Preparation and application of an environmentally friendly compound lubricant based biological oil for drilling fluids

2.3.1 Preparation of freshwater slurry

The preparation method is according to a special enterprise standard formulated by China National Petroleum Corporation (CNPC) Liquid Lubricants for Drilling Fluids Q/SY 17088–2016 (CNPC, 2016) and Bentonite, National Standards of the People's Republic of China, Standards Press of China (GB/T 20973, 2020). Take four high-speed mixing cups, add 400 mL of fresh water, 0.6 g (accurate to 0.01 g) Na₂CO₃, 20 g (accurate to 0.01 g) calcium-based bentonite, stir in a high-speed mixer (Inverter high-speed mixer, Qindao ChuangMeng Instrument Co., Ltd, China) 11000 rpm for 20 min, the mixture was in an airtight curing condition at room temperature for 16 h.

2.3.2 Preparation of salt-water slurry

The preparation method is according to Liquid lubricants for drilling fluids Q/SY 17088–2016 (CNPC, 2016), the salt-water base slurry is prepared on the basis of fresh water slurry as mentioned previously. For a 4% NaCl slurry, add 16 g (accurate to 0.01 g) NaCl to 400 mL fresh water slurry and stir stir in a high-speed mixer (Inverter high-speed mixer, Qindao ChuangMeng Instrument Co., Ltd, China) 11000 rpm for 20 min, the mixture was in an airtight curing condition at room temperature for 16 h.

2.4.1 Lubricity performance test

The lubrication inclination angle (α) and lubrication coefficient reduced rate (Δf) are evaluation indicators of lubricity. The evaluation methods are according to Liquid Lubricants for Drilling Fluids Q/SY 17088–2016 (CNPC, 2016), that is also the test method commonly used in the world oil drilling industry. Lubrication inclination angle (α) is a relatively simple method to evaluate lubricity, and the repeatability of the experiment is poor and the error of the experimental data is large. It is only used for simple lubrication performance evaluation in the drilling field laboratory. Therefore, we use the extreme pressure lubrication coefficient reduction rate (Δf) to evaluate the lubrication performance, the evaluation is divided into the following steps: step 1, turn on the extreme pressure lubricator (Extreme Pressure Lubrication Device, OFI, USA) and preheat for 15 min. Step 2, fix the slider to the holder with the concave side outwards, against the test ring. Step 3, adjust speed to 60 rpm and adjust torque zero knob to zero torque. Step 4, take the cured fresh water base slurry, pour it into a high mixing cup, and stir for 10 min at 11000 rpm, then pour it into tray, press the lubricator to 16.95 N·m, and test the base slurry lubrication coefficient, read after 10 min and record as T₁. Step 5, clean lubrication test rings and test blocks, then take 400 mL of fresh water base slurry and add 2 mL of lubricant sample to it, then continue with the same operation in step 4, take the reading after ten minutes, and record it as T₂. Then calculate its Δf, calculated as:

In the formula:

• Δf - reduction rate of extreme pressure lubrication coefficient, %;

• T₁ - Extreme pressure lubrication coefficient of the base paste;

• T₂ - The extreme pressure lubrication coefficient after the base slurry is added to the specimen.

2.4.2 Rheological performance

Since bentonite drilling fluids belongs to a kind of pseudoplastic fluid, pseudoplastic fluid obeys power law equation: τ = Kγⁿ, where τ is shear stress, γ is shear rate, n is fluidity index and K is consistency coefficient, and they are two important parameters of pseudoplastic fluid (Huang, 2016). The performance of drilling fluids is evaluated by rheological data and filtration loss, followed by API standard (API 13B-1, 2009). The usual parameters are apparent viscosity (AV), plastic viscosity (PV), yield point (YP), filtration loss (FL), and friction coefficient Kf.

In the formula:

• AV -Apparent viscosity (mPa·s).

• PV-Plastic viscosity (mPa·s).

• YP-Yield point (Pa).

• α-Lubrication inclination angle.

• Φ₆₀₀-Viscometer dial reading at 600 r/min (dia).

• Φ₃₀₀-Viscometer dial reading at 300 r/min (dia).

• FL-Filtration volume at ambient temperature under API

• standard (mL);

• V-Filtrate volume between 7.5 min and 30 min (mL).

• F-Friction force (N).

• P-Positive pressure (Pa).

2.4.3 Biological toxicity test

Refer to Biotoxicity Classification and Detection Methods of Oilfield Chemicals and Drilling Fluids: Luminescent Bacteria Method (Q/SY 111-2007, 2007)“, using BM-6000 luminescent bacteria toxicity detector to determine the biological toxicity of samples.

3.3.1 Effect of glycerol addition on esterification

The effect of glycerol addition on esterification was investigated at 220 °C for 3 h. The results are shown in Fig. 4.

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Fig. 4

Effect of GL addition on the acid value of esterification products.

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From Fig. 4, the amount of GL addition has a significant effect on the esterification process, especially the acid value which decreases when the amount of GL addition increases from 5% to 10%. When adding GL at 20–25%, the acid value is only about 3 mg KOH/g, and the esterification rate rises to more than 98%, and the reaction tends to slow down. However, the excessive amount of GL does not only increase the production cost, but also easily cause harmful reactions, so the final choice of GL addition amount is 20% of the oil sample.

3.3.2 Effect of reaction temperature on esterification

The effect of reaction temperature on esterification was investigated, and the experimental conditions are chosen to be 20% of GL addition and 3 h. The results are shown in Fig. 5.

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Fig. 5

Effect of reaction temperature on acid value of esterification products.

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From Fig. 5, the acid value decreases and sands the esterification rate increases as the temperature increased. The acid value was already 3.44 mg KOH/g and the esterification rate reached more than 98% when the temperature is 220 ℃, so the optimized reaction temperature is 220 ℃.

3.3.3 Effect of reaction time on esterification

The effect of reaction time on esterification was investigated, and the experimental condition is chosen to have a GL addition of 20% and a reaction temperature of 220 °C. The results are shown in Fig. 6.

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Fig. 6

The effect of reaction time on acid value of esterification products.

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From Fig. 6, the acid value decreased and the esterification rate increased with the increase of reaction time. At a reaction time of 3 h, the acid value was only 3.18 mg KOH/g, and the esterification rate reached more than 98%. At this time, increasing the reaction time cannot effectively improve the esterification effect. Moreover, if the reaction is maintained too long at 220 ℃, it invariably increases the danger and consumed energy, which also lead to the blackening and viscosity of the reactants. Therefore, the optimized reaction time is 3 h.

Optimal process conditions for GL esterification are finally determined as follows: 100 g AO is added with 20% GL (20 g), 1% NaOH (0.2 g), and the reaction is carried out at 220 °C for 3 h.

3.5.1 Characterization of modification results

Fig. 7 shows the FT-IR of AO modified by three modification methods. There are three groups in AO, –CH₂, –COOH and -C = CH. –CH₂ and –COOH correspond to the strong absorption peaks of 2928 cm⁻¹, 2856 cm-¹ and 1711 cm⁻¹ in FT-IR, -C = C-H corresponds to the peak at 3007 cm⁻¹. AO is recorded as V-AO after vulcanization, and the disappearance of the peak at 3007 cm⁻¹ (-C = C-H) indicates the occurrence of this process. After AO esterification, it is denoted as E-AO. The disappearance of the peak at 2928 cm-1 (–CH₂-) and the peak at 1711 cm⁻¹ (–COOH) indicates the conversion of –CH₂ to –CH₃ during the esterification process, the appearance of absorption peaks at 1041 cm⁻¹ and 1087 cm⁻¹ also indicates that this process is taking place, with both the formation of -C-O-C-. The AO that is first vulcanized and then esterified is recorded as VE-AO, and the disappearance of the peak at 3007 cm⁻¹ (-C = C-H) and the appearance of absorption peaks at 1041 cm⁻¹ and 1087 cm⁻¹ indicates the occurrence of this process. For VE-AO, the peak at 1742 cm⁻¹ may be caused by water.

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Fig. 7

Fourier transform infrared spectroscopy (FT-IR) of samples of oil.

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3.5.2 Comparison of the performance of several modification methods

AO modification experiments are compared, and the experimental results are shown in Table 4 and Fig. 8.

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Fig. 8

Evaluation the lubricity performance of AO modified by different methods. (a): Fresh water-based slurry; (b): Salt water-based slurry.

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Comparing the results of modification, it is found that different modification methods improved the lubricity of various oils to a great extent, especially in the salt-water-based slurry. In saltwater -based slurry, the lubricity Δf of AO is increased from 58.33% to 85.32%, which exceeded the industry required liquid lubricant index and could be used as liquid lubricant base oil.

3.5.3 Adjustment and optimization

AO modified by sulfide esterification (denoted as VEAO) exhibits excellent performance in lubricity and can be used as a base oil, and then diluents, wetting agents and emulsifiers are added to adjust and optimize the comprehensive performances. Therefore, the design of tempering program F-1 is as follows.

F-1: VEAO + WO + SP-80 + QT. The results of the performance tests on F-1 are shown in Table 5. Where, Δf_fb: fresh-water slurry before aging, Δf_fa: fresh-water slurry after aging, Δf_sb: salt-water slurry before aging, Δf_sa: salt-water slurry before aging.

3.5.4 Temperature tolerance and salt resistance

For the sample F-1, the test evaluation of Δf is performed at different temperatures (150 ℃ and 180℃) after ageing for 16 h and different salinities (4% NaCl, 15% NaCl, 36% NaCl, and 7% KCl). The freshwater base slurry is prepared by: 400 mL water + 20 g standard calcium-based bentonite + 0.6 g Na₂CO₃, high stirring for 20 min and then maintained at room temperature for 16 h. For making a saltwater base slurry, a specified quantified NaCl/KCl is added to the well-maintained freshwater base slurry. The specified amount of lubricant specimen added to the base slurry, and then to evaluate its lubricity. The test results are shown in Fig. 9.

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Fig. 9

Performance evaluation of different mud. (a): AO; (b): F-1.

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From the above test results, we can find that AO itself has poor lubrication anti-salt performance, and the temperature has a large effect on its Δf. F-1 is better than AO, because of dilution, surfactant addition making lubrication effective and molecules dispersed even.

In terms of salt resistance, its Δf is 83.87% in 4% NaCl based mud, which also still reach 75.19% in 36% NaCl based mud and 76.35% after aging at 150 ℃, as the aging temperature rises from 150 ℃ to 180 ℃, its Δf decreases about 8%, In general, F-1 has excellent temperature and salt resistance, and is a good temperature and salt resistant lubricant.

3.5.5 Pilot test performance

The pilot production is selected in an oilfield auxiliary production enterprise in Karamay, Xinjiang. A lot of lubricants are consumed yearly in oil wells of the Xinjiang oilfield, and there are a lot of by-products AO in the local cotton production, so it will be beneficial for production and sales to make use of local conditions and take local materials. According to the laboratory formula, 12 t products are formulated and produced. Samples are then taken for evaluation and testing respectively after production. Table 6 shown the performance of four batches industrial samples F-1 (noted as F-1a ∼ F-1d).

From the test results, we can observe that the F-1 pilot production product fully meets the requirements of the standard indicators and is a vegetable oil lubricant with excellent lubrication performance and high-cost performance.

3.6.1 Comparison with different lubricants

The F-1 optimized sample was evaluated in Xinjiang Tuha Oilfield Technical Service, and compared the basic performances with their common-used better commercial lubricant products such as LU-99, PGCS-1, LUSXR and HLB. Comparison of test results are shown in Table 7.

From the test results in Table 7, we can find that F-1 is not much different from LU-99 and HLB in all performance comparisons, and they are all excellent drilling fluid lubricants. Compared with their samples, F-1 is more inexpensive and vegetable oil-based, which is more environmentally friendly.

3.6.2 Effect on rheological performances of drilling fluids

The effect of the lubricant sample on the rheological performances of the drilling fluids system are evaluated. The base drilling fluid system (Mud-1) formula is: 4% calcium-based bentonite slurry + 0.5% NH₄PAN + 1% SPNH + 0.3% FA-367 + 0.5% SP-80 + 0.5% NaOH + 10% KCl, the dosage of all the evaluated lubricant samples in Mud-1 is 0.5%, and the rheological properties are evaluated.

According to the above experimental method, prepare Mud-1, add lubricant samples respectively, subject to high stirring for 30 min, pour into an aging tank, after aging at 150 ℃×16 h, put to room temperature, high stirring for 5 min, and test the rheological performances and filtration loss after aging. The test results are shown in Figs. 10, 11. Several most common drilling fluid additives in China are used in this Mud-1 formula including hydrolyzed polyacrylonitrile ammonium (NH₄PAN) filtrate reducer, sulfonated lignite phenol formaldehyde resin (SPNH) high temperature filtrate reducer, copolymer coating inhibitor (FA-367) and spartan emulsifier (SP-80).

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Fig. 10

Test results of rheological properties. (a): AV; (b): FL.

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Fig. 11

Test results of rheological properties. (a): YP; (b): PV.

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From the test results in Fig. 10 and Fig. 11, we can observe that after adding 0.5% (2 g) lubricant sample to Mud-1, the filtration loss of suspension decreased from 10 mL to 6.5 mL, the apparent viscosity and plastic viscosity have little change before and after aging at high temperature, which indicated that the stability of the suspension has been strengthened. These data can show that F-1 does not only improve the apparent and plastic viscosity of the bentonite suspension at room temperature as well as high temperature, but also reduce the filtration loss of bentonite suspension. As a result, the fluidity of the suspension has been improved and the cutting carrying capacity has been greatly improved.

3.6.3 Evaluation of on-site well slurry

Field well-site drilling mud slurry test: well Hongtai 23-P12-2 in CNPC Dagang Oilfield, well depth 2614 m, drilling fluid density 1.36 g/cm³, sand content 0.3%, bentonite content 50.05 g/L, friction coefficient K_f 3°/0.0524. The test results are shown in Table 8.

From the results of the well-site drilling mud slurry test in Table 8, we can observe that F-1 has a little effect on the rheological performances after it is added to the well-site slurry, it has good lubricating properties because of its α of mud cake is only 1.5°, and is an environment-friendly compound lubricant with higher price competitiveness suitable for the water-based drilling fluids system.