Method for preparing water-based drilling fluid by treating and recycling water-based drilling hydraulic filtrate

Abstract

The invention discloses a method for preparing water-based drilling fluid by treating and recycling water-based drilling hydraulic filtrate. Comprising the following steps: (1) adding a polyether demulsifier for demulsification and deoiling; adding polyaluminum chloride and a nonionic polyacrylamide flocculant to precipitate impurities and reduce COD (Chemical Oxygen Demand); soluble carbonate is added to reduce the content of calcium and magnesium ions; sterilizing by stable C < l > O2, and adjusting the pH value of the pressure filtrate to 7-9; and (2) taking the treated pressure filtrate, and adding additives accounting for the total mass percent of the water-based drilling fluid pressure filtrate according to the following proportion: 4% of bentonite, 0.2% of sodium carbonate, 0.3% of high-viscosity sodium carboxymethyl cellulose, 3% of sulfonated phenolic resin, 2% of polymer filtrate reducer, 0.5% of potassium polyacrylate and 2% of modified asphalt. The oil content, the COD content, the calcium and magnesium ion content and the bacteria content of the treated drilling fluid are obviously reduced, the prepared drilling fluid has excellent index performance, and the repeated comprehensive utilization of the treated drilling pressure filtrate can be realized. The technical scheme is used for solving the problems that the existing water-based drilling hydraulic filtrate treatment cost is high, the operation is tedious and the environment is polluted.

Description

Technical Field

[0001] The invention relates to the field of waste drilling fluid treatment in oil and gas fields of the petroleum industry, and in particular to a method for treating and reusing water-based drilling hydraulic filtrate to prepare water-based drilling fluid. Background Art

[0002] Drilling fluid plays an important role in oil extraction projects. It mainly includes oil-based, water-based, synthetic and special drilling fluids, which are widely used in oil exploration and production stages. The toxic components in water-based waste drilling fluids mainly include hydrocarbons, salts, various polymers, impurities in barite, asphalt, etc. Its composition is complex, with high mineralization, high suspended matter content and high pollution load. The wastewater-based drilling fluid is degelled and then filtered and separated. The resulting liquid is called water-based drilling hydraulic filtrate.

[0003] Patent No. 201910730260.7 discloses a method for treating a filtrate, wherein a deionized chelating agent is added to the filtrate at room temperature, and the chelating agent is continuously stirred until a chelation reaction occurs between the deionized chelating agent and all metal ions in the filtrate. However, there is a free deionized chelating agent in the treated filtrate. Since the water-based drilling fluid is a complex dispersion, the free ion chelating agent has a negative impact on the stability of the drilling fluid system. Patent No. 202211012410.9 discloses a method for preparing a drilling fluid from a water-based drilling hydraulic filtrate. By measuring the C1 - , Ca 2+ 、A1 3+ , Fe 2+ Drilling fluid is prepared when the content meets the corresponding indicators. If it does not meet the standards, the water-based drilling hydraulic filtrate is mixed with water to meet the preparation standards. While consuming water resources, the solid impurities, oil stains and bacteria in the water-based drilling hydraulic filtrate cannot be removed. After mixing with water, they still remain in the filtrate, affecting the performance of the prepared water-based drilling fluid.

[0004] Water-based drilling hydraulic filtrate is highly polluting to the environment and cannot be discharged directly. It needs professional sewage treatment. However, due to the treatment conditions at the drilling construction site, the treatment effect is not good. At present, the main treatment method in China is to transport the on-site filtrate by tanker to the sewage treatment plant for treatment. It is necessary to establish a sewage treatment plant in the work area. The treatment cost is high and difficult, which increases the construction cost and restricts the green and sustainable development of oil and gas. Therefore, it is of great significance to solve the problem of difficult treatment of filtrate waste liquid at the drilling site, realize the reduction and harmless disposal of water resources, and conduct research on the recycling and reuse of filtrate waste liquid at the drilling site. Summary of the invention

[0005] The purpose of the present invention is to provide a method for treating and recycling water-based drilling hydraulic filtrate to prepare water-based drilling fluid, in order to solve the above technical problems and reduce the impact of water-based drilling hydraulic filtrate on the environment. After treatment, the calcium and magnesium ion content, bacteria content, solid suspended pollutants and oil content of the filtrate are significantly reduced, and the filtrate can be repeatedly recycled to prepare water-based drilling fluid with excellent performance in various indicators.

[0006] To this end, the technical solution of the present invention is as follows:

[0007] A method for treating and reusing water-based drilling hydraulic filtrate waste liquid to prepare water-based drilling fluid, the treatment steps of which are: adding a demulsifier to the water-based drilling hydraulic filtrate to break the emulsion under normal temperature conditions, adding a flocculant for flocculation and precipitation treatment, adding an ion complexing agent to remove calcium and magnesium ions in the filtrate for solid-liquid separation, using a bactericide for sterilization, adjusting the pH value of the filtrate, and preparing a water-based drilling fluid to evaluate performance.

[0008] The beneficial effects of the above technical scheme are as follows: the present invention selects polyester demulsifier to demulsify and remove residual oil in the filtrate, uses flocculation precipitation method to remove solid chemical treatment agent impurities and pollutants in the filtrate, and uses complexing agent to reduce calcium and magnesium ion content. After solid-liquid separation, the removal rate of suspended matter, calcium and magnesium ion content, and oil content in the filtrate reaches more than 90%; bactericide is used to remove saprophytic bacteria and sulfate-reducing bacteria from the filtrate, pH regulator is used to adjust the pH value of the filtrate to 7-9, and the treated filtrate is used to prepare water-based drilling fluid for recycling.

[0009] Furthermore, the polyester demulsifier was added in an amount of 5 ml / L to demulsify the filtrate to remove oil stains, the stirring speed was 100 r / min, and the stirring time was 1 min.

[0010] The beneficial effect of the above technical solution is that the polyether demulsifier is a mixed cationic and non-ionic surfactant, which has a better ability to destroy the emulsification of oil droplets, makes small oil droplets easier to condense, and can make the oil removal rate of the filtrate reach more than 90%.

[0011] Furthermore, the flocculants are polyaluminium chloride and non-ionic polyacrylamide. In the first step, polyaluminium chloride is added in an amount of 1 g / L in the form of a 10% aqueous solution, and stirred.

[0012] Furthermore, 1 part of polyaluminium chloride solid was weighed and added into 10 parts of deionized water solution, and stirred for 10 minutes at a stirring speed of 200 r / min to prepare a polyaluminium chloride aqueous solution with a concentration of 10%.

[0013] Furthermore, after adding the polyaluminium chloride solution, the stirring speed was 100 r / min and the stirring time was 1 min.

[0014] Furthermore, the nonionic polyacrylamide flocculant is added in the second step, the addition amount is 0.02 g / L, and the addition form is 0.1% aqueous solution, and stirring is performed.

[0015] Furthermore, 1 part of nonionic polyacrylamide solid was weighed and added into 1000 parts of deionized water solution, and stirred for 40 minutes at a stirring speed of 200 r / min to prepare a polyacrylamide aqueous solution with a concentration of 0.1%.

[0016] Further, after adding the polyaluminium chloride solution, stirring was carried out at a stirring speed of 100 r / min for 1 min.

[0017] The beneficial effects of the above technical solution are: the non-ionic flocculant has a fast flocculation effect and low biological toxicity. By treating the filtrate with a very low usage amount, the solid suspended matter and turbidity can reach more than 90%, reducing the filtrate treatment cost, the risk of environmental pollution and improving the portability of on-site operations.

[0018] The inventors have found that the calcium and magnesium ion content is relatively high. The calcium and magnesium ions will cause the condensation of the polymer molecules of the water-based drilling fluid treatment agent to cause the molecular chain to shrink, and hydration will occur at the same time, resulting in polymer flocculation and precipitation. The use of water-based drilling hydraulic filtrate with high calcium and magnesium ion content to prepare water-based drilling fluid will seriously affect its rheological properties.

[0019] Furthermore, an ion complexing agent soluble carbonate is added to reduce the calcium and magnesium ion content, and the added amount is 20g / L.

[0020] Furthermore, after stirring at a stirring speed of 200 r / min for 10 min, the mixture was centrifuged at a rotation speed of 5000 r / min for 5 min to perform solid-liquid separation.

[0021] The beneficial effect of the above technical scheme is that: soluble carbonate is added to complex calcium and magnesium ions in the filtrate, so that the calcium and magnesium ions are precipitated and removed in the form of calcium carbonate and magnesium carbonate solids, the calcium and magnesium ion content of the filtrate is reduced to a calcium and magnesium ion content of ≤2 mmol / L, and the influence of heavy metal ions in the water-based drilling fluid prepared by the filtrate on the rheology of the drilling fluid is reduced.

[0022] The inventors found that the most harmful bacteria in water-based drilling fluids are saprophytes and sulfate-reducing bacteria, which can cause bubbles and foul odors in the fluid. Saprophytes can biodegrade various organic treatment agents, and while degrading the organic treatment agents, they will also produce a large number of bacteria and viscous metabolites, which will affect the performance of the drilling fluid; sulfate-reducing bacteria refers to the general term for bacteria that can reduce sulfate to hydrogen sulfide. Since hydrogen sulfide is smelly and toxic, and has strong corrosiveness, it will seriously corrode drilling tools and downhole equipment and endanger the health of operators.

[0023] Furthermore, stable ClO2 was added to remove saprophytic bacteria and sulfate-reducing bacteria in the filtrate, and the addition amount was 1 g / L.

[0024] Furthermore, after sterilization, the content of saprophytic bacteria in the filtrate is ≤2 / mL, the content of sulfate-reducing bacteria is ≤1 / mL, and the sterilization rate reaches more than 95%.

[0025] The beneficial effects of the above technical solution are: the addition of stable ClO2 has a significant sterilization effect, preventing the organic treatment added to the preparation of water-based drilling fluid from being biodegraded due to the presence of bacteria, and stable ClO2 is widely used and low-priced, reducing the cost of filtrate treatment.

[0026] Furthermore, anhydrous citric acid, a pH adjuster, is added to adjust the pH value of the filtrate to 7-9.

[0027] Furthermore, the water-based drilling fluid is formulated as 4% bentonite + 0.2% soda ash + 0.3% high-viscosity sodium carboxymethyl cellulose + 3% sulfonated phenolic resin + 2% polymer fluid loss reducer + 0.5% potassium polyacrylate + 2% modified asphalt.

[0028] Furthermore, the performance of water-based drilling fluid prepared by recycling the filtrate was evaluated. After the drilling fluid was aged at 120° for 16 hours, the rheological properties and filtration loss properties of the drilling fluid were experimentally determined to meet the application standards.

[0029] The additives include high-viscosity sodium carboxymethyl cellulose, polymer fluid loss reducer, sulfonated phenolic resin, sulfonated lignite, emulsified asphalt and bentonite, wherein the high-viscosity sodium carboxymethyl cellulose can improve the viscosity of the drilling fluid; the polymer fluid loss reducer can reduce the API fluid loss; the sulfonated phenolic resin can reduce the HPHT fluid loss of the drilling fluid; the sulfonated lignite can effectively control the fluid loss and viscosity of the drilling fluid; and the emulsified asphalt can improve the quality of the mud cake and improve the lubrication performance.

[0030] The beneficial effects of the above technical solution are: using anhydrous citric acid solid to adjust the pH value of the drilling fluid, the operation is simple and the medicine is easy to obtain, and the recycling of the filtrate to prepare the drilling fluid can solve the problems of difficult filtrate treatment at the drilling site and high treatment cost. At the same time, it has the advantages of saving water resources and protecting the environment.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) It can realize the recycling of water-based drilling hydraulic filtrate to prepare water-based drilling fluid, which can be produced and sold at the drilling site, thus saving on-site water resources.

[0033] (2) Overcome environmental constraints and reduce the cost of water-based drilling hydraulic filtrate treatment and transportation and the use of chemicals.

[0034] (3) Reduce the impact of drilling filtrate on the environment and implement the green development requirements of volume reduction and harmless disposal.

[0035] (4) The water-based drilling hydraulic filtrate treatment method of the present invention has a simple treatment preparation process, can be treated on site by a plate filter press, is feasible for on-site personnel to operate, and has significant adaptability to on-site environmental applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The present invention is a flow chart for preparing water-based drilling fluid by treating and reusing water-based drilling hydraulic filtrate. DETAILED DESCRIPTION

[0037] In the present invention, the polyester demulsifier is a compound polyether demulsifier produced by Jinhu Jinling New Material Technology Co., Ltd. on the market.

[0038] The preparation process of the compound polyether demulsifier is as follows:

[0039] The initiator bisphenol A, diethylenetriamine or formaldehyde and a bimetallic catalyst are placed in a reactor for reflux reaction to obtain a mixed solution of a branched polyamine compound and a bimetallic catalyst bimetallic cyanide; the obtained mixed solution is transferred to a high-pressure cap, sealed, heated to a temperature of 100-150°C and evacuated; ethylene oxide and propylene oxide are added to the high-pressure cap (pressure of 0.1-0.7MPa), and after the addition is completed, the reaction is continued under the condition of a pressure of -0.2-0.2MPa to obtain a multi-branched poly(ethylene oxide) compound; and the compound is reacted with a halogenated hydrocarbon to obtain a multi-branched cationic poly(ethylene oxide) reverse demulsifier; the obtained multi-branched cationic polyether reverse demulsifier is dissolved with a biological demulsifier PRJ-1 demulsifying bacteria, a flocculant polyaluminum chloride FeC13·6H2O or A1 C13·6H2O, one or more, and a cross-linking agent diisocyanate in a solvent, and stirred evenly to obtain a composite polyether demulsifier. The solvent is one or more of ethanol, propanol, isopropanol, and terpene, the molar ratio of the branched polyamine compound, the double metal cyanide, ethylene oxide and propylene oxide is (6-10):(1-4):(40-60):(40-60), and the molar ratio of the multi-branched polyamine compound to the halogenated hydrocarbon is 1:(3-10).

[0040] For the specific preparation method, see the Chinese invention patent with authorization announcement number CN111592910.

[0041] The present invention will be further described below in conjunction with specific examples, but the following examples are by no means intended to limit the present invention in any way.

[0042] The water-based drilling hydraulic filtrate treatment method of the present invention comprises the following steps, wherein the additives used are all commercially available:

[0043] Example 1 Comparison of demulsification effects of filtrate treated with polyester demulsifiers at different concentrations.

[0044] Q1-24-98 well water-based drilling hydraulic filtrate (i.e., the liquid obtained after the Q1-24-98 well water-based drilling waste liquid is degelled and compressed by a plate and frame filter press to remove solid impurities such as cuttings) was selected, with an oil content of 20.9 g / L. Three equal volumes of the filtrate were taken, and polyester demulsifiers of the same concentration of 5 mg / L, 10 mg / L, and 15 mg / L were added respectively. The mixture was stirred at a stirring speed of 100 r / min for 1 min. The oil removal rate and demulsification effect of the filtrate treated with polyester demulsifiers of different concentrations were compared. The results are shown in Table 1.

[0045] Table 1 Comparison of demulsification and oil removal effects of polyester demulsifiers with different concentrations

[0046] Polyester demulsifier concentration, mg / L 5 10 15 Oil removal rate of filter press liquid from Q1-24-98 well, % 73.9 84.6 95.6

[0047] It can be seen from Table 1 that the demulsification and oil removal effect is better when the polyester demulsifier is added at a concentration of 15 mg / L.

[0048] Example 2 Evaluation of treatment effects of different flocculants

[0049] Based on the factors affecting the performance of water-based drilling fluid, the flocculation effect of using flocculants to treat water-based drilling hydraulic filtrate is optimized. Two flocculants, PAC (polyaluminium chloride) and PFS (polyferric sulfate), are selected for use with PAM (non-ionic polyacrylamide). The flocculation effect of the filtrate is evaluated by measuring the COD content in the filtrate using a COD rapid tester. The experimental results are shown in Table 2.

[0050] The specific experimental operation method is as follows:

[0051] S1. Select the water-based drilling hydraulic filtrate after demulsification of Q1-24-98 well, with a COD content of 1183 mg / L. Take 4 equal volumes of the demulsified filtrate, first add PAC (polyaluminium chloride) in an amount of 0.5 g / L, 1 g / L and 1.5 g / L in the form of a 10% aqueous solution, and stir for 1 min at a stirring speed of 100 r / min; then add PAM (non-ionic polyacrylamide) in an amount of 0.02 g / L in the form of a 0.1% aqueous solution, and stir for 1 min at a stirring speed of 100 r / min, and determine the COD content in the filtrate after flocculation.

[0052] S1. Select the water-based drilling hydraulic filtrate after demulsification of Q1-24-98 well, with a COD content of 1183 mg / L. Take 4 equal volumes of the demulsified filtrate, PFS (polymerized ferric sulfate), added in amounts of 0.5 g / L, 1 g / L, and 1.5 g / L in the form of a 10% aqueous solution, and stir at a speed of 100 r / min for 1 min; then add PAM (non-ionic polyacrylamide) in an amount of 0.02 g / L in the form of a 0.1% aqueous solution, and stir at a speed of 100 r / min for 1 min, and determine the COD content in the filtrate after flocculation.

[0053] Table 2 Evaluation of flocculation effect of different types of flocculants

[0054]

[0055] According to the experimental results, under the same dosage, PAC (polyaluminium chloride) has better flocculation effect than PFS (polyferric sulfate), and the COD content of the filtrate after treatment is lower. At the same time, it can be found that when the dosage of the two flocculants is 1g / L and 1.5g / L, there is little difference in COD content. A better flocculation effect can be achieved with a smaller dosage.

[0056] Example 3: The amount of soluble carbonate added as the calcium and magnesium ion complexing agent is preferred.

[0057] Measure 5 equal volumes of the filtrate after demulsification and flocculation treatment, add soluble carbonate at concentrations of 5g / L, 10g / L, 15g / L, 20g / L, and 25g / L, respectively, stir for 10min at a stirring speed of 200r / min, centrifuge for 5min at a speed of 5000r / min, separate the solid and liquid, and determine the calcium and magnesium ion content of the clear liquid obtained in each group with reference to the "EDTA titration method for the determination of calcium and magnesium ions in industrial circulating cooling water" (GB / T15452-2009), and use a pH meter to determine the pH value of the filtrate to evaluate the deionization effect. The results are shown in Table 3.

[0058] Table 3 Optimal amount of soluble carbonate added

[0059] Soluble carbonate concentration, g / L 0 5 10 15 20 25 Calcium and magnesium ion content, mmol / L 17 12 8 3 1 1 pH 7.20 8.22 9.12 9.92 10.85 11.34

[0060] It can be seen from Table 3 that when the addition amount of soluble carbonate is 20g / L, the treatment effect is the best; when the addition amount is greater than 20g / L, the pH value increases with the increase of soluble carbonate addition, and the content of calcium and magnesium ions does not change; when the addition amount is less than 2%, the removal rate of calcium and magnesium ions is low and the effect is poor.

[0061] Wherein, during the treatment of the filtrate, the room temperature is 25°C.

[0062] Example 4 Filtrate sterilization experiment and effect.

[0063] The filtrate treated in Examples 1, 2 and 3 was sterilized to ensure that the content of saprophytic bacteria (TGB) in the filtrate after sterilization was ≤2 cells / mL, the content of sulfate-reducing bacteria (SRB) was ≤1 cell / mL, and the sterilization rate was above 95%.

[0064] Stable ClO2 was added to the filtrate to remove saprophytic bacteria (TGB) and sulfate-reducing bacteria (SRB). The addition amount was 1 g / L and the mixture was stirred at a speed of 100 r / min for 5 min.

[0065] The contents of saprophytic bacteria and sulfate-reducing bacteria in the filtrate were determined with reference to the “Plate Count Method for Determination of Total Bacterial Count in Water Quality” (HJ1000-2018), and the sterilization effect was evaluated. The results are shown in Table 4.

[0066] Table 4 Sterilization effect of stable ClO2

[0067]

[0068]

[0069] It can be seen from Table 4 that after the filtrate was sterilized by stable ClO2, the sterilization rate of saprophytic bacteria (TGB) was 97.1%, and the sterilization rate of sulfate-reducing bacteria (SRB) was 100%.

[0070] Example 5: Evaluation of slurry preparation performance by adjusting the pH value of the filtrate.

[0071] After adding anhydrous citric acid as a pH adjuster to adjust the pH value of the filtrate to 7-9, a water-based drilling fluid is prepared. The specific formula is as follows:

[0072] 4% bentonite + 0.2% soda ash + 0.3% high viscosity sodium carboxymethyl cellulose + 3% sulfonated phenolic resin + 2% polymer fluid loss reducer + 0.5% potassium polyacrylate + 2% modified asphalt.

[0073] A total of 6 groups of filtrate, untreated filtrate, Example 1, Example 2, Example 3, Example 4, and Example 5 filtrate were taken to evaluate the performance of water-based drilling fluid prepared by recycling the filtrate. After the drilling fluid was aged at 120°C for 16 hours, the rheological properties and filtration loss properties of the drilling fluid were experimentally evaluated. The results are shown in Table 5.

[0074]

[0075] As can be seen from Table 5, the performance of each group is compared. The rheological properties and filtration properties of the water-based drilling fluid prepared by the filtrate treated in Example 5 are better than those of other groups that are not treated or not treated at all. The apparent viscosity is 34 mPa·s, the plastic viscosity is 22 mPa·s, the dynamic shear force is 12 Pa, the API filtration loss is 6.2 ml, and the HTHP filtration loss is 11.8 ml. At the same time, the drilling fluid performance meets the on-site construction standards and the time cycle requirements for the preparation of drilling fluid by filtrate treatment.

Claims

1. A method for preparing water-based drilling fluid by treating and reusing water-based drilling hydraulic filtrate, characterized in that: The following steps are involved: Under normal temperature conditions, demulsifiers were added to the water-based drilling hydraulic filtrate for demulsification, flocculants were added for flocculation and precipitation, ion complexing agents were added to remove calcium and magnesium ions in the filtrate for solid-liquid separation, bactericides were used for sterilization, the pH value of the filtrate was adjusted, and water-based drilling fluid was prepared to evaluate its performance.

2. The method for preparing water-based drilling fluid by treating and reusing water-based drilling hydraulic filtrate according to claim 1, characterized in that: The demulsifier is a polyether demulsifier, the addition amount is 5 ml / L, the stirring time is 1 min, and the oil content of the filtrate after demulsification and oil removal is ≤0.5 g / L.

3. The method for preparing water-based drilling fluid by treating and reusing water-based drilling hydraulic filtrate according to claim 1, characterized in that: The flocculant is polyaluminium chloride, the addition amount is 1 g / L, the addition form is a 10% aqueous solution, and the stirring time is 1 min.

4. The method for preparing water-based drilling fluid by treating and reusing water-based drilling hydraulic filtrate according to claim 1, characterized in that: The flocculant is non-ionic polyacrylamide, the addition amount is 0.02 g / L, the addition form is 0.1% aqueous solution, and the stirring time is 1 min.

5. The method for preparing water-based drilling fluid by treating and reusing water-based drilling hydraulic filtrate according to claim 4 and claim 5, characterized in that: Weigh 10 g of polyaluminium chloride solid, add it to 100 ml of deionised water and stir for 10 min. Weigh 0.1 g of non-ionic polyacrylamide solid, add it to 100 ml of deionised water and stir for 40 min.

6. The method for preparing water-based drilling fluid by treating and reusing water-based drilling hydraulic filtrate according to claim 1, characterized in that: The complexing agent is a water-soluble carbonate, the addition amount is 20 g / L, the complexing is carried out until the calcium and magnesium ion content is ≤ 2 mmol / L, the stirring time is 10 min, and the solid-liquid separation is carried out by centrifugation at a speed of 5000 r / min for 5 min.

7. The method for preparing water-based drilling fluid by treating and reusing water-based drilling hydraulic filtrate according to claim 1, characterized in that: The bactericide is stable ClO2, the addition amount is 1g / L, and after sterilization, the saprophytic bacteria content is ≤2 / mL, and the sulfate-reducing bacteria content is ≤1 / mL.

8. The method for preparing water-based drilling fluid by treating and reusing water-based drilling hydraulic filtrate according to claim 1, characterized in that: The pH value adjuster is anhydrous citric acid, and the pH value is adjusted to 7-9.

9. The method for preparing water-based drilling fluid by treating and reusing water-based drilling hydraulic filtrate according to claim 1, characterized in that: The water-based drilling fluid formula is 4% bentonite + 0.2% soda ash + 0.3% high-viscosity sodium carboxymethyl cellulose + 3% sulfonated phenolic resin + 2% polymer fluid loss reducer + 0.5% potassium polyacrylate + 2% modified asphalt. The room temperature for water-based drilling fluid performance evaluation is 25°C.

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