Download - 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 !