Unidade 05 - Prop. Das Rochas

8/12/2019 Unidade 05 - Prop. Das Rochas

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Fundamentos daIndstria Petrolfera


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Unidade 5

Propriedades das Rochas


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Rock Properties

Basic Rock Parameters Used in Reservoir Engineering

(Porosity, Permeability, Saturations, Compressibility)


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Scanning Electron MicrographNorphlet Formation, Offshore Alabama, USA

Pores Provide theVolume to Contain

Hydrocarbon Fluids

Pore Throats RestrictFluid Flow

PoreThroat

Porosityin a Sandstone


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Sandstone Composition Framework

Grains

Norphlet Sandstone, Offshore Alabama, USAGrains are About =< 0.25 mm in Diameter/Length

PRF KF

P

KF = PotassiumFeldspar

PRF = Rock Fragment

P = Pore

Potassium Feldspar isStained Yellow With aChemical Dye

Pores are ImpregnatedWith Blue-Dyed Epoxy

CEMENT


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What is Porosity? And why is it

important?

Total Porosity

Total Porosity isthe ratio of thevoid space to the

total rock volume

Effective Porosity

Effective Porosityis the ratio of the

interconnectedvoid space to thetotal rock volume


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Porosity = 48%

Cubic Packing of Spheres


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Porosity = 27 %

Rhombic Packing of Spheres


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Porosity = 14%

Packing of Two Sizes of Spheres


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Inter-granular Porosity

rombohedrally packed

spheres: = 26%

grain sorting, silt, clay and

cementation effect porosity


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Permeability (k)

Permeability is the measure of capacity of rock to transmitfluid.

Symbol : k

Units : Darcy or milliDarcy (D or mD) in SI units m21 mD = 10**(-15) m2

Source : Well tests, core analysis

Range : 0.001 mD - 10,000 mD

pA

Lqk

L

pkAq

or


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Definition of 1 Darcy

Darcy is a unit of

Area

1 mm2=

1,013,250 Darcy

1 Darcy =

0.986923 m2


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Effect of Grain Size in Permeability


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Shale

Sand

h3

h2

h1

hnet= h1+ h2+ h3


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Saturations (Sw, So, Sg)H2O

During deposition of the

sedimentary rock the pore space issaturated with water of varyiingsalinity (20,000 to 200,000 ppm)The HC migrate into these porespaces and displace most of this

water down to the irreducible

water saturation.Sandstones are usually water wet.This means that the sand grainsare covered with a film of water(10-30%), and the oil or gasoccupies the more central part of

the pores. These central positionsare also more beneficial for flow.Carbonates are usually oil or ofmixed wettability and hence theoil occupies a more difficultflowpath.


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Open Hole Logs to determine Saturation

Resistivity log

Induction tools

Laterolog tools

Porosity log Neutron tools

Density tools

Sonic tools

Magnetic resonance tools

We run tools into the freshly

drilled reservoir section whichmeasure physical rock propertieswhich we in turn use to calculatethe properties that we really areafter. Resistivitiy tools are used tocalculate saturations (why do think

this could be used ????).The neutron measures the capacityof Hydrogen absorption and hencegives an indication of thehydrocarbon charge. The densitylog measures the density and

hence is an indicator of porosity.From the sonic travel timesporosities can also bebackcalculated. Magneticresonance logs give a measure ofpermeability.


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Archies Equation

where:

Sw: water saturation

a: constant

: porositym: cementation factor

Rw: formation waterresistivity

Rt: true resistivity (measuredby deep resistivitymeasurement)

t

w

2

2w

t

w

15.2

2w

t

w

m

nw

R

R1S

)estone(lim

R

R62.0S

)sandstone(

R

RaS


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Exercise

Calculate oil saturation in the following case

Rock type: sandstone

Rw: 0.0912 (at bottom hole temperature)

: 0.2 Rt: 20 ohm meter


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7.0S3.0S

20

0912.0

2.0

62.0S

20

0912.0

2.0

62.0S

o

w

15.2w

15.2

2

w


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Total Compressibility (Ct)

ggwwooft cScScScc Typically,

Cw: 3E-6

Co: 3E-6(Black oil)

Cg: 1/pressure

Cf: 4E-6


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Exercise

Calculate total compressibility in the following case

cf: 3.6E-06

co: 1.158E-05 So: 0.83

cw: 2.277E-06 Sw: 0.17cg: 6.023E-05 Sg: 0


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Solution

Ct = 1.36 x 10-5 psi-1


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Exercise

Calculate total compressibility in the following case

cf: 3.6E-06

co: 1.158E-05 So: 0.73

cw: 2.277E-06 Sw: 0.17cg: 6.023E-05 Sg: 0.1

Compare solution with previous Example


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Additional Reading Requirements

Please read the chapters 26,27 and 28 of the PetroleumEngineering Handbook !

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Unidade 05 - Prop. Das Rochas