MODELING OF PARAFFIN DEPOSITION IN PIPELINE

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MODELING OF PARAFFIN DEPOSITION IN PIPELINE AND
WELLBORE (AN OVERVIEW) DR AHMAD BAZLEE MAT
ZAIN FACILITIES ENGINEERING GROUP
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OUTLINE

• BACKGROUNDWhy do we need to model ?
• METHODS AND TOOLSWhat do we need ? How to model
  ? What do we know ? Application ?
• FUTURE RD EFFORTSWhat else do we need ?

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BACKGROUND Why do we need to model ?
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BACKGROUND
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BACKGROUND
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BACKGROUND

• Why do we have to model ?
• Understand the conditions for the paraffin
  deposition
• Understand the extent of paraffin deposition in
  the production system
• Understand the kinetic and thermodynamic behavior
  of the waxy production fluids

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BACKGROUND
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METHODS AND TOOLS What do we need ? How to
model ? What do we know ? Application of models
?
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METHODS AND TOOLS

• Pressure loss (hydrodynamics)
• Temperature loss (heat transfer)
• Diffusion/convection of dissolved paraffin
  molecules to the pipe wall
• Shear stripping of solids from the pipe wall
• Aging of solids (incorporation into crystal
  lattice)
• Trapping of oil

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METHODS AND TOOLS
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DEPOSITION KINETIC
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DEPOSITION KINETIC
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DEPOSITION KINETIC

• Turbulence decreases deposition rate by
  shear stripping mechanism
• Amount of oil trapped in wax deposits is
  greater in laminar flow than in turbulent
  flow
• Nature of deposits varies depending on
  flow conditions
• Aging phenomena is currently not well understood

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DEPOSITION KINETIC

• Use of lab based deposition data is crucial to
  describe the kinetic behavior (deposition
  tendency correlation)

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HYDRODYNAMICS

• The pressure along a multiphase flowline have
  been found to have a significant effect on the
  fluid compositions
• The changes in pressure may affect the fluid
  compositions and other liquid properties, such as
  density, viscosity and thermal capacity.
• The pipeline or wellbore under consideration is
  usually divided into a number of pipe segments
  and the flow conditions in each of these segments
  are evaluated

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HYDRODYNAMICS

• The mechanistic model by Xiao et al. (1990) is
  often used to predict flow patterns, pressure
  gradients and liquid holdups for pipe inclination
  angles from 15 to 15.
• The mechanistic models by Kaya (1998) and Ansari
  et al. (1989) are widely used to predict flow
  patterns, pressure gradients and liquid holdups
  for pipe inclination angles from 15 to 90
  from horizontal.

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HEAT TRANSFER

• Wax deposition has been described as a
  non-isothermal flowing system that appears to be
  driven by the heat flux
• Success in predicting wax deposition rates in
  single-phase and multiphase flow environments
  depends on how heat transfer characteristics are
  evaluated

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HEAT TRANSFER

• These characteristics include the forced
  convective film heat transfer coefficient, bulk
  and wall temperatures, and local heat flux across
  the pipe wall
• Numerous heat transfer coefficient correlations
  and experimental data for forced convective heat
  transfer during gas-liquid two-phase flow in
  vertical and horizontal pipes have been published
  over the past 40 years

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HEAT TRANSFER

• The temperature gradient is derived through a
  heat balance at the interface between the wax and
  the multiphase mixture
• The temperature at this interface is derived from
  the following overall heat balance at the
  interface
• The internal, flow-pattern-dependent, two-phase
  convective film heat transfer coefficient is
  obtained from several correlations
• Thermal conductivity of solid wax is not known,
  1.7 to 2 times of oil

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HEAT TRANSFER
Inside Convective Film Heat Transfer Coefficient
Correlations
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Predicted and Experimental hTP for Horizontal
Flows
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Predicted and Experimental hTP for Vertical
Flows
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THERMODYNAMICS

• The precipitation scenario appears to be
  dependent upon the amount of normal paraffins
  presence in a hydrocarbon system. When vapor is
  present, rigorous treatments of the
  vapor-liquid-solid equilibrium state usually
  include the vapor phase
• Four types of relationships are required to
  describe a three-phase state they are phase
  equilibrium of vapor-liquid and liquid-solid,
  component material balances, total material
  balance and stoichiometric.

Solid Concentration Gradient
Solid Liquid Equilibrium Constant
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THERMODYNAMICS

• A thermodynamic model for predicting
  vapor-liquid-solid equilibria of hydrocarbon
  systems developed by Brown et al. (1997) can be
  used to generate tables of dissolved paraffin
  (mole fraction) and concentration gradient
  (dww/dT) at various temperatures and pressures
• The multiphase flash algorithms are based on the
  Gibbs energy minimization methods as proposed by
  Michelsen (1982a,b).

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THERMODYNAMICS

• The mole fraction and concentration gradient can
  be obtained for the lumped paraffin components,
  where paraffin was considered as one pseudo
  component

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PREDICTED VS EXPERIMENTAL
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PREDICTED VS EXPERIMENTAL
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APPLICATION

• Thermodynamic models applies the general
  two-phase equilibrium calculations which
  include
• Bubble point calculations given a specified
  temperature or pressure
• Dew point calculations given a specified
  temperature or pressure
• Critical point calculation
• Flash calculation given a specified temperature
  and pressure
• Generation of a full phase envelope for the
  specified fluid

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APPLICATION

• Wax thermodynamic calculations
• Wax Appearance Temperature WAT (or cloud point)
  at a different pressure
• Solid fraction isobar
• Tuning to laboratory measured Wax Appearance
  Temperatures
• Tuning to laboratory measured wax contents

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APPLICATION

• Wax deposition calculations includes
• Calculation of wax deposition rates at steady
  state conditions
• Calculation of wax deposition build-ups as a
  function of time

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APPLICATION
Applies the pressure, temperature and wax
deposition calculations

• Temperature versus distance
• Wax thickness versus distance
• Pressure versus distance
• Liquid holdup versus distance
• Heat transfer coefficient versus distance
• Deposit rate versus distance
• Deposit thickness versus time
• Deposit volume versus time
• Pressure drop versus time

Optimize the Design and Operation of Oil and Gas
Production System (Waxy Fluids) Design of
Remedial Solutions
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APPLICATION
Defining Fluids Separator Gas Separator
Oil Flashed Separator Oil Standard
Compositional Analysis out to at least
C30 Extended, Quantitative, High Temperature
Gas Chromatographic Analysis to as high as a
carbon number as is detectable
Gas
Oil
FlashedOil
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THERMODYNAMIC INPUT
Standard Compositional Analysis
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THERMODYNAMIC INPUT
Extended Analysis
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MODEL PREDICTIONS
Vapor-Liquid-Solid Phase Plot
Production Path
WAT
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MODEL PREDICTIONS
Solids Fraction Plot at Atmospheric Pressure
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MODEL PREDICTIONS
Solids Fraction Plot at Atmospheric Pressure
Commingle with non-waxy fluids (more gas
etc) Amount of solids isslightly lower
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KINETIC INPUT
Defining Pipelines, Surrounding and Operating
Conditions Diameter 2.7 in ID, 3 in
OD Length 14383 ft, 7892 ft, 1380 ft, 200
ft Angle 0,0,90,0 Ambient 40 F to 60
F Operating 150 bbl/d at 600 psi, and 125 F
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MODEL PREDICTIONS
Temperature profile Insulation effect
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MODEL PREDICTIONS
Time to reach critical thickness Location of
deposits
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MODEL PREDICTIONS
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MODEL PREDICTIONS
Model can be used to design remedialsolutions
insulation, heat tracing etc.
Insulated/Heat Tracing
Un-Insulated/No Heat Tracing
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• FUTURE RD EFFORTS
• What else do we need ?

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RD EFFORTS

• Improve Paraffin Deposits Characterization,
  Deposition Physics, Deposition Tendency
  Correlation and Heat Transfer
• Fluid and Wax Characterization
• Wax Strength Measurements
• Address the Aging and Shear Stripping Processes
• Understanding of the Role Water
• Improvements of Heat Transfer for Gas-Liquid Flow
  in Pipes
• Solids Thermal Conductivity and Insulation Effect
• Comprehensive Kinetic, Hydrodynamic, Heat
  Transfer and Thermodynamic Modeling
• etc

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CONCLUDING REMARKS

• Models are now available to understand the
  conditions, extent and behavior of paraffin
  deposition of waxy hydrocarbon fluids
• Available models, however may require further
  improvements on the deposits characterization,
  deposition physics and heat transfer
• Modeling activities must be coupled with
  laboratory analyses to ensure predicted behaviors
  are within acceptable accuracies
• Modeling activities can assist in designing
  remedial solutions and deposition control for
  paraffin deposition problems

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THANK YOU QA