Method for sealing drill holes in potassium-magnesium salt mine

Abstract

The invention relates to the field of geological drilling hole sealing, in particular to a potassium-magnesium salt mine drilling hole sealing method which comprises the following steps that a drilling rod with the diameter smaller than the hole diameter of a drilling hole is lowered into the drilling hole, and the drilling hole is circularly flushed through brine; according to the distribution of the salt layers at the drilling position, a second preset distance position above the uppermost salt layer in the stratum serves as a hole sealing segmentation position, a magnesium cement solution is pumped into the drill rod from the top of the drill rod, brine is injected into the drill rod from the top of the drill rod in a pressing mode, the liquid level of the magnesium cement solution in the drill rod is made to be located at the hole sealing segmentation position, and the drill rod is taken out; and after the magnesium cement solution is solidified, ordinary cement slurry is pumped from the magnesium cement sealing face to the hole opening cement slurry returning so as to seal the hole sealing area of the upper section. The upper-section non-salt layer adopts common cement paste for hole sealing, and the lower-section salt layer area adopts brine-resistant magnesium cement for hole sealing, so that the whole-hole sealing cost is reduced by using the common cement, high-concentration brine erosion is resisted through the magnesium cement, the common cement is prevented from losing efficacy in the salt layer, and the balance of economy and functionality is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of geological drilling hole sealing, in particular to a sealing method for a potassium-magnesium salt mine drilling hole. BACKGROUND

[0002] In geological drilling engineering, "sealing" refers to filling and closing the completed drilling hole to prevent underground water, pollutants or mineral layer substances from flowing through the drilling hole, thereby ensuring geological safety and resource protection. For special minerals such as potassium salt mines, sealing technology is particularly critical - the main components of potassium salt mines (such as potassium-magnesium salt mines) are potassium chloride, magnesium chloride and other water-soluble minerals, which will gradually dissolve when they come into contact with water. If the drilling hole is not closed or not closed tightly, external underground water or surface water will seep into the mineral layer, causing the mineral layer to be continuously eroded, resulting in not only resource waste but also serious problems such as ground subsidence and environmental pollution.

[0003] Traditional geological drilling hole sealing often uses ordinary Portland cement, which will gradually solidify after mixing with water to form a hard solid, thereby plugging the drilling hole. However, in potassium salt mine drilling, the "shortcomings" of ordinary Portland cement are quite obvious: the drilling hole is often filled with high-concentration brine, and the salt (such as sodium chloride and magnesium chloride) in the brine will hinder the solidification reaction of ordinary cement, resulting in a long time for the cement to harden and form a "soft mud" substance with insufficient strength. After sealing, the drilling hole may still leak, the mineral layer continues to be eroded, and the mineral layer cannot be effectively closed.

[0004] Therefore, in view of the characteristics of potassium salt mines, the industry has gradually explored the use of "magnesium cement" (cement prepared with magnesium oxide and magnesium chloride as main raw materials) resistant to brine, and has tried different sealing strategies, such as using magnesium cement in the entire hole or using magnesium cement only in the mineral layer position and ordinary cement in other positions. Magnesium cement uses magnesium oxide as the main raw material, and its raw material cost is much higher than that of ordinary Portland cement. If magnesium cement is used in the entire hole, it will significantly increase the economic investment of the sealing engineering, which is economically poor in large-scale potassium salt mine drilling. If magnesium cement is used only in the mineral layer position and ordinary cement is used in other positions (such as the halite layer), the high-concentration brine in the halite layer will cause the ordinary cement to solidify slowly or incompletely, resulting in a sealing layer with many gaps, and the brine can still penetrate. Over time, it can cause the halite layer to be eroded, the hole wall to be unstable, and even collapse. SUMMARY

[0005] In order to solve the problem that the formed sealing layer has many gaps and the brine can still penetrate, which can cause the halite layer to be eroded, the hole wall to be unstable, and even collapse over time, the present application provides a sealing method for a potassium-magnesium salt mine drilling hole.

[0006] The sealing method for a potassium-magnesium salt mine drilling hole provided by the present application adopts the following technical solution: A sealing method for a potassium-magnesium salt mine drilling hole, comprising the following steps: a drill rod with a diameter less than the borehole diameter is provided and lowered into the borehole, with the bottom end of the drill rod spaced a first predetermined distance from the borehole bottom, and the borehole is flushed with circulating brine; According to the salt layer distribution at the borehole, a second predetermined distance above the uppermost salt layer in the formation is taken as the hole sealing segmentation position, the area between the borehole mouth and the hole sealing segmentation position is the upper hole sealing area, and the area between the hole sealing segmentation position and the borehole bottom is the lower hole sealing area; A magnesium cement solution is prepared; The magnesium cement solution is pumped into the drill rod from the top of the drill rod according to the required amount of the magnesium cement solution determined according to the volume of the lower hole sealing area; Brine is pressure injected into the drill rod from the top of the drill rod, part of the magnesium cement solution in the drill rod is pressed out of the drill rod from the lower end of the drill rod, the liquid level of the magnesium cement solution in the drill rod is at the hole sealing segmentation position, and the drill rod is removed; A predetermined time is waited, after the magnesium cement solution solidifies, ordinary cement slurry is pumped from the magnesium cement sealing surface to the borehole mouth cement slurry return to seal the upper hole sealing area.

[0007] By using the above technical solution, a drill rod with a diameter less than the borehole diameter is used, the bottom end of the drill rod is spaced a first predetermined distance from the borehole bottom, and the borehole is flushed with circulating brine to remove the sediment at the borehole bottom, which not only avoids the influence of the sediment on bonding but also facilitates subsequent magnesium cement replacement, and at the same time, space is reserved to prevent sticking and ensure that the key area at the borehole bottom can be covered by magnesium cement; the second predetermined distance above the uppermost salt layer is taken as the hole sealing segmentation position, the borehole is divided into the upper hole sealing area and the lower hole sealing area, ordinary cement is used to seal the non-salt layer in the upper hole sealing area to reduce the cost, and magnesium cement that is resistant to brine is used to seal the salt layer in the lower hole sealing area to resist erosion by high-concentration brine, which solves the problem of hole sealing in different formations; the amount of magnesium cement is determined according to the volume of the lower hole sealing area and is pumped in, the magnesium cement solution is pressed out of the drill rod by pressure injection of brine, the liquid level is accurately at the hole sealing segmentation position, the magnesium cement is ensured to fully fill the lower area without overflowing, and after the drill rod is removed, the magnesium cement is allowed to solidify, and then ordinary cement slurry is pumped from the sealing surface to seal the upper hole sealing area, which realizes the reasonable selection and accurate construction of the hole sealing materials in the upper and lower sections, effectively blocks the infiltration of external water into the ore bed, reduces resource erosion and safety hazards, avoids the high cost problem of using magnesium cement in the whole hole, ensures the durability of hole sealing while taking into account the economy, and forms a reliable and efficient segmented hole sealing technical solution.

[0008] Optionally, the step of "waiting for a predetermined time, after the magnesium cement solution solidifies, pumping ordinary cement slurry from the magnesium cement sealing surface to the borehole mouth cement slurry return to seal the upper hole sealing area" includes: Wait for a first preset time, and use a drilling tool to drill a core at the top of the lower section sealing area, and check the sealing effect of the magnesium cement; If the magnesium cement is hard, determine whether the magnesium cement sealing surface is above the uppermost salt layer according to the obtained magnesium cement core; If the magnesium cement sealing surface is above the uppermost salt layer, pump ordinary cement slurry from the magnesium cement sealing surface to the hole mouth cement slurry return to seal the upper section sealing area.

[0009] By adopting the above technical solution, after waiting for a first preset time, a core is drilled at the top of the lower section sealing area by using a drilling tool, and whether the magnesium cement is hard can be directly checked by obtaining the magnesium cement core, so that it is ensured that the magnesium cement is completely solidified to have sufficient strength to resist brine erosion, and whether the sealing surface is above the uppermost salt layer is accurately determined according to the position of the magnesium cement core. Only when the sealing surface is in the correct position, can it be ensured that the lower section high-concentration brine area is completely sealed by the magnesium cement. At this time, ordinary cement slurry is pumped from the sealing surface to seal the upper section non-salt layer area, which can ensure that the ordinary cement is normally solidified in a low brine concentration environment, thereby avoiding the risk of upper section sealing failure and brine infiltration into the ore bed due to the magnesium cement not being solidified or the sealing surface being in the wrong position. In addition, the applicability and construction accuracy of the sealing materials of the upper and lower sections are guaranteed through segmented verification, a quality control closed loop of “detection-judgment-implementation” is formed, and the reliability and safety of the sealing engineering are effectively improved.

[0010] Optionally, after the step of “if the magnesium cement is hard, determining whether the magnesium cement sealing surface is above the uppermost salt layer according to the obtained magnesium cement core”, the method further comprises: If the magnesium cement sealing surface is below the uppermost salt layer, the amount of magnesium cement solution required is determined according to the volume of the lower section sealing area that is not sealed by the magnesium cement, the magnesium cement solution is pumped into the drill pipe from the top of the drill pipe, and the step of injecting brine is repeated.

[0011] By adopting the above technical solution, when it is detected that the magnesium cement sealing surface is below the uppermost salt layer, the amount of magnesium cement solution to be supplemented is determined by calculating the volume of the lower section sealing area that is not sealed, which can accurately supplement the missing sealing material and avoid material waste or deficiency caused by blind supplement. The magnesium cement solution is pumped into the drill pipe from the top of the drill pipe and the step of injecting brine is repeated, which can accurately push the supplemented magnesium cement solution to the unsealed salt layer area by using the brine pressure, so as to ensure that the lower section sealing area is completely covered by the magnesium cement, effectively block the channel through which the high-concentration brine penetrates through the unsealed part, and avoid safety hazards such as ore bed corrosion and ground subsidence caused by “leakage”. This step completes local supplementing under the premise of not damaging the solidified qualified sealing section through targeted defect repair, which not only ensures the overall quality of the sealing engineering, but also reduces the cost and time consumption of full-section rework, forms a closed loop control mechanism of “detection-quantification-repair”, and effectively improves the reliability and economy of the sealing construction.

[0012] Optionally, after the step of "waiting for a first preset time, drilling the top of the lower section sealing area with the drilling tool, and checking the sealing effect of the magnesium cement", the method further comprises: If the magnesium cement has not solidified, waiting for a second preset time to check the sealing effect of the magnesium cement again. If the magnesium cement still has not solidified, repeating the steps of pumping the magnesium cement solution and injecting the brine.

[0013] By adopting the above technical solution, when it is detected that the magnesium cement has not solidified, waiting for a second preset time to check again, avoiding misjudgment caused by insufficient reaction time, and providing a more sufficient solidification period for the magnesium cement. If it is still not solidified after checking again, the magnesium cement residue that has not solidified and impurities that may affect solidification can be removed by circulating flushing the borehole with brine, creating a clean environment for resealing. Then, repeating the steps of pumping the magnesium cement solution and injecting the brine, ensuring that the lower section sealing area is refilled with qualified magnesium cement material. The brine pressure is used to push the solution to be evenly distributed and reach the preset sealing position, effectively solving the solidification failure problem caused by abnormal material reaction, deviation in proportioning, or brine interference, and avoiding the unsealed area becoming a brine infiltration channel. Through the progressive processing of "delayed detection-cleaning hole-repeated construction", a targeted repair mechanism for solidification abnormalities is formed, ensuring the solidification effect of the sealing material in a complex brine environment, eliminating the risk of sealing failure caused by un-solidified cement from the construction link, and improving the stability and durability of the entire sealing project.

[0014] Optionally, the magnesium cement solution is prepared by mixing water, halogen piece (MgCl2·6H2O), and magnesium oxide in a mass ratio of 2:2:3~3.5.

[0015] By adopting the above technical solution, the magnesium cement solution is prepared by mixing water, halogen piece (MgCl2·6H2O), and magnesium oxide in a mass ratio of 2:2:3~3.5. The halogen piece contains crystal water, and the heat absorption during dissolution can neutralize the heat generated by the reaction of magnesium oxide with water, avoiding the solution from boiling and splashing due to rapid heating, and significantly improving the safety of construction. The sequence of dissolving the halogen piece first and then adding the solidifying agent (magnesium oxide) allows the slow release of Mg²⁺ and a mild reaction with magnesium oxide, providing sufficient time for pumping construction and avoiding premature solidification of magnesium cement in the drill pipe, which can cause pipe blockage. Precise proportioning ensures that the solid volume before and after the reaction is basically equal, which can prevent brine leakage caused by shrinkage cracks and damage to the hole wall caused by expansion, allowing the magnesium cement solution to closely adhere to the hole wall, ensuring the sealing performance and durability of the sealing in the lower section of the salt layer area, and solving the problems of safety hazards, uncontrollable solidification time, and volume change in traditional magnesium cement preparation, which can cause sealing failure.

[0016] Optionally, the step of "preparing the magnesium cement solution" comprises: providing a stirring barrel with a volume of 1m 3 ; 400kg or 0.4m 3 of clean water is added into the stirring barrel, then 400kg of halogen piece (MgCl2·6H2O) is added, fully dissolved and stirred, and finally 600-700kg of magnesium oxide is added to form the required magnesium cement solution.

[0017] By adopting the technical scheme, the magnesium cement solution is prepared by using a stirring barrel with a volume of 1m³, the adding sequence and amount of clean water, halogen piece and magnesium oxide are specified, the standardization and operability of material proportioning are realized, and the solidification time is controlled and the sealing performance is stable.

[0018] Optionally, the diameter of the drill pipe is 2 / 5-3 / 5 of the diameter of the drill hole.

[0019] By adopting the technical scheme, the volume of the annular space formed between the drill pipe and the drill hole is approximately equal to the volume inside the drill pipe, so that when the magnesium cement solution in the drill pipe is pressed to the sealing segment position, the magnesium cement solution outside the drill pipe does not rise too much, thereby avoiding the risk of increasing the mixing of magnesium cement solution and brine due to the high rise of magnesium cement solution outside the traditional large-diameter drill pipe, reducing the dilution effect of brine on the magnesium cement solution, and ensuring the bonding strength of the magnesium cement and the hole wall; the drill pipe can reduce the resistance between the drill pipe and the drill hole and the material in the hole, and is more conducive to the lifting of the drill pipe; a drill pipe with too small a diameter will increase the pumping time and is prone to magnesium cement pipe blockage or drill burying accidents; the drill pipe creates favorable conditions for efficient replacement of brine and tight sealing of the hole from the perspective of spatial structure design, and improves the combination quality of the sealing material and the hole wall and the controllability of the construction operation.

[0020] Optionally, the diameter of the drill hole is 95-110mm, and the diameter of the drill pipe is 50mm.

[0021] By adopting the technical scheme, the 50mm drill pipe is suitable for conventional construction equipment and is easy to obtain, and the lowering and lifting operation is convenient in a 95-110mm diameter hole.

[0022] Optionally, the sealing segment position is located 8-12m above the uppermost salt layer in the stratum.

[0023] By adopting the technical scheme, the distance of 8-12m can ensure that the upper sealing area is completely in a non-salt layer (surface soil layer, rock layer), and a sufficient safety distance is reserved to prevent misjudgment of the top of the salt layer due to geological exploration errors, to ensure that the ordinary cement sealing segment is completely separated from the influence of brine in the salt stratum, and to avoid the situation that the lower magnesium cement sealing area is insufficient due to the proximity of the segment position to the salt layer, thereby ensuring the applicability of the upper and lower sealing materials and the stability of the sealing interface from the perspective of geological structure.

[0024] Optionally, the ordinary cement slurry is ordinary 425 cement slurry, and the water-cement ratio of the cement slurry is 0.6-0.8.

[0025] By adopting the technical scheme, the strength grade of the 425 cement is adapted to the non-high-halogen water environment of the upper hole sealing area (surface soil layer and rock layer), so that the cement slurry has sufficient compressive strength and bonding force after solidification, and tightly fills the annular space between the hole wall and the drill pipe; the water-cement ratio of 0.6-0.8 takes into account the fluidity and solidification performance of the cement slurry, which is convenient for uniform distribution of the cement slurry to the upper hole sealing area through pumping construction, avoids large pumping resistance and non-dense filling due to excessive thickness, prevents insufficient strength or shrinkage cracking after solidification due to excessively high water-cement ratio, and ensures normal hydration reaction of ordinary cement under low halogen water concentration to form a continuous and dense hole sealing structure.

[0026] Optionally, after the upper hole sealing area is closed, the method further comprises: Supplementing cement to the ground and setting a cement bench mark at the hole mouth.

[0027] By adopting the technical scheme, after the upper hole sealing area is closed, supplementing cement to the ground can fill the difference or gap between the hole mouth and the ground, form a continuous and complete cement sealing layer, effectively prevent rainwater, sewage or sundries on the ground from entering the drill hole, avoid the infiltration of external water along the joint of the hole mouth and the ground into the lower salt layer area, and ensure the sealing performance of the hole sealing structure from the hole bottom to the ground; the cement bench mark is set at the hole mouth, the drill hole position is intuitively marked by the obvious ground mark, which is convenient for quick positioning during subsequent geological exploration, engineering maintenance or safety inspection, prevents the drill hole from being mis-dug, buried or damaged by human beings due to missing marks, and provides a physical reference for drill hole basic data recording (such as coordinates, hole sealing time, etc.), which strengthens the integrity and traceability of the hole sealing project from the end of construction, improves the safety of long-term use of the drill hole, and is convenient for engineering management and later maintenance.

[0028] In summary, the present application has at least one of the following beneficial technical effects: 1. The second preset distance above the uppermost salt layer is used as the hole sealing segmentation position, the upper non-salt layer is sealed by ordinary 425 cement slurry, and the lower salt layer area is sealed by halogen water resistant magnesium cement, which not only reduces the hole sealing cost of the whole hole by using ordinary cement, but also prevents the failure of ordinary cement in the salt layer by using magnesium cement to resist high-concentration halogen water erosion, and realizes the balance between economy and functionality.

[0029] 2. By using small-diameter drill pipe to seal the hole, the magnesium cement solution in the drill pipe is pressed to the sealing segment position, and the magnesium cement solution outside the drill pipe does not rise too high, avoiding the risk of increasing the mixing of magnesium cement solution and brine due to the high rise of magnesium cement outside the drill pipe, reducing the dilution effect of brine on magnesium cement solution, and at the same time, the first preset distance hole bottom interval is reserved to prevent drill pipe from being stuck by sediment, ensuring that the magnesium cement covers the key mineral layer at the bottom of the hole and forms a "bottom" seal.

[0030] 3. The magnesium cement is prepared by using water, halogen pieces and magnesium oxide in a mass ratio of 2:2:3~3.5, the halogen pieces are dissolved to absorb heat and avoid reaction heat runaway, the initial setting time is prolonged, and the risk of pipe blockage is eliminated; accurate proportioning makes the volume stable before and after the reaction, avoids shrinkage cracks or expansion damage, and ensures that the sealing material is tightly bonded to the hole wall.

[0031] 4. The magnesium cement setting state and sealing surface position are detected by drilling core, and for the problems of incorrect sealing surface position or unsetting, repair measures such as supplementing magnesium cement and repeating construction are used respectively, forming a quality control mechanism of "detection-judgment-repair", avoiding the safety hazards and mineral layer erosion caused by leakage or setting failure. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is a flowchart of the hole sealing method of the potash and magnesium salt mine in the embodiments of the present application; Figure 2 is a schematic diagram of pumping magnesium cement solution into the drill pipe to replace brine; Figure 3 is a schematic diagram of the magnesium cement solution liquid surface being at the sealing segment position after pumping magnesium cement solution into the drill pipe. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be described in detail below with reference to the accompanying drawings. Figures 1-3 The technical solutions in the embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0034] The embodiments of the present application disclose a hole sealing method for a potash and magnesium salt mine. Referring to Figure 1 , the hole sealing method for the potash and magnesium salt mine includes the following steps: A drill rod with a diameter smaller than the borehole diameter is provided. Specifically, a drill rod with a diameter of 2 / 5 to 3 / 5 of the borehole diameter can be selected. The typical borehole diameter is 95 to 110 mm, but a 50 mm diameter drill rod can be used in actual operation. The drill rod is lowered into the borehole, with the bottom of the drill rod at a first preset distance from the bottom of the borehole. The first preset distance can be determined according to the borehole depth; in this example, the first preset distance is 1 m. The borehole is flushed with circulating brine. This serves two purposes: firstly, it clears the drill rod and the borehole, ensuring unobstructed flow within the drill rod and normal water return in the borehole; secondly, it removes sediment from the bottom of the hole. Rock cuttings and undissolved mineral powder remaining during drilling can affect the adhesion between the magnesium cement and the borehole wall. After flushing, the cement can directly contact the mineral or rock layer, ensuring the quality of the borehole sealing.

[0035] Generally, large-diameter drill rods are used for sealing boreholes. When the magnesium cement solution inside the drill rod is forced to the sealing section, the magnesium cement solution outside the drill rod rises too high, increasing the risk of the magnesium cement solution mixing with brine, further affecting the solidification effect, and resulting in a loose bond between the sealing material and the borehole wall. This application uses small-diameter drill rods, which are easier to replace with magnesium cement and facilitate drill rod lifting.

[0036] Based on the salt layer distribution at the borehole location, the second predetermined distance above the uppermost salt layer in the formation is designated as the sealing section location. The salt layer distribution at the borehole location can be determined based on geological logging data. For example, during drilling, formation information at each depth can be recorded using core sampling and logging instruments (such as resistivity logging and density logging), including: Lithology (clay, sandstone, halite, potassium magnesium salt deposits, etc.); The thickness of the mineral layer and the depth of its top and bottom (the top depth of the uppermost salt layer is the key dividing point).

[0037] The second preset distance can be set to 8~12m; in this embodiment, the second preset distance is 10m. The area between the borehole opening and the sealing section is the upper sealing area. The upper sealing area is surrounded by surface soil and rock layers (non-salt layers), and does not contain potassium magnesium salt minerals. Ordinary cement can solidify normally thereafter, so ordinary cement can be used for sealing. The area between the sealing section and the bottom of the borehole is the lower sealing area. The lower sealing area is surrounded by halite layers and potassium magnesium salt mineral layers (salt layers), which are rich in high-concentration brine. Ordinary cement will fail there, and brine-resistant magnesium cement must be used.

[0038] Potassium magnesium salt deposits often occur in association with halite (NaCl). Although halite layers do not contain potassium, they are still highly soluble and have high brine concentrations, causing ordinary cement to solidify poorly within them. This application uses the "uppermost salt layer" as the starting point, delineating all salt strata (halite + potassium magnesium salt deposits) into the next section. This ensures that the entire high brine concentration area is sealed with magnesium cement, preventing "missed sealing" of the halite layer and subsequent dissolution.

[0039] The magnesium cement solution is prepared by water, halogen piece (MgCl2·6H2O) and magnesium oxide with a mass ratio of 2:2:3~3.5.

[0040] In actual operation, the amount of material per bucket is determined according to the volume of the mixing bucket at the construction site, and the effective volume of the mixing bucket at the construction site is 1m 3 The step of "preparing a magnesium cement solution" includes: 400kg or 0.4m 3 of water (if it is not easy to weigh, the volume of 0.4m 3 can be measured) is added to the mixing bucket with an effective volume of 1m 3 , then 400kg of halogen piece (MgCl2·6H2O) is added, fully dissolved and stirred, and finally 600~700kg of magnesium oxide is added to prepare the required magnesium cement solution.

[0041] The existing magnesium cement preparation method has safety hazards: the traditional formula uses anhydrous magnesium oxide (which reacts violently with water), and after adding water, it will generate a large amount of heat, and the solution may boil and splash, which is easy to scald workers during operation, and the solution must be cooled before use, which is dangerous and delays the construction period; if the magnesium chloride solution is not fully cooled, the magnesium cement reaction speed is fast, from mixing to setting only 10-15 minutes, the construction time is extremely short, and often the pipe is blocked due to the setting of the magnesium cement before it is pumped into the borehole.

[0042] Unreasonable material ratio and construction technology: the ratio of magnesium cement (i.e. the ratio of magnesium oxide, water and additives) lacks a unified standard, and different ratios will lead to uncontrollable setting speed - either premature setting in the drill pipe, blocking the pipeline and making it impossible to construct, or "intermittent" setting in the borehole, forming many unsealed voids.

[0043] The present application uses halogen piece (magnesium chloride containing crystal water) instead of anhydrous magnesium oxide, which absorbs heat during dissolution and neutralizes the reaction heat, making the reaction heat mild and avoiding boiling and splashing of the solution. Dissolve the halogen piece first and then add the solidifying agent (magnesium oxide), slowly release Mg²⁺ after dissolution, and the reaction with magnesium oxide is more moderate, the setting time is controllable (from mixing to initial setting for more than 3 hours, the properties are stable after uniform stirring, and it will not set prematurely in the drill pipe, which is sufficient for pumping construction. Through accurate proportioning, the solid volume before and after the reaction is basically equal (water participates in the reaction but does not increase the solid volume, achieving non-shrinkage and non-expansion), which avoids the failure of hole sealing due to volume shrinkage (cracks) or expansion (damage to the hole wall).

[0044] Pumping magnesium cement solution: the required amount of the magnesium cement solution is determined according to the volume of the lower hole sealing area, and the volume of the halogen water required for pressure injection can be calculated according to the diameter and length of the borehole, which is cylindrical, and the volume calculation formula of the cylindrical shape.

[0045] ReferenceFigure 2 Pumping the magnesium cement solution into the drill pipe from the top of the drill pipe, and the excess brine outside the drill pipe is discharged from the top of the drill hole.

[0046] Pressure injection of brine: injecting brine into the drill pipe from the top of the drill pipe, and part of the magnesium cement solution in the drill pipe is pressed to the outside of the drill pipe from the lower end of the drill pipe. The pressure injection of brine is the power source for the flow of magnesium cement solution, and the magnesium cement reaches the deep ore layer by pressure. If the pressure injection is not used, the magnesium cement will be deposited at the bottom of the hole or halfway. The required volume of brine is calculated in advance, and the liquid level of the magnesium cement solution in the drill pipe is kept at the sealing section position of the drill pipe (refer to Figure 3 ) by pressure injection to avoid pushing too far or not far enough. The drill pipe is removed, and the drill is quickly pulled out to prevent the magnesium cement from solidifying in the drill pipe and to avoid plugging caused by long residence time.

[0047] A first predetermined distance is reserved between the bottom of the drill pipe and the bottom of the drill hole. On the one hand, it prevents the drill pipe from being buried by sediment and causing pipe sticking. On the other hand, it ensures that the magnesium cement covers the bottom of the hole. The key area of sealing is the ore layer near the bottom of the hole. The bottom of the drill pipe is 1 meter away from the bottom of the hole. The pumped magnesium cement can fill 1 meter downward and fill the area around the drill pipe upward, forming a "bottom" closure.

[0048] After waiting for a predetermined time, the ordinary cement slurry is pumped from the magnesium cement sealing surface to the hole mouth cement return slurry to seal the upper sealing area. The ordinary cement slurry is ordinary 425 cement slurry, and the water-cement ratio of the cement slurry is 0.6-0.8.

[0049] Specifically, the method comprises the following steps: Waiting for a first predetermined time, which can be one day or determined according to the amount of magnesium cement solution. The top of the lower sealing area is drilled by using drilling tools to take core. Through coring, the sealing effect of the magnesium cement can be checked. The checking indicators include whether the magnesium cement is hard and whether the magnesium cement sealing surface is correctly positioned.

[0050] If the magnesium cement is hard, it is determined whether the magnesium cement sealing surface is above the uppermost salt layer according to the obtained magnesium cement core. If the magnesium cement sealing surface is above the uppermost salt layer, it indicates that the magnesium cement has completely solidified and the sealing surface is correctly positioned. The magnesium cement sealing of the lower sealing area is successful. The ordinary cement slurry is pumped from the magnesium cement sealing surface to the hole mouth cement return slurry to seal the upper sealing area.

[0051] If the magnesium cement sealing surface is below the uppermost salt layer, it indicates that the amount of magnesium cement is not enough, and the lower sealing area is not completely sealed by the magnesium cement. The required amount of magnesium cement solution is determined according to the volume of the lower sealing area that is not sealed by the magnesium cement. The magnesium cement solution is pumped into the drill pipe from the top of the drill pipe, and the step of pressure injection of brine is repeated.

[0052] Specifically, according to the drilling depth of the drilling tool and the position of the magnesium cement sealing surface in the drilling tool, the depth of the magnesium cement sealing surface can be calculated, and according to the distance between the magnesium cement sealing surface and the position of the hole sealing section, the volume of the lower hole sealing area not sealed by the magnesium cement can be calculated to determine the required amount of the magnesium cement solution.

[0053] If the magnesium cement has not solidified, wait for a second preset time to check the magnesium cement hole sealing effect, if the magnesium cement still has not solidified, use the brine circulation to flush the drilling hole, repeat the steps of pumping the magnesium cement solution and injecting the brine, and re-perform the magnesium cement hole sealing operation until the hole sealing is qualified.

[0054] Pump the ordinary cement slurry from the magnesium cement sealing surface, specifically, after the magnesium cement hole sealing is qualified, lower the drilling rod to 1 meter above the magnesium cement sealing surface, and circulate the drilling hole. The effective volume of the mixing barrel at the construction site is 1m 3 First, add 650kg~700kg of water (not easy to weigh, just measure the volume), add 900kg~1100kg of ordinary 425# cement, and mix thoroughly. Pump the cement slurry into the hole continuously until the thick cement slurry liquid returns from the hole.

[0055] After the cement solidifies, if it is lower than the ground, clean it up, supplement the cement to the ground, and make a cement platform at the ground hole, and record the basic information of the drilling hole.

[0056] In the key positions of the rock salt layer and the ore layer, magnesium cement resistant to brine is used, which effectively resists the risk of water-soluble minerals such as potassium chloride and potassium sulfate being eroded by water, avoids the problem of water leakage caused by the formation of "soft mud" due to the obstruction of cement solidification, fundamentally blocks the channel for external water to infiltrate into the ore layer, reduces resource waste and reduces safety hazards such as ground subsidence and environmental pollution, while ensuring the durability of hole sealing, avoids the high cost of using magnesium cement in the whole hole, balances economy and function, provides a reliable and efficient hole sealing technical solution for potassium salt mine drilling engineering, and has significant geological safety protection and resource protection value.

[0057] In the description of the present application, it should be understood that the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined as "first", "second" can be explicitly or implicitly included one or more features.

[0058] The above are preferred embodiments of the present application, which do not limit the protection scope of the present application, therefore: any equivalent changes made on the structure, shape, principle of the present application shall be covered within the protection scope of the present application.

Claims

1. A method of sealing a borehole in a potash mine, characterized in that, The method comprises the following steps: providing a drill rod with a diameter smaller than the diameter of the borehole, lowering the drill rod into the borehole, with the bottom end of the drill rod being spaced apart from the bottom of the borehole by a first preset distance, and flushing the borehole with brine circulation; according to the distribution of salt layers at the borehole, taking a second preset distance above the uppermost salt layer in the stratum as a hole-closing segmentation position, the region between the borehole mouth and the hole-closing segmentation position being an upper hole-closing region, and the region between the hole-closing segmentation position and the bottom of the borehole being a lower hole-closing region; preparing a magnesium cement solution; pumping the magnesium cement solution into the drill rod according to the required amount of the magnesium cement solution determined based on the volume of the lower hole-closing region, and pumping the magnesium cement solution into the drill rod from the top of the drill rod; injecting brine into the drill rod from the top of the drill rod, pressing part of the magnesium cement solution in the drill rod to the outside of the drill rod from the lower end of the drill rod, and making the liquid level of the magnesium cement solution in the drill rod be at the hole-closing segmentation position, and taking out the drill rod; waiting for a preset time, pumping ordinary cement slurry from the magnesium cement sealing surface to the borehole mouth cement slurry return after the magnesium cement solution solidifies, and sealing the upper hole-closing region.

2. The method of sealing a potash mine borehole according to claim 1, wherein, The step of "waiting for a preset time, pumping ordinary cement slurry from the magnesium cement sealing surface to the borehole mouth cement slurry return after the magnesium cement solution solidifies, and sealing the upper hole-closing region" comprises: waiting for a first preset time, drilling a core at the top of the lower hole-closing region with a drilling tool, and checking the hole-closing effect of the magnesium cement; if the magnesium cement is hard, judging whether the magnesium cement sealing surface is above the uppermost salt layer according to the obtained magnesium cement core; if the magnesium cement sealing surface is above the uppermost salt layer, pumping ordinary cement slurry from the magnesium cement sealing surface to the borehole mouth cement slurry return, and sealing the upper hole-closing region.

3. The method of sealing a potash mine borehole according to claim 2, wherein, After the step of "if the magnesium cement is hard, judging whether the magnesium cement sealing surface is above the uppermost salt layer according to the obtained magnesium cement core", further comprising: if the magnesium cement sealing surface is below the uppermost salt layer, determining the required amount of the magnesium cement solution according to the volume of the lower hole-closing region that is not sealed by the magnesium cement, pumping the magnesium cement solution into the drill rod from the top of the drill rod, and repeating the step of injecting brine.

4. The method of sealing a potash mine borehole according to claim 2, wherein, After the step of "waiting for a first preset time, drilling a core at the top of the lower hole-closing region with a drilling tool, and checking the hole-closing effect of the magnesium cement", further comprising: if the magnesium cement has not solidified, waiting for a second preset time to check the hole-closing effect of the magnesium cement again, if the magnesium cement still has not solidified, flushing the borehole with brine circulation, and repeating the steps of pumping the magnesium cement solution and injecting brine.

5. The method of sealing a potash mine borehole according to claim 1, wherein, The magnesium cement solution is prepared by water, halite (MgCl2·6H2O) and magnesium oxide in a mass ratio of 2:2:3-3.

5.

6. The method of sealing a potash mine borehole according to claim 5, wherein, The step of "preparing a magnesium cement solution" comprises: A mixing tank is provided having a volume of 1 m 3 . Into the stirring tank, 400 kg or 0.4 m 3 of clean water is added, and then 400 kg of halogen piece (MgCl2·6H2O) is added, dissolved and stirred, and finally 600-700 kg of magnesium oxide is added, and stirred to form the desired magnesium cement solution.

7. The method of sealing a potash mine borehole according to claim 1, wherein, The diameter of the drill rod is 2 / 5-3 / 5 of the diameter of the borehole.

8. The method of sealing a potash mine borehole according to claim 7, wherein, The diameter of the drill rod is 2 / 5-3 / 5 of the diameter of the borehole.

9. The method of sealing a potash mine borehole according to claim 1, wherein, The hole-closing segmentation position is located 8-12 m above the uppermost salt layer in the stratum; and / or, The ordinary cement slurry is ordinary 425 cement slurry, and the water-cement ratio of the cement slurry is 0.6-0.

8.

10. The method of sealing a potash mine borehole according to claim 1, wherein, After sealing the upper hole-closing region, further comprising: Cement the surface and set the cement bench mark at the mouth of the hole.

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