Filtrate reducer for oil-based drilling fluid and preparation method of filtrate reducer

Abstract

The invention aims to provide a filtrate reducer for oil-based drilling fluid and a preparation method of the filtrate reducer, and belongs to the technical field of petroleum drilling. The filtrate reducer for the oil-based drilling fluid comprises the following raw materials in parts by weight: 20-40 parts of natural rubber powder; 10 to 20 parts of asphalt powder; 10 to 20 parts of calcium carbonate; 5 to 15 parts of modified humic acid amide; 5 to 15 parts of oil soluble resin; 1-5 parts of an oxidant; 1-5 parts of a temperature stabilizer; 1-5 parts of an emulsifier; wherein the natural rubber powder, the asphalt powder, the modified humic acid amide, the oil-soluble resin and the oxidizing agent are mixed and then subjected to heat treatment at 120-130 DEG C, and after cooling, the mixture is mixed with the remaining raw materials. The invention has the characteristics of wide raw material source, good compatibility with the oil-based drilling fluid, easy industrial production, and controllable environmental pollution problem.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum drilling, in particular to a fluid loss reducer for oil-based drilling fluid and a preparation method thereof. Background Art

[0002] Oil-based drilling fluids are widely used in drilling operations in complex formations such as deep wells, ultra-deep wells, and horizontal wells due to their excellent lubricity, inhibition, and high temperature resistance. However, oil-based drilling fluids also have the problem of large filtration loss, which can easily cause formation damage, well wall instability, and other complex downhole situations. Therefore, it is of great significance to develop efficient and environmentally friendly filtration reducers for oil-based drilling fluids.

[0003] The Chinese invention (name: "A preparation method and fluid loss reducer for drilling fluid", announcement number: CN114591464B, announcement date: 20231128) discloses that the fluid loss reducer for drilling fluid is obtained by polymerization reaction of 60-100 parts of distilled water; 20-40 parts of 2-acrylamide-2-methylpropane sulfonic acid; 20-40 parts of sodium styrene sulfonate; 20-40 parts of liquid paraffin; 2-10 parts of dispersant; 2-10 parts of initiator; 10-20 parts of hydroxyethyl methacrylate. The fluid loss reducer prepared by the preparation method has good fluid loss reduction performance, dispersibility and temperature resistance, can withstand high temperatures above 200°C, has good compatibility with drilling fluid, can effectively improve the safety and drilling speed of drilling, and is non-toxic, harmless and easily degradable. However, the preparation method requires a polymerization reaction, the generation process is relatively complicated, and the preparation cost (including equipment investment) is high.

[0004] The Chinese invention (name: "A fluid loss reducer for asphalt-based drilling fluid and its preparation method", announcement number: CN117757445B, announcement date: 20240430) discloses that the fluid loss reducer includes raw materials such as modified asphalt, white oil, modified lignin and polyacrylamide; wherein the modified asphalt is asphalt after hydrophilic modification, and the modified lignin is the introduction of sodium carboxyl groups into the lignin structure. The fluid loss reducer for asphalt-based drilling fluid in the present invention is used in combination with water-based drilling fluid, which can effectively reduce the filtration loss of water-based drilling fluid and prevent drill bit sticking. However, the method uses modified asphalt as the main raw material, which involves serious environmental pollution problems. Summary of the invention

[0005] The present invention aims to provide a fluid loss reducer for oil-based drilling fluid and a preparation method thereof, which has the characteristics of wide raw material sources, good compatibility with oil-based drilling fluid, easy industrial production and controllable environmental pollution problems.

[0006] The technical solution adopted by the present invention is: A fluid loss reducer for oil-based drilling fluid, comprising the following raw materials in parts by weight: Natural rubber powder, 20-40 parts; Asphalt powder, 10-20 parts; Calcium carbonate, 10-20 parts; Modified humic acid amide, 5-15 parts; Oil-soluble resin, 5-15 parts; Temperature stabilizer, 1~5 parts; Oxidant, 1-5 parts; Emulsifier, 1-5 parts; The natural rubber powder, the asphalt powder, the modified humic acid amide, the oil-soluble resin and the oxidant are mixed and then heat-treated at 120-130° C., and then mixed with the remaining raw materials after cooling.

[0007] Furthermore, the natural rubber powder is a natural rubber powder with a softening point of 80-120°C.

[0008] Furthermore, the asphalt powder is petroleum asphalt powder with a softening point of 80-120°C.

[0009] Furthermore, the calcium carbonate is composed of 40-50wt% of hard calcium carbonate with a particle size of 200 meshes, 30-40wt% of hard calcium carbonate with a particle size of 400 meshes, and 20-25wt% of hard calcium carbonate with a particle size of 1000 meshes.

[0010] Furthermore, the modified humic acid amide is prepared by mixing humic acid amide with nano silicon dioxide or nano aluminum oxide in a weight ratio of 5:1.

[0011] Furthermore, the oxidant is benzoyl peroxide, dicumyl peroxide, potassium permanganate or sodium hypochlorite.

[0012] Furthermore, the temperature stabilizer is calcium stearate or zinc stearate.

[0013] Furthermore, the oil-soluble resin is a C5 petroleum resin or a C9 petroleum resin having a softening point of 80-120°C.

[0014] Furthermore, the emulsifier is Span-80 or Tween-80.

[0015] Based on the same inventive concept, the present invention also provides a method for preparing a fluid loss reducer for oil-based drilling fluid, comprising the following steps: Step S1: adding natural rubber powder, asphalt powder, modified humic acid amide, oil-soluble resin and oxidant into a reaction kettle in proportion; Step S2: Start stirring at a speed of 300-400 r / min to mix evenly in advance; Step S3: dilute the emulsifier with an appropriate amount of ethanol and add it to the mixture in step S2 by spraying, and continue stirring to mix evenly.

[0016] Step S4: setting the temperature of the reactor to 120-130° C., and heat treating the mixture in step S3 at this temperature for 2-3 hours; Step S5: The mixture in step S4 is cooled to room temperature, crushed to 150-200 mesh, and then mixed with calcium carbonate and a temperature stabilizer and stirred for 30 minutes to obtain a fluid loss reducer for oil-based drilling fluid.

[0017] The beneficial effects of the present invention are: 1. The oil-based drilling fluid fluid loss reducer of the present invention uses natural rubber powder, asphalt powder and calcium carbonate as main raw materials, and the raw materials are widely available and low in cost. Meanwhile, compared with the asphalt-based fluid loss reducer, the oil-based drilling fluid fluid loss reducer of the present invention uses asphalt powder, and the dosage is reduced, so the environmental pollution problem is relatively controllable.

[0018] 2. In the present invention, an appropriate amount of oxidant is added to the fluid loss reducer for oil-based drilling fluid, and a heat treatment process at 120-130° C. is introduced. An appropriate amount of C-C bonds and C-H bonds on the surface of natural rubber powder and oil-soluble resin are opened to form more oxygen-containing groups such as hydroxyl and carbonyl groups. These active groups undergo esterification reactions with sulfoxide, carboxyl and anhydride groups in asphalt and humic acid amide (the synthetic raw material components of asphalt and humic acid amide are relatively complex and may contain sulfoxide, carboxyl and anhydride groups), thereby improving the interaction force at the interface of natural rubber powder, asphalt powder, humic acid amide and oil-soluble resin, which is beneficial to improving the stability and plugging effect of the fluid loss reducer after being matched with the oil-based drilling fluid, and the effect of reducing the filtration loss is more obvious.

[0019] 3. The oil-based drilling fluid fluid loss reducer of the present invention contains an appropriate amount of humic acid amide, which has hydrophilicity, lipophilicity, complexing ability and strong adsorption and dispersion ability, is not easy to decompose at high temperature, and the humic acid amide modified by the added nano-silicon dioxide or nano-aluminum oxide has a more stable network structure, which improves the rigidity and thermal stability of the humic acid amide, thereby effectively improving the temperature resistance and salt resistance of the fluid loss reducer.

[0020] 4. The oil-based drilling fluid filtration reducer of the present invention contains an appropriate amount of oil-soluble resin, which has good dispersibility in the oil-based drilling fluid and can be well compatible with other components in the drilling fluid without affecting the emulsification stability of the drilling fluid; at the same time, the oil-soluble resin can be compatible with natural rubber powder, asphalt powder, and humic acid amide in the drilling fluid to form a dense filter cake, effectively reducing the filtration loss of the drilling fluid.

[0021] 5. The filtrate reducer for oil-based drilling fluid in the present invention has good compatibility with oil-based drilling fluid and can be widely used in drilling operations. The filtrate reducer for oil-based drilling fluid contains calcium carbonate with different particle size gradations, which can widely block micro-cracks. Moreover, the filtrate reducer for oil-based drilling fluid contains film-forming particles that can be softened. By participating in the formation of the mud cake, a high-strength adsorption film is formed on the surface of the mud cake, which can reduce the permeability of the mud cake and improve the quality of the mud cake. Under the dual plugging effects of rigid particles and film-forming particles, the plugging effect is better.

[0022] 6. In the preparation process of the filtrate reducer for oil-based drilling fluid in the present invention, heat treatment is mainly involved. Compared with the polymerization reaction process, the production process is relatively simple, and the preparation cost (including equipment investment) is relatively low, making it easy for industrial production. Specific embodiments

[0023] The embodiments of the invention will be described in detail below.

[0024] Example 1

[0025] Add 20 kg of natural rubber powder (softening point 80 - 120 °C), 10 kg of asphalt powder (softening point 80 - 120 °C), 5 kg of modified humic acid amide (humic acid amide and nano-silica are mixed and modified according to a weight ratio of 5:1), 5 kg of C5 petroleum resin (softening point 80 - 120 °C) and 1 kg of benzoyl peroxide into the reaction kettle, start stirring, and pre-mix evenly at a stirring speed of 350 r / min. Atomize and add 1 kg of Span-80 (diluted with 0.5 kg of ethanol, and the ethanol volatilizes when heated during subsequent heat treatment), continue stirring, and mix evenly. Set the temperature of the reaction kettle at 120 °C, and stir and heat-treat at 120 °C for 3 h, then cool to room temperature, crush to 150 mesh, and then mix evenly with 10 kg of calcium carbonate (calcium carbonate is composed of 45 wt% of hard calcium carbonate with a particle size of 200 mesh, 30 wt% of hard calcium carbonate with a particle size of 400 mesh, and 25 wt% of hard calcium carbonate with a particle size of 1000 mesh) and 1 kg of calcium stearate to obtain the filtrate reducer for oil-based drilling fluid.

[0026] Example 2

[0027] Add 30kg natural rubber powder (softening point 80~120℃), 15kg asphalt powder (softening point 80~120℃), 10kg modified humic acid amide (humic acid amide and nano-silicon dioxide are mixed and modified according to the weight ratio of 5:1), 10kg C5 petroleum resin (softening point 80~120℃) and 3kg benzoyl peroxide into the reactor, start stirring, stir at a speed of 350r / min and pre-mix evenly. Add 3kg Span-80 (diluted with 1.5kg ethanol, ethanol evaporates by heat during subsequent heat treatment) by atomization, continue stirring, and mix evenly. The reactor temperature was set at 125°C, and the mixture was heat treated at 125°C with stirring for 2.5 hours, then cooled to room temperature, crushed to 150 mesh, and then evenly mixed with 15kg of calcium carbonate (the calcium carbonate consisted of 45wt% of hard calcium carbonate with a particle size of 200 mesh, 30wt% of hard calcium carbonate with a particle size of 400 mesh, and 25wt% of hard calcium carbonate with a particle size of 1000 mesh) and 3kg of calcium stearate to obtain a filtrate reducer for oil-based drilling fluid.

[0028] Example 3

[0029] Add 40kg natural rubber powder (softening point 80~120℃), 20kg asphalt powder (softening point 80~120℃), 15kg modified humic acid amide (humic acid amide and nano-silicon dioxide are mixed and modified according to the weight ratio of 5:1), 15kg C5 petroleum resin (softening point 80~120℃) and 5kg benzoyl peroxide into the reactor, start stirring, stir at a speed of 350r / min and pre-mix evenly. Add 5kg Span-80 (diluted with 2.5kg ethanol, ethanol evaporates by heat during subsequent heat treatment) by atomization, continue stirring, and mix evenly. The reactor temperature was set at 130°C, and the mixture was heat treated at 130°C with stirring for 2 hours, then cooled to room temperature, crushed to 150 mesh, and then evenly mixed with 20 kg of calcium carbonate (the calcium carbonate consisted of 45 wt% of hard calcium carbonate with a particle size of 200 mesh, 30 wt% of hard calcium carbonate with a particle size of 400 mesh, and 25 wt% of hard calcium carbonate with a particle size of 1000 mesh) and 5 kg of calcium stearate to obtain a fluid loss reducer for oil-based drilling fluid.

[0030] Comparative Example 1 Add 20kg natural rubber powder (softening point 80~120℃) and 10kg asphalt powder (softening point 80~120℃) to the reactor, start stirring, and pre-mix at a stirring speed of 350r / min. Add 1kg Span-80 (diluted with 0.5kg ethanol, ethanol evaporates by heat during subsequent heat treatment) by atomization, continue stirring, and mix evenly. Set the reactor temperature to 120℃, and heat-treat at 120℃ for 3h, then cool to room temperature, crush to 150 mesh, and then mix evenly with 10kg calcium carbonate (calcium carbonate consists of 45wt% hard calcium carbonate with a particle size of 200 mesh, 30wt% hard calcium carbonate with a particle size of 400 mesh, and 25wt% hard calcium carbonate with a particle size of 1000 mesh) and 1kg calcium stearate to obtain a fluid loss reducer for oil-based drilling fluid.

[0031] Comparative Example 2 Add 20kg natural rubber powder (softening point 80~120℃), 10kg asphalt powder (softening point 80~120℃), 5kg modified humic acid amide (humic acid amide and nano-silicon dioxide are mixed and modified according to the weight ratio of 5:1) and 5kg C5 petroleum resin (softening point 80~120℃) into the reactor, start stirring, and pre-mix at a stirring speed of 350r / min. Add 1kg Span-80 (diluted with 0.5kg ethanol, and ethanol evaporates by heat during subsequent heat treatment) by atomization, and continue stirring to mix evenly. The reactor temperature was set at 120°C, and the mixture was heat treated at 120°C with stirring for 3 hours, then cooled to room temperature, crushed to 150 mesh, and then evenly mixed with 10kg of calcium carbonate (the calcium carbonate consisted of 45wt% of hard calcium carbonate with a particle size of 200 mesh, 30wt% of hard calcium carbonate with a particle size of 400 mesh, and 25wt% of hard calcium carbonate with a particle size of 1000 mesh) and 1kg of calcium stearate to obtain a fluid loss reducer for oil-based drilling fluid.

[0032] Comparative Example 3 20kg natural rubber powder (softening point 80~120℃), 10kg asphalt powder (softening point 80~120℃), 5kg modified humic acid amide (humic acid amide and nano-silicon dioxide are mixed and modified according to the weight ratio of 5:1), 5kg C5 petroleum resin (softening point 80~120℃) and 1kg benzoyl peroxide are added to the reactor, and stirring is started at a stirring speed of 350r / min to pre-mix evenly. 1kg Span-80 is added by atomization (diluted with 0.5kg ethanol, and the ethanol evaporates naturally during the subsequent mixing treatment), and stirring is continued. Mix evenly, and then mix evenly with 10kg calcium carbonate (calcium carbonate is composed of 45wt% hard calcium carbonate with a particle size of 200 mesh, 30wt% hard calcium carbonate with a particle size of 400 mesh and 25wt% hard calcium carbonate with a particle size of 1000 mesh) and 1kg calcium stearate to obtain a fluid loss reducer for oil-based drilling fluid.

[0033] Comparative Example 4 Add 20kg natural rubber powder (softening point 80~120℃), 10kg asphalt powder (softening point 80~120℃) and 1kg benzoyl peroxide into the reactor, start stirring, and pre-mix at a stirring speed of 350r / min. Add 1kg Span-80 (diluted with 0.5kg ethanol, ethanol evaporates by heat during subsequent heat treatment) by atomization, continue stirring, and mix evenly. Set the reactor temperature to 120℃, and heat-treat at 120℃ for 3h, then cool to room temperature, crush to 150 mesh, and then mix evenly with 10kg calcium carbonate (calcium carbonate consists of 45wt% hard calcium carbonate with a particle size of 200 mesh, 30wt% hard calcium carbonate with a particle size of 400 mesh, and 25wt% hard calcium carbonate with a particle size of 1000 mesh) and 1kg calcium stearate to obtain a fluid loss reducer for oil-based drilling fluid.

[0034] The fluid loss reducers for oil-based drilling fluid prepared in Examples 1-3 and Comparative Examples 1-4 were added to the oil-based drilling fluid, and their performance indicators were tested.

[0035] Experimental method [1]: 320 mL of diesel was placed in a 1000 mL enamel mixing cup. 16.0 g of organic bentonite, 20.0 g of Span-80 and 4.0 g of Tween-80 were added while stirring with a high-speed mixer at a speed of 10000 r / min. After stirring for 10 min, 80 mL of 20% calcium chloride aqueous solution was slowly added. After high-speed stirring for 20 min, 16 g of oil-based drilling fluid filter loss reducer was slowly added and stirred at high speed for 5 min. The prepared oil-based drilling fluid was placed in a high-temperature aging kettle and placed in a high-temperature roller heating furnace. After aging at 150 °C for 16 h, it was taken out, cooled to room temperature and stirred at high speed for 20 min. According to the method specified in GB / T 16783.2, the apparent viscosity and high-temperature and high-pressure filter loss (150 °C, 3.5 MPa) of the oil-based drilling fluid were measured at 65 °C. The test results are shown in Table 1.

[0036] Table 1 Performance test results of fluid loss reducer for oil-based drilling fluid

[0037] As can be seen from Table 1, the high temperature and high pressure fluid loss of the fluid loss reducers for oil-based drilling fluids prepared in Examples 1-3 of the present invention are significantly lower than those in Comparative Examples 1-4, indicating that the fluid loss reducers provided by the present invention have excellent fluid loss reduction performance. At the same time, the apparent viscosity of the fluid loss reducers for oil-based drilling fluids prepared in Examples 1-3 of the present invention is higher than that in Comparative Examples 1-4, indicating that the fluid loss reducers provided by the present invention can effectively improve the rheological properties of the oil-based drilling fluids.

[0038] Experimental method [2]: Prepare oil-based drilling fluid using oil-based drilling fluid system materials produced by Chengdu Xiyou Huawei Technology Co., Ltd. Add 3.20g of oil-based drilling fluid main emulsifier HW Pmul-1, 8.80g of oil-based drilling fluid auxiliary emulsifier HW Smul-1, 3.20g of oil-based drilling fluid wetting agent HW Wet-1, and 320mL of 0# diesel in a high-stirring cup. Add 12.00g of organic bentonite while stirring at 1000r / min. Stir at 11000r / min for 20min, then add 12.00g of calcium oxide and stir at high speed for 10min. Then add 80mL of 25% calcium chloride aqueous solution and stir at high speed for 20min. Then add 20.00g of oil-based drilling fluid filter loss reducer and stir at high speed for 10min. Finally, add first-grade barite powder while stirring to increase the density to 1.80g / cm 3 , and then stir at high speed for 30 minutes. The prepared weighted slurry was placed in a high-temperature aging kettle and aged and rolled at 150°C for 16 hours. Take it out, cool it to room temperature, stir it at high speed for 10 minutes, and test the medium-pressure filtration loss and high-temperature and high-pressure filtration loss (150°C, 3.5MPa) according to the method specified in GB / T 16783.2. The test results are shown in Table 2.

[0039] Table 2 Performance test results of fluid loss reducer for oil-based drilling fluid

[0040] It can be seen from Table 2 that the fluid loss reducers for oil-based drilling fluids prepared in Examples 1-3 of the present invention have good compatibility with the oil-based drilling fluid system, and the medium-pressure fluid loss and high-temperature and high-pressure fluid loss are significantly lower than those in Comparative Examples 1-4, indicating that the fluid loss reducer provided by the present invention has excellent fluid loss reduction performance and compatibility.

[0041] Experimental method [3]: According to the formula of 240mL 0# diesel + 12g integrated emulsifier HW Pmul-3 + 6g organic bentonite + 9g quicklime + 60mL 25% calcium chloride brine, two portions of oil-based emulsion were prepared. 4.5% of the oil-based drilling fluid filter loss reducer prepared in Example 3 was added to one portion. After high stirring at 10000r / min for 20min, the rheological parameters, medium pressure filter loss, and high temperature and high pressure filter loss (150℃, 3.5MPa) were tested at 50℃. The test results are shown in Table 3.

[0042] Table 3 Test data of oil-based drilling fluid filtrate reducer in oil-based emulsion

[0043] It can be seen from the test results in Table 3 that after adding the fluid loss reducer for oil-based drilling fluid of the present invention to the oil-based emulsion, the fluid loss reduction property of the oil-based drilling fluid is significantly improved, the quality of the filter cake is improved, and there is no significant effect on the performance of the oil-based drilling fluid, and the compatibility is good.

[0044] Experimental method [4]: ​​Take the oil-based drilling fluid slurry from a well on site for the experiment. Add 2% of the oil-based drilling fluid filtrate reducer prepared in Example 3 to the slurry, stir at 10000r / min for 20 minutes, and then test the rheological parameters and high temperature and high pressure filtration (150℃, 3.5MPa) at 50℃. The test results are shown in Table 4.

[0045] Table 4 Test results of fluid loss reducer for oil-based drilling fluid in a well slurry on site

[0046] The test results in Table 4 show that after adding the fluid loss reducer for oil-based drilling fluid of the present invention to the well slurry, the fluid loss reduction effect is obvious, and the reduction rate can reach 50%; the mud cake becomes thinner, and the mud cake quality is significantly improved; and the rheological properties and electrical stability of the well slurry are not affected.

Claims

1. A fluid loss reducer for oil-based drilling fluid, characterized in that: In parts by weight, the following raw materials are included: Natural rubber powder, 20-40 parts; Asphalt powder, 10-20 parts; Calcium carbonate, 10-20 parts; Modified humic acid amide, 5-15 parts; Oil-soluble resin, 5-15 parts; Oxidant, 1-5 parts; Temperature stabilizer, 1~5 parts; Emulsifier, 1-5 parts; The natural rubber powder, the asphalt powder, the modified humic acid amide, the oil-soluble resin and the oxidant are mixed and then heat-treated at 120-130° C., and then mixed with the remaining raw materials after cooling.

2. The fluid loss reducer for oil-based drilling fluid according to claim 1, characterized in that: The natural rubber powder has a softening point of 80-120°C.

3. The fluid loss reducer for oil-based drilling fluid according to claim 1, characterized in that: The asphalt powder is petroleum asphalt powder with a softening point of 80-120°C.

4. The fluid loss reducer for oil-based drilling fluid according to claim 1, characterized in that: The calcium carbonate is composed of 40-50 wt% of hard calcium carbonate with a particle size of 200 meshes, 30-40 wt% of hard calcium carbonate with a particle size of 400 meshes and 20-25 wt% of hard calcium carbonate with a particle size of 1000 meshes.

5. The fluid loss reducer for oil-based drilling fluid according to claim 1, characterized in that: The modified humic acid amide is prepared by mixing humic acid amide and nano silicon dioxide or nano aluminum oxide in a weight ratio of 5:

1.

6. The fluid loss reducer for oil-based drilling fluid according to claim 1, characterized in that: The oxidant is benzoyl peroxide, dicumyl peroxide, potassium permanganate or sodium hypochlorite.

7. The fluid loss reducer for oil-based drilling fluid according to claim 1, characterized in that: The temperature stabilizer is calcium stearate or zinc stearate.

8. The fluid loss reducer for oil-based drilling fluid according to claim 1, characterized in that: The oil-soluble resin is a C5 petroleum resin or a C9 petroleum resin having a softening point of 80-120°C.

9. The fluid loss reducer for oil-based drilling fluid according to claim 1, characterized in that: The emulsifier is Span-80 or Tween-80.

10. A method for preparing a fluid loss reducer for oil-based drilling fluid, characterized in that: The following steps are involved: Step S1: adding natural rubber powder, asphalt powder, modified humic acid amide, oil-soluble resin and oxidant into a reaction kettle in proportion; Step S2: Start stirring at a speed of 300-400 r / min to mix evenly in advance; Step S3: dilute the emulsifier with an appropriate amount of ethanol and add it to the mixture in step S2 by spraying, and continue stirring to mix evenly; Step S4: setting the temperature of the reactor to 120-130° C., and heat treating the mixture in step S3 at this temperature for 2-3 hours; Step S5: The mixture in step S4 is cooled to room temperature, crushed to 150-200 mesh, and then mixed with calcium carbonate and a temperature stabilizer and stirred for 30 minutes to obtain a fluid loss reducer for oil-based drilling fluid.

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