Geochemical Modeling of Inorganic Scale onsets: Is it useful ? Model Verification and Validation using HPHT and LTHP NIR Technology

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Geochemical Modeling of Inorganic Scale onsets
Is it useful ? Model Verification and
Validation using HPHT and LTHP NIR Technology

• J. D. Lynn
• Technical Specialist
• Advanced Fluid Studies
• Pencor Division

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Outline

• Why is scale a problem
• Inorganic scale
• Types
• Causes
• Prediction
• Geochemical modeling overview
• Near Infrared spectrography
• Case studies

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Problems Imposed by Unexpected Scale Onset

• Scale is a consequence
• Changes in Equilibrium States
• Temp, Pressure, Volumes
• Mixing of Incompatible Fluids
• Injection and influx
• Drilling, Stimulation, Completion and Workover
  fluids
• Scale is not vindictive
• Its Formation Follows Well Defined Thermodynamic
  Laws
• The Laws Dont Change
• Understanding the Laws as Applied to the
  Reservoir is Key

WHY DO WE SAY UNEXPECTED Scale Onset???
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Problems Imposed by Unexpected Scale Onset

• Drilling and Completion Issues
• Production Issues
• Deep Water Flow Assurance Issues
• Field Maintenance Issues
• Facility Issues
• Safety Issues
• Less Discussed Issues

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Problems Imposed by Unexpected Scale Onset

• Drilling and Completion Issues
• Fluid incompatibility issues
• HEC (nonionic) not compatible with Formates and
  NaCl brines
• XC and XCD (anionic) Ca problems
• High Ca completion brines
• Naphthenates
• Iron in make-up brines
• Sulfate in sea water
• TCT vs. PCT

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Problems Imposed by Unexpected Scale Onset

• Production Issues
• Produced Water incompatibility
• Formation
• Formation / injection
• Formation / injection / aquifer
• Formation Plugging
• Gravel Packs, Perfs and Screens
• ESPs
• Production Tubular Plugging
• Emulsions

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Problems Imposed by Unexpected Scale Onset

• Deep Water Flow Assurance Issues
• Well Heads
• Pipe Lines
• Separators
• Deep Sea and Remote Remediation

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Problems Imposed by Unexpected Scale Onset

• Field and Facility Maintenance Issues
• Water Flood
• Injection Well Failure
• Water Disposal
• Multiple Water Sources
• Water Supply
• Source Water Interruption
• Particulate Plugging of Filters

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Problems Imposed by Unexpected Scale Onset

• Safety Issues
• SSSV plugging
• Gate Valves on Pipelines
• NORMS and TENORMS

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Typical Impression of Scale
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A Less Discussed Incarnation of Scale
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Emulsion Stabilizing Solids
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Back scatter SEM
Na-K-chloride
-
-


Calcium sulfate
Fe-Phosphonate
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What is Inorganic Scaling?

• Scales are deposited from oilfield brines when
  there is a disturbance in thermodynamic and
  chemical equilibrium that may result in certain
  degree of super saturation.

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Inorganic Scale Basic Facts

• Free Water Phase
• Crystallization is a Kinetic Process
• Super-cooling
• Nucleation
• Crystal Growth Mechanisms
• Thermodynamic Control
• Temperature, Pressure, Ph
• A Function of
• Ionic Composition of the Fluids
• Solubility Constants of the Scale Products

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Thermodynamic VS. Kinetic Equilibrium
Generalized Ostwald-Miers Diagram
Zone III Unstable or supersaturated labile zone.
Spontaneous nucleation is most likely to occur
Zone III Supersaturated Unstable labile
Solute Concentration
ZONE II Spontaneous nucleation is improbable. A
previously formed crystal which now exists in
this zone will continue to grow.
ZONE II Supersaturated metastable
dsdwsaf
Zone I Undersaturated And Stable
Temperature
Zone I Undersaturated brine solution. No
precipitation possible
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Inorganic Scale Types

• Carbonates
• Sulfates
• Sulfides
• corrosion
• H2S
• Oxides
• Corrosion
• silica
• Hydroxides
• Corrosion
• stimulation

• Naturally occurring radioactive materials (NORMs
  and TENORMs)
• Naphthanates
• High Naphthenic Acid content (gt.6)
• Calcium or divalent cation source
• High pH (gt6.0)

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Inorganic Scale Carbonates

• Carbonates (Acid Soluble)
• Usually the result of pressure reduction
• pH and Temperature dependent
• Changes in pH due to C02 interactions
• Other divalent Carbonates are similar
• Strontianite (SrCO3)
• Witherite (BaC03)

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Inorganic Scale Types

• Carbonates
• Sulfates
• Sulfides
• corrosion
• H2S
• Oxides
• Corrosion
• silica
• Hydroxides
• Corrosion
• stimulation

• Naturally occurring radioactive materials (NORMs
  and TENORMs)
• Naphthanates
• High Naphthenic Acid content (gt.6)
• Calcium or divalent cation source
• High pH (gt6.0)

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Inorganic Scale Sulfates

• Sulfates (Acid Insoluble)
• Usually The Result of Mixing of Waters
• E.G. High Sulfate in Seawater
• High Ca Or Barium in Formation Water
• Retrograde Solubility
• More Soluble in Cold Water
• Dissolution/Precipitation Problems in Injection
  Wells
• CaSO4, BaSO4 ,or SrSO4 PPT.
• Anhydrite, Gypsum, Barite, Celestite, Etc.

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Inorganic Scale Types

• Carbonates
• Sulfates
• Sulfides
• corrosion
• H2S
• Oxides
• Corrosion
• silica
• Hydroxides
• Corrosion
• stimulation

• Naturally occurring radioactive materials (NORMs
  and TENORMs)
• Naphthanates
• High Naphthenic Acid content (gt.6)
• Calcium or divalent cation source
• High pH (gt6.0)

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Naphthenates

2R--CO2- Ca2 gt (R--CO2) 2Ca






Ca2


R--CO2-
Oil




Water


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Selected Napthentic Acids
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Inorganic Scale Types

• Carbonates
• Sulfates
• Sulfides
• corrosion
• H2S
• Oxides
• Corrosion
• silica
• Hydroxides
• Corrosion
• stimulation

• Naturally occurring radioactive materials (NORMs
  and TENORMs)
• Naphthanates
• High Naphthenic Acid content (gt.6)
• Calcium or divalent cation source
• High pH (gt6.0)

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Scale Prediction Techniques

• Standard Bottle Mixing Tests
• Thermodynamic Geochemical Modeling
• Near Infrared Spectroscopy (NIR)
• PFI System (Pressurized Fluid Imaging)
• Capillary Tube Blocking

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Geochemical Model Software

• Commercially Available
• ScaleChem (OLI, USA)
• Multiscale (Petrotech, Norway)
• Geochemists Work Bench (Bekthe)
• University programs
• OKscale (U. of OK)
• ScaleSoft (Rice U.)
• In-house
• SPAM (BP)
• SASP (Saudi Aramco)
• US GOVT
• PHREEQC Version 2.8 (Parkhurst and Appelo, 2003)
  USGS (TDS lt35,000)
• Solmineq
• Tequil (Geothermal simulator)

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Types of Geochemical Models

• Mass Balance
• Evaluates Reactions Along a Flow Path
• Speciation Models
• Calculates Aqueous Species and Saturation Levels
• Mass Transfer
• Calculates Aqueous Species and Transfer of Mass
  Between Phases
• Chemical And Mass Transport Codes
• Mass Transfer Models Coupled with Hydrodynamic
  Codes (Advection and Dispersion)

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Speciation of Brines

• Typical Brine Analysis
• Ca2
• Na
• Cl-
• SO4-2
• pH 7.0

• Speciated Data

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Log Log Log Species
Molality Activity Molality Activity
Gamma OH- 1.836e-007 9.277e-008
-6.736 -7.033 -0.296 H
1.395e-007 1.000e-007 -6.855 -7.000
-0.145 H2O 5.551e001 9.267e-001
1.744 -0.033 0.000 Ca
1.000e000 CaSO4 5.175e-001
1.055e000 -0.286 0.023 0.309 Ca2
4.825e-001 1.871e-001 -0.316
-0.728 -0.411 CaHSO4 4.396e-007
6.179e-007 -6.357 -6.209 0.148 CaOH
2.047e-007 2.877e-007 -6.689
-6.541 0.148 Cl 1.000e000 Cl-
1.000e000 5.622e-001 -0.000
-0.250 -0.250 H(0) 6.947e-026 H2
3.473e-026 7.079e-026 -25.459
-25.150 0.309 Na 2.000e000 Na
1.831e000 1.675e000 0.263
0.224 -0.039 NaSO4- 1.688e-001
2.372e-001 -0.773 -0.625 0.148 NaOH
5.032e-008 1.026e-007 -7.298
-6.989 0.309 O(0) 0.000e000 O2
0.000e000 0.000e000 -42.455
-42.146 0.309 S(6)
1.000e000 CaSO4 5.175e-001
1.055e000 -0.286 0.023 0.309 SO4-2
3.137e-001 2.826e-002 -0.503
-1.549 -1.045 NaSO4- 1.688e-001
2.372e-001 -0.773 -0.625 0.148 CaHSO4
4.396e-007 6.179e-007 -6.357
-6.209 0.148 HSO4- 1.955e-007
2.747e-007 -6.709 -6.561 0.148

• Speciation is a function of
• Ionic Composition
• Ionic Concentration
• Thermodynamic conditions
• Temperature
• Pressure

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Thermodynamic Geochemical Modeling

• Based on Thermodynamic Stability Equations
• Good for Evaluation of Worst Case Scenarios
• Can Include Gas Saturations and Partial Gas
  Pressures
• Can be Equilibrated to Reservoir Mineralogy
• Wide Range of Scales Can Be Evaluated
• No limit, Assuming Accurate Speciation and Ksp
• Multiple Waters Can Be Easily Intermixed
• Very Complex Programs can be Modeled
• Good for Monitoring Operations

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Key Equations

• Ksp Solubility Constant
• Function Enthalpy, Entropy and Gibbs free energy
  of a system
• Generally available only at 25 C
• Temperature Effects Estimated using a form of the
  Vant Hoff equation.

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Key Equations

• SI Scaling index
• Defines the degree of supersaturation of a
  solid in a solvent .
• Indicates the likelihood that precipitation will
  occur
• Controlled by ionic concentration in solvent
  fluid and Ksp of dissolved species
• Dependent on Thermodynamic parameters

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Key Equations

• SP Scaling Potential
• Determines the amount of a solid which can
  precipitate
• Controlled by ionic concentration in solvent
  fluid and Ksp of dissolved species
• However, Also Very Dependent on Kinetic
  parameters (nucleation, supersaturation,
  turbulence, pressure drop, etc)

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Geochemical Model of Brine Mixing
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Thermodynamic Geochemical Modeling

• Ksp Data Lacking At High Temperatures
• Estimated For Most Applications at T gt 25 C
• Gives Data Only On Potential, Not Real World
  Events
• Models Can Be Tuned To Reflect Real World
• No Data On Inhibitor Control
• Need A Real World Model To Help Tune Data And
  Verify Data From Geochemical Studies

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Near Infrared Spectroscopy (NIR)

• Instrumental Measurement of Onset Pressure and
  Temperatures (NIR frequency 500 3200 nm)
• HPHT, HPLT system
• 15,000 psig
• -40 to 300 F
• Incremental Scans from 1540 to 1700 Nm, every 2
  nm
• Light Blocking System (Rayleigh Scattering)
• Brine/Oil/Gas Compatible
• Evaluation of Inhibitors
• Applications for Inorganic and Organic Scales

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NIR System
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NIR System
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Measurements obtained by NIR

• Nucleation onset for scale formation
• Temperature
• Pressure
• pH
• Physical measurements
• Gas (CO2, H2S) partitioning can be evaluated
• Not dependent on Ksp
• Effects of inhibitors evaluated

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Benefits to Using NIR in Conjunction with
Geochemical Modeling

• Geochemical model calculations can be verified
• Once verified, model becomes invaluable as
  monitoring tool
• Geochemical upsets can be evaluated field wide
  (production, injection, and facilities)
• Theoretical Ksp values can be verified
• Verification of Ksp will then extend geochemical
  model range
• Inhibitors and production control of scaling
  problems can be evaluated

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Case Studies