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Synthesis and Performance Evaluation of Quaternary Ammonium Salt as Potential Shale Inhibitor.

Byline: Zhang Jie, Li Lili, Chen Gang, Tang Ying, Zhao Jingrui and Tang Deyao

Summary: Melamine and sodium chloroacetate were used as raw materials to synthesize a kind of quaternary ammonium salt (QAS) as potential clay swelling inhibitor and water-based drilling fluid additive, and the reaction conditions were screened based on the linear expansion rate of bentonite. The inhibitive properties of QASs were investigated by various methods, including montmorillonite (MMT) linear expansion test, mud ball immersing test, particle distribution measurement, thermogravimetric analysis and scanning electron microscopy etc.

The results indicate that QAS can inhibit expansion and dispersion of clay in water effectively. At the same condition, the bentonite linear expansion rate in QAS-2 solution is much lower than those of others, and the hydration expansion degree of the mud ball in 0.5% QAS-2 solution is appreciably weaker than the control test. The compatibility test indicates QAS-2 could be compatible with the conventional additives in water-based drilling fluids, and the temperature resistance of modified starch was improved effectively. Meanwhile, the inhibitive mechanism was discussed through the particle distribution measurement, thermogravimetric analysis and scanning electron microscopy.

Keywords: Quaternary ammonium salts; Inhibitor; Clay; Swelling; Particle size

Introduction

Montmorillonite (MMT) is a 2:1 clay, which has two tetrahedral sheets sandwiching a central octahedral sheet. The particles are plate-shaped with an average diameter of approximately one micrometer. Bentonite, mainly containing montmorillonite, is used in the oil drilling industry as a basic component of drilling fluid, making the drilling fluid viscous, which helps in keeping the drill bit cool and removing drilled solids[1]. However, when water-sensitive clays are exposed to the conventional water-based drilling fluids, depending on the chemical characteristics of the shale, shale has an immediate tendency to take up water from the water-based oilfield working fluid [2-3].

On the other hand, during the drilling of oilfield, great quantities of water-based mud are used, in this process, borehole stability problems such as bit balling, disintegration of cuttings, borehole wash-out and stuck pipe mostly occur in shale formations due to shale hydration and swelling [4]. In recent years, organic amine compounds with high performance shale inhibitor draw much attention of the researchers. This system has obtained wide application around the world with great success because of excellent inhibition, lubrication and stable rheological property and so on [5-6]. As the key additive, quaternary ammonium salt has higher inhibitory and anti-balling abilities, and it is not poisonous and non-hazardous, the use of this drilling fluid could eliminate cost of oil contaminated drilled cuttings disposal [7-8].

Currently, quaternary ammonium compound can be used in various kinds of water-based oilfield working fluid and has superior compatibility with traditional additives, and it can meet environmental protection requirements [9]. In the present work, a series of quaternary ammonium inhibitor were developed with good comprehensive performances which were evaluated through linear expansion, mud balls, particle distribution measurement, thermogravimetric analysis and scanning electron microscopy.

Experimental

Materials

Melamine and sodium chloroacetate were provided by Sinopharm Chemical Reagent Co., Ltd., Potassium chloride and sodium carbonate were purchased from Zhiyuan Chemical Reagent Factory in Tianjin. Bentonite was obtained from Changqing bentonite Group Co., Ltd., China.

Synthesis

A series of quaternary ammonium salts (QASs) was synthesized using melamine and sodium chloroacetate as raw materials. A certain amount of melamine and sodium chloroacetate was dissolved in water with different ratio, refluxing for a certain time. After reaction, the water was evaporated under vacuum pressure, and the product was obtained by recrystallization in ethanol. The reaction process is shown in Scheme-1.

Equations

Scheme-1: Synthesis of quaternary ammonium salt.

Swelling Inhibition and Mud Ball Immersing Test

The hydration swelling of shale is tested by a NP-01 shale expansion instrument according to petroleum and natural gas industry standard SY/T6335-1997 of China. Evaluation of clay inhibitors for water injection Mud ball immersing test is as follows: bentonite (10 g) was used to make a mud ball and the mud ball was immersed in 80mL tap water and other additive aqueous solutions for 36 h. Watch the details of the immersed mud balls, check whether there are cracks or dilapidation on the surface.

Bentonite Inhibition Test

400 mL of water containing certain amount of inhibitor was treated by 2 m/m% drilling fluid bentonite. After stirred for 20 min, the dispersion was hot rolled at 70 for 16 h. Then the rheological properties were measured after the samples were cooled to the room temperature. After that the equivalent amount of drilling fluid bentonite was added and the procedure was repeated until the dispersion became too viscous to be measured [10].

Compatibility Test

350 mL of water-based mud with different additives, such as 0.5%QAS-2, 1.0% modified starch. After aged for 16h, the rheological properties and filtration of the fluid samples were measured using a model ZNN-D6S viscometer (Hai tongda, Co., Ltd., Qingdao, China), including Apparent viscosity (AV), Plastic viscosity (PV), Yield point (YP), Dynamic plastic ratio (YP/PV), API Filtration (FL) and Friction coefficient (). The apparent viscosity, plastic viscosity and yield point were calculated from 300 and 600 rpm readings using following formulas from API Recommended Practice of Standard procedure for field testing drilling fluids (Recommended Practice, 1988):

Equations

Particle Distribution Test 4 m/m% bentonite dispersion was prepared and prehydrated for 24 h. Inhibitors with certain concentrations were added into the dispersion and stirred for 20min, after aged for 24 h, and then the size distribution of the particles was measured by LS-13 320 laser particle size analyzer (Beckman Coulter, Inc., USA) using standard operating procedure.

TGA Analysis

Thermal gravimetric analysis (TGA) experiments were carried out using a TGA/DSC 1/1600 thermal analysis machine (METTLER TOLEDO, Inc, Switzerland) under a flow of nitrogen. The sample weight is about 10 mg, and the temperature ranges from 50 to 800 with a ramping rate of 10 /min under nitrogen flow rate of 20 mL/min.

Scanning Electron Microscopy

The surface morphology of the samples under study in the absence and presence of inhibitors was investigated using a Digital Microscope Imaging scanning electron microscope (Model SU6600, Serial no. HI-2102-0003) at accelerating voltage of 20.0 kV. Samples were attached on the top of an aluminum stopper by means of carbon conductive adhesive tape. All micrographs of the specimen were taken at 5009 magnification.

Results and Discussion

Inhibitor Synthesis

In the reaction of inhibitor synthesis, melamine with three sp hybridized N atoms and three sp hybridized N atoms, can react with sodium chloroacetate in two ways. One is sp hybridized N atoms reacting with sodium chloroacetate, and the other is sp3 hybridized N atoms' reaction. In fact, there is a natural selection due to the different kinds of N atoms. The sp2 hybridized N atom with a pair of unconjugated free electrons can react with sodium chloroacetate in priority. Since there are three sp2 hybridized N atoms, the products of QAS may be various, as shown in Fig. 1. But with the similar structure, it is hard to separate each compound.

Equations

Swelling Inhibition

In order to investigate the influence of quaternary ammonium salts as swelling inhibiter for clay, the swelling rate of bentonite in different QAS solution were evaluated by bentonite linear expansion test. As shown in Table-1, the effect of molar ratio of melamine and sodium chloroacetate on the products' inhibition was investigated as first. The result shows that the linear expansion rate of montmorillonite in QAS-2 solution is much lower than others within 90 min. So QAS-2 was studied in detail.

Table-1: Name and inhibitory activity of quaternary ammonium salts.

###Linear

###Material###Ratio Nomenclature###expansion

###Rate /%

###1:1###QAS-1###64.44

###1:2###QAS-2###57.28

###1:3###QAS-3###59.97

###Sodium

Melamine###1:4###QAS-4###63.52

###chloroacetate

###1:5###QAS-5###58.31

###1:6###QAS-6###60.12

###1:7###QAS-7###61.96

As shown in Fig 2, the swelling rates of bentonite with time in different concentration of QAS-2 solutions were recorded. It shows that the clay swelling rate increases dramatically at the initial 10 min, followed by slow increase. Compared with blank, the swelling rate in 0.5% QAS-2 solution is much lower that of 1.0% QAS-2 solution with the rate of 57.3% and 59.9% respectively within 90 min, indicating that 0.5% QAS-2 can restrain the water affinity of the MMT effectively and 0.5% should be an economical concentration.

Mud Ball Immersing Test

The mud ball immersing test provides a more intuitive way to describe the inhibitive property of QAS. The mud balls were immersed into water and 0.5% QAS-2 solution respectively. Fig. 3 shows the status of the mud balls after immersed for 36 hours. The mud ball immersed in water swelled obviously, and surface loose, while the mud ball immersed in 0.5% QAS-2 solution swelled slightly and the surface is smoother. It is clear that QAS-2 has significant clay swelling inhibition. These phenomena can be explained by the hydrophobic film resulting from absorption of quaternary ammonium compounds on MMT, which blocks the water penetrating into the clay and prevents clay from hydrating swelling.

Bentonite Inhibition Test

The test was projected to simulate the relatively slow incorporation of yielding clays into a drilling fluid. This simulated process usually happens when drilling active clays in the field. As shown in Fig. 4, with the amount of bentonite concentration increasing, yield point of drilling fluid keeps increasing. And yield point increased sharply with the addition of bentonite in fresh water system due to the hydration and dispersion of MMT. Comparing to blank, the lower rheological profile of 0.5% QAS-2 proves that it performs good inhibitive capacity.

Compatibility Test

The results of the compatibility test were shown in Table-2. QAS-2 had influence obviously on the inhibitive property, rheological properties and filtrate loss of the mud systems before and after adding the shale inhibitive additives, indicating that quaternary ammonium inhibitor can effectively restrain the bentonite slurry, but apparent viscosity, yield point, dynamic plastic ratio and API filtration of polymer drilling fluid with QAS-2 were significantly increased at the room temperature, due to flocculation effect of organic amine, and QAS-2 can effectively improve the temperature resistance of modified starch. Thus, quaternary ammonium salts could be compatible with the conventional additives in water-based drilling fluids.

Particle Size Distribution Test

Fig. 5 depicts the particle size distribution of the bentonite dispersions treated with different ways. Compared to control sample, the average size of hydrated bentonite particles was much smaller, and the addition of QAS-2 can only influence the particle size slightly, as shown in Table 3. But it should be noticed that it is different when QAS-2 was added before and after the hydration of bentonite. When QAS-2 was added with virgin bentonite into water together, the dissolved QAS-2 can inhibit the swelling and disperse of bentonite in the way discussed above. When 0.5% QAS-2 was added in the hydrated bentonite mud, the particle size hardly changed.

Thermogravimetric Analysis

Thermogravimetric analysis (TGA) was used to inquiry the thermal stability of bentonite treated with different method, and the result was shown in Fig. 6. Generally, several mass loss steps are observed in the process of decomposition of bentonite immersed in tap water and QAS-2 solution.

Before 300 , the mass loss is assigned to the dehydration of physically adsorbed water and water molecules around metal cations such as Na and Ca2 on exchangeable sites in MMT [11-12]. As shown in Fig. 6, from 50 to 300 , the weight loss of MMT treated with tap water is 4.09%, while the weight loss of QAS-2 modified MMT is 2.47%, indicating that the intercalation of QAS-2 and MMT reduces the water content of bentonite. From 300 to 800 , the two samples keep losing weight, and it is obvious that the weight loss of QAS-2 modified bentonite is less than that of the control sample, which indicates the QAS-2 modified bentonite contains less water than that of the control sample. From this test, it can be conclude that QAS-2 can inhibit the water absorption of bentonite effectively.

Table-2: Compatibility of QAS with common additives in drilling fluid.

T/###Additives###AV###PV###YP###YP/PV###FLAPI###

###/mPas###/mPas###/Pa###Pa/mPas###/mL

###Blank###3.5###2.8###0.7###0.3###13.3###0.0875

25###0.5% QAS-2###4.6###1.4###3.3###2.3###17.5###0.0787

###1.0%Modified starch###6.0###4.0###2.0###0.5###7.5###0.0699

###1.0% Modified starch +0.5% QAS-2###8.9###3.6###5.4###1.5###7.5###0.0875

###Blank###2.4###1.8###0.6###0.3###16.0###0.4348

120###0.5% QAS-2###6.0###2.0###4.1###2.0###22.4###0.0963

###1.0%Modified starch###7.1###4.2###2.8###0.7###2.9###0.0437

###1.0% Modified starch +0.5% QAS-2###9.5###4.2###5.2###1.2###3.8###0.0524

Table-3: Mean and median of bentonite particle dealt with different ways.

###Additives###Mean/m###Median/m

###Virgin bentonite###33.26###26.65

###Hydrated bentonite###10.97###6.11

###Virgin bentonite+0.5% QAS-2###12.34###6.80

###Hydrated bentonite+0.5% QAS-2###10.05###5.58

Scanning Electron Microscopy

In order to evaluate the bentonite particles treated by different ways, SEM was carried out. Fig. 7(a) shows an SEM image of the virgin particles without any treatment. Fig. 7(b) shows SEM images of the particles after immersed in 0.5% QAS-2 solution for 24 h, and Fig. 7(c) shows the particles after immersed in water for 24 h. From the three micrographs, it can be found that after immersed in water or QAS-2 solution, the particles dispersed and change to smaller particles. It also can be seen that the particle size of bentonite treated with QAS-2 solution is larger than that of bentonite treated with water, which is consistent with the results of particle size distribution test [13]. Thus, it could be assumed that, except for electrostatic interaction, hydrogen bonding between amine group and siloxane of clay can further restrict the swelling and hydration of clay minerals.

Conclusions

In this work, quaternary ammonium salts (QASs) were synthesized with melamine and sodium chloroacetate for the use of clay swelling inhibitor. The inhibitive properties were evaluated through bentonite linear expansion, mud balls immersing test, compatibility test, bentonite inhibition test, meanwhile, QAS could be compatible with the conventional additives in water-based drilling fluids. The results showed that 0.5% QAS-2 can inhibit the bentonite linear expansion much effective than others. In addition, the particle distribution measurement, thermogravimetric analysis and scanning electron microscopy results all further prove the efficient inhibition of QAS-2.

Acknowledgment

This work was financially supported by the grants from National Science Foundation of China (50874092) and Scientific Research Program Funded by Shaanxi Provincial Education Department (2013JK0647).

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Publication:Journal of the Chemical Society of Pakistan
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Date:Oct 31, 2015
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