Interaction of phosphonates onto the immobilized surface:Nan Zhang
Rice Universitynanzhang@rice.eduMarch, 2013
Application to scale control in oil and gas flow assurance
1OutlineBackground and previous batch studyHypothesis/ObjectivesChallenges and MethodsResultsConclusions
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.)
Scale in water transporting system
In addition to corrosion and gas hydrates scale is one of the three important problems in any water transporting system (Figure 1-2). 3How much scale could potentially form ?
Scale tendency In addition to corrosion and gas hydrates scale is one of the three important problems in any water transporting system (Figure 1-2). 4Scale control with threshold inhibitorConventional onshore and Unconventional offshore reservoirPushing and fixing inhibitors into the formation via squeeze treatmentInject trace inhibitors downhole via a treat stringUnconventional onshore reservoirInject trace inhibitors with the fracturing fluid
DTPMP (methylene phosphonic acid)NTMP (Methylene phosphonic acid)Earlier understanding and optimizing squeeze design was based on the empirical differences between different scale with a specific inhibitor performance and the assumption that inhibitors reduce the growth rate by the fraction of inhibitor critical coverage adsorbed on the crystal surface 5Inhibitor return after squeeze treatmentWell NameDownhole Temperature (F)TDS (mg/L)Ca (mg/L)SI Minimum Inhibitor Needed Gladys McCall2989634041301.040.18N.R. Smith160508994800.43 0.9, Ca concentration control the inhibitor attachment SICaCO3 > 0.6, Phosphonates concentration control the inhibitor attachmentFor 1 hour 18Inhibitor releaseDTPMP return starts with a short desorption and then followed by a long term dissolution process. doesnt change with the amount of inhibitor attachment on the surface conc.0.250.02 mg/L Cca= 680 mg/L, SI= 0.6, No DTPMP, pH= 5.9, 70C, Q=100ml/hq= 4.75 mg/m2q= 27.9 mg/m2q= 125 mg/m2q= 267 mg/m219Memory effect of inhibitor release
DTPMP(injected)Injection timeDTPMP(retained)qProtectiontimemg/Lhrmg%mg/m2hr0.2210.0031.040.415.747.410.691.4512517SI_CaCO3=0.59With this amount of 20Ca Concentration effect Ca precipitation and dissolution were both prevented.
DTPMP failed when SI_CaCO3 > 1.1
DTPMP return increased with a lower SI_CaCO3 .
SI=0.74SI=1.1SI=-3.3SI=-0.28CaHCO3SIpHmg/Lmg/L612.371643.730.295.891703.861643.730.745.903969.951643.731.115.920.1751643.73-3.255.88163.691691.89-0.285.88SI=0.29In order to prevent a solution from scaling with a higher SI CaCO3, it is desired to increase the return conc. We already know the ppt on the surface is control by the CaCO3ppt and CaPhn ppt21QLinear VelocityReturnDTPMPSteady stateml/hrcm/secmg/L100.0171.3500.080.41000.170.252500.420.12Flow rate effect on the inhibitor releaseLinear VelocityReturnDTPMPSteady stateSolubility (cs)Overall Dissolution rate constant (k)Mass transfer rate constantcm/secmg/Lmg/Lsec-1cm/sec0.0171.31.73 0.00182.86 E-40.080.40.170.250.420.12
Dissolution can be described as a first order reaction ???0.17 cm/sec= ~480 ft/d23Pipe length at equilibrium (c=cs) Q=1000 bbl/d, I.D.=2.5-4 inch, v=22.7-57.9 cm/sec, km=2.86 E-4 cm/sec,c/cs=1-exp(-3)=0.95 L=1250-3200 ft Inhibitor-Saturation Index RelationshipAt a specific T, SI, pH, and molar ratio (cation/anion) for each specific inhibitor concentration, , there is a unique saturation index value, , for those conditions. These were solved for using Goal Seek. Illustrated here for barite, the same applies for calcite.
25Conclusion 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.
Conclusion + Implication 27Acknowledgements Rice Brine Chemistry Consortium (BCC)
Fellowship, China Scholarship Council [Grant 2008102375] (2008-prsent)
Dr. Mason Tomson and Dr. Amy Kan
28InhibitorStoichiometrySolubility productPKsp at 1 M I, 70 CSolubility1 (mg/L)
PPCACa3(AAA)2 (aged)16.35 + 0.24I(M) 252.1/(T((K) - 252.1)13.821.45