l2 reservoir fluid properties

8/9/2019 L2 Reservoir Fluid Properties

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Reservoir EngineeringENG 591Dr. Amjad Shah


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Outline

Resrvoir Engineer Role and Typical Tasks

Petroleum Reservoirs, their Classification andImportant Terms

Reservoir Fluids, i.e. Gas, Oil and Water

Ideal vs Real Gases

Oil and Water Important Properties

Cores and Their Characteristics and Analysis


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Realm of Reservoir Engineer

Estimate how much is there? (volumetrics)

Investigate whether oil can f low

(permeability), and if so,

at what rate and how long (ageing).

Well design/control (qo, Pr) needed

for optimal production (optimization)

Test, separate, monitor, pipeline

transportation, safe handling,

environmental and disposal issues,

investment and design forecast

Maintain production target, projectfuture production capacities, coordinate

with clients (e.g. refineries)


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Reservoir Engineering as defined

in Literature.Art of developing and producing oil and gas fields in such manner asto obtain a high economic recovery Moore 1955

. Application of scientific principles to the drainage problems arisingduring the development and production of oil and gas reservoirs Craftand Hawkins, 1959.

.One of the great underground sciences of the oil industry,attempting to describe what occurs in the wide open spaces of thereservoirs between the sparse points of observation the wells Dake,1994.

Key elements in reservoir engineering are:

Observations

AssumptionsCalculations, and

Development decisions


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Reservoir Engineer-Job Profile 1

Keeping updated and develop deeper knowledge with the latestadvances in the field of numerical simulation, reservoir management .

Strong evidence of experiences in numerical modeling of primary,secondary and EOR processes and individual contribution inaugmenting the field production and recovery in their previouscompanies.

Hands on experiences with reservoir modeling packages likeECLIPSE, CMG, TEMPEST, etc..

Good knowledge of PETREL-RE package , economic evaluationsoftwares will be an asset.

A good knowledge of related disciplines like petro-physics, Petroleumtechnology, G&G, etc.

Fluent in English both written and verbal. Be well aware of SPE resources and resource classification .

Job Profile; Qualifications required for a Senior Reservoir Engineer by Deep Water International in Malaysia 15/05/2014


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Reservoir EngineeringHENCE

Reservoir Engineering is a multi-disciplinary effort that goes into the heart of anintegrated strategy and planning for field development

(R&D, drilling, production, fluid-f low in the reservoir, workover and reservoirmanagement), design of facilities & infrastructure and overall economics.

. And it is the continuous process throughout the life of the reservoir

KEY RESPONSIBILITES OF A RESERVOIR ENGINEER Reserves estimation: estimate hydrocarbons and other fluids in place, in

collaboration with geoscientists Recovery factor: Determine the recoverable reserves with economic considerations

Forecasting: Production forecasting based on reservoir data and analysis Field development, Monitoring and operation, strategy decisions


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Role of Reservoir Engineer

Geology &Geophysics

EconomicsReservoirEngineering

Project Engineering

ProductionProcessEngineering

Petro-physicsFormation properties data(net pay thicknesses, porosities,fluid saturations)

Efficiency ofProduction flow

Economy of theProject e.g.Recovery factor

Passing required datae.g. production/injection

profiles for constructionof required facilitiese.g. platforms

Structural contours/mapsReservoir characterization


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Petroleum IndustryREFINING (Distillation of crudeoil)

Drilling Engineering:Getting to oil by drilling

various types of wells

Reservoir Engineering: Reservoir behavior, reserve estimates,

material balance calculations, fluid flow equations, reservoirsimulation & predicting performance, pressure transientanalysis, well-test design, Reservoir screening for Improved/Enhanced recoveries, its design and maintenance

Exploration (Searching andPredicting where oil and/or gas can be found

Production Engineering (extracting/producing oil& gas, workover, well completion and pressurecontrol, production log interpretation, prediction

of prod schedules

Processing facilities (Separators, Centralprocessing units: removal / separation ofimpurities and reservoir fluid contents oil,

water, sediments etc.), treatment, metering

Distribution (delivering (shipping,truckingetc) petroleum productsto customers in different area)

U p s t r e a m

Down Stream


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Petroleum Reservoirs, theirClassification andimportant Terms


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Figure 1. Typical p-T diagram for a multicomponent system


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Pressure-Temperature Diagram

Figure 1 shows a typical pressure-temperature diagram of a multicomponentsystem with a specific overall composition. Although a differenthydrocarbon system would have a different phase diagram, the generalconfiguration is similar.

These multicomponent pressure-temperature diagrams are essentially used to:

Classify reservoirs

Classify the naturally occurring hydrocarbon systems

Describe the phase behavior of the reservoir fluid


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Critical point The critical point for a multicomponent mixture is referred to as the stateof pressure and temperature at which all intensive properties of the gas and liquid phasesare equal (point C). At the critical point, the corresponding pressure and temperature arecalled the critical pressure Pc and critical temperature Tc of the mixture.

Bubble-point curve The bubble-point curve (line BC) is defined as the line separatingthe liquid-phase region from the two-phase region.

Dew-point curve The dew-point curve (line AC) is defined as the line separating the vapor-phase region from the two-phase region.

Cricondentherm (Tct)T he maxi mum temperature above which liquid cannot be formed regardless ofpressure (point E).

Cricondenbar (pcb) The Cricondenbar is the maximum pressure above which no gas can be formedregardless of temperature (point D).

Phase envelope (two-phase region) The region enclosed by the bub ble-point curve and the dew-pointcurve (line BCA), Quality lines The dashed lines within the phase diagram are called quality lines. Theydescribe the pressure and temperature conditions for equal volumes of liquids. Note that the quality linesconverge at the critical point (point C).


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Oil reservoirs If the reservoir temperature T is less than

the critical temperature Tc of the reservoir uid, thereservoir is classied as an oil reservoir.

Gas reservoirs If the reservoir temperature is greater thanthe critical temperature of the hydrocarbon uid, thereservoir is considered a gas reservoir.


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Types of Crude Oils: Black Oil

Quality lines approximately equallyspaced and characterize this black oilphase diagram

The liquid shrinkage curveapproximates a straight line

Except at very low pressures. Whenproduced, ordinary black oils

1. yield gas-oil ratios between 200and 700 scf/STB

2. Oil gravities of 15 to 40 API

3. The stock tank oil is usuallybrown to dark green in color.

Ordinary Black Oil

Gas Phase

Pressure path in

reservoir 1

Critical

point

C

Liquid Phase

90

80

70

60 % Liquid

50

40

F

30

20

10

G

0

Separator

B

A typical pressure-temperature phase diagram for ordinary black oil


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Gas Cap Reservoir

Gas-cap reservoir: If the initial reservoirpressure is below the bubble- point pressure ofthe reservoir fluid, as indicated by point 3 on

Figure 1-1, the reservoir is termed a gas-cap ortwo-phase reservoir, in which the gas or vaporphase is underlain by an oil phase. Theappropriate quality line gives the ratio of thegas-cap volume to reservoir oil volume


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Gas Reservoirs

In general, if the reservoir temperature is above the criticaltemperature of the hydrocarbon system, the reservoir isclassied as a natural gas reservoir. On the basis of theirphase diagrams and the prevailing reservoir conditions,natural gases can be classied into 3 categories:

Retrograde gas-condensate

Wet gas

Dry gas .


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If the reservoir temperature T lies between the criticaltemperature Tc and cricondentherm Tct of thereservoir fluid, the reservoir is classified as a

retrograde gas-condensate reservoir. the gas-oil ratio for a condensate system increases

with time due to the liquid dropout and the lossof heavy components in the liquid.

Condensate gravity above 50 API

Stock-tank liquid is usually water-white or slightlycolored.

Retrograde gas-condensate reservoir


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Temperature of wet-gas reservoir

is above the cricondentherm of the

hydrocarbon mixture. Because thereservoir temperature exceeds thecricondentherm of the hydrocarbonsystem, the reservoir uid willalways remain in the vapor phase

region as the reservoir is depletedisothermally, along the vertical lineA-B.

Wet-gas reservoir


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Wet-gas reservoirs are characterized by the following

properties:

Gas oil ratios between 60,000 to 100,000 scf/STB

Stock-tank oil gravity above 60 API

Liquid is water-white in color

Separator conditions, i.e., separator pressure and temperature, lie within the two-phase region

Wet-gas reservoir


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Properties of Reservoir Fluids:Gas


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Ideal Gas properties

According to kinetic theory of gases

Gases are composed of large number of molecules

For an ideal gas the volume of these molecules is insignificant comparedto the total volume of the occupied gas

No inter-molecular attractive or repulsive forces

All molecular collisions perfectly elastic

p = absolute pressure, psia

V = volume, ft 3

T = absolute temperature, Rn = number of moles of gas, lb-mole

R = the universial gas constant and for the above units has a value of 10.730psia ft 3 /lb-mole R

pV = nRT


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Behavior of Real Gases

At low pressures, ideal gas equation is a greatconvenient, however,

At higher pressures the error can be upto 500%

compared to only 2-3% at atm pressure

Gases are highly compressible (upto 500% volumetric change)


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Properties of GasesDensity of gas/mixture

Apparent Molecular Weight Ma (for mixtures)

Specific volume

Specific Gravity

M a =

yi M ii = 1!

! g =

m

v=

pM

RT

v =v

m=

RT

pM a=

1

! g

! g = M a

M g


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Real vs Ideal Gases: Equation ofState

For Real gases ideal gas equation becomes

Z can be generalized with sufficient accuracies for most engineering purposes

with using the

Standing and Katz generalized gas compressibility factor chart.

PV = znRT where z = compressibility factor

Z =V acturalV actural

=

V nRT p

P pr =P

P pc where P pr = Pseudo ! reduced pressure

T pr =T

T pc where T pr = Pseudo ! reduced temperature


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Real vs Ideal Gases: Example A gas reservoir has the following gas composition: the initial reservoir pressureand temperature are 3,000 psia and 180F, respectively.

Component y i TciR Y iTci Pci yiPci

CO2 0.02 547.91 10.96 1071 21.42

N2 0.01 227.49 2.27 493.1 4.93

C1 0.85 343.33 291.83 666.4 566.44

C2 0.04 549.92 22.00 706.5 28.26

C3 0.03 666.06 19.98 616.4 18.48

i C4 0.03 734.46 22.03 527.9 15.84

n C4 0.02 765.62 15.31 550.6 11.01

=383.38 =666.38


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Real vs Ideal Gases: ExampleCalculating densities using ideal and real gas equations

Step 1. Calculate the apparent molecular weight from Equation: Ma = 20.23

Step 2. Determine the pseudo-critical pressure from Equation:

Ppc = 666.18

Step 3. Calculate the pseudo-critical temperature from Equation: T pc = 383.38

Step 4. Calculate the pseudo-reduced pressure and temperature by applying theirrespective equations:

Step 5. Determine the z-factor from Standing and Karts

chart: z = 0.85

Step 6. Calculate the density from its equation:

P pr =3000

666.38= 4.50

T pr =640

383.38

= 1.67

U sin g equation for real gases

! g =(3000)(20.23)

(0.85)(10.73)(640)= 10.4 lb / ft 3

U sin g equation for ideal gases

! g =

(3000)(20.23)(10.73)(640)

= 8.84 lb / ft 3


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Pseudo-reduced Properties fromcorrelation

When composition of a natural gas is notavailable than

Case 1: Natural Gas Systems 1

Case 2: Gas-Condensate Systems 2

T pc = 168 + 325 ! g ! 12.5 ! g2

P pc = 677 + 15.0 ! g ! 12.5 ! g2

T pc

= 187 + 330 ! g

! 71.5 ! g

2

P pc = 706 ! 51.7 ! g ! 11.1 ! g2

Specific Gravity of the Gas1Brown et al. (1948), Natural Gasoline and the Volatile Hydrocabons, Tulsa:NGAA.2Standing (1977), Volumetric and Phase Behavior of Oil Field Hydrocarbon Systems, pp.125-126. Dallas:SPE.


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Properties of Reservoir Fluids:Oil & Water


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Properties of Oils & WaterOil

Gravity

Rs (Gas Solubility)

Bubble-Point Pressure

Oil Formation Volume Factor

Viscosity

Surface/Interfacial Tension

Water

Water Formation Volume Factor

Viscosity

API =141.5

! o

! 131.5

! o = Specific Gravity of Oil


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Laboratory Analysis ofReservoir Fluids


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Core Plugs

Core plugs:1.5 inch in diameter3 inch in length


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Core Plugs


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Core Plug Characteristics

3.75cm (1.5 inch) diameter Avoid heterogeneities Piece together core Multiple orientations


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Core Plug Analysis


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Cleaning of Core

For Conventional Core Analysis Dean Stark Extraction (1 plug) Soxhlet extraction (>1 plug) Destructive Not efficient for the whole core

Special Core Analysis Miscible flushing (brine-methanol-toluene-methanol-brine) Non-destructive

Solvent Remove salt (methanol) Remove crude oil (toluene)

l2 reservoir fluid properties

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