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A strong inhibition of polyethyleneimine as shale inhibitor in drilling fluid
Journal of Petroleum Science and Engineering 161 (2018) 1–8
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A strong inhibition of polyethyleneimine as shale inhibitor in drilling fluid Yuxiu An *, Peizhi Yu College of Engineering and Technology China University of Geosciences (Beijing), Haidian District, Beijing 100083, China
A R T I C L E I N F O
A B S T R A C T
Keywords: Swelling Inhibition Mechanism Polyethyleneimine Shale
In this paper, the inhibition property of polyethyleneimine (PEI) in montmorillonite solution was studied. The inhibition property was evaluated by linear swelling test and rolling recovery test. Compared with other inhibitors, the addition of PEI resulted in the lowest swelling height in drilling fluid. In rolling recovery rate study, the addition of PEI resulted in the highest recovery rate after rolled at 120 C.More importantly, PEI was environmental friendly inhibitor. The inhibition mechanism was investigated by Fourier transform infrared spectroscopy, X-ray diffraction, Transmission electron microscope, Scanning electron microscopy, Atomic force microscope, Zeta potential and Particle-size analyzer. The spectrums and images showed that the negative charge in the surface of montmorillonite (MMT) was neutralized by the positive charge in amino group of PEI. PEI was adsorbed in the surface and intercalated into interlayer of MMT, which reduced the hydration repulsion of diffuse electric double layer and prevented the invasion of water. Hydrogen bonding between hydroxyl in the surface of clay and amino groups in the backbone and side chain of PEI can be formed in the process. The adsorption and intercalation of PEI in the surface and interlayer of MMT was the major factor to prevent water molecules from invading into the gallery of clay. There were a quantity of positive ions in solution because of the protonation of nitrogen in water. More positive ions resulted in the stronger force between inhibitor and clay.
1. Introduction In oil and gas drilling operations, wellbore instability problem of shale is frustrating drilling engineers and exporters as these rocks make up over 75% of drilled formation (Rajnauth, 2012). The instability of shale formation results in serious operational problems, following major economic consequences for petroleum production and exploration (Al-Bazali, 2011; Akhtarmanesh et al., 2013; Karatela et al., 2016; Ma et al., 2015). More than 90% of wellbore instability problems are caused by problematic shale (Josh et al., 2012). It is one of the most significant technical problems in petroleum exploration and a major source of lost time and revenue. Cuttings from drilling shale and swelling of shale lead to various problems such as tight hole, stuck pipe, hole collapse and hole enlargement in drilling operation. These problems result in wellbore instability (Bybee, 2009; Rahman et al., 2000; Yu et al., 2003; Chen et al., 2003; Mohiuddin et al., 2007). In drilling operations, one important function of drilling fluid is to prevent compacted clay minerals from taking up water continuous from drilling fluid (Suter et al., 2011). The invasion of water resulted in the swelling and hydration of clay minerals, which is considered as a major causal factor that leads to instability of shale (van Oort, 2003). The
* Corresponding author. E-mail address: [email protected] (Y. An).
degree of swelling of different clay minerals exhibited great difference. Smectite caused serious hydration when encountering water whereas kaolinite was unhydrated in water solution. Different composition of clay mineral exhibited different hydration capacity. In clay minerals, montmorillonite is considered as a major causal composition to cause the swelling of clay. Inhibiting the swelling of montmorillonite is an effective way to control wellbore instability (Díaz-Perez et al., 2007; Paikaray et al., 2008; Bunger et al., 2014). The clay is unhydrated in oil based fluid. Oil based fluid is the preferred system in drilling these shale formations (Shivhare and Kuru, 2014). But fatal environment issues exist in the use of oil based fluid (Patel et al., 2007). Oil based fluid is not biodegradable and harmful for health and environment. Due to potential detrimental effects in the application of non-environment friendly oil based fluid, Environment Protection Agency and other regulatory bodies are imposing increasingly stringent regulations on the use and disposal of non-environment friendly oil based drilling fluid. It has been desirable to drill shale formations with water based fluid. Inhibitor is an available means to prevent clay from swelling in drilling shale formation with water based fluid. The drilling fluid industry has been searching for inhibitive water based fluid for years. Recently, the development of high-performance inhibitor has caused extensive research. Qiu group reported poly(oxypropylene)-amidoamine (POAA) was a potential inhibitor in water based fluid (Zhong et al., 2012). Qu group studied the inhibition of polyoxyalkyleneamine as shale inhibitor (Qu et al., 2009). Borges group evaluated the swelling ability of clay with different organic
https://doi.org/10.1016/j.petrol.2017.11.029 Received 26 June 2017; Received in revised form 26 September 2017; Accepted 13 November 2017 Available online 16 November 2017 0920-4105/© 2017 Elsevier B.V. All rights reserved.
Y. An, P. Yu
Journal of Petroleum Science and Engineering 161 (2018) 1–8
Montmorillonite (MMT drilling fluid level) was supplied by Weifang Huawei Bentonite Group Co., Ltd. Shale was obtained from oil field. The other experimental chemicals were purchased from domestic reagent company. All the chemical materials were used without further purification.
compounds and inorganic salt solutions (Balaban et al., 2015). Shadizadeh group reported a novel nonionic surfactant for inhibiting shale hydration (Shadizadeh et al., 2015). Our group evaluated the inhibition of chitosan quaternary ammonium salt (HTCC) (An et al., 2015). The commonly used inhibitors include KCl, CaCl2, NH4Cl, modified gilsonites and asphalts (Davis and Tooman, 1989; Gholizadeh-Doonechaly et al., 2009; Xiong et al., 2012). However, these approaches have some disadvantages such as short effectiveness, toxicity, low heat and salinity tolerance and pH sensitivity. Although some issues have been solved (Bonini et al., 2009), the hydration of water-sensitive shale is still not controlled completely, especially in drilling shale formation with water based fluid. Clay-particle is electronegative (Tang et al., 2014), then the effective shale inhibitor ought to be electropositive or nonionic. Coveney group recently reported the rule based design of clay swelling inhibitors (Suter et al., 2011). The rule showed that water soluble, hydrophobic backbone and primary di-amine or mono-quaternary amine functionality should be possessed by cationic inhibitors. Polyethyleneimines(PEIs) are water soluble polymers with a quantity of cationic groups (Poghosyan et al., 2015; Foundas et al., 2015; Neville et al., 2013). Their solutions were alkaline (Rajagopalan et al., 2015). More importantly, it was environmental friendly. Polyethyleneimines have been widely applied in bioengineering (Wang et al., 2015a,b; Liu et al., 2015; Zhu et al., 2015), paper industry (Wang et al., 2015a,b), waste water treatment industry (Adewunmi et al., 2015), catalyst (Park and Kim, 2015; Zakharova and Syakaev, 2009) and sensor (Li et al., 2015). Polyethyleneimines are synthesized by ring opening polymerization of ethylene mine. There are a series of products which are classified by molecular weight and structure. In our previous work, our group evaluated the inhibition capacity of PEIs with montmorillonite. PEIs exhibited high performance of inhibiting montmorillonite to hydrate compared with other commonly used inhibitors. We studied the effect of molecular weight on inhibition property of PEIs. The results showed that the addition of PEI10000 resulted in the lowest swelling height. But the detailed interaction mechanism between PEI10000 and montmorillonite was not studied especially for the effect of temperature. In this paper, we evaluate the inhibiting property of PEI10000 at different temperatures and explore the inhibition mechanism with a variety of characterization methods. We wish to provide the guide of the application of polyethleneimines in drilling shale formation with water based fluid. The swelling mechanism of MMT with PEI was showed in Fig. 1.
2.2. Inhibitive properties 2.2.1. Linear swelling tests The expansion height of montmorillonite solution with polyethyleneimine or other inhibitors is determined by CPZ-2 channel linear swellmeter (QingdaoTongchun,China). 5 g MMT or MMT(KSF) is poured into pressure tank, then be kept for 5 min at 10 MPa pressure by hydraulic press. A certain concentration inhibitor solution is prepared. Then the solution is poured into pressure tank and the value is recorded zero. The expansion height with time is recorded. 2.2.2. Rolling recovery tests Shale was sieved and crushed between 6 meshes and 10 meshes. 20 g shale debris was prepared. The concentration of shale inhibitors solution is fixed on 2 wt%. 300 ml solution and 20 g shale debris was put into digestion tank. Then the digestion tanks were put into the BGRL-5 roller furnace (Qing dao, China) and rolled at 150 Cfor 16 h. The upper suspension was poured away after the solution is cooled to room temperature. Then adding 200 ml deionized water, and the procedure was repeated for three times. Precipitate is dried at 100 C for 48 h. And then these precipitates were sieved to 40 meshes and weighted. Changing the rolled temperature to 80 C, 100 C, 120 C, 130 C and 140 C. Hot rolled, cooled, washed suspension, dried and weighted, then the procedure was repeated. The rolling recovery rate is calculated by the following formula: Recovery ¼ W2/W1. Shale debris denoted by W1 and that after hot rolling denoted by W2.
2. Materials and methods
2.2.3. Preparation of MMT/PEI hybrids and the purification of PEI 300 ml aqueous solutions of PEI were prepared. The concentrations of PEI solution are fixed on 0, 0.5 wt%, 1 wt%, 2 wt% and 4 wt%. Then 6 g MMT was added into PEI solutions to make PEI/MMT suspension and the suspension was under vigorous stirring for 30 min at 8 000 rpm. Then the suspension bear rolling at 80 C for 16 h to balance the adsorption and hydration between MMT and PEI. Centrifugal treatment was carried out at 10 000 rpm for 15 min. The precipitate was washed several times by deionized water until the upper liquid was clear. Finally the precipitate was dried at 100 C for 24 h. Then be grinded into powder for FT-IR. and XRD.
2.1. Materials
2.3. Structure characterization techniques
Polyethleneimine (PEI10000) was purchased from Gobekie Reagent Company. Chitosan quaternary ammonium salt (HTCC) (Mn 54 000 Da, Quaternary salt graft degree 60–80%, Purity 95%) was purchased from Jiaxing Kerui Biological Technology Co., Ltd. Polyether amine was obtained from MI-SWACO. Montmorillonite (KSF) was purchased from Aladdin Inc.
2.3.1. Fourier transforms infrared spectroscopy (FT-IR) measurements FT-IR spectral analyses of MMT/PEI hybrid were recorded by MagnaIR 560 spectrometer. 2 mg sample and 200 mg KBr was fully blend. The mixture was put into the mold and kept at 50 MPa pressure by hydraulic press.
Fig. 1. Schematic representation of MMT swelling mechanism: (a) without PEI and (b) with PEI. 2
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Journal of Petroleum Science and Engineering 161 (2018) 1–8
Fig. 2. Linear swelling curves of MMT (KSF) in inhibitors solutions: (a) different concentration of PEI solutions and (b) solutions of different inhibitors (the concentration of inhibitor solutions was 4 wt %).
2.3.2. X-ray diffraction (XRD) measurements MMT and MMT/PEI hybrid spectra analyses of XRD were recorded by D8 Advance Diffractometer. The patterns were collected with 2θ angle scanning between 0.5 and 10 . The basal spacing was analyzed by using Bragg's equation. The value for n ¼ 1 was calculated from 2dsinθ ¼ nλ (λ ¼ 1.5406 nm). The samples were put into mold, and then be compacted.
ultrasonicator at room temperature for 20 min. Different dosage of PEI solutions were added in MMT aqueous suspension to make a series of MMT/PEI suspensions.
2.3.3. Scanning electron microscopy (SEM) SEM analyses were performed by a Quanta 200F scanning electron microscope. 10 ml PEI solutions were prepared. The concentrations of PEI were 0, 0.5 wt%, 1 wt%, 2 wt% and 4 wt%. Then every 10 mg MMT was poured into PEI solutions. The mixed solutions were dispersed by ultrasonicator at room temperature for 10 min, and then the solutions were kept for 24 h. 1 drop of solution was added to filter cake. The filter cakes were dried at 80 C for 6 h. The dried samples were adhered to adhesive tapes, and then metal sprayed for 2 min.
Based on evaluation procedure of shale inhibitor in drilling fluid, the most frequently methods are to evaluate the performance of linear swelling test and rolling recovery rate test. The linear swelling test reveals the property of inhibiting clay from swelling that prevents wellbore instability. The rolling recovery rate test is designed to simulate the change of shale caused by inhibitor. Herein the two methods are combined to estimate the inhibiting property of PEI, from which we can make a clear judgment on the prospect of PEI as an excellent shale inhibitor.
3. Results and discussion 3.1. Inhibition evaluation
3.1.1. Linear swelling tests The linear swelling heights of MMT (KSF) in water solution with and without PEI were exhibited in Fig. 2. The swelling curves of all samples showed a similar tendency with strong increase in first 120 min and kept stable after 180 min. The swelling heights of MMT (KSF) in different inhibitor solutions were similar to those in water, indicating the serious hydration of MMT (KSF) (Fig. 2b). MMT (KSF) was purchased from Aladdin Inc. The specific surface area of MMT (KSF) was 20–40 m2/g. It is possible that the high specific surface area resulted in the strong hydration capability. Despite the fact that the addition of PEI resulted in the lowest swelling height, the height was up to 8.28 mm. Compared with that in water solution, the anti-swelling rate of PEI solution was only 19%, indicting the worse inhibition ability at this condition. Continuing to add PEI, the swelling height of MMT (KSF) declined slightly (Fig. 2a). The results further proved the worse inhibition of PEI with MMT (KSF). To further exhibit the different inhibition ability of inhibitors, we used montmorillonite (MMT) in place of MMT (KSF). The linear swelling heights of pristine MMT in water and different addition of PEI solutions were exhibited in Fig. 3. The swelling curves of all samples showed a similar tendency with strong increase in first 120 min and slower growth after 120 min, according with swelling behavior of MMT in aqueous solution. But the swelling heights of MMT were significantly different between in water and in PEI solution. The MMT continues to swell in water until 960 min, but the swelling heights of MMT in PEI solutions were nearly stable after 600 min. It is observed the growth of swilling curves of MMT in PEI solutions is slower than that in water, leading to the significant decrease of swelling height at the end of test. The phenomenon results from interaction between PEI and montmorillonite because PEI was water-soluble polymer with a quantity of cation groups and MMT was sheet with a quantity of negative charges in the side of sheet. PET
2.3.4. Transmission electron microscopy (TEM) TEM analyses were performed by a F20 transmission electron microscope. 10 ml PEI solutions were prepared. The concentrations of PEI were 0, 0.001 wt%, 0.010 wt% and 0.100 wt%. Then every 5 mg MMT was poured into PEI solutions. The mixed solutions were dispersed by ultrasonicator at room temperature for 2 min, and then the solutions were kept for 24 h. 1 drop of solution was added to carbon membrane. The carbon membranes were dried at infrared light for 20 min. 2.3.5. Atomic force microscopy (AFM) AFM analyses were performed using a SPM-9 600 instrument. 50 ml PEI solution was prepared. The concentrations of PEI were 0 and 0.01 wt %. Then every 5 mg MMT was poured into PEI solutions. The mixed solutions were dispersed by ultrasonicator at room temperature for 2 min, and then the solutions were diluted 5 times and kept for 24 h. 10 μL solution was added to mica sheet. The samples were dried at room temperature for 6 h. 2.3.6. Particle size analysis The suspensions were analyzed by Zetasizer Nano ZS instrument. A series of 0.1 wt% MMT suspensions were prepared and dispersed by ultrasonicator at room temperature for 20 min. Different dosage of PEI solutions were added into MMT aqueous suspension to make a series of MMT/PEI suspensions. 2.3.7. Zeta potential measurements The suspensions were analyzed by Zetasizer Nano ZS instrument. A series of 0.1 wt% MMT suspensions were prepared and dispersed by
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Journal of Petroleum Science and Engineering 161 (2018) 1–8
was similar to polyether amino. They were both adsorption groups in backbone and cation ions in the side chain. The quantity of positive ions in HTCC was more than that in polyether amino. The reasons of this phenomenon are as follows. Repeat unit with one positive ion was in HTCC, if the grafted percent of HTCC was 100%. The quantity of positive ions were calculated by polymerization degree multiply by grafted percent. Grafted percent of quaternary ammonium salt was about 60%– 80% and polymerization degree (Mn) of HTCC was about 54000Da. The quantity of positive ions was more than 32 400 in one polymer. But the positive ions of polyether amino were in the end group, and there are two positive ions in one polymer. So the quantity of positive ions in HTCC was far more than that in polyether amino. The positive ions in HTCC and polyether amino were attracted by the negative ions in clay particle, and the more positive ions the bigger force between polymer and clay particle, and the better inhibiting ability of polymer. The inhibiting ability of KCl was evidently weaker than that of other inhibitors in the same condition. KCl was inorganic substance, and the interaction mechanism with clay was different from organic polymers, and the durability of inhibition property was shorter than the polymer inhibitors. PEI contained a quantity of nitrogen atoms in the backbone and side chain, leading to more positive ions than in HTCC because of the protonation of nitrogen in water. As mentioned above, the more positive ions resulted in the stronger force between inhibitor and clay particle, leading to the better inhibition ability of PEI.
Fig. 3. Linear swelling curves of MMT with different concentrations of PEI solutions.
was adsorbed in the side of MMT through attraction between cation groups and negative charges. Meanwhile there were a few of nitrogen and hydrogen atoms in PEI and hydrogen bonds were formed between PEI and MMT. The swelling curves increased strongly in the first 180 min, but grew more slowly after 180 min. With the addition of PEI, the swelling height of MMT reduced significantly. The interaction mechanism between PEI and MMT was a key factor to control the inhibition ability of PEI. Possibly the molecular motion of PEI made great contribution to inhibition capability. However, the dosage of PEI was still a key factor to control inhibition capability. The increasing dosage of PEI improved the inhibiting ability of PEI. Fig. 4 showed the inhibition ability of different inhibitors. KCl and polyether amino were commonly used in oil field as inhibitor. The diameter of Kþ was fairly with interlamellar spacing of MMT, so the Kþ entered into the interlamellar of MMT, preventing the water from invading. Polyether amino was a kind of watersoluble polymer with polyether in backbone and amino groups in the end group. Polyether amino was adsorbed in the surface of MMT through a few of ether groups and amino groups. It was taken as inhibitor in recent years and was core additive in high performance water based fluid system. HTCC was water-soluble chtiosan quaternary ammonium salt with a quantity of quaternary ammonium groups in the side chain. The detailed inhibiting ability of HTCC was studied in our earlier work. The concentrations of inhibitors were fixed 4 wt%. The swelling curve of MMT in water increased gradually within 960 min. With the addition of inhibitors, the swelling curves of MMT grew strong in the first 120 min, but increased slowly significantly after 120 min. The swelling heights of MMT in KCl, polyether amino, HTCC and PEI solutions were 2.92 mm, 2.35 mm, 1.98 mm and 1.41 mm. The corresponding reduction rates were 50.7%, 60.3%, 66.6% and 76.2%. It was clear that PEI solution exhibited high performance as inhibitor. Structure composition of HTCC
3.1.2. Rolling recovery tests The rolling recovery rate tests exhibited the change of shale in inhibitor solution. The shale was hydrated seriously once put into water. The hydration of shale resulted in weight decrease. Inhibitor solution prevented the shale from hydrating. The ability of inhibitor was characterized by the weight change of shale. The rolling recovery rate was linear relation with weight change of shale during rolled progress. The higher rolling recovery rate exhibited better inhibiting ability. Fig. 5 showed that the rolling recovery rate of shale debris in different inhibitor solutions at different temperature. In water, the shale debris exhibited the lowest rolling recovery rate both at low temperature and high temperature. In KCl solution, the rolling recovery rate of debris was higher than that in water, but significantly lower than that in other inhibitor solutions. The debris kept highest rolling recovery rate in polyether amino solution before 120 C. But debris exhibited hightest rolling recovery rate in PEI solution after 120 C. The rolling recovery rate of debris in HTCC solution was always between that in polyether amino solution and that in PEI solution at different temperature. The rolling recovery rate of debris in PEI solution was up to 96% after rolled at 150 C, however, it was only 17% in water at some condition. The value of rolling recovery rate in polyether amino solution reduced with
Fig. 4. Linear swelling curves of MMT in different inhibitor solutions. The concentrations of inhibitor solutions were 4 wt%.
Fig. 5. Rolling recovery of inhibitors at different temperature. The concentrations of inhibitors were 2 wt%. 4
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water stretching bond were blue-shift 24 cm1 and 36 cm1. With the addition of PEI, the shift of physisorbed water stretching peak increased, exhibiting the incorporation of PEI with physisorbed water in MMT solution. The shift of water deformation bond increased with the addition of PEI, indicating hydrogen bonds were formed between deformation water and PEI. The quantity of hydrogen bonds increased with the addition of PEI, but red-shift of Si-O had nothing to do with the dosage of PEI, exhibiting hydrogen bonds between Si-O and N-H were saturated quickly. The vibration bonds of Al-O and Si-O (500-1000 cm1) were shifted in different degree. It further indicated the formation of hydrogen bond between MMT and PEI. PEI was adsorbed in the surface of MMT through hydrogen bond and entered into the interlayer of MMT through ionic bond and hydrogen bond. 3.2.2. X-ray diffraction As showed in Fig. 7. XRD patterns of pristine MMT and MMT/PEI hybrids were presented. A typical monolayer hydration interlayer d(001) spacing of 1.31 nm was displayed in XRD pattern of pristine MMT. With the addition of PEI, XRD patterns of MMT were modified due to the interlayer adsorption of PEI in the surface of MMT. With addition of PEI the d(001) spacing of MMT increased from 1.31 nm to 1.38 nm, 1.40 nm, 1.41 nm and 1.40 nm. The gallery height contributed by water was about 0.15 nm after 0.96 nm of layer thickness and 0.2 nm of hydrogen bond length were subtracted, exhibiting the MMT swelled seriously. With the addition of PEI, the gallery heights of MMT/PEI were about 0.22 nm, 0.24 nm, 0.25 nm and 0.24 nm. The results indicated that the monolayer structure of PEI could be observed in interlayer. The hydrogen bonds were formed between the N atoms and H atoms of N-H and H atoms and O atoms on the interlayer of MMT. The expansion of d(100) spacing increased and then no longer continued increasing with the addition of PEI, resulting from the intercalation of PEI. PEI was inserted into interlayer of MMT and then prevented the invasion of water.
Fig. 6. FT-IR spectra of MMT and MMT/PEI hybrids with different addition of PEI.
temperature because of the hydrolyzation of ether bond at high temperature. However, the value of rolling recovery rate in PEI solution increased with temperature, exhibiting the opposite change compared with polyether amino solution. There was no hydrolysable group in PEI molecule, resulting in the stability of PEI solution. But another factor should be considered. The water molecule acted acutely at high temperature, and then desorption between clay particle and water molecule became violent. The hydration of clay particle was weaker. The stability of PEI solution and the weaker hydration of clay particle at high temperature were two key contributions to high-performance of PEI solution, comparing to other inhibitors. 3.2. Inhibition mechanism analysis 3.2.1. Infrared spectroscopy The infrared spectra of pristine MMT and MMT/PEI hybrids were showed in Fig. 6. A typical characteristic of smectite group was presented in FT-IR pattern of pristine MMT. Some of the major peaks of functional group were showed as follow: stretching band of O-H (3622 cm1), physisorbed water stretching band (3441 cm1), water deformation band (1641 cm1), stretching band of Si-O (1035 cm1), vibration bands of AlAl-OH (914 cm1), vibration band of (797 cm1). In the spectrums of MMT/PEI hybrids, some relatively peaks assigned to PEI were observed. The new stretching bonds of N-H (2951 cm1, 2851 cm1and1472 cm1) were appeared, which indicated the incorporation of PEI to MMT. Compared with pristine MMT, the peaks of stretching bond of O-H and physisorbed water streching bond were blue shifted. Therefore, the peaks of water deformation bond and stretching band of Si-O were red shifted, but the peaks of vibration bonds of Al-AlOH and Al-O and Si-O were almost unchanged. The peaks of stretching bond of O-H were about blue-shift 1 cm1, but the peaks of physisorbed
3.2.3. Scanning electron microscopy MMT and PEI/MMT were also characterized by Scanning electron microscopy (SEM) and their images were reflected in Fig. 8. The images revealed different association modes of pristine MMT and MMT/PEI. The pristine MMT was seriously hydrated and swelled (Fig. 8). But PEI/MMT hybrids were mild hydrated and clay particle were bigger than pristine MMT (Fig. 8b–e). The addition of PEI resulted in the hydration of clay particle sharply reduced. The size of clay particle increased obviously, compared with the size of clay particle without PEI. It revealed that PEI exhibited high performance as inhibitor to prevent the clay particle from hydrating. 3.2.4. Transmission electron microscopy The transmission electron microscope (TEM) images were showed in Fig. 9. The image of pristine MMT revealed that the clay sheets reduced, resulting from the hydration of MMT (Fig. 9a). There was a large quantity of small nano sheets under 200 nm. With the addition of PEI, small nano sheets were not observed and taken place by larger sheets (Fig. 9b–d). The hydration of clay particle was inhibited in PEI solution. 3.2.5. Atomic force microscopy The atomic force microscopy (AFM) images were exhibited in Fig. 10. A large quantity of nano sheets were observed in Fig. 11a. The height of nano sheets was about 8.91 nm, indicating the sheets dispersed well. But the opposite observation was showed in Fig. 11b. The size of sheets was in the range of micron. The height of clay sheets was about 401.74 nm, exhibiting the clay sheets aggregated seriously. The results showed clay particle hydrated seriously in water, but the hydration of clay particle was inhibited in PEI solution. The observations were accordant with the observations in TEM images. 3.2.6. Particle size analysis As showed in Fig. 11, particle size analysis of pristine MMT and
Fig. 7. X-ray diffraction patterns of MMT/PEI hybrids with different addition of PEI. 5
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Journal of Petroleum Science and Engineering 161 (2018) 1–8
Fig. 8. SEM images of pristine MMT and MMT/PEI hybrid with different addition of PEI: (a) pristine MMT; (b) 0.5 wt%; (c) 1.0 wt%; (d) 2.0 wt%; (e) 4.0 wt%.
size of MMT increased after the addition of PEI. The results showed that a small number of positive charges benefited the dispersion of MMT and a large quantity of positive charges resulted in serious aggregation. It further proved that the interaction between clay MMT and PEI occurred through ionic bonds.
MMT/PEI hybrid was presented. The average size of pristine MMT was about 500 nm. 0.001 wt% PEI was added into MMT suspension. The average size of MMT was under 100 nm. A small number of positive charges of PEI was attracted by the negative charges of MMT, resulting in better dispersion of clay sheets. With the addition of PEI, the number of positive charges increased. The attraction force between PEI and MMT is strengthened. There were many more MMT sheets around one PEI molecule, leading to serious aggregation of MMT. And then the average
3.2.7. Zeta potential The zeta potential evaluations of MMT and MMT/PEI solutions were
Fig. 9. TEM images of pristine MMT and MMT/PEI hybrid with different addition of PEI: (a) pristine MMT; (b) 0.001 wt%; (c) 0.010 wt%; (d) 0.100 wt%. . 6
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Journal of Petroleum Science and Engineering 161 (2018) 1–8
Fig. 10. AFM images of pristine MMT and MMT/PEI hybrid with 0.010 wt% of PEI: (a) pristine MMT; (b) 0.010 wt% PEI.
MMT. Then PEI intercalated the interlayer of MMT. On the account of large quantities of side chains in PEI, it was easy to enter into the interlayer of MMT, strengthening the driven force between PEI and MMT.
presented in Fig. 12. The negative surface charges were formed by the isomorphous substitution in the octahedral layer [46]. The addition of positive charges in the interlayer space broke charge balance. The zeta potential of MMT after hydrated was 1.23 mV and presented worse dispersion in water. The addition of PEI resulted in the decrease of zeta potential of MMT suspension. The zeta potential of MMT was reversed due to the addition of 0.001 wt% PEI solution, indicating better dispersion. With the addition of PEI, the zeta potential of MMT declined and kept stable at 0.100 wt% PEI solution, indicating that the colloidal of MMT became agglomerate. The positive charges in the backbone and side chain of PEI were neutralized by the negative charges in MMT, leading to the instability of MMT. Continuing to add PEI, the zeta potential of PEI/MMT waved between 0 eV and 2.5 eV, indicating the instability of MMT colloidal. PEI molecules were adsorbed and desorbed simultaneously in the surface of MMT. Then the adsorption and desorption reached equilibrium, leading to the hydration repulsion of double electrostatic layer and dispersion of clay particle. The results of Zeta potential test were according with particle size tests.
4. Conclusions In summary, the adsorption of PEI in the surface of MMT and the intercalation in interlayer of MMT inhibited the hydration of MMT, and positive ions in PEI interacted with negative ions in clay particle. Inhibition mechanism of MMT in PEI solution was studied. The conclusions provided us the method to develop shale inhibitor with high performance in montmorillonite solution and the guidance of operational parameters in drilling operations. The value of linear swelling height showed the inhibiting ability of PEI was better than that of other inhibitors. The addition of PEI solution resulted in largest rolling recovery rate after rolled at 120 C. The rolling recovery rate of debris in PEI solution was up to 96% after rolled at 150 C, compared with that 17% in water at same condition. The rolling recovery rate of debris in PEI solution increased with temperature, but it exhibited opposite change in polyether amino solution. It further proved the poor temperature resistance resulting from serious hydrolyzation of ether bond at high temperature. PEI solution showed high-performance at high temperature compared with other inhibitors. The structure composition of PEI was similar to that of HTCC and polyether amino, and all the backbone contained adsorption groups and the side chain was with cation ions. Polyether amino lost the
3.2.8. Probable inhibition mechanism The experimental and mechanism analysis of inhibiting ability of PEI was studied. PEI solution contacted with MMT suspension, and negative charges were neutralized by positive charges in the backbone and side chain of PEI through the coordination of electrostatic attraction and hydrogen bond, and then PEI was adsorbed in the side surface of MMT. The amino groups as adsorption groups were adsorbed in the surface and the interlayer of MMT, which leaded to the weakening and even the collapse of the diffuse double layer, further resulted in the aggregation of
Fig. 11. Particle size of pristine MMT and MMT/PEI hybrid with different addition of PEI.
Fig. 12. Zeta potential of MMT particles in PEI solutions. 7
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inhibiting ability because of the hydrolyzation of ether bond at high temperature. But HTCC with higher molecular weight was curl and reduced the hydrolyzation of ether bond, leading to better inhibiting ability of HTCC. Compared with HTCC, there was a quantity of nitrogen atoms in the backbone and side chain of PEI, leading to more positive ions than those in HTCC molecular because of the protonation of nitrogen in water. As mentioned above, more positive ions resulted in stronger force between inhibitor and clay particle, leading to better inhibition ability. Meanwhile some problems still exist. PEI is more expensive than HTCC and polyether amino, and then how to reduce cost is the key issue. On the other side, the compatibility of PEI with other agents commonly used in drilling fluid needs further research. The next work is in progress.
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Acknowledgements We would like to thank for the financial support from National Natural Science Foundation of China (51474231), Foundation for innovative Research Groups of the Natural Science Foundation of China (51221003), National 863 Foundation of China (2013AA064803 and 2012AA091502) and New method and technology Foundation of China National Petroleum Corporation (2014A-4212) for this work. References Adewunmi, A.A., Ismail, S., Sultan, A.S., 2015. Study on strength and gelation time of polyacrylamide/polyethyleneimine composite gels reinforced with coal fly ash for water shut-off treatment. J. Appl. Polym. Sci. 132 (n/a-n/a). Akhtarmanesh, S., Shahrabi, M.J.A., Atashnezhad, A., 2013. Improvement of wellbore stability in shale using nanoparticles. J. Petroleum Sci. Eng. 112, 290–295. Al-Bazali, T.M., 2011. The consequences of using concentrated salt solutions for mitigating wellbore instability in shales. J. Petroleum Sci. Eng. 80, 94–101. An, Y., Jiang, G., Ren, Y., 2015. An environmental friendly and biodegradable shale inhibitor based on chitosan quaternary ammonium salt. J. Petroleum Sci. Eng. 135, 253–260. Balaban, R. d. C., Vidal, E.L.F., Borges, M.R., 2015. Design of experiments to evaluate clay swelling inhibition by different combinations of organic compounds and inorganic salts for application in water base drilling fluids. Appl. Clay Sci. 105–106, 124–130. Bonini, M., Debernardi, D., Barla, M., Barla, G., 2009. The mechanical behaviour of clay shales and implications on the design of tunnels. Rock Mech. Rock Eng. 42, 361–388. Bunger, A.P., Sarout, J., Kear, J., Delle Piane, C., Detournay, E., Josh, M., Dewhurst, D.N., 2014. Experimental chemoporoelastic characterization of shale using millimeterscale specimens. J. Petroleum Sci. Eng. 118, 40–51. Bybee, K., 2009. Wellbore-stability Performance of Water-based-mud Additives. Society of Petroleum Engineers. SPE-0909-0078-JPT. Chen, G., Chenevert, M.E., Sharma, M.M., Yu, M., 2003. A study of wellbore stability in shales including poroelastic, chemical, and thermal effects. J. Petroleum Sci. Eng. 38, 167–176. Davis II, N., Tooman, C.E., 1989. New Laboratory Tests Evaluate the Effectiveness of Gilsonite Resin as a Borehole Stabilizer. Society of Petroleum Engineers, p. 17203. Díaz-P erez, A., Cortes-Monroy, I., Roegiers, J.C., 2007. The role of water/clay interaction in the shale characterization. J. Petroleum Sci. Eng. 58, 83–98. Foundas, M., Britcher, L.J., Fornasiero, D., Morris, G.E., 2015. Effects of polyethyleneimine–phosphonate–carboxylic copolymers on the dispersion of boehmite particles. Colloids Surfaces A Physicochem. Eng. Aspects 466, 10–17. Gholizadeh-Doonechaly, N., Tahmasbi, K., Davani, E., 2009. Development of Highperformance Water-based Mud Formulation Based on Amine Derivatives. Society of Petroleum Engineers, p. 121228. Josh, M., Esteban, L., Delle Piane, C., Sarout, J., Dewhurst, D.N., Clennell, M.B., 2012. Laboratory characterisation of shale properties. J. Petroleum Sci. Eng. 88–89, 107–124. Karatela, E., Taheri, A., Xu, C., Stevenson, G., 2016. Study on effect of in-situ stress ratio and discontinuities orientation on borehole stability in heavily fractured rocks using discrete element method. J. Petrol. Sci. Eng. 139, 94–103.
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Journal of Petroleum Science and Engineering journal homepage: www.elsevier.com/locate/petrol
A strong inhibition of polyethyleneimine as shale inhibitor in drilling fluid Yuxiu An *, Peizhi Yu College of Engineering and Technology China University of Geosciences (Beijing), Haidian District, Beijing 100083, China
A R T I C L E I N F O
A B S T R A C T
Keywords: Swelling Inhibition Mechanism Polyethyleneimine Shale
In this paper, the inhibition property of polyethyleneimine (PEI) in montmorillonite solution was studied. The inhibition property was evaluated by linear swelling test and rolling recovery test. Compared with other inhibitors, the addition of PEI resulted in the lowest swelling height in drilling fluid. In rolling recovery rate study, the addition of PEI resulted in the highest recovery rate after rolled at 120 C.More importantly, PEI was environmental friendly inhibitor. The inhibition mechanism was investigated by Fourier transform infrared spectroscopy, X-ray diffraction, Transmission electron microscope, Scanning electron microscopy, Atomic force microscope, Zeta potential and Particle-size analyzer. The spectrums and images showed that the negative charge in the surface of montmorillonite (MMT) was neutralized by the positive charge in amino group of PEI. PEI was adsorbed in the surface and intercalated into interlayer of MMT, which reduced the hydration repulsion of diffuse electric double layer and prevented the invasion of water. Hydrogen bonding between hydroxyl in the surface of clay and amino groups in the backbone and side chain of PEI can be formed in the process. The adsorption and intercalation of PEI in the surface and interlayer of MMT was the major factor to prevent water molecules from invading into the gallery of clay. There were a quantity of positive ions in solution because of the protonation of nitrogen in water. More positive ions resulted in the stronger force between inhibitor and clay.
1. Introduction In oil and gas drilling operations, wellbore instability problem of shale is frustrating drilling engineers and exporters as these rocks make up over 75% of drilled formation (Rajnauth, 2012). The instability of shale formation results in serious operational problems, following major economic consequences for petroleum production and exploration (Al-Bazali, 2011; Akhtarmanesh et al., 2013; Karatela et al., 2016; Ma et al., 2015). More than 90% of wellbore instability problems are caused by problematic shale (Josh et al., 2012). It is one of the most significant technical problems in petroleum exploration and a major source of lost time and revenue. Cuttings from drilling shale and swelling of shale lead to various problems such as tight hole, stuck pipe, hole collapse and hole enlargement in drilling operation. These problems result in wellbore instability (Bybee, 2009; Rahman et al., 2000; Yu et al., 2003; Chen et al., 2003; Mohiuddin et al., 2007). In drilling operations, one important function of drilling fluid is to prevent compacted clay minerals from taking up water continuous from drilling fluid (Suter et al., 2011). The invasion of water resulted in the swelling and hydration of clay minerals, which is considered as a major causal factor that leads to instability of shale (van Oort, 2003). The
* Corresponding author. E-mail address: [email protected] (Y. An).
degree of swelling of different clay minerals exhibited great difference. Smectite caused serious hydration when encountering water whereas kaolinite was unhydrated in water solution. Different composition of clay mineral exhibited different hydration capacity. In clay minerals, montmorillonite is considered as a major causal composition to cause the swelling of clay. Inhibiting the swelling of montmorillonite is an effective way to control wellbore instability (Díaz-Perez et al., 2007; Paikaray et al., 2008; Bunger et al., 2014). The clay is unhydrated in oil based fluid. Oil based fluid is the preferred system in drilling these shale formations (Shivhare and Kuru, 2014). But fatal environment issues exist in the use of oil based fluid (Patel et al., 2007). Oil based fluid is not biodegradable and harmful for health and environment. Due to potential detrimental effects in the application of non-environment friendly oil based fluid, Environment Protection Agency and other regulatory bodies are imposing increasingly stringent regulations on the use and disposal of non-environment friendly oil based drilling fluid. It has been desirable to drill shale formations with water based fluid. Inhibitor is an available means to prevent clay from swelling in drilling shale formation with water based fluid. The drilling fluid industry has been searching for inhibitive water based fluid for years. Recently, the development of high-performance inhibitor has caused extensive research. Qiu group reported poly(oxypropylene)-amidoamine (POAA) was a potential inhibitor in water based fluid (Zhong et al., 2012). Qu group studied the inhibition of polyoxyalkyleneamine as shale inhibitor (Qu et al., 2009). Borges group evaluated the swelling ability of clay with different organic
https://doi.org/10.1016/j.petrol.2017.11.029 Received 26 June 2017; Received in revised form 26 September 2017; Accepted 13 November 2017 Available online 16 November 2017 0920-4105/© 2017 Elsevier B.V. All rights reserved.
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Journal of Petroleum Science and Engineering 161 (2018) 1–8
Montmorillonite (MMT drilling fluid level) was supplied by Weifang Huawei Bentonite Group Co., Ltd. Shale was obtained from oil field. The other experimental chemicals were purchased from domestic reagent company. All the chemical materials were used without further purification.
compounds and inorganic salt solutions (Balaban et al., 2015). Shadizadeh group reported a novel nonionic surfactant for inhibiting shale hydration (Shadizadeh et al., 2015). Our group evaluated the inhibition of chitosan quaternary ammonium salt (HTCC) (An et al., 2015). The commonly used inhibitors include KCl, CaCl2, NH4Cl, modified gilsonites and asphalts (Davis and Tooman, 1989; Gholizadeh-Doonechaly et al., 2009; Xiong et al., 2012). However, these approaches have some disadvantages such as short effectiveness, toxicity, low heat and salinity tolerance and pH sensitivity. Although some issues have been solved (Bonini et al., 2009), the hydration of water-sensitive shale is still not controlled completely, especially in drilling shale formation with water based fluid. Clay-particle is electronegative (Tang et al., 2014), then the effective shale inhibitor ought to be electropositive or nonionic. Coveney group recently reported the rule based design of clay swelling inhibitors (Suter et al., 2011). The rule showed that water soluble, hydrophobic backbone and primary di-amine or mono-quaternary amine functionality should be possessed by cationic inhibitors. Polyethyleneimines(PEIs) are water soluble polymers with a quantity of cationic groups (Poghosyan et al., 2015; Foundas et al., 2015; Neville et al., 2013). Their solutions were alkaline (Rajagopalan et al., 2015). More importantly, it was environmental friendly. Polyethyleneimines have been widely applied in bioengineering (Wang et al., 2015a,b; Liu et al., 2015; Zhu et al., 2015), paper industry (Wang et al., 2015a,b), waste water treatment industry (Adewunmi et al., 2015), catalyst (Park and Kim, 2015; Zakharova and Syakaev, 2009) and sensor (Li et al., 2015). Polyethyleneimines are synthesized by ring opening polymerization of ethylene mine. There are a series of products which are classified by molecular weight and structure. In our previous work, our group evaluated the inhibition capacity of PEIs with montmorillonite. PEIs exhibited high performance of inhibiting montmorillonite to hydrate compared with other commonly used inhibitors. We studied the effect of molecular weight on inhibition property of PEIs. The results showed that the addition of PEI10000 resulted in the lowest swelling height. But the detailed interaction mechanism between PEI10000 and montmorillonite was not studied especially for the effect of temperature. In this paper, we evaluate the inhibiting property of PEI10000 at different temperatures and explore the inhibition mechanism with a variety of characterization methods. We wish to provide the guide of the application of polyethleneimines in drilling shale formation with water based fluid. The swelling mechanism of MMT with PEI was showed in Fig. 1.
2.2. Inhibitive properties 2.2.1. Linear swelling tests The expansion height of montmorillonite solution with polyethyleneimine or other inhibitors is determined by CPZ-2 channel linear swellmeter (QingdaoTongchun,China). 5 g MMT or MMT(KSF) is poured into pressure tank, then be kept for 5 min at 10 MPa pressure by hydraulic press. A certain concentration inhibitor solution is prepared. Then the solution is poured into pressure tank and the value is recorded zero. The expansion height with time is recorded. 2.2.2. Rolling recovery tests Shale was sieved and crushed between 6 meshes and 10 meshes. 20 g shale debris was prepared. The concentration of shale inhibitors solution is fixed on 2 wt%. 300 ml solution and 20 g shale debris was put into digestion tank. Then the digestion tanks were put into the BGRL-5 roller furnace (Qing dao, China) and rolled at 150 Cfor 16 h. The upper suspension was poured away after the solution is cooled to room temperature. Then adding 200 ml deionized water, and the procedure was repeated for three times. Precipitate is dried at 100 C for 48 h. And then these precipitates were sieved to 40 meshes and weighted. Changing the rolled temperature to 80 C, 100 C, 120 C, 130 C and 140 C. Hot rolled, cooled, washed suspension, dried and weighted, then the procedure was repeated. The rolling recovery rate is calculated by the following formula: Recovery ¼ W2/W1. Shale debris denoted by W1 and that after hot rolling denoted by W2.
2. Materials and methods
2.2.3. Preparation of MMT/PEI hybrids and the purification of PEI 300 ml aqueous solutions of PEI were prepared. The concentrations of PEI solution are fixed on 0, 0.5 wt%, 1 wt%, 2 wt% and 4 wt%. Then 6 g MMT was added into PEI solutions to make PEI/MMT suspension and the suspension was under vigorous stirring for 30 min at 8 000 rpm. Then the suspension bear rolling at 80 C for 16 h to balance the adsorption and hydration between MMT and PEI. Centrifugal treatment was carried out at 10 000 rpm for 15 min. The precipitate was washed several times by deionized water until the upper liquid was clear. Finally the precipitate was dried at 100 C for 24 h. Then be grinded into powder for FT-IR. and XRD.
2.1. Materials
2.3. Structure characterization techniques
Polyethleneimine (PEI10000) was purchased from Gobekie Reagent Company. Chitosan quaternary ammonium salt (HTCC) (Mn 54 000 Da, Quaternary salt graft degree 60–80%, Purity 95%) was purchased from Jiaxing Kerui Biological Technology Co., Ltd. Polyether amine was obtained from MI-SWACO. Montmorillonite (KSF) was purchased from Aladdin Inc.
2.3.1. Fourier transforms infrared spectroscopy (FT-IR) measurements FT-IR spectral analyses of MMT/PEI hybrid were recorded by MagnaIR 560 spectrometer. 2 mg sample and 200 mg KBr was fully blend. The mixture was put into the mold and kept at 50 MPa pressure by hydraulic press.
Fig. 1. Schematic representation of MMT swelling mechanism: (a) without PEI and (b) with PEI. 2
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Journal of Petroleum Science and Engineering 161 (2018) 1–8
Fig. 2. Linear swelling curves of MMT (KSF) in inhibitors solutions: (a) different concentration of PEI solutions and (b) solutions of different inhibitors (the concentration of inhibitor solutions was 4 wt %).
2.3.2. X-ray diffraction (XRD) measurements MMT and MMT/PEI hybrid spectra analyses of XRD were recorded by D8 Advance Diffractometer. The patterns were collected with 2θ angle scanning between 0.5 and 10 . The basal spacing was analyzed by using Bragg's equation. The value for n ¼ 1 was calculated from 2dsinθ ¼ nλ (λ ¼ 1.5406 nm). The samples were put into mold, and then be compacted.
ultrasonicator at room temperature for 20 min. Different dosage of PEI solutions were added in MMT aqueous suspension to make a series of MMT/PEI suspensions.
2.3.3. Scanning electron microscopy (SEM) SEM analyses were performed by a Quanta 200F scanning electron microscope. 10 ml PEI solutions were prepared. The concentrations of PEI were 0, 0.5 wt%, 1 wt%, 2 wt% and 4 wt%. Then every 10 mg MMT was poured into PEI solutions. The mixed solutions were dispersed by ultrasonicator at room temperature for 10 min, and then the solutions were kept for 24 h. 1 drop of solution was added to filter cake. The filter cakes were dried at 80 C for 6 h. The dried samples were adhered to adhesive tapes, and then metal sprayed for 2 min.
Based on evaluation procedure of shale inhibitor in drilling fluid, the most frequently methods are to evaluate the performance of linear swelling test and rolling recovery rate test. The linear swelling test reveals the property of inhibiting clay from swelling that prevents wellbore instability. The rolling recovery rate test is designed to simulate the change of shale caused by inhibitor. Herein the two methods are combined to estimate the inhibiting property of PEI, from which we can make a clear judgment on the prospect of PEI as an excellent shale inhibitor.
3. Results and discussion 3.1. Inhibition evaluation
3.1.1. Linear swelling tests The linear swelling heights of MMT (KSF) in water solution with and without PEI were exhibited in Fig. 2. The swelling curves of all samples showed a similar tendency with strong increase in first 120 min and kept stable after 180 min. The swelling heights of MMT (KSF) in different inhibitor solutions were similar to those in water, indicating the serious hydration of MMT (KSF) (Fig. 2b). MMT (KSF) was purchased from Aladdin Inc. The specific surface area of MMT (KSF) was 20–40 m2/g. It is possible that the high specific surface area resulted in the strong hydration capability. Despite the fact that the addition of PEI resulted in the lowest swelling height, the height was up to 8.28 mm. Compared with that in water solution, the anti-swelling rate of PEI solution was only 19%, indicting the worse inhibition ability at this condition. Continuing to add PEI, the swelling height of MMT (KSF) declined slightly (Fig. 2a). The results further proved the worse inhibition of PEI with MMT (KSF). To further exhibit the different inhibition ability of inhibitors, we used montmorillonite (MMT) in place of MMT (KSF). The linear swelling heights of pristine MMT in water and different addition of PEI solutions were exhibited in Fig. 3. The swelling curves of all samples showed a similar tendency with strong increase in first 120 min and slower growth after 120 min, according with swelling behavior of MMT in aqueous solution. But the swelling heights of MMT were significantly different between in water and in PEI solution. The MMT continues to swell in water until 960 min, but the swelling heights of MMT in PEI solutions were nearly stable after 600 min. It is observed the growth of swilling curves of MMT in PEI solutions is slower than that in water, leading to the significant decrease of swelling height at the end of test. The phenomenon results from interaction between PEI and montmorillonite because PEI was water-soluble polymer with a quantity of cation groups and MMT was sheet with a quantity of negative charges in the side of sheet. PET
2.3.4. Transmission electron microscopy (TEM) TEM analyses were performed by a F20 transmission electron microscope. 10 ml PEI solutions were prepared. The concentrations of PEI were 0, 0.001 wt%, 0.010 wt% and 0.100 wt%. Then every 5 mg MMT was poured into PEI solutions. The mixed solutions were dispersed by ultrasonicator at room temperature for 2 min, and then the solutions were kept for 24 h. 1 drop of solution was added to carbon membrane. The carbon membranes were dried at infrared light for 20 min. 2.3.5. Atomic force microscopy (AFM) AFM analyses were performed using a SPM-9 600 instrument. 50 ml PEI solution was prepared. The concentrations of PEI were 0 and 0.01 wt %. Then every 5 mg MMT was poured into PEI solutions. The mixed solutions were dispersed by ultrasonicator at room temperature for 2 min, and then the solutions were diluted 5 times and kept for 24 h. 10 μL solution was added to mica sheet. The samples were dried at room temperature for 6 h. 2.3.6. Particle size analysis The suspensions were analyzed by Zetasizer Nano ZS instrument. A series of 0.1 wt% MMT suspensions were prepared and dispersed by ultrasonicator at room temperature for 20 min. Different dosage of PEI solutions were added into MMT aqueous suspension to make a series of MMT/PEI suspensions. 2.3.7. Zeta potential measurements The suspensions were analyzed by Zetasizer Nano ZS instrument. A series of 0.1 wt% MMT suspensions were prepared and dispersed by
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Journal of Petroleum Science and Engineering 161 (2018) 1–8
was similar to polyether amino. They were both adsorption groups in backbone and cation ions in the side chain. The quantity of positive ions in HTCC was more than that in polyether amino. The reasons of this phenomenon are as follows. Repeat unit with one positive ion was in HTCC, if the grafted percent of HTCC was 100%. The quantity of positive ions were calculated by polymerization degree multiply by grafted percent. Grafted percent of quaternary ammonium salt was about 60%– 80% and polymerization degree (Mn) of HTCC was about 54000Da. The quantity of positive ions was more than 32 400 in one polymer. But the positive ions of polyether amino were in the end group, and there are two positive ions in one polymer. So the quantity of positive ions in HTCC was far more than that in polyether amino. The positive ions in HTCC and polyether amino were attracted by the negative ions in clay particle, and the more positive ions the bigger force between polymer and clay particle, and the better inhibiting ability of polymer. The inhibiting ability of KCl was evidently weaker than that of other inhibitors in the same condition. KCl was inorganic substance, and the interaction mechanism with clay was different from organic polymers, and the durability of inhibition property was shorter than the polymer inhibitors. PEI contained a quantity of nitrogen atoms in the backbone and side chain, leading to more positive ions than in HTCC because of the protonation of nitrogen in water. As mentioned above, the more positive ions resulted in the stronger force between inhibitor and clay particle, leading to the better inhibition ability of PEI.
Fig. 3. Linear swelling curves of MMT with different concentrations of PEI solutions.
was adsorbed in the side of MMT through attraction between cation groups and negative charges. Meanwhile there were a few of nitrogen and hydrogen atoms in PEI and hydrogen bonds were formed between PEI and MMT. The swelling curves increased strongly in the first 180 min, but grew more slowly after 180 min. With the addition of PEI, the swelling height of MMT reduced significantly. The interaction mechanism between PEI and MMT was a key factor to control the inhibition ability of PEI. Possibly the molecular motion of PEI made great contribution to inhibition capability. However, the dosage of PEI was still a key factor to control inhibition capability. The increasing dosage of PEI improved the inhibiting ability of PEI. Fig. 4 showed the inhibition ability of different inhibitors. KCl and polyether amino were commonly used in oil field as inhibitor. The diameter of Kþ was fairly with interlamellar spacing of MMT, so the Kþ entered into the interlamellar of MMT, preventing the water from invading. Polyether amino was a kind of watersoluble polymer with polyether in backbone and amino groups in the end group. Polyether amino was adsorbed in the surface of MMT through a few of ether groups and amino groups. It was taken as inhibitor in recent years and was core additive in high performance water based fluid system. HTCC was water-soluble chtiosan quaternary ammonium salt with a quantity of quaternary ammonium groups in the side chain. The detailed inhibiting ability of HTCC was studied in our earlier work. The concentrations of inhibitors were fixed 4 wt%. The swelling curve of MMT in water increased gradually within 960 min. With the addition of inhibitors, the swelling curves of MMT grew strong in the first 120 min, but increased slowly significantly after 120 min. The swelling heights of MMT in KCl, polyether amino, HTCC and PEI solutions were 2.92 mm, 2.35 mm, 1.98 mm and 1.41 mm. The corresponding reduction rates were 50.7%, 60.3%, 66.6% and 76.2%. It was clear that PEI solution exhibited high performance as inhibitor. Structure composition of HTCC
3.1.2. Rolling recovery tests The rolling recovery rate tests exhibited the change of shale in inhibitor solution. The shale was hydrated seriously once put into water. The hydration of shale resulted in weight decrease. Inhibitor solution prevented the shale from hydrating. The ability of inhibitor was characterized by the weight change of shale. The rolling recovery rate was linear relation with weight change of shale during rolled progress. The higher rolling recovery rate exhibited better inhibiting ability. Fig. 5 showed that the rolling recovery rate of shale debris in different inhibitor solutions at different temperature. In water, the shale debris exhibited the lowest rolling recovery rate both at low temperature and high temperature. In KCl solution, the rolling recovery rate of debris was higher than that in water, but significantly lower than that in other inhibitor solutions. The debris kept highest rolling recovery rate in polyether amino solution before 120 C. But debris exhibited hightest rolling recovery rate in PEI solution after 120 C. The rolling recovery rate of debris in HTCC solution was always between that in polyether amino solution and that in PEI solution at different temperature. The rolling recovery rate of debris in PEI solution was up to 96% after rolled at 150 C, however, it was only 17% in water at some condition. The value of rolling recovery rate in polyether amino solution reduced with
Fig. 4. Linear swelling curves of MMT in different inhibitor solutions. The concentrations of inhibitor solutions were 4 wt%.
Fig. 5. Rolling recovery of inhibitors at different temperature. The concentrations of inhibitors were 2 wt%. 4
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Journal of Petroleum Science and Engineering 161 (2018) 1–8
water stretching bond were blue-shift 24 cm1 and 36 cm1. With the addition of PEI, the shift of physisorbed water stretching peak increased, exhibiting the incorporation of PEI with physisorbed water in MMT solution. The shift of water deformation bond increased with the addition of PEI, indicating hydrogen bonds were formed between deformation water and PEI. The quantity of hydrogen bonds increased with the addition of PEI, but red-shift of Si-O had nothing to do with the dosage of PEI, exhibiting hydrogen bonds between Si-O and N-H were saturated quickly. The vibration bonds of Al-O and Si-O (500-1000 cm1) were shifted in different degree. It further indicated the formation of hydrogen bond between MMT and PEI. PEI was adsorbed in the surface of MMT through hydrogen bond and entered into the interlayer of MMT through ionic bond and hydrogen bond. 3.2.2. X-ray diffraction As showed in Fig. 7. XRD patterns of pristine MMT and MMT/PEI hybrids were presented. A typical monolayer hydration interlayer d(001) spacing of 1.31 nm was displayed in XRD pattern of pristine MMT. With the addition of PEI, XRD patterns of MMT were modified due to the interlayer adsorption of PEI in the surface of MMT. With addition of PEI the d(001) spacing of MMT increased from 1.31 nm to 1.38 nm, 1.40 nm, 1.41 nm and 1.40 nm. The gallery height contributed by water was about 0.15 nm after 0.96 nm of layer thickness and 0.2 nm of hydrogen bond length were subtracted, exhibiting the MMT swelled seriously. With the addition of PEI, the gallery heights of MMT/PEI were about 0.22 nm, 0.24 nm, 0.25 nm and 0.24 nm. The results indicated that the monolayer structure of PEI could be observed in interlayer. The hydrogen bonds were formed between the N atoms and H atoms of N-H and H atoms and O atoms on the interlayer of MMT. The expansion of d(100) spacing increased and then no longer continued increasing with the addition of PEI, resulting from the intercalation of PEI. PEI was inserted into interlayer of MMT and then prevented the invasion of water.
Fig. 6. FT-IR spectra of MMT and MMT/PEI hybrids with different addition of PEI.
temperature because of the hydrolyzation of ether bond at high temperature. However, the value of rolling recovery rate in PEI solution increased with temperature, exhibiting the opposite change compared with polyether amino solution. There was no hydrolysable group in PEI molecule, resulting in the stability of PEI solution. But another factor should be considered. The water molecule acted acutely at high temperature, and then desorption between clay particle and water molecule became violent. The hydration of clay particle was weaker. The stability of PEI solution and the weaker hydration of clay particle at high temperature were two key contributions to high-performance of PEI solution, comparing to other inhibitors. 3.2. Inhibition mechanism analysis 3.2.1. Infrared spectroscopy The infrared spectra of pristine MMT and MMT/PEI hybrids were showed in Fig. 6. A typical characteristic of smectite group was presented in FT-IR pattern of pristine MMT. Some of the major peaks of functional group were showed as follow: stretching band of O-H (3622 cm1), physisorbed water stretching band (3441 cm1), water deformation band (1641 cm1), stretching band of Si-O (1035 cm1), vibration bands of AlAl-OH (914 cm1), vibration band of (797 cm1). In the spectrums of MMT/PEI hybrids, some relatively peaks assigned to PEI were observed. The new stretching bonds of N-H (2951 cm1, 2851 cm1and1472 cm1) were appeared, which indicated the incorporation of PEI to MMT. Compared with pristine MMT, the peaks of stretching bond of O-H and physisorbed water streching bond were blue shifted. Therefore, the peaks of water deformation bond and stretching band of Si-O were red shifted, but the peaks of vibration bonds of Al-AlOH and Al-O and Si-O were almost unchanged. The peaks of stretching bond of O-H were about blue-shift 1 cm1, but the peaks of physisorbed
3.2.3. Scanning electron microscopy MMT and PEI/MMT were also characterized by Scanning electron microscopy (SEM) and their images were reflected in Fig. 8. The images revealed different association modes of pristine MMT and MMT/PEI. The pristine MMT was seriously hydrated and swelled (Fig. 8). But PEI/MMT hybrids were mild hydrated and clay particle were bigger than pristine MMT (Fig. 8b–e). The addition of PEI resulted in the hydration of clay particle sharply reduced. The size of clay particle increased obviously, compared with the size of clay particle without PEI. It revealed that PEI exhibited high performance as inhibitor to prevent the clay particle from hydrating. 3.2.4. Transmission electron microscopy The transmission electron microscope (TEM) images were showed in Fig. 9. The image of pristine MMT revealed that the clay sheets reduced, resulting from the hydration of MMT (Fig. 9a). There was a large quantity of small nano sheets under 200 nm. With the addition of PEI, small nano sheets were not observed and taken place by larger sheets (Fig. 9b–d). The hydration of clay particle was inhibited in PEI solution. 3.2.5. Atomic force microscopy The atomic force microscopy (AFM) images were exhibited in Fig. 10. A large quantity of nano sheets were observed in Fig. 11a. The height of nano sheets was about 8.91 nm, indicating the sheets dispersed well. But the opposite observation was showed in Fig. 11b. The size of sheets was in the range of micron. The height of clay sheets was about 401.74 nm, exhibiting the clay sheets aggregated seriously. The results showed clay particle hydrated seriously in water, but the hydration of clay particle was inhibited in PEI solution. The observations were accordant with the observations in TEM images. 3.2.6. Particle size analysis As showed in Fig. 11, particle size analysis of pristine MMT and
Fig. 7. X-ray diffraction patterns of MMT/PEI hybrids with different addition of PEI. 5
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Fig. 8. SEM images of pristine MMT and MMT/PEI hybrid with different addition of PEI: (a) pristine MMT; (b) 0.5 wt%; (c) 1.0 wt%; (d) 2.0 wt%; (e) 4.0 wt%.
size of MMT increased after the addition of PEI. The results showed that a small number of positive charges benefited the dispersion of MMT and a large quantity of positive charges resulted in serious aggregation. It further proved that the interaction between clay MMT and PEI occurred through ionic bonds.
MMT/PEI hybrid was presented. The average size of pristine MMT was about 500 nm. 0.001 wt% PEI was added into MMT suspension. The average size of MMT was under 100 nm. A small number of positive charges of PEI was attracted by the negative charges of MMT, resulting in better dispersion of clay sheets. With the addition of PEI, the number of positive charges increased. The attraction force between PEI and MMT is strengthened. There were many more MMT sheets around one PEI molecule, leading to serious aggregation of MMT. And then the average
3.2.7. Zeta potential The zeta potential evaluations of MMT and MMT/PEI solutions were
Fig. 9. TEM images of pristine MMT and MMT/PEI hybrid with different addition of PEI: (a) pristine MMT; (b) 0.001 wt%; (c) 0.010 wt%; (d) 0.100 wt%. . 6
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Fig. 10. AFM images of pristine MMT and MMT/PEI hybrid with 0.010 wt% of PEI: (a) pristine MMT; (b) 0.010 wt% PEI.
MMT. Then PEI intercalated the interlayer of MMT. On the account of large quantities of side chains in PEI, it was easy to enter into the interlayer of MMT, strengthening the driven force between PEI and MMT.
presented in Fig. 12. The negative surface charges were formed by the isomorphous substitution in the octahedral layer [46]. The addition of positive charges in the interlayer space broke charge balance. The zeta potential of MMT after hydrated was 1.23 mV and presented worse dispersion in water. The addition of PEI resulted in the decrease of zeta potential of MMT suspension. The zeta potential of MMT was reversed due to the addition of 0.001 wt% PEI solution, indicating better dispersion. With the addition of PEI, the zeta potential of MMT declined and kept stable at 0.100 wt% PEI solution, indicating that the colloidal of MMT became agglomerate. The positive charges in the backbone and side chain of PEI were neutralized by the negative charges in MMT, leading to the instability of MMT. Continuing to add PEI, the zeta potential of PEI/MMT waved between 0 eV and 2.5 eV, indicating the instability of MMT colloidal. PEI molecules were adsorbed and desorbed simultaneously in the surface of MMT. Then the adsorption and desorption reached equilibrium, leading to the hydration repulsion of double electrostatic layer and dispersion of clay particle. The results of Zeta potential test were according with particle size tests.
4. Conclusions In summary, the adsorption of PEI in the surface of MMT and the intercalation in interlayer of MMT inhibited the hydration of MMT, and positive ions in PEI interacted with negative ions in clay particle. Inhibition mechanism of MMT in PEI solution was studied. The conclusions provided us the method to develop shale inhibitor with high performance in montmorillonite solution and the guidance of operational parameters in drilling operations. The value of linear swelling height showed the inhibiting ability of PEI was better than that of other inhibitors. The addition of PEI solution resulted in largest rolling recovery rate after rolled at 120 C. The rolling recovery rate of debris in PEI solution was up to 96% after rolled at 150 C, compared with that 17% in water at same condition. The rolling recovery rate of debris in PEI solution increased with temperature, but it exhibited opposite change in polyether amino solution. It further proved the poor temperature resistance resulting from serious hydrolyzation of ether bond at high temperature. PEI solution showed high-performance at high temperature compared with other inhibitors. The structure composition of PEI was similar to that of HTCC and polyether amino, and all the backbone contained adsorption groups and the side chain was with cation ions. Polyether amino lost the
3.2.8. Probable inhibition mechanism The experimental and mechanism analysis of inhibiting ability of PEI was studied. PEI solution contacted with MMT suspension, and negative charges were neutralized by positive charges in the backbone and side chain of PEI through the coordination of electrostatic attraction and hydrogen bond, and then PEI was adsorbed in the side surface of MMT. The amino groups as adsorption groups were adsorbed in the surface and the interlayer of MMT, which leaded to the weakening and even the collapse of the diffuse double layer, further resulted in the aggregation of
Fig. 11. Particle size of pristine MMT and MMT/PEI hybrid with different addition of PEI.
Fig. 12. Zeta potential of MMT particles in PEI solutions. 7
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inhibiting ability because of the hydrolyzation of ether bond at high temperature. But HTCC with higher molecular weight was curl and reduced the hydrolyzation of ether bond, leading to better inhibiting ability of HTCC. Compared with HTCC, there was a quantity of nitrogen atoms in the backbone and side chain of PEI, leading to more positive ions than those in HTCC molecular because of the protonation of nitrogen in water. As mentioned above, more positive ions resulted in stronger force between inhibitor and clay particle, leading to better inhibition ability. Meanwhile some problems still exist. PEI is more expensive than HTCC and polyether amino, and then how to reduce cost is the key issue. On the other side, the compatibility of PEI with other agents commonly used in drilling fluid needs further research. The next work is in progress.
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