A natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid and its preparation method and application

Abstract

The present invention provides a natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid, and its preparation method and application, which belongs to the technical field of oilfield chemical drilling fluid. The preparation method of the emulsifier of the present invention comprises the steps of: fully dissolving alkali lignin in an organic solvent; filtering, adding the filtrate drop by drop into deionized water, fully dispersing, and dialyzing; then performing ultrasonic treatment, centrifuging, washing, and drying to obtain the product. The emulsifier of the present invention uses biomass-based polymer industrial alkali lignin as raw material, which 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.

Description

Technical Field

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

[0002] With the continuous development of unconventional oil and gas resources in deep and ultra-deep formations, oil and gas well drilling faces increasingly complex formation conditions, including extreme pressures and temperatures. Compared to water-based drilling fluids, oil-based drilling fluids offer superior high-temperature resistance, lubricity, inhibition, and anti-pollution properties. They effectively stabilize wellbore walls and protect oil and gas formations, making them an important tool for addressing unconventional drilling challenges in high-temperature deep wells, highly deviated directional wells, and long horizontal wells.

[0003] Oil-based drilling fluids are emulsions with oil-like properties. The risk of emulsification failure exists throughout the drilling process, particularly in high-temperature and deep well drilling, where high temperature and high pressure environments can cause emulsion instability, exacerbating the instability of the drilling fluid system. Emulsifiers are the core treatment agents for oil-based drilling fluids, ensuring the uniform dispersion of the oil and water phases to form a stable emulsion and stable performance. Therefore, emulsifiers play a key role in regulating the performance and quality of oil-based drilling fluids. However, existing emulsifiers have complex chemical compositions and are difficult to degrade in formations, causing serious pollution. They are also inadequately adaptable to ultra-high temperature and high pressure environments, making them difficult to meet existing operating conditions. During use, even high emulsifier dosages have little effect on improving drilling fluid stability, increasing project costs and causing further pollution to the formation.

[0004] Solid nanoparticles have been proven to be highly effective emulsifiers, forming stable emulsions at low doses. Their irreversible adsorption at the oil-water interface imparts high stability to the emulsion. Currently, some inorganic nanoparticles are used as emulsifiers in oil-based drilling fluids. For example, Chinese patent document CN114479780A provides amphiphilic-modified nanoparticles, obtained by uniformly modifying hydrophilic SiO2 particles with the silane coupling agents KH550 and OTS. The oil-based drilling fluid based on these particles exhibits high temperature resistance and high density. However, the emulsion described in this patent requires the addition of other treatment agents, and the addition amount is high, resulting in a complex composition. The potential environmental impact of the preparation and construction of the amphiphilic-modified nanoparticles is not addressed. The temperature stability of the oil-based drilling fluid based on these particles also needs to be further improved.

[0005] Therefore, the development of a solid particle emulsifier that is resistant to high temperatures, has simple preparation methods and ingredients, 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 shortcomings of the existing technology, the present invention provides a natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid, and its preparation method and application. 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; 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 existing oil-based drilling fluids at ultra-high temperatures.

[0007] The technical solutions of the present invention are 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 for full dispersion 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] According to the preferred embodiment of 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] According to the preferred embodiment of the present invention, in step (1), the sufficient dissolution is carried out under stirring conditions, the stirring speed is 800-1200 rpm, and the stirring time is 1-3 h.

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

[0015] According to the preferred embodiment of the present invention, in step (2), the dropwise addition is carried out under stirring conditions, and the dropwise addition 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] According to the preferred embodiment of the present invention, in step (2), the sufficient dispersion is carried out under stirring conditions, and the stirring time is 20-28 hours.

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

[0019] According to the preferred embodiment of the present invention, 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 20-30h, and replacing the deionized water every 1-3 hours during the dialysis process.

[0020] According to the preferred embodiment of 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 a 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] According to the preferred embodiment of 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 the 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 anti-solvent precipitation method is used to prepare lignin nanoparticles; by optimizing the organic solvent, the assembly behavior of the 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 ultrasonic treatment improves the dispersibility of the lignin nanoparticles, reduces the size of the lignin nanoparticles, and improves their stability; by controlling the ultrasonic time, the surface polarity of the lignin nanoparticles is regulated. The emulsifier obtained by the present invention is an amphiphilic lignin nanoparticle formed by self-assembly, which avoids the tedious 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 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 unadsorbed lignin nanoparticles form a three-dimensional network structure in the oil phase through interaction, thereby restricting 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 can be obtained from commercial channels 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 the stirring was continued for 24 h to obtain a mixed system of lignin nanoparticles-tetrahydrofuran-water.

[0035] (3) The mixed system of lignin nanoparticles-tetrahydrofuran-water in step (2) was introduced into a dialysis bag (molecular weight cut-off 6 kDa), and the dialysis bag was immersed in 2500 ml of deionized water, the water temperature was maintained at 10 ° C, and dialyzed for 24 h. The deionized water was replaced every 2 h during the dialysis process, and tetrahydrofuran was 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 30s using an ultrasonic cell disruptor with an ultrasonic frequency of 20kHz and an ultrasonic power of 900W 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 minute; 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 minute; 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 minute; 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 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] Example 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 is as described in Example 1, except that the alkali lignin is not treated in step (1). The specific steps are as follows:

[0060] Dissolve 1g of alkali lignin in 1275mL of water and stir magnetically at 1000rpm for 2h to obtain an alkali lignin solution. Filter the alkali lignin solution through a syringe filter (membrane pore size, 0.45μm) and transfer it into a dialysis bag (molecular weight cutoff, 6kDa). The bag is immersed in 2500ml of deionized water at 10°C for 24h, with the deionized water replaced every 2h during the dialysis process, to obtain a lignin nanoparticle suspension. The lignin nanoparticle suspension is then ultrasonically treated in an ice-water bath at 0°C for 30s using an ultrasonic cell disruptor at a frequency of 20kHz and a power of 900W to obtain a lignin nanoparticle dispersion. The lignin nanoparticle dispersion is then 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] 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 fluids. The emulsification index is used to evaluate the effect of emulsifiers on emulsion stability. This is done by measuring the ratio of the height of the emulsion layer to the total height of the mixture after emulsification and after a period of standing. 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 beaker, followed by the addition of 7.5 g of Span 80 and 3 g of the example or comparative example sample. The mixture was stirred at 10,000 rpm for 10 minutes. Then, 60 ml of water was slowly added to the beaker and stirring continued for 20 minutes. The prepared emulsion was transferred to a 100 ml stoppered graduated cylinder. 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 was measured after standing at room temperature for 24 hours and 48 hours, 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 emulsion stability. 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 with the addition of micron-sized industrial alkali lignin is difficult to completely emulsify, and after long-term standing, a large amount of upper oil precipitates, and the oil-water separation is obvious. The lignin nanoparticle emulsifier prepared using low initial lignin concentration or high initial lignin concentration has a good emulsification effect, but the emulsion stability is poor. At higher ultrasonic temperatures, the lignin nanoparticles have poor dispersibility, a high degree of aggregation, and are difficult to emulsify. This 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 subjected to rolling aging at 200°C for 16 hours before the drilling fluid performance was tested.

[0079] The performance of the oil-based drilling fluid prepared with lignin nanoparticle emulsifier was determined using 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] As can be seen from Examples 1-3, after 16 hours of continuous high-temperature aging at 200°C, 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. Examples 4-9 change 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 highly 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, increasing the size of the lignin nanoparticles, which is not conducive to the stability of the emulsion in the oil-based drilling fluid. In Examples 10 and 11, when preparing lignin nanoparticles, the initial concentrations of lignin in the organic solvent were 2 wt% and 8 wt%, 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, thus causing the emulsion to be unstable. However, if the initial concentration was too high, the viscosity of the lignin solution increased, causing the lignin nanoparticles to swell, the particle size to increase, and the performance of the resulting emulsifier to decrease. In Comparative Example 1, micron-sized industrial alkali lignin was used as an emulsifier. It was larger in size, had a lower specific surface area, and had a weaker adsorption capacity at the oil-water interface. Therefore, the prepared oil-based drilling fluid was unstable and had a lower demulsification voltage. At higher ultrasonic temperatures, the lignin nanoparticles had poor dispersibility and a high degree of aggregation, making it difficult to emulsify the drilling fluid.

Claims

1. An application of a natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid, characterized in that: Used as an emulsifier to stabilize oil-based drilling fluids; The method for preparing the natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid comprises the following steps: (1) fully dissolving alkali lignin in an organic solvent to obtain an alkali lignin solution; the organic solvent is tetrahydrofuran; the mass ratio of alkali lignin to the organic solvent is 1:25 g / mL; (2) The alkaline lignin solution is filtered, and the filtrate is added dropwise into deionized water to fully disperse it to obtain a mixed system of lignin nanoparticles-organic solvent-water; then, the lignin nanoparticle suspension is obtained by dialysis; (3) The lignin nanoparticle suspension was ultrasonically treated, and then centrifuged, washed, and dried to obtain a lignin nanoparticle emulsifier; the ultrasonic treatment conditions were: 20 kHz, 600-900 W, and 0°C for 30 seconds to 5 minutes.

2. The use of 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, with the stirring speed being 800-1200 rpm and the stirring time being 1-3 h.

3. The use of 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 dropwise addition is carried out under stirring conditions, and the dropwise addition rate 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, and the stirring time is 20-28h.

4. The use of 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 6~8 kDa.

5. The use of 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.

6. The use of 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~1min.

7. The use of the natural amphiphilic lignin nanoparticle emulsifier for oil-based drilling fluid according to claim 1, characterized in that: The amount of the lignin nanoparticle emulsifier added to the oil-based drilling fluid is 3-15 g / L.

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