tech reservoir tamu fluidsat

8/16/2019 Tech Reservoir Tamu FluidSat

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Fluid Saturations

Introduction



Fluid Saturations

• Definition - The fluid saturation for a particular fluid is the

fraction of pore volume occupied by that fluid

– Saturation is an intensive property

– Equation Form: So!o"! p# S$!$"! p# S%!%"! p

• These fluid volumes are measured under specific conditions of pressure and

temperature &e'%' reservoir# or laboratory(

– reservoir conditions are often noted as )in situ*



Fluid Saturations

• Fundamental +elationships

– ,ore volume is occupied by fluids &$ater# oil# and"or %as(

• for the t$o phase case# only one of the t$o saturations is independent# the other

must mae the sum of the saturations equal to unity &.(

• similarly# for the three phase case# only t$o saturations are independent

%o$

p

%o$

%o$ p

SSS!

!!!

.

!!!!

++=

++

=

++=



Fluid Saturations

• Fundamental +elationships &continued(

– /ass of fluids in the pore volume is comprised of: $ater# oil#

and"or %as

• at laboratory conditions it is often assumed that %as density is ne%li%ible

[ ]%%oo$$ p

%%oo$$

%o$

S0S0S0!!0!0!0

mmmmassfluid

++=

++=

++=



Initial Fluid Saturations in +eservoir

• 1oncepts: typical petroleum accumulation scenario

– pores are initially saturated $ith $ater &S$.(

– hydrocarbons mi%rate up dip into traps due to havin% density less than $ater density

&%ravity force(

– hydrocarbons &oil and"or %as( is distributed such that %ravity and capillary forces are

in equilibrium

• minimum interstitial $ater saturation remains in hydrocarbon 2one# even after accumulation occurs

– $ater $et# draina%e accumulation process

3 irreducible $ettin% phase saturation

– oil $et# imbibition accumulation process

3 residual non-$ettin% phase saturation



Initial Fluid Saturations in +eservoir

• /ethods for determination of reservoir fluid saturations

– Direct /easurement

• 1ore 4nalysis &current topic(

– Indirect /easurement

• 1apillary ,ressure /easurement &previous topic(

• 5ell 6o% 4nalysis &future topic(

– electrical conductivity depends primarily on $ater saturation



Fluid Saturations - 1ore 4nalysis

• Factors affectin% fluid saturations in cores

– flushin% of core by filtrate from drillin% fluids &especially for overbalanced drillin%(

• $ater filtrate

– $ater based mud

– oil emulsion mud

• oil filtrate – oil based mud

– inverted oil emulsion mud

• %as filtrate

– air drillin%

– foam drillin%




• Factors affectin% fluid saturations in cores &continued(

– 1han%es in pressure and temperature as core sample is

brou%ht from bottomhole conditions to surface conditions

– E7ample: 8il 2one at minimum interstitial $ater saturation#

$ater based drillin% mud

FlushingDuringDrilling

Trip toSurface

Saturation at SurfaceCompared to Reservoir

Sw

? probably

So

Sg -




• Factors affectin% fluid saturations in cores &continued(

– E7ample: 8il 2one at minimum interstitial $ater saturation# oil based drillin% mud

– Self Study: other e7amples in 6ecture9.'pdf

FlushingDuring

Drilling

Trip to

Surface

Saturation at SurfaceCompared to

Reservoir

Sw - - -

So -

Sg -



4pplication of 1ore Saturations

• 4pplication of 1ore Saturations: 5ater ;ased /ud

– presence of oil 2one – ori%inal oil"%as contact

– ori%inal oil"$ater contact

• 4pplication of 1ore Saturations: 8il ;ased /ud

– fairly accurate minimum interstitial $ater saturation – ori%inal oil"$ater contact

• 8ther 4pplications of 1ore Saturations

– correlation of indirect methods



Estimatin% Fluid 1ontact Depths

from 1ore SaturationsSo

Gas

ater

!il

"##

Depth

So ≈ 0 in gas zone

So > ≈0.15 in oil production

zone

0 < So < ≈0.15 in water

production zone



/a7imum 5ater Saturation

for 8il and <as ,roduction

The trend shown here

continues for even lower

permeability with productive

reservoirs e!isting with

Sw>0."0 for #<0.01 md



1ommentary on 1ore Saturations

• =ualitative !alue# 4;5 &pa%e .>?# bracets added(: )The

saturation values obtained directly from roc samples @coresA are usually notreliable for determinin% the quantity of each fluid in the roc @reservoirsA'

8ther uses e7ist for fluid-saturation determinations from core samples'*

•8verall !alue# 4;5 &pa%e ..>(:

)Thus# in summary# it is seen that

althou%h fluid-saturation determinations made on core samples at the surface

may not %ive a direct indication of the saturations $ithin the reservoir# they

are of value and do yield very useful and necessary information*

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