PowerPoint Presentation
Flow AssuranceWAT Testing MethodsCross Polar Microscopy (CPM)
most sensitiveUses polarized light and temperature controlled stage
to visually determine both wax appearance and disappearance
temperatures.Disadvantages: Loss of light end componentsRequires
careful temperature calibrationDependent on cooling rate and
pre-treatment methodImagingLight
ScatteringPrecipitationFiltrationCold Finger Deposition
TestIndirectDifferential Scanning Calorimetry (DSC)Compositional
Model#2Source: Flow Assurance Course - PETRONAS 2009 + Cranfield
UniversityWAT Testing MethodsTest
MethodAdvantagesDisadvantagesRecommendationEstimated Accuracy
(C)Cross-Polarized Microscopy (CPM)Detection of first wax crystal
and subsequent detection of growth rates and morphology via
microscopeSmall sample size requiredDifficult to use at high
pressure.Can be compromised for highly contaminated
samplesRecommended method for WAT measurement.Widely used reliable
method with high sensitivity.Requires low cooling rates and high
quality samples.1 - 3Differential Scanning Calorimetry (DSC)Detects
phase change, relying on exothermic and endothermic phase
transition (i.e. melting/solidification) Quick, easy, reliableCan
infer solid phase contentFast, unrealistic cooling rates required
for good sensitivity.Can give low values (typically ~5C lower than
CPM measurements)Less used in industryRepeatable method.Requires
good sample quality.Sensitivity can be poor for low wax contents.3
- 5Filter pluggingCan be used for high-pressure testsSimple
equipmentVery fine filters required for accurate determination of
WATSomewhat subjective method that shouldnt be used as primary WAT
measurement.May be confused by precipitation of other solids.8 -
10Near-Infrared (NIR)Simple, visual methodRely on light
transmittance, which can be impacted by types of paraffinCan be
misleading when asphaltenes are presentCan be used as
back-up/confirmation for CPM test2-4ViscosityLarge sample size adds
to representativeness. Can use high-pressure viscometer.Subjective
interpretationDoes not work for low wax content fluids.Possibly
recommended for live crudes with marked WAT, but should be used
with caution.10 - 15Cold FingerSample sizeRelatively quick/simple
test methodLimited control over cooling rateLimited ability to
monitor crystal growthCan be used as screening-level analysis to
determine bulk WAT or CWDT5 - 10#3Source: Flow Assurance Course -
PETRONAS 2009 + Cranfield UniversityCross Polarization Microscopy
(CPM)
34C28C27C25C20C#4Source: Flow Assurance Course - PETRONAS
2009
Wax Appearance vs. DissolutionWax deposits melt at significantly
higher temperature than the form- ~10-20C above WAT- Could be as
high as 64C (hard deposit)
Wax will re-dissolve into oil at temperature higher than WAT but
less than melting point- form slurry flow of wax particles in bulk
liquid- impact on fluid rheology
#5Source: Flow Assurance Course - PETRONAS 2009
Wax Content Precipitation MethodPrecipitation Method
(BP237/75)Asphaltenes removed from the sampleCrude is dissolved in
DCMChilled at -32CPrecipitated wax filtered offWeight of wax
collected expressed as % of the amount of starting material
In comparison to an HTGC analyses, wax content measurements from
precipitation methods provide a quick screening method to determine
the amount of wax in the sample, but they should be used with
caution, as they do not provide any information regarding the
n-paraffin distribution of the sample.
#6Source: Flow Assurance Course - PETRONAS 2009
Wax Content HTGC Method(Extended n-Paraffin Analysis)High
Temperature Gas Chromatography: Compositional method. Determines
n-paraffin composition of all n-paraffin components between C15 and
C100Required to identify content of higher number of n-paraffin
chains. A simple lumped C30+ composition is not
sufficientImportance in system design / wax deposition
modeling:
Wax content heavily influenced by n-paraffin components at
relatively low carbon numbers (C15 to C30) BUT WAT is heavily
influenced by n-paraffin distribution at much higher carbon
numbers#7Source: Flow Assurance Course - PETRONAS 2009
Similar wax content Similar WAT
Similar wax content. Different WAT Different wax content.
Similar WAT#Crude Oil ViscosityViscosities should be measured by
shearing the samples at a constant rate and by cooling the sample
at a constant rate from above the WAT to the minimum ambient
temperature expected in the field. Care should be taken to ensure
the fluids are properly handled prior to starting the measurements,
A reasonable cooling rate should be used. It is recommended that a
cooling rate of 0.5C/minute be used to obtain the most accurate
viscosity dataA sealed viscometer should be used to minimize
light-ends loss in the sample.
#9Source: Flow Assurance Course - PETRONAS 2009
