Natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid as well as preparation method and application of natural amphiphilic lignin nanoparticle emulsifier

Abstract

The invention provides a natural amphiphilic lignin nanoparticle emulsifier for an oil-based drilling fluid as well as a preparation method and application of the natural amphiphilic lignin nanoparticle emulsifier, and belongs to the technical field of oilfield chemical drilling fluids. The preparation method of the emulsifier comprises the following steps: fully dissolving alkali lignin in an organic solvent; filtering, dropwise adding filtrate into deionized water, fully dispersing, and dialyzing; and then carrying out ultrasonic treatment, centrifuging, washing and drying. The emulsifier takes the biomass-based polymer industrial alkali lignin as a raw material, and is green, non-toxic, cheap and easy to obtain; the preparation method is simple, short in period and free of harmful by-products, the organic solvent can be recycled, and the cost is low. The lignin nanoparticles are added into the oil-based drilling fluid as an emulsifier, so that the stability of the oil-based drilling fluid under a high-temperature condition can be remarkably improved; a compact interfacial film can be formed at an oil-water interface, and a three-dimensional network structure with viscoelasticity can be formed in a continuous phase, so that the stability of a water-in-oil emulsion is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of oilfield chemical drilling fluid, and in particular relates to a natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid, and a preparation method and application thereof. Background Art

[0002] With the continuous development of unconventional oil and gas resources such as deep and ultra-deep layers, oil and gas well drilling is facing increasingly complex formation conditions such as extreme pressure and temperature. Compared with water-based drilling fluids, oil-based drilling fluids have better high temperature resistance, lubricity, inhibition and anti-pollution properties, which can effectively stabilize the well wall and protect the oil and gas layer. It is an important means to solve unconventional drilling problems such as high-temperature deep wells, high-angle directional wells, and long horizontal wells.

[0003] Oil-based drilling fluid is a type of emulsion drilling fluid with oil properties. The risk of emulsification failure exists throughout the drilling process; especially in the drilling of high-temperature wells and deep wells, the high temperature and high pressure environment will cause the emulsion to become unstable, exacerbating the instability of the drilling fluid system. Emulsifiers are the core treatment agents of oil-based drilling fluids, which promote the uniform dispersion of the oil and water phases to form a stable emulsion and ensure the stability of the drilling fluid. Therefore, emulsifiers play a key role in regulating the performance and quality of oil-based drilling fluids. However, the existing emulsifiers have complex chemical compositions and are difficult to degrade in the formation, causing serious pollution; and they are not adaptable enough to ultra-high temperature and high pressure environments, making it difficult to meet existing use conditions; during use, the amount of emulsifier added is high, but the effect of improving the stability of the drilling fluid is not obvious, but it increases the project cost and causes more serious pollution to the formation.

[0004] Solid nanoparticles have been proven to be highly efficient emulsifiers that can form stable emulsions at low doses; their irreversible adsorption at the oil-water interface gives the emulsion high stability. At present, in the application of oil-based drilling fluids, some inorganic nanoparticles are used as emulsifiers. For example, Chinese patent document CN114479780A provides an amphiphilic modified nanoparticle, which is obtained by uniformly modifying hydrophilic SiO2 particles with silane coupling agent KH550 and silane coupling agent OTS; the oil-based drilling fluid based on the particles has high temperature resistance and high density performance. However, the emulsion in this patent also needs to add other treatment agents, and the addition amount is high and the composition is complex; the potential impact on the environment is not explained during the preparation and construction of the amphiphilic modified nanoparticles; the temperature stability of the oil-based drilling fluid based on the particles also needs to be further improved.

[0005] Therefore, the development of a solid particle emulsifier that is resistant to high temperatures, has a simple preparation method and composition, is green, low-cost, and has excellent emulsification stability is expected to solve the problems of high environmental pollution caused by emulsifiers used in conventional oil-based drilling fluids and poor stability in unconventional drilling. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention provides a natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid, and a preparation method and application thereof. The emulsifier of the present invention uses bio-based polymer industrial alkali lignin as raw material, is green, non-toxic, cheap and easy to obtain; the preparation method is simple, the cycle is short, there are no harmful by-products, and the organic solvent can be recycled and reused, and the cost is low. The lignin nanoparticles of the present invention are added to the oil-based drilling fluid as an emulsifier, which can significantly improve the stability of the oil-based drilling fluid under high temperature conditions; it can not only form a dense interfacial film at the oil-water interface, but also form a three-dimensional network structure with viscoelasticity in the continuous phase, thereby improving the stability of the oil-in-water emulsion, and solving the problems of poor stability and high contamination of the existing oil-based drilling fluid at ultra-high temperatures.

[0007] The technical solution of the present invention is as follows:

[0008] A method for preparing a natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid comprises the following steps:

[0009] (1) fully dissolving alkali lignin in an organic solvent to obtain an alkali lignin solution;

[0010] (2) filtering the alkaline lignin solution, and adding the filtrate dropwise into deionized water to fully disperse it to obtain a mixed system of lignin nanoparticles-organic solvent-water; and then dialyzing to obtain a lignin nanoparticle suspension;

[0011] (3) The lignin nanoparticle suspension is subjected to ultrasonic treatment, and then centrifuged, washed, and dried to obtain a lignin nanoparticle emulsifier.

[0012] Preferably according to the present invention, in step (1), the organic solvent is one of dimethyl sulfoxide, acetone or tetrahydrofuran; and the volume ratio of the mass of alkali lignin to the organic solvent is 1-2:25-50 g / mL, preferably 1:25 g / mL.

[0013] Preferably, in step (1), the dissolution is carried out under stirring at a speed of 800-1200 rpm and a stirring time of 1-3 h.

[0014] Preferably according to the present invention, in step (2), the pore size of the filter membrane used for filtration is 0.4-0.5 μm.

[0015] Preferably, according to the present invention, in step (2), the dropping is carried out under stirring conditions, and the dropping speed of the filtrate is 1-3 drops / min.

[0016] Preferably, according to the present invention, the mass ratio of the alkali lignin in step (1) to the deionized water in step (2) is 1:1100-1400.

[0017] Preferably, according to the present invention, in step (2), the sufficient dispersion is carried out under stirring conditions, and the stirring time is 20-28 hours.

[0018] Preferably according to the present invention, in step (2), the molecular weight cut-off of the dialysis bag used for dialysis is 6 to 8 kDa.

[0019] Preferably, according to the present invention, in step (2), the dialysis method is as follows: placing a mixed system of lignin nanoparticles-organic solvent-water in a dialysis bag, immersing the dialysis bag in deionized water, and dialyzing at 10°C-25°C for 20-30h, and replacing the deionized water every 1-3 hours during the dialysis process.

[0020] Preferably, according to the present invention, in step (3), the ultrasonic device is an ultrasonic cell disruptor, and ultrasonication is performed for 30s to 5min at 20kHz, 600-900W, and 0°C-30°C; preferably, the ultrasonic temperature is 0°C and the ultrasonic time is 30s to 1min.

[0021] A natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid is prepared by the above method. The obtained natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid is brown powder.

[0022] The present invention also provides the use of the natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid, which is used as an emulsifier to stabilize the oil-based drilling fluid.

[0023] Preferably according to the present invention, the amount of the lignin nanoparticle emulsifier added to the oil-based drilling fluid is 3-15 g / L.

[0024] The technical features and beneficial effects of the present invention are as follows:

[0025] 1. The emulsifier of the present invention uses bio-based polymer industrial alkali lignin as raw material, which is green, non-toxic, cheap and easy to obtain. First, the alkali lignin is fully dissolved in an organic solvent, and then the lignin nanoparticles are prepared by the anti-solvent precipitation method; by optimizing the organic solvent, the assembly behavior of lignin is regulated, and the particle size of the synthesized lignin nanoparticles is controlled to form nanoparticles with uniform size distribution and regular shape. Then, the mixed system of lignin nanoparticles-organic solvent-water is dialyzed to obtain a lignin nanoparticle suspension, and the lignin nanoparticle suspension is ultrasonically treated to obtain a lignin nanoparticle suspension with smaller particle size, uniform dispersion and stability; the dispersibility of lignin nanoparticles is improved by ultrasonic treatment, and the size of lignin nanoparticles is reduced to improve their stability; by controlling the ultrasonic time, the surface polarity of lignin nanoparticles is regulated. The emulsifier obtained by the present invention is an amphiphilic lignin nanoparticle formed by self-assembly, which avoids the cumbersome steps of additional modification of conventional solid particles, simplifies the process flow and reduces costs.

[0026] 2. The preparation method of the lignin nanoparticle emulsifier of the present invention is simple, has a short cycle, has no harmful by-products, and the organic solvent can be recycled and reused, thereby reducing production costs.

[0027] 3. The lignin nanoparticle emulsifier obtained by the present invention can significantly improve the stability of oil-based drilling fluid under high temperature conditions. Oil-based drilling fluid belongs to oil-in-water emulsion drilling fluid, so the stability of the emulsion is crucial to the stability of the oil-based drilling fluid. Lignin nanoparticles form a dense interfacial film through irreversible adsorption at the oil-water interface to prevent the aggregation of droplets; the unabsorbed lignin nanoparticles form a three-dimensional network structure in the oil phase through interaction, thereby limiting the movement of droplets and reducing the frequency of mutual aggregation and collision of droplets; thereby improving the stability of the oil-in-water emulsion and solving the problems of poor stability and high contamination of existing oil-based drilling fluids at ultra-high temperatures.

[0028] 4. In the preparation method of the present invention, the type of organic solvent, ultrasonic treatment time and initial concentration of alkali lignin have an important influence on the performance of the obtained emulsifier. If they are not suitable, the emulsification performance and high temperature resistance of the obtained emulsifier will be reduced. DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to specific embodiments, but is not limited thereto.

[0030] Meanwhile, the experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials are commercially available unless otherwise specified.

[0031] Example 1

[0032] A method for preparing a natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid comprises the following steps:

[0033] (1) Dissolve 1 g of alkali lignin in 25 ml of tetrahydrofuran and stir the mixture under magnetic stirring at 1000 rpm for 2 h to obtain an alkali lignin solution.

[0034] (2) The alkaline lignin solution in step (1) was filtered through a syringe filter (the pore size of the filter membrane was 0.45 μm), and the filtrate was dripped into 1250 mL of deionized water at a rate of 2 drops per minute under stirring conditions, and stirring was continued for 24 hours to obtain a mixed system of lignin nanoparticles-tetrahydrofuran-water.

[0035] (3) The mixed system of lignin nanoparticles-tetrahydrofuran-water in step (2) is introduced into a dialysis bag (molecular weight cutoff 6 kDa), and the dialysis bag is immersed in 2500 ml of deionized water. The water temperature is maintained at 10° C. and dialyzed for 24 h. The deionized water is replaced every 2 h during the dialysis process. The tetrahydrofuran is dialyzed to obtain a lignin nanoparticle suspension.

[0036] (4) The lignin nanoparticle suspension in step (3) was ultrasonically treated in an ice-water bath at 0° C. for 30 s, using an ultrasonic cell disruptor with an ultrasonic frequency of 20 kHz and an ultrasonic power of 900 W to obtain a lignin nanoparticle dispersion.

[0037] (5) The lignin nanoparticle dispersion in step (4) is centrifuged and washed with deionized water until there is no organic solvent in the supernatant, and then dried to obtain a lignin nanoparticle emulsifier.

[0038] Example 2

[0039] A method for preparing a natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid is as described in Example 1, except that in step (4), the ultrasonic treatment time is 1 min; the other steps and conditions are the same as in Example 1.

[0040] Example 3

[0041] A method for preparing a natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid is as described in Example 1, except that in step (4), the ultrasonic treatment time is 5 minutes; the other steps and conditions are the same as in Example 1.

[0042] Example 4

[0043] A method for preparing a natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid is as described in Example 1, except that in step (1), tetrahydrofuran is replaced by dimethyl sulfoxide; the other steps and conditions are the same as in Example 1.

[0044] Example 5

[0045] A method for preparing a natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid is as described in Example 4, except that in step (4), the ultrasonic treatment time is 1 min; the other steps and conditions are the same as in Example 4.

[0046] Example 6

[0047] A method for preparing a natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid is as described in Example 4, except that in step (4), the ultrasonic treatment time is 5 minutes; the other steps and conditions are the same as in Example 4.

[0048] Example 7

[0049] A method for preparing a natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid is as described in Example 1, except that in step (1), tetrahydrofuran is replaced by acetone; the other steps and conditions are the same as in Example 1.

[0050] Example 8

[0051] A method for preparing a natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid is as described in Example 7, except that in step (4), the ultrasonic treatment time is 1 min; the other steps and conditions are the same as in Example 7.

[0052] Example 9

[0053] A method for preparing a natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid is as described in Example 7, except that in step (4), the ultrasonic treatment time is 5 minutes; the other steps and conditions are the same as in Example 7.

[0054] Example 10

[0055] A method for preparing a natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid is as described in Example 1, except that the amount of tetrahydrofuran used in step (1) is 50 ml; the other steps and conditions are the same as in Example 1.

[0056] Embodiment 11

[0057] A method for preparing a natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid is as described in Example 1, except that the amount of alkali lignin used in step (1) is 2 g; the other steps and conditions are the same as in Example 1.

[0058] Comparative Example 1

[0059] A lignin nanoparticle emulsifier, as described in Example 1, except that in step (1), the alkali lignin is not subjected to any treatment. The specific steps are as follows:

[0060] 1g of alkali lignin was fully dissolved in 1275mL of water, and magnetically stirred for 2h at a speed of 1000rpm to obtain an alkali lignin solution. The alkali lignin solution was filtered through a syringe filter (the pore size of the filter membrane was 0.45μm), introduced into a dialysis bag (molecular weight cutoff 6kDa), and the dialysis bag was immersed in 2500ml of deionized water, the water temperature was maintained at 10℃, and dialyzed for 24h. The deionized water was replaced every 2h during the dialysis process to obtain a lignin nanoparticle suspension. The lignin nanoparticle suspension was ultrasonically treated in an ice water bath at 0℃ for 30s, the ultrasonic equipment was an ultrasonic cell disruptor, the ultrasonic frequency was 20kHz, and the ultrasonic power was 900W to obtain a lignin nanoparticle dispersion. The lignin nanoparticle dispersion was centrifuged, washed with deionized water, and dried to obtain a lignin nanoparticle emulsifier.

[0061] Comparative Example 2

[0062] A method for preparing a natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid is as described in Example 1, except that in step (4), the lignin nanoparticle suspension is ultrasonically treated at 60° C. for 30 seconds, the ultrasonic equipment is an ultrasonic cell disruptor, the ultrasonic frequency is 20 kHz, and the ultrasonic power is 900 W to obtain a lignin nanoparticle dispersion.

[0063] The other steps and conditions are the same as in Example 1.

[0064] Test example

[0065] The emulsifiers prepared in the examples and comparative examples were evaluated for their performance as follows.

[0066] 1. Evaluation of emulsion stability

[0067] Emulsion stability is directly related to the performance of oil-based drilling fluid. The emulsification index is used to evaluate the effect of emulsifier on emulsion stability, that is, the ratio of the height of the emulsion layer to the total height of the mixture after emulsification with the emulsifier and after standing for a period of time is measured. The calculation formula is:

[0068]

[0069] EI—emulsification index, %;

[0070] H e —Height of emulsion layer, cm;

[0071] H t —Total height of the mixture, cm.

[0072] 240 ml of biodiesel was poured into a high-stirring cup, followed by the addition of 7.5 g of Span80 and 3 g of the example or comparative sample, and the mixture was stirred at 10000 rpm for 10 min. Then, 60 ml of water was slowly added into the high-stirring cup, and the stirring was continued for 20 min. The prepared emulsion was transferred into a 100 ml stoppered graduated cylinder, and the height of the emulsion layer and the total height of the mixture were measured and the emulsification index was calculated. The height of the emulsion layer after standing at room temperature for 24 h and 48 h was measured and the emulsification index was calculated.

[0073] Table 1 shows the emulsification index.

[0074]

[0075]

[0076] As can be seen from Table 1, the lignin nanoparticle emulsifier prepared by the present invention has a positive effect on the stability of the emulsion. Compared with lignin nanoparticles using dimethyl sulfoxide and acetone as organic solvents, the use of tetrahydrofuran as an organic solvent can prepare a lignin nanoparticle emulsifier with high efficiency and stability. The emulsion to which micron-sized industrial alkali lignin is added is difficult to be completely emulsified, and after long-term standing, a large amount of upper oil is precipitated, and the oil-water separation is obvious. The lignin nanoparticle emulsifier prepared using a low initial lignin concentration or a high initial lignin concentration has a good emulsification effect, but the emulsion stability is poor. At a relatively high ultrasonic temperature, the lignin nanoparticles have poor dispersibility, a high degree of aggregation, and are difficult to emulsify. It shows that when the present invention adopts a suitable initial lignin concentration, tetrahydrofuran as an organic solvent, and a suitable ultrasonic dispersion time, the prepared lignin nanoparticle emulsifier can form an efficient and stable emulsion.

[0077] 2. Drilling fluid system performance test

[0078] The emulsifiers prepared in the examples and comparative examples were used to prepare oil-based drilling fluids. The basic formula used was: 300 ml biodiesel + 4 g emulsifier + 2 g Span80 + 3 g organic soil + 6 g sulfonated asphalt + 60 ml 30 wt% calcium chloride aqueous solution + 8 g calcium oxide. Barite was added to adjust the drilling fluid density to 1.4 g / cm 3 The prepared oil-based drilling fluid was placed in a high-temperature aging tank, and after rolling aging at 200°C for 16 hours, the drilling fluid performance was tested.

[0079] The performance of the oil-based drilling fluid prepared with lignin nanoparticle emulsifier was determined by the method specified in "GB / T 16783.2 Field Test of Drilling Fluids in Petroleum and Natural Gas Industry Part 2 Oil-based Drilling Fluids". The test results are shown in Table 2.

[0080] Table 2 Oil-based drilling fluid properties

[0081]

[0082]

[0083] It can be seen from Examples 1-3 that after continuous high-temperature aging at 200°C for 16h, the dynamic shear force of the oil-based drilling fluid is ≥10Pa, the dynamic plastic ratio is ≥0.28, and the demulsification voltage is ≥774V, reflecting good emulsification, rheology and long-term stability. Example 4-9 changes the organic solvent. Compared with Example 1, the apparent viscosity, plastic viscosity and dynamic shear force are reduced, and the demulsification voltage is greatly reduced. This is mainly because dimethyl sulfoxide is a strong polar solvent with strong permeability. The prepared lignin nanoparticles have low lipophilicity and are prone to agglomeration, resulting in poor stability of the prepared drilling fluid. Although acetone has medium polarity, the solubility of lignin in it is lower than that of tetrahydrofuran. As a proton acceptor, acetone can form a strong interaction with the hydroxyl groups in the lignin molecules to form larger aggregates, increase the size of the lignin nanoparticles, and is not conducive to the stability of the emulsion in the oil-based drilling fluid. In Example 10 and Example 11, when preparing lignin nanoparticles, the initial concentration of lignin in the organic solvent was 2wt% and 8wt%, respectively. Under low initial concentration conditions, the evaporation of the organic solvent was reduced, resulting in a decrease in the internal pressure of the lignin nanoparticles. The formed lignin nanoparticles were prone to collapse and did not have a regular spherical morphology, resulting in instability of the emulsion. If the initial concentration is too high, the viscosity of the lignin solution increases, causing the lignin nanoparticles to swell, the particle size becomes larger, and the performance of the resulting emulsifier is reduced. In Comparative Example 1, micron-sized industrial alkali lignin is used as an emulsifier. It is larger in size, has a lower specific surface area, and has a weaker adsorption capacity at the oil-water interface. Therefore, the prepared oil-based drilling fluid is unstable and has a lower demulsification voltage. At higher ultrasonic temperatures, the lignin nanoparticles have poor dispersibility and a high degree of aggregation, making it difficult to emulsify the drilling fluid.

Claims

1. A method for preparing a natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid, comprising the steps of: (1) fully dissolving alkali lignin in an organic solvent to obtain an alkali lignin solution; the organic solvent is one of dimethyl sulfoxide, acetone or tetrahydrofuran; (2) filtering the alkaline lignin solution, and adding the filtrate dropwise into deionized water to fully disperse the solution to obtain a mixed system of lignin nanoparticles-organic solvent-water; and then dialyzing the solution to obtain a lignin nanoparticle suspension; (3) The lignin nanoparticle suspension is subjected to ultrasonic treatment, and then centrifuged, washed, and dried to obtain a lignin nanoparticle emulsifier; the ultrasonic treatment conditions are: ultrasonic treatment at 20 kHz, 600-900 W, and 0° C.-30° C. for 30 s to 5 min.

2. The method for preparing the natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid according to claim 1, characterized in that: In step (1), the volume ratio of the mass of alkali lignin to the organic solvent is 1-2:25-50 g / mL.

3. The method for preparing the natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid according to claim 1, characterized in that: In step (1), the complete dissolution is carried out under stirring conditions, the stirring speed is 800-1200 rpm, and the stirring time is 1-3 h.

4. The method for preparing the natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid according to claim 1, characterized in that: In step (2), one or more of the following conditions are included: i. The pore size of the filter membrane used for filtration is 0.4-0.5μm; ii. The dropping is carried out under stirring conditions, and the dropping speed of the filtrate is 1-3 drops / min; iii. The mass ratio of the alkali lignin in step (1) to the deionized water in step (2) is 1:1100-1400; iv. Full dispersion is carried out under stirring conditions with a stirring time of 20-28 hours.

5. The method for preparing the natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid according to claim 1, characterized in that: In step (2), the molecular weight cut-off of the dialysis bag used for dialysis is 6 to 8 kDa.

6. The method for preparing the natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid according to claim 1, characterized in that: In step (2), the dialysis method is as follows: placing the mixed system of lignin nanoparticles-organic solvent-water in a dialysis bag, immersing the dialysis bag in deionized water, and dialyzing at 10°C-25°C for 20-30 hours, and replacing the deionized water every 1-3 hours during the dialysis process.

7. The method for preparing the natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid according to claim 1, characterized in that: In step (3), the ultrasonic device is an ultrasonic cell disruptor, the ultrasonic temperature is 0°C, and the ultrasonic time is 30s to 1min.

8. A natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid, characterized in that: Prepared by the method according to any one of claims 1 to 7.

9. The use of the natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid according to any one of claims 1 to 7, characterized in that: Used as an emulsifier to stabilize oil-based drilling fluids.

10. The use according to claim 9, characterized in that: The amount of lignin nanoparticle emulsifier added to the oil-based drilling fluid is 3-15 g / L.

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