JP2009125680A - Method of removing scale on steam well in geothermal power generation facility - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently remove calcium-based scale such as anhydrite at a comparatively low cost even from a deep and narrow position such as a feed point. <P>SOLUTION: A method comprises the shaft suppressing process for suppressing a pressure of a shaft and cooling by storing water in the shaft of a steam well after stopping the spout of the steam well, the chelate liquid injection process for forming a layer of chelate liquid above a water layer by injecting the chelate liquid above the water layer stored in the shaft, the pushing process for disposing the layer of the chelate liquid at a region with the scale adhered thereon in the shaft by further injecting water above the layer of the chelate liquid so as to pushing back the layer of the chelate liquid with a newly injected water layer, and the finishing process for dissolving the scale with the chelate liquid by holding the state of disposing the layer of the chelate liquid at the region with the scale adhered thereon. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for removing calcium-based scale adhered to a steam well in a geothermal power generation facility.

  In geothermal power generation, geothermal fluid in the ground is taken out from a well drilled to the deep underground, and power is generated by turning a turbine with steam separated from the geothermal fluid. In this case, since the steam well for pumping up the geothermal fluid and ejecting the steam takes out the hot geothermal fluid in the deep underground, the well is excavated to a depth of 2 to 3 km, for example. In addition, the pit wall is generally protected by a steel pipe and cement and is isolated from the rock, and a steel pipe with a hole (perforated pipe) is used as a part for taking out the geothermal fluid.

The geothermal fluid pumped up by such a steam well contains various components in the ground, and the scale tends to adhere to the well due to metal ions such as calcium. As measures against this scale, conventionally, in addition to a method of physically removing the attached scale by inserting a drill bit into a well, Patent Document 1 and Patent Document are used as a technique for preventing the adhesion of calcium carbonate scale. 2 is disclosed. In these techniques, a drug injection tube is inserted into the well, and a scale inhibitor (inhibitor) made of a chemical such as acrylic acid is injected through the drug injection tube into a portion where there is a risk of scale adhesion. .
Japanese Patent Publication No. 1-19520 JP-A-5-195684

  By the way, since a perforated pipe is used as a part for extracting the geothermal fluid in the steam well, the scale adheres not only to the inner peripheral surface of the perforated pipe but also to the outer peripheral surface. Therefore, in the method of physically removing the drill bit by inserting it into the well, only the scale attached to the inner peripheral surface can be removed. For this reason, even if it removes, the adhesion area | region of a scale will spread at an early stage, and a well will be narrowed, and removal work will be needed frequently. Moreover, the construction using such excavation equipment tends to be expensive.

On the other hand, in the technique of injecting the scale inhibitor into the well, the chemical injection tube is inserted into the well, which hinders the flow of steam. In the case of the scale by calcium carbonate, since the geothermal fluid is generated in the vicinity of the flash point of steam by vacuum is a relatively shallow position, for example anhydrite if the scale by (CaSO ₄₎ or the like at feedpoint It is generated in a certain perforated tube portion, and this perforated tube is smaller in diameter than the flash point portion, and it is not appropriate to keep the medicine injection tube inserted because the steam flow rate is reduced.

  Although a method of dissolving a scale by injecting a strong acid such as hydrochloric acid is also conceivable, the damage to the steel pipe is great and impractical, and calcium carbonate can be dissolved, but anhydrite cannot be dissolved.

  The present invention has been made in view of such circumstances, and scale removal that can remove calcium-based scales such as anhydrite relatively inexpensively and efficiently even at deep and narrow positions such as feed points. The purpose is to provide a method.

  A method for removing scale of a steam well in a geothermal power generation facility according to the present invention is a method for removing calcium-based scale adhered to a well in a steam well of a geothermal power generation facility, and after the steam well is stopped, the steam well A well suppression step in which water is held in the well to suppress and cool down the well pressure, and a chelating solution is injected onto the water layer stored in the well to inject the water onto the water layer. A chelating liquid injection step for forming a chelating liquid layer; and by injecting further water onto the chelating liquid layer, the chelating liquid layer is boosted by a newly injected water layer to form a chelating liquid in the well. A boosting step for disposing the scale in the scale adhesion region, and a curing step for dissolving the scale by the chelating solution by maintaining the state in which the layer of the chelating solution is disposed in the scale adhesion region. To.

  That is, it is a method of dissolving calcium-based scale using a chelate solution that is complex-bonded with metal ions such as calcium ions, and a layer of water into which the chelate solution is injected first and a layer of water that is injected later. Layered in a layer so as to be sandwiched between them and sent into the well, this chelate solution layer is placed in the scale generation area deep in the ground while being pushed up by this water layer, and stays in contact with the scale generation area. This will dissolve the scale. In this case, since the chelate solution also goes to the outer peripheral portion from the hole of the perforated pipe constituting the well, the scale attached to the outer peripheral surface can also be dissolved.

  The scale removal method according to the present invention is characterized in that the chelating solution injection step to the curing step are repeated a plurality of times while a new chelating solution and water are alternately injected into the well. That is, since the diameter of the deep hole in the well is narrow, and the amount of the chelating liquid stored in the portion is limited, it dissolves while replacing with a new chelating liquid every predetermined time. In this case, the portion of the chelate solution that has been in contact with the scale adhesion region is released after being dissolved after its capacity has been dissolved, so that the chelate solution is discharged to the outside through the holes of the perforated tube.

  Further, in the scale removal method according to the present invention, the chelate solution layer is formed by a multiple of an amount that satisfies the scale adhesion region, and in the boosting step, the tip portion of the chelate solution layer is formed. In the curing step, the scale is dissolved by intermittently shifting the portion in contact with the scale adhesion region by pushing the chelating solution layer by a predetermined amount by the water layer on the chelating solution in the curing step. It is characterized by doing.

  In the above-described removal method, an amount of new chelating liquid that can cover the scale adhesion region is supplied by being added onto the boosting water layer. In order to utilize the volume in the well, a large amount of chelate solution is poured in advance and stored at a position above the scale adhesion region, and this is boosted by a predetermined amount, so that the dissolution of the scale is sequentially performed from the lower end. It is provided for use.

  Further, in the scale removing method according to the present invention, the calcium-based scale is mainly composed of anhydrite, and the chelating solution is any one selected from nitrilotriacetic acid, ethylenediaminetetraacetic acid, and diethylenetriaminepentaacetic acid. Alternatively, the main component is a mixture of two or more of these. Anhydrite adheres to the position of the deep feed point of the well, but it is a method of feeding the chelate solution while pushing the chelate solution layer with the water layer, so the chelate solution can be sent to the deep underground position, Nitrilotriacetic acid, ethylenediaminetetraacetic acid, and diethylenetriaminepentaacetic acid used as the chelating solution are particularly effective in dissolving anhydrite.

  A method for removing scale from a steam well in a geothermal power generation facility according to the present invention is a method in which a chelate solution is sent to a deep position of a well with water and stayed in a scale adhesion region to dissolve the scale. Since it is not used, it can be carried out at a low cost and the chelating solution can be fed to the feed point of the steam well, so that scales made of anhydrite generated in the deep part of the well can also be dissolved and removed. Since it is a liquid, the scale adhered to the outer peripheral surface of the perforated tube can be removed, and the scale removal effect is extremely high.

  Hereinafter, an embodiment of a steam well scale removing method in a geothermal power generation facility according to the present invention will be described with reference to the drawings.

  FIG. 1 shows a steam well in a geothermal power generation facility. The steam well 1 includes a plurality of steel pipes 3 to 6 disposed inside a pit wall 2 formed by excavation, and a cement 7 so as to fill the space between the steel pipes 3 to 6 with the pit wall 2. Is provided. In this case, the steel pipes 3 to 6 having a large diameter are embedded near the ground surface 8, and a long steel pipe having a gradually small diameter is embedded inside the large diameter steel pipe 3 to extend deep into the ground. ing. As a whole, for example, it reaches a depth of 2.5 km, and the pit wall 2 is protected by the cement 7 at a depth of about 1.3 km, which is half of the depth. In order to pump up hot water in the ground, a relatively small diameter perforated pipe 6 having a large number of holes 9 in the pipe wall is arranged inside the pit wall 2. The plurality of steel pipes 3 to 6 form a well 10 in which the geothermal fluid rises, of which the portion constituted by the perforated pipe 6 at the distal end in the depth direction is the feed point 11 and the center in the depth direction. The flashing point 12 is the vicinity where the inner diameter is enlarged and the cross section is changed near the portion.

  Further, on the ground, a main valve 16 is provided at a portion of the wellhead 15, and by opening the main valve 16, the pumped geothermal fluid is sent to a steam / water separator (not shown) and hot water and Separated into steam. Further, in the illustrated example, two pipes 17 and 18 are connected on the upstream side of the main valve 16 so as to branch, and a valve 19 for opening and closing the flow path is provided in the pipes 17 and 18. One of the pipes 17 is selectively connected to a supply pipe (not shown) of a chelate solution and water.

Next, a first embodiment of a method for removing scale adhered to the well 10 of the steam well 1 configured as described above will be described with reference to the flowchart of FIG. 2 and the schematic diagram of FIG. In FIG. 3, the symbol S indicates a scale attached to the feed point 11 of the well 10, and the symbol H indicates a scale adhesion region along the depth direction of the well 10.
(1) Foam stopping process First, the main valve 16 of the wellhead 15 is closed to stop the fuming of the steam well 1.
(2) Well suppression step By opening the valve 19 of the pipe 17 connected to the well opening 15 and injecting water, the inside of the well 10 is cooled, and the internal pressure is suppressed and lowered. In this state, as shown in FIG. 3A, the well 10 is filled with water W.
(3) Chelate Solution Injection Step Next, a necessary amount of the chelate solution C is injected from above the water W layer. The amount is an amount sufficient to cover the length of the scale adhesion region H in a state where the chelate solution is stored in the feed point 11 portion of the well 10, and is slightly more than the necessary amount. A large amount. FIG. 3B shows a state in which the chelate solution C is formed by injecting the chelate solution C onto the previously injected water W layer. First, for suppression of the well 10. The layer of water W injected into the layer, the layer of chelate solution C, and the layer of water W newly injected are arranged in the well 10.
(4) Boosting Step Next, water W is further injected into the upper water W layer in the three-layer structure shown in FIG. Then, the whole is pushed to the deep part of the well 10, and the layer of the chelating solution C is arranged at a position where the scale adhesion region H in the well 10 can be covered.
(5) Curing step And when the layer of the chelating liquid C reaches a position where the scale adhesion region H in the well 10 can be covered, the injection of the water W is stopped, so that the layer of the chelating liquid C is positioned at that position. To stay in. FIG. 3 (c) shows this state. In this state, the layer of the chelating liquid C is in contact with the entire surface of the scale adhesion region H, and this state is maintained for a predetermined time. The scale S is dissolved by C. In this case, the scale S may adhere not only to the inner peripheral surface of the well 10 but also to the outer peripheral surface, but the chelate solution C is supplied from the hole 9 (see FIG. 1) of the bore 6 of the well 10. Since it also oozes out to the outside of the scale 10, the scale adhering to the outer peripheral surface of the perforated pipe 6 can also be dissolved.

  Then, after the chelate solution C is retained in the scale adhesion region H, for example, for about half a day to about 1 day, the chelate solution is further injected from above the upper water W layer as necessary. A new chelate layer similar to the previous chelate solution layer is formed, and water is further injected from above to boost the chelate solution layer so that it is replaced with the previous chelate solution layer. It arrange | positions to the adhesion | attachment area | region H and is made to stay for a predetermined time. In this way, by repeating a plurality of times from the chelating solution injection process to the curing process as necessary, almost all of the scale S in the well 10 can be dissolved. Then, the main valve 16 of the wellhead 15 is opened to induce fumarole, and normal operation is resumed.

It should be noted that the position of the scale S attached in the well 10 is determined in advance by measuring the change in the hole diameter of the well 10 in the depth direction by caliper logging beforehand. This is done by specifying the depth position and the range of the region. The adhesion amount of the scale S can be specified by calculating the adhesion volume based on the inner diameter of the well 10, the inner diameter (or adhesion thickness) in the adhesion area H, and the length of the adhesion area H. The density of the scale S From the relationship with the porosity, the adhesion weight of the scale S can be calculated. The required number of repetitions from the chelating solution injection process to the curing process is such that the molar ratio of the anhydrite to the chelating liquid is 1: 1, and the chelating liquid is determined from the ratio between the molecular weight of the chelating liquid and the molecular weight of the anhydrite. Since the dissolution capacity per unit weight is required, the required number of times can be determined from the weight of the scale, the volume of the adhesion area, the density of the chelating solution, and the concentration. For example, by using 20 m ³ of EDTA (ethylenediaminetetraacetic acid) solution having a concentration of 5 to 10% in a hollow tube having an inner diameter of about 16 cm, curing is repeated 5 to 10 times over 12 to 24 hours. The total number of days is about 1 week, and the work is about 2 weeks including the work before and after the stop of the fumarole and the fumarole induction.

  4 and 5 show a scale removal method according to a second embodiment of the present invention. In the removal method of the second embodiment, the operations in the “fountain stop process” and the “well suppression process” are the same as those in the previous first embodiment, and the first implementation in the next “chelate injection process” In the case of the embodiment, the amount of the chelating solution to be injected is an amount that covers the length of the scale adhesion region H. However, in the case of the second embodiment, the amount of the chelate solution that covers the length of the scale adhesion region H. Multiple times the amount of chelate solution C is injected. In the “boost process”, the chelating liquid C layer is boosted by the water W layer and fed to the deep part of the well 10, and as shown in FIG. Stop at a position in contact with the target scale adhesion region H.

  Then, in the “curing step”, after holding for a predetermined time in the state shown in FIG. 5A, the length of the scale adhesion region H is boosted again by the layer of water W, thereby FIG. As shown in b), the portion of the chelate solution that has been in contact with the scale adhesion region H is discharged, a new portion of the chelate solution is placed in the scale adhesion region H, and the same operation is performed after holding for a predetermined time. repeat. In this way, by pushing the layer of the chelate solution approximately by the length of the scale adhesion region H, a new chelate solution is brought into contact with the scale adhesion region H while intermittently shifting the portion in contact with the scale adhesion region H. To dissolve the scale. By repeating this, the operation is completed when all the chelating liquid C is consumed.

  That is, the scale removal method of the second embodiment is the same as the scale removal method of the first embodiment, in which an amount of a chelating solution capable of covering the scale adhesion region is alternately injected with the water layer, and the chelating solution layer Are placed in the scale adhesion region one by one, while the chelating solutions for these multiple layers are injected at once, and the tip of the chelating solution layer is placed in the scale adhesion region H. A large amount of the chelating solution is stored at a position above the adhesion region H, and this is boosted by a predetermined amount (intermittent feed), so that the chelating solution layer is shifted from the lower end of the chelating solution to be used for dissolving the scale. It is a thing.

  Next, the experimental results of dissolving anhydrite as a scale with various chelating solutions will be described.

  Two types of plaster were used: mineral specimens from Peru and scales actually collected from production wells at the Sumikawa Geothermal Power Plant in Akita Prefecture. In any case, according to X-ray diffraction, no impurity diffraction peak was observed only with anhydrite.

  As the chelating solution, four products shown in Table 1 were selected from three chelating agent sales manufacturers. These are referred to as CH agent, NCS agent, NCC agent, and BJ agent described in the table. These chelating agents are all organic (aminocarboxylic acid) chelating agents, such as EDTA (Ethylene Diamine Tetraacetic Acid), NTA (Nitrilo Triacetic Acid), and DTPA (diethylenetriamine pentamine). Acetic acid: Diethylene Triamine Pentaacetic Acid). The NCS agent is a mixture based on EDTA. In any case, the heat-resistant temperature is as high as 200 ° C. or higher, and it is suitable for use in a geothermal environment.

  Using these chelating solutions, change the concentration, solid-liquid ratio, etc. into each beaker and keep them at the prescribed test temperature, and immerse one of the two types of anhydrite in it to dissolve it. Was measured. Among them, the test temperature was set to three conditions of room temperature of about 20 ° C., 50 ° C., and 80 ° C. Concentrations include powder and liquid chelating agents. As a guideline, powder is 5 to 40% wt / vol, liquid is undiluted solution, 4 times dilution, 10 times dilution Concentration. The solid-liquid ratio was implemented by adding 10 ml and 20 ml as a condition with a low ratio of the chelating solution in consideration of the situation in the well, based on 100 ml of the chelating solution with respect to 1 g of solid scale. Stir at 300 rpm in all conditions. These test conditions are listed in Table 2.

  These test results are shown in FIGS. 6 to 14. Hereinafter, various test results will be described with reference to these drawings. In these figures, “dissolved amount (g) / anhydrite 1 g” represents the amount dissolved in 1 g of anhydrite, and 1.0 indicates that the entire amount was dissolved.

  FIG. 6 shows the results of measuring the change in solubility according to three conditions of 20 ° C., 50 ° C., and 80 ° C. using a 5% solution of a CH agent as a chelating solution. As is apparent from FIG. 6, in the temperature range from room temperature (about 20 ° C.) to 80 ° C., the dissolution rate increases as the temperature rises and dissolves in a short time. Even at room temperature, more than half was dissolved in 24 hours, and the chelating agent was found to be effective for chemical cleaning of anhydrite. At 80 ° C., the highest temperature, the entire amount was dissolved in 15 hours. This means that even when applied to an actual well, the chelate solution is injected and the temperature inside the well is stopped during the curing, so that the temperature rises. The fact that such characteristics are shown is also advantageous from the field work. In addition, in this FIG. 6, the value shown with the thin line | wire has shown the solubility when an anhydrite is immersed in the pure water of 20 degreeC which does not add a chelating agent, By comparison with the result of this pure water, It can be seen that dissolution is significantly accelerated by the chelating solution.

  7 to 10 show the relationship between the concentration of the chelating solution and the solubility. FIG. 7 shows the case of the CH agent, FIG. 8 shows the NCS agent, FIG. 9 shows the BJ agent, and FIG. 10 shows the NCC agent. Yes. In all cases, the temperature was uniform at 50 ° C. Among these, as shown in FIG. 7 to FIG. 9, with respect to the solution concentration, in the range of 5% to 20%, the dissolution rate increases as the concentration increases, but is slightly different at 10% or more. In other words, the increase in concentration shows a tendency to increase the dissolution rate, but there is no proportional relationship, and the effect of increasing the dissolution rate commensurate with the increase in concentration is slow. Therefore, use at a high concentration is not preferred from the viewpoint of cost effectiveness, and as a molar concentration, the chelating solution is consumed for dissolution of anhydrite in a short time even under conditions where there is less chelating solution than an anhydrite sample. The chelate concentration at the time of washing is optimally about 5 to 10%. That is, it can be said that it is more effective to reduce the concentration of the chelating solution and increase the number of washings. In addition, in the case of the NCC agent of FIG. 10, it was shown that the effect of the diluted solution is greater than that of the stock solution as it is. Of these four chelating agents, it can be said that the CH agent of FIG. 7 and the NCS agent of FIG. 8 have higher dissolving ability than other chelating agents.

  FIG.11 and FIG.12 has shown the result of having measured the solubility when changing the molar ratio of an anhydrite and a chelate liquid. An anhydrite and a chelate solution are dissolved in a molar ratio of 1: 1. In each test shown in FIGS. 6 to 10, the chelating solution is used in a state where the amount of the chelating solution is larger than that of the hard plaster sample. Therefore, the hard plaster continues to dissolve over time. FIG. 11 and FIG. 12 show the results of confirming what kind of influence is exerted on the solubility by reducing the ratio of the chelating solution compared with the anhydrite. In other words, in an actual well, the amount of chelating liquid that can be stored in a small diameter part such as a feed point is limited, so especially when the scale is thick, the chelate is larger than the scale. It is also assumed that the liquid is consumed first and the scale remains. In order to reproduce such conditions, the dissolution characteristics when the chelating solution was reduced compared to the anhydrite sample were investigated.

  In these figures, for the CH agent shown in FIG. 11, the 10% solution is 0.3, 0.6, 3.0 in molar ratio to the anhydrite sample, and the 20% solution. The samples were soaked in 0.6, 1.2, and 6.0, respectively, and the anhydrite sample was immersed therein. On the other hand, for the NCS agent shown in FIG. 12, a stock solution and a 4-fold diluted solution are used, and the stock solution has a molar ratio of 0.8, 1.6, 8.0. The ratio was 0.2, 0.4, and 2.0. In either case, the reaction temperature was 80 ° C.

  As can be seen from these figures, the amount of dissolution is stable over time under the condition that there is less chelating solution than the anhydrite sample in any chelating agent. It was confirmed that the reaction was consumed under all conditions, and the reaction efficiency was high. Such characteristics mean that the more the scale grows in the well, the more effective the cleaning with the chelating solution is.

  Fig. 13 and Fig. 14 show the influence of the source of an anhydrite sample, Fig. 11 shows an anhydrite mineral sample produced in Peru, and Fig. 12 shows the production well of the Sumikawa Geothermal Power Plant in Akita Prefecture. The collected scale is used. According to the comparison of these figures, in the sample produced in Peru, the dissolution rate of the CH agent was higher than that of the NCS agent, but the dissolution rate was reversed in the sample of the Sumikawa geothermal power plant. Differences in dissolution rate were observed. Since anhydrite is a natural product, it is considered that differences due to trace components and crystal grain size appear.

  In addition, this invention is not limited to the said embodiment, A various change can be added in the range which does not deviate from the meaning of this invention. For example, as an intermediate embodiment between the first embodiment and the second embodiment, a plurality of chelating liquid layers that can cover the scale adhesion region are provided in a long well through an appropriate amount of water layer. It is good also as a method of making the layer of a chelate solution contact a scale adhesion area | region sequentially by forming a layer and sending this out intermittently.

It is a longitudinal cross-sectional view which shows the steam well of the geothermal power generation equipment with which the scale removal method which concerns on this invention is applied. It is a flowchart which shows 1st Embodiment of the scale removal method which concerns on this invention. It is a longitudinal cross-sectional view which shows the state of the steam well for every process in the scale removal method of 1st Embodiment in order. It is a flowchart which shows 2nd Embodiment of the scale removal method which concerns on this invention. It is a longitudinal cross-sectional view which shows the state of the steam well for every process in the scale removal method of 2nd Embodiment in order. It is a graph which shows the result of having measured the change of the solubility by the difference in temperature at the time of melt | dissolving an anhydrite with a chelating liquid. It is a graph which shows the relationship between the density | concentration and solubility of the chelate liquid which uses CH agent. It is a graph which shows the relationship between the density | concentration of a chelating liquid using an NCS agent, and solubility. It is a graph which shows the relationship between the density | concentration of a chelating liquid using a BJ agent, and solubility. It is a graph which shows the relationship between the density | concentration of a chelating liquid using an NCC agent, and solubility. It is a graph which shows the result of having measured the solubility when changing the molar ratio of the chelate liquid using CH agent, and an anhydrite. It is a graph which shows the result of having measured the solubility when changing the molar ratio of the chelate liquid using an NCS agent, and an anhydrite. It is a graph which shows the result of having measured the solubility with respect to the mineral specimen of the anhydrite produced in Peru. It is a graph which shows the result of having measured the solubility with respect to the scale extract | collected in the production well of Sumikawa geothermal power station of Akita Prefecture.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steam well 2 Well wall 3-5 Steel pipe 6 Steel pipe (perforated pipe)
7 Cement 8 Surface 9 Hole 10 Well 11 Feed Point 12 Flushing Point 15 Wellhead 16 Main Valve 17, 18 Piping 19 Valve S Scale H Scale Adhesion Area W Water C Chelate Solution

Claims (4)

A method for removing calcium-based scale attached to a well in a steam well of a geothermal power generation facility,
A well suppression step of cooling the well by suppressing the pressure of the well by storing water in the well of the steam well after stopping the fumarole of the steam well;
A chelating liquid injection step of injecting a chelating liquid onto the water layer stored in the well to form a chelating liquid layer on the water layer;
A step of boosting the chelating solution layer by injecting more water onto the chelating solution layer to place the chelating solution layer in a newly deposited layer of water and placing it in the scale adhesion region in the well; and
And a curing step of dissolving the scale by the chelating liquid by maintaining the state in which the chelating liquid layer is disposed in the scale adhering region.   2. The steam well descaling method in a geothermal power generation facility according to claim 1, wherein the chelating solution injection process and the curing process are repeated a plurality of times while alternately injecting a new chelating solution and water into the well. .   The chelating solution layer is formed by a multiple of the amount that fills the scale adhesion region, and in the boosting step, the tip of the chelating solution layer is disposed in the scale adhesion region, and the curing step Then, the scale is dissolved by intermittently shifting a portion in contact with the scale adhesion region by pushing the chelate solution layer by a predetermined amount by the water layer thereon. Descaling method of steam well in geothermal power generation facility. The calcium-based scale is mainly composed of anhydrite, and the chelating solution is mainly composed of any one selected from nitrilotriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, or a mixture of two or more of these. The steam well scale removing method in a geothermal power generation facility according to any one of claims 1 to 3, wherein

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