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Synthesis and Characterization of Modified Aliphatic Polycarbonates as Environmentally-Friendly Oilfield Scale Inhibitors Mohamed F. Mady, Preeyarad Charoensumran, Hiroharu Ajiro, and Malcolm A. Kelland Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b01168 • Publication Date (Web): 21 May 2018 Downloaded from http://pubs.acs.org on May 22, 2018

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is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

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Energy & Fuels

Synthesis

and

Characterization

of

Modified

Aliphatic

Polycarbonates as Environmentally-Friendly Oilfield Scale Inhibitors

Authors: Mohamed F. Madya,b,, Preeyarad Charoensumran,c Hiroharu Ajiro,c Malcolm A. Kellanda,* a

Department of Chemistry, Biological Science and Environmental Technology, Faculty of

Science and Technology, University of Stavanger, N-4036 Stavanger, Norway b

Department of Green Chemistry, National Research Centre, 33 El Bohouth st. (former El Tahrir

st.), Dokki, Giza, Egypt, P.O. 12622 c

Graduate School of Materials Science and Institute for Research Initiatives, Nara Institute of

Science and Technology, 8916-5, Takayama-cho, Ikoma, Nara 630-0192, Japan

*Corresponding author: Malcolm A. Kelland (M.A. Kelland) E-mail: [email protected]

Abstract: Oilfield scale inhibitors have been used for many decades, mostly to fight carbonate and sulfate scaling. Many inhibitors are known but only a few show good biodegradation to make them environmentally-acceptable in area with strict regulations such as offshore Norway. Often high 1

ACS Paragon Plus Environment

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biodegradation is at the expense of other useful properties such as thermal stability for high temperature squeeze applications. We have now synthesized and investigated a new class of polycarbonate polymer with pendant anionic functional groups (carboxylate and phosphonate) as potential oilfield scale inhibitors. These polymers have a carbonate group in the backbone. Polymers with carboxylate and phosphonate side groups were prepared. We report here the scale inhibition performance of these polymers at 100 oC against both calcite and barite scaling at typical North Sea conditions in dynamic tube blocking equipment, both before and after ageing at 130 oC. The phosphonated copolymer gave very good performance against calcite scaling and showed good thermal stability. This polymer also gave a biodegradation of 36% in 28 days in seawater by the OECD306 test.

1. Introduction Deposition of sparingly soluble inorganic salts is a major problem to the upstream oil industry.1-4 Salts such as calcium carbonate (calcite) as well as the sulfate salts of barium (barite), strontium (celesite) and calcium (anhydrite or gypsum) are common examples. Less common scales are sodium chloride (halite), calcium fluorite and sulfides of zinc, lead, iron. The collective name for these deposits is ”scale.” Scale formation can cause formation damage, blockage of wells and topside flow lines as well as forming accumulations in processing equipment. A common method for prevention of scale deposits is the use of scale inhibitors (SIs). For carbonate and sulfate scales these SIs are usually organic molecules with specific functional groups designed to prevent nucleation and/or crystal growth. The most important functional groups are carboxylate, 2


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phosphonate or sulfonate groups, which are of similar size and mimic the carbonate and sulfate dianions in the scales. Phosphate, phosphinate, amide, alcohol, quaternary ammonium and other functional groups may also be found in some SIs but these groups are not the primary scale inhibition groups. One way to apply SIs is the so-called squeeze treatment in which fluids containing the SI are pumped into the formation and shut in for some hours to allow the inhibitor to adsorb onto the formation rock. Well production is then restarted and this store of SI slowly desorbs off the rock into the produced water giving sufficient concentration to prevent scaling. The concentration of SI in the water will slowly diminish and when it approaches a level that does not give complete scale control the well is re-squeezed. SIs with phosphonate groups give high performance, and particular useful for squeeze treatments as they adsorb well onto the rock giving long squeeze lifetimes. Phosphonates are also easier to detect than carboxylate or sulfonate groups. However, many of the classic phosphonate scale inhibitors such as diethylenetriaminepentakis-(methylenephosphonic acid) (DTPMP) and aminotris-(methylenephosphonic acid) (ATMP) show poor biodegradability which means they are not allowed for use in regions with strict environmental regulations such as offshore Norway or Denmark.1,4,6-7 In general classic carboxylate SIs such as those based on acrylates and methacrylates, as well as many maleic-based SIs are also poorly biodegradable due to the polyvinyl backbone. A few more biodegradable polycarboxylate SIs are commercially available and include polyaspartate (PAsp), polyepoxysuccinic acid (PESA) and carboxymethylinulin

3


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(CMI).8-19 The first two of these SIs have linear backbones but containing heteroatoms to improve the biodegradability compared to polyvinyl based polymers (Figure 1).

Figure 1. Polyepoxysuccinic acid (PESA), left; polyaspartic acid (PAsp), right.

Another class of linear polymers with heteroatoms in the backbone are the aliphatic polycarbonates (APC). This class has attracted attention, due to good biodegradability, biocompatibility and low toxicity.20-22 An example from this class is poly(trimethylenecarbonate) (PTMC). TMC can be copolymerized with other cyclic comonomers such as lactide, glycolide, and e-caprolactone to vary the properties of the polymer. Alternatively, functional end-groups can be added such as carboxylate groups (Figure 2).23

4


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Figure 2. General structure of aliphatic polycarbonates.

In this work, we have synthesized linear polycarbonates with pendant carboxylate and/or phosphonate groups. We report the calcite and barite scale inhibition performance of these polymers before and after thermal ageing at 130 oC, as well as their calcium compatibility and seawater biodegradation properties.

2. EXPERIMENTAL SECTION 2.1. Chemicals All chemicals were purchased from Tokyo Chemical Industry Co., Ltd. and Nacalai tesque. All solvents were used as purchased without further purification. A low molecular weight polyaspartic acid (PAsp) was obtained from NanoChem Solutions. The sodium salts of diethylenetriaminepentakis-(methylenephosphonic

acid)

(DTPMP)

and

aminotris-

(methylenephosphonic acid) (ATMP) were obtained from Solvay. A sample of a low molecular weight (ca. 8000 g/mole) sodium polyacrylate (PAA) called Sokalan PA30 was obtained from BASF.

2.2. Characterization of Scale Inhibitors Nuclear magnetic resonance (NMR) spectra were recorded on a 400 MHz Varian NMR spectrometer in Chloroform-d (CDCl3) and Dimethyl sulfoxide-d6 (DMSO-d6). 1H and 5


13

C

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chemical shifts were obtained by using TMS as an internal standard. The molecular weight and molecular weight distribution of the new polymers were determined by gel permeation chromatography, using polystyrene (for DMF solution) and polyethylene glycol (for water solution) samples as molecular-weight standards. Gel permeation chromatography was performed with a HLC 8220 chromatograph (Tosoh Co., Tokyo, Japan) equipped with TSK gel super HM-H H4000/H3000/H2000 (7.8 mm diameter, 150 mm × 3), Tosoh Company (Two polymers did give high polydispersity index (PDI) values; attempts were first made to obtain good Mw data using water and PEB standards, but the results were not meaningful for interpretation).

2.3. Synthesis of Scale inhibitors (SIs) (Figure 3) 2.3.1. Synthesis of aliphatic polycarbonates blended carboxylic group (PCA-COOH) 5

Synthesis of Benzyl 2,2-bis(hydroxymethyl) propionate (Bn-MPA) 2. To a solution of 2,2bis(hydroxymethyl) propionic acid (10 g, 74.5 mmol) in dry DMF (40 mL) was added potassium hydroxide (5 g, 89.5 mmol). The mixture was stirred vigorously at 100 oC until it turned homogenous (1h). Benzyl bromide (10.64 mL, 89.5 mmol) was then added dropwise slowly. The solution was heated at reflux for 18 h and then concentrated by evaporation under vacuum. The residue was extracted with Et2O four times. The starting material can then be separated out as it dissolves in an aqueous phase. The organic phase was washed with saturated NH4Cl then dried over anhydrous Na2SO4 filtered and concentrated providing pale yellow viscous liquid. The 6


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residue was purified by recrystallization in toluene: hexane (1:9, v:v). A total of Bn-MPA (8.8 g, 39.2 mmol) was obtained at Rf = 0.2 with EtOAc:hexane (6:4, v:v). Yield 53%. 1

H NMR (CDCl3, 400MHz) δ: 1.08 (s, 3H, -CH3), 3.73-3.96 (dd, J =2.33 Hz and 1.77 Hz, 2H×2,

CH2-OH), 5.21 (s, 2H, CH2-OBn), 7.36 (m, 5H, -C6H5)

Synthesis of 5-Methyl-2-oxo-1,3-dioxane-5-carboxylic acid (TMC-OBn) 3 A solution of Bn-MPA 2 (3.3 g, 14.7 mmol) and ethyl chloroformate (5.6 mL, 59 mmol) in THF (15 mL) at 0 oC under N2 atmosphere was prepared. Then trimethylamine (6.73 mL, 48.5 mmol) was added dropwise with stirring via an addition funnel. After that stirring was continued for 1 h at 0 oC. The solution was further stirred for 2 h at room temperature and then concentrated under vacuum. The residue was extracted with EtOAc four times. The starting material can then be separated out as it dissolves in an aqueous phase. The organic phase was washed with saturated NH4Cl then dried over anhydrous Na2SO4, filtered and concentrated providing a pale pink solid. The residue was purified by recrystallization in EtOAc as a good solvent and hexane as poor solvent. A total of TMC-OBn (2.9 g, 11.4 mmol) was obtained at Rf = 0.15 with EtOAc:hexane (4:6, v:v). Yield 78%. 1

H NMR (CDCl3, 400MHz) δ: 1.32 (s, 3H, CH3), 4.18-4.71 (dd, J= 2.12 Hz and 1.89 Hz, 2H×2,

-CH2-C=O), 5.21 (s, 2H, -CH2-OBn), 7.36 (m, CH5, -C6H5)

7


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Polymerization Synthesis of aliphatic polycarbonates 4 To a solution of TMC-OBn 3 (2.8g, 11.2 mmol) in anhydrous CH2Cl2 (15 mL) with CaH2 was stirred overnight to remove the humidity. Using a cannula with glass filter to transfer the monomer solution to the other flask with a three-way stop cock, and the solvent (CH2Cl2) was evaporated under reduced pressure. Then, the required amount of anhydrous CH2Cl2 under nitrogen atmosphere was introduced. Into the monomer solution, benzyl alcohol (0.12 mL, 1.1 mmol) and 1,8-Diazabicyclo(5.4.0)undec-7-ene (DBU) (17 µL, 0.1 mmol) as catalyst were added to start the polymerization at room temperature for 36 h. The reaction was stopped by adding small portion of acetic acid, and then the reaction mixture was poured into a large amount of hexane. The product was recovered by decantation and centrifugation and dried under vacuum (75% yield). 1

H NMR (CDCl3, 400MHz) δ: 1.24 (s, 3H, CH3), 4.29 (br t, 2H×2, -CH2), 5.17 (s CH2-C6H5),

7.29 (m, CH×5, C6H5) Deprotection of TMC-OBn (PCA-COOH) 5 To a solution of TMC-OBn 4 (4.7 g, 18.9 mmol) in 1/1; THF/CH2Cl2 was added Pd/C (0.2 mg, 1.89 mmol). The solution was stirred at 40o C under H2 atmosphere with balloon for corresponding time. To remove the Pd/C, the solution was filtered under silica gel. The filtrate was concentrated under vacuum obtaining a white fluffy solid (98 % yield). Mw = 2500 g/mole, PDI = 1.33. 8


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1

H NMR (DMSO, 400MHz) δ: 1.18 (s, 3H, CH3), 4.24 (br d, 2H×2, -CH2)

2.3.2. Synthesis of aliphatic polycarbonates blended phosphonate groups (PCA-PO3H2COOH) 7 To a solution of TMC-COOH 5 (2.6 g, 12 mmol) in deionized water (2.5% w/v) was added 2iminodimethyl-phosphonic acid 6 (3.69 g, 18 mmol) and NHS (2.18 g, 36 mmol) respectively. The solution was adjusted to pH 4.7 by using aqueous NaOH, then the EDC (3.34 mL, 36 mmol) was added. The mixture was stirred at room temperature overnight. It was dialyzed against deionized water by using a dialysis membrane with a molecular weight cut-off 4.5 kDa then concentrated under vacuum. The residue was precipitated in weak acid aqueous solution (pH ~4) then the precipitate was collected by centrifugation and dried under vacuum. A total of 2.18 g of biphosphonated product, PCA-PO3H2-COOH, was obtained. Mw = 21000 g/mole, PDI = 2.62 . 1

H NMR (DMSO, 400MHz) δ: 1.1 (br s, 3H×2, CH3), 2.82 (br d, 2H×2, CH2-PO3H2), 3.11 (br s,

2H×2, O-(CH2)2-CCH3CON(CH2PO3H2)2), 4.22 (br s, O-(CH2)2-CCH3COOH)

9


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Figure 3. (A) Synthesis of aliphatic polycarbonates containing carboxylic group (PCA-COOH) 5, (B) Functionalization of PCA-COOH with phosphonate groups to PCA-PO3H2-COOH 7. 10


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2.4. High-Pressure Dynamic Tube Blocking Test Methods Scale inhibition performance tests for calcite and barite scales were carried out using dynamic tube blocking test equipment. This equipment is an automated rig (built by Scaled Solutions Ltd., Scotland) using a 1 mm internal diameter 316 steel test coil. (Figures 4-5). Tests were carried out at 100 oC and 80 bar as previously described by injecting the cation and anion separately and mixing them at the test temperature in the test coil.24 Scale inhibitor is also added to measure its efficacy. The stock solution of each inhibitor was a 1000 ppm solution at pH 6-7. Usually the maximum starting scale inhibitor concentration in the test was 100 ppm for 1 h, followed by 1 h each at 50, 20, 10, 5, 2 and 1 ppm. The SI concentration at which rapid tube blocking occurs giving a differential pressure of 9 psi (ca. 0.6 bar) was taken as the fail inhibitor concentration (FIC) of the SI (The choice of 9 psi is due to a balance of factors. If we used more than 9 psi we might risk plugging the coil if scale forms very fast, e.g. with barium sulfate. If we use less than 9 psi we may misinterpret the formation of true scale. For example, there may be an incompatibility of the scale inhibitor with calcium ions, which would lead to a deposit of Ca-SI causing a slow rise in differential pressure. We would not want to confuse this with a true inorganic scaling situation). The time during the hour interval at which rapid scaling occurred was also recorded. In the field operators often refer to the minimum inhibitor concentration (MIC) which prevents scale formation. The MIC may be somewhat higher than the FIC. For example, if we find that a SI gives rapid scale during the hour when 5 ppm SI was used, then 5 ppm is the FIC. The MIC will be somewhat higher, usually somewhere between 5 ppm and the 11


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next highest concentration that gave no scaling, i.e. somewhere between 5-10 ppm. However, a kinetic factor must also be considered. Our tests are only for 1 h at any one SI concentration, but scale formation in the field may need to be controlled for longer times than this.

Figure 4. The dynamic tube blocking equipment for scale inhibitor performance testing.

12


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Figure 5. Diagram of fluid flow in the dynamic tube blocking equipment for scale inhibitor testing.

The aqueous fluids used in this study were based on produced fluids from the Heidrun oilfield, Norway. We used a 1/1 volume mixture of synthetic seawater and formation water to produce barium sulfate scaling using all the ions in Table 1 except bicarbonate ions. The same ratio was used for calcite scaling but instead of sulfate ions we used bicarbonate ions. All brines were degassed using a vacuum pump for 15 min.

Table 1. The composition of formation water, seawater and a 50/50 mixture.

Ion

Heidrun formation water

Seawater 13


50/50 Mixed brine

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(ppm)

(ppm)

(ppm)

Na+

19,510

10,890

15,200

Ca2+

1020

428

724

Mg2+

265

1368

816.5

K+

545

460

502.5

Ba2+

285

0

142.5

Sr2+

145

0

72.5

SO42-

0

2960

1480

HCO3-

880

120

500

2.5. Hydrothermal Stability Test A 20 wt.% solution of a polymer is made up in deionized water. The solution is purged with nitrogen gas for 1 h to remove dissolved oxygen and then placed in a pressure tube. The tube is also purged with nitrogen and then heated at 100 °C for one week. Samples of the thermally aged solution were then checked for calcite and barite scale inhibition in the dynamic tube blocking equipment.

2.6. Compatibility Tests The calcium compatibility of PCA-COOH and PCA-PO3H2-COOH were investigated using a mixture of deionized water and synthetic brine. In this procedure 10 ml of aqueous sodium 14


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chloride at 30000 ppm (3.0 wt.%) was placed in a 50 ml glass bottle. Calcium chloride (as the dihydrate salt) was added to give the required calcium concentration of 100 ppm to 10000 ppm. The SI was dissolved in this solution to give the required concentration from 100 ppm to 50000 ppm. The bottles were placed in an oven at 100 oC and viewed after 0.5, 1, 2, 4 and 24 hours to check for turbidity and/or precipitation.

2.7. Scale Inhibitor Seawater Biodegradability Tests Seawater biodegradability was carried out using the OECD306 method.25-27 This constitutes measuring the biological oxygen demand (BOD) of a chemical over a 28 day period and comparing it to the calculated theoretical oxygen demand (ThOD). The equipment used was the OxiTop ® Control manometric system (WTW, Germany) with 510 ml volume amber bottles. Seawater was obtained from Byfjorden, a fjord outside Stavanger, Norway from a pipe 70 m down and at temperature 12 °C. 297 ml seawater with nutrients were added to ensure nonlimiting conditions for microbial activity and growth. Each chemical was tested in triplicate plus three different types of control flasks. The control flasks included: (1) blanks with nutrientamended seawater only, (2) negative controls with autoclaved seawater, nutrients and the test compounds at 60 mg/l final concentration, and (3) positive controls with nutrient-amended seawater and sodium benzoate, an easily biodegradable substrate. After incubation, a 1.8 ml sample of a 1.0 w/w % solution of each chemical was added to the test and negative control flasks, while 1.0 ml of a 30 g/l sodium benzoate solution was added to the positive control flasks. The bottles were sealed with heads containing a stirrer bar and sodium hydroxide to remove CO2 15


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gas produced. They were placed on magnetic stirrers in an unlit incubator cabinet at 20 oC. From the pressure drop the oxygen consumption is recorded for 28 days. After this time ThOD of the chemicals was calculated as laid out in the OECD 306 guidelines, taking into account complete nitrification. Calculation of the percentage biodegradability (BOD28) according to the OECD 306 guidelines was carried out after deducting blank oxygen consumption values, which represent seawater background respiration.

3. RESULTS AND DISCUSSION 3.1 High-pressure scale inhibition tube blocking experiments Two new polycarbonate polymers, PCA-COOH and PCA-PO3H2-COOH, were synthesised. The yields were high and the purity is at least 98% from NMR spectroscopic analysis. No other substance was identified in the isolated products. Infra red (IR) spectroscopy was used to confirm the presence of carboxylic acid groups (See Supplementary Material). Tables 2 and 3 summarises the results from the dynamic tube blocking scale inhibition tests for barite scaling and calcite scaling respectively. Besides the two new polycarbonate polymers, PCA-COOH and PCA-PO3H2-COOH we also tested for comparison purposes several commercial products: sodium polyaspartate (PAsp), which is a known biodegradable polycarboxylic acid derivative, sodium polyacrylate (PAA) and the sodium salts of two nonpolymeric phosphonates, diethylenetriaminepentakis-(methylenephosphonic acid) (DTPMP) and aminotris-(methylenephosphonic acid) (ATMP). The columns in these tables summarise the four 16


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test results from a single “run” of the equipment: a blank test, a scale inhibitor test, a repeat scale inhibitor test and a new blank test. The first test is a blank test with no inhibitor, just the scaling ions. For barite scale in Table 2 the blank time before a rapid change in differential pressure is about 4-7 min; for calcite scale in Table 3 the delay time is slightly longer, about 7-9 min. Between each test an automatic cleaning of the tubing with 5 wt.% Na2EDTA and deionized water takes place. For the barite SI tests, the two commercial non-polymeric phosphonates, ATMP and DTPMP gave good performance with FIC values of 10 and 5 ppm respectively. The much more biodegradable PAsp gave an exceptional performance under the test conditions: it gave no pressure change across the coil, and therefore no scaling, after 1 h at 2 min and only gave rapid scaling after 7-9 min at 1 ppm. PAA which is a classic scale inhibitor and dispersant with poor biodegradability gave rapid scaling only when the concentration reached 2 ppm. However, we noticed a pressure build-up across the coil even at 50 ppm but it never reached the 9 psi differential pressure that shuts off the injection of the scaling ions and starts the coil cleaning process. We repeated this experiment with fresh solution and obtained the same result. A graph of one of these experiments is shown in Figure 6. We do not think this is due to calcium incompatibility since the tests for calcite scaling showed only a weak incompatibility effect (if any) and yet had higher calcium concentration (Table 1, Figure 7). Another reason that this is not a calcium incompatibility effect is because the differential pressure drops very rapidly at least twice, once at 50 ppm and again at 20 ppm PAA. We propose this may be due to the dispersant properties of PAA, suddenly loosening a particles or particles in the coil. In contrast, the new polycarbonate polymer with pendant carboxylate groups PCA-COOH gave poor performance, 17


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scaling rapidly at 13 min at 100 ppm. The phosphonated polycarbonate PCA-PO3H2-COOH performed somewhat better. In both tests a pressure difference was observed due to scaling during the end of the first hour at 100 ppm and rapid scaling occurred 1 min inside the 50 ppm window. The graphical results for this test are given in Figure 8.

For the calcite SIs tests, the two phosphonates ATMP and DTPMP gave reasonable performances with FIC values of 20 and 10 ppm respectively. PAA was not so effective giving an FIC of 20 ppm (Figure 7) whereas PAsp gave again excellent performance with an FIC of 1 ppm. For the new polymers, PCA-COOH showed poor performance with an FIC of 100 ppm. However, PCA-PO3H2-COOH gave very good calcite scale inhibition with an FIC of 2 ppm, which was significantly better than either of the non-polymeric phosphonates. The graphical results for this test are given in Figure 9. Clearly, for both calcite and barite scales the carboxylated polymer PCA-COOH is a poor inhibitor. The density of carboxylate groups could be one factor in this observation, as there is only one pendant carboxylate group for every 6 backbone atoms. In PAA or PAsp this number is 2 or 3 backbone atoms. PCA-PO3H2-COOH showed itself to be a very good calcite inhibitor but this polymer has two phosphonate groups for every 6 backbone atoms.28-29 For squeeze treatments it is important that the scale inhibitor has thermal stability at the reservoir temperature where it is squeezed. Therefore, we investigated the thermal stability of PCAPO3H2-COOH and the biodegradable PAsp at 130 oC. PCA-COOH was not tested for thermal stability due to its poor performance. After one week under anaerobic conditions at 130 oC the 18


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scale inhibitor was retested. The results in Tables 2 and 3 show that PAsp lost its performance greatly, going from a FIC of 1 ppm to 50 ppm for barite scaling and from a FIC of 1 to 20 ppm for calcite scaling. This suggests that this sample of PAsp would not be useful for squeezing at 130 oC (Other PAsp products may possibly have given greater thermal stability). In contrast PCA-PO3H2-COOH showed much better thermal stability. For barite scaling, the performance dropped slightly but it wasn’t very good before thermal ageing anyway (Figure 10). For calcite scaling, the FIC dropped from 2 to 5 ppm, showing that this polymer was only partially degraded after thermal ageing and still retained relatively good performance (Figure 11).

Table 2. Summary of barite scale inhibition tests showing FIC values. Inhibitor

First blank

First scale test

Second scale test Concn. Time (ppm) (mins) 10 16

Second blank Time (mins) 6

Time (mins) 4

Concn. (ppm) 10

Time (mins) 13

DTPMP

5

5

9

5

11

7

PAA

11

2

10

2

17

8

PAsp

4

1

7

1

9

6

PCA-COOH

7

100

13

100

13

8

PCA-PO3H2-COOH

6

50

1

50

1

8

PAsp a

5

50

20

50

22

6

PCA-PO3H2-COOH a

5

100

30

100

35

7

ATMP

19


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 33

a

PAsp and PCA-PO3H2-COOH were tested for sulfate scale after thermal ageing at 130oC for one week under anaerobic conditions.

Table 3. Summary of calcite scale inhibition tests showing FIC values. Inhibitor

First blank

First scale test

Second scale test Second blank Concn. Time Time (ppm) (mins) (mins) 20 26 9

Time (mins) 7

Concn. (ppm) 20

Time (mins) 26

DTPMP

7

10

20

10

20

9

PAA

9

20

8

20

5

9

PAsp

8

1

35

1

38

8

PCA-COOH

9

100

25

100

20

7

PCA-PO3H2-COOH

7

2

16

2

16

9

PAsp a

8

20

30

20

27

9

PCA-PO3H2-COOH a

9

5

1

5

6

8

ATMP

a

PAsp and PCA-PO3H2-COOH were tested for carbonate scale after thermal ageing at 130oC for one week under anaerobic conditions.

20


Page 21 of 33

1600

18

1400

16 14

Abs pressure (psi)

12 1000

10

800

8

20 ppm

50 ppm

600

5 ppm

5 2 ppm ppm

10 ppm

6

2 ppm

4

Diff pressure (psi)

1200

400 2 200 0

0 0

50

100

150

200

250

300

350

400

450

0

50

100

150

200

250

300

350

400

450

-2

Time (min) abs tdx1

abs tdx2

diff 1

Figure 6. FIC and time values from high-pressure dynamic tube blocking experiments of PAA

1600

48

1400

43 38 33

1200 1000 800

28 23 18 13

50 ppm

600 400

Diff pressure (psi)

for barite scale.

Abs pressure (psi)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

8 3 -2

200 0 0

20

40

60

80

100

120

140

160

180

200

Time (min) abs tdx1

abs tdx2

diff 1

Figure 7. FIC and time values from high-pressure dynamic tube blocking experiments of PAA for calcite scale. 21


Energy & Fuels

1200

16 14

1000

800 10 600

8 6

400

100 ppm

50 ppm

100 ppm

50 ppm

Diff pressure (psi)

12

Abs pressure (psi)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 33

4

200 2 0

0 0

50

100

150

200

Time (min) abs tdx1

abs tdx2

diff 1

Figure 8. FIC and time values from high-pressure dynamic tube blocking experiments of PCAPO3H2-COOH for sulfate (barite) scale.

22


Page 23 of 33

1200 15 1000

13 11

800

9 600

100 ppm

50 ppm

20 ppm

10 ppm

2 5 ppm ppm

5 ppm

2 ppm

7 5

400

3

Diff pressure (psi)

Abs pressure (psi)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

200 1 0

-1 0

50

100

150

200

250

300

350

400

450

500

Time (min) abs tdx1

abs tdx2

diff 1

Figure 9. FIC and time values from high-pressure dynamic tube blocking experiments of PCAPO3H2-COOH for carbonate (calcite) scale.

23


Energy & Fuels

1200

20 18

1000 16

800 12 600

10 ppm

20 ppm

50 ppm

5 ppm

10 ppm

10

5 ppm

8

400

Diff pressure (psi)

14

Abs pressure (psi)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 33

6 4 200 2 0

0 0

50

100

150

200

250

300

350

Time (min) abs tdx1

abs tdx2

diff 1

Figure 10. FIC and time values from high-pressure dynamic tube blocking experiments of PCAPO3H2-COOH after aging at 130 °C for carbonate (calcite) scale.

24


1200

12

1000

10

800

8

600

6

Abs Pressure (psi)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

100 ppm

100 ppm

400

4

200

2

0

Diff Pressure (psi)

Page 25 of 33

0 0

50

100

150

Time (mins) abs tdx1

abs tdx2

diff 1

Figure 11. FIC and time values from high-pressure dynamic tube blocking experiments of PCAPO3H2-COOH after aging at 130 °C for sulfate (barite) scale.

3.2 Calcium compatibility From the tube blocking scale inhibitor test of PCA-PO3H2-COOH on calcite scaling we see a slow rise in the differential pressure when the concentration was 50 ppm and even more so for 100 ppm (Figures 9-10). The calcium concentration in these tests is 724 ppm. This is a typical observation of an incompatibility between the inhibitor solution and the calcium ions in the brine. Many phosphonate-based SIs are known to have worse calcium compatibility than 25


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

polycarboxylate or polysulfonate-based SIs.1,30 This incompatibility is not seen with PCACOOH in the carbonate tube blocking tests because the actual SI performance is poor such that pressure changes due to calcium carbonate formation rapidly masked any incompatibility effects. Calcium compatibility is important when squeezing scale inhibitors. You do not want a calciumscale inhibitor complex to precipitate, epecially in the near-well area where it could cause formation damage and block fluid flow. To get a better understanding of the compatibility of the new polymers PCA-COOH and PCA-PO3H2-COOH with calcium ions we carried out a matrix of compatibility tests at 100 oC. The results are summarised in Tables 4-9. The inhibitor concentration was varied from 100 ppm to 50000 ppm whilst the calcium ion concentration was varied from 100 ppm to 10000 ppm. A brine concentration of 30000 ppm was also used to give some representation of a typical salinity of a field formation water. PCA-COOH showed good calcium compatibility at all inhibitor concentrations and 100 ppm calcium ions. For 1000 ppm calcium ions no precipitate was observed throughout the 24 h test period and at all inhibitor concentrations. This haze that resulted at the two higher inhibitor concentrations showed no signs of precipitate. This indicates that formation damage by deposition should not be a problem at these concentrations. For 10000 ppm calcium ions the compatibility was worse since a precipitate formed with 10000 and 50000 ppm of the polymer. PCA-PO3H2-COOH gave no incompatibility at all concentrations tested with 100 ppm calcium ions. At 1000 ppm calcium ions we only observed a minor amount of precipitate after 24 h with the 50000 ppm (5 wt.%) polymer solution. These observations indicate that the phosphonated polymer has somewhat worse compatibility with calcium ions at the test temperature of 100 oC 26


Page 26 of 33

Page 27 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

than the carboxylated polymer, in line with the pressure increase observed with the calcite tube blocking tests. At 10000 ppm calcium ions the incompatibility with PCA-PO3H2-COOH is more pronounced. Both PCA-COOH and PCA-PO3H2-COOH are first generation prototype polymers in this new class of scale inhibitors. Incorporation of other functional groups such as sulfonate would undoubtedly improve the calcium compatibility. This is on the agenda for our future work on this polymer class.

Table 4. Compatibility tests in 100 ppm of Ca2+ and 30000 (3.0 wt.%) NaCl for PCA-COOH.

Scale inhibitor

Dose

Appearance

(ppm)

At Mixing

30 mins

1 hour

4 hours

24 hours

PCA-COOH

100

Clear

Clear

Clear

Clear

Clear

PCA-COOH

1000

Clear

Clear

Clear

Clear

Clear

PCA-COOH

10000

Clear

Clear

Clear

Clear

Clear

PCA-COOH

50000

Clear

Clear

Clear

Clear

Clear


Scale inhibitor

PCA-COOH

Dose (ppm)

100

Appearance At Mixing

30 mins

1 hour

4 hours

24 hours

Clear

Clear

Clear

Clear

Clear

27


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Page 28 of 33

PCA-COOH

1000

Clear

Clear

Clear

Haze

Haze

PCA-COOH

10000

Haze

Haze

Haze

Haze

Haze

PCA-COOH

50000

Haze

Haze

Haze

Haze

Haze


Scale inhibitor

Dose

Appearance

(ppm)

At Mixing

30 mins

1 hour

4 hours

24 hours

PCA-COOH

100

Clear

Clear

Clear

Clear

Clear

PCA-COOH

1000

Clear

Haze

Haze

PCA-COOH

10000

Haze

PCA-COOH

50000 Precipitated Precipitated Precipitated Precipitated Precipitated

Haze

Haze

Haze

Precipitated Precipitated Precipitated

Table 7. Compatibility tests in 100 ppm of Ca2+ and 30000 ppm (3.0 wt.%) NaCl for PCAPO3H2-COOH.

Scale inhibitor

Dose

Appearance

(ppm)

At Mixing

30 mins

1 hour

4 hours

24 hours

PCA-PO3H2-COOH

100

Clear

Clear

Clear

Clear

Clear

PCA-PO3H2-COOH

1000

Clear

Clear

Clear

Clear

Clear

PCA-PO3H2-COOH

10000

Clear

Clear

Clear

Clear

Clear

PCA-PO3H2-COOH

50000

Clear

Clear

Clear

Clear

Clear

28


Page 29 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

Table 8. Compatibility tests in 1000 ppm of Ca2+ and 30000 ppm (3.0 wt.%) NaCl for PCAPO3H2-COOH.

Scale inhibitor

Dose

Appearance

(ppm)

At Mixing

30 mins

1 hour

4 hours

24 hours

PCA-PO3H2-COOH

100

Clear

Clear

Clear

Clear

Clear

PCA-PO3H2-COOH

1000

Clear

Clear

Clear

Clear

Clear

PCA-PO3H2-COOH

10000

Haze

Haze

Haze

Haze

Haze

PCA-PO3H2-COOH

50000

Haze

Haze

Haze

Haze

Precipitated

Table 9. Compatibility tests in 10000 ppm of Ca2+ and 30000 pm (3.0 wt.%) NaCl for PCAPO3H2-COOH.

Scale inhibitor

Dose (ppm)

Appearance At Mixing

30

1 hour

4 hours

24 hours

mins PCA-PO3H2-COOH

100

Clear

Clear

Clear

Clear

Clear

PCA-PO3H2-COOH

1000

Clear

Clear

Clear

Clear

Clear

PCA-PO3H2-COOH

10000

Haze

Haze

Haze

Haze

Haze

PCA-PO3H2-COOH

50000

Haze

Haze

Precipitated Precipitated

29


Precipitated

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 33

3.3 Biodegradation activities Table 10 summarises the percentage of biodegradation after 28 days in seawater (BOD28) according to the OECD306 test procedure. Each chemical was tested in triplicate and average values are given here. The deviation was ±10 wt.%. The standard used, sodium benzoate gave the expected biodegradation in the range 80-90 %. In comparison, PCA-COOH gave only an average of 7% biodegradation and PCA-PO3H2-COOH gave 36 %. Based on these results we speculate that the backbone of the polycarbonate may be quite stable to biodegradation and that the aminobismethylenephosphonate side groups contribute to most of the biodegradation of PCA-PO3H2-COOH. The nitrogen and phosphorus in these side chains are also nutrients to the biodegrading organisms and therefore may also contribute to stimulate growth and biodegradation.

Table 10. Biodegradability activity measured by the OECD 306 procedure over 28 days. Inhibitor

% BOD

Seawater

0

Sodium benzoate

86

PCA-COOH

7

PCA-PO3H2-COOH

36

30


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4. CONCLUSION A new class of polycarbonate polymer with pendant anionic functional groups (carboxylate and phosphonate) has been investigated for the first time for their potential as oilfield scale inhibitors. The carboxylated homopolymer PCA-COOH gave poor performance against both calcite and barite scaling but the phosphonated copolymer PCA-PO3H2-COOH gave good performance, particularly against calcite scaling. In addition, PCA-PO3H2-COOH showed good thermal stability, giving only a small loss of scale inhibition performance when aged anaerobically for 1 week at 130 oC. PCA-PO3H2-COOH also showed reasonable biodegradation of 36% in 28 days in seawater by the OECD306 test. The calcium compatibility of PCA-PO3H2COOH was shown to be limited but could be improved by incorporating other functional groups such as sulfonate.

ACKNOWLEDGMENTS We gratefully acknowledge Total E&P Norge AS for financial support.

REFERENCES 1. Kelland, M. A. Production Chemicals for the Oil and Gas Industry, Second Edition, CRC Press: Baton Rouge, Florida, U.S.A, 2014. 31


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2. Amjad, Z. The Science & Technology of Industrial Water Treatment, CRC Press: Boca Raton Florida, 2010. 3. Sallis, J. D.; Juckes, W.; Anderson, M. E. In Mineral Scale Formation and Inhibition; Amjad, Z., Ed.; Plenum Press: New York, 1995; pp 87−98, DOI: 10.1007/978-1-4899-1400-2_8. 4. Frenier, W. W.; Ziauddin, M. Formation, Removal and Inhibition of Inorganic Scale in the Oilfield Environment, SPE Publishing: Houston, U.S., 2008. 5. Popov, K. I.; Kovaleva, N. E.; Rudakova, G. Y. Therm. Eng. 2016, 63, 122. 6. Mady, M. F.; Kelland, M. A. Energy Fuels 2017, 31, 4603−4615. 7. Fisher, H. C.; Miles, A. F.; Bodnar, S. H.; Fidoe, S. D.; Sitz, C. D. Progress Towards Biodegradable Phosphonate Scale Inhibitors, RSC Chemistry in the Oil Industry XI, Manchester, UK, November 2–4, 2009. 8. Ross, R. J.; Low, K. C.; Shannon, J. E. Mater. Perform. 1997, p53. 9. Kohler, N.; Courbin, G.; Estievenart, C.; Ropital, F. Polyaspartates: Biodegradable Alternatives

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17. Bazin, B.; Kohler, N.; Zaitoun, A.; Johnson, T.; Raaijmakers, H. A New Class of Green Mineral Scale Inhibitors for Squeeze Treatments, SPE 87453 (paper presented at the SPE International Symposium on Oilfield Scale, Aberdeen, UK, May 26–27, 2004). 18. Baraka-Lokmane, S.; Sorbie, K. S.; Poisson, N. The Use of Green Scale Inhibitors for Squeeze Treatments, Carbonate Coreflooding Experiments, Geophysical Research Abstracts 9: 02444, 2007. 19. Baraka-Lokmane, S.; Sorbie, K.; Poisson, N.; Kohler, N. Petr. Sci. Techn. 2009, 27, 427. 20. Rokicki, G. Prog. Polym. Sci. 2000, 25, 259–342. 21. Nair, L. S.; Laurencin, C. T. Prog. Polym. Sci. 2007, 32, 762–798. 22. Zhu, Y.; Romain, C.; Williams, C . K. Nature 2016, 540, 354–362. 23. Jaworska, J.; Kawalec, M.; Pstusiak, M.; Reczynska, K.; Janeczek, H.; Lewicka, K.; Pamula, E.; Dobrzynski, P. J. Poly. Sci. Part A: Polym. Chem. 2017, 55, 2756-2769. 24. Mady, M. F.; Bagi, A.; Kelland, M. A. Energy Fuels 2016, 30, 9329-9338. 25. Organization for Economic Cooperation and Development (OECD). Guideline for testing of chemicals, biodegradability in seawater. Adopted by the council on July 17, 1992; p 27. 26. Rittmann, B. E.; McCarty, P. L. Environmental Biotechnology: Principles and Applications, International ed.; McGraw-Hill, Inc.: Singapore, 2001; p 128. 27. Del Villano, L.; Kommedal, K.; Kelland, M. A. Energy Fuels 2008, 22, 3143-3149. 28. Guo, J.; Severtson, S. J. Industrial & Engineering Chemistry Research 43, 5411, 2004. 29. Bromley, L. A.; Cottier, D.; Davey, R. J.; Dobbs, B.; Smith, S.; Heywood, B. R. Langmuir 1993, 9, 3594. 30. Zhang, B. R.; Zhang, L.; Li, F. T.; Hu, W.; Hannam, P. M. Corrosion Science 2010, 52, 3883.

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