for promoting the hydration reaction in a low-temperature well section (<80℃).

[0038] In some embodiments, the hydrothermal geothermal composite salt cement slurry system meets the following conditions: (a) density 1.1-1.5 g / cm 3 ; (b) thermal conductivity ≤0.07 W / (m·K); (c) permeability ≤0.0028 mD.

[0039] In some embodiments, the application further provides a performance verification method, which comprises: dynamic corrosion flux testing: placing the solidified cement stone in an environment with a CO2 partial pressure of 2 MPa, monitoring the H2S / CO2 permeation flux within 28 days, and requiring ≤1.0×10 -5 mol / (m 2 ·h); pore stability testing: evaluating the gel network denudation rate in a pH=4.0 acid environment by a beta elimination method, and requiring ≤5%; thermal conductivity testing: measuring the thermal conductivity of the slurry with a density of 1.2 g / cm 3 at 110℃.

[0040] The test results of the application are as follows:

[0041] The hydrothermal geothermal composite salt cement slurry system of the application has a multi-scale corrosion resistance mechanism, specifically through three-level synergistic modification: ① metakaolin reacts with Ca(OH)2 to generate C-S-H gel; ② nano-SiO2 optimizes the high-temperature hydration activity; ③ microsilica fills the interstitial gap. A nano-micron level gel network is formed, the corrosion inhibitor core is released through the nano-SiO2 coating layer (particle size 1-10 μm, coating layer accounting for 30-50%), thereby obtaining a dynamic barrier effect.

[0042] The corrosion medium penetration path is physically and chemically blocked, the micro-silicon filling reduces the substrate permeability to 0.0028 mD (97% lower than traditional slurry), the nano-SiO2 coating layer delays the release of corrosion agents, and the 28-day CO2 / H2S permeation flux is ≤1.0×10 -5 mol / (m 2 ·h). The gel network stability is improved at high temperature (110°C), the stripping rate is ≤5% in the pH=4.0 acidic environment by the beta elimination method, and the free additive residual rate is <5%. The nano-silicon shell unit remains intact under fracturing stress, and the 150MPa high-pressure forming ensures the uniformity of the coating layer, and the corrosion inhibition efficiency is improved by more than 40%.

[0043] The hydrothermal geothermal composite salt cement slurry system of the present application has a gradient heat preservation design. Specifically, the foam is formed by mechanical aeration method, and is treated by 150MPa micropore gradient homogenization. The average pore size of the foam is ≤100μm, and the closed cell rate is ≥85%. The closed cell foam forms a gas-solid two-phase thermal insulation layer, and the thermal conductivity is ≤0.07W / (m·K) (65% lower than traditional slurry). The gradient pore size design (20-100μm) effectively blocks heat convection, and the heat energy loss rate is <8% when the simulated well depth is 3000m (ΔT=120℃). The foam structure is verified by the beta elimination method, and the pore stability is >95% at high temperature, the peeling reaction ratio is <10%, and the geothermal transmission efficiency is significantly prolonged.

[0044] The present application provides a permeability control system, which mainly fills the gap between cement particles by micro-silicon (12%-18%), and superimposes C-S-H gel densification, so that the final product has a "nano-filling-micron-densification-macroscopic barrier" structure. And the permeability is ≤0.0028mD (dense rock level), which is 31 times higher than the background technology of 0.088mD. The micro-silicon particle size (0.1-1μm) precisely matches the cement pore, and the permeability increase value is ≤0.0005mD after 28 days of CO2 corrosion. The anti-channeling capacity is improved in the fractured formation (such as mudstone interlayer), and the fluid breakthrough pressure is ≥18MPa.

[0045] The present application maintains an alkaline environment by a calcium hydroxide buffer, avoids additive competitive adsorption, and increases the film formation rate of the fluid loss additive by 35%, with a filtration loss of <50mL / 30min. The high-pH environment inhibits H2S ionization, and the corrosion rate is reduced to 0.02mm / year. The nano-CaCO3 crystal nucleus material (addition amount 0.1%-0.5%) promotes hydration in low-temperature well sections (<80℃), and the initial setting time is shortened by 20%.

[0046] The application has environmental adaptability enhancement, sandstone / carbonate rock thermal reservoir verification: monitor temperature difference 200-3000 meters insulation efficiency. In carbonate rock formation (high CO2 partial pressure 2 MPa), 28-day strength retention rate ≥95%, better than industry standard 30%. Anti-formation fluid channeling capacity: when the fracture width is >200μm, the plugging rate is 100%. Under the condition of temperature difference 3000 meters, the insulation efficiency decay rate is <3% / year.

[0047] In the foregoing specification, examples have been described with reference to specific example embodiments. It will be evident, however, that various modifications and changes can be made thereto without departing from the scope as set forth in the following claims. The claims are not limited to the specific examples described above.

Claims

1. A hydrothermal geothermal composite brine slurry system, characterized in that: The following components are included in mass percentage: Base material cement 40%-60%, metakaolin 4%-8%, microsilica 12%-18%, nano-silica 1%-3%, mechanical aeration foaming stabilizer 0.5%-1.5%, fluid loss additive 1.2%-1.8%, drag reducer 0.2%-0.5%, corrosion inhibitor 0.1%-0.3%; The corrosion inhibitor is a nano-silicon shell slow-release unit, which is composed of a corrosion inhibitor core and a nano-silicon dioxide coating layer.

2. A method for preparing a hydrothermal geothermal composite brine slurry system, characterized in that: The following steps are involved: Modification step: applying a modifier capable of achieving multi-scale synergistic modification to a mixture comprising base cement and functional additives, wherein the modifier is used to promote the construction of a densified gel network from micro to nano scale by microsilica, metakaolin and nano-silica; Foaming and liquid addition steps: add 40%-60% of the system mass of water and drag reducer, and use mechanical aeration to the slurry density of 1.1-1.5g / cm 3 ; Functionalization treatment step: adding a fluid loss agent and a corrosion inhibitor in sequence, stirring until the slurry is uniform, and allowing the system subjected to the multi-scale synergistic modification to contact the fluid loss agent and the corrosion inhibitor in sequence, wherein when adding the fluid loss agent and the corrosion inhibitor, first add the fluid loss agent and stir for 5-8 minutes, and then add the corrosion inhibitor and stir for 10-15 minutes; Performance control steps: inject a foam stabilizer foamed by mechanical inflation into the functionalized slurry to ensure the formation of a foam structure with a closed-cell ratio of ≥85% to achieve a gradient insulation design; Performance verification steps: testing and analyzing the thermal conductivity, permeability and corrosion resistance of the slurry.

3. The method for preparing the hydrothermal geothermal composite salt water slurry system according to claim 2, characterized in that: The multi-scale collaborative modification includes: In the first stage of treatment, metakaolin reacts with cement hydration product Ca(OH)2 to generate CSH gel, which improves the density of cement paste; The second stage of treatment uses nano-silica to optimize the cement hydration reaction activity at high temperatures; The third stage of treatment is to fill the gaps between cement particles with microsilicon to make the system permeability ≤0.0028mD.

4. The method for preparing the hydrothermal geothermal composite salt water slurry system according to claim 3, characterized in that: The first stage treatment and / or the second stage treatment is performed using a solution containing a hydration reaction accelerator, wherein the hydration reaction accelerator contains a silicate activator or a nanocrystalline core material.

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

6. The method for preparing the hydrothermal geothermal composite salt water slurry system according to claim 2, characterized in that: The corrosion inhibitor is a nano-silicon shell slow-release unit, which is composed of a corrosion inhibitor core and a nano-silicon dioxide coating layer.

7. The method for preparing the hydrothermal geothermal composite salt water slurry system according to claim 6, characterized in that: The particle size of the nano-silicon shell sustained-release unit is 1-10 μm, and the thickness of the coating layer accounts for 30%-50% of the total mass of the unit.

8. The method for preparing the hydrothermal geothermal composite salt water slurry system according to claim 6 or 7, characterized in that: The preparation method of the nano-silicon shell sustained-release unit comprises: (i) ball milling the corrosion inhibitor and nano-silica in a mass ratio of 1:2-1:5; (ii) adding a silica sol binder and pressing and molding 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 screening to obtain particles with a size of 1-10 μm.

9. The method for preparing the hydrothermal geothermal composite salt water slurry system according to claim 1, characterized in that: In the performance control step, the mechanical aeration process applies a 150 MPa micropore gradient homogenization treatment to make the average pore size of the foam ≤100 μm.

10. The method for preparing the hydrothermal geothermal composite salt water slurry system according to claim 1, characterized in that: The pH of the slurry is maintained at ≥12.5 during the functionalization treatment step by adding a calcium hydroxide buffer.

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