JPH1036825A - Low-specific-gravity geothermal well cement slurry for use at high temperature - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stable low-specific-gravity cement slurry suitable for cementing a geothermal well. SOLUTION: This slurry is prepared by dispersing a high-temperature-use cement composition mainly consisting of 35-65wt.% pulverized portland cement and 65-35wt.% finely powdered silicaceous admixture in water and has a specific gravity of 1.40-1.65 (desirably 1.40-1.60). In this slurry, the finely powdered silicaceous admixture comprises 10-90wt.% fine crystalline silica powder and 90-10wt.% fine amorphous silica powder, both powders having a fineness (Blaine value) of 8,500cm<2> /g or above, and the fine amorphous silica powder has a fineness (BET specific surface area) of 120,000cm<2> /g or above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-density geothermal well cement slurry for high temperatures. More specifically, the present invention relates to a low specific gravity cement slurry suitable for cementing a geothermal well, which is a well having a very high formation temperature.

[0002]

2. Description of the Related Art When excavating a geothermal well, a cement slurry is filled in an annulus portion between a formation and a casing inserted into the well. In this case, in order to more effectively prevent collapse or cementing of the pit wall, a specific gravity prepared by dispersing a high-temperature cement mainly composed of Portland cement and a siliceous mixture material in water is 1.60.
A slurry having a specific gravity of 1.about.2.0 is used.
Slurries with a low specific gravity of about 20 to 1.65 (particularly, 1.20 to 1.60) have been used.

Conventionally, as a method for reducing the specific gravity of a cement slurry, there are known methods such as increasing the amount of dissolved water, adding a material having a low specific gravity, or introducing bubbles. Of these, the increase in the amount of dissolved water is due to the help of water having a small specific gravity,
In this method, material separation in slurry (increase of free water)
Becomes noticeable. In order to prevent this, bentonite having high swelling property is often added. However, in this method, at a high temperature of 250 ° C. or more, the strength decreases due to the addition of bentonite. There is.

In the method of adding a material having a low specific gravity, pearlite or microsphere (hollow particulate material) is generally used. However, flotation separation of low specific gravity material in slurry, large increase in specific gravity of slurry due to pressure destruction of low specific gravity material shell part (shell) during construction, and even in high temperature geothermal environment exceeding 250 ° C After the curing, a large shrinkage or a decrease in strength occurs due to the elution of the particle shell portion due to the reaction with the cement at the time.

[0005] The introduction of bubbles into the slurry is performed by air or nitrogen gas. In this case, since the particle size of the air bubbles greatly changes depending on the temperature and the pressure (depth) of the geothermal well, hardware for the ground equipment and software for control are required for the adjustment.

[0006] On the other hand, the formation part of the geothermal well is a permeable formation,
There are many joints, cracks, faults, etc., and the dewatering phenomenon occurs in which the water in the slurry is filtered and absorbed into the stratum at the time of construction, so that defects are likely to occur in the cementing portion. For this reason, although the dehydration regulator is added at the time of slurry preparation, the conventional dehydration regulator has low heat resistance, deteriorates its function under high-temperature conditions exceeding 250 ° C., and cannot be used.

On the other hand, JP-A-6-42281 discloses that
A mixture of finely powdered Portland cement and a finely divided siliceous material such as hard silica is weighed at a Blaine value of 5000-13000 c.
A cement slurry obtained by adjusting the fineness to a range of m ² / g and adding a retarder thereto to water is used for a method for preventing water loss in drilling of wells such as oil wells, geothermal wells and general civil engineering. The invention to be used is described. The cement slurry described in this official gazette is used for repairing a location where the muddy fluid for excavation escapes into the stratum, that is, used for preventing water loss, and has a high heat resistance. No consideration was given to the characteristics or specific gravity reduction. Therefore, there is no suggestion for producing a low specific gravity and stable cement slurry suitable for cementing hot geothermal wells.

[0008]

As described above, in the prior art, as described above, especially when considering the use of cementing geothermal wells, the limit of low specific gravity, the heat resistance of low specific gravity material, or the difficulty in introducing air bubbles, There are technical or economic problems that are not easily solved, such as software complexity.
Therefore, an object of the present invention is to improve the workability and long-term hardening characteristics of a low-specific-gravity cement slurry under geological conditions of an extremely high-temperature geothermal well such as exceeding 250 ° C., particularly exceeding 300 ° C. It is in.

[0009]

SUMMARY OF THE INVENTION The present invention provides 35 to 65% by weight of finely powdered Portland cement and 65 to 35% by weight.
A high-temperature cement composition containing a finely divided siliceous mixture as a main component is dispersed in water, and the specific gravity of the slurry is 1.40.
To 1.65 (preferably 1.40 to 1.60) cement slurry, wherein the finely divided siliceous mixture is
It consists of 90% by weight of crystalline silica fine powder and 90 to 10% by weight of amorphous silica fine powder, and each of the fine powder Portland cement and the crystalline silica fine powder is 8500 cm ^2.
/ G or more and the fineness of amorphous silica fine powder is 120,000 cm ² / g or more (B
Low specific gravity geothermal well cement slurry for high temperature characterized by having a high specific gravity (ET specific surface area).

The fineness (Brain value) of both the above-mentioned fine Portland cement and crystalline silica fine powder is 850.
It is preferably in the range of 0 to 13000 cm ² / g, and the fineness of the amorphous silica fine powder is B
120,000 to 250,000 cm ² / g in ET specific surface area
Is preferable. Examples of such ultrafine amorphous silica fine powder include silica fume. Further, it is preferable to use different additives depending on construction conditions (well conditions) at the time of cementing, and one or more additives among a retarder, a dispersant, a dehydration regulator and an antifoaming agent can be used. .

[0011]

DETAILED DESCRIPTION OF THE INVENTION The present invention, as described above,
An object of the present invention is to provide a low-specific-gravity cement slurry having excellent workability and long-term hardening properties under a very high temperature geothermal environment such as exceeding 300 ° C., particularly exceeding 300 ° C. The low specific gravity cement slurry for geothermal wells of the present invention is obtained by dispersing a high heat resistant high temperature cement component in water. Heat resistance is an essential property of cement and other optional ingredients. Lowering the specific gravity of cement slurry is basically due to an increase in the amount of dissolved water, but as a result of detailed examination on the type of material used, fineness or mixing ratio, etc., by combining them in a specific range ,
It has been found that characteristics that are difficult to achieve with the conventional general method by increasing the amount of dissolved water can be obtained.

The high-temperature cement is roughly composed of a base cement (Portland cement) and a siliceous mixture. The fineness of each of these materials is required to be fine.
500 cm ² / g or more (preferably, 9000 cm ² /
g or more) is effective. Therefore, the fineness as a high-temperature cement is 8500 cm ² / blaine value.
g or more. That is, in order to secure the material non-separability in the slurry and the excellent curing characteristics in an extremely high temperature geothermal environment, it is indispensable to pulverize the used material.

Further, in the present invention, crystalline silica and amorphous (glassy) silica are used in combination as the siliceous mixture. Examples of the crystalline silica include hard silica and silica. Silica fume is particularly preferred as the amorphous silica. Amorphous silica has a fineness (BET specific surface area by N ₂ gas adsorption) of 120,000 to 250.
It is preferably in the range of 000 m ² / g, particularly preferably in the form of granules. The amorphous amorphous fine particles are particularly effective for improving the stability (dispersion stability) of the cement slurry for geothermal wells of the present invention under high-temperature conditions and improving the reactivity in cementing. Granular amorphous silica is
It has excellent handling properties during cement production, dispersibility during cement slurry preparation, and hardening properties.

The additives which can be added to the low-density geothermal well cement slurry for high temperature use of the present invention include a retarder for delaying the hardening of cement, and an agglomerate of cement particles which are sufficiently disintegrated in the slurry to improve fluidity. A dispersing agent that enhances, a dehydration regulator that prevents the escape of dissolved water in the slurry to the formation,
Alternatively, an antifoaming agent for preventing air bubbles from being mixed during the preparation of the cement slurry (at the time of dissolving and stirring the cement) can be used. These additives are combined depending on the formation conditions, the composition of the cement for high temperature, or the type and amount of the additive to be used, and the total amount of these additives is preferably 10% or less based on the cement. Its particularly important additives are retarders and dehydration regulators. As a retarder,
As the formation temperature increases, organic systems (eg, TR-14, T
A combination of R-16 (all manufactured by Ternite Co., Ltd.) and an inorganic type (for example, TR-18 (manufactured by Ternite Co., Ltd.)) is particularly effective. Dehydration regulators are apt to deteriorate at high temperatures, and their heat resistance has been strongly desired to be improved. However, when the circulation temperature of cement slurry exceeds 200 ° C., AMPS (Acryla) is used as the dehydration regulator.
Mido Methyl Propane Sulphonic Acid) or a copolymer of vinylamide and vinylsulfonic acid can significantly reduce the amount of dehydration. The high-temperature low-density geothermal well cement slurry of the present invention may optionally contain various other cement additives. Examples of such additives other than those described above are disclosed in
No. 42281.

[0015]

【Example】

[Examples 1 to 3, Comparative Examples 1 to 6] Table 1 shows the fineness and chemical composition of the base cement and the siliceous mixture used.

[0016]

[Table 1] Table 1 種 別 Type Brain value Chemical composition (% ) (Cm ² / g) SiO ₂ Al ₂ O ₃ Fe ₂ O ₃ CaO SO ₂ ────────────────────────────── ────── Belite I 8700 30.1 1.7 2.3 61.0 1.9 Base cement Belite II 9400 25.0 3.6 3.8 62.0 1.9 Class G 9200 22.2 3.1 4.8 64.4 1.9 ──────────────── ──────────────────── Siliceous material Silica powder 11300 97.5 0.8 0.4 0.2 − Silica fume 148000 ^* 97.6 1.1 0.0 0.1 − ────────── ────────────────────────── Note) The value of silica fume is the BET specific surface area.

Using a base cement of Belite II and a siliceous admixture in different mixing ratios, a dispersant (TD-
55 (manufactured by Ternite Co., 0.5%) and a required amount of water were added to prepare a cement slurry. The amount of water is A
The condition was that the standard consistency of the PI standard be satisfied (the consistency after 20 minutes was 11ABc). About the cement slurry obtained above, specific gravity and viscosity (5
(Second consistency) and curing properties (compression strength, water permeability, curing conditions: 350 ° C., 211 kgf / c)
m ² , 24 hours). The preparation of the slurry and the test method were performed in accordance with the API standard. Table 2 shows the results of these tests.

[0018]

[Table 2] Table 2 ──────────────────────────────────── Mixing ratio (%) Water / Cement Slurry Consistency Compressive Strength Water Permeability Belite II Silica Powder Silica Fume Ratio (%) Specific Gravity Sea (ABc) (kgf / cm ³ ) (md) ─────────────────比 Ratio 1 70 20 10 92 1.53 5 56 3.01 × 10 ^-1 Ratio 2 70 10 20 101 1.49 5 70 2.30 × 10 ^-1 Ratio 3 70 0 30 109 1.46 5 74 2.80 × 10 ^-1 ──────────────────────────────────── Actual 1 55 30 15 92.5 1.51 4 103 1.06 × 10 ^-1 real 2 55 15 30 103 1.47 7 85 2.85 × 10 ^-2 real 3 35 22 43 111 1.42 10 102 3.35 × 10 ^-2 ─────────── ───────────比 Ratio 4 35 0 65 119 1.39 14 152 5.63 × 10 ^-3 Ratio 5 10 90 138 1.32 18 24 2.54 × 10 ^-1 Ratio 6 10 90 0 64 1.628 5 1.87 ────────────────────────────────────

From the above results, the slurry does not stiffen immediately after kneading (consistency is 11 ABc or less), and
It can be seen that those having excellent curing characteristics at 0 ° C. (strength and resistance to water penetration) are cement slurries using a combination of crystalline silica and silica fume (amorphous silica) as a siliceous mixed material.

Examples 4 to 6 The base cements (Belite I, Belite II, Class G), silica powder and silica fume shown in Table 1 were 55% by weight and 30% by weight, respectively.
15% by weight, a dehydration regulator (copolymer of vinylamide and vinylsulfonic acid), a retarder (TR-18, T
R-16) and water were added to prepare a cement slurry. For these slurries, a geothermal well temperature of 300 ° C
And the amount of free water and dehydration (20
After heat treatment at 0 ° C for 2 hours, 90 ° C, differential pressure 70kgf / cm
² conditions), thickening time (test condition is 2
00 ° C, 600 kgf / cm ² ), compressive strength (conditions: 3
00 ° C, 211 kgf / cm ² ) and water permeability (conditions: 3
00 ° C, 211 kgf / cm ² ). The results are shown in Tables 3 and 4.

[0021]

[Table 3] Table 3 ──────────────────────────────────── Base cement additive (%) ¹⁾ water / semen dehydration regulator ²⁾ TR-18 TR-16 ratio (%) ───────────────────────────── ─────── Example 4 Belite I 0.50 2.50 2.10 82.0 Example 5 Belite II 0.50 2.50 2.20 92.5 Example 6 Class G 50 3.00 1.70 89.0 ──────────────────────────────────── Note 1) High temperature Weight basis for cement for use. 2) A copolymer of vinyl amide and vinyl sulfonic acid. Slurry specific gravity: Example 4 (1.55), Examples 5 and 6 (both 1.51)

[0022]

[Table 4] Table 4 ──────────────────────────────────── Dewatering amount of free water Thickening time Compressive strength Water permeability (%) (ml / 30 minutes) (hours: minutes) (kgf / cm ² ) (md) 7 days 28 days 7 days 28 days ────────────── ────────────────────── Example 4 0.04 215 4:01 105 98 1.10 × 10 ^-2 3.19 × 10 ^-2 Example 5 0.10 344 4:03 89 81 1.57 × 10 ^-3 2.99 × 10 ^-3 Example 6 0.00 320 4:23 79 87 1.39 × 10 ^-2 2.30 × 10 ^-2 ────────────────── ──────────────────

[Examples 7 to 9] The three kinds of cement for high temperature used in Examples 4 to 6 were mixed with a dehydration modifier (copolymer of vinylamide and vinylsulfonic acid) and a dispersant (TD-
60), retarders (TR-18, TR-16), and water were added to prepare a cement slurry. For each of these cement slurries, a geothermal well temperature of 350 ° C.
And free water and dehydration amount (after heat treatment at 230 ° C. for 2 hours, 90 ° C., differential pressure 70 ° C.)
kgf / cm ² ), thickening time (test conditions: 230 ° C, 600 kgf / cm ² ), compressive strength (test conditions: 350 ° C, 211 kgf / cm ² ), water permeability (test conditions: 350 ° C, 211 kgf / cm ² ). The results of these tests are shown in Tables 5 and 6.

[0024]

[Table 5] Table 5 ──────────────────────────────────── Base cement additive (%) ¹⁾ Water / cement dehydration regulator ²⁾ TD-60 TR-18 TR-16 ratio (%) ────────────────────────── ────────── Example 7 Belight I 0.50 0.75 3.50 2.80 82.0 Example 8 Belight II 0.50 0.75 4.20 3.00 92.5 Example 9 Class G 0.50 0.75 4.20 3.00 89.0 ──────────────────────────────────── Note 1) Outer weight for high-temperature cement Standards. Note 2) Copolymer of vinylamide and vinylsulfonic acid.

[0025]

[Table 6] Table 6 ──────────────────────────────────── Dewatering amount of free water Thickening time Compressive strength Water permeability (%) (ml / 30 minutes) (hours: minutes) (kgf / cm ² ) (md) 7 days 28 days 7 days 28 days ────────────── ────────────────────── Example 7 0.00 395 4:52 123 98 1.06 × 10 ^-2 2.57 × 10 ^-2 Example 8 0.14 428 5:00 96 107 1.79 × 10 ^-2 2.20 × 10 ^-2 Example 9 0.00 408 4:50 82 100 3.62 × 10 ^-2 2.37 × 10 ^-2 ────────────────── ──────────────────

[Comparative Examples 7 to 10] Using belite II and silica powder having different degrees of fineness (expressed in terms of a Bray value), an additive and water were added to a cement for high temperature to which silica fume was added, and a specific gravity of 1 was obtained. A slurry of 0.5 was prepared. For these slurries, free water and thickening time (test conditions: 200 ° C., 600 kgf / cm ² ) were measured. The results are shown in Tables 7 and 8. For reference, the results of Example 5 described above are also shown.

[0027]

[Table 7] Table 7 ────────────────────────────────────Blending ratio (%) Silica High temperature Cement Belite II Silica powder Fume Brain value (cm ² / g) 3200 6300 9400 6300 7300 11300 ────────────────────────── ────────── Example 5 0 0 55 0 0 30 15 11 300 Comparative Example 7 0 55 0 0 30 0 15 8100 Comparative Example 8 55 0 0 30 0 15 5900 Comparative Example 9 55 0 0 30 0 0 15 4900 Comparative Example 10 55 0 0 15 0 0 30 7000 ─────────────────────────────────── ─

[0028]

[Table 8] Table 8 ──────────────────────────────────── Additives (%) ¹⁾ Water cement Free water Thickening time Dehydration regulator ²⁾ TD-60 TR-18 TR-16 ratio (%) (ml) (hour: minute) ───────────────── ─────────────────── Example 5 0.50 0 2.50 2.20 92.5 0.1 4:03 Comparative Example 7 0.50 0.60 0 92.5 2.8 4:53 Comparative Example 8 0.50 0.50 0 0 92.5 2.8 4:37 Comparative Example 9 0.50 0.45 0 92.5 3.2 3:41 ³⁾ Comparative Example 10 0.50 1.25 0 0 92.5 1.6 4:30 ─────────────────────────── Note 1) Based on the outer weight of high-temperature cement. Note 2) Copolymer of vinylamide and vinylsulfonic acid. Note 3) TD-60 (0.40%)

From the above results, it can be seen that when the fineness (Brain value) of the high-temperature cement is 8100 cm ² / g or less, material separation occurs in the cement slurry and the amount of free water increases, which is undesirable.

[Comparative Examples 11 to 16] In order to reduce the specific gravity by increasing the amount of dissolved water using the conventional geothermal well cement materials shown in Table 9 to suppress material separation in the slurry at that time. , A cement slurry having a specific gravity of 1.50 was prepared by adding bentonite. In that case, as a cement additive, a dispersant (TD-55) and a retarder (TR-1)
8, TR-14) was added. About this slurry,
Assuming a geothermal well temperature of 350 ° C, the thickening time (2
30 ° C., 600 kgf / cm ² ), compressive strength (350
° C, 211 kgf / cm ² ), water permeability (350 ° C, 2
11 kgf / cm ² ). Table 10 shows the results of these tests.

[0031]

Table 9 Table ──────────────────────────────────── Base Cement Brain Value Chemical Composition ( %) (Cm ² / g) SiO ₂ Al ₂ O ₃ Fe ₂ O ₃ CaO SO ₂ ───────────────────────────── ─────── Geothermal well cement 3520 44.6 2.5 3.7 45.5 1.4 ────────────────────────────────── ──

[0032]

[Table 10] Table 10 ──────────────────────────────────── Additives Vent ¹⁾ Water Thickening Compressive strength Water permeability (%) Night ratio Time (kgf / cm ² ) (md) TD-55 TR-18 TR-14 (%) (%) (h: min) 7 days 28 days 7 days 28 JP ──────────────────────────────────── Comparative Example 11 0.5 2.5 1.1 1.5 101.8 3:50 42 60 2.51 6.32 ──────────────────────────────────── Note 1) Based on the outer weight of geothermal well cement.

Taking the above test results into consideration, using a 5.94 g / l aqueous solution of CMHEC (carboxymethyl hydroxyethyl cellulose), a commonly used dehydration regulator, the treatment temperature was changed to 120 to 200 ° C. Time autoclave curing was performed. Separately, Comparative Example 11
The geothermal well cement, dispersant (TD-55) and the heat-treated CMHEC aqueous solution described above were used at a water-cement ratio of 50.50.
After adding 5%, the amount of dehydration was measured at 27 ° C. under the condition of a differential pressure of 70 kgf / cm ² . The dehydration test apparatus used was of API specification. The results are shown in Table 11. As can be seen from Table 11, the heat resistance of the conventional dehydration regulator is low, and the amount of dehydration increases when the test temperature exceeds 180 ° C.

[0034]

Table 11 Table ──────────────────────────────────── TD-15 Cement ratio Slurry Dewatering Dehydration amount of modifier (%) (%) Specific gravity Heat treatment temperature (℃) ─────────────────────────────────比較 Comparative Example 12 0.5 50.5 1.80 Untreated 222 Comparative Example 13 0.5 50.5 1.80 120 236 Comparative Example 14 0.5 50.5 1.80 150 256 Comparative Example 150 5.5 50.5 1.80 180 1299 Comparative Example 16 0.5 50.5 1.80 200 1364 ──────────

[0035]

The cement slurry of the present invention has low specific gravity suitable for use in geothermal wells, but does not easily separate components when used in geothermal wells having extremely high formation temperature, and has high stability. After hardening, it shows properties essential for cementing geothermal wells, such as high compressibility and low water permeability.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shigeo Okabayashi 1-12-32 Nishihonmachi, Ube City, Yamaguchi Prefecture Ube Industries, Ltd. Ube Head Office (72) Inventor Kazuo Konishi 1-1-12 Nishihonmachi, Ube City, Yamaguchi Prefecture No. 32 Ube Industries, Ltd.Ube head office

Claims (4)

[Claims] 1. A high-temperature cement composition comprising 35 to 65% by weight of finely divided Portland cement and 65 to 35% by weight of a finely divided siliceous mixture as a main component is dispersed in water. 1 to 1.65, wherein the finely divided siliceous admixture is 10 to 90%.
% Of crystalline silica fine powder and 90 to 10% by weight of amorphous silica fine powder, and each of the fine powder Portland cement and the crystalline silica fine powder is 8500 cm ² / g.
And the fineness of the amorphous silica fine powder is 120,000 cm ² / g or more (BET).
Low-density geothermal well cement slurry for high temperature, characterized by having a specific surface area). 2. The fineness (Brain value) of both the fine powder Portland cement and the fine crystalline silica powder is 8500 or more.
2. The high specific gravity geothermal well cement slurry for high temperature use according to claim 1, which is in a range of 13000 cm ² / g. 3. Fineness of amorphous silica fine powder (BET
The specific surface area) is high-temperature low-density geothermal well cement slurry according to claim 1 or 2 in the range of 120000~250000cm ² / g. 4. The cement slurry according to claim 1, wherein the amorphous silica fine powder is silica fume.