Foamed cement channeling sealing system and preparation method thereof

Abstract

The invention relates to the technical field of oil and gas field development engineering, and particularly provides a foam cement channeling sealing system and a preparation method thereof. The foam cement channeling sealing system comprises cement, a foaming agent, a retarder, a fluid loss agent, an early strength agent and water. By regulating and controlling the water cement ratio, the fluidity of the channeling sealing system is guaranteed, and the requirement that the foam cement channeling sealing system is injected into the stratum to achieve sealing is met; the strength of a foam cement channeling sealing system is guaranteed, and the requirement for blocking channeling channels generated under the condition of large cracks and large karst caves in a fracture-cavity stratum is met; the permeability is relatively high. In addition, by adopting the superfine cement, the foam cement channeling sealing system is cured under the condition of high water cement ratio; the curing time is controlled by adjusting the concentration of the retarder, and the foam stabilizing time and the cement curing time are coupled.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development engineering technology, specifically providing a foamed cement sealing system and its preparation method. Background Technology

[0002] In oil and gas field development, reservoir heterogeneity and fluid viscosity differences are often significant factors affecting oil recovery. Heterogeneity refers to the significant spatial differences in the physical properties of the rocks within the reservoir, such as porosity and permeability. It also includes natural large fractures and caverns, as well as artificial fractures and large channeling pathways formed during fracturing or prolonged extraction. This heterogeneity easily leads to channeling of injected fluids. In areas with high permeability and within fractures and caverns, the injected fluid flows rapidly, resulting in a small and uneven swept volume, failing to effectively cover the entire oil and gas reservoir. Furthermore, the viscosity difference between the displacement fluid and crude oil exacerbates this problem, leading to inefficient displacement and hindering the effective flow of crude oil, thus limiting overall recovery. To overcome these problems, a series of improvement measures are often required. For example, injecting modified fluids (such as foam flooding) can increase the viscosity difference of the displacing fluid and improve the displacing efficiency; or injecting special fluids (such as gels, cement, etc.) can modify the reservoir, block high-permeability channels, increase the sweep of low-permeability areas, minimize the impact of heterogeneity, and improve the swept volume and recovery rate.

[0003] Chinese patent document CN 105238380 A discloses a novel inorganic microparticle-reinforced foam system for oil and gas fields. The foaming agent in this system is a compound system composed of camellia saponin and sodium lauroyl glutamate. The novel inorganic microparticles are fine particulate matter captured from the atmosphere, composed of mullite and quartz. This system can be used for oil displacement, profile control, and water shut-off processes, and can work effectively in high-temperature and high-pressure reservoirs. The system forms a granular layer in which microparticles encapsulate air bubbles, resulting in a stable foam skeletal structure and good sealing effect.

[0004] Chinese patent document CN 113897189 A discloses a gel system suitable for profile control in fractured-vuggy reservoirs. This system consists of an AM / AMPS copolymer, nonionic polyacrylamide, hexamethylenetetramine, hydroquinone, and the remainder water. Under the high temperature and pressure environment of fractured-vuggy reservoirs, this system can accelerate the cross-linking reaction while maintaining gel stability and strength, reducing the adverse effects of formation water dilution on the gel, and lowering the cost of the gel system. It meets the requirements for profile control in fractured-vuggy reservoirs. After injection into the formation, the system can seal the flow channels and possesses a certain strength, effectively suppressing flow.

[0005] Cement baffles are also a commonly used water-blocking technology in oilfield development, mainly used to control water channeling and optimize oil recovery. Injecting cement slurry into the reservoir can seal high-permeability channels, inhibit water channeling, and improve recovery rates. However, cement can damage the reservoir, especially with large-scale injection. Furthermore, cement can completely block channels, hindering subsequent development. Cement also has poor injectability, requiring high injection pressure. Additionally, due to its high density, it is difficult to effectively seal high-permeability areas within the reservoir.

[0006] Fractured-vuggy reservoirs possess highly complex and heterogeneous storage spaces, containing numerous natural fractures and caverns, while heavy oil thermal recovery wells and fractured wells typically also have artificial fractures. For these reservoirs, the aforementioned measures are often ineffective. Foam flooding systems, which improve the viscosity of the displacement fluid, are less effective in large fractures and caverns; the foam lacks shear resistance after defoaming and is difficult to regenerate. Systems like gels and cement, which modify the reservoir, completely block the channels, causing significant damage. Therefore, there is an urgent need to construct a new reservoir modification system that does not completely block the channels but rather transforms the flow channels into a porous medium, enabling the subsequent injection of fluids to amplify and achieve balanced displacement.

[0007] Foamed cement is a common type of lightweight foam material, widely used in the construction industry due to its lightweight, excellent thermal insulation, good fire resistance, and economic and environmentally friendly characteristics. Foamed cement consists of cementitious materials and foaming agents. Cement is typically used as the cementitious material, while foaming agents are broadly classified into chemical and physical foaming agents. In recent years, some scholars have applied foamed cement to oil and gas field development, achieving good results. In well cementing, foamed cement systems have characteristics such as rapid strength development and low permeability, achieving the purpose of sealing the wellbore, supporting the wellbore, and preventing fluid leakage. However, it has not yet been applied in the field of oil and gas reservoir stimulation, and four major challenges remain: ① Pore formation problem: how to achieve "plugging without completely sealing"; ② Injectability problem: how to improve the injectability of the system and ensure that the system does not block the wellbore and near-wellbore area; ③ Curing time control problem: how to couple the foam defoaming time with the cement curing time, as well as the system curing time and ripple distance; ④ Density control problem: how to control the system density to achieve stimulation of different parts of the reservoir (upper, middle, and lower). This demonstrates that foamed cement systems still have enormous untapped potential in the field of oil and gas field development.

[0008] Therefore, this patent aims to construct a foam cement sealing system applicable in the field of oil and gas field development. This system can both suppress crossflow and realize reservoir transformation, transforming large fractures and karst caves into a porous medium, converting free flow into seepage, and achieving more efficient foam injection and fluid control. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the prior art and provide a foamed cement sealing system and its preparation method.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: A foamed cement sealing system includes cement, foaming agent A, foaming agent B, foaming agent C, co-solvent, chelating agent, retarder, water loss reducing agent, early strength agent, and water.

[0011] The foamed cement sealing system comprises the following components by weight: 20-50 parts cement, 0.1-1 part foaming agent A, 0.1-0.5 parts foaming agent B, 0.1-1 part foaming agent C, 1-5 parts co-solvent, 0.1-0.5 parts chelating agent, 0.1-0.4 parts retarder, 0.1-3 parts water loss reducing agent, 0.5-2 parts early strength agent, and 100 parts water.

[0012] The water-cement ratio is 2.0-5.0. If the water-cement ratio is too high, the cement curing time will be shorter than the foam defoaming time, and liquid separation will occur during system curing. The higher the water-cement ratio, the less thoroughly the system will cure, until the system cannot cure at all. If the water-cement ratio is too low, the fluidity of the system will be poor, making it impossible to inject into the formation or even foam.

[0013] The curing time of the foamed cement sealing system is 2-10 hours.

[0014] The permeability of the solidified foamed cement sealing system is 0.3~3.4D, and the compressive strength is 1.4~8.1MPa.

[0015] The cement is ultrafine cement; Preferably, the cement has a mesh size of 600-1500 mesh; Preferably, the water is mineralized water, which is prepared in the laboratory to simulate formation water, and the mineralization of the mineralized water is 0-25 × 10⁻⁶. 4 mg / L; The retarder is at least one of calcium saccharide, gluconate, citrate, tartrate, phosphate, tartrate, lignosulfonate, and 2-acrylamide-2-methylpropanesulfonic acid. The water loss reducing agent is at least one of polyvinyl alcohol water loss reducing agents, hydroxyethyl cellulose, carboxymethyl cellulose salt, butadiene-styrene latex, and vinyl acetate-ethylene latex; The early strength agent is at least one of calcium chloride, sodium aluminate, calcium oxide, potassium chloride, calcium sulfate dihydrate, lithium chloride, sodium sulfate, calcium formate, calcium lactate, potassium aluminum sulfate, lithium hydroxide, potassium hydroxide, and calcium hydroxide.

[0016] The foaming agent A is sodium α-alkenyl sulfonate; The foaming agent B is at least one of fatty alcohol polyoxyethylene ether, alkyl glycoside, polysorbate, and dehydrated sorbitol ester; The foaming agent C is sodium fatty alcohol polyoxyethylene ether sulfate.

[0017] The co-solvent is at least one of ethanol, isopropanol, urea, and glycerol; The chelating agent is at least one of disodium ethylenediaminetetraacetate and sodium citrate.

[0018] The foamed cement sealing system of this invention combines the advantages of good foam filling and flowability with the high curing strength and good temperature resistance of cement. It allows the foamed cement sealing system to foam before injection into the formation, effectively avoiding problems such as poor underground foaming effect and easy agglomeration. After injection into the formation, this system can reach the target fractures and cavities in fractured reservoirs. Under high temperature, high pressure, and high salinity conditions, it solidifies into a material with a porous structure. This not only seals the underground fractures and cavities, but the porous structure after foam curing does not completely block the formation. Instead, it adjusts the free flow in the fractures and cavities to seepage flow within the foamed cement system, maintaining a certain degree of permeability. This provides shear regeneration conditions for subsequent foam injection, increasing the foam's migration depth.

[0019] This invention provides a method for preparing a foamed cement sealing system, comprising the following steps: Step 1: Cement mortar preparation: Add cement, chelating agent, retarder, water loss reducer, accelerator, and water in sequence, and stir continuously until homogeneous to obtain cement mortar. Step 2, Preparation of foamed cement: Foaming agent A, foaming agent B, foaming agent C, and co-solvent are added to cement mortar and stirred. After stirring, foaming is stopped to obtain a foamed cement sealing system.

[0020] Preferably, the water in step 1 is mineralized water, which simulates formation water. More preferably, the salinity of the mineralized water is 0-25×10⁻⁶. 4 mg / L; Preferably, the continuous stirring state in step 1 is low-speed stirring, with a rotation speed of 100 r / min-500 r / min and a stirring time of 10 min-30 min; Preferably, the stirring in step 2 is high-speed stirring, with a rotation speed of 5000 r / min-10000 r / min and a stirring time of 3 min-15 min.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The foamed cement sealing system provided by this invention, through the synergistic effect of ultrafine cement, foaming agent, retarder, and other components, and controlled by the water-cement ratio and retarder concentration, ensures both the fluidity of the sealing system, meeting the requirements for injection into the formation to achieve sealing, and the strength of the foamed cement sealing system, meeting the requirements for sealing the flow channels generated under the conditions of large fractures and karst caves in fractured formations. It also has high permeability, realizing the transformation from free flow to seepage in the reservoir. After solidification, it has certain porosity and seepage channels, which can solve the problem of foam lacking mechanical shearing action in fractures and cavities and being difficult to regenerate after defoaming. The constructed porous structure realizes the shearing and regeneration of foam, improving the foam migration depth.

[0022] 2. This invention improves the permeability of the system by increasing the water-cement ratio and achieves curing of the foamed cement sealing system under high water-cement ratio conditions by using ultrafine cement. In addition, by adjusting the concentration of retarder to control the curing time, the stabilization time of the foam and the curing time of the cement are coupled, which can ensure that the system accurately reaches the target cracks and large fissures to achieve curing and sealing.

[0023] 3. The foamed cement sealing system in this invention can also adjust the density of the system by changing the water-cement ratio, achieving a density of 0.59-1.12 g / cm³. 3 The range is adjustable to meet the needs of injection and plugging at different locations in the high, middle, and low parts of the reservoir.

[0024] 4. The foamed cement sealing system in this invention has a high water-cement ratio, which effectively reduces the amount of cement used. This not only reduces costs and meets the needs of large-dose injection in fractured-vuggy oil reservoirs, but also reduces the energy consumption and pollution associated with cement production, making it more environmentally friendly.

[0025] 5. The foamed cement sealing system in this invention has good temperature and salt resistance, and can adapt well to the high temperature and high salt environment of fractured reservoirs. At the same time, the foamed cement system can be directly prepared using produced water during on-site construction, which improves the utilization rate of produced water reinjection and further reduces costs. Attached Figure Description

[0026] Figure 1 The image shows the cured foamed cement sealing system obtained in Example 1. Figure 2 The image shows a microscopic view of the solidified foamed cement sealing system obtained in Example 1. Figure 3 The image shows the solidified foamed cement sealing system prepared in Comparative Example 2. Figure 4 For displacement device; Figure 5 For permeability evaluation; Figure 6 For evaluating the recyclability of foam; Figure 7 For injection evaluation device; Figure 8 The results of the injection performance evaluation of the foamed cement sealing system prepared in Example 1 are as follows; Figure 9 To evaluate the injection performance of the foamed cement sealing system prepared in Comparative Example 6. Detailed Implementation

[0027] In the following examples and comparative examples, the ultrafine cement was purchased from Zhucheng Jiuqi Building Materials Co., Ltd., model UHPCPI52.5; the ordinary silicate cement was purchased from Zhucheng Jiuqi Building Materials Co., Ltd., model PO42.5 (particle size 400~450 mesh); the fatty alcohol polyoxyethylene ether was purchased from Jiangsu Senhe Chemical Technology Co., Ltd., model AEO-9; the sodium fatty alcohol polyoxyethylene ether sulfate was purchased from Jiangsu Senhe Chemical Technology Co., Ltd.; the sodium carboxymethyl cellulose was purchased from Henan Qimeng Chemical Technology Co., Ltd.; and the hydroxyethyl cellulose was purchased from Henan Qimeng Chemical Technology Co., Ltd. (viscosity 3×10). 4 (mPa·s). Unless otherwise specified, all other raw materials are commercially available.

[0028] In the following examples and comparative examples, formation water with high salinity was used to simulate the high-salinity environment in fractured-vuggy reservoirs. The salinity of the water was 0-25 × 10⁻⁶. 4 mg / L. In the following examples and comparative examples, the curing process of the foamed cement sealing system under formation conditions was simulated by high-temperature curing.

[0029] Example 1: A foamed cement sealing system, comprising cement, foaming agent, solvent, chelating agent, retarder, water loss reducing agent, early strength agent and mineralized water; In this embodiment, the cement is ultrafine cement with a mesh size of 1350 mesh, and the cement weight is 20 parts. The water-cement ratio is 5.0. Foaming agent A is sodium α-alkenyl sulfonate, and the weight of foaming agent A is 0.4 parts. Foaming agent B is fatty alcohol polyoxyethylene ether, and the weight of foaming agent B is 0.2 parts. Foaming agent C is fatty alcohol polyoxyethylene ether sulfate, and the weight of foaming agent C is 0.4 parts. The co-solvent is ethanol, and the weight of co-solvent is 2 parts. The chelating agent is sodium citrate, and the weight of chelating agent is 0.3 parts. The retarder is sodium dihydrogen phosphate, and the weight of retarder is 0.3 parts. The water loss reducing agent is sodium carboxymethyl cellulose, and the weight of water loss reducing agent is 0.3 parts. The early strength agent is calcium chloride, and the weight of early strength agent is 1 part. The weight of mineralized water is 100 parts.

[0030] In this embodiment, a method for preparing a foamed cement sealing system is as follows: Step 1: Prepare mineralized water; Step 2, Cement Pretreatment: Pass the cement through a square-hole sieve to remove hard lumps or particles from the cement. Step 3, Cement mortar preparation: Step 31: Add cement, chelating agent, retarder, water loss reducer, early strength agent and mineralized water to the mixer in sequence; Step 32: Set the mixer to continuous mixing mode and continuously mix the cement, chelating agent, retarder, water loss reducer, early strength agent and mineralized water in the mixer until a uniform state is achieved to obtain cement mortar. Step 4: Preparation of foamed cement: Step 41: Add foaming agent A, foaming agent B, foaming agent C, and co-solvent to the mixer and stir to mix the cement mortar and foaming agent evenly. Step 42: Stop foaming after mixing to obtain the foamed cement sealing system.

[0031] Specifically, in step 1 of this embodiment, formation water is simulated using mineralized water with a mineralization degree of 22 × 10⁻⁶. 4 The formulation of mineralized water with a concentration of mg / L is shown in Table 1: Table 1. Water formulation based on mineralization

[0032] Specifically, in step 2 of this embodiment, the cement is ultrafine cement with a mesh size of 1350 mesh, and the square hole sieve has a mesh size of 1300 mesh. Specifically, in step 32 of this embodiment, the speed of the mixer is 300 r / min, and the mixing time is 20 min; Specifically, in step 41 of this embodiment, the speed of the mixer is 8000 r / min, and the mixing time is 3 min; In this embodiment, formation water is simulated using mineralized water with a mineralization of 22 × 10⁻⁶. 4 mg / L. The curing process of the foamed cement sealing system under formation conditions was simulated by high-temperature curing at 130℃ for 8 hours. After curing, the foamed cement sealing system successfully cured, as shown in the image below. Figure 1 As shown, the cured foamed cement sealing system exhibits high strength and stability under high temperature and high salt conditions, with no significant defoaming. Visible pores are present after curing. Microscopic images are shown below. Figure 2 As shown in the microscopic image, the pores are quite obvious, indicating that the system has good permeability.

[0033] Comparative Example 1: The difference between the foamed cement sealing system provided in this comparative example and Example 1 is that the foamed cement is prepared by a mixing method, while the other preparation methods and parameters are the same as in Example 1.

[0034] The preparation method of the foamed cement sealing system is as follows: Step 1: Prepare mineralized water; Step 2, Cement Pretreatment: Pass the cement through a square-hole sieve to remove hard lumps or particles from the cement. Step 3, Cement mortar preparation: Step 31: Add cement, chelating agent, retarder, water loss reducer, early strength agent and mineralized water to the mixer in sequence; Step 32: Set the mixer to continuous mixing mode and continuously mix the cement, chelating agent, retarder, water loss reducer, early strength agent and mineralized water in the mixer until a uniform state is achieved to obtain cement mortar. Step 4: Preparation of foamed cement: Step 41: Add foaming agent A, foaming agent B, foaming agent C, cosolvent, and mineralized water to another mixer, and introduce air to prepare a uniform and stable foam; Step 42: Add the foam to the mixer and mix it with the cement slurry to form foamed cement slurry.

[0035] Specifically, the mineralization of the water in step 1 is 22 × 10⁻⁶. 4 mg / L; Specifically, in step 2, the cement is ultrafine cement with a mesh size of 1350 mesh, and the square-hole sieve has a mesh size of 1300 mesh. Specifically, in step 32, the mixer speed is 300 r / min, and the mixing time is 20 min; Specifically, in step 41, the mixer speed is 8000 r / min, and the mixing time is 3 min; Specifically, in step 42, the mixer speed is 100 r / min and the mixing time is 5 min.

[0036] This comparative example uses mineralized water to simulate formation water, with a mineralization of 22 × 10⁻⁶. 4 mg / L. The curing process of the foamed cement sealing system under formation conditions was simulated by high-temperature curing, with a curing temperature of 130℃ and a curing time of 8 hours. The foamed cement sealing system prepared by the mixing method has lower stability than that prepared by the direct foaming method, and partial liquid separation occurs during the curing process, making it difficult to meet the requirements of deep formation regulation and displacement.

[0037] The curing time and compressive strength of the foamed cement sealing systems provided in Example 1 and Comparative Example 1 were measured respectively, and the results are shown in Table 2: Table 2 Curing time and compressive strength of the system under different foaming methods

[0038] Table 2 shows that the compressive strength of the foamed cement sealing system prepared by the mixing method is significantly lower than that prepared by the direct foaming method. This is because the secondary stirring during the mixing process disrupts the stability of the foam, resulting in more foam separation, larger bubbles, and reduced compressive strength. The mixing method can be used for the preparation of conventional foamed cement because conventional foamed cement has a low water-cement ratio of only 0.4-0.7 and a short curing time. Even if the secondary stirring disrupts the stability of the foam, it can still complete curing before the foam defoams.

[0039] Comparative Example 2: The difference between the foamed cement sealing system provided in this comparative example and Example 1 is that ordinary Portland cement of equal mass is used instead of ultrafine cement; all other preparation methods and parameters are the same as in Example 1. This comparative example uses mineralized water to simulate formation water, with a mineralization of 22 × 10⁻⁶. 4 mg / L. The curing process of the foamed cement sealing system under formation conditions was simulated through high-temperature curing, with a curing temperature of 130℃ and a curing time of 8 hours. Ordinary Portland cement exhibits poor curing performance after foaming under high water-cement ratio conditions, with significant foam defoaming. Figure 3 As shown.

[0040] Comparative Example 3: The foamed cement sealing system provided in this comparative example differs from that in Comparative Example 2 in that the weight of ordinary Portland cement is 50 parts, and the water-cement ratio is 2.0. All other preparation methods and parameters are the same as in Comparative Example 1. This comparative example uses mineralized water to simulate formation water, with a mineralization of 22 × 10⁻⁶. 4 mg / L. The curing process of the foamed cement sealing system under formation conditions was simulated through high-temperature curing, with a curing temperature of 130℃ and a curing time of 8 hours. Ordinary Portland cement can cure at high temperatures after foaming under low water-cement ratio conditions, but its high solid content results in a low foaming ratio, poor fluidity, and poor formation injectability, failing to meet on-site requirements.

[0041] The curing time and compressive strength of the foamed cement sealing systems provided in Example 1 and Comparative Examples 2-3 were measured respectively, and the results are shown in Table 3: Table 3 Curing time and compressive strength using different cement systems

[0042] Comparing Example 1 and Comparative Example 2, it can be seen that the curing time of ordinary Portland cement under high water-cement ratio conditions is much longer than the foam defoaming half-life, resulting in more foam defoaming and failure to form a foamed cement system. Comparing Example 1 and Comparative Example 3, it can be seen that ordinary Portland cement can only achieve the coupling of cement curing time and foam defoaming half-life to form a foamed cement system under low water-cement ratio conditions. Although the compressive strength is high, the low water-cement ratio, high solid content, low foaming ratio, poor system fluidity, and poor formation injection properties make it unable to meet the requirements of the field.

[0043] Comparative Example 4: The foamed cement sealing system provided in this comparative example is the system provided in Formula 3 of Example 1 in Chinese Patent Document CN 104946220 A. The foaming agent A is calcium nitrate, the foaming agent B is ammonium chloride, the foam stabilizer is a mixture of sodium N-dodecyliminodiacetic acid, polyoxyethylene polyoxypropylene block polyether, and hexadecyltrimethylammonium chloride, with the following mass fractions: sodium N-dodecyliminodiacetic acid 45%, polyoxyethylene polyoxypropylene block polyether 30%, and hexadecyltrimethylammonium chloride 25%. The water loss reducing agent is a terpolymer of 2-acrylamido-2-methylpropanesulfonic acid, acrylic acid, and allyl polyoxyethylene ether, with the following mass fractions: 2-acrylamido-2-methylpropanesulfonic acid 45%, acrylic acid 40%, and allyl polyoxyethylene ether 15%. The retarder is an aqueous solution of citric acid and organophosphonic acid, with the following mass percentages: citric acid 25%, organophosphonic acid 30%, and water 45%. Compared to Example 1, this system is a foamed cement system for well cementing. To achieve the purpose of sealing the wellbore, supporting the wellbore, and preventing fluid leakage, it features high strength and low permeability. However, after curing, the system has low permeability, easily causing complete formation blockage, which is detrimental to subsequent development. Furthermore, this system only needs to cure between the casing and the wellbore, resulting in a low water-cement ratio, poor fluidity, and difficulty in injection into the formation. Additionally, this system is suitable for low-temperature, easily leaking formations and cannot cure under high-temperature conditions.

[0044] Example 2: The difference between the foamed cement sealing system provided in this embodiment and that in Embodiment 1 is that the weight of the ultrafine cement is 25 parts and the water-cement ratio is 4.0. The other preparation methods and parameters are the same as in Embodiment 1.

[0045] Example 3: The difference between the foamed cement sealing system provided in this embodiment and that in Example 1 is that the weight of the ultrafine cement is 33 parts and the water-cement ratio is 3.0. The other preparation methods and parameters are the same as in Example 1.

[0046] Example 4: The difference between the foamed cement sealing system provided in this embodiment and that in Embodiment 1 is that the weight of the ultrafine cement is 50 parts and the water-cement ratio is 2.0. The other preparation methods and parameters are the same as those in Embodiment 1.

[0047] The density, curing time, and compressive strength after curing of the foamed cement systems provided in Examples 1-4 and Comparative Example 4 were measured respectively, and the results are shown in Table 4: Table 4 Curing time and compressive strength of the system under different water-cement ratios

[0048] In Examples 1-4, the curing temperature used was 130℃. According to Table 4, the density of Example 1 was 0.59 g / cm³. 3 The curing time was 5.5 hours, and the compressive strength after curing was 2.6 MPa, which meets the design requirements. As the water-cement ratio decreased and the solid content increased, the density of the foamed cement sealing system increased, the curing time decreased, and the compressive strength increased. This shows that the higher the content of ultrafine cement in the system, the greater the system density, the faster the curing speed, and the higher the strength after curing. Comparative Example 4 showed good curing performance under low-temperature curing conditions, but failed to cure under high-temperature curing conditions, making it unsuitable for use in underground high-temperature environments.

[0049] Example 5: The difference between the foamed cement sealing system provided in this embodiment and that in Example 1 is that the weight of the retarder is 0.1 parts, while the other preparation methods and parameters are the same as in Example 1.

[0050] Example 6: The difference between the foamed cement sealing system provided in this embodiment and that in Example 1 is that the weight of the retarder is 0.2 parts, while the other preparation methods and parameters are the same as in Example 1.

[0051] Example 7: The difference between the foamed cement sealing system provided in this embodiment and that in Example 1 is that the weight of the retarder is 0.4 parts, while the other preparation methods and parameters are the same as in Example 1.

[0052] Comparative Example 5: The difference between the foamed cement sealing system provided in this comparative example and Example 1 is that the weight of the retarder is 0.5 parts, while the other preparation methods and parameters are the same as in Example 1.

[0053] Table 5. Curing time and compressive strength of the system under different retarder concentrations

[0054] The curing temperature for Examples 5-7 and Comparative Example 5 was 130℃. According to Table 5, the higher the retarder concentration, the longer the curing time required. When the retarder weight part reached 0.5 parts, the curing time was longer than the foam defoaming half-life, resulting in complete foam defoaming and failure to form a foamed cement sealing system. When the retarder weight part was 0.4 parts, small bubbles coalesced into large bubbles during curing, reducing the system strength. When the retarder weight part was less than 0.3 parts, the curing time increased with increasing retarder concentration, but had little impact on strength.

[0055] Example 8: The difference between the foamed cement sealing system provided in this embodiment and that in Example 1 is that the foaming agent is sodium dodecyl sulfonate, the retarder is 2-acrylamide-2-methylpropanesulfonic acid, the water loss reducing agent is hydroxyethyl cellulose, and the early strength agent is calcium oxide.

[0056] Comparative Example 6: The foamed cement system provided in this comparative example is the solidified foam profile control agent for steam injection wells provided in Example 1 of Chinese Patent Document CN 118146776 A.

[0057] In Comparative Example 6 of this invention, the water-to-solid ratio is 2.0, and water glass is added to promote cement hydration and improve curing strength; while in Example 1 of this invention, a water-to-solid ratio of 5.0 is used, which can not only block the dominant channels, but also increase the permeability to provide mechanical shearing for the subsequent fluid, and also improve fluidity and reduce costs.

[0058] Comparative Example 7: The difference between the foamed cement sealing system provided in this comparative example and Example 1 is that the foaming agent A is sodium dodecylbenzenesulfonate, while the other preparation methods and parameters are the same as in Example 1.

[0059] Although sodium dodecylbenzenesulfonate and sodium α-alkenylsulfonate are both anionic surfactants, the foamed cement sealing system provided in Comparative Example 7 failed to foam successfully. This is because sodium dodecylbenzenesulfonate has poor compatibility with cement slurry.

[0060] Comparative Example 8: The difference between the foamed cement sealing system provided in this comparative example and Example 1 is that it is cured at room temperature, while the other preparation methods and parameters are the same as in Example 1.

[0061] Under normal temperature curing conditions, the cement hydration rate in high water-cement ratio foamed cement systems is relatively slow, and the cement curing time is difficult to couple with the foam stabilization time. By the time the cement has cured, the foam has already defoamed.

[0062] Comparative Example 9: The difference between the foamed cement sealing system provided in this comparative example and that in Comparative Example 8 is that the water-cement ratio is 4.0, while the other preparation methods and parameters are the same as in Example 1.

[0063] Experiment Example 1: Liquidity Evaluation Experiment like Figure 3 As shown, the flowability of the foamed cement sealing systems provided in Examples 1-8 and Comparative Examples 2-5 was measured using a standard flowmeter. The specific experimental steps are as follows: Step 1: Prepare the mortar self-leveling test board: Clean the mortar self-leveling test board (32*32cm) and the 30×50mm test mold, and place the mortar self-leveling test board on a stable surface; Step 2, Filling the mold: Slowly pour the prepared foamed cement system into the mold, ensuring even filling and avoiding air inclusions; pour the foamed cement sealing system into the mold in three batches, gently compacting it with a small stick after each filling to remove air bubbles; fill to the upper edge of the mold, ensuring the height of the foamed cement sealing system is equal to the mold body; gently smooth the surface of the foamed cement sealing system in the mold with a scraper to ensure a smooth surface; Step 3, Release the mold: Lift the mold vertically with even force, ensuring that the mold is lifted vertically from the foamed cement sealing system; note that the operation should be quick and stable to avoid any tilting or shaking of the mold; Step 4: Measure the expansion diameter: Immediately after the mold is lifted, start timing and observe the expansion diameter of the foamed cement sealing system on the standard flowability scale; record the maximum expansion diameter of the foamed cement sealing system after 30 seconds of expansion, which is the flowability of the system.

[0064] Specifically, the indoor temperature during Experiment Example 1 was 20℃.

[0065] Table 6. Fluidity Experiment Results for Different Systems

[0066] If the diameter of the foamed cement sealing system extending on the mortar self-leveling test plate is large (greater than or equal to 100 mm), the foamed cement sealing system has good fluidity. If the diameter of the foamed cement sealing system extending on the mortar self-leveling test plate is between 60 mm and 100 mm, the foamed cement sealing system has relatively good fluidity. If the diameter of the foamed cement sealing system extending on the mortar self-leveling test plate is small (less than or equal to 60 mm), the foamed cement sealing system has poor fluidity. Table 6 shows that the higher the water-cement ratio, the better the fluidity of the foamed cement sealing system. At the same water-cement ratio, the concentration of cement and retarder has little effect on fluidity. The foamed cement sealing system provided in Comparative Example 4 has poor fluidity and cannot meet the requirements for sealing the formation when injected with the foamed cement sealing system.

[0067] Experiment Example 2: Permeability Evaluation Experiment Through such Figure 4 , Figure 5 The experimental setup shown measures the permeability of the foamed cement sealing systems provided in Examples 1-8, Comparative Examples 3-4, and Comparative Example 9. The specific experimental steps are as follows: Step 1, according to Figure 4 Connect the experimental apparatus, pour the foamed cement sealing system prepared in each embodiment and comparative example into the intermediate container, open the valve, turn on the pump, adjust the pump speed to 0.5 mL / min, and drive the foamed cement system into the high temperature and high pressure visualization test tube; after foamed cement flows out of the outlet, continue to drive for 10 min, turn off the pump, and tighten the valves at the inlet and outlet of the high temperature and high pressure visualization test tube. Step 2: Place the high temperature and high pressure visualization test tube in a 130℃ oven for 8 hours. After the foam cement sealing system has solidified, open the valves at the inlet and outlet and dry it in the oven for 6 hours. Step 3, according to Figure 5 Connect the experimental setup, open the valve, turn on the pump, adjust the pump speed to 0.5 mL / min, and start measuring the permeability after water comes out of the outlet; Step 4: Adjust the pump speed to 1 mL / min, wait for the pressure gauge reading to stabilize for 5 minutes and then record the pressure gauge reading. Change the pump speed and continue to measure, and record the pressure gauge readings when the pump speed is 1 mL / min, 3 mL / min, 5 mL / min, 7 mL / min and 9 mL / min respectively. Step 5: After the test, pack up the experimental setup and clean the experimental instruments. Step 6: Calculate the permeability of different foamed cement systems according to the following formula. The experimental results are shown in Table 4.

[0068] The formula for calculating penetration rate is: ; Where k is the permeability, D; Q is the flow rate of fluid passing through the high-temperature and high-pressure visual test tube per unit time, cm3 / s; μ is the viscosity of the fluid, cP; L is the length of the high-temperature and high-pressure visual test tube, cm; A is the cross-sectional area of ​​the high-temperature and high-pressure visual test tube, cm2; ΔP is the pressure difference between the two ends of the high-temperature and high-pressure visual test tube, atm.

[0069] Table 7. Permeability Experiment Results of Different Systems

[0070] Table 7 shows that a higher water-cement ratio results in higher permeability; at the same water-cement ratio, the retarder concentration has little effect on permeability. This is because a higher water-cement ratio leads to a larger foam volume, lower foam liquid film strength, and more pronounced foam drainage, coalescence, and coarsening, resulting in higher system permeability. The significant difference in permeability between Example 2 and Comparative Example 9, both with a water-cement ratio of 4.0, is due to different curing temperatures. Example 2 underwent high-temperature curing, which significantly reduces slurry viscosity, further weakening the foam liquid film strength, accelerating drainage between air bubbles, and causing bubble coalescence to form larger pores, thus enhancing pore connectivity. The accelerated evaporation rate of water in cement under high-temperature conditions also leads to changes in the pore structure. Therefore, Example 2 has a higher permeability than Comparative Example 9.

[0071] Experiment Example 3: Foam Regeneration Experiment pass Figure 4 The experimental setup shown evaluates the foam regeneration performance of a cured foamed cement system. The specific experimental steps are as follows: Step 1, according to Figure 4 Connect the experimental setup, pour the foamed cement sealing system prepared in Example 1 into the intermediate container, open the valve, turn on the pump, adjust the pump speed to 0.5 mL / min, and displace the foamed cement system into the high-temperature and high-pressure visualization test tube. After foamed cement flows out of the outlet, continue displacement for 10 minutes, turn off the pump, and tighten the valves at the inlet and outlet of the high-temperature and high-pressure visualization test tube. Step 2: Place the high-temperature and high-pressure visualization test tube in a 130℃ oven for 8 hours to cure the system. Step 3, according to Figure 6 Reconnect the experimental setup, put the foaming solution into the intermediate container, open the valve, turn on the pump, and inject the foaming solution at a rate of 0.5 mL / min and N2 at a rate of 1 mL / min. Step 4: The appearance of foam at the outlet proves that the cured foamed cement system can provide mechanical shearing action, achieving foam shear regeneration. The experiment concludes; the experimental setup is disassembled and the equipment is cleaned.

[0072] Specifically, the foaming liquid in step 3 includes 100 parts by weight of water and 0.4 parts by weight of sodium α-olefin sulfonate.

[0073] Experiment Example 4: Injection Evaluation Experiment Through such Figure 7 The experimental setup shown evaluates the injectability of the foamed cement sealing systems provided in Example 1 and Comparative Example 6. The specific experimental steps are as follows: Step 1: Prepare 3 sand-filled pipes with different permeabilities, namely 0.05D, 1D, and 2D; Step 2, according to Figure 7Connect the experimental apparatus, pour the foamed cement sealing systems prepared in each embodiment and comparative example into the intermediate container, open the valve, turn on the pump, adjust the pump speed to 0.5 mL / min, and start the test; Step 3: Record the pressure gauge readings when the displacement is 0.2, 0.4, 0.6, 0.8, and 1 PV respectively; Step 4: After the test, pack up the experimental setup and clean the experimental instruments. Experimental results are as follows Figure 8 , Figure 9 As shown.

Claims

1. A foamed cement sealing system, characterized in that, Includes cement, foaming agent A, foaming agent B, foaming agent C, co-solvent, chelating agent, retarder, water loss reducer, early strength agent, and water; The foamed cement sealing system comprises the following components by weight: 20-50 parts cement, 0.1-1 part foaming agent A, 0.1-0.5 parts foaming agent B, 0.1-1 part foaming agent C, 1-5 parts co-solvent, 0.1-0.5 parts chelating agent, 0.1-0.4 parts retarder, 0.1-3 parts water loss reducer, 0.5-2 parts early strength agent, and 100 parts water. The water-cement ratio is 2.0-5.0; The cement is ultrafine cement.

2. The foamed cement sealing system according to claim 1, characterized in that, The curing time of the foamed cement sealing system is 2-10 hours, and the permeability of the cured foamed cement sealing system is 0.3-3.4D, and the compressive strength is 1.4-8.1MPa.

3. The foamed cement sealing system according to claim 1, characterized in that, The cement mesh size is 600-1500 mesh.

4. The foamed cement sealing system according to claim 1, characterized in that, The retarder is at least one of calcium saccharide, gluconate, citrate, tartrate, phosphate, tartrate, lignosulfonate, and 2-acrylamide-2-methylpropanesulfonic acid.

5. The foamed cement sealing system according to claim 1, characterized in that, The water loss reducing agent is at least one of polyvinyl alcohol water loss reducing agents, hydroxyethyl cellulose, carboxymethyl cellulose salt, butadiene-styrene latex, and vinyl acetate-ethylene latex.

6. The foamed cement sealing system according to claim 1, characterized in that, The early strength agent is at least one of the following: calcium chloride, sodium aluminate, calcium oxide, potassium chloride, calcium sulfate dihydrate, lithium chloride, sodium sulfate, calcium formate, calcium lactate, potassium aluminum sulfate, lithium hydroxide, potassium hydroxide, and calcium hydroxide. The co-solvent is at least one of ethanol, isopropanol, urea, and glycerol; The chelating agent is at least one of disodium ethylenediaminetetraacetate and sodium citrate.

7. The foamed cement sealing system according to claim 1, characterized in that, The foaming agent A is sodium α-alkenyl sulfonate; The foaming agent B is at least one of fatty alcohol polyoxyethylene ether, alkyl glycoside, polysorbate, and dehydrated sorbitol ester; The foaming agent C is sodium fatty alcohol polyoxyethylene ether sulfate.

8. A method for preparing the foamed cement sealing system as described in any one of claims 1 to 7, characterized in that, Includes the following steps: Step 1: Cement mortar preparation; add cement, retarder, water loss reducer, accelerator, and water in sequence, and stir continuously until homogeneous to obtain cement mortar: Step 2: Preparation of foamed cement; Add foaming agent to cement mortar and stir. Stop foaming after stirring to obtain foamed cement sealing system.

9. The preparation method of the foamed cement sealing system according to claim 8, characterized in that, In step 1, the stirring speed is 100 r / min to 500 r / min, and the stirring time is 10 min to 30 min.

10. The method for preparing the foamed cement sealing system according to claim 8, characterized in that, In step 2, the stirring speed is 5000r / min-10000r / min, and the stirring time is 3min-15min.

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