Fly ash curing foam system and preparation method thereof

Abstract

The invention relates to the technical field of oil-gas field development engineering, in particular to a coal ash curing foam system and a preparation method thereof. The fly ash curing foam system comprises cement, fly ash, an alkali activator, a foaming agent A, a foaming agent B, a water reducing agent and simulated formation water, the fly ash is adopted as a curing main agent of the curing foam system, part of cement can be replaced, the cost is reduced, resource utilization and storage of the fly ash are achieved, the permeability of the curing foam system is improved, and the service life of the curing foam system is prolonged. And foam regeneration is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas field development engineering, and particularly relates to a fly ash solidified foam system and a preparation method thereof. BACKGROUND

[0002] Fly ash is the main solid waste produced in the coal combustion process of coal-fired power plants, and its main components are silicon, aluminum, iron, calcium oxides and a small amount of unburned carbon. Large amounts of fly ash not only occupy valuable land resources, but also easily fly with the wind to cause air pollution, and the heavy metals and soluble salts contained therein also pose a risk of polluting the soil and groundwater under the action of rainwater leaching, posing a potential threat to the ecological environment. Therefore, it is urgent to seek a large-scale, high-value-added and environmentally friendly resource utilization approach for fly ash, especially to convert it into an engineering material with practical value, which has become an environmental protection and solid waste management problem to be solved.

[0003] At present, more than 80% of fly ash is used for building materials and road paving, and the rest is expanded to the fields of environmental protection (heavy metal adsorption), agriculture (soil conditioner) and the like. In recent years, some researchers including the present team have gradually used fly ash in the enhanced oil recovery process in oil and gas field development, forming many systems such as particle-strengthened foam and particle-strengthened gel. However, in the process of popularization and application of such systems, it is found that with the increase of injection volume, part of the fly ash particles will flow to the ground with the production of formation fluid, and cannot be effectively sealed in the underground. By referring to the fly ash filling process in the easy collapse area of the coal mining process, it is proposed to use fly ash solidified foam to fill and transform the natural or artificial flow channels such as large fractures, large channels and caves in the reservoir, to control the heterogeneity of the reservoir, so as to realize the balanced flow of injected fluid and formation fluid, and also to realize the solidification and filling of fly ash particles in the formation, so as to achieve the purpose of solid waste storage. This process has broad application prospects in the flow space transformation of the reservoir in the development process of the fractured-vuggy reservoir in China and the flow space transformation of the reservoir in the later stage of the development of the medium-high permeability reservoir (such as the formation of large flow channels due to long-term flushing of steam and the like in the later stage of the development of heavy oil thermal recovery).

[0004] For example, the development of fractured-vuggy reservoirs in China currently faces many difficulties: the geological environment is complex, large-scale fractures and caves are widely developed, and the size of the fractures and caves varies; the reservoir conditions are harsh, the reservoir temperature is 110-140℃, the formation water salinity is 20×10 4 -22×10 4mg / L; water channeling, gas channeling is serious, fluid through the fracture quickly leaks to the bottom of the well, resulting in un-impinged area can not be effectively displaced, low exploitation efficiency. Conventional plugging and adjusting system has two extremes, one is similar to foam channeling sealing system, poor stability, short sealing effective period; two is the gel, cement and other systems, the sealing strength is too high, often is a kind of irreversible plugging, damage the fluid mobility in the formation.

[0005] In addition, like heavy oil thermal recovery reservoir, the permeability is relatively high, under the scouring action of long-term injection of steam and other fluids, it is easy to form large pore in the late production period, resulting in the subsequent injected fluid channeling along the channel and unable to balance the sweep. This kind of reservoir also needs a kind of reservoir reconstruction fluid which can "block but not die", which can increase the flow resistance of fluid in the channel and weaken the channeling, but not completely block and still retain certain flow capacity.

[0006] Chinese patent document CN 117447758 A discloses a normal temperature chemical foaming solidified foam filling material and its preparation method, which is composed of modified urea-formaldehyde resin, foaming agent, suspending agent, multi-component curing agent, foam stabilizer and water. The system has the characteristics of normal temperature foaming, normal temperature curing, good diffusion performance, good thermal stability and good plugging performance. However, the system is mainly used in the process of mining in mines or coal mines to solve the problems of coal spontaneous combustion and air leakage plugging, without considering the problems of high temperature foaming and high temperature curing, and without considering the stability of the system under high salt conditions.

[0007] Chinese patent document CN 118146776 A discloses a solidified foam profile control agent for steam channeling well of steam stimulation and a profile control method, which is composed of water glass, cement, inorganic solid filler, flow modifier, retarder and foaming agent. The system can be used for steam channeling profile control of steam stimulation well, and has good suspensibility, high foaming multiple and high solidification strength. Although the system is mainly applied to thermal recovery well, since the injection of steam is after the solidification of the solidified foam profile control agent, the system only considers the foaming performance without considering the temperature resistance and salt resistance performance; the system has poor fluidity, low foaming volume, resulting in high cost; the system has low permeability, which blocks the channel after being injected into the formation, and cannot realize the shear regeneration of the subsequent injected foam.

[0008] Therefore, the present patent aims to form a new type of channeling sealing system which can be used in oil and gas field development, to realize the spatial remodeling of reservoir channeling, to change the "highway" of fluid easy channeling into the "shady path" of fluid slow flow, to realize the expansion of fluid sweep, and at the same time, to permanently seal the fly ash as a remodeling skeleton in the ground during the process of reservoir spatial remodeling, to realize the solid waste storage. SUMMARY

[0009] In order to overcome the above-mentioned deficiencies of the prior art, the present application provides a fly ash solidification foam system and a preparation method thereof, which uses fly ash as a solidification main agent and cement as a solidification auxiliary agent, so as to not only reduce the cost and realize the resource utilization and storage of fly ash, but also avoid the stratified settlement of fly ash under the condition of high water-cement ratio through the synergistic effect of foam and cement, so as to ensure the carrying capacity of the system to fly ash; and through the synergistic effect with cement, the system can not only have the solidification capacity under the condition of high water-cement ratio, but also store fly ash underground; and through the synergistic effect with high water-solid ratio, the system can improve the permeability of the foam cement system; the present application comprehensively considers multiple factors such as fly ash, cement, high water-solid ratio, high temperature and high salt, and is matched to obtain a foaming agent A and a foaming agent B, so as to realize the coupling of the foam stabilizing time and the cement solidification time.

[0010] In order to achieve the above-mentioned purposes, the present application adopts the following technical solutions: A fly ash solidification foam system, comprising cement, fly ash, an alkali activator, a foaming agent A, a foaming agent B, a water reducing agent and water.

[0011] The fly ash solidification foam system comprises the following components by weight: 20-25 parts of cement and fly ash, wherein the mass ratio of cement to fly ash is 0.2-1; 0.75-2.5 parts of an alkali activator; 0.1-1 parts of a foaming agent A; 0.1-1 parts of a foaming agent B; and 0.1-0.5 parts of a water reducing agent.

[0012] The water-solid ratio is 4.0-5.0, and the water-solid ratio in the present application is the mass ratio of water to solid particles (i.e. cement and fly ash).

[0013] The solidification time of the fly ash solidification foam system is 2-10 h, and the solidification temperature is 110-140 DEG C.

[0014] The permeability of the fly ash solidification foam system after solidification is 2.7-3.4 D, and the compressive strength is 0.8-1.6 MPa.

[0015] Preferably, the cement is ultra-fine cement. Preferably, the mesh number of the cement is 600-1500 mesh. Preferably, the fly ash is at least one of primary fly ash and ultra-fine fly ash. Preferably, the mesh number of the primary fly ash is 325-400 mesh. Preferably, the mesh number of the ultra-fine fly ash is 600-1000 mesh, and the activity is 80-95%.

[0016] Preferably, the water is simulated formation water, and the simulated formation water is used to simulate the high-salt environment of a fracture-vug type oil reservoir in the laboratory, and the salinity of the simulated formation water is 0-25 x 10 4 mg / L. Preferably, the alkali activator is at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, ammonia, sodium silicate; Preferably, the water reducing agent is at least one of a naphthalene series water reducing agent, a lignin sulfonate, an aminosulfonate series water reducing agent, a polycarboxylic acid water reducing agent, a fatty acid series water reducing agent; Preferably, the foaming agent A is at least one of lauryl amidopropyl betaine, cocamidopropyl betaine, glycerol acyl amino acid, sodium lauroyl glutamate, sodium cocoyl glutamate; Preferably, the foaming agent B is at least one of tea saponin, oil tea saponin.

[0017] The fly ash solidification foam system provided by the application realizes resource utilization of fly ash, improves flowability and pumpability of the system, and enables the system to reach a target fracture and cavity in a fracture and cavity reservoir stratum after being injected into the stratum, to be solidified to form a lightweight material with a porous structure under high temperature and high pressure, and to be stored underground; the system can realize plugging of an underground channeling flow passage, the porous structure after the foam is solidified does not completely block the stratum, but adjusts free flow in the fracture and cavity to seepage in the solidified foam, so that the system still has a certain permeability, provides shearing regeneration conditions for subsequent injected foam, and improves migration depth of the foam; addition of fly ash also effectively reduces cost, realizes recycling of resources, has certain environmental protection benefits, and can reduce 0.8 tons of carbon emission per ton of fly ash used to replace cement.

[0018] The fly ash solidification foam system provided by the application utilizes synergistic action of fly ash and high water-solid ratio to optimize performance of a foam cement system: (1) the fly ash solidification foam system has excellent flowability, can realize foaming of the fly ash solidification foam system before being injected into a stratum, can avoid poor foaming effect caused by shearing action of the stratum on one hand, and can effectively solve the problem of easy stratification and sedimentation of fly ash under high water-cement ratio on the other hand; (2) on one hand, fly ash generates a porous structure by oxidation of residual carbon under high temperature, and water in cement evaporates to form a pore under high water-solid ratio, so as to improve permeability of the system; on the other hand, under high water-solid ratio, a foam liquid film has low strength, so as to further improve pore-forming ability of fly ash and improve permeability of the system.

[0019] The application provides a preparation method of a fly ash solidification foam system, which comprises the following steps: Step 1, fly ash-cement mortar preparation: cement, fly ash, an alkali activator, a water reducing agent and water are sequentially added, and continuous stirring is performed until uniformity is achieved, to obtain fly ash-cement mortar; Step 2, system preparation: the foaming agent A, foaming agent B are added into fly ash-cement mortar in sequence and stirred, and the foaming is stopped after the stirring is completed, so that the fly ash solidification foam system is obtained; Preferably, the water in step 1 is simulated formation water, and the salinity is 0-25×10 4 mg / L; Preferably, the continuous stirring state in step 1 is low-speed stirring, and the rotating speed is 100r / min-500r / min, and the stirring time is 20min-40min. Preferably, the stirring in step 2 is high-speed stirring, and the rotating speed is 5000r / min-10000r / min, and the stirring time is 3min-15min.

[0020] Compared with the prior art, the beneficial effects of the present application are: 1. The fly ash solidification foam system provided in the present application is different from the conventional foam cement in that fly ash is used as a solidification main agent, and cement is only used as a solidification auxiliary agent, so that the resource utilization of fly ash is realized. The addition of fly ash has a foam stabilizing effect on the foam, so that the system is more stable, and the defoaming time of the foam is prolonged. On the other hand, the addition of fly ash improves the fluidity and pumpability of the system, so that it is easier to inject into the formation. At the same time, through the synergistic effect of the foam and the cement, the stratified settlement of fly ash under the condition of high water-cement ratio is avoided, and the carrying capacity of the system for fly ash is ensured.

[0021] 2. Fly ash has a pozzolanic effect, and after the addition of fly ash in the system, it can react with the cement hydration product to improve the long-term strength stability of the material, effectively inhibit the high-temperature strength decay of the system, and more effectively plug the channeling channels generated under the condition of large cracks and large caves in the fracture-cave formation.

[0022] 3. The fly ash solidification foam system in the present application is prepared with high salinity brine, which provides feasibility for using produced water as water source for large-scale injection, further reduces the cost, and realizes the resource utilization of produced water.

[0023] 4. In the present application, fly ash is used as a solidification main agent, the amount of cement is reduced, carbon emission and energy consumption are reduced, the damage to the formation is reduced, and for every ton of fly ash used, 0.8 tons of CO2 emission can be reduced.

[0024] 5. After the system of the present application is injected into the formation, it is solidified in the fracture-cave and large cracks, and the fly ash is sealed in the underground, so that the resource utilization of fly ash is realized, and at the same time, the underground storage of fly ash is realized.

[0025] 6.The fly ash solidified foam system provided by the present application combines the advantages of foam and cement, on the one hand, has high fluidity of foam, and can enter the target fracture and cavity after being injected into the stratum; on the other hand, inherits the solidifiable advantage of cement, and can be solidified after entering the target fracture and cavity, and has high plugging strength.

[0026] 7.The fly ash solidified foam system in the present application realizes the transformation of free flow to seepage in the reservoir, has a certain porosity and permeability channel after being solidified, can solve the problem that the foam lacks mechanical shearing in the fracture and cavity and is difficult to regenerate after defoaming, and realizes the shearing regeneration of the foam through the constructed porous structure, and improves the migration depth of the foam. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is an image of the fly ash solidified foam system after being solidified in Example 1; Figure 2 is a displacement experiment device; Figure 3 is a permeability evaluation experiment device; Figure 4 is a foam regeneration evaluation experiment device; Figure 5 is an injection evaluation experiment device; Figure 6 is the injection evaluation experiment result of Example 1; Figure 7 is the injection evaluation experiment result of Comparative Example 4. DETAILED DESCRIPTION

[0028] In the following examples and comparative examples, the ultra-fine cement is purchased from Zhucheng Jiuli Building Material Co., Ltd., and the type is UHPCPI52.5; the ultra-fine fly ash is purchased from Guolun Zhonghe Science and Technology Development Co., Ltd.; the first-grade fly ash, the second-grade fly ash and the third-grade fly ash are purchased from Zhucheng Jiuli Building Material Co., Ltd., and the type is C-class fly ash; the calcium lignosulfonate is purchased from Tianjin Huasheng Chemical Reagent Co., Ltd.; the polyester polycarboxylic acid water reducing agent is purchased from Sichuan Dongrun Baisheng New Material Co., Ltd. The remaining raw materials can be obtained from commercial channels, unless otherwise specified.

[0029] In the following examples and comparative examples, the high-temperature curing is used to simulate the solidification process of the fly ash solidified foam system under the stratum condition.

[0030] Example 1: A fly ash solidified foam system, which is composed of cement, fly ash, alkali activator, foaming agent A, foaming agent B, water reducing agent and simulated stratum water; In this embodiment, the cement is selected as superfine cement, the weight of cement is 10 parts, the fly ash is selected as superfine fly ash, the weight of fly ash is 15 parts, the water-solid ratio is 4.0, the proportion of fly ash replacing cement is 60%, the foaming agent A is selected as cocamide propyl betaine, the weight of foaming agent A is 0.3 parts, the foaming agent B is selected as tea saponin, the weight of foaming agent B is 0.2 parts, the alkali activator is selected as sodium carbonate, the weight of alkali activator is 1.5 parts, and the water reducing agent is selected as calcium lignin sulfonate, the weight of water reducing agent is 0.3 parts.

[0031] In this embodiment, the preparation method of the fly ash solidified foam system is as follows: Step 1, configure simulated formation water; Step 2, material pretreatment: pass the cement through the square hole sieve 1, pass the fly ash through the square hole sieve 2, and sieve out the hard blocks or particles in the cement and fly ash; Step 3, preparation of fly ash-cement mortar: Step 31, add the cement, fly ash, alkali activator, water reducing agent and simulated formation water into the mixer in sequence; Step 32, set the mixer to a continuous stirring state, continuously stir the cement, fly ash, alkali activator, water reducing agent and water in the mixer until a uniform state is reached to obtain the cement mortar; Step 4, preparation of solidified foam system: Step 41, add the foaming agent A and foaming agent B into the mixer and stir to uniformly mix the cement mortar and foaming agent; Step 42, stop foaming after stirring to obtain the fly ash solidified foam system.

[0032] Specifically, in step 1 of this embodiment, simulated formation water is used to simulate the high-salt environment of the fracture-vug type oil reservoir, the salinity of the simulated formation water is 22×10 4 mg / L, and the formula of the simulated formation water is shown in Table 1.

[0033] Table 1 Formula of simulated formation water

[0034] Specifically, in step 2 of this embodiment, the cement is superfine cement with a mesh number of 1350, and the mesh number of the square hole sieve 1 is 1300; Specifically, in step 2 of this embodiment, the fly ash is superfine fly ash with a mesh number of 800, and the mesh number of the square hole sieve 2 is 800; Specifically, in step 32 of this embodiment, the stirring speed of the mixer is 300 r / min, and the stirring time is 20 min; Specifically, in step 31 of this embodiment, the stirring speed of the mixer is 8000 r / min, and the stirring time is 3 min; The present embodiment simulates the solidification process of the fly ash solidified foam system under stratum conditions by high temperature curing, wherein the curing temperature is 130℃ and the curing time is 8h. After curing, the fly ash solidified foam system is successfully solidified, and the image after solidification is shown in Figure 1 The solidified fly ash solidified foam system has high strength and is relatively stable at high temperature without obvious defoaming. After solidification, there are visible pores.

[0035] Comparative Example 1 The system provided in the present comparative example is the solidified foam profile control agent for steam huff and puff channeling wells provided in Example 1 of Chinese patent document CN 118146776 A. Compared with Example 1, the applicable reservoir temperature of the system is 40-60℃, so the curing temperature of Comparative Example 1 is 50℃.

[0036] Comparative Example 2 The difference between the present comparative example and Comparative Example 1 is that the curing temperature of the system is 130℃, and the other preparation methods and parameters are the same as those of Comparative Example 1.

[0037] Comparative Example 3 The difference between the present comparative example and Comparative Example 1 is that the water used in the system is simulated stratum water, and the salinity of the simulated stratum water is 22×10 4 mg / L, and the other preparation methods and parameters are the same as those of Comparative Example 1.

[0038] Comparative Example 4 The system provided in the present comparative example is the solidified foam profile control agent for steam huff and puff channeling wells provided in Example 5 of Chinese patent document CN 118146776 A. Compared with Example 1, the applicable reservoir temperature of the system is 40-60℃, so the curing temperature of Comparative Example 4 is 50℃.

[0039] Comparative Example 5 The difference between the present comparative example and Comparative Example 4 is that the curing temperature of the system is 130℃, and the other preparation methods and parameters are the same as those of Comparative Example 4.

[0040] Comparative Example 6 The difference between the present comparative example and Comparative Example 4 is that the water used in the system is simulated stratum water, and the salinity of the simulated stratum water is 22×10 4 mg / L, and the other preparation methods and parameters are the same as those of Comparative Example 4.

[0041] The system in Comparative Examples 1 and 3 has good curing effect in a 50℃ environment, while the system in Comparative Examples 2 and 4 has obvious defoaming phenomenon after curing at 130℃, and it is difficult to form a complete solidified foam. The system in Comparative Examples 3 and 6 cannot foam under high salt conditions.

[0042] The solidified foam profile control agent provided in Chinese patent document CN 118146776 A performs poorly under high temperature and high mineralization conditions, because cement particles, temperature, and mineralization all affect the stability of the foam, and the foam, temperature, and mineralization also affect the hydration of the cement. The solidified foam profile control agent provided in Chinese patent document CN 118146776 A only considers the compatibility of the foaming agent with the cement, without considering the effects of temperature and mineralization.

[0043] Example 2: The fly ash solidified foam system provided in this example differs from that of Example 1 in that the fly ash is replaced with equal amounts of first-grade fly ash instead of superfine fly ash, and the other preparation methods and parameters are the same as those of Example 1.

[0044] Comparative Example 7: The fly ash solidified foam system provided in this comparative example differs from that of Example 1 in that the fly ash is replaced with equal amounts of second-grade fly ash instead of superfine fly ash, and the other preparation methods and parameters are the same as those of Example 1.

[0045] Comparative Example 8: The fly ash solidified foam system provided in this comparative example differs from that of Example 1 in that the fly ash is replaced with equal amounts of third-grade fly ash instead of superfine fly ash, and the other preparation methods and parameters are the same as those of Example 1.

[0046] The solidification time and compressive strength of the fly ash solidified foam systems provided in Examples 1-2 and Comparative Examples 7-8 were measured, and the results are shown in Table 2.

[0047] Table 2 Effects of different fly ashes on the solidification time and compressive strength of the system

[0048] As can be seen from Table 2, the system can be solidified after the addition of superfine fly ash and first-grade fly ash, and the solidification time of the system after the addition of superfine fly ash is slightly shorter than that of the system after the addition of first-grade fly ash, and the compressive strength of the system after the addition of superfine fly ash is significantly higher than that of the system after the addition of first-grade fly ash, while the system cannot be solidified after the addition of second-grade fly ash and third-grade fly ash. This is because fly ash has a pozzolanic effect and can react with cement hydration products, but different fly ashes have different reactivity, among which the reactivity of superfine fly ash is the strongest, and the reactivity of third-grade fly ash is the weakest. Therefore, the addition of superfine fly ash to the system has the best effect, followed by the addition of first-grade fly ash, while the addition of second-grade fly ash and third-grade fly ash results in the system being unable to be solidified due to the too weak reactivity.

[0049] Example 3: The fly ash solidified foam system provided in the embodiment differs from that of embodiment 1 in that the weight part of the ultra-fine cement is 12.5 parts, the weight part of the ultra-fine fly ash is 12.5 parts, the proportion of fly ash replacing cement is 50%, and other preparation methods and parameters are the same as those of embodiment 1.

[0050] Embodiment 4: The fly ash solidified foam system provided in the embodiment differs from that of embodiment 1 in that the weight part of the ultra-fine cement is 7.5 parts, the weight part of the ultra-fine fly ash is 17.5 parts, the proportion of fly ash replacing cement is 70%, and other preparation methods and parameters are the same as those of embodiment 1.

[0051] Embodiment 5: The fly ash solidified foam system provided in the comparative example differs from that of embodiment 1 in that the weight part of the ultra-fine cement is 5 parts, the weight part of the ultra-fine fly ash is 20 parts, the proportion of fly ash replacing cement is 80%, and other preparation methods and parameters are the same as those of embodiment 1.

[0052] The solidification time and compressive strength of the fly ash solidified foam systems provided in embodiments 1, 3-5 were measured respectively, and the results are shown in Table 3.

[0053] Table 3 Influence of different proportions of fly ash replacing cement on the solidification time and compressive strength of the system

[0054] According to Table 3, as the proportion of fly ash replacing cement increases, the solidification time of the system increases and the compressive strength decreases.

[0055] Comparative example 9: The fly ash solidified foam system provided in the comparative example differs from that of embodiment 1 in that the weight part of the alkali activator is 0 parts, and other preparation methods and parameters are the same as those of embodiment 1.

[0056] The solidification time and compressive strength of the fly ash solidified foam systems provided in embodiment 1 and comparative example 9 were measured respectively, and the results are shown in Table 4. Table 4 Influence of activator on the solidification time and compressive strength of the system

[0057] According to Table 4, the system without adding alkali activator cannot be solidified, because the reactivity of fly ash itself is low under normal conditions, and the chemical activity of fly ash can be improved after adding alkali activator. The alkali activator can react with the aluminum-silicon components in fly ash, promote the dissolution of silica and aluminate in fly ash, and form substances that can react with cement hydration products, thereby improving the reactivity of fly ash.

[0058] Embodiment 6: The fly ash solidified foam system provided by the embodiment differs from that of Example 1 in that the foaming agent A is selected to be glycerol amido acid, the foaming agent B is selected to be oil tea saponin, the alkali activator is selected to be sodium hydroxide, the water reducing agent is selected to be a polyester polycarboxylic acid water reducing agent, and other preparation methods and parameters are the same as those of Example 1.

[0059] Comparative Example 10: The fly ash solidified foam system provided by the comparative example differs from that of Example 1 in that the foaming agent A is selected to be dodecyl glycol amido acid, and other preparation methods and parameters are the same as those of Example 1.

[0060] Although dodecyl glycol amido acid and cocamidopropyl betaine are both amphoteric surfactants, the fly ash solidified foam cement system provided by Comparative Example 10 failed to successfully foam, because dodecyl glycol amido acid has poor compatibility with the fly ash cement slurry.

[0061] Comparative Example 11: The fly ash solidified foam system provided by the comparative example differs from that of Example 1 in that the curing condition is normal temperature curing, and other preparation methods and parameters are the same as those of Example 1.

[0062] Under the condition of normal temperature curing, the cement hydration speed of the fly ash solidified foam system provided by Comparative Example 11 is slow, and it is difficult to couple the cement solidification time with the foam stabilization time, and the foam has already defoamed when the cement solidifies.

[0063] Comparative Example 12: The fly ash solidified foam system provided by the comparative example differs from that of Example 4 in that the curing condition is normal temperature curing.

[0064] Experimental Example 1, fly ash carrying experiment: The carrying capacity of water, foam and the system provided by Experimental Example 1 for fly ash was respectively evaluated, the amount of fly ash carried by water and foam was the same as that of Example 1, the foaming agent used by the foam and the amount thereof were the same as those of Example 1, and the three systems were poured into a measuring cylinder and left to stand, and the fly ash sedimentation phenomenon was observed.

[0065] The carrying capacity of water for fly ash was poor, and the fly ash completely settled at the bottom after 3 minutes. The carrying capacity of foam for fly ash was strong, and the fly ash settled at the bottom after 20 minutes. The carrying capacity of the system in Experimental Example 1 for fly ash was the strongest, and no sedimentation phenomenon occurred before the system solidified.

[0066] Experimental Example 2, permeability evaluation experiment: The permeability of the fly ash solidified foam system provided by Experimental Example 1 was evaluated by the method of Example 2. Figure 2 、 Figure 3The experimental apparatus shown measures the permeability of the fly ash solidified foam systems provided by Examples 1-5, Comparative Example 1, Comparative Example 4, and Comparative Example 12. The specific experimental steps are as follows: Step 1, according to Figure 2 Connect the experimental apparatus, pour the foam system prepared by each example and comparative example into the middle container, open the valve, open the pump, adjust the pump speed to 0.5 mL / min, and drive the foam cement system into the high temperature and high pressure visualization test tube; continue to drive for 10 min after the foam cement flows out at the outlet, 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 the oven for 8 h, and after the foam cement channeling system is solidified, open the valves at the inlet and outlet in the oven for 6 h; Step 3, according to Figure 3 Connect, open the valve, open the pump, adjust the pump speed to 0.5 mL / min, and start measuring the permeability after water comes out at the outlet; Step 4, adjust the pump speed to 1 mL / min, record the pressure gauge reading after waiting for 5 min when the pressure indication is stable, 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, test is completed, clean up the experimental apparatus, and clean the experimental apparatus; Step 6, calculate the permeability of different foam cement systems according to the following formula, and the experimental results are shown in Table 5.

[0067] The permeability calculation formula is: ; Wherein, k is the permeability, D; Q is the flow rate of fluid through the high temperature and high pressure visualization test tube per unit time, cm 3 / s; μ is the viscosity of the fluid, cP; L is the length of the high temperature and high pressure visualization test tube, cm; A is the cross-sectional area of the high temperature and high pressure visualization test tube, cm 2 ; ΔP is the pressure difference between the two ends of the high temperature and high pressure visualization test tube, atm.

[0068] Specifically, the required curing temperature of the system provided by Comparative Example 1 in Step 2 is 50℃, and the required curing temperature of the rest of the systems is 130℃.

[0069] Table 5 Permeability and porosity experimental results of different systems

[0070] According to Table 5, the greater the proportion of fly ash replacing cement, the higher the permeability; the permeability of the first fly ash is smaller when the proportion of fly ash replacing cement is the same. The reason is that fly ash reacts to form a porous structure under high temperature conditions (pore forming by oxidation of residual carbon), which improves the permeability of the system, and the first fly ash has a higher content of residual carbon; the reason for the large difference in permeability between Example 4 and Comparative Example 12 is that the curing temperatures are different. Example 4 is high-temperature curing, and high-temperature conditions can significantly reduce the viscosity of the slurry, further weaken the strength of the foam liquid film, accelerate the drainage of the liquid film between bubbles, and lead to the coalescence of bubbles to form large-sized pores, enhancing the connectivity of the pores. The evaporation rate of water in cement under high-temperature conditions is accelerated, which also leads to changes in the pore structure. Fly ash reacts to form a porous structure under high-temperature conditions. When cured at room temperature, fly ash will also fill in large pores due to its small particle size, thereby reducing the permeability of the system. Therefore, the permeability of Example 4 is higher than that of Comparative Example 12.

[0071] Experimental Example 3, Foam Regeneration Experiment: The foam regeneration performance of the fly ash solidified foam system after solidification was evaluated by the experimental device shown in Figure 3 The specific experimental steps are as follows: Step 1, according to Figure 2 Connect the experimental device, pour the fly ash solidified foam system prepared in each example and comparative example into the middle container, open the valve, open the pump, adjust the pump speed to 0.5 mL / min, and drive the system into the high-temperature high-pressure visualization test tube. After the foam flows out at 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 high-pressure visualization test tube; Step 2, place the high-temperature high-pressure visualization test tube in the oven for curing for 8 h, and wait for the system to solidify; Step 3, according to Figure 4 Reconnect the experimental device, pour the foam blowing liquid into the middle container, open the valve, open the pump, and the injection speed of the foam blowing liquid is 0.5 mL / min and the injection speed of N2 is 1 mL / min; Step 4, foam appears at the outlet, proving that the solidified system can provide mechanical shear to realize foam shear regeneration. After the experiment is completed, disassemble the experimental device and clean the experimental equipment.

[0072] Specifically, the required curing temperature of the system provided by Comparative Example 1 in Step 2 is 50℃, and the required curing temperature of the remaining systems is 130℃.

[0073] Specifically, the foam blowing liquid in Step 3 includes 100 parts by weight of water and 0.4 parts by weight of AOT.

[0074] Conclusion: After the foam regeneration experiment, the foam cement systems obtained by Examples 1-5 all have foam at the outlet, and the foam cement systems obtained by Comparative Examples 1, 4 and 12 all do not have foam at the outlet.

[0075] Experimental Example 4, injectivity evaluation experiment: The injectivity of the systems provided by Examples 1 and Comparative Example 4 was evaluated by using the experimental device as shown in Figure 5 The specific experimental steps are as follows: Step 1, prepare three sandpacks with different permeabilities, the permeabilities are 0.05D, 1D and 2D respectively; Step 2, according to Figure 4 Connect the experimental device, pour the systems prepared by each example and comparative example into the middle container, open the valve, open the pump, adjust the pump speed to 0.5 mL / min, and start the test; Step 3, record the pressure gauge readings at 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1 PV respectively; Step 4, after the test, clean up the experimental device and clean the experimental instrument; The experimental results are shown in Figure 6 , Figure 7 .

Claims

1. A fly ash solidified foam system, characterized in that, Including cement, fly ash, alkali activator, foaming agent A, foaming agent B, water-reducing agent, and water; The water-to-solid ratio is 4.0 to 5.0, where the water-to-solid ratio is the mass ratio of water to solid particles, and the solid particles are cement and fly ash. The foaming agent A is at least one of lauramidopropyl betaine, cocamidopropyl betaine, glyceryl amino acid, sodium lauroyl glutamate, and sodium cocoyl glutamate. The foaming agent B is at least one of tea saponin and tea oil saponin.

2. The fly ash solidified foam system according to claim 1, characterized in that, It includes the following components by weight: 20-25 parts cement and fly ash, 0.75-2.5 parts alkali activator, 0.1-1 part foaming agent A, 0.1-1 part foaming agent B, and 0.1-0.5 parts water-reducing agent; The mass ratio of cement to fly ash is 0.2 to 1.

3. The fly ash solidified foam system according to claim 1, characterized in that, The curing time of the fly ash solidified foam system is 2-10 hours, and the curing temperature is 110-140℃.

4. The fly ash solidified foam system according to claim 1, characterized in that, The solidified fly ash foam system has a permeability of 2.7-3.4D and a compressive strength of 0.8-1.6MPa after solidification.

5. The fly ash solidified foam system according to claim 1, characterized in that, The cement is ultrafine cement; The cement mesh size is 600-1500 mesh.

6. The fly ash solidified foam system according to claim 1, characterized in that, The fly ash is at least one of grade I fly ash and ultrafine fly ash; The grade I fly ash has a mesh size of 325-400 mesh. The ultrafine fly ash has a mesh size of 600-1000 mesh and an activity of 80-95%.

7. The fly ash solidified foam system according to claim 1, characterized in that, The alkaline activator is at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, ammonia, and sodium silicate. The water-reducing agent is at least one of naphthalene-based water-reducing agents, lignin sulfonate, aminosulfonate-based water-reducing agents, polycarboxylate-based water-reducing agents, and fatty acid-based water-reducing agents.

8. The method for preparing the fly ash solidified foam system according to claim 1, characterized in that, The water is simulated formation water with a salinity of 0-25×10⁻⁶. 4 mg / L.

9. A method for preparing a fly ash solidified foam system as described in any one of claims 1 to 8, characterized in that, Includes the following steps: Step 1, Preparation of fly ash-cement mortar: Add cement, fly ash, alkali activator, water-reducing agent and water in sequence, and stir continuously until uniform to obtain fly ash-cement mortar; Step 2, System Preparation: Add foaming agent A and foaming agent B to fly ash-cement mortar in sequence and stir. Stop foaming after stirring to obtain fly ash solidified foam system.

10. The method for preparing the fly ash solidified foam system according to claim 9, characterized in that, The stirring speed in step 1 is 100 r / min-500 r / min, and the stirring time is 20 min-40 min; The stirring speed in step 2 is 5000 r / min-10000 r / min, and the stirring time is 3 min-15 min.

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