Early-strength anti-channeling ultralow-density well cementation cement slurry as well as preparation method and application thereof

Abstract

The invention provides early-strength anti-channeling ultralow-density well cementation cement slurry as well as a preparation method and application thereof. The well cementation cement slurry comprises the following raw material components in parts by weight: 100 parts of oil well cement, 0-35 parts of silicon powder, 20-100 parts of a glass bead lightening agent, 0-3 parts of an expanding agent, 1-5 parts of a stabilizer, 0.01-5 parts of an early strength agent, 1-2 parts of a dispersing agent, 1-3 parts of a suspending agent, 1-3 parts of a flexible agent, 2-10 parts of a retarder, 2-10 parts of a fluid loss agent and 45-100 parts of water, wherein the density of the glass bead lightening agent is less than or equal to 0.40 g / cm < 3 >, and the density range of the well cementation cement slurry is 0.90-1.20 g / cm < 3 >. The ultralow-density well cementation cement paste is wide in density and temperature application range, and has the characteristics of high compressive strength, adjustable thickening time, low permeability, good cement paste sedimentation stability, low water loss and the like.

Description

Technical Field

[0001] The present invention relates to the field of oil and gas well cementing engineering, and particularly to an early-strength anti-channeling ultra-low density cement slurry for well cementing, its preparation method and application. Background Art

[0002] At present, due to the easy loss of drilling fluid in low-pressure reservoirs during drilling, the density of the drilling fluid is required to be reduced to 0.6 - 0.8 g / cm 3 , and correspondingly, the density of the cement slurry in well cementing is required to be 0.95 - 1.3 g / cm 3 . During underbalanced drilling, the hydrostatic pressure of the drilling fluid is lower than the formation pore pressure. Usually, the density of the drilling fluid is very low, and in many cases, it is foam drilling and air drilling. Therefore, the specific gravity of the drilling fluid is required to be below 1.0 (preferably the specific gravity of the drilling fluid is 0.7 - 0.85 g / cm 3 ), and correspondingly, the specific gravity of the cement slurry is required to be 0.95 - 1.10 g / cm 3 to effectively form a supporting underbalanced drilling system. Some low-permeability (0.025 - 15.6 mD), low-porosity, low-abundance, and low-productivity oil and gas reservoirs have multiple pressure systems, and the equivalent density of the formation fracture pressure is 1.0 - 1.3 g / cm 3 . In order to improve the success rate of exploration, prevent loss and formation pollution, reduce costs, and achieve one-time sealing, it is currently necessary to use ultra-low density cement slurry for effective isolation; at the same time, the emergence of problems such as serious loss and excessive use of plugging materials has also brought new challenges to drilling and well cementing, making the ultra-low density cement slurry system an urgent technical problem to be solved. In existing low-density cement slurries, the effect of conventional weighting agents in reducing the density of the cement slurry is limited (generally greater than 1.20 g / cm 3 ), and ultra-low density cement slurries with a density lower than 1.20 g / cm 3 are usually mainly foam cement slurries, but foam cement slurries have disadvantages such as great difficulty in on-site construction and instability of foam under high pressure. Summary of the Invention

[0003] To solve the above technical problems, the purpose of the present invention is to provide an early-strength anti-channeling ultra-low density cement slurry for well cementing, its preparation method and application. By adding additives, an ultra-low density cement slurry with low-temperature early-strength anti-gas-channeling performance is prepared, which can meet the application requirements in a wide temperature range.

[0004] To achieve the above object, the present invention provides an early-strength anti-channeling ultra-low density cement slurry for well cementing. Among them, in parts by weight, the raw material components of the cement slurry for well cementing include: 100 parts of oil well cement, 0-35 parts of silica fume, 20-100 parts of glass microsphere weight reducer, 0-3 parts of expander, 1-5 parts of stabilizer, 0.01-5 parts of early-strength agent, 1-3 parts of dispersant, 1-3 parts of suspending agent, 1-3 parts of flexible agent, 2-10 parts of retarder, 2-10 parts of fluid loss reducer, and 45-100 parts of water.

[0005] According to a specific embodiment of the present invention, preferably, the density of the glass microsphere weight reducer ≤ 0.40 g / cm 3 .

[0006] In some specific embodiments, preferably, the density of the glass microsphere weight reducer is 0.10-0.40 g / cm 3 , the particle size is 1-120 μm, and the pressure-bearing capacity is 3.5-50 MPa. Among them, using glass microspheres as a weight reducer to prepare low-density cement slurry, the adjustable range of the density of the obtained cement slurry is wide, and the effect of reducing the density is obvious; the rheology is good (since the microspheres are regular spheres and have a "ball-bearing effect" in the cement slurry); it helps to reduce the water loss rate (the microspheres have a small particle size and are easy to block the microvoids on the filter cake surface to form a dense filter cake); the gas channeling prevention performance is excellent (the cement slurry containing glass microspheres can form a dense network structure and has a high bonding strength with the casing / formation); the compressive strength is high and the stability is good under high temperature and high pressure (the microspheres belong to inorganic non-metallic materials, are heat-resistant, and have good chemical stability), which is beneficial to protecting and sealing the oil and gas layers.

[0007] In some specific embodiments, preferably, the weight part of the glass microsphere weight reducer is 50-100 parts.

[0008] According to a specific embodiment of the present invention, preferably, the density range of the cement slurry for well cementing is 0.90-1.20 g / cm 3 .

[0009] According to a specific embodiment of the present invention, preferably, the silica fume is 140-mesh silica fume with a silica mass content ≥ 98% and / or 200-mesh silica fume with a silica mass content ≥ 98%.

[0010] In some specific embodiments, preferably, the silica fume is mixed in a ratio of 140-mesh silica fume: 200-mesh silica fume = 2-7: 3-8, preferably 5: 5.

[0011] According to a specific embodiment of the present invention, preferably, the early-strength agent includes one or a combination of two or more of triethanolamine, sodium aluminate, microsilica, calcium aluminate, metakaolin, inorganic fiber, etc.

[0012] In some specific embodiments, preferably, the weight portion of the early strength agent is 1.5 - 3 portions.

[0013] According to the specific embodiments of the present invention, preferably, the expansive agent includes one or a combination of two or more of calcium sulfoaluminate, calcium oxide, calcium carbonate, SDP-1 (Sichuan Chuanqing Downhole Technology Co., Ltd.), etc.

[0014] According to the specific embodiments of the present invention, preferably, the stabilizer is microsilica and / or bentonite, and the microsilica preferably includes SD100 (Sichuan Chuanqing Downhole Technology Co., Ltd.), etc.

[0015] According to the specific embodiments of the present invention, preferably, the dispersant is an aldehyde-ketone condensate and / or a polynaphthalenesulfonate, and the aldehyde-ketone condensate preferably includes SD35 (sulfonated ketone aldehyde condensate, Sichuan Chuanqing Downhole Technology Co., Ltd.), etc.

[0016] According to the specific embodiments of the present invention, preferably, the suspending agent includes one or a combination of two or more of 2-acrylamide-2-methylpropanesulfonic acid, diatomite, concave pottery clay, xanthan gum, etc.; the xanthan gum preferably includes SD85 (Sichuan Chuanqing Downhole Technology Co., Ltd.), etc.

[0017] According to the specific embodiments of the present invention, preferably, the flexibilizer is high-temperature resistant rubber powder and / or resin elastomer microspheres, and preferably includes commercially available rubber powder products such as SD77 (Sichuan Chuanqing Downhole Technology Co., Ltd.), etc.

[0018] According to the specific embodiments of the present invention, preferably, the retarder is polymerized from itaconic acid, 2-acrylamide-2-methylpropanesulfonic acid, N,N-dimethylacrylamide, and ethene phosphoric acid.

[0019] In some specific embodiments, preferably, the mass ratio of the polymerization raw materials of the retarder meets the following requirements: itaconic acid:2-acrylamide-2-methylpropanesulfonic acid:N,N-dimethylacrylamide:ethene phosphoric acid = 10 - 70:20 - 75:3 - 15:2 - 15.

[0020] According to the specific embodiments of the present invention, preferably, the fluid loss reducer is polymerized from 2-acrylamide-2-methylpropanesulfonic acid, acrylic acid, N,N-dimethylacrylamide, N-vinylpyrrolidone, and microcrystalline cellulose.

[0021] In some specific embodiments, preferably, the mass ratio of the polymerization raw materials of the fluid loss reducer meets the following requirements: 2-acrylamide-2-methylpropanesulfonic acid:acrylic acid:N,N-dimethylacrylamide:N-vinylpyrrolidone:microcrystalline cellulose = 20 - 70:8 - 40:5 - 27:2 - 10:3 - 10.

[0022] The present invention also provides a method for preparing the above-mentioned cement slurry for well cementing, wherein the preparation method includes:

[0023] (1) According to the weight parts of the raw material components of the cement slurry for well cementing, mix well the oil well cement, silica fume, glass microsphere weighting agent, expansive agent, stabilizer, early strength agent, dispersant, suspending agent, and flexible agent to obtain a dry blend;

[0024] (2) According to the weight parts of the raw material components of the cement slurry for well cementing, mix well the retarder, fluid loss reducer, and water to obtain the slurry-making water;

[0025] (3) Add the dry blend to the slurry-making water, and mix well to obtain the early strength and gas channeling prevention ultra-low density cement slurry for well cementing.

[0026] The present invention also provides the application of the above-mentioned cement slurry for well cementing in the well cementing operation of oil and gas wells.

[0027] According to the specific implementation scheme of the present invention, preferably, the application temperature of the cement slurry for well cementing is 40 - 200 °C.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] (1) Incorporating the glass microsphere weighting agent can greatly reduce the density of the cement slurry with a very small dosage, thereby enabling the cement slurry system of the present invention to have good comprehensive properties of the cement slurry, such as good fluidity, good stability, and adjustable thickening time;

[0030] (2) Incorporating the low-temperature early strength agent can accelerate the cement hydration reaction but has little influence on the thickening time, thereby enabling the cement slurry system of the present invention to have good low-temperature early strength and gas channeling prevention performance;

[0031] (3) The early strength and gas channeling prevention ultra-low density cement slurry for well cementing prepared by the present invention can meet the requirements of a circulating temperature of 40 °C - 200 °C by using additives with excellent performance and low sensitivity, has a very wide temperature application range, and at the same time, the density and thickening time are adjustable, and the top strength develops rapidly, and can meet the application requirements of the "low temperature (<80 °C) - medium temperature (80 - 140 °C) - high temperature (>140 °C)" cross-temperature zone. Description of the Drawings

[0032] Figure 1 It is the thickening test curve graph of Example 2.

[0033] Figure 2 It is the thickening test curve graph of Example 3. Detailed Description of the Invention

[0034] For a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the following detailed description of the technical solution of the present invention is provided, but it should not be construed as a limitation on the scope of implementation of the present invention.

[0035] The preparation method of the early-strength anti-channeling ultra-low density cement slurry for well cementing is as follows:

[0036] (1) According to the weight parts of the raw material components of the well cementing cement slurry, mix and stir evenly the oil well cement, silica fume, glass microsphere weighting agent, expansive agent, stabilizer, early-strength agent, dispersant, suspending agent, and flexible agent to obtain a dry blend;

[0037] (2) According to the weight parts of the raw material components of the well cementing cement slurry, mix and stir evenly the retarder, fluid loss reducer, and water to obtain the slurry-making water;

[0038] (3) Add the dry blend to the slurry-making water, mix and stir evenly to obtain the early-strength anti-channeling ultra-low density cement slurry for well cementing.

[0039] Example 1

[0040] This example provides an early-strength anti-channeling ultra-low density cement slurry for well cementing with a density of 1.20 g / cm 3 and an application temperature of 70 °C, which is composed of the following components in parts by weight: 100 parts of oil well cement, 26 parts of glass microsphere weighting agent with a density of 0.30 g / cm 3 , 1 part of SDP-1 expansive agent, 1.5 parts of SD35 dispersant, 2 parts of SD85 suspending agent, 1.5 parts of calcium aluminate, 2 parts of SD77 flexible agent, 2 parts of retarder, 2 parts of fluid loss reducer, and 63.5 parts of water.

[0041] Among them, the mass ratio of the polymerization raw materials of the retarder meets the following requirements: itaconic acid: 2-acrylamide-2-methylpropanesulfonic acid: N,N-dimethylacrylamide: vinyl phosphonic acid = 25:70:3:2; the mass ratio of the polymerization raw materials of the fluid loss reducer meets the following requirements: 2-acrylamide-2-methylpropanesulfonic acid: acrylic acid: N,N-dimethylacrylamide: N-vinylpyrrolidone: microcrystalline cellulose = 45:35:5:2:3. The preparation methods of the retarder and the fluid loss reducer refer to CN116410715A.

[0042] Example 2

[0043] This example provides an early-strength anti-channeling ultra-low density cement slurry for well cementing with a density of 1.05 g / cm 3 and an application temperature of 120 °C, which is composed of the following components in parts by weight: 100 parts of oil well cement, 30 parts of silica fume (composed of 140-mesh silica fume and 200-mesh silica fume in a mass ratio of 5:5), 30 parts of glass microsphere weighting agent with a density of 0.30 g / cm 352 parts of glass microsphere weighting agent, 5 parts of SD100 stabilizer, 1 part of SDP-1 expander, 3 parts of sodium aluminate, 2.5 parts of SD35 dispersant, 2.5 parts of SD85 suspending agent, 1 part of SD77 flexibilizer, 2 parts of retarder, 3 parts of fluid loss reducer, 66 parts of water.

[0044] Among them, the mass ratio of the polymerization raw materials of the retarder meets the following requirements: itaconic acid: 2-acrylamide-2-methylpropanesulfonic acid: N,N-dimethylacrylamide: vinyl phosphonic acid = 25:68:5:2; the mass ratio of the polymerization raw materials of the fluid loss reducer meets the following requirements: 2-acrylamide-2-methylpropanesulfonic acid: acrylic acid: N,N-dimethylacrylamide: N-vinylpyrrolidone: microcrystalline cellulose = 50:30:15:2:3. The preparation methods of the retarder and the fluid loss reducer refer to CN116410715A.

[0045] Example 3

[0046] This example provides an early-strength anti-channeling ultra-low density cement slurry with a density of 0.90 g / cm 3 and an application temperature of 140 °C, which is composed of the following components in parts by weight: 100 parts of oil well cement, 25 parts of silica fume (composed of 140-mesh silica fume and 200-mesh silica fume in a mass ratio of 5:5), glass microsphere weighting agent with a density of 0.30 g / cm 3 85 parts, 1.5 parts of SDP-1 expander, 5 parts of SD100 stabilizer, 1 part of SD35 dispersant, 1.5 parts of SD85 suspending agent, 1.5 parts of SD77 flexibilizer, 2.5 parts of sodium aluminate, 3.5 parts of retarder, 4 parts of fluid loss reducer, 91 parts of water.

[0047] Among them, the mass ratio of the polymerization raw materials of the retarder meets the following requirements: itaconic acid: 2-acrylamide-2-methylpropanesulfonic acid: N,N-dimethylacrylamide: vinyl phosphonic acid = 38:50:7:5; the mass ratio of the polymerization raw materials of the fluid loss reducer meets the following requirements: 2-acrylamide-2-methylpropanesulfonic acid: acrylic acid: N,N-dimethylacrylamide: N-vinylpyrrolidone: microcrystalline cellulose = 60:8:27:2:3. The preparation methods of the retarder and the fluid loss reducer refer to CN116410715A.

[0048] Example 4

[0049] This example provides an early-strength anti-channeling ultra-low density cement slurry with a density of 1.20 g / cm 3 and an application temperature of 180 °C, which is composed of the following components in parts by weight: 100 parts of oil well cement, 25 parts of silica fume (composed of 140-mesh silica fume and 200-mesh silica fume in a mass ratio of 5:5), glass microsphere weighting agent with a density of 0.40 g / cm 333 parts of glass microsphere weighting agent, 1 part of SDP-1 expander, 5 parts of SD100 stabilizer, 2.5 parts of SD35 dispersant, 2 parts of calcium aluminate, 1.5 parts of SD85 suspending agent, 1 part of SD77 flexibilizer, 6 parts of retarder, 5 parts of fluid loss reducer, and 68 parts of water.

[0050] Among them, the mass ratio of the polymerization raw materials of the retarder meets the following requirements: itaconic acid: 2-acrylamide-2-methylpropanesulfonic acid: N,N-dimethylacrylamide: vinyl phosphonic acid = 38:50:7:5; the mass ratio of the polymerization raw materials of the fluid loss reducer meets the following requirements: 2-acrylamide-2-methylpropanesulfonic acid: acrylic acid: N,N-dimethylacrylamide: N-vinylpyrrolidone: microcrystalline cellulose = 60:8:27:2:3. The preparation methods of the retarder and the fluid loss reducer refer to CN116410715A.

[0051] Comparative Example 1

[0052] This comparative example provides a conventional ultra-low density cement slurry with a density of 1.20 g / cm 3 and an application temperature of 180°C, which is composed of the following components in parts by weight: 100 parts of oil well cement, 25 parts of silica fume (composed of 140-mesh silica fume and 200-mesh silica fume in a mass ratio of 5:5), 65 parts of hollow glass beads with low density, 2 parts of calcium aluminate, 1 part of SDP-1 expander, 2 parts of SD35 dispersant, 2 parts of SD85 suspending agent, 5 parts of SD210 retarder (Sichuan Chuanqing Downhole Technology Co., Ltd.), 6 parts of SD130 fluid loss reducer (Sichuan Chuanqing Downhole Technology Co., Ltd.), and 80 parts of water.

[0053] Test Example 1

[0054] This test example conducts performance tests on the density, fluidity, free fluid, API fluid loss, thickening time and other conventional engineering properties of the early strength and anti-channeling ultra-low density cement slurries prepared in Examples 1-4 and the cement slurry prepared in Comparative Example 1. The results are shown in Table 1. Among them, the thickening test curves of representative Example 2 and Example 3 are respectively as Figure 1 and Figure 2 shown.

[0055] Table 1. Test results of the conventional engineering properties of the cement slurry

[0056]

[0057] It can be seen from the data in Table 1 that the early strength and anti-channeling ultra-low density cement slurries of Examples 1-4 have good fluidity, good stability, and adjustable thickening time, and can meet the requirements of engineering construction operations. From Figure 1 and Figure 2It can be seen that the initial consistency of the early-strength anti-channeling ultra-low density cement slurry is relatively low, and the curve form is normal during the experiment, without phenomena such as core wrapping and bulging.

[0058] Comparing Examples 1-4 with Comparative Example 1 shows that the low-temperature early-strength agent has no adverse effects on the conventional properties of the cement slurry. The retarder used in the present invention has good thickening time linear performance and can effectively adjust the thickening time of the cement slurry to ensure safe construction. The fluid loss reducer used in the present invention has good high-temperature resistance. The same type of fluid loss reducer can effectively control the fluid loss of the cement slurry and maintain the stability of the slurry from low temperature to high temperature.

[0059] Test Example 2

[0060] In this test example, the long-term compressive strength evolution of the early-strength anti-channeling ultra-low density set cement stone prepared in Examples 1-4 and the cement stone prepared in Comparative Example 1 was tested, and the results are shown in Table 2.

[0061] Table 2. Test results of compressive strength and elastic modulus of cement stone

[0062]

[0063] From the data in Table 2, it can be seen that the early-strength anti-channeling ultra-low density set cement stone of Examples 1-4 not only has high early strength, but also after curing for 7 days, when the compressive strength reaches a stable value, the elastic modulus of the cement stone is tested, and its elastic modulus is also better than that of the comparative example. It can be seen from this that the ultra-low density set cement stone of the present invention has the properties of high early strength and low elastic modulus.

[0064] By matching corresponding additives, the applicable density range of the early-strength anti-channeling ultra-low density cement slurry of the present invention is 0.90 - 1.20 g / cm 3 , and the applicable temperature range is 40 - 200 °C. The applicable ranges of density and temperature are wide, and it has the characteristics of high compressive strength (greater than 7.0 MPa), adjustable thickening time, low permeability, good sedimentation stability of the cement slurry, and low water loss (less than 50 mL). The said cement slurry for well cementing can well meet the needs of ultra-low density cement slurry well cementing required for low-pressure easy leakage, underbalanced drilling, gas and foam drilling, and can simplify the construction process, replace secondary cementing to achieve one-time cementing of long cementing sections, greatly reduce the well cementing cost, improve the long-term integrity of the well cementing cement sheath, and thus effectively solve the problems of well cementing leakage in extremely low-pressure easy-leakage formations and low strength of conventional low density.

Claims

1. An early-strength anti-channeling ultra-low density cement slurry, wherein, In parts by weight, the raw material components of the well cement slurry include: 100 parts of oil well cement, 0 - 35 parts of silica fume, 20 - 100 parts of glass microsphere weighting agent, 0 - 3 parts of expansive agent, 1 - 5 parts of stabilizer, 0.01 - 5 parts of early strength agent, 1 - 3 parts of dispersant, 1 - 3 parts of suspending agent, 1 - 3 parts of flexible agent, 2 - 10 parts of retarder, 2 - 10 parts of fluid loss reducer, and 45 - 100 parts of water; Among them, the density of the glass microsphere reducing agent ≤ 0.40 g / cm 3 ; The density range of the cement slurry for well cementing is 0.90 - 1.20 g / cm 3 .

2. The cement slurry for well cementing according to claim 1, wherein, The density of the glass microsphere weighting agent is 0.10 - 0.40 g / cm 3 , the particle size is 1 - 120 μm, and the pressure bearing capacity is 3.5 - 50 Mpa.

3. The cement slurry for well cementing according to claim 1 or 2, wherein, The weight parts of the glass microsphere weighting agent are 50 - 100 parts.

4. The cement slurry for well cementing according to claim 1, wherein The silica fume is 140 - mesh silica fume with a silica mass content of ≥98% and / or 200 - mesh silica fume with a silica mass content of ≥98%; Preferably, the silica fume is mixed in a ratio of 140 - mesh silica fume:200 - mesh silica fume = 2 - 7:3 - 8.

5. The well cement slurry according to claim 1, wherein, The early strength agent includes one or a combination of two or more of triethanolamine, sodium aluminate, microsilica, calcium aluminate, metakaolin, and inorganic fiber; Preferably, the weight parts of the early strength agent are 1.5 - 3 parts.

6. The cement slurry for well cementing according to claim 1, wherein, The expansive agent includes one or a combination of two or more of calcium sulfoaluminate, calcium oxide, calcium carbonate, and SDP - 1.

7. The cement slurry for well cementing according to claim 1, wherein, The stabilizer is microsilica and / or bentonite.

8. The cement slurry for well cementing according to claim 1, wherein, The dispersant is aldehyde - ketone condensate and / or polynaphthalene sulfonate.

9. The well cement slurry according to claim 1, wherein, The suspending agent includes one or a combination of two or more of 2 - acrylamide - 2 - methylpropanesulfonic acid, diatomite, concave pottery clay, and xanthan gum.

10. The cement slurry for well cementing according to claim 1, wherein, The flexible agent is high - temperature - resistant rubber powder and / or resin elastomer microspheres.

11. The well cement slurry according to claim 1, wherein, The retarder is polymerized from itaconic acid, 2 - acrylamide - 2 - methylpropanesulfonic acid, N,N - dimethylacrylamide, and vinyl phosphonic acid; the mass ratio of itaconic acid:2 - acrylamide - 2 - methylpropanesulfonic acid:N,N - dimethylacrylamide:vinyl phosphonic acid is 10 - 70:20 - 75:3 - 15:2 - 15.

12. The well cement slurry according to claim 1, wherein, The fluid loss reducer is polymerized from 2 - acrylamide - 2 - methylpropanesulfonic acid, acrylic acid, N,N - dimethylacrylamide, N - vinylpyrrolidone, and microcrystalline cellulose; the mass ratio of 2 - acrylamide - 2 - methylpropanesulfonic acid:acrylic acid:N,N - dimethylacrylamide:N - vinylpyrrolidone:microcrystalline cellulose is 20 - 70:8 - 40:5 - 27:2 - 10:3 - 10.

13. The preparation method of the well cement slurry according to any one of claims 1-12, wherein, The preparation method includes: (1) Mix and stir evenly oil well cement, silica fume, glass microsphere weighting agent, expansive agent, stabilizer, early strength agent, dispersant, suspending agent, and flexible agent to obtain a dry mix; (2) Mix and stir evenly the retarder, fluid loss reducer, and water to obtain the slurry - making water; (3) Add the dry mix to the slurry - making water and mix and stir evenly to obtain an early strength anti - channeling ultra - low density well cement slurry.

14. Application of the well cement slurry according to any one of claims 1 - 12 in oil and gas well cementing operations; Preferably, the application temperature of the well cement slurry is 40 - 200°C.

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