The document summarizes a study investigating the interaction of phosphonate scale inhibitors with calcium carbonate surfaces. The objectives were to develop a method to study crystal growth kinetics and inhibition using a calcium carbonate pre-coated steel tubing reactor. Results showed that inhibitor attachment increased with calcium concentration and saturation index, and that calcium carbonate facilitated phosphonate retention on the surface. Inhibitor release exhibited a "memory effect" where residual inhibitor provided protection even after the injection period ended.

1. Interaction of phosphonates onto the
immobilized surface:
Application to scale control in oil and gas flow assurance
Nan Zhang
Rice University
nanzhang@rice.edu
March, 2013

2. Outline
• Background and previous batch study
• Hypothesis/Objectives
• Challenges and Methods
• Results
• Conclusions

3. Scale in water transporting system
 Scale in oil and gas flow assurance (CaCO3,
FeCO3 ,CaSO4, BaSO4, SrSO4 , etc.)
 Changes of temperature and pressure.
 Variations of pH and CO2/H2S partial pressure during
operation.
 Mixing of incompatible waters.
 Effect of other constitnents.
 Fouling in heat exchanger (CaCO3, CaSO4, etc.)
 Fouling on the membrane surface (CaSO4,
BaSO4 ,etc.)

4. How much scale could potentially form ?
Scale tendency
0, " undersatur ated" and calcite dissolves
SI zero, " equilibriu m" and scale doesn' t form
0, " supersatur ated" and calcite precipitates

5. Scale control with threshold inhibitor
 Conventional onshore and Unconventional offshore reservoir
 Pushing and fixing inhibitors into the formation via squeeze
treatment
 Inject trace inhibitors downhole via a treat string
 Unconventional onshore reservoir
 Inject trace inhibitors with the fracturing fluid
DTPMP NTMP
(methylene phosphonic acid) (Methylene phosphonic acid)

6. Inhibitor return after squeeze treatment
1000 1000
Phosphonate (mg/L)
100
Phosphonate (mg/L)
100 Gladys McCall
N. R. Smith
10
10
1
1
0
0
3.E+01 1.E+07 2.E+07
3.E+01 5.E+05 1.E+06 2.E+06 Volumes of Produced Water (bbl)
Volumes of Produced Water (bbl)
Minimum
Downhole Ca
Well Name TDS (mg/L) ΔSI Inhibitor
Temperature (F) (mg/L)
Needed
Gladys
298 96340 4130 1.04 0.18
McCall
N.R. Smith 160 50899 480 0.43 <0.7
Inhibitor return concentration is dropping to a few mg/L level in the early flowback stage,
but the interaction mechanism between the phosphonate inhibitor and scale is unclear,
so the return concentration of the inhibitor is unpredictable.

7. Phosphonates attachment to calcite surface
(Previous Batch Study)
Solid Phase NTMP Conc. ( mol/m2 )
100000
10000
3, Heterogeneous crystal growth
1000
precipitation
100
10
2, Crystal growth
1
0.1 Tomson et al., SPE, 2003
1, Langmuir adsorption
0.01
0.00001 0.001 0.1 10 1000
Solution Phase NaNa42NTMP Conc. (mmol/L)
Solution Phase 4H H2 NTMP Conc. (mmol/L)
Adsorption
Langmuir adsorption
Crystal growth
CaCO3
Amorphous growth
Kan et al., JCIS, 2005

8. Solubility of Ca-Inhibitor precipitates
(Previous Batch Study)
Inhibitor Stoichiometry Solubility product PKsp at 1 M Solubility1
I, 70 ºC (mg/L)
NTMP CaH4P 32.46 32.46 22502
Ca2.5HP (am) 32.96 - 6.88 I(M) 2.17 I(M) 2380 / T(  K ) 21.31 174
Ca2.5HP (cr) 32.92 - 5.32 I(M) 1.76 I(M) 2023 / T(  K ) 23.46 0.92
Fe2.5HP (aged) 39.54 - 6.14 I(M ) 2.18 I(M ) 1315 / T(  K ) 31.74 0.0953
DTPMP Ca3H4P (am) 50.5 @ 1 - 2 M I, 70 C 50.5 250
Ca3H4P (cr) 58.95 0.048 I(M) 2084.5 / T(  K) 52.9 1.05
BHPMP Ca4H2P (am) 35.41 385
48.11 - 2.65 I(M) 3448 / T(  K )
Ca4H2P (cr) 48.46 - 2.60 I(M) 2998 / T(  K ) 37.12 7.0
PPCA Ca3(A·A·A)2 16.35 + 0.24·I(M) –252.1/(T( K) - 252.1) 13.82 1.45
(aged)
Kan et al. Biogeochemistry of chelating agents chapter 15, 2005
The formation of CaPhn/FePhn precipitates with a low solubility may contribute to the
low inhibitor return concentrations

9. Hypothesis
 Inhibitor may deposit and retain on the surface by working with
the possible scale, such as CaCO3
 Scaling risk can be controlled with a pulse injection of inhibitor
Objectives
1. Develop a CaCO3 pre-coated steel tubing for studies of
CaCO3 crystal growth kinetics and inhibition kinetics.
2. Evaluate the attachment kinetics of inhibitor on the surface
3. Investigate the detachment kinetics and equilibrium of
inhibitor from the surface and its inhibition impact on the
CaCO3 scaling to the pipe.

10. Challenges
 No robust experimental method for kinetics study
 Difficult to convert beaker result to real prediction
 Limited information on inhibitor performance
Modified
Conventional Rotating Constant Plug flow Plug flow
Method
free drift disc composition reactor reactor
(this study)
Surface area Variable Constant Variable Variable Constant
Saturation index Variable Variable Constant Constant Constant
Ionic strength Variable Variable Constant Constant Constant
pH Variable Variable Constant Constant Constant
Hydraulic
No Yes No Yes Yes
condition
Ultra High
Hard Hard Hard Easy Easy
Temp/Pressure

11. Modified Plug flow reactor
Modified carbon steel tube (AISI1010, 5in length, ¼ in OD)
1. Coat the outer surface with rust-oleum for corrosion control
2. Polish inner surface with sandpaper to create a smooth surface for
CaCO3 deposition

12. Modified Plug flow reactor
3. Precoat uniform CaCO3 layer on the subsurface
Provide constant surface area
Tubing surface area
Eliminate initial preferential attachment A=18.3 cm2
Crystal surface area
A=55 cm2
1.02
1.00
Ca Conc.
Calcite
0.98
0.96
C/C0
0.94
0.92
0.90
0.88
0.86
0.84
Aragonite
0 2 4 6 8 10 12
Time (hr)

13. Apparatus pump Sample Collection &
Analysis: ICP, ICP-MS
Soln. A
Reactor:
CaCl2+ NaCl
Carbon steel AISI1010 tubing pre-
100% CO2
coated with CaCO3
75 psi
Soln. B
pump
NaHCO3+ NaCl
Water Bath
Parameter Value
ICP_MS STD P
Flow rate 10 -250 ml/min
0.6
Reactor I.D. 1/8 inch
0.5
Intensity
Reactor Length 5 inch 0.4 y = 0.001x
0.3 R² = 0.999
Temperature 70 °C 0.2
Reactor volume 2.09 cm3 0.1
Residence time 75sec- 12.6 min 0
Reynolds’s 0 200 400 600
9-100 P conc. (ug/L)
number

14. Inhibitor attachment
C0= 680ppm, ΔSI_CaCO3= 0.6, 0.2-1330 mg/L DTPMP, pH= 5.9, 70C, Q=100ml/h for 1 hr
1.2
DTPMP Effluent C/C0
1
0.8
0.6
0.4
0.2
Time (min)
0
0 10 20 30 40 50
0.2 mg/L 2.5 mg/L 5 mg/L 50 mg/L
100 mg/L 363 mg/L 1331 mg/L K tracer
• The break through occurs in 20 min
• Inhibitor cannot accumulate on the surface with time

15. .
Inhibitor conc. effect on the attachment
Inhibitor attachment on the calcite surface (surface area 55cm2)
DTPMP
f=129.4087*(1-exp(-0.0145*x))
DTPMP (retaine
140
(injected) d)
120
q
100
mg/L mg/m2
q (mg/m2)
80
0.22 0.20
60 2.5 2.01
40 5 7.05
10 18.73
20
47 56.89
0
0 200 400 600 800 1000 1200 1400
102 107.39
DTPMP (mg/L) 363.6 127.10
1331.8 128.78

16. Ca conc. effect on the attachment
Cca= 612-3833 mg/L, 100 mg/L DTPMP, pH= 6.2, 70C, Q=100ml/h
1.2
1
C/C0
0.8
0.6
0.4
0.2
Time (min)
0
0 60 120 180 240 300 360 420 480
Ca=612 mg/L Ca=1704 mg/L Ca=3833 mg/L
• The break through didn’t occur
• Inhibitor can accumulate on the surface with time

17. Ca conc. effect on the attachment
SI_CaCO3
0.8 1.0 1.2 1.4 1.6 1.8
1100
SI_ DTPMP
SI_
1000 Ca vs q Ca Ca3H4 (retained q
SI_CaCO3 vs q DTPM CaCO3 for 1 hour
900 P injection)
q (mg/m2)
mg/
800 mg/L mg %
m2
700 612 1.76 0.9 3.4 33 618
1704 1.85 1.35 4.6 50 836
600
3833 1.77 1.73 5.3 52 1019
500
0 1000 2000 3000 4000
Injected Ca (mg/L)
• Both Ca3H4DTPMP and CaCO3 precipitates affect the inhibitor attachment

18. CaCO3 facilitates phosphonate retention
SI_
1200
SI_
Ca HCO3 Ca3H4 q
1000 DTPM CaCO3
P
800 mg/
q (mg/m2)
mg/L
m2
600 579 1224 2.09 0.01 59.2
583 1770 2.02 0.34 60.64616
400
581 2538 1.86 0.66 71.1
200
612 3274 1.76 0.9 609
0 1704 3274 1.85 1.35 835
0.0 0.5 1.0 1.5 2.0
CaCO3 SI 3833 3274 1.77 1.73 966
• SICaCO3 > 0.9, Ca concentration control the inhibitor attachment
• SICaCO3 > 0.6, Phosphonates concentration control the inhibitor attachment

19. Inhibitor release
Cca= 680 mg/L, ΔSI= 0.6, No DTPMP, pH= 5.9, 70C, Q=100ml/h
DTPMP conc. (mg/L) 100 q= 4.75 mg/m2
102.5 mg/L DTPMP
2
47.4 27.9 mg/m
q= mg/L DTPMP
10 2
10 mg/L mg/m
q= 125 DTPMP
2.5 mg/Lmg/m2
q= 267 DTPMP
1 0.25 0.02 mg/L
0.1
0.01
60 80 100 120 140
Time (min)
DTPMP return
• starts with a short desorption and then followed by a long term dissolution process.
• doesn’t change with the amount of inhibitor attachment on the surface conc.

20. “Memory effect” of inhibitor release
100 800 0.30 800
0.25
80
600 600
DTPMP (mg/L)
DTPMP (mg/L)
Ca (mg/L)
0.20
Ca (mg/L)
60
400 0.15 400
40
0.10
DTPMP 200 200
20 Ca
0.05 DTPMP
Ca
0 0 0.00 0
0 500 1000 1500 2000 2500 0 100 200 300 400 500 600 700
Time (min) Time (min)
DTPMP Injection DTPMP Protection
q
(injected) time (retained) time
mg/L hr mg % mg/m2 hr
0.22 1 0.003 1.04 0.41 5.7
47.4 1 0.69 1.45 125 17
SI_CaCO3=0.59

21. Ca Concentration effect
2.5 4500
4000
2.0
DTPMP (mg/L)
3500
Ca (mg/L)
3000
1.5 2500
SI=0.29 SI=0.74 SI=1.1 SI=-3.3 SI=-0.28
1.0 2000
1500
0.5 1000
500
0.0 0
180 240 300 360 420 480
DTPMP Ca Time (min)
Ca HCO3 SI pH
mg/L mg/L • Ca precipitation and dissolution were both prevented.
612.37 1643.73 0.29 5.89
1703.86 1643.73 0.74 5.90 • DTPMP failed when SI_CaCO3 > 1.1
3969.95 1643.73 1.11 5.92
5.88
• DTPMP return increased with a lower SI_CaCO3 .
0.175 1643.73 -3.25
163.69 1691.89 -0.28 5.88

22. Flow rate effect on the inhibitor release
100
10 ml/hr Return
Linear
DTPMP (mg/L)
Q DTPMP
50 ml/hr Velocity
10 Steady state
100 ml/hr
250 ml/hr ml/hr cm/sec mg/L
10 0.017 1.3
1 50 0.08 0.4
100 0.17 0.25
250 0.42 0.12
0
60 110 160 210 260 310 360
Time (min)

23. 1.4
DTPMP S.S. Effluent Conc. (mg/L)
1.2
1.0
Advection Dissolution 0.8
0.6
0.4
0.2
0.0
0 200 400 600 800
L/v £s(sec)
Return Overall Mass
Linear DTPMP Solubility Dissolution transfer
Velocity Steady (cs) rate rate
state constant (k) constant
cm/sec mg/L mg/L sec-1 cm/sec
0.017 1.3
0.08 0.4 2.86
1.73 0.0018
0.17 0.25 E-4
0.42 0.12

24. Pipe length at equilibrium (c=cs)
Q=1000 bbl/d, c/cs(DTPMP)
I.D.=2.5-4 inch, 1.2
v=22.7-57.9 cm/sec, 1
km=2.86 E-4 cm/sec,
0.8
c/cs=1-exp(-3)=0.95
L=1250-3200 ft 0.6
0.4 ID=4 inch ID=2.5 inch
0.2
0
0 1000 2000 3000 4000
pipe length (ft)

25. Inhibitor-Saturation Index Relationship
At a specific T, SI, pH, and molar ratio (cation/anion) for
Barite
each specific inhibitor concentration, CInh (mg / L)there is a
,
unique saturation index value, SI Bartiefor those conditions.
,
These were solved for using Goal Seek. Illustrated here for
barite, the same applies for calcite.
a2 a3 a4
t0Barite 10 ^ a1
SI Barite TK SI BartieTK
Barite b3 [ Ba 2 ]M
b Inh b1 b2 SI Bartie b4 pH b5 log10 2
TK [ SO4 ]M
Barite Bartie
Barite 1 f safety t Inh
CInh (mg / L) Barite
log10
bInh t0Barite

26. 2.5 2.25
Barite
Calcite and barite Saturation Indexes
DTPMP (mg/L), blue diamonds
2
2
1.75
1.5 1.5
Calcite
1 1.25
1
0.5
0.75
0 0.5
0 1000 2000 3000 4000 5000 6000
Feet of flow in 2.5in. pipe with
Ca-DTPMP on steel surface

27. Conclusion
 The phosphonate inhibitor layer was built up on the pipe
surface with CaCO3 pre-coated layer.
 Amount of inhibitor attached is related with the DTPMP
adsorption on the CaCO3 surface.
 CaCO3 can facilitate the inhibitor attachment on the
surface, may suggest the copercipitation of CaCO3 and
CaPhn crystal.
 The DTPMP return is controlled by the dissolution of the
Ca3H4DTPMP precipitates attached on the surface with a
dissolution rate about 0.0018 cm-1.
 Ca precipitation and dissolution were both prevented.

28. Acknowledgements
• Rice Brine Chemistry Consortium (BCC)
• Fellowship, China Scholarship Council
[Grant 2008102375] (2008-prsent)
• DOE (DE-FE0001910)
•Dr. Mason Tomson and Dr. Amy Kan