modul 7-saturation computation

8/8/2019 Modul 7-Saturation Computation

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Petrophysical InterpretationSaturation Computation


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The ideal logThe ideal log

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

1000 1005 1010 1015 1020 1025 1030

porGas

porOil

porWat

% of rock filled with gas,% of rock filled with oil,% of rock filled with water,recovery factorsrelative permeability

Unfortunately we currently

cannot directly measure anyof these quantities

10

100

1000

10000

1000 1005 1010 1015 1020 1025 1030

permGas

perm

Oil

permWat

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

1000 1005 1010 1015 1020 1025 1030

recGas

recOil


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In reality w e have to make indirect measurementsIn reality w e have to make indirect measurements

GR GR Resistivity in various flavorsResistivity in various flavors Spectroscopy (natural or induced)Spectroscopy (natural or induced) Density and PEFDensity and PEF Neutron PorosityNeutron Porosity

SigmaSigma etc.etc.


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Water Saturation : Volumes


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Fraction of porosity

VwPorosity,

Vo

Sw = Vw /

So = Vo /


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Archie


7/31

Resistivity variation due to fluids

Resistivity is the resistance of 1 m 3 of a material.Oil has high resistivity, saline water has low resistivity.

Rt Rt


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Resistivity variation due to porosity

Higher porosity rock has lower resistivitythan lower porosity rock, given the same Sw.

Rt Rt


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Saturation Equations:Saturation Equations: Archie 1942 Archie 1942

t

w m

n w R

R a S

=m

w

o a

R

R F

==

t

o n w R

R S =

a

C S C w

n

w m

t

=F = Formation factor Rt = True formation resistivityRo = True formation resistivity when Sw=1Rw= Resistivity of the formation water = Total formation porositym = empirical fudge factor (cementation factor)n = empirical fudge factor (saturation exponent)a = yet another fudge factor


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R o /

R w

( l o g s c a l e )

(log scale)

Slope = -m

1.00.01

a

Archie a, m and n Archie a, m and n

t

w m

n w R

R a S =

R t / R o (

l o g s c a l e )

Sw(log scale)

Slope = -n

1.0

0.01 1.0

Effect of m(tortuosity)

Effect of m+n(tortuosity)


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Archie a & m values Archie a & m values

General formwhere a ~ 1and m ~2

sandstones a = .81, m=2

Humble formula

carbonates a = 1, m > 2


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Archie equation - complications

Archies equation assumes clean sand, with saline water.

In shaley sand, with fresh water, the simple Archie equation is not accurate:

There are many variations on Archie equation derived for differentenvironments. They all reduce to simple Archie in the case of clean sandwith various values of a, m & n.


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Water Saturation : n

n is saturation dependent infresh water, the error due tovariation on n decreases athigher saturations.

n measurements can be madeon core, but they are difficultand expensive.

n may also be saturationequation dependent.


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Water Saturation : Archie equation - variations

Nigeria EquationNigeria Equation

Indonesia EquationIndonesia Equation

WaxmanWaxman --Smits EquationSmits Equation

Dual Water EquationDual Water Equation ( )

+=

wwbwt

wbw

nwt

mt

t C C SS

C aS

C

n

w

w

m

e

cl

cl S aR R

V Rt

2

24.11

+=

2

2

211

w

w

e

cl

V

cl S R R

V

Rt

cl

+=

**

21F

S BQ

R F

S

R w v

w

w

t

+=

h


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The CCDThe CCD

modelmodel

( )

2 / 1

''

127.079.1'

3.17.01

'93.1)28.01(

+=

+

++=

v

v m

w

n w

v w

m v

m t

Q m

Q

C

S

Q m C Q C

Clavier, Coats, Dumanoir

h SGS


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The SGSThe SGS

modelmodel= Swn m w+ 1.93 m T QV 1+0.7 T Sw-

n / w+ 0 T

mQV

T = 1+0.0414 T -22

m= 1.62 +1.37 QV

1-

1/2

Sen, P.N.; Goode, P.A.; and Sibbit, A.M.: Electrical conduction in clay bearing sandstones at low and high salinities, Journal

of Applied Physics63 no.10 (15 May 1988), pp 4832-4840.

Sen, P.N.; Goode, P.A.:Influence of temperature on electrical conductivity in shaly sands, Geophysics57 no. 1 (January1992) pp 89-96.

Sen, P.N.; Goode, P.A.: Shaly sand conductivity at low and high salinities, presented at the 29th annual logging symposiumof the SPWLA (June 1988) paper F.


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For this course simple Archie is enoughFor this course simple Archie is enough

t

w

m

n w

R

R a S

=


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Resistivity of Resistivity of NaClNaCl SolutionsSolutions

0.16 Ohm-m

25C 120C

0.052 Ohm-m

Chart Gen-9


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Water Saturation : Rw

Rwdepends on the water salinity and the temperature.

Even if water salinity is know,temperature can be an issue.

Temperature sensors in the toolstring measure the mud temperatureor the temperature inside the tool(slightly warmer than the mudtemperature).Formation temperature is usuallyhigher than mud temperature.


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Formation temperature from gradientFormation temperature from gradientChart Gen-6

Formation temperature can beestimated from a knowntemperature gradient, andmay be more accurate than

mud temperature.


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Quick Look Quick Look D Log R D Log R


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Quick Look Quick Look D Log R D Log R


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Flow chart of Flow chart of PetrophysicalPetrophysical Analysis Analysis


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Interpretation M ethodInterpretation M ethod

Quick Look : D LOG R (DELTA LOG R)Quick Look : D LOG R (DELTA LOG R) Interpretation (Cross Plot Method)Interpretation (Cross Plot Method)

a.a. LithologicalLithological ModelModel-- Cross Plot NCross Plot N --DD-- Cross Plot NCross Plot N --SS-- Cross Plot SCross Plot S --DD-- Cross Plot MCross Plot M --NN

b.b. PetrophyisicalPetrophyisical ParameterParameter-- Picket Plot (a, m &Picket Plot (a, m & RwRw))-- HingleHingle Plot (Plot ( RwRw))-- Cross Plot RWACross Plot RWA --GR (GR (RclayRclay & water salinity)& water salinity)-- Cross Plot PHIECross Plot PHIE --RHOMAU (RHOMAU ( RhoHRhoH))

c. Permeabilityc. Permeability

K = (K = ( kcoef kcoef x PHIEx PHIE kexpkexp ) / (SWirr) / (SWirr 22 ) ,) , mDmD


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Cross Plot SCross Plot S -- DD

Cross Plot MCross Plot M -- NN


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Picket Plot (a, m &Picket Plot (a, m & RwRw))

HingleHingle Plot (Plot ( RwRw))


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Cross Plot RWACross Plot RWA --GRGR

Log Header


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Log Header

D LOG R (DELTA LOG R)D LOG R (DELTA LOG R)


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D LOG R (DELTA LOG R)D LOG R (DELTA LOG R)


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Composite LogComposite Log

SUMUR-X


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PETRANPETRAN

modul 7-saturation computation

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