Practical Scale Tendencies Reaction kinetics as reported in the literature

Scale risks as defined by various operators Scale Type Risk Scale Tendency Scale Mass (mg/l) Comments Calcite Low 1-3 <50 Moderate 5-15 50-250 Severe >20 >250 FeCO3 1-5 <15 Found with CaCO3 15-50 BaSO4 <10 8-20 10-40 Rarely from self scaling >30 >50 Generally due to mixing SrSO4 Found with BaSO4 NaCl >1 30,000 Precipitates immediately Scale risks as defined by various operators

Factors governing Scale buildup & Risk All scale prediction models are equilibrium- based A separate model is needed to predict scale kinetics Three mechanisms of scale buildup Nucleation – (Homogeneous or heterogeneous) Crystal growth (Primary or secondary) Transport to surface (secondary) Adhesion (Secondary) Scale growth is limited by these mechanisms Speciation Adsorption Particle Dynamics Factors governing Scale buildup & Risk

Scale buildup is prevented by Threshold inhibition prevent nucleation Growth inhibition/Crystal Distortion prevent stable growth and large crystals Dispersion prevent large crystal agglomeration Scale buildup is prevented by

Scale Prediction-Scale Risk relationship What are the fundamentals of nucleation, crystal growth, and adhesion Crystal growth and nucleation: tracking precursors to polymorphs Patrick R. Unwin. Faraday Discuss., 2007,136, 409-416. as per: https://www.google.com/search?q=solid+nucleation&rlz=1C1CHFX_enUS581US581&espv=2&biw=1080&bih=1859&source=lnms&tbm=isch&sa=X&ei=WZupVKuUAYOQyQTZt4HQAQ&ved=0CAcQ_AUoAg#tbm=isch&q=crystal+nucleation&facrc=_&imgdii=_&imgrc=8pS8gF0egaeTrM%253A%3BBRpzrAoK6BKVrM%3Bhttp%253A%252F%252Fpubs.rsc.org%252Fservices%252Fimages%252FRSCpubs.ePlatform.Service.FreeContent.ImageService.svc%252FImageService%252FArticleimage%252F2007%252FFD%252Fb707653n%252Fb707653n-f1.gif%3Bhttp%253A%252F%252Fpubs.rsc.org%252Fen%252Fcontent%252Farticlehtml%252F2007%252Ffd%252Fb707653n%3B498%3B268

Scaling mechanisms Scale Mechanisms Control Chemicals Threshold scale inhibitor Nucleation Crystal Growth Modifier Crystal Growth Adhesion Dispersants Scaling mechanisms Growth of ZnO Crystals with Branched Spindles and Prismatic Whiskers from Zn3(OH)2V2O7·H2O Nanosheets by a Hydrothermal Route. Hai-Sheng Qian, Shu-Hong Yu*, Jun-Yan Gong, Lin-Bao Luo, Lan-Lin Wen Crystal Growth Design 2005, 5(3), 935-939 Synthetic nanoparticles functionalized with biomimetic leukocyte membranes possess cell-like functions Alessandro Parodi, et. al. Nature Nanotechnology.  8,  61–68  (2013)  doi:10.1038/nnano.2012.212 Polymer Directed Formation of Unusual CaCO3 Pancakes with Controlled Surface Structures Shao-Feng Chen, Shu-Hong Yu*, Tong-Xin Wang, Jun Jiang, H. Cölfen*, Bing Hu, B. Yu Adv. Mater. 2005, 17(12), 1461-1465. (Top 10 paper).

Nucleation – three types Primary Secondary (Crystal growth) scale grows on existing crystals https://www.youtube.com/watch?v=BLq5NibwV5g Homogeneous Heterogeneous Nucleation in clean water Scale grows on foreign particles, like dust https://www.youtube.com/watch?v=5lEF-eav70s This occurs during production Nucleation – three types https://www.youtube.com/watch?v=bcuyhImiBCM

Primary-Homogeneous Nucleation System is free of any solids Solids (e.g., calcite) spontaneously form The solid formed is pure. No other materials present (e.g., sand, dust, clay, etc.) Primary-Homogeneous Nucleation http://facstaff.gpc.edu/~mkim/C1211&1212Lec/C1211_Lecture.htm

Primary-Heterogeneous Nucleation Primary Heterogeneous Reaction The System contains an existing solid surface (e.g., clay, sand, pipe wall) the scale molecules (e.g., CaCO30) adsorb to the surface The surface lowers the energy barrier to aggregation growth continues on the new surface Lower S is needed to initiate scale Primary-Heterogeneous Nucleation S. Labille, A Neville, G Grapham, and L Boak. 2002. An Assessment of Adhesion of Scale and Electrochemical Pretreament for the Prevention of Scale Depositionon Metal Surfaces. SPE 74676. http://iramis.cea.fr/Pisp/antoine.thill/thill_fr.html

Secondary Nucleation The System already contains calcite CaCO30 molecules adsorb to calcite surface and grow off it The calcite surface lowers the energy barrier to reaction Lower supersaturation is required to form scale Secondary Nucleation http://brotherjohns.wordpress.com/2008/04/15/40/bigseedcrystal/

Experimental Data

Experimental measurements Nucleation (primary) Induction time (time before solids start to form) particle size and distribution crystal structure (what minerals form) Crystal growth (secondary) crystal size growth rate concentration changes vs. time Adhesion (particle transport) Pressure buildup in a capillary labs measure one or more of variables in an experiment Experimental measurements

Dynamic tube-blocking studied Dynamic tube-blocking studies is a common method to test for scale inhibitor performance

Dynamic tube blocking studies http://www.vinci-technologies.com/products-explo.aspx?IDM=753795&IDR=113221&IDR2=113220 http://www.scaledsolutions.com/Equipment%20Design%20and%20Build/Tube%20Blocking%20Rig

Generalized flow schematic Cation solution Pressure Measurement Anion solution Scale Inhibitor Pressure Measurement Generalized flow schematic

Experimental Results B. Bazin, N. Kohler, A. Zaitoun, T. Johnson, and H. Raaijmakers. 2004. A new class of green mineral scale inhibitors for squeeze treatments. SPE87453

Experimental results using Bellasol™ inhibitors

Static tests Jar tests or light scatter tests

Example results from static jar test Ba+2 concentration @70C after 12 hours MAT PPPC VSCo DETA DTPA Base 1.4 1.6 1.3 0.9 1.1 2.5 ppm 4.8 6.5 2.7 2.2 5.2 5 ppm 9.8 13.1 10.3 7.8 9.4 7.5 ppm 12.1 13.2 11.4 12.5 10 ppm 13 12.9 12.7 13.3 Example results from static jar test http://www.oms.clariant.com/en-us/oil/Pages/Clariant-Oil-Services-Polymeric-Halite-Scale-Inhibitor-Proves-Highly-Efficient-and-Effective.aspx (bottle image)

Example output from light scatter test “Primary Nucleation” experiments, showing the impact of saturation ratio on the length of time elapsed before calcite start to form. 1 m NaCl brine Saturation (1=equilibrium) Example output from light scatter test He et al., 1997. Inhibition of calcium carbonate precipitation in NaCl brines from 25 to 90 C. Applied Geochemistry

Crystallographic studies U. Leeds scale growth and inhibition studies T. Chen and A. Neville, K. Sorbie, and Z. Zhong. 2006. Using synchroton radiation wide-angle X-ray scattering (WAXS) to study inhibition effect of DTPMP on CaCO3 scale formation. SPE100440

CaCO3 growth at 80C on a Si capillary cell SPE100440

CaCO3 growth at 80C on a Si capillary cell Crystal planes with 2 theta angles Calcite C104 – 6.9o C110 – 8.5o C113 – 9.2o C202 – 10.1o No inhibitor Aragonite 4ppm DTPMP A111 – 6.2o Vaterite V110 – 5.9o V112 – 6.5o CaCO3 growth at 80C on a Si capillary cell SPE100440

Plot Explanation - Crystal Projections Calcite projection Projection numbering http://www.answers.com/topic/crystallography http://pubs.rsc.org/en/content/articlelanding/2010/nr/b9nr00287a/unauth#!divAbstract. From google search calcite crystal projections Plot Explanation - Crystal Projections

Viewed vs. time – no inhibitor ~16 minutes to 900 Cps intensity Calcite Vaterite Aragonite C104 – 6.9o C110 – 8.5o C113 – 9.2o C202 – 10.1o V110 – 5.9o V112 – 6.5o A111 – 6.2o Viewed vs. time – no inhibitor SPE100440

When viewed in time with inhibitor ~16 minutes to 100 Cps intensity When viewed in time with inhibitor SPE100440

What is learned in the experiment Crystals precipitates and dissolve Crystals do not adhere to surface The more soluble crystals form first The most stable solid eventually dominates What is learned in the experiment SPE100440

Kinetic models How kinetics are predicted

Illustration of nucleation kinetics Primary-homogeneous nucleation Clun … Ca+CO3=Clu1 Clu1+Ca=Clu1’ Clu1’+CO3=Clu2 Clu2+Ca=Clu2’ Clu2’’+CO3=Clu3 … CO3 Clu3 Clu2’ Ca Gactivation=energy required to form the cluster containing n components CO3 G or System Energy Clu2 Clu1 Clu1’ Ca Greaction=energy released when the cluster contains z components Critical nuclei radius* Critical nuclei radius* Cluz Stable solid Size (radius) of crystal cluster (nanometer scale) Illustration of nucleation kinetics Clu=cluster of molecules (e.g., CaCO30) forming the nuclei that turns into the precipitate. Based on a diagram created by Prof. M. Tomson at Rice University (calcite scale handbook, reference needed)

Saturation and cluster size distribution average cluster radius at a specific saturation ratio critical radius nucleation is spontaneous r* Saturation and cluster size distribution Nucleation induction times are based on the probability of forming a particle with a radius greater than the critical radius

Generalized Model for Nucleation Energy gained from creating the bonds Work needed to create the surface Where: Gf = Free energy of formation of the new crystal (J) r = radius of the new scale cluster (cm) V = molecular volume (cm3)  = surface tension of cluster (erg/cm2) a/ao = saturation condition (scaling tendency) k = Boltzmann’s constant (1.303e-19 J/K) Generalized Model for Nucleation Gibbs-Thomson equation (Gibbs-Kelvin)

Induction time and saturation using log-scale Primary-homogeneous nucleation 1hr 1min 1 m NaCl brine Induction time and saturation using log-scale He et al., 1997. Inhibition of calcium carbonate precipitation in NaCl brines from 25 to 90 C. Applied Geochemistry

Induction time model Primary-homogeneous nucleation log 𝑡 𝑜, 𝐶𝑎𝑙𝑐𝑖𝑡𝑒 (𝑠𝑒𝑐𝑜𝑛𝑑𝑠)=4.22− 13.8 log⁡(𝑆) − 1876.4 𝑇(𝐶𝑒𝑙𝑐𝑖𝑢𝑠) + 6259.6 log⁡(𝑆)∗𝑇 Curve fitting of the induction time. The process variable are the measured temperature and supersaturation Induction time model He et al., 1997. Inhibition of calcium carbonate precipitation in NaCl brines from 25 to 90 C. Applied Geochemistry

Effects of adding ATMP inhibitor Primary-homogeneous nucleation ATMP, ppm 0.01 0.025 0.037 0.05 0.075 Effects of adding ATMP inhibitor

Secondary Nucleation & Crystal Growth http://www.britannica.com/EBchecked/media/929/Mechanisms-of-crystal-growth

Current theory postulate that inhibitors adsorb on growth sites slowing growth Adsorb to high-energy kink sites and prevent further crystal growth Interacts with critical nuclei (6-8 molecules grouped together) and prevents them from growing to a stable crystal Edges Kinks Good growth area Excellent growth area Poor growth area Sides Corners Mechanisms

Secondary Nucleation-Crystal Growth curves Seeded growth of BaSO4 with and without inhibitor long-term growth conforms to: ks=rate constant function of surface area and activity of seed crystal C=measured conc C0=equilibrium conc Inhibitor retards growth 𝒅𝑪 𝒅𝒕 =𝒌𝒔 𝑪− 𝑪 𝟎 𝟐 Secondary Nucleation-Crystal Growth curves R.M.S. Wat, K.S. Sorbie, A.C. Todd, P. Chen, and P. Jiang. 1992. Kinetics of BaSO4 Crystal Growth and Effect in Formation Damage. SPE23814

General crystal growth model for Secondary Nucleation Solid surfaces or particles (e.g., walls, sand grains) increase nucleation rate because it decreases activation energy 𝑩= 𝒅𝑵 𝒅𝒕 = 𝒌 𝒔 𝒄− 𝒄 ∗ 𝒏 B = is the number of nuclei formed per unit volume per unit time. N = is the number of nuclei per unit volume. ks  = is rate constant c = solute concentration c* = solute concentration at saturation n = empirical exponent General crystal growth model for Secondary Nucleation

Primary-heterogeneous nucleation Secondary nucleation is influenced by particle shear and collision Fluid shears a Crystal, sweeping away growing nuclei that become new crystals Crystals collide creating further growth 𝑩= 𝒅𝑵 𝒅𝒕 = 𝒌 𝟏 𝑴 𝑻 𝒋 𝒄− 𝒄 ∗ 𝒃 B = is the number of nuclei formed per unit volume per unit time. k1 = rate constant MT = suspension density j = empirical exponent b = empirical exponent Secondary Nucleation

Practical Nucleation issues Homogeneous nucleation does not exist during production Studied in basic research laboratory to understand reaction mechanisms Heterogeneous nucleation occurs during production Studied in applied technology laboratories to evaluate product performance Field performance and Case studies describe results Technique in commercial processes sugar, salts, fertilizers, etc. designed to fix crystal size and distribution Practical Nucleation issues

Controlling factors in nucleation and crystal growth

Increase Mg:Ca ratio slows down nucleation rates

We do not use the G-T equation We don’t care about the Gibbs-Thomson equation because it includes many assumptions it also assumes primary homogeneous nucleation It does explain the factors that control nucleation We do not use the G-T equation

Transport to surface and adhesion Diffusion or dispersion of crystallites or precipitating species to the static surface Electrostatic and chemical bonding to surface Transport to surface and adhesion

Proposed nucleation equation Kan, A., G. Fu, C. Fan, and M. Tomson. 2009. Quantitative evaluation of calcium sulfate precipitation kinetics in the presence and absence of scale inhibitors. SPE121563

Generalized Model for Nucleation 𝑱=𝑨 𝒆 𝟏𝟔 𝑽 𝟐 𝝅 𝜸 𝟑 𝟑 𝒌𝑻 ln 𝑎 𝑎 𝑜 𝟐 𝒌𝑻 =𝒇𝒍𝒖𝒙 𝒐𝒇 𝒏𝒖𝒄𝒍𝒆𝒂𝒕𝒊𝒏𝒈 𝒄𝒍𝒖𝒔𝒕𝒆𝒓𝒔 Where: Gf = Free energy of formation of the new crystal (J) r = radius of the new scale cluster (cm) V = molecular volume (cm3) = surface tension of cluster (erg/cm2) a/ao = saturation condition (scaling tendency) k= Boltzmann’s constant (1.303e-19 J/K) A= Comstant Generalized Model for Nucleation

How then do we control scale

Burton-Cabrera -Frank (BCF) surface diffusion model describing crystal growth A crystal face grows via progression of equidistant steps originating at a dislocation source Step 1 – a solvated growth unit (6-coordinated) arrives at a crystal surface and adsorbs Step 2 – a) Surface migration occurs followed by a desorption back into solution, or b) a step is reached Step 3 – Incorporation into the crystal lattice at a kink site 2 3 1 Crystal Growth

Energy cost or gained released at each step 2 3 1 ∆Gdissolv Energy needed to move cluster ∆Gk ∆Gs-diff Energy released when bonded Cluster reaches Kink (3) Cluster reaches edge (2) Cluster on surface (1) Cluster in water Energy cost or gained released at each step

Entry into kink site requires inhibitor desorption New pseudo-kink sites are created and growth units accept impurity as its neighbor Adsorbed inhibitors act as barriers to growth unit diffusion 3 2 1 SI SI SI SI ∆Gdissolv Cluster reaches Kink (3) Cluster reaches edge (2) Cluster on surface (1) ∆Gk ∆Gs-diff Cluster in water Energy needed to move cluster Energy released when bonded Effects of inhibitor on Energy cost Effect of inhibitors

Nucleation Inhibition Current theory postulate that inhibitors poison the nuclei Nucleus Formation begins as two ion pairs combine… O O Critical Nucleus OH CH P 2 OH N O CH 2 CH P 2 O P O O O O Nucleation Inhibition One phopshonate molecule can inhibit 5,000 to 10,000 scalant molecules

Worthless trivia: Carboxymethyl cellulose is added to ice cream to keep ice crystals from forming

FIGURE 5 - Assessment of the growth rate of the three different polymorphs formed on a metallic substrate at 80°C with no inhibitor and with 4ppm of PPCA CaCO3 growth on SS-316 From: Martinod, A, A Neville, K Sorbie, & Z Zhong (2008) Assessment of CaCO3 inhibition by the use of SXRD on a a metallic substrate. Corrosion 2008. No. 1403.

Gypsum nucleation kinetics 1 day 1hr 1min Gypsum nucleation kinetics He, S.L, J. Oddo, and M . Tomson., 1994. Nucleation and inhibition of calcium sulfate dihydrate in NaCl solutions up to 6m and 90 C . JCIF 162(2) 297.

SrSO4 nucleation kinetics 1 day 1hr 1 min SrSO4 nucleation kinetics

Compare NaCl, gypsum, SrSO4,CaCO3, & BaSO4 induction times 1 day BaSO4 1hr SrSO4 25C/1mIS 1 min NaCl CaSO4.2H2O Compare NaCl, gypsum, SrSO4,CaCO3, & BaSO4 induction times Data extracted from papers described in this presentation

Compare NaCl, gypsum, SrSO4,CaCO3, & BaSO4 induction times 1 day BaSO4 1hr 1 min Compare NaCl, gypsum, SrSO4,CaCO3, & BaSO4 induction times Data extracted from papers described in this presentation

NaCl Kinetics S=1.148 S=1.199* ~10 minutes ~5 minutes * Data from Figure 4 inserted onto image of Figure 3 NaCl Kinetics From Chen, T, Montgomerie, H, Chen, P, Jackson, T, and Vikane, O. 2009. Understanding te mechanisms off halite inhibition and evaluation of halite scale inhibitor by static and dynamic tests. SPE 121458

CaSO4 scale risk plot

Four Regions of Saturation Values (calcite) S>200, scale cannot be prevented with existing technology S=150 (SI=2.3) Region 3 10<S<150, scale can be delayed till the brine exits the process. About 1 mg/l of active inhibitor is sufficient to inhibit scale in this region S= 10 (SI=1) Region 2 1<S<10, scale occurs if other scale is present, but will not form on clean surfaces. Brines can be produced for long periods without risk S=1 (SI=0) Region 1 Below S=1 scale is sub saturated and will dissolve existing solids. Brines with S<1 are often corrosive to mild steel S<1 (SI<0) Time Adapted from Tomson, M.B., and J.E. Oddo. 1998. Calcite Scale Handbook, Measurement, Prediction, and control. Gas research Institute, Chicago, IL. Four Regions of Saturation Values (calcite)

Scale buildup Nucleation Crystal Growth Transport Adherence Mixed phases Scale buildup Scale buildup is sequential

Crystal Growth http://www.google.com/imgres?imgurl=http://www.fz-juelich.de/ibn/datapool/page/264/Fig2.jpg&imgrefurl=http://www.fz-juelich.de/ibn/index.php%3Findex%3D264&usg=__N4iCDTO2jpRlY6adxLKdAu5pYwE=&h=560&w=568&sz=87&hl=en&start=30&zoom=1&tbnid=YIcFQIpapdZLSM:&tbnh=145&tbnw=147&prev=/images%3Fq%3Dnucleation%2Bcrystal%26um%3D1%26hl%3Den%26sa%3DN%26biw%3D1599%26bih%3D815%26tbs%3Disch:1&um=1&itbs=1&iact=hc&vpx=696&vpy=464&dur=6124&hovh=267&hovw=271&tx=44&ty=240&ei=7FCwTLWaJcH6lwfs65WCCQ&oei=sFCwTOy6IYL68Aa05PidCQ&esq=2&page=2&ndsp=35&ved=1t:429,r:3,s:30

Example real time image https://www.fz-juelich.de/ibn/voigtlaender/40908300.gif Example real time image

Scale buildup prediction Predictive models for scale buildup are unavailable The uncertainty in identifying scale location is too great to develop a consistent model Tomson (1996) developed a model to predict tube fouling as a result of CaCO3 scaling Where: S = Slope of calcium concentration versus distance up the pipe (general range between 0.015-0.025 (mg/l)/ft) Q = Brine flow (bbl/month) R = pipe radius (generally 2.5 in) Km = CaCO3 Mass transport constant (10-3 works well for most cases) x = pipe length (generally 3,000 to 10,000 ft) Scale buildup prediction

Scale Buildup – Flux Example Result Example scale buildup plot using Tomson’s flux model for Calcute Above 2000 BWPD, it will take 2 to 8 months to produce a scale 3/8” thick or ~50% tubing constriction (2 ½” ID) Model has not been tested against known well production 10,000 ft 8,000 ft 6,000 ft 4,000 ft 2,000 ft Scale Buildup – Flux Example Result S=0.02 mg/l/ft, r=1.25 in, km=0.001 cm/s,

Buildup of suspended particles onto wall Electrostatic attraction between surface and particle Sedimentation (gravity effects) Shear effects of fluid (dispersion) Brownian motion (random movement) Inertial forces (elbow, choke) Eddy diffusion (turbulence movement) 𝑩𝒖𝒊𝒍𝒅𝒖𝒑=𝑷𝒂𝒓𝒕𝒊𝒄𝒍𝒆 𝒇𝒍𝒖𝒙 𝒕𝒐 𝒔𝒖𝒓𝒇𝒂𝒄𝒆 𝒈 𝒎 𝟐 𝒔 ∗𝑭𝒓𝒂𝒄𝒕𝒊𝒐𝒏 𝒕𝒉𝒂𝒕 𝒔𝒕𝒊𝒄𝒌𝒔 Buildup of suspended particles onto wall I.R. Collins. 2002. A new model for mineral scale adhesion. SPE74655. Oilfield scale symposium, Jan 30-31. Aberdeen Scotland

Electrostatic attraction is important when the distance is less than 1m Important only when particle is adjacent to wall Eddies generally keep material in suspension Gravity is important in horizontal pipes What it probably isn’t

CaCO3 nucleation kinetics, NTNU (Norway) Primary-homogeneous nucleation CaCO3 nucleation kinetics, NTNU (Norway) 1Ostvold, T. and P. Randhol. 2001. Kinetics of CaCo3 scale formation. The influence of temperature, supersaturation, and ionic composition.

Calcite nucleation kinetics (comparing three experiments) Primary-homogeneous nucleation 1 day 1hr 1min Calcite nucleation kinetics (comparing three experiments) Data from IFE (date) – citation name not shown here – request information

Calcite nucleation kinetics (additional results) Data from IFE (date) – citation name not shown here – request information

Gypsum nucleation kinetics in pure water

Barite nucleation kinetics 1 day 1hr 1 min Barite nucleation kinetics SPE 121559 – barite nucleation