JP2001270770A - Geothermal well cement, admixture for geothermal well cement, and method for cementing geothermal well - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an effective usage of scales recovered from a geothermal well, and more precisely, to aim the lowering of the specific weight of cement slurry without causing material separation by using the scales when cementing of a geothermal well is carried out. SOLUTION: The geothermal well cement is constituted by including a dried matter of scales, recovered from a geothermal well and a cement.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a geothermal well cement and an admixture for a geothermal well cement used for cementing a geothermal well, and to a cementing method for a geothermal well.

[0002]

2. Description of the Related Art In extracting a geothermal heat source from a geothermal well that is currently operating or a geological formation deeper than the geothermal well, cementing such a geothermal well requires a cement. In order to prevent the slurry from being lost to the cracks in the formation, it is required to reduce the specific gravity of the cement slurry to be injected.

In general, it is conceivable to reduce the specific gravity of the cement slurry by including as much water as possible in the cement slurry. However, the ratio of water in the cement slurry, that is, the water-cement ratio is increased. If this is the case, material separation is likely to occur, causing a problem in construction, or a problem of poor construction in which the strength of the cured product at the time of cementing becomes uneven. Therefore, the amount of water to be added is limited to a range where no material separation occurs.

Therefore, as a means for reducing the specific gravity, the use of a siliceous admixture has been studied in the past, and Japanese Patent Publication No. 6-99171 and the 53rd Annual Meeting of the Japan Cement Technology Conference, pages 86-87. Is disclosed. The point is to focus on the selection of a siliceous substance as an admixture for a cement slurry, and it is effective to use silica fume among amorphous silica, and it is effective to use the silica fume in a granular form. It is a description of. However, there is a problem that silica fume is expensive as a cementitious material and needs to be granulated, and the production process is complicated.

[0005] In a geothermal power plant, silica scale in hot water spouting together with steam causes various adverse effects such as a decrease in power generation efficiency, so that its treatment is a problem. Generally, a geothermal production well has a depth of about 500 to 3000 m, and water is in a state of high temperature and high pressure. Therefore, components such as silicon, calcium, and iron in rocks are dissolved in hot water. Among such dissolved components, amorphous silica containing silicon as a main component is concentrated when steam is released by a steam-water separator, and the temperature of hot water is also lowered, so that the solubility is reduced and the silica becomes supersaturated. Precipitates as scale. This scale adheres to hot water transport pipes, valves, heat exchangers, etc. on the ground, causing flow obstruction and valve operation obstruction. In addition, there is also a problem that the scale adheres to the inside of the reduction well where the hot water is directly reduced to the underground or to a crack in the stratum and becomes clogged, thereby shortening the life of the reduction well.

[0006] In order to solve such a problem caused by scale adhesion, as a method for reducing supersaturated silica or the like in hot water, a silica seed method or a flocculant addition method is known. The scale has been removed. However, the recovered scale has not been found to be any effective method at present, except for a report as a zeolite raw material (Japanese Patent Publication No. 57-135717). ing.

[0007] The present invention has been made in view of the above points, and an object of the present invention is to provide an effective use of a scale recovered in a geothermal well, and more specifically, by using the scale, It is an object of the present invention to reduce the specific gravity of a cement slurry without causing material separation when performing cementing of a geothermal well.

[0008]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and found that the scale is:
Focusing on the property that amorphous silica is the main component and that it is possible to form very bulky aggregates with fine particles, and as a result of further intensive studies to utilize this, the scale has a low specific gravity action I found that.

[0009] That is, a solution of the present invention is a geothermal well cement characterized in that it contains cement and dried scale recovered from geothermal hot water.

[0010] The inclusion of the scale dry matter recovered from the geothermal hot water makes it possible to knead a large amount of water into the geothermal well cement, thereby reducing the specific gravity of the cement slurry. It is possible to prevent the slurry from being lost to the cracks in the stratum.

[0011] The present invention further includes a cement, a silica source powder, and a scale dried product recovered from geothermal hot water, wherein the scale dried product is based on 100 parts by weight of a mixture of the cement and the silica source powder. Is contained in a ratio of 1 to 10 parts by weight.

Further, there is provided an admixture for a geothermal well cement, which comprises a scale recovered from geothermal hot water.

Further, the means of the present invention relates to a cement containing scale recovered from geothermal hot water, cement, silica source powder, and water in such an amount that the real water weight / cement weight ratio becomes 2 to 5; A method for cementing a geothermal well, comprising preparing a slurry and injecting the cement slurry.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. In the present invention, the scale recovered from geothermal hot water concentrates the silica concentration in the hot water by steam separation of the geothermal hot water, and forcibly and rapidly removes the solution from the supersaturated state due to the temperature decrease. A scale that is deposited, for example, a scale obtained in normal geothermal power generation using steam obtained from geothermal heat, a scale obtained in binary cycle power generation using geothermal water, or geothermal hot water for multipurpose use ( A scale obtained from deep hot water or hot spring water) can be used.

The composition of the scale varies depending on the place where hot water is collected and the method of separating the scale. However, it is generally composed of silica whose main component is 80% or more of the solid content. is there. In addition, iron, calcium,
Although it contains components such as aluminum, all of them are constituents of cement and work advantageously when developing strength in a cured body of geothermal well cement.

The scale is formed by forming aggregates (hereinafter, also referred to as secondary particles) by aggregating scale-forming particles (hereinafter, also referred to as primary particles). As the primary particles, the particle shape and composition are not particularly limited, but as the secondary particles, those having a small true specific gravity containing a large amount of bound water are preferable, and further containing a large amount of free water inside the aggregate. Thus, it is preferable to form an aggregate having a small apparent specific gravity, that is, a bulky aggregate. In addition, since the amount of scale contained in geothermal hot water is generally very low, that is, several hundred ppm or less, from the viewpoint that the secondary particles can be easily separated and recovered by separation means such as filtration, The larger the diameter, the better.

In consideration of such characteristics, the primary particles preferably have a small particle size, and more preferably have a particle size of 0.01 to 1 μm. The secondary particles have an average particle size of 5
３００300 μm, more preferably 5-100
More preferably, it is μm. If the average particle size of the secondary particles is 5 μm or less, the fine particles are increased, so that they are easily collected on the upper portion, and the material is easily separated. On the other hand, if the thickness is 300 μm or more, it is difficult to uniformly mix with the cement mineral and other silica components, which adversely affects the properties of the cured product.

The scale in such a state can be obtained by adding a precipitant or coagulant such as a compound containing a polyvalent metal cation or an allylic nitrogen-containing compound, or a silica seed to geothermal hot water. However, a scale that adheres to and grows on a pipe or the like over a long period of time is not preferable.

The scale obtained by filtration is usually in the form of a paste containing water (hereinafter, also referred to as “raw scale”), and can be used as it is by adding it to geothermal well cement. . The raw scale contains a large amount of free water in the aggregate, and its weight ratio reaches 90% or more. Such free water does not cause material separation, and when kneaded with cement, part of the free water is used for a hydration reaction with cement. Accordingly, by adding such a raw scale containing a large amount of free water, it is possible to increase the proportion of water in the entire cement slurry without causing material separation, and to reduce the specific gravity of the cement slurry.

Further, by drying the raw scale, the scale becomes powdery (hereinafter referred to as “dry scale”).
) And can be used by adding to geothermal well cement. When drying the raw scale, it is preferable to dry while maintaining the shape of the bulky agglomerate. Therefore, the drying temperature is preferably about 80 to 400 ° C, more preferably 80 to 200 ° C. . If the green scale is dried at higher temperatures, very small amorphous primary particles will undergo grain growth, forming strong and dense aggregates. Such aggregates are not preferable because even if water is injected again, they do not become original bulky aggregates, and as a result, the apparent specific gravity of the scale increases.

When the dry scale is mixed with the cement, the dry scale which has formed a bulky aggregate when kneading water with the cement absorbs a large amount of water, and becomes the above-mentioned raw scale state. Therefore, more water can be added within a range that does not cause material separation, and as a result, the specific gravity of the cement slurry can be reduced.

An embodiment of the geothermal well cement according to the present invention is a geothermal well cement in which cement, a silica source powder, and the scale are mixed. Here, as a mixing ratio of each material, it is preferable to mix the silica source powder at a ratio of 80 to 20 parts by weight with respect to 20 to 80 parts by weight of cement. The amount is preferably 1 to 10 parts by weight (in terms of dry weight) based on 100 parts by weight of the mixture with the silica source powder. If the amount of the scale added is less than 1 part by weight, the amount of water kneaded into the cement is limited within a range that does not cause material separation, and it is not preferable because the specific gravity of the cement slurry cannot be effectively reduced. On the other hand, if the amount of the scale exceeds 10 parts by weight, the viscosity of the cement slurry becomes high, and it becomes difficult to control the fluidity, which is not preferable.

Here, as the cement, various portland cements or various mixed cements can be used, and among them, low heat portland cement and sulfate resistant portland cement are preferable. Silica powder can be used as the silica source powder and has a Blaine specific surface area of 50%.
Silica fine powder of 00 to 20000 cm ² / g is preferred,
Further, 8000 to 15000 cm ² / g fine silica powder is more preferable.

Further, when cementing the geothermal well using the geothermal well cement, or when cementing the geothermal well using the admixture for geothermal well cement containing the scale and another cement mixture. In
The amount of water added when preparing the cement slurry is preferably 2 to 5 in terms of a substantial water weight / cement weight ratio, and more preferably 4 to 5 in the same manner. By adding such an amount of water, the specific gravity of the cement slurry can be effectively reduced. Here, the substantial water weight is the total weight of the water to be added and the water contained in the scale.

As described above, the dried scale obtained by drying the raw scale can be mixed with cement to prepare a suitable geothermal well cement having a low specific gravity and no material separation. In addition, raw scale and dry scale,
It can be suitably used as an admixture for geothermal well cement which is added and used when kneading other geothermal well cement with water.

[0026]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples.

<Production Example of Silica Aggregate Collected from Geothermal Well> Separated from a steam well of a geothermal power plant (location: production well No. 134, Onikobe Geothermal Power Station, Miyagi Prefecture, produced from a depth of 1455 m) via a wellhead separator. 20 mg / l of an organic precipitation accelerator ("Daidol EC" manufactured by Daido Kasei Kogyo Co., Ltd.) as an active ingredient was added to the hot water and mixed with a line mixer to precipitate aggregates. A raw scale containing silica aggregates was prepared by filtering the suspension in which the aggregates were precipitated.

<Analysis of Silica Aggregate> The moisture content of the prepared raw scale was measured, and the dried scale obtained by firing the raw scale at 750 ° C. was analyzed. Table 1 shows the results.

[0029]

[Table 1]

When the raw scale was dried at 105 ° C. and the particle shape was observed with a scanning electron microscope, particles having a particle size of about 0.1 to 0.3 μm were aggregated to form a porous and bulky aggregate. (Secondary particles). Further, the average particle size of the secondary particles measured by a laser diffraction type particle size distribution analyzer was 50.7 μm, the specific gravity was 2.03, and the BET specific surface area was 6.9 m ² / g.
Met.

<Preparation of Geothermal Well Cement Slurry> Examples 1 and 2 The recovered raw scale and commercially available low heat Portland cement (manufactured by Sumitomo Osaka Cement Co., Ltd., specific gravity 3.24, Blaine specific surface area 3300 cm ² / g) Silica fine powder (specific gravity 2.65, Blaine specific surface area 10,000 cm ² / g)
And polycarboxylic acid-based high-performance AE water reducing agent (FPK)
And water were simultaneously mixed in the composition shown in Table 2 to prepare cement slurries of Examples 1 and 2. One liter of the cement slurry was dispensed into a measuring cylinder and the specific gravity was measured.

Examples 3 and 4 The recovered raw scale was dried at 105 ° C. to obtain a dry scale. The dry scale commercial low heat Portland cement (Sumitomo Osaka Cement Co., Ltd., specific gravity 3.24, Blaine specific surface area of 3300 cm ² / g) and, silica fine powder (specific gravity 2.65, Blaine specific surface area of 10000 cm ² /
g) and a polycarboxylic acid-based high-performance AE water reducing agent (manufactured by FPK) at a ratio shown in Table 2 and mixed in Examples 3 and 4.
Geothermal well cement was prepared. Water was added to the geothermal well cement and kneaded to prepare a cement slurry, and the specific gravity was measured in the same manner as described above.

Comparative Example 1 Low heat Portland cement (manufactured by Sumitomo Osaka Cement Co., Ltd., specific gravity 3.24, Blaine specific surface area 3300 cm ² /
g), fine silica powder (specific gravity 2.65, Blaine specific surface area 10000 cm ² / g), and polycarboxylic acid-based high-performance A
A water reducing agent (manufactured by FPK) and water were mixed to prepare a cement slurry of Comparative Example.

[0034]

[Table 2] * 1) In the comparative example, white carbon was used as the fine particle silica. * 2) Since material separation occurred, the apparent specific gravity was measured.

As is apparent from Table 2, it is impossible to reduce the specific gravity of the slurry without causing material separation in the comparative example, whereas according to the embodiment of the present invention,
It is possible to reduce the specific gravity of the slurry to 1.35 or less without causing material separation.

Example 5 The recovered raw scale, commercially available Portland cement (manufactured by Sumitomo Osaka Cement Co., Ltd., specific gravity 3.24, Blaine specific surface area 3300 cm ² / g), and fine silica powder (specific gravity 2.65, Blaine ratio Surface area 10000 cm ² / g)
And polycarboxylic acid-based high-performance AE water reducing agent (FPK)
Was mixed in the composition shown in Table 3 to obtain a cement mixture of Example 5.

Example 6 The recovered raw scale was dried at 105 ° C. to obtain a dried scale. The dried scale and commercial low heat Portland cement (Sumitomo Osaka Cement Co., Ltd., specific gravity 3.24, Blaine specific surface area of 3300 cm ² / g) and, silica fine powder (specific gravity 2.65, Blaine specific surface area of 10000 cm ² /
g) and a polycarboxylic acid-based high-performance AE water reducing agent (manufactured by FPK) were mixed in the composition shown in Table 3 to prepare a cement mixture of Example 6.

After the addition of water to the cement compositions of Examples 5 and 6, stirring and standing were performed with different amounts of water, whereby the maximum amount of water that could be added without causing material separation was measured. The specific gravity of the slurry at that time was measured. Table 3 shows the results.

[0039]

[Table 3]

Table 3 confirms the lowering limit of the specific gravity of the slurry without causing the material separation. In the conventional comparative example shown in Table 2, when the specific gravity of the slurry is 1.34 or more, the material separation is already performed. In contrast, in Examples 5 and 6 according to the present invention, water was added without causing material separation until the actual water weight / cement weight ratio was 5.0 and the slurry specific gravity was 1.20. It is possible to That is, according to the geothermal well cement and the admixture for geothermal well cement according to the present invention, it is possible to effectively reduce the specific gravity of the slurry.

[0041]

As described above, according to the present invention, since the specific gravity of the cement slurry can be reduced by adding scale, it is suitable as a geothermal well cement or an admixture for a geothermal well cement. And the scale recovered in the geothermal well can be effectively used.

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Claims (4)

[Claims] 1. A geothermal well cement comprising: a scale dried product recovered from geothermal hot water; and cement. 2. A dry product of a scale containing cement, a silica source powder, and a dried product of a scale recovered from geothermal hot water, wherein 100 parts by weight of a mixture of the cement and the silica source powder is dried. 1 to 10 parts by weight of a geothermal well cement. 3. An admixture for geothermal well cement, comprising a scale recovered from geothermal hot water. 4. A cement slurry containing scale recovered from geothermal hot water, cement, silica source powder, and water in an amount such that a real water weight / cement weight ratio becomes 2 to 5 is prepared. A cementing method for a geothermal well, comprising injecting a cement slurry.