evaluating remaining oil saturation in middle east carbonates · drainage and imbibition archie...

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Evaluating Remaining Oil Saturation in

Middle East Carbonates

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rivateRaghu Ramamoorthy

Petrophysics Domain Head

Schlumberger Wireline Middle East

Abu Dhabi, U.A.E.

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Outline

� Some definitions to lay the ground

– Implications of ROS and Sor– Conditions required for Sor

� Log measurements of ROS

– When is this Sor?

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� Log measurements for Sor– MicroPilot*

� Summary and Conclusions

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Remaining Oil Saturation

� I define ROS as Remaining Oil Saturation

– It is the fractional pore volume occupied by oil at any point in

the reservoir at any given time in the production of the asset

– The process by which this saturation is arrived at is not defined

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– The process by which this saturation is arrived at is not defined

– It is a snapshot of the reservoir in space and time

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Residual Oil Saturation

� I define Sor as Residual Oil Saturation

– It is the ultimate fractional pore volume of oil at the end of a

specified displacement process with a given fluid

– It is achieved after an infinite number of Pore Volumes of the

displacing fluid has passed through the given point in the

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displacing fluid has passed through the given point in the

reservoir

– It is specific to the displacing fluid and is denoted by Sorxwhere

‘x’ denotes the displacing fluid, eg. Sorw– It requires that the displacement reproduces the conditions

achievable in the far field in a typical reservoir flood

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ROS versus Sor

� ROS is simply a snapshot of the reservoir. It has no

petrophysical significance beyond an assessment of the

amount of oil remaining in the rock. There is no appreciation

of the process up to that point

– Remaining oil may include oil mobile to that process

S , on the other hand, is a very important Reservoir

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lic� Sor, on the other hand, is a very important Reservoir

Engineering quantity. It is an endpoint for relative

permeability in the simulator. It signifies the ultimate recovery

under a given displacement process. Very specific conditions

need to be ensured both during displacement and during

measurement

– Residual oil is immobile to that displacement process

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Residual Oil versus Remaining Oil Saturation

Sor Sor SorROS ROS ROS

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ratioviscosity

k

kf

w

o

rw

ro

o

ww =

⋅+

=µ

µ

µ

µ1

1

05.0=w

o

µ

µ5=

w

o

µ

µ500=

w

o

µ

µ

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Conditions for Sor

� Ultimate recovery: requires several tens of pore volumes of

displacing fluid to pass through

� Displacement velocities must be comparable to actual flood

– Ensure capillary numbers are comparable

Displacement direction should not reverse

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� Displacement direction should not reverseSPE 13213 Chatzis et.al

SPE 5050 Abrams et.al

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Outline





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So what do logs measure?

� Logs measure ROS (remaining oil saturation)

� Conditions in reservoir may render ROS = Sorw– Behind water flood front in light oil reservoir

– Invaded zone in a light oil reservoir

• No control on capillary number

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• Need to avoid use of surfactants in mud

– Log-inject-log methods


• Need to ensure sufficient injection is achieved

• MicroPilot* is a new downhole SCAL technique for Sor to a wide

range of displacing fluids

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Saturation Logs

� Resistivity-based Methods

– Open or Cased Hole

– Deep and Shallow Measurement

– Cross-well Resistivity Mapping

� Resistivity Independent Methods

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lic– NMR and Dielectric

• Open Hole only (fiber glass casing possible)

• Shallow Measurement only

– Pulsed Neutron Logs

• Open or Cased Hole, even while drilling

• Inelastic C/O Ratio and Thermal Neutron Capture (Sigma)


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Resistivity-based Saturation Monitoring: Saturation from Resistivity Logging

n

m

T

ww

a

R

RS

1

=

φ

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T

a, m, n: rock properties typically derived from core plugs in laboratories

φ: reservoir porosity from logs

Rw: formation water resistivity/salinity (?)

RT: true formation resistivity from resistivity logging

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Challenges in Carbonates

Presence of vugs affects Archie Cementation Exponent – m

– m varies between

• 1.7 for intergranular rocks (mudstones, wackestones,

packstones)

• Over 3 for vuggy rocks (grainstones)

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licMixed salinity due to water flood

– Formation water salinity ~ 250,000 ppm

– Injection water salinity 10,000 ppm – 80,000 ppm

Mixed-wet rocks have different Archie Saturation Exponent, n,

for drainage and imbibition

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Texture sensitivity of Cementation Exponent

Vuggy porosity in carbonates increases ‘m’

Acoustics can provide estimate of vuggy porosity

� Needs high porosity rock

Macro-porosity from P3A can be used as vuggy porosity

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Macro-porosity from P3A can be used as vuggy porosity

estimate

Cementation exponent can be determined from pore

partitioning

�Method of Nugent (empirical)

�Method of Brie (grounded in physics)

KSST 2012

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Variable ‘m’ from Pore Geometry

� The Bruggeman-Ramakrishnan effective medium model uses

all three pore partitions – micro, meso and macro

� Tortuosity is enhanced when one type of pore exists in a

background of another type

� Purely micritic rock or purely intergrannular rock have a low

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� Purely micritic rock or purely intergrannular rock have a low

‘m’ – approximately 1.7

� Mixing intragranular micro-porosity with intergranular meso-

porosity results in an increase in ‘m’

� Vugs or macro-porosity increases ‘m’ further

KSST 2012

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Challenges in Carbonates

Presence of vugs affects Archie Cementation Exponent – m

– m varies between

• 1.7 for intergranular rocks (mudstones, wackestones,

packstones)

• Over 3 for vuggy rocks (grainstones)

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licMixed salinity due to water flood

– Formation water salinity ~ 250,000 ppm

– Injection water salinity 10,000 ppm – 80,000 ppm

Mixed-wet rocks have different Archie Saturation Exponent, n,

for drainage and imbibition

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Resistivity RSM: Drainage vs Imbibition

Plug 107: Primary Drainage and Imbibition Pc Curves

20

40

60

80

100

imbibition

drainage

Oil Migration

100

1000

RI

Carbonate Reservoir Rcok

m=1.95 ♦♦♦♦ =2.78 g/cc k=1.22 md ♦♦♦♦=0.143

nimb=2.3232

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-100

-80

-60

-40

-20

0

0 0.2 0.4 0.6 0.8 1

Sw

Pc,

psi

Waterflood

1

10

0.01 0.1 1

Sw

RI

Drainage Dr_fit Imbibition Imb_fit

ndr=1.7654

SPE 92426 Ma et.al

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Resistivity RSM: Saturation from Resistivity Logging

ndr: drainage saturation exponent

Rw,dr: connate water resistivity/salinity

RT,dr: true virgin formation resistivity

drn

m

drT

drw

drw

a

R

RS

1

,

,

,

=

φ

Drainage: oil migration

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imbn

m

imbT

imbw

imbw

a

R

RS

1

,

,

,

=

φ

Imbibition: waterflooding

nimb: imbibition saturation exponent

Rw,imb: injected water resistivity/salinity

RT,imb: true flushed formation resistivity

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Cased-Hole RSM: Resistivity Time Lapse (W-A)

RDD_FAL.VOL_CALCITE_1

V/V CALCITE0 1

RDD_FAL.VOL_DOLOM_1

V/V DOLOMITE0 1

RDD_FAL.VOL_ANHYDR_1

V/V ANHYDRITE0 1

RDD_FAL.PHIT_1

V/V POROSITY1 0

7050

7100

DE

PT

H (

MD

)F

EE

T

RDD.GR_1

GAPI0 50

RDD.CALI_1

IN0 10

RDD_FAL.SWT_1

V/V WATER SAT1 0

RDD_FAL.SALT_1

PPK0 300

RDD.RHOB_1

G/CC1.95 2.95

RDD.NPHI_1

V/V0.45 -0.15

RDD.PEF_1

B/E-3 7

RDD.DRHO_1

G/CC-0.1 0.9

POST ARAB-D STRINGERBASE POST-D STRINGER

TOP ARAB-D ZONE 1

TOP ARAB-D ZONE 2

Water-Oil Contact

RDD.RXO_1

OHMM, 92 OH1 1000

RDD.ILM_3

OHMM, 92 OH1 1000

RDD_FAL.RT_2

OHMM, 92 OH1 1000

RDD_FAL.PHIT_1

V/V OIL0.5 0

RDD_FAL.VOL_UWAT_1

V/V WATER0.5 0

MODEL_DR.N_1

1 6

D050

D100

RDD_FAL.VOL_CALCITE_1

V/V CALCITE0 1

RDD_FAL.VOL_DOLOM_1

V/V DOLOMITE0 1

RDD_FAL.VOL_ANHYDR_1

V/V ANHYDRITE0 1

RDD_FAL.PHIT_1

V/V POROSITY1 0

7050

7100

DE

PT

H (

MD

)F

EE

T

RDD.GR_1

GAPI0 50

RDD.CALI_1

IN0 10

RDD_FAL.SWT_1

V/V WATER SAT1 0

RDD_FAL.SALT_1

PPK0 300

RDD.RHOB_1

G/CC1.95 2.95

RDD.NPHI_1

V/V0.45 -0.15

RDD.PEF_1

B/E-3 7

RDD.DRHO_1

G/CC-0.1 0.9

POST ARAB-D STRINGERBASE POST-D STRINGER

TOP ARAB-D ZONE 1

TOP ARAB-D ZONE 2

Water-Oil Contact

RDD.RXO_1

OHMM, 92 OH1 1000

RDD.ILM_3

OHMM, 92 OH1 1000

RDD_FAL.RT_2

OHMM, 92 OH1 1000

RDD_FAL.PHIT_1

V/V OIL0.5 0

RDD_FAL.VOL_UWAT_1

V/V WATER0.5 0

MODEL_DR.N_1

1 6

D050

D100

FLM_19920917.QW_PCT_1

WATER0 100

FLM_19920917.QT_PCT_1

OIL0 100FLM_19930417.QW_PCT_1

WATER0 100

FLM_19930417.QT_PCT_1

OIL0 100

POST ARAB-D STRINGER (7031)BASE POST-D STRINGER (7034)

TOP ARAB-D ZONE 1 (7043)


Water-Oil Contact

93 PLT92 PLT

FLM_19920917.QW_PCT_1

WATER0 100

FLM_19920917.QT_PCT_1

OIL0 100FLM_19930417.QW_PCT_1

WATER0 100

FLM_19930417.QT_PCT_1

OIL0 100




Water-Oil Contact

93 PLT92 PLT

FLM_19920917.QW_PCT_1

WATER0 100

FLM_19920917.QT_PCT_1

OIL0 100FLM_19930417.QW_PCT_1

WATER0 100

FLM_19930417.QT_PCT_1

OIL0 100




Water-Oil Contact

93 PLT92 PLT

Lithology VolumeResistivityPorosity

Drainag

e

WOC, S

wc


RDD.RT_1

V/V WATER0.2 2000

FALMD_SALTS.RT_B_1

KPPM0.2 2000

0.5

0.5

0.5

0

1

Massive

water flushing

Abnormal CHFR readingPOST ARAB-D STRINGER (7031)BASE POST-D STRINGER (7034)

RDD.RT_1

V/V WATER0.2 2000

FALMD_SALTS.RT_B_1

KPPM0.2 2000

0.5

0.5

0.5

0

1

Massive

water flushing

Abnormal CHFR reading

04-Rt

92-Rt

Drainage and Imbibition Archie Saturation1992

11 years

WOC, S

wc

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7150

7200

7250

7300

TOP ARAB-D ZONE 3

TOP ARAB-D ZONE 4

BASE ARAB-D RESERVOIR

D300

D150

D200

D250

7150

7200

7250

7300

TOP ARAB-D ZONE 3

TOP ARAB-D ZONE 4

BASE ARAB-D RESERVOIR

D300

D150

D200

D250



BASE ARAB-D RESERVOIR (7342)







Imbibition

Variable Archie parameter processing


Time-Lapse

ResistivityBASE ARAB-D RESERVOIR (7342)

Time-Lapse

Resistivity

SPE 92426 Ma et.al

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Saturation Logs






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Nuclear Magnetic Resonance

Total Porosity

Swirr

Pore Size Distribution

Derived Permeability

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Derived Permeability

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Nuclear Magnetic Resonance

Saturation Measurements Independent of

� Formation Water Resistivity

� Saturation Exponents (Archie’s)

0.00

0.50

1.00

1.50

2.00

0.1 1 10 100 1000 10000

T2 [msec]

Incre

menta

l P

oro

sity [

pu]

0

2

4

6

8

10

12

14

16

Cum

ula

tive P

oro

sity [

pu]

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(Archie’s)

Saturation Based on

� Differences in Fluid Properties

� Sensitivity to MnCl2

T2 [msec]

1 10 100 1000

TT2A 2A , , msecmsec..

OilOilWaterWater

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NMR ROS Determination

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Oil OilWater

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1 10 100 1000

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TT2A 2A , , msecmsec ..

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NMR Results Compared to Sponge Core

SPE 90339 Eyvazzadeh et. al

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Magnetic Resonance Fluid Characterization

0.1 1.0 10.0 100.0 1000.0 10000.0

Rock Bulk Volume

Rock

MatrixClay

Clay

bound

water

Total Porosity

Effective Porosity

Capillary bound

water

Free

waterHydrocarbons

Minerals

T2 cutoff

T2 Distribution

T2 Relaxation (msec)

Am

plit

ud

e

0.1 1.0 10.0 100.0 1000.0 10000.0

Rock Bulk Volume

Rock

MatrixClay

Clay

bound

water

Total Porosity

Effective Porosity

Capillary bound

water

Free

waterHydrocarbons

Minerals

T2 cutoff

T2 Distribution

T2 Relaxation (msec)

Am

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Oil Filtrate

Bound

Water

Oil Filtrate

Bound

Water

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ROS from Array Dielectric Measurement

� Uses dielectric permittivity for Archie independent saturation

– Weak dependence on water salinity

� Uses dielectric dispersion to estimate water space tortuosity

– Can be combined with NMR for an appreciation of wettability

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– Can be combined with NMR for an appreciation of wettability

effects

� Shallow measurement only

� Open hole measurement only

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ROS from Dielectric

� Dielectric tools are sensitive to the water filled porosity PHIWdielectric

� The remaining/residual oil volume is computed by difference to a total

porosity PHIT externally supplied:

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VOILremaining = PHIT - PHIWdielectric

� Residual saturation is obtained by comparison to PHIT

ROS = (PHIT – PHIWdielectric) / PHIT

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Benchmarking ROS

from NMR LIL to

Dielectric logs

ADT Run 1: before

doping

ADT Run 2: after

reaming and

doping

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doping

NMR LIL

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ROS – NMR LIL vs. Dielectric

NMR LILPro’s:

� Proven, accurate technique

� Practically no parameters

� Residual oil and total porosity measured simultaneously in the same volume of rock

Con’s:

� Additional costs:

Dielectric

Pro’s:

� No extra runs (rig time)

� No exotic chemicals in the mud

� Always get results

Con’s:

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� Additional costs:– 2 NMR logs (optional)

– Rig time for reaming and logging

– MnCl2 (cost, logistics, availability)

� Doping incomplete > 50% of the time and results inconclusive*

� The technique only works with light oils with narrow T2 distributions (… we still could kill all water signal, high MnCl2 concentration)

� Both PHIT and PWXO have to be

measured accurately

� Good knowledge of EPSI_MATR

required

� More certainty when salinity < 50 ppk

NaCl

* NMR LIL successful 2 times out of 7 in 2008-2010

SPE-149131 – D. Schmitt et al, 2011

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Very Good Repeatability of Dielectric Measurement

First runSecond run 2 days later, after doping the mud

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ROS measurement

Dielectric

Measurement

confirmed by core

analysis

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analysis

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Carbonate – Comparison with MRF station -1S

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Flushed Zone ROS from NMR and Array Dielectric

MRF

x

x

x

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SXO from ADT

SXO from MCFL

x

x

x

x

x

SXO from NMR

SPE 134841 Zielinski et.al

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Saturation Logs






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Carbon-Oxygen Tools

Concentric Detector Tool

� 1 11/16” Tool

� Spectral Calibration

� High Count Rate

1 11/16-in.RST Sonde

2 1/2 -in.RST Sonde

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� Not Shielded from Borehole

Eccentric Detector Tool

� 2 1/2” Tool

� Spectral Calibration

� Lower Count Rate

� Shielded from Borehole

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C/O – NMR – Core Comparisons

Slim

Flowing

Slim

Shut-In

Large

Flowing

Large

Shut-In

SPE 90339 Eyvazzadeh et. al

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Other benefits of C/O Logging

� Superior lithology through neutron spectroscopy

– Ca, Fe, Si, S, Ti, Gd from Capture Spectrum

– Inelastic Mg helps in calcite-dolomite quantification

� Apparent formation salinity through chlorine/hydrogen ratio

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� Apparent formation salinity through chlorine/hydrogen ratio

– Useful to determine effective Rw

– Well based salinity variations may be incorporated into Eclipse

simulations to history match field-wide salinity and saturation

variations

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Dielectric ROS compared to Sigma and C/O

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SPE-149131 – D. Schmitt et al, 2011

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Outline





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The MicroPilotTM Concept

The MicroPilot™ concept is an offering for the EOR projects for quick

screening of EOR processes by altering formation properties through the

controlled injection of EOR-agents while measuring the “recovery and/or

displacement behavior” in-situ.

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licInformation acquired is critical for comparative elimination:

� Fast tracking of EOR screening studies

� Evaluation of dynamic petrophysical properties

� Evaluation / optimization of EOR simulation parameters

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• Phase 1─ Log across the zone of interest (10 to 15 min)

� Fluids T2 distributions and Sw after invasion are inferred

� The So inferred that way is an estimate of the in-situ

ROS after invasion

• Phase 2─ Water injection with the CHDT module

Water based mud

Station Logs: Acquisition Sequence

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Mud filtrate

─ Water injection with the CHDT module

� Injection aims at simulating water-flood and achieving

ROS status

• Phase 3─ Log across the zone of interest after injection

� Fluids T2 distributions and Sw after injection are inferred

� The So inferred that way is an estimate of the in-situ

ROS after water-flood

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SPE 129069: FMI Images Clearly Show Injection

Point at X06.9m After InjectionBefore Injection

Scale represent close to a 1:1

vertical : horizontal perspective

We can see the actual de-

saturation and resultant oil bank

caused by the ASP injection.

Top of upper oil rim

Bottom of upper oil rim

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Bottom of upper oil rim

Injection Depth

Top of lower oil rim

Bottom of lower oil rim

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Results Summary

This plot shows a summary

of the results shown in the

previous slides.

NMR, MRF, and Dielectric

are all in agreement.

The NMR and Dielectric are

two very different techniques

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Sxo CMR Phi CMR Pwxo ADTSxo ADT

two very different techniques

physically. They are also of

two different vertical

resolution.

The comparison of the two

results are in very good

agreement, and also

supported visually by the

Electrical images.

SPE 129069 Arora et.al

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MicroPilot Modeling WorkflowModeling Step:

1: Grid calibration

2: Mud filtrate invasion

Method of validation:

Single phase

analytical solution

Post-invasion

NMR saturation

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3: Production pretests

4: ASP injection

NMR saturation

Measured pressure

Electrical image log

NMR saturation

Measured pressure

Pressure match, high CDC, Kh = 6.75D

Measured Pressure

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Step 4: ASP Injection Modeling

Post-injection oil saturation:

Vertical Horizontal Azimuthal S

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28cm 28cm

0 0.2 0.4 0.6 0.8 1

26cm

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Simulated salt concentration Electrical Image Log

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Unit: ppm

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0 0.2 0.4 0.6 0.8x06.0

x06.2

x06.4

Oil saturation vs. depth

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x06.6

x06.8

x07.0

x07.2

x07.4

x07.6

x06.0

MD

[m

]

Measured (NMR)

ECLIPSE

Vertical resolution

of NMR

measurement =

7.5”

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Outline


– Implications of ROS and SOR

– Conditions required for SOR


– When is this SOR?

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– When is this SOR?

� Log measurements for SOR

– MicroPilot*


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Concluding Remarks

� Sor and ROS represent very different concepts

– Terminology relating to the two has been proposed

� Logs measure ROS

– Conditions need to be carefully engineered to ensure

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– Conditions need to be carefully engineered to ensure

downhole measurement of Sor

� Several logging technologies can be used

– Resistivity, NMR, Dielectric, Pulsed Neutron Logs

� New logging service introduced for downhole Sor– MicroPilot*

evaluating remaining oil saturation in middle east carbonates · drainage and imbibition archie...

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