Low-density acid-soluble consolidation plugging agent, plugging slurry and drilling plugging method thereof

Abstract

The invention belongs to the field of plugging of petroleum drilling, and discloses a low-density acid-soluble consolidation plugging agent, plugging slurry and a drilling plugging method thereof. The plugging agent comprises magnesium oxide, a curing auxiliary material, a time regulator and a structuring agent, wherein the structuring agent comprises acid-soluble fibers, graded rigid particles and elastic particles. According to the plugging agent and the plugging slurry provided by the invention, the components are optimized, the retention effect of the plugging slurry is optimized by adopting the structuring agent, a grid structure is formed by mutual traction among fibers of the acid-soluble fibers, and meanwhile, rigid particles, elastic particles and graded rigid particles are captured for bridging at narrow positions of cracks, so that the whole plugging layer stops moving to the deep positions of the cracks, and the plugging effect is improved. The elastic particles are extruded to deform, the elastic force of the elastic particles acts on the crack surface, the friction force between the plugging layer and the crack surface is enhanced, and the retention effect of the plugging slurry is enhanced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lost circulation control in oil drilling, and in particular to a low-density acid-soluble consolidation lost circulation agent, a lost circulation slurry and a drilling lost circulation control method. BACKGROUND

[0002] Lost circulation is a common downhole problem in drilling and completion operations, often accompanied by significant loss of drilling fluid, which in turn leads to significant extension of drilling operation cycle, decrease of borehole cleanliness, and even chain reaction such as sticking of drill pipe. This series of complex problems not only deeply affect the efficiency of drilling operation, but also directly lead to sharp rise of drilling cost, causing obstacles and challenges for safe and efficient completion of drilling and completion tasks.

[0003] Lost circulation can be divided into the following five categories according to the speed of loss: micro leakage, small leakage, medium leakage, large leakage and severe loss. The loss speed of micro leakage is generally less than 5m 3 / h, and the loss often occurs under the action of pressure difference, with very small amount and slow speed, and usually bridging plugging is used. When the leakage rate is 5~15m 3 / h, it belongs to small leakage, and when the leakage rate is 5~30m 3 / h, it belongs to medium leakage. Small leakage and medium leakage can be plugged by bridging plugging. When the leakage rate is 30~60m 3 / h, it belongs to large leakage. When the leakage rate exceeds 60m 3 / h, it belongs to severe loss. For severe loss of large cracks or solution cavities, consolidation plugging technology is currently used. Acid-soluble cement is mainly used for plugging. Cement material has hydraulic properties, and after entering the leakage layer, it can form a solid sealing wall with time, which can effectively prevent the occurrence of leakage, thereby playing a plugging role. However, for severe leakage with large crack width and high longitudinal direction, the cement retention capacity is weak, and because the cement slurry has good rheological properties and poor dilution resistance, it is not easy to form a continuous plug between the wellbore and the leakage channel, and the success rate of plugging is low.

[0004] For example, patent document CN108751924A discloses a magnesium oxychloride cement slurry prepared from raw materials including the following mass fractions: fresh water 16~25 parts, magnesium oxide 45~60 parts, magnesium chloride 20~30 parts, fluid loss reducer 1~3 parts, dispersing agent 1~3 parts, and retarder 3~8 parts. The magnesium oxychloride cement slurry provided by the patent has high strength. However, the patent does not test and evaluate the retention effect of the cement slurry, and the density is high, which cannot be effectively retained in the leakage layer with severe loss.

[0005] Therefore, how to effectively plug the solution cavity or crack in the reservoir has become a problem to be solved in the field. SUMMARY

[0006] In order to solve the above problems, the present application provides a low-density acid-soluble consolidation plugging agent, a plugging slurry and a drilling plugging method.

[0007] According to an aspect of the present application, a low-density acid-soluble consolidation plugging agent is provided, which comprises the following components: magnesium oxide, curing auxiliary, time regulator, and structure agent, wherein the structure agent comprises acid-soluble fiber, graded rigid particles, and elastic particles.

[0008] According to an embodiment of the present application, the components in the plugging agent are mixed in the following proportions by weight: 80-120 parts of magnesium oxide, 30-60 parts of curing auxiliary, 5-50 parts of time regulator, and 10-50 parts of structure agent, and the mass ratio of the acid-soluble fiber, the graded rigid particles, and the elastic particles in the structure agent is 3-5:5-8:2-4.

[0009] According to an embodiment of the present application, the curing auxiliary is selected from at least one of magnesium sulfate or magnesium chloride.

[0010] According to an embodiment of the present application, the content of active magnesium oxide in the magnesium oxide is 30%-55%.

[0011] According to an embodiment of the present application, the time regulator is selected from at least one of monohydrate citric acid, malic acid, tartaric acid, borax, and boric acid.

[0012] According to an embodiment of the present application, the time regulator adjusts the thickening time of the slurry to be 2-8 hours.

[0013] According to an embodiment of the present application, the acid-soluble fiber is sepiolite, and the length of the sepiolite is 1-2 mm.

[0014] According to an embodiment of the present application, the graded rigid particles are limestone powder.

[0015] According to an embodiment of the present application, the graded rigid particles comprise three kinds of particles with large, medium, and small sizes, and the mass ratio of the three kinds of particles is 100-120:1-5:30-40.

[0016] According to an embodiment of the present application, the plugging agent is used to plug a crack with a width of 1-3 mm, and the particle sizes of the three kinds of particles are 1-1.5 mm, 260-300 μm, and 60-80 μm, respectively.

[0017] According to an embodiment of the present application, the structure agent further comprises silicate cement and / or quicklime.

[0018] According to an embodiment of the present application, the elastic particles are selected from at least one of rubber powder or asphalt particles.

[0019] According to another aspect of the present application, there is provided a low-density acid-soluble consolidation plugging slurry, the plugging slurry comprising the plugging agent according to any one of the preceding embodiments.

[0020] According to still another aspect of the present application, there is provided a method for preparing the low-density acid-soluble consolidation plugging slurry according to any one of the preceding embodiments, the method comprising the following steps: Step S1: uniformly pre-mixing the acid-soluble fiber, the graded rigid particles and the elastic particles to obtain a structuring agent; Step S2: preparing a bentonite slurry; Step S3: sequentially adding magnesium oxide, a curing auxiliary, a time regulator and the structuring agent obtained in Step S1 into the bentonite slurry, and uniformly stirring to obtain the plugging slurry.

[0021] According to an embodiment of the present application, in Step S2, the preparation of the bentonite slurry comprises adding bentonite powder into water, uniformly stirring and then standing to hydrate to prepare the bentonite slurry.

[0022] According to an embodiment of the present application, the hydration time is greater than 3 hours.

[0023] According to an embodiment of the present application, the mass fraction of the bentonite in the bentonite slurry is 3% to 6%.

[0024] According to still another aspect of the present application, there is provided a method for drilling plugging using the plugging slurry prepared by the method according to any one of the preceding embodiments, the method comprising the following steps: Step S11: determining an injection position; Step S12: lowering a drilling tool to the injection position; Step S13: injecting an isolation fluid; Step S14: injecting the plugging slurry; Step S15: injecting an isolation fluid; Step S16: replacing the plugging slurry into the water eye of the drilling tool with a well slurry; Step S17: standing and waiting for setting; Step S18: drilling and plugging, circulating and testing, and if the drilling fluid returns normally, the plugging is successful.

[0025] With the above technical scheme, the low-density acid-soluble solidified plugging agent and the plugging slurry provided by the application optimize components, realize overall solidification by cooperation of magnesium oxide, solidification auxiliary materials and time adjusting agents, form a continuous phase between a formation leakage channel and a wellbore, and finally form a solidified body with high strength; the structure agent is used to optimize the retention effect of the plugging slurry, the acid-soluble fibers in the structure agent are mutually attracted to form a net rack structure, and meanwhile, the acid-soluble fibers capture rigid particles and elastic particles, the graded rigid particles bridge at a narrow crack, so that the whole plugging layer stops moving to a deep part of the crack, and plays a role of a plugging layer skeleton, and the elastic particles are deformed under extrusion, and the elastic force of the elastic particles acts on a crack surface, so as to enhance the friction between the plugging layer and the crack surface, and enhance the retention effect of the plugging slurry. The plugging slurry has low density (the density is 1.40-1.50 g / cm 3 ), is acid-soluble (the acid-soluble rate is greater than 80%), and has moderate strength. The plugging slurry body does not solidify within 24 hours of being placed on the ground, the construction process is safe and controllable, and the plugging slurry is suitable for popularization and application in the field of well plugging. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 Figure is a retention comparison evaluation diagram of the plugging slurry according to the example 1 and the comparative example 1 of the application; Figure 2 Figure is a retention comparison evaluation diagram of the plugging slurry according to the example 2 and the comparative example 2 of the application; Figure 3 Figure is a retention comparison evaluation diagram of the plugging slurry according to the example 3 and the comparative example 3 of the application. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical scheme and advantages of the application clearer, further detailed description will be made to the application by combining with specific examples. It should be understood that the specific examples described herein are only used to explain the application, and are not used to limit the application.

[0028] An aspect of the application provides a low-density acid-soluble solidified plugging agent, which comprises the following components: magnesium oxide, solidification auxiliary materials, a time adjusting agent, and a structure agent, wherein the structure agent comprises acid-soluble fibers, graded rigid particles and elastic particles.

[0029] In some examples, the components in the plugging agent are matched in the following proportions by weight: 80-120 parts of magnesium oxide, 30-60 parts of solidification auxiliary materials, 5-50 parts of the time adjusting agent, and 10-50 parts of the structure agent, and the mass ratio of the acid-soluble fibers, the graded rigid particles and the elastic particles in the structure agent is 3-5:5-8:2-4.

[0030] The main material of the plugging agent is magnesium oxide, and the solidification auxiliary materials are selected from at least one of magnesium sulfate or magnesium chloride.

[0031] The active magnesium oxide in the main material contacts with water to release OH- The specific reactions are as follows: .

[0032] During the reaction, a hydration film [Mg(H2O)] is rapidly formed. x OH] + This causes the solution pH to rise. The hydration layer [Mg(H₂O)] x OH] + Adhering to the surface of magnesium oxide, giving it a large surface energy, this hydration layer rapidly reacts with the gradually increasing OH- ions in the solution. - Combined, Mg(OH)₂ is formed. As magnesium oxide hydrates, the OH groups in the slurry... - Gradually increase, when OH - When a certain concentration is reached, Mg is adsorbed. 2+ and SO4 2- / Cl - The complexed ion hydration layer will then react with OH- - The reaction generates 5•1•7 phase nuclei. As the number of nuclei gradually increases, the hydration layer is gradually destroyed. With the growth of the 5•1•7 phase, the crystallization stress in the system gradually increases, thus exposing the magnesium oxide encased inside, allowing it to continue reacting, and the slurry gradually hardens.

[0033] As can be seen from the above reaction mechanism, the main material, magnesium oxide, should have a certain degree of activity, and after mixing with auxiliary materials and water, it can form a hydrate with a certain strength. However, due to the need for safe construction time and extended consolidation time during well drilling and plugging, the activity of magnesium oxide should not be too high.

[0034] Therefore, in some embodiments, the active magnesium oxide content in the magnesium oxide used in this invention is 30%~55%. The active magnesium oxide content in the magnesium oxide is determined using the following test method: Approximately 2.0g of lightly calcined magnesium oxide sample is weighed and placed in a glass weighing bottle. 20mL of distilled water is added, the bottle is capped with a small gap, and the sample is allowed to stand at 25℃±2℃ for 24 hours to hydrate. It is then placed in an oven and dried at 105℃ until constant weight. After cooling, the mass of the hydrated sample is weighed. The active magnesium oxide content is calculated using the following formula:

[0035] Where W is the active MgO content in the lightly calcined magnesium powder, %; W1 is the mass of the sample before hydration, g; and W2 is the mass of the sample after hydration, g.

[0036] Magnesium-based cementitious materials mainly include two types: magnesium oxychloride and magnesium oxysulfate. These are produced by mixing magnesium oxide with either magnesium chloride or magnesium sulfate and then adding the mixture to water, both of which generate crystalline products with high strength. There are no special requirements regarding the activity of the solidifying additives, magnesium chloride or magnesium sulfate.

[0037] In some embodiments, the time regulator is selected from at least one of citric acid monohydrate, malic acid, tartaric acid, borax, and boric acid, and the time regulator can adjust the thickening time of the slurry to 2-8 hours.

[0038] In some embodiments, the acid-soluble fiber is sepiolite wool, with a length of 1-2 mm. During leak sealing, the acid-soluble fiber can form bridging structures and capture other passing fibers. The fibers intertwine to form a mesh structure, which effectively reduces the cross-sectional area of ​​the crack, gradually transforming leakage into filtration and reducing pressure propagation deeper into the crack. As the pressure differential increases, when the pressure exceeds the fiber's yield strength, the fiber mesh structure penetrates the crack as a whole, forming a denser mesh structure. This also makes it easier for other sealing materials to bridge and fill, enhancing the overall structural stability of the sealing layer.

[0039] In some embodiments, the graded rigid particles are limestone powder, comprising particles of three sizes: large, medium, and small, with a mass ratio of 100-120:1-5:30-40. When the sealing agent is used to seal cracks 1-3 mm wide, the particle sizes of the large, medium, and small particles are 1-1.5 mm, 260-300 μm, and 60-80 μm, respectively. The particle size of the rigid particles must match the crack width. The graded rigid particles act as a skeleton in the sealing layer structure. This invention uses graded rigid particles of different sizes for sealing; large particles bridge narrow cracks, medium particles fill the channels between large particles, and small particles fill the channels between large and medium particles, forming an accumulation.

[0040] In some embodiments, the elastic particles are selected from at least one of rubber powder or asphalt particles, and the particle size of the elastic particles is selected to be slightly larger than the crack width, so that the elastic particles are compressed and deformed when flowing into the crack, and their own elastic force acts on the crack surface, enhancing the friction between the sealing layer and the crack surface, and enhancing the retention effect of the sealing grout. For example, for cracks with a width of 1 to 3 mm, the particle size of the elastic particles is controlled to be about 1.2 to 3.1 mm.

[0041] Optionally, in some embodiments, the structural agent may also include silicate cement and / or quicklime.

[0042] Another aspect of the present invention provides a low-density, acid-soluble, solidified sealing grout, which includes the sealing agent as described in any of the above embodiments. The preparation method of this sealing grout is as follows: Step S1: Premix acid-soluble fibers, graded rigid particles and elastic particles evenly to obtain a structural agent; Step S2: Prepare bentonite slurry; Step S3: Add magnesium oxide, curing additive, time conditioner and structural agent obtained in step S1 to the bentonite slurry in sequence, stir evenly to obtain the plugging slurry.

[0043] In step S2, bentonite powder is added to water, stirred evenly, and then allowed to stand to hydrate and prepare a bentonite slurry. The bentonite mass fraction in the slurry is 3%~6%. Soda ash with a bentonite content of 3% can be added during preparation, and the hydration time should be greater than 3 hours.

[0044] Another aspect of the present invention provides a method for well plugging using the above-mentioned plugging slurry, the method comprising the following steps: Step S11: Determine the injection site; Step S12: Lower the drill string to the injection position; Step S13: Inject isolation fluid; Step S14: Inject sealing grout; Step S15: Inject isolation fluid; Step S16: Use well slurry to replace the plugging slurry into the water hole of the drill string; Step S17: Allow to stand still and allow to solidify; Step S18: Run the drilling plug and circulate it for leak testing. If the drilling fluid returns normally after the plug is drilled, the leak has been successfully plugged.

[0045] The grouting location can be determined using the following formula: Injection location = Leakage depth - Dynamic and static fluid level difference - (Pluging slurry density / Drilling fluid density) × Expected plug length (the height can be adjusted appropriately according to the actual situation).

[0046] Adjust the drill string water inlet to the injection plug position and begin construction. The injection position should not be higher than 300m above the leaking layer.

[0047] After the preparations are completed, the drill string is lowered to the injection position and construction begins.

[0048] Inject 2-3 m³ of isolation fluid; the discharge rate is not required.

[0049] Inject plugging slurry at 1 / 2 to 2 / 3 of the normal drilling flow rate (the flow rate can be increased as much as possible when the leakage rate is low and the drilling fluid is sufficient, and it can be the normal flow rate), and ensure that the injection volume is accurately measured.

[0050] Inject 1~2m³ of isolation fluid; the discharge rate is not required.

[0051] Use well slurry to replace the plugging slurry into the water hole of the drill string, 50-100m above the annulus. Determine the replacement volume based on the amount of plugging slurry that leaks into the formation (i.e., calculate the amount of leakage after the plugging slurry exits the water hole). When replacing the slurry to the water hole of the plugging slurry, adjust the discharge rate to the normal drilling discharge rate or slightly larger, so as to allow the plugging slurry to enter the leaking formation as much as possible.

[0052] Allow the grout to set for 24 hours. If the leakage is significant during the injection and replacement of the plugging slurry, pull out the drill string to a safe section after the slurry has been balanced and allow the grout to set. If no leakage occurs or the leakage is small, pull out the drill string to a safe section above the slurry surface, shut in the well, and squeeze out excess slurry into the leaking layer, leaving a plug of 50-100m in the wellbore. Allow the slurry to set. During the setting period, do not inject grout while ensuring well control safety to prevent the plug from being left too short.

[0053] Run the drill string to test for leaks and circulate it for testing. Run the drill string in sections for circulation, starting the pump 100-200m in advance and slowly lowering the test string to prevent sticking due to excessive speed. After encountering the actual plug, circulate it fully above the plug to verify that there is no leakage in the section above it (for sections requiring pressure sealing, consider conducting a pressure test first to verify the pressure-bearing capacity of the upper open hole section), before proceeding with the plugging operation. If the drilling fluid returns normally after plugging, the plugging is successful.

[0054] The present invention will be further illustrated by the following examples, but the scope of protection of the present invention is not limited thereto.

[0055] Example 1 Add 800 mL of pre-prepared 3% bentonite slurry to a 2 L slurry cup. Then, add 80 parts magnesium oxide, 30 parts magnesium sulfate, 5 parts citric acid monohydrate, and 10 parts structural agent to the bentonite slurry in sequence. The magnesium oxide contains 30% active magnesium oxide. The structural agent consists of sepiolite wool, graded limestone powder, and rubber powder in a mass ratio of 3:5:2. The graded limestone powder includes particles with diameters of 1 mm, 260 μm, and 60 μm in a mass ratio of 100:1:30. Stir the slurry thoroughly.

[0056] The sealing grout prepared in this embodiment was subjected to performance testing: its density was 1.40 g / cm³. 3 The grout was thickened at 50℃ for 2 hours, with an acid solubility >90% and a solidified body strength of 2 MPa. The retention effect of the plugging grout was tested indoors. The retention performance was evaluated by measuring the starting pressure and flow pressure loss of the grout as it was brought to a certain flow rate (0.1 m / s) within a 12 mm diameter straight pipe. Higher starting pressure and flow pressure loss indicate better retention. Test results showed a starting pressure of 13.3 kPa and a flow pressure loss of 10.7 kPa per unit length.

[0057] Field application tests were conducted on the plugging slurry, which successfully sealed leaks with fractures approximately 1-2 mm wide. The drill pipe was lowered to 2477m, and the leaking zone was circulated and flushed. No slurry returned to the wellhead. 2 m³ of pre-filled fluid was injected, followed by 22 m³ of low-density, acid-soluble, solidified plugging slurry. The pump was stopped, the well was shut in, and another 8 m³ of plugging slurry was injected, replacing 1 m³ of post-filled fluid. When the mud pump was displacing nearly 10 m³ of mud at a rate of 10 L / s, the stand pressure continued to rise. The pump was stopped, and the well was reopened. At this point, approximately 14.84 m³ of low-density, acid-soluble, solidified slurry had entered the leaking zone. The drill pipe was circulated at a rate of 30 L / s to pull the drill string out, resulting in a loss of approximately 9 m³. After 24 hours of static curing, the drill string was lowered to 2045m and a solidified plug was encountered. The plug was drilled to 2477m, and circulation was successful with no loss of slurry. Drilling resumed.

[0058] Example 2 Add 700 mL of pre-prepared 5% bentonite slurry to a 2 L slurry cup. Then, add 100 parts magnesium oxide, 50 parts magnesium chloride, 30 parts borax, and 35 parts structural agent to the bentonite slurry in sequence. The magnesium oxide contains 40% active magnesium oxide. The structural agent consists of sepiolite wool, graded limestone powder, and asphalt particles in a mass ratio of 4:6:3. The graded limestone powder includes particles with diameters of 1 mm, 280 μm, and 70 μm, in a mass ratio of 110:3:35. Stir the slurry thoroughly.

[0059] The sealing grout prepared in this embodiment was subjected to performance testing: its density was 1.45 g / cm³. 3 The grout thickened at 50℃ for 2.5 hours, exhibited an acid solubility >85%, and a solidified body strength of 3 MPa. The retention effect of the plugging grout was tested indoors. The retention performance was evaluated by measuring the starting pressure and flow pressure loss of the grout as it was brought to a certain flow rate (0.1 m / s) within a 12 mm diameter straight pipe. Higher starting pressure and flow pressure loss indicate better retention. Test results showed a starting pressure of 33.3 kPa and a flow pressure loss of 23.2 kPa per unit length.

[0060] Field application tests were conducted on the plugging slurry, which successfully sealed leaks with cracks approximately 2-3 mm wide. The drill pipe was lowered to 2306 m, and the leaking zone was circulated and flushed. No slurry returned to the wellhead. 2 m³ of pre-filled fluid was injected, followed by 15 m³ of low-density, acid-soluble, solidifying plugging slurry. The pump was stopped, the well was shut in, and another 5 m³ of plugging slurry was injected, replacing 1 m³ of post-filled fluid. The pumping rate was 1 m³ / min, and the pressure was 5 MPa. 18 m³ of slurry was replaced at a pumping rate of 26 L / s. The maximum pump pressure was 10 MPa, gradually decreasing to a stable 8 MPa. During the replacement, 8.4 m³ of slurry was lost, and approximately 10 m³ of plugging slurry entered the leaking zone. The drill string was pulled out to the casing toe or a safe section and allowed to stand for 24 hours to solidify. The drill string was then lowered to 2245 m, where a solidified plug was encountered. The plug was drilled to 2306 m, and circulation was successful with no leakage. Drilling resumed.

[0061] Example 3 Add 700 mL of pre-prepared 6% bentonite slurry to a 2 L slurry cup. Then, add 120 parts magnesium oxide, 50 parts magnesium chloride, 10 parts magnesium sulfate, 50 parts boric acid, and 50 parts structural agent to the bentonite slurry in sequence. The magnesium oxide contains 55% active magnesium oxide. The structural agent consists of sepiolite wool, graded limestone powder, and asphalt particles in a mass ratio of 5:8:4. The graded limestone powder includes particles with diameters of 1 mm, 300 μm, and 80 μm in a mass ratio of 120:5:40. Stir the slurry thoroughly.

[0062] The sealing grout prepared in this embodiment was subjected to performance testing: its density was 1.50 g / cm³. 3 The grout had a thickening time of 2.8 hours at 50℃, an acid solubility >80%, and a solidified body strength of 4 MPa. The retention effect of the plugging grout was tested indoors. The retention performance was evaluated by measuring the starting pressure and flow pressure loss of the grout as it was brought to a certain flow rate (0.1 m / s) within a 12 mm diameter straight pipe. Higher starting pressure and flow pressure loss indicate better retention. Test results showed a starting pressure of 41.9 kPa and a flow pressure loss of 35.2 kPa per unit length.

[0063] The plugging slurry was tested in the field and successfully sealed a leak with a crack width of approximately 2-3 mm. The drill pipe was lowered to 2415m at the bottom of the well. The leaking layer was circulated and flushed, but no slurry returned to the wellhead. 2m³ of pre-filling fluid was injected, followed by 25m³ of low-density, acid-soluble, solidifying plugging slurry. 1m³ of post-filling fluid was then added. The operating pressure was initially 0, gradually increasing to 3MPa. A mud pump was used to replace 20m³ of slurry at a rate of 1.8m³ / min, maintaining a vertical pressure of 5MPa. Logging showed no decrease in the height of the solidified slurry within the wellbore. The drill string was pulled out to the casing foot or a safe section and allowed to stand for 24 hours to solidify. The drill string was then lowered to 2345m where a solidified plug was encountered. The plug was drilled down to 2415m, and circulation was successful with no leakage. Drilling resumed.

[0064] Comparative Example 1 Prepare magnesium sulfate cement slurry according to the conventional water-cement ratio, add acid-soluble calcium carbonate particles to the cement slurry at a ratio of 40%, stir evenly, and obtain the corresponding proportion of plugging mud.

[0065] The prepared acid-soluble cement slurry was tested for performance: its density was 1.84 g / cm³. 3 The thickening time at 50℃ was 2 hours, the acid solubility was <70%, and the solidified body strength was 20 MPa. The retention effect of this comparative cement slurry was tested indoors. The retention properties of the slurry were evaluated by measuring the starting pressure and flow pressure loss of the slurry as it was brought to a certain flow rate (0.1 m / s) within a 12 mm diameter straight pipe from a static state. The test results showed that the starting pressure per unit length was 6.6 kPa and the flow pressure loss per unit length was 6.0 kPa.

[0066] Comparative Example 2 Magnesium oxychloride cement slurry is prepared according to the conventional water-cement ratio. Acid-soluble calcium carbonate particles are added to the cement slurry at a rate of 30% of the slurry mass, and borax is added at a rate of 20% of the slurry mass. The mixture is stirred evenly to obtain the corresponding proportion of plugging slurry.

[0067] The prepared acid-soluble cement slurry was tested for performance: its density was 1.86 g / cm³. 3 The thickening time at 90℃ was 2 hours, the acid solubility was <60%, and the solidified body strength was 20 MPa. The retention effect of this comparative cement slurry was tested indoors. The retention properties of the slurry were evaluated by measuring the starting pressure and flow pressure loss of the slurry when it was allowed to flow at a certain velocity (0.1 m / s) from a static state in a 12 mm diameter straight pipe. The test results showed that the starting pressure per unit length was 7.2 kPa and the flow pressure loss per unit length was 6.1 kPa.

[0068] Comparative Example 3 Magnesium oxychloride cement slurry is prepared according to the conventional water-cement ratio. Acid-soluble calcium carbonate particles are added to the cement slurry at a rate of 20% of the slurry mass, and borax is added at a rate of 30% of the slurry mass. The mixture is stirred evenly to obtain the corresponding proportion of plugging slurry.

[0069] The prepared acid-soluble cement slurry was tested for performance: its density was 1.87 g / cm³. 3 The thickening time at 120℃ was 2.5 h, the acid solubility was <50%, and the solidified body strength was 20 MPa. The retention effect of this comparative cement slurry was tested indoors. The retention properties of the slurry were evaluated by measuring the starting pressure and flow pressure loss of the slurry when it was placed in a 12 mm diameter straight pipe from a static state to a certain flow rate (0.1 m / s). The test results showed that the starting pressure per unit length was 7.1 kPa, and the flow pressure loss per unit length was 6.2 kPa.

[0070] Figure 1 The figure shows a comparison of the retention properties of the plugging grouts of Example 1 and Comparative Example 1 according to the present invention. As can be seen from the figure, the retention properties of the plugging grout using the components of the present invention are improved compared with those of the existing magnesium oxysulfate cement grout.

[0071] Figure 2 The figure shows a comparison of the retention properties of the plugging grouts of Example 2 and Comparative Example 2 according to the present invention. As can be seen from the figure, the retention properties of the plugging grout using the components of the present invention are significantly improved compared with those of the magnesium oxychloride cement grout of Comparative Example 2.

[0072] Figure 3The figure shows a comparison of the retention properties of the plugging grouts of Example 3 and Comparative Example 3 according to the present invention. As can be seen from the figure, the retention properties of the plugging grout using the components of the present invention are significantly improved compared with those of the magnesium oxychloride cement grout of Comparative Example 3.

[0073] The embodiments described above are merely illustrative of implementation methods of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A low-density, acid-soluble, solidifying sealant, characterized in that, It includes the following components: magnesium oxide, curing additives, time conditioners, and structural agents, wherein the structural agents include acid-soluble fibers, graded rigid particles, and elastic particles.

2. The low-density, acid-soluble, solidifying sealant according to claim 1, characterized in that, The components of the sealing agent are formulated in the following proportions by weight: 80-120 parts magnesium oxide, 30-60 parts curing additive, 5-50 parts time regulator, and 10-50 parts structural agent. The mass ratio of acid-soluble fiber, graded rigid particles and elastic particles in the structural agent is 3-5:5-8:2-4.

3. The low-density, acid-soluble, solidifying sealant according to claim 1, characterized in that, The curing additive is selected from at least one of magnesium sulfate or magnesium chloride.

4. The low-density, acid-soluble, solidifying sealant according to claim 1, characterized in that, The active magnesium oxide content in the magnesium oxide is 30%~55%.

5. The low-density, acid-soluble, solidifying sealant according to claim 1, characterized in that, The time regulator is selected from at least one of citric acid monohydrate, malic acid, tartaric acid, borax, and boric acid.

6. The low-density, acid-soluble, solidifying sealant according to claim 5, characterized in that, The time regulator adjusts the thickening time of the slurry to 2-8 hours.

7. The low-density, acid-soluble, solidifying sealant according to claim 1, characterized in that, The acid-soluble fiber is sepiolite wool, and the length of the sepiolite wool is 1~2mm.

8. The low-density, acid-soluble, solidifying sealant according to claim 1, characterized in that, The graded rigid particles are made of limestone powder.

9. The low-density, acid-soluble, solidifying sealant according to claim 8, characterized in that, The graded rigid particles include particles of three sizes: large, medium, and small, with a mass ratio of 100~120:1~5:30~40.

10. The low-density, acid-soluble, solidifying sealant according to claim 9, characterized in that, The sealing agent is used to seal cracks with a width of 1-3 mm, wherein the particle sizes of the large, medium and small particles are 1-1.5 mm, 260-300 μm and 60-80 μm, respectively.

11. The low-density, acid-soluble, solidifying sealant according to claim 1, characterized in that, The structural agent also includes silicate cement and / or quicklime.

12. The low-density, acid-soluble, solidifying sealant according to claim 1, characterized in that, The elastic particles are selected from at least one of rubber powder or asphalt particles.

13. A low-density, acid-soluble, solidifiable plugging grout, characterized in that, Includes the sealant as described in any one of claims 1-12.

14. A method for preparing the low-density, acid-soluble, solidified plugging grout according to claim 13, characterized in that, Includes the following steps: Step S1: Premix acid-soluble fibers, graded rigid particles and elastic particles evenly to obtain a structural agent; Step S2: Prepare bentonite slurry; Step S3: Add magnesium oxide, curing additive, time regulator and the structural agent obtained in step S1 to the bentonite slurry in sequence, stir evenly to obtain the plugging slurry.

15. The method according to claim 14, characterized in that, In step S2, preparing bentonite slurry involves adding bentonite powder to water, stirring evenly, letting it stand, hydrating, and preparing bentonite slurry.

16. The method according to claim 15, characterized in that, The hydration time is greater than 3 hours.

17. The method according to claim 15, characterized in that, The bentonite slurry contains 3% to 6% bentonite by mass.

18. A method for drilling and plugging leaks using a plugging slurry prepared according to any one of claims 14-17, characterized in that, Includes the following steps: Step S11: Determine the injection site; Step S12: Lower the drill string to the injection position; Step S13: Inject isolation fluid; Step S14: Inject the sealing grout; Step S15: Inject isolation fluid; Step S16: Use well slurry to replace the plugging slurry into the water hole of the drill string; Step S17: Allow to stand still and allow to solidify; Step S18: Run the drilling plug and circulate it for leak testing. If the drilling fluid returns normally after the plug is drilled, the leak has been successfully plugged.

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