L3-Reservoir Fluids Classification

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Termodinamica de Hidrocarburos

Classification of Reservoir FluidsOil & Gas Properties From

Correlations

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Methods to Evaluate Fluid Properties

Two main models to quantify real oil and gas volumes

Black Oil modelsCompositional models

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Methods to Evaluate Fluid Properties

G

GO,

nyyyy ...,, 321

nxxxx ...,, 321

Black Oil Compositional

Model Formulations

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Methods to Evaluate Fluid Properties

Compositional ModelOil and gas are mixtures of several componentsAll components may be present in liquid and gas phasesVolumetric properties function (P,T, compositions) are evaluated using an Equation of State (EOS) for all phases.

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Phase Behavior and Fluid Properties

Black Oil ModelHas only two components named as the phases: Gas (G) and Oil (O).G may be dissolved in the oil phase and accounted by the solution gas oil ratio (Rs). O cannot dissolve in the gas phase.Phase volumetric properties determined from separate correlations

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Classification of Reservoirs based on Phase Diagram

Gas Reservoirs (Single Phase)

Gas Condensate Reservoirs (Dew-Point Reservoirs):

Undersaturated Solution-Gas Reservoirs (Bubble-Point Reservoirs):

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Phase Diagram of a Dry Gas Reservoir

Temperature

Pres

sure

Path of Production

Initial Reservoir Conditions

Separator Conditions

CP

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Phase Diagram of a Wet Gas Reservoir

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Phase Diagram of a Retrograde Gas Reservoir

Temperature

Pres

sure

Initial Reservoir Conditions

CP

Path of Production

Separator Conditions

Temperature

Pres

sure

Initial Reservoir Conditions

CP

Path of Production

Separator Conditions

Temperature

Pres

sure

Initial Reservoir Conditions

CP

Path of Production

Separator Conditions

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Phase Diagram of a Volatile Oil Reservoir

Temperature

Pres

sure

Initial Reservoir Conditions

CP

Path of Production

Separator Conditions

75%

50%25%

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Phase Diagram of a Black Oil Reservoir

Temperature

Pres

sure

Initial Reservoir Conditions

CPPath of Production

Separator Conditions

25%50%75%

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Phase envelopes of mixtures with different proportions of same HC components

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Typical Compositions of Reservoir Fluids

Component Black Oil Volatile Oil Gas Condensate Wet Gas Dry Gas

C1 48.83 64.36 87.07 95.85 86.67

C2 2.75 7.52 4.39 2.67 7.77

C3 1.93 4.74 2.29 0.34 2.95

C4 1.60 4.12 1.74 0.52 1.73

C5 1.15 3.97 0.83 0.08 0.88

C6 1.59 3.38 0.60 0.12

C7+ 42.15 11.91 3.80 0.42

MwC7+ 225 181 112 157

GOR 625 2000 18,200 105,000 -

Tank oAPI 34.3 50.1 60.8 54.7 -

LiquidColor

GreenishBlack

MediumOrange

LightStraw

WaterWhite

-

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Components of Typical Petroleum Gases

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Typical Crude Oil Fractions

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DRY GAS RESERVOIRS:GOR greater than 100,000 SCF/STBNo liquid produced at surface

WET GAS RESERVOIRS:GOR > 100,000 SCF/STBNo liquid is formed in the reservoirSeparator conditions lie within phase envelope and liquid is produced at surface

Classification of Reservoirs based on Production and PVT data

(see updated rules Mc Cain SPE paper)

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Classification of Reservoirs based on Production and PVT data

GAS CONDENSATE RESERVOIRS:GOR between 70,000-100,000 SCF/STBDensity greater than 60 ºAPILight in colorC7

+ composition < 12.5%

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Classification of Reservoirs based on Production and PVT data

VOLATILE OIL RESERVOIRS:GOR between1,000-8,000 SCF/STBDensity between 45-60 ºAPIOil FVF greater than 2.00 (high shrinkage oils)Light brown to green in colorC7

+ composition > 12.5%

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BLACK OIL RESERVOIRS:GOR less than 1,000 SCF/STBDensity less than 45 ºAPIReservoir temperatures less than 250 ºFOil FVF less than 2.00 (low shrinkage oils)Dark green to black in colorC7

+ composition > 30%

Classification of Reservoirs based on Production and PVT data

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Additional Guidelines

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Fluid Properties for Black-Oil Reservoir Simulation

Oil and Gas Propertiesoil formation volume factor Bo [=] res bbl/STB

gas formation factor Bg [=] cu ft/SCF or res bbl/SCF

total formation volume factor Bt [=] res bbl/STB

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Fluid Properties for Black-Oil Reservoir Simulation

Oil and Gas Propertiessolution gas-oil ratio

Rs [=] SCF/STB

oil and gas viscosities o, g [=] cp

compressibility and thermal expansion coefficients.

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Typical pressure, & temperature ranges

Location Pressure (psia)

Temperature (oF)

Reservoir 500-10,000 100-300 (500+ thermal) Separator 100-600 75-150 Stock tank 14.7 Ambient Standard Conditions

14.7 60

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DRY GAS RESERVOIRS:

GOR > 100,000 SCF/STBNo liquid produced at surfaceMostly methane

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Standard Conditions

Unify volumes to common grounds for sales and regulatory purposes

T = 60 0FP = 14.65 – 15.025 (State dependent) ThenVM = RTsc/Psc

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Reservoir Engineering Properties of Dry Gases

Gas formation volume factor Bg

Reservoir ConditionsReservoir ConditionsStandard ConditionsStandard Conditions

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[res bbl/SCF] or [ft3/SCF]

Gas Formation Volume Factor

SC

Rg V

VB

Volume of an arbitrary amount Volume of an arbitrary amount of gas at reservoir T & P of gas at reservoir T & P

Volume of Volume of SAMESAME amount at amount at

standard T & P standard T & P

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[res bbl/SCF] or [ft3/SCF]

Gas Formation Volume Factor

SC

SCSC

PnRTZP

ZnRT

Bg

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Gas Formation Volume Factor (McCain)

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[res bbl/SCF] or [ft3/SCF]

Gas Formation Volume Factor

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Viscosity Definition & Units

Viscosity is a measure of the resistance to flow exerted by a fluidThis is called dynamic viscosity and has units of centipoise = g mass / 100 sec cm

Kinematic viscosity is viscosity / density, units are in centistokes = centipoise /g/cc

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Reservoir Engineering Properties of Dry Gases

Gas Viscosity

Visc

osity

(cp)

Visc

osity

(cp)

PressurePressure

T increasingT increasing

100oF150oF

200oF

100oF

150oF

200oF

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Viscosity of Ethane (from McCain book)

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Viscosity of Gases at Atmospheric Pressure

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Viscosity of Gas Mixtures

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Example

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Example

Read Molecular Weights Read Viscosities figure 6-7Apply formula…

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Gas Viscosity if Composition is Unknown

Still at atmospheric Still at atmospheric pressure!pressure!

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Viscosity Corrections

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Viscosity of Gases at High Pressure

==ratioratio**atat

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Viscosity of Gases at High Pressure

make suremake sureyou checkyou checkthe the specificspecificgravity gravity rangerange

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Accuracy for Viscosity Correlations?

At low Ppr and low gravities + 2%

Agreement is less accurate as specific gravity increases (fig. 6-12 has about 20% accuracy)

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Isothermal Compressibility

Definition

Derivative is evaluated at constant T = TA and specified pressure P = PA

AT

AAg PV

VTPC

1,

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Isothermal Gas Compressibility

P1

V2V1

TB

P2

Vave= (V1+V2)/2

ATaveAAg PP

VVV

TPC

21

211,

TA

PA

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Isothermal Compressibility (Cg)

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Isothermal Compressibility

Using ideal gas equation

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Isothermal Compressibility

Using real gas equation

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GasGasCompressibilityCompressibility

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Properties of Black Oils Definitions

Material summarized fromMcCain book

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Phase Diagram of a Black Oil Reservoir

Temperature

Pres

sure

Initial Reservoir Conditions

CPPath of Production

Separator Conditions

25%50%75%

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Properties of Black Oils Needed for Reservoir Engineering Calculations:

Formation Volume Factor of oil Bo

Total Formation Volume Factor of oil Bt

Solution Gas oil Ratio Rs

Coefficient of Isothermal Compressibility Co

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Properties of Black Oils Needed for Reservoir Engineering Calculations:

Coefficient of isobaric thermal expansion o

Oil Viscosity o

Interfacial Tension

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Learning Goals

Understand the behavior of those PVT properties (Bo,Rs,…) vs P and type of fluid Evaluate PVT properties from

Field dataLaboratory studiesCorrelationsEquations of State

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Definitions

Specific gravity of a liquid

API gravity

),(),(

11

11

TPTP

w

oo

5.1315.141APIo

o

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Definitions

Formation Volume Factor of Oil

Gas out of Gas out of SolutionSolution

Reservoir Reservoir (P,T)(P,T)

Surface Surface (Ps,Ts)(Ps,Ts)

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Definitions

Volume of Oil + Dissolved gas at Reservoir Pressure & Temperature Volume of Oil entering Stock tank at Tsc, Psc

Units = Reservoir barrels (bbl) /Stock tank barrels (STB)Units = Reservoir barrels (bbl) /Stock tank barrels (STB)

Bo =

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General Shape of BoGeneral Shape of Bo

BoBo

Reservoir PressureReservoir PressurePPbb

Reservoir T = constantReservoir T = constant

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Solution Gas Oil Ratio (Rs)

How much gas is dissolved in the oil volume per volume basisRs depends upon pressure

Units [= ] SCF gas /STB oilUnits [= ] SCF gas /STB oil

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General Shape of Solution Gas General Shape of Solution Gas Oil Ratio (Rs)Oil Ratio (Rs)

RsRs

Reservoir PressureReservoir PressurePbPb

Reservoir T = constantReservoir T = constant

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Total Formation Volume Factor Bt

HgHg

OilOil BBobob

HgHg

GasGas

OilOil BBoo

BBgg(R(Rsbsb-R-Rss))

PPbb

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Definition of Bt

Also called Two-phase formation volume factor

ssbgot RRBBB

Units…Units…

bbl/STB + bbl/SCF * (SCF/STB)bbl/STB + bbl/SCF * (SCF/STB)

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General Shape of BGeneral Shape of BttBB

oo, B, B

tt

Reservoir PressureReservoir PressurePPbb

Reservoir T = constantReservoir T = constant

BBtt=B=Boo

BBtt

BBoo

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Sep

arat

or g

as

gas gas

Decreasing Pressure

Sep

arat

or g

as

Sep

arat

or g

as

gas

StandardConditions S

epar

ator

gas

Sep

arat

or g

as

oiloil oiloil

oil

STB

STBSTB STB

StandardConditions

Bg =

Rv =

Bo= Rs=

P2 P1

P4 P3 Reservoir

Definition of Oil & Gas PVT PropertiesDefinition of Oil & Gas PVT Properties

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The Coefficient of Isothermal Compressibility of Oil

Provides Instantaneous change of volume with P at constant T

AT

AAo PV

VTPC

1,

Total, molar or specific volumeTotal, molar or specific volume

05/03/23 65(Use in Steam Injection Processes)

Coefficient of Thermal Expansion

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Oil Viscosity

Viscosity is a measure of the resistance to flow exerted by a fluidThis is called dynamic viscosity and has units of centipoise = g mass / 100 sec cm

Kinematic viscosity is viscosity / density, units are in centistokes = centipoise /g/cc

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Needs of Crude Oil Viscosity

Calculation of two-phase flowGas-lift and pipeline designCalculate oil recovery either from natural depletion or from recovery techniques such as waterflooding and gas-injection processes

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InjectionWell

Separation andStorage Facilities Production Well

1 2Oil Zone Oil Bank /Miscible Front

2

HC GasInjectionfrom Pipelineor Recycle

1

InjectionWell

Separation andStorage Facilities Production Well

11 22Oil Zone Oil Bank /Miscible Front

2

HC GasInjectionfrom Pipelineor Recycle

1

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Variation of Oil Viscosity O

il Vi

scos

ityO

il Vi

scos

ity

T = constantT = constant

PPbb

Single Phase FlowSingle Phase FlowTwo Phase FlowTwo Phase Flow

Gas Out of Gas Out of SolutionSolution

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Fluid Properties for Reservoir Engineering

The fluid properties of interest are the those that affect the fluid mobility these are used in material balance calculations

PVT properties are determined from 5 specific lab procedures

Flash liberation testsDifferential Liberation TestsViscosity MeasurementsSeparator TestsCompositional measurements

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Fluid Properties Determined

Oil PropertiesBubble Point PressureBo

Rs

Bt

Co and o

Gas propertieszBg and g

Compositions oil & gas

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Constant Compostion Expansion test (CCE)

Temperature of Test = Reservoir TemperatureTemperature of Test = Reservoir Temperature

V t1 V t2

Vt3

=V

b

V t5V t4

oil oil oil oil

oil

gas gas

Hg Hg Hg HgHg

P 1 >> P b P 2 > P b P 3 = P b P 4 < P b P 5 < P 4

1 2 3 4 5

Also called flash vaporization testAlso called flash vaporization test

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Flash Vaporization Test or CCE

Properties determinedPb

Co

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Determination of Pb

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Determination of Co

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2.Differential Liberation Test

gas

oil

oil oil oil

oil

gas

Hg

Hg

Hg Hg

Hg

P 1 = P b P 2 < P b P 2 < P b P 2 < P b P 3 < P 2 < P b

1 2 3 4 5

gasoil

Gas off

Temperature of Test = Reservoir TemperatureTemperature of Test = Reservoir Temperature

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2.Differential Liberation (or Separation) Test

Properties DeterminedOil formation volume factor at the Bubble Point pressure Bodb and below the bubble point pressure Bod

Solution gas-oil ratio at the Bubble Point pressure Rsdb and below the bubble point pressure Rsd

Isothermal compressibility (derived property)

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3. Separator Tests

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3. Separator TestsGoals: Maximize API, minimize BoSb & RsSb

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Optimization of Separator 2 Conditions

3160

3180

3200

3220

3240

3260

3280

3300

Sol

utio

n G

as O

il R

atio

at P

b (R

sb)

2.76

2.78

2.80

2.82

2.84

2.86

Form

atio

n V

olum

e Fa

ctor

at P

b (B

ob)

50 100 150 200 250 300

Separator 2 Pressure (psia)

High Pressure Separator @ 900 psia and

TSep2 = 75oF

100 ºF

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Comparison between 1 & 2 Separators Stages (volatile oil)

3360

3380

3400

3420

3440

3460

Solu

tion

Gas

Oil

Rat

io a

t Pb

(Rsb

)

2.90

2.92

2.94

2.96

Form

atio

n Vo

lum

e Fa

ctor

at P

b (B

ob)

400 500 600 700 800 900 1000Separator 1 Pressure (psia)

Low Pressure Separator @ 300 psia and

TSep1 = 160oF 75ºF

One Separator Stage

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Typical PVT Properties for a Black Oil and a Volatile Oil

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0

3.2

Form

atio

n V

olum

e Fa

ctor

(Bo)

0 1000 2000 3000 4000 5000Pressure (psia)

Black OilVolatile OilBlack Oil Correlation

TR =180 oF

PbPb

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Typical PVT Properties for a Black Oil and a Volatile Oil

0

1000

2000

3000

4000

Solu

tion

Gas

Oil

Rat

io (R

s)

0 1000 2000 3000 4000 5000Pressure (psia)

Black OilVolatile OilBlack Oil Correlation

TR =180 oF

PbPb

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Nomenclature

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Water in Petroleum Engineering

Presence of WaterConnate WaterAquiferProductionWell Log AnalysisInjectionWater Treatment

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Water in Petroleum Engineering

Formation Water (Brine) PropertiesSolubility of Gas in WaterWater CompressibilityWater Formation Volume FactorWater ViscosityChemical PropertiesResistivity

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Chemical Analysis of Water

All formation water contains dissolved ions. The ions may be classified into two groups. Positively charged, or cations, and negatively charged or anions, these ions proceed from salts in solution and conduct electricity offering more or less resistance depending upon the salt concentration (property used in electric logs).

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Chemical Analysis of Water

Formation waters are neutral, that is positive and negative charges balanceRequire brine compatibility with injection fluids (clay swelling, precipitations)

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Additional PVT Tests

ChromatographySwelling tests (miscibility tests) by gas injection

See notes (and given references) for chomatography techniques and additional material for this moduleClick to see an animation of separation.

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Chromatography Principles & Applications

Know what are the principles of operation of a chromatographLearn the different types and capabilities of chromatographsCalibration fluidsComponents of a GC / HPLCHow to interpret/read chromatographs

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Reading Material

FilesVisco models.pdfReservoir Fluid Classification-guidelines.pdfViscosity-MAB-Dominique.pdf