Introduction

The selection of a frilling fluid with good performances to meet anticipated conditions is considered to be one of the most important processes in oil and gas extraction from subsurface reservoirs [1]. Drilling fluids perform critical roles such as cleaning and transporting the rock cuttings, maintaining the sidewall, lubricating and cooling the drilling bit, and avoid collapse information [2, 3]. Drilling fluids are mainly classified into three types, i.e., water-based drilling fluids (WDFs), oil-based drilling fluids, and synthetic drilling fluids. WDFs are the most commonly used drilling fluids and have been utilized in approximately 80% of all walls. The advantages of WDFs are low cost, superior cooling and cutting removal ability, rapid information breaking-down rate, and environmental friendliness. However, one of the main drawbacks of WDFs is their poor lubricating ability. The WDFs generally produce higher friction and torque values and the oil-based and synthetic-based drilling fluids [4]. In order to reduce friction between the drilling string and the borehole and the drilling string and the casing, and to reduce the drill string torque and tripping resistance, lubricant is added to the drilling fluids. This helps to avoid sticking accidents and improve the drilling speed [5].

Drilling fluid rheological properties such as apparent viscosity (AV), plastic viscosity (PV), and yield point (YP) are highly important for the success of drilling operations. These properties serve many purpose: [6]

•transport of cuttings from the wellbore bottom to the surface,

•cooling and lubricating the rotating drill string and bit,

•stabilizing the wellbore,

•forming a filter cake on the walls of the wellbore to reduce fluid loss across permeable formation.

In the previous studies, the effects of lubricants on the rheological properties of WDFs has been examined. Liu et al. [7] studied the effect of the lubricant BDLU-100L based on the white oil, high efficiency emulsifiers, extreme pressure agent chlorinated paraffins, and penetrant succinate sodium alkyl sulfonates on the rheological properties of low-solid bentonite fluids under low pressure-low temperature and high pressure-high temperature (180°C) conditions. He came up with the result that only a 1-2% of increase in AV, PV, and YP values of the drilling fluid was observed after adding BDLU-100L with percentage of 3% by weight, and then concluded that BDLU-100L had little effect in rheological properties of fresh water-based drilling fluids and high-temperature high-density water-based drilling fluids. Ahmet Sönmez et al. [8] selected three lubricants for analysis: fatty acid and glyceride based lubricant LUBE-1, triglyceride and vegetable oil based lubricant LUE-2, and vegetable oil based and polypropylene glycol based lubricant LUBE-3. Each type of lubricant was added to the water-based lignosulfonate drilling fluid at a concentration of 1, 2, and 3 vol.%, and then the rheological analysis was conducted at 120°F. The authors finally concluded that all three lubricants have acceptable PV values calculated from the viscosity experiments. LUBE-3 also have acceptable YP values. However, LUBE-1 demonstrated increasing YP values with increasing concentration, which is undesirable for drilling fluids.

In this study, a low-fluorescence anti-seize lubricant JXFQ-6 was selected as friction reducer. The influence of JXFQ-6 on rheological properties of the water-based drilling fluid under different temperature conditions is investigated in detail. Data analysis reveals that JXFQ-6 has little effect on the rheological properties of the drilling fluid at room temperature. However, it demonstrate favorable performance in controlling the rheological properties of the water-based drilling fluid under high temperatures; this ability has not been reported in previous studies on the effect of lubricants on the water-based drilling fluid. The methods of Fourier transform-infrared spectroscopy (FTIR) and thermogravimetric and differential-thermal analysis (TG-DTA) of the JXFQ-6 and filter cake samples were supplied to gain deep insights into the mechanism of rheological control performance of JXFQ-6.

Experimental Section

Materials

The lubricant JXFQ-6 was supplied by Tianjin Juxian Science &Trading company (China), and the given density was 0.95~1.05g/cm3. Sodium montmorillonite (Na-Mt), which is a type of natural bentonite, was provided by Xinjiang Xiazijie Bentonite Company (China). All other additives, including lignin humic acid condensate (HBF-1 thinner), amide cation polymer as a coating inhibitor (CHM), small cation organic quaternary ammonium polymer as a filtration control agent (HS-1), and carboxyl-sulfo-copolymer as a filtration control agent (HS-2) were obtained from Three Extension Chemical Products Company, Baoding City (China).

Drilling fluid preparation

First, an initial water-based drilling fluid was prepared by adding 40.0g of Na-Mt and 4.0g of Na2CO3 to distilled water (1000 ml) in accordance with the American Petroleum Institute (API) standard procedure [9], and then the mixture was pre-hydrated for 24 hours at room temperature. After that, the measured quantities of 1.0 wt. % of HBF-1, 4.0 wt. % of HS-1, 0.4 wt. % of CHM, 0.4 wt. % of NW-1, 3.0 wt. % of HS-2, and 3.0 wt. % of SFT were slowly added into the mixture, followed by vigorously mechanical stirring at a speed of 3000 rpm.

Preparation of samples

Samples of the water-based drilling fluids containing different concentrations of JXFQ-6 (in wt. %, relative to the total mass of the drilling fluids) were prepared by adding different amounts of JFXQ-6 into the drilling fluid, and then the samples were adjusted to pH 10 by adding the 20% NaOH solution.

Rheological determination

A rotational viscometer (ZNN-D6, Haitongda, Qingdao) was used to measure the rheological properties of each sample at fixed rates of 600 and 300 rpm. Sample were tested before and after aging at 120°C and 150°C for 16h in a roller oven (XGRL-4A, Haitongda, Qingdao). The drilling fluid rheological behavior was described by the Bingham plastic model. The apparent viscosity (AV), plastic viscosity (PV), and yield point (YP) were calculated for the rotation speed values of 600 and 300 rpm:

$$ AP={\theta}_{600}/2 $$
(1)
$$ PV={\theta}_{600}-{\theta}_{300} $$
(2)
$$ YP=0.511\left({\theta}_{300}- PV\right) $$
(3)

Structural characterization

After aging at 150°C for 16h in a roller oven, the samples of the drilling fluid containing 0, 1.0 and 10.0 wt. % of JXFQ-6 were compressed to obtain filter cake samples by using a high-temperature high-pressure filtration apparatus (SD6, Haitongda, Qingdao, China) at 150°C, under a constant pressure differential of 3.45 MPa over 30 min, according to the API recommended practice. The samples were obtained after drying in an oven at 90°C.

FTIR spectra of the samples and the original JXFQ-6 were conducted on a NEXUS-650 FTIR spectrometer (Thermo Nicolet Corporation, USA). High resolution thermogravimetric analysis (TGA) was done using a SDT Q600 apparatus (TA Instruments Inc., USA) with a heating rate of 10°C/min, from room temperature to 900°C, in air.

Results and Discussion

Effects of JFXQ-6 on the rheological properties of water-based drilling fluids

Samples of the drilling fluids with JXFQ-6 concentrations ranging from 0 to 10.0 wt. % were prepared and tested under aged and non-aged conditions. The plots of AV, PV, and YP versus JXFQ-6 concentrations under different temperature conditions (Fig. 1a, b, and c) revealed that JXFQ-6 had little impact on the AV, PV, and YP values of the non-aged drilling fluid. Without the addition of JXFQ-6, the aged drilling fluids showed noticeably low AV, PV, and YP values of the drilling fluid without JXFQ-6 were 48.5 (mPa · s), 31 (mPa · s), and 17.885 (Pa), showing a decrease of 56.3, 61.3 and 43.5%, respectively, when compared to the non-aged blank drilling fluid. IT has been reported that drilling fluids with very low plastic viscosity (PV) and yield points (YP) can form turbulence, resulting in borehole collapse. However, these experimental results also demonstrated that JFXQ-6 exhibited favorable performance in maintaining the AV, PV, and YP values of the drilling fluid. When the concentration of JXFQ-6 was 1.0 wt. %, the drilling fluids aged at 150°C presented AV, PV, YP values of 99 (mPa · s), 70 (mPa · s), and 29.638 (Pa), only showing a decrease of 11.2, 12.5, and 7.9%, respectively, when compared to the non-aged drilling fluid containing 1.0 wt. % JXFQ-6 AV, PV, and YP values of the drilling fluids aged at 150°C were almost unchanged with increase in JXFQ-6 concentration. The results for the drilling fluids aged at 120°C were similar to those aged at 150°C.

Fig. 1.
figure 1

Rheological properties of water-based drilling fluids, for different concentrations of JXFQ-6, at different temperatures: a) apparent viscosity; b) Plastic viscosity; c) yield point; d) shear-thinning characteristics (1 – at room temperature; 2,3 – after aging 16h at 120 and 150°C, respectfully).

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Drilling fluids are usually considered as shear-thinning fluids, which have high AV at low shear rates to carry or suspend the cuttings from the wellbores, and low apparent viscosity at high shear rates to be rapidly pumped into the bottom of wellbores as well as release the cuttings. The value of YP/ PV is used as an indicator of the shear-thinning characteristics of a drilling fluid. It has been reported that a ratio of YP equal to \( \frac{3}{4}-1\left(\frac{1b/100{ft}^2}{mPa\cdot s}\right) \) or in the range from 0.36 to 0.48 (Pa/mPa · s) is the optimal value for better cutting ability of the drilling fluids [1]. The plots of YP/PV versus the JXFQ-6 concentration for the drilling fluids (Fig. 1d) demonstrated that the YP/PV values of all non-aged drilling fluids were about 0.39 (Pa/mPa · s), indicating perfect shear-thinning behavior. After aging at 120°C and 150°C for 16h, the YP/PV values of the aged drilling fluids without JXFQ-6 are 0.55 and 0.58, respectively. It has been reported that drilling fluids with a high value of YP/PV can increase the pump pressure and threaten drilling safety. However, with the addition of JXFQ-6 ranging from 1.0 wt. % to 10.0 wt. % the YP/PV ratio of the aged drilling fluids have values ranging from 0.38 to 0.43 (Pa/mPa · s), indicating the improvement of the shear-thinning behavior. These results confirm that the addition of JXFQ-6 ranging from 1.0 to 10.0 wt.% can maintain the rheological properties of drilling fluids at a temperature as high as 150°C. Further research must be performed in order to investigate the mechanism of such effect.

Fourier transform infrared spectroscopy and thermogravimetric and differential-thermal analysis

FTIR spectra of original JXFQ-6 and the aged (150°C) drilling fluid samples containing 0, 1.0, and 10.0 wt. % JXFQ-6 were obtained, as shown in Fig. 2. For the drilling fluid without JXFQ-6, the adsorption peaks at 3435, 2850-2930, and 1580 cm-1 correspond to –OH bending, –CH3 and –CH2– stretching vibrations of the alkyl group, and Si–O–Si stretching vibrations in Na–Mt, respectively. However, in the presence of JXFQ-6, a new peak corresponding to the C=O bending emerges gradually at 1621–1500 cm-1.

Fig. 2.
figure 2

FTIR spectra of original JXFQ-6 and the drilling fluids containing different concentrations of JXFQ-6.

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Thermogravimetric and differential thermal analysis (TG-DTA) of the aged (150°C) drilling fluid samples containing 0, 1.0, and 10.0 wt.% JXFQ-6 were also conducted, as shown in Fig. 3. All three samples indicated two major degradation stages. The initial stage in the temperature range of 50°C-120°C corresponding to the first endothermic peak emerging at 100°C in the DTA curves is due to the loss of free and interlayer water absorbed in the interlayer media of Na–Mt. The second stage corresponding to the second endothermic peak emerging at 480°C occurs in the range 250-500°C. It can be seen that, after the second stage of degradation, and the drilling fluid samples containing 1.0 and 10.0 wt.% JXFQ-6 show 35% and 53% mass loss, respectively, in comparison with the samples without JXFQ-6. The mass loss increases remarkably with increase in concentration of JXFQ-6, suggesting that the second stage of degradation involves the loss of JXFQ-6. The results further confirm that JXFQ-6 is successfully intercalated into the drilling fluid structure, and drilling fluids with the addition of JXFQ-6 ranging from 1.0 to 10.0 wt.% can resist temperatures as high as 150°C.

Fig. 3.
figure 3

TG (black lines) and DT (gray lines) patterns of the drilling fluid containing different concentrations of JXFQ-6, wt.% (see numerics on cirves).

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Conclusions

The results showed that addition of JXFQ-6 ranging from 0.1 to 10.0 wt.% can maintain rheological properties of water-based drilling fluids at temperatures as high as 150°C. JXFQ-6 could effectively improve the thermal stability of the WDF. The FTIR analysis and TG-DTA indicated that JXFQ-6 is successfully intercalated into the Na-Mt structure and improved the thermal stability of drilling fluids at temperatures up to 150°C. It was shown that JXFQ-6 is an excellent thermal-resistance viscosifying additive for drilling fluids.