Article pubs.acs.org/EF
Amphoteric Polymer as an Anti-calcium Contamination Fluid-Loss Additive in Water-Based Drilling Fluids Fan Liu,* Guancheng Jiang, Shuanglei Peng, Yinbo He, and Jinxi Wang College of Petroleum Engineering, China University of Petroleum (Beijing), Beijing 102249, People’s Republic of China ABSTRACT: Calcium ion contamination in water-based drilling fluids (WBDs) dramatically increases filtration volume loss and worsens rheological properties, especially in high-temperature bore holes. This study demonstrated two types of acrylamide polymers as anti-calcium contamination fluid-loss additives in WBDs, including an amphoteric polymer (ADD) synthesized by 2acrylamide-2-methylpropanesulfonic acid (AMPS), acrylamide (AM), and diallyl dimethylammonium chloride (DMDAAC) and an anionic polymer (AD) synthesized by AMPS and AM. In transmission electron microscopy (TEM) of sodium bentonite (NaBT)-based mud under 11.1% CaCl2 contamination and 150 °C hot rolling, a typical “star-net” structure was observed between the ADD and Na-BT layers; however, polymer AD could not form such a net structure. Energy-dispersive spectrometry (EDS) analysis of the Na-BT layer indicated that ADD could greatly decrease the amount of Ca2+ on Na-BT layers in comparison to AD. Accordingly, in an American Petroleum Institute (API) filtration test and a rheological test of Na-BT-based mud with 11.1% CaCl2 contamination after 150 °C hot rolling, Na-BT-based mud with 1.5% ADD could maintain an API filtration volume (FLAPI) as low as 9.6 mL, whereas Na-BT-based mud with 1.5% AD maintained a FLAPI of 36 mL. The rheological properties of Na-BT-based mud also showed that ADD could maintain higher viscosity and shear stress than AD, suggesting that amphoteric polymer ADD was suitable for making WBDs more resistant to calcium contamination and high temperature.
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INTRODUCTION Water-based drilling fluids (WBDs) are the most common drilling fluids in drilling engineering and are composed of bentonite clay, various polymer agents (thinner, fluid-loss additive, shale stabilizer, etc.), and wetting materials (barite and calcium carbonite).1 Drilling fluids flowing in well bores must endure high temperatures and various types of cationic contamination. In particular, gypsum layers contain large amounts of Na+ and Ca2+; sometimes, the Ca2+ concentration will reach as high as 40 000 mg/L; and the temperature in the borehole can reach up to 150 °C.2 Furthermore, gypsum layers are good cap rocks for oil and gas; nearly 30% of the oil and gas covers in large oil fields around the world are made of substances similar to gypsum and salt rock.3,4 Therefore, large amounts of Ca2+ contamination and high temperatures for drilling fluids are inevitable in gypsum drilling operations for oil and gas extraction. Bentonite, the most essential additive in WBDs, is a colloid plate with a natural negative charge on its face and a conditionally changed charge on the edge, depending upon pH. Bentonite layers in water can form “card-house” structures through Coulombic interactions.5−7 For example, the sodium bentonite (Na-BT) suspension exhibits particular rheological properties, such as shear thinning and gel formation, that are fundamental to WBDs for suspending weighting additives and cuttings under the wellbore, and the dispersed bentonite layers could form a thin filtration cake.8 However, bentonite layers in suspension, such as colloidal plates with a negative charge, are obviously sensitive to Na+ and Ca2+.9 Because Ca2+ can adsorb on the surface of bentonite and greatly compact the double electrical layer, bentonite layers coagulate and the rheology properties of the suspension worsen.5,10 Additionally, coagulation of bentonites in WBDs can dramatically increase filtration loss volume and form thick, loose filtration cakes, © 2016 American Chemical Society
which will cause sticking of pipes and wellbore instability. To ensure drilling safety in gypsum and salt rock layers, other additives in WBDs, especially fluid-loss additives,11,12 must maintain excellent abilities to enhance the dispersion of bentonite and form good rheology and fluid-loss properties under large amounts of Ca2+ contamination. Various fluid-loss additives in WBDs can maintain good filtration properties under most conditions. One major additive is natural polymers, such as starch, carboxymethyl cellulose (CMC), and polyanionic cellulose (PAC); these natural polymers usually degrade and become unsuitable for use at high temperatures.13−18 Another major additive is synthetic polymers, especially acrylamide-based polymers, including monomers, such as acrylamide (AM) and acrylic acid (AA), and vinyl sulfonates, such as 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and sodium styrenesulfonate (SSS), and some cationic monomers, such as dimethyl diallyl ammonium chloride (DMDAAC) and N-vinylpyrrolidone (NVP). These copolymers exhibit better anti-high-temperature performance and salt resistance than natural polymers.19−22 Much research has focused on Na+ contamination, high-temperature resistance, and saturated brine contamination. In 1984, Hille used vinyl sulfonate and vinyl acrylamide to synthesize a VS/VA copolymer, which had good anti-high-temperature and anticationic-ion-contamination performance. In the field experiment, WBDs with the VS/VA copolymer could maintain a low high-temperature−high-pressure (HTHP) fluid loss in 6000 mg/L Ca2+ contamination.23 In 1986, Perricone et al. synthesized a fluid-loss agent (named COP) with AMPS, Received: June 28, 2016 Revised: August 5, 2016 Published: August 16, 2016 7221
DOI: 10.1021/acs.energyfuels.6b01567 Energy Fuels 2016, 30, 7221−7228
Article
Energy & Fuels AM, and alkyl acrylamide monomers, and the field experiment showed that the COP could withstand 150 °C and 800 mg/L Ca2+ contamination.24 These fluid-loss additives were anionic polymers without a cationic group. However, few papers have focused on Ca2+ contamination, especially high-concentration Ca2+ contamination. According to the Derjaguin, Landau, Verwey, and Overbeek (DLOV) theory and the Schulze− Hardy rule, Ca2+ has worse impact for bentonite and the ratio of the coagulation value between Ca2+ and Na+ is nearly 100:1.6.25,26 Moreover, most acrylamide polymers in drilling fluids will become ineffective under Ca2+ contamination because Ca2+ will screen the acrylate and induce polymer coiling. An amphoteric polymer,27−30 which contains positive and negative groups and anionic groups, can maintain higher viscosity than an anionic polymer in saline solution because of an anti-polyelectrolyte effect.31−36 In addition, an amphoteric polymer could have a strong charge attraction force on the negatively charged Na-BT layers, which enhance the performance in control fluid loss in WBDs. With regard to the Ca2+ contamination for WBDs, we used AMPS/AM/DMDAAC and AMPS/AM monomers to synthesize an amphoteric polymer (ADD) and an anionic polymer (AD) as a fluid-loss additive. Through a series of filtration and rheology tests, ADD showed better properties in controlling filtration loss under 11.1% CaCl2 contamination and 150 °C hot rolling than with anionic polymer AD. Finally, a distinctive mechanism of ADD in anti-calcium contamination was revealed through investigation of the microstructure of filtration cakes and Na-BT-based mud.
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was dissolved in the 4% Na-BT-based mud with 10 000 rpm stirring for 20 min; calcium ion contamination (CaCl2) was then added with 10 000 rpm stirring for 20 min and static standing for 12 h to let the polymer and calcium ion have thorough contact with bentonite. To study the anti-temperature performance of poly(AMPS-AMDMDAAC) and poly(AMPS-AM), an aging test was conducted by hot rolling in a roller oven (Fann Instrument Company) at 150 °C for 16 h. American Petroleum Institute (API) Fluid-Loss Test. A fluidloss test was conducted using a low-pressure−low-temperature (LPLT) filter press API (Fann Instrument Company) under API guidelines for drilling fluids. All of the tests were conducted at 25 °C; fluids were pressed under 100 psi purging by nitrogen; and the filter paper was G50 Whatman quantitative filter paper (9 mm diameter and 2.7 μm pore size). Filtration volumes were measured 30 min after starting the test.38 Rheology Analysis. The rheological properties of Na-BT-based mud were measured with a Haake Mars rheometer (Thermo Electron Corporation, Waltham, MA). The apparent viscosity and shear stress were measured under the shear rate from 1 to 1000 s−1, and all of the measurements were conducted at 25 °C. Before the rheological measurement, the suspensions were stirred vigorously for 30 min.39 Common rheological parameters in the drilling industry, such as apparent viscosity (AV), plastic viscosity (PV), and yield point (YP), were measured by a six-speed rotating viscometer (model 35A viscometer, Fann Instrument Company, Houston, TX). The measurement was calculated through dial reading at 600 and 300 rpm by the following equations:
AV = 0.5θ600 PV = θ600 − θ300 YP = θ300 − 0.5θ600
EXPERIMENTAL SECTION
Microstructure of Filtration Cake and Base Mud. After the API fluid-loss test, the filtration cakes were slowly washed in distilled water and dried in a vacuum oven at 45 °C and the surface features of the filtrate cake was characterized by field-emission scanning electron microscopy (Quanta 200F, FEI Corporation). All of the samples were coated with Au before the test. A solution of 4% Na-BT-based mud with different additives and calcium ion contamination amounts were diluted 40 times. Then, the fluid was dropped on carbon film (7−10 nm thickness), and the water was evaporated under an infrared lamp. The carbon film was then placed in transmission electron microscopy (F20, FEI Corporation) to observe the bentonite dispersion. The atomic elements in the Na-BT layers were revealed by energy-dispersive spectrometry (EDS) spectra, and Si, Al, Mg, O, N, S, Ca, and Cl elements were selected to analyze the Ca2+ contamination for Na-BT-based mud.
Materials. AMPS, DMDAAC (60% solution), AM (99%), and ammonium persulfate (98%) were obtained from Sigma-Aldrich Corporation (Shanghai, China). NaOH (99%), CaCl2 (99%), and bentonite (sodium form) were purchased from Alfa Aesar (Shanghai, China). Synthesis of Poly(AMPS-AM-DMDAAC). Poly(AMPS-AMDMDAAC) was produced in radical polymerization, and orthogonal tests were used to optimize the main four factors (monomer mole ratio, reaction temperature, reaction time, and initiator amount) to obtain better performance in reducing fluid loss under calcium ion contamination. A certain mole ratio of AMPS, AM, and DMDAAC was dissolved in 50 mL of distilled water at 25 °C (pH adjusted to 7 with sodium hydroxide), and the total monomer mass ratio was kept at 20%. Then, the solution was put in a reaction flask and deoxygenated with purging nitrogen for half an hour. After the solution was heated to the reaction temperature, the ammonium persulfate solution (the initial ratio was based on the total monomer mass, and the ammonium persulfate was dissolved in 2 mL of distilled water) was slowly lowered over 2 min. After the reaction finished, the viscous solution was dialyzed with a dialysis bag (MD 10 000) in distilled water for 24 h. Then, the remaining viscous solution was dried at 80 °C under a vacuum, and the dried product was ground to a powder. Poly(AMPSAM) was synthesized and dried under the same conditions, but the DMDAAC monomer was not added. Characterization of AAD and AD. 1H nuclear magnetic resonance (NMR) analysis is the most common method to determine molecular structures and functional groups. The 1H NMR test was conducted using a NMR spectrometer (JEOL JNM-ECA600, Tokyo, Japan), and samples were diluted in D2O. A thermogravimetric analysis (TGA) was performed under an argon atmosphere with a heating rate of 5 °C/min (Thermo Fisher Scientific Corporation). Preparation of Water-Based Mud. A 4% Na-BT-based mud was prepared by adding 4% (w/v) Na-BT in distilled water and stirring at 2000 rpm for 2 h,37 followed by static standing for 24 h. A certain amount (w/v) of poly(AMPS-AM-DMDAAC) and poly(AMPS-AM)
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RESULTS AND DISCUSSION Orthogonal Test of Poly(AMPS-AM-DMDAAC). The four main synthesis factors of poly(AMPS-AM-DMDAAC) are shown in Table 1. In the API fluid-loss test (after the 150 °C aging test), the sample and CaCl2 amounts were 1.5 and 11.1% (w/v) in 4% Na-BT-based mud, respectively, and the optimal condition depended upon the minimum FLAPI. The results in Table 2 indicate that the mole ratio had the most important effect on filtration loss under calcium contamination, which Table 1. Factors and Levels of the Synthetic Experiment
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factor level
mole ratio (AMPS/AM/DMDAAC)
reaction temperature (°C)
reaction time (h)
initiator ratio (%)
level 1 level 2 level 3
7:2:1 6:3:1 5:4:1
30 50 60
2 3 4
0.15 0.25 0.35
DOI: 10.1021/acs.energyfuels.6b01567 Energy Fuels 2016, 30, 7221−7228
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Energy & Fuels Table 2. Orthogonal Experiment Results for Poly(AMPSAM-DMDAAC) sample 1 2 3 4 5 6 7 8 9 K1 K2 K3 R
mole ratio
reaction temperature (°C)
7:2:1 7:2:1 7:2:1 6:3:1 6:3:1 6:3:1 5:4:1 5:4:1 5:4:1 19.000 30.967 50.467 31.467
30 50 60 30 50 60 30 50 60 19.200 38.867 42.367 23.167
reaction time (h)
initiator ratio (%)
FLAPI (mL)
2 3 4 3 4 2 4 2 3 38.933 33.100 28.400 10.533
0.15 0.25 0.35 0.35 0.15 0.25 0.25 0.35 0.15 35.300 24.967 40.167 15.200
12 15.5 29.5 23 33.1 36.8 22.6 68 60.8
Figure 2. TGA analysis of ADD and AD.
30 to 150 °C corresponded to free water and crystal water combined with hydration groups in the polymer. After the temperature increased to 400 °C, ADD and AD obtained nearly the same weight value of 38%. In the DTG curve, the AD weight started to dramatically decrease at 290 °C and the weight curve of ADD with cationic groups started to decline at 300 °C, indicating that the cationic group had a slight improvement in thermal stability. Because borehole temperatures in gypsum layers are far below 300 °C, polymers ADD and AD would not thermally decompose underground. Filtration Properties of ADD and AD in Na-BT-Based Mud. A series of API filtration tests for ADD and AD was conducted in 4% Na-BT-based mud under different amounts of CaCl2 contamination and 150 °C hot rolling. In Table 3, we can see that polymers ADD and AD showed good performance in controlling FLAPI without Ca2+ contamination. When the polymer amount ranged from 0.5 to 1.5%, viscosity of Na-BTbased mud increased and FLAPI with ADD and AD decreased from 28 to 6.8 and 9.6 mL, respectively. After 150 °C hot rolling, 4% Na-BT-based mud with ADD or AD could decrease FLAPI to 7.0 and 10.2 mL, which revealed that ADD and AD had good anti-high-temperature properties without cation contamination as a fluid-loss additive. For different amounts of CaCl2 contamination, FLAPI results are shown in Figure 3. From 1 to 20% (w/v) CaCl 2 contamination, 4% Na-BT-based mud with 1.5% (w/v) ADD or AD polymer greatly reduced FLAPI from approximately 100 mL (20% CaCl2 contamination, blank group) to less than 10 mL and Na-BT-based mud with amphoteric polymer ADD had a lower FLAPI than with AD. Additionally, the filtration volume curve was nearly flat for different CaCl2 contaminations, which meant ADD and AD polymers could resist 20% CaCl2 without an aging test. However, after 150 °C hot rolling, ADD could maintain FLAPI below 15 mL under 20% CaCl2 contamination compared to 58 mL for AD polymer. Particularly, in 11.1% CaCl2 contamination, as Figure 4 shows, ADD exhibited better filtration properties, reducing FLAPI to 9.6 mL, and the fluidloss volume was nearly linear after 7.5 min. Therefore, the final filtration rate (FFR) was calculated by the slope of the line between 7.5 and 30 min.17 Before the hot rolling test, ADD and AD could decrease FFR from 0.45 (blank group) to 0.18 and 0.16 mL/min, respectively. After the 150 °C hot rolling test, a strong contrast appeared between Na-BT-based mud with ADD and AD. Na-BT-based mud with ADD and AD maintained FFR of 0.20 and 0.78 mL/min compared to 0.56 mL/min of the blank group. These results clearly demonstrate that ADD exhibited better anti-high-temperature and anti-
means that the functional group ratio was crucial to the fluidloss-control performance of additives in drilling fluids. The optimal synthesis conditions were as follows: n(AMPS)/ n(AM)/n(DMDAAC), 7:2:1; reaction temperature, 30 °C; time, 4 h; total monomer mass ratio and initiator amounts, 25 and 0.25% (w/v), respectively; and solution pH value, 7. Under optimal conditions, amphoteric fluid-loss additive ADD was synthesized and dried. To research the cationic group of the polymer in anti-Ca2+ anionic contamination, polymer poly(AMPS-AM) was synthesized under the same conditions but without the cationic monomer DMDAAC. Characteristics of Polymers ADD and AD. The spectrum result for ADD and AD is shown in Figure 1. In the 1H NMR
Figure 1. 1H NMR of ADD and AD.
spectrum of polymer AD, σ = 1.35 and 1.51 ppm for −CH3 in AMPS, σ = 1.66 and 1.78 ppm for −CH2− in the backbone of the polymer, σ = 2.24 ppm for −CH− connected to the amide group in AMPS, σ = 2.47 ppm for −CH− connected to the amide group in AM, and σ = 3.22−3.69 ppm for −CH2− connected to −SO3Na in AMPS. For ADD, typical chemicalshift values in poly(AMPS-AM) were also presented in the 1H NMR spectrum: σ = 2.16 ppm for −CH− in DMDAAC and σ = 3.07 ppm for −CH2−N+ and CH3−N+ in DMDAAC, indicating that AMPS, AM, and DMDAAC had polymerized successfully. The TGA result is shown in Figure 2. On the basis of the thermogravimetry (TG) and derivative thermogravimetry (DTG) curves, the slight weight loss for ADD and AD from 7223
DOI: 10.1021/acs.energyfuels.6b01567 Energy Fuels 2016, 30, 7221−7228
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Energy & Fuels Table 3. API Filtration Test of ADD and AD in Na-BT-Based Mud condition
after 150 °C hot rolling
before hot rolling
sample
AV (mPa s)
PV (mPa s)
YP (Pa)
FLAPI (mL)
AV (mPa s)
PV (mPa s)
YP (Pa)
FLAPI (mL)
4% Na-BT-based mud +0.5% ADD +0.5% AD +1.0% ADD +1.0% AD +1.5% ADD +1.5% AD
8.5 12.5 12 31 22 48 30
4 7 8 22 15 36 22
4.5 5.5 4 9.0 7.0 12.0 8.0
28 17.4 18.6 8.5 12.2 6.8 9.6
8 10 10 21 18 36 27
6 6 6 17 12 29 22
2.0 4.0 4.0 4.0 6 7.0 5
32 26 30 10.8 15.2 7.0 10.2
Figure 3. FLAPI of Na-BT-based mud under different CaCl2 contaminations (sample 1, 4% Na-BT-based mud; sample 2, 4% Na-BT-based mud + 1.5% AD; sample 3, 4% Na-BT-based mud + 1.5% ADD, and HR-reflected sample, under 150 °C hot rolling for 16 h).
Filtration cakes of different Na-BT-based mud show various surface topographies in Figure 5. In comparison to cake a, cake
Figure 4. FL API of Na-BT-based mud under 11.1% CaCl 2 contamination [sample 1, 4% Na-BT-based mud (blank group, without calcium contamination); sample 2, 4% Na-BT-based mud + 1.5% AD; sample 3, 4% Na-BT-based mud + 1.5% ADD; and HRreflected sample, under 150 °C hot rolling for 16 h].
calcium-ion-contamination properties than ionic polymer AD as a fluid-loss additive in WBDs. According to the static filtration equation,40 the filtration rate dVf/dt (cm3/s) can be calculated by the following equation (eq 1): (1)
Figure 5. SEM of Na-BT-based mud cake after 150 °C hot rolling for 16 h (a, 4% Na-BT-based mud; b, 4% Na-BT-based mud + 11.1% CaCl2; c, 4% Na-BT-based mud + 1.5% ADD + 11.1% CaCl2; and d, 4% Na-BT-based mud + 1.5% AD + 11.1% CaCl2).
where K is the permeability of the filtration cake, A is the filtrate area (cm2), μ is the viscosity of the filtrate, hmc is the thickness of the filtrate cake (cm), and Δp is the press drop (0.69 MPa). Obviously, the viscosity of fluids and the permeability of the filtration cake were crucial to obtaining good filtration properties. To determine the reasons for the difference between ADD and AD in controlling fluid loss, we analyzed the microstructure of filtration cakes and Na-BT-based mud and conducted a series of rheology tests.
b of 4% Na-BT-based mud with 11.1% CaCl2 contamination had more cracks and bentonites accumulated in “face-to-face” style and the corresponding Na-BT-based mud maintained a dramatically larger FLAPI in the API filtration test. However, when we added 1.5% ADD to 4% Na-BT-based mud before 11.1% CaCl2 contamination, the filtration cake c became more compact with no obvious cracks and showed lower permeability. In comparison, cake d with 1.5% AD added was
KAΔp dVf = dt μhmc
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DOI: 10.1021/acs.energyfuels.6b01567 Energy Fuels 2016, 30, 7221−7228
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Figure 6. Rheology property of Na-BT-based mud (sample 1, 4% Na-BT-based mud + 11.1% CaCl2; sample 2, 4% Na-BT-based mud + 1.5% AD + 11.1% CaCl2; sample 3, 4% Na-BT-based mud + 1.5% ADD + 11.1% CaCl2; and HR-reflected sample, under 150 °C hot rolling for 16 h).
Table 4. Yield Point τ0 of Na-BT-Based Mud (Sample 1, 4% Na-BT-Based Mud; Sample 2, 4% Na-BT-Based Mud + 11.1% CaCl2; Sample 3, 4% Na-BT-Based Mud + 1.5% ADD + 11.1% CaCl2; and Sample 4, 4% Na-BT-Based Mud + 1.5% AD + 11.1% CaCl2) after 150 °C hot rolling
before hot rolling sample sample sample sample sample
1 2 3 4
τ0 (Pa)
μp (mPa s)
R2
τ0 (Pa)
μp (mPa s)
R2
5.74 3.28 10.48 11.06
10.29 5.97 10.16 18.52
0.991 0.999 0.992 0.999
3.99 3.05 5.00 13.94
9.12 4.78 7.55 5.49
0.996 0.997 0.996 0.984
perfectly with a high R2 (close to 1), and the yield point τ0 and plastic viscosity μp were listed in Table 4.
less compact than cake c and obtained nearly the same surface topography as cake a. As a result, after 150 °C hot rolling, 4% Na-BT-based mud with 1.5% AD (under 11.1% CaCl2 contamination) maintained relatively the same FLAPI as the blank group (4% Na-BT-based mud with no Ca2+ commination) but was much higher than the FLAPI of Na-BT-based mud with ADD. A bentonite suspension is a typical Bingham fluid model with a shear thinning property.41,42 As Figure 6 shows, under 11.1% (w/v) CaCl2 contamination, polymers ADD and AD could increase the viscosity of 4% Na-BT-based mud and enhance the shear thinning property. After 150 °C hot rolling, Figure 6 shows that Na-BT-based mud with ADD also maintained a high viscosity and better shear thinning than AD, such as under the shear rate of 1000 s−1; the apparent viscosities for Na-BT-based mud with ADD or AD were 25 and 15 mPa s, respectively. High viscosity and better shear thinning behavior could improve the ability of WBDs to suspend weighting materials and cuttings in collar spaces (low shear rate) and reduce flowing fractional drag in bits. Additionally, high viscosity can reduce FLAPI, according to the static filtration equation.43 On the other hand, the shear stress of Na-BT-based mud with ADD also obtained a relatively higher shear stress under 11.1% (w/v) CaCl2 contamination, especially after 150 °C hot rolling. Shear stress results conformed to the Bingham model
τ = τ0 + μp γ ̇
(2)
Under 11.1% CaCl2 contamination, τ0 values of 4% Na-BTbased mud with AD and ADD were 10.48 and 5.00 Pa, respectively. After 150 °C hot rolling, ADD maintained a relatively higher τ0 of 13.94 Pa compared to AD (τ0 = 5.00 Pa). It is well-known that the yield point τ0 means the minimum shear stress to make a suspension flow and reflects the net structure of the suspension.6 For WBDs in drilling industry, a relatively high yield point could suspend larger drill cuttings and keep the wellbore clean. With the combination of the rheology test and the API filtration test, we find that amphoteric polymer ADD can maintain better rheological and fluid-loss-control properties than anionic polymer AD under ultrahigh CaCl2 contamination and high temperature. The further research in the microstructure of Na-BT-based mud had revealed the difference between ADD and AD in anti-calcium contamination. Through TEM of the Na-BT-based mud, we distinctly observed Na-BT layers in Na-BT-based mud after 150 °C hot rolling. In Figure 7, picture a presents the “card-house” structure of Na-BT layers in aqueous solution; the Na-BT layers were sufficiently dispersed. After 11.1% CaCl2 contamination, Na-BT layers agglomerated, as Figure 7b shows. 7225
DOI: 10.1021/acs.energyfuels.6b01567 Energy Fuels 2016, 30, 7221−7228
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Figure 8. Net sturcture model of ADD and Na-BT layers.
layers, because most negative charges in the Na-BT layers had formed ionic bonds with the ammonium salt group of ADD. In contrast, the anionic group in polymer AD could only form hydrogen bonds with Na-BT layers, which were not as steady as an ionic bond after calcium contamination, especially under high temperatures. These hypothesizes were confirmed by the results of EDS analysis of the Na-BT layers in Na-BT-based muds (Figure 9 and Table 5). When 4% Na-BT-based muds were contaminated with 11.1% CaCl2, the Ca and Cl element ratios were dramatically increased, which reflected a large amount of Ca2+ and Cl− being adsorbed on Na-BT. After 1.5% ADD was added to the 4% Na-BT-based mud, the Ca and Cl elements were decreased and large amounts of N element and small amounts of S element appeared on the surface of Na-BT. These results indicated that the functional groups of ADD adsorbed on the surface of Na-BT. For Na-BT-based mud with AD before hot rolling, a large amount of N elements appeared on the surface of Na-BT layers and the number of Ca elements decreased dramatically. However, after 150 °C hot rolling, the N elements decreased sharply and large amounts of Ca occurred on the surface of Na-BT layers. It can be concluded that amide groups were desorbed from Na-BT layers under high temperature and CaCl2 contamination.
Figure 7. TEM of Na-BT-based mud after 150 °C hot rolling [a, 4% Na-BT-based mud; b, 4% Na-BT-based mud + 11.1% CaCl2; c, 4% Na-BT-based mud + 1.5% ADD + 11.1% CaCl2; c1, net structure of ADD in the aqueous phase; d, 4% Na-BT-based mud + 1.5% AD + 11.1% CaCl2 (before hot rolling); and d1, 4% Na-BT-based mud + 1.5% AD + 11.1% CaCl2 (after 150 °C hot rolling)].
When 1.5% ADD is added, as Figure 7c exhibits, Na-BT layers were dispersed again under 11.1% CaCl2 contamination and a typical “star-net” structure was found between ADD and Na-BT layers. Particularly, in Figure 7c1, the polymer chain of ADD could also form a net structure. However, in Figure 7d1, Na-BT layers coagulated and Na-BT-based mud with AD under the same condition could not form the typical net structure; just a weak net structure was found before hot rolling (Figure 7d). Obviously, this “star-net” structure would increase the repulsive force between Na-BT layers and decrease the agglomeration of Na-BT layers under 11.1% CaCl2 contamination, increasing the yield stress and viscosity of Na-BT-based mud. This process explains the rheology results presented above. Why could ADD form a “star-net” structure under 11.1% CaCl2 contamination? Na-BT layers are naturally negatively charged with lattice replacement, and on the broken bond of the Al−O octahedral, the Al−OH group would present negative (−Al−O−), neutral (−Al−OH), and positive (−Al− OH2+) charges corresponding to a high pH value, moderate pH value, and low pH value, respectively. As Figure 8 shows, amphoteric polymer ADD had a cationic group (ammonium salt), a neutral group (amide), and an ionic group (sulfonic salt). With the hydrogen bond and ionic bond, ADD could absorb on Na-BT layers strongly and a strong net structure was formed. The sulfonic group and the amide group would enhance the double electronic layers of Na-BT layers and increase the repulsive force between Na-BT layers. After 11.1% CaCl2 contamination, a large amount of Ca2+ would be prevented from forming ion exchange adsorption with Na-BT
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CONCLUSION We synthesized an amphoteric polymer ADD as a highperformance fluid-loss additive for anti-Ca2+ contamination. The API filtration test and rheology test showed that Na-BTbased mud with ADD could resist 11.1% CaCl2 contamination and 150 °C aging. In comparison to anionic polymer AD, ADD had a strong force with Na-BT layers through ionic bonding and hydrogen bonds. This strong force could prevent large amounts of Ca2+ adsorption on the surface of Na-BT layers and protected the Na-BT layers from coagulation under high amounts of Ca2+ contamination. On the basis of this strong force, a typical “star-net” structure was formed between Na-BT layers and ADD polymer chain under 11.1% CaCl 2 contamination and 150 °C hot rolling. This “star-net” structure could dramatically improve the rheological properties of WBDs, such as high shear stress, viscosity, and better shear thinning behavior, and also lock more free water around Na-BT layers. As a result, Na-BT-based mud could form a compact filtrate cake and maintain a low FLAPI under Ca2+ contamination. With its superior rheological and filtration properties, amphoteric polymer ADD has potential for use in deep gypsum drilling 7226
DOI: 10.1021/acs.energyfuels.6b01567 Energy Fuels 2016, 30, 7221−7228
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Figure 9. EDS analysis of Na-BT layers in Na-BT-based mud (hot rolling at 150 °C for 16 h).
Table 5. Ca, Cl, N, and S Element Amounts in Different Samples (Sample 1, 4% Na-BT-Based Mud + 11.1% CaCl2; Sample 2, 4% Na-BT-Based Mud + 1.5% AD + 11.1% CaCl2; Sample 3, 4% Na-BT-Based Mud + 1.5% ADD + 11.1% CaCl2; and HRReflected Sample, under 150 °C Hot Rolling for 16 h) sample sample sample sample
Ca (atomic ratio %)
Cl (atomic ratio %)
N (atomic ratio %)
S (atomic ratio %)
7.78 2.87 4.56 0.82
0.23 1.63 8.99 0.09
0 11.37 0.69 14.66
0 0.11 0 0.07
1 (HR) 2 2 (HR) 3 (HR)
operations containing large amounts of Ca2+ and high temperatures underground.
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AUTHOR INFORMATION
Corresponding Author
*Telephone: 010-89732239. E-mail:
[email protected]. edu.cn. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This research was financially supported by the National Natural Science Foundation of China (Grants 51521063 and 51474231), the National Major Scientific and Technological Special Project (Grant 2016ZX05022-001-001-001), the National 863 Foundation of China (2013AA064803), and the New Method and Technology Foundation of China National Petroleum Corporation (2014A-4212).
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DOI: 10.1021/acs.energyfuels.6b01567 Energy Fuels 2016, 30, 7221−7228
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Energy & Fuels
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DOI: 10.1021/acs.energyfuels.6b01567 Energy Fuels 2016, 30, 7221−7228
