afes nmr seminar 25th april · afes nmr seminar 25th april snr geoscientist edmund smith grain-size...

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AFES NMR Seminar 25th April

Snr Geoscientist

Edmund Smith

Grain-size Determination From NMR T2 Data

Petrophysical Advisor

Geoff Page

Outline

• T2 is there a relationship to grain-size?

• Factors which hamper direct grain-size determination.

• Pore-scale Geometric Models

• Micro-structural Rock Modelling

- Correcting for partial saturation

- Accounting for varying surface relaxitivities

- Cementation

• Case Study; Sand Control

• Conclusions

2 © 2012 Baker Hughes Incorporated. All Rights Reserved.

Ech

o A

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litu

de

0 45 150 15 135 120 105 90 75 60 30

Time (ms)

25

20

15

10

5

1

2 T = r + S

V

+ 1

T 2D

1

T 2b

NMR Relaxation - T2 Decay Effects

3 components

Wetting Phase Relaxivity Non-wetting Phase Relaxivity

© 2011 Baker Hughes Incorporated. All Rights Reserved.

Ech

o A

mp

litu

de

0 45 150 15 135 120 105 90 75 60 30

Time (ms)

25

20

15

10

5

1

2 T = r + S

V + 1

T 2D

1

T 2b

100% Water Saturated

T2 and Grain-size

4

When water saturated,

the wetting phase

relaxivity dominates:

→ T2 is a function of

pore size and grain-

surface.

In unconsolidated

formations pore-size is

dominantly controlled

by grain-size, packing

and sorting.

Therefore in water saturated unconsolidated formations (once grain-surface

effects are taken into account and the affect of minor cementation)

→ NMR response may reflect grain-size


Fastest dominates

T2 and Grain-size

5

• Is there a relation between T2, pore size and grain size rgrain ?

– Yes, in case of the simplest model of perfectly sorted and

shaped uniform spheres with perfect packing:

graingrain

grain

matrix

matrix

rr

r

V

S 3

34

4

3

2

==

Cubic

48%

Rhombohedral

26%


1

2 T

= r + S

V +

1

T 2D

1

T 2b

=

=

131

grainmatrix

matrix

pore

pore

rV

S

V

S

2

1

TNMRr

13

grainr

Direct Pore and Grain-Size Determination from T2 ?

• Linear/simple relationship commonly does not exist.

© Baker Hughes Incorporated. All Rights Reserved. 6

Incremental Volume (%)

0

2

4

6

8

10

12

14

16

18

20

0.001 0.01 0.1 1 10

Grain size (mm)

Inc

rem

en

tal V

olu

me

(%

)

BSS-1-1 BSS-3-3 BSS-8

T2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0.1 1 10 100 1000 10000 100000

T2 (msec)A

mp

BSS-1-1 BSS-3-3 BSS-8

Grain Size of 3 cores T2 Distribution of 3 cores


??

Real World

7

• Complications raised due to:

o Non-uniform grain shape and

size

o Poor sorting

o Rough surfaces (e.g. due to

weathering, dissolution & other

diagenetic changes)

o Complex mineralogy affecting

surface properties

o Hydrocarbon saturation He porosity 29.80 pu XRD Data

Air perm 13263 md Quartz 47 %

Average grain radius 200 microns Feldspar 29 %

NMR porosity 31.05 pu Calcite 13 %

Illite 9 %

Anhydrite 2 %


Pore-scale Geometric Models

• Synthesise T2 based on

model cell S/V

• Adjust model grain sizes

and distribution to match

logged T2

→ NMR Grain size

© 2012 Baker Hughes Incorporated. All Rights Reserved. 8

Initially random, dense packing of equal spheres

Delaunay cell

Creating a numerical model and cross-section

Problems to Address

• Mixed fluids – Hydrocarbons

• Pore Geometry – Surface Roughness Factor

– Grain Sorting

• Mineralogy – Single vs. Multi-mineral Grains

– Distribution of multi-mineral grains

0

0.5

1

1.5

2

2.5

3

3.5

1E-1 1E+0 1E+1 1E+2 1E+3 1E+4

T2 (ms)

f

Sw = 1 Measured T2

(Water only)

Sw = 0.7

Sw = 0.4


10

T 2w,syn MSRM Simulation

NMR Post T 2w,meas

Sw MPHS

Processing

Mineralogy

Quartz

Feldspar

Calcite

Illite Smectite

Chlorite

Solution - Grain Size Determination via MSRM

SPE 128011

Micro

Structural

Rock

Modelling


Grain Size Distribution

Calibrate to core if available

Illustration of Sandstone MSRM

isopachous

Cement

A

B

pore-filling

cement: calcite

pore-filling clays:

illite, smectite, kaolinite

pore-lining clays:

chlorite


• Core NMR Measurements at 3 Sw States

• MSRM Uses Partial Sw NMR Data to Predict the Sw=1

State

• Consistent Grain-Size Distribution Obtained Using Any of

these Sw State Data

0

0.5

1

1.5

2

2.5

3

3.5

1E-1 1E+0 1E+1 1E+2 1E+3 1E+4

T2 (ms)

f

0

0.5

1

1.5

2

2.5

3

3.5

1E-1 1E+0 1E+1 1E+2 1E+3 1E+4

T2 (ms)

f

Sw = 1 Simulated T2

(Sw = 1)

Measured T2

Sw = 0.7

Sw = 0.4

Core Sample Studies: Partial Sw


10-1

100

101

102

103

104

0

0.2

0.4

0.6

0.8

1

Grain Diameter (micron)

f

Measured, Incre.

Measured, Cumu.

Calculated, Incre.

Calculated, Cumu.

Sw=0.7

10-1

100

101

102

103

104

0

0.2

0.4

0.6

0.8

1


f

Measured, Incre.

Measured, Cumu.

Calculated, Incre.

Calculated, Cumu.

Sw=0.7

10-1

100

101

102

103

104

0

0.2

0.4

0.6

0.8

1


f

Measured, Incre.

Measured, Cumu.

Calculated, Incre.

Calculated, Cumu.

Sw=0.41

10-1

100

101

102

103

104

0

0.2

0.4

0.6

0.8

1


f

Measured, Incre.

Measured, Cumu.

Calculated, Incre.

Calculated, Cumu.

Sw=0.41

Grain-size Determination Core vs NMR


Surface Relaxivity & Roughness

Data points are based on entries in Shell Rock Catalogue (1995)

•• ••• •• •

••••

•

••

••

•

••• •

•

• ••

•

•

••

Q F

C

Ternary w/symbols

•• ••• •• •

••••

•

••

••

•

••• •

•

• ••

•

•

••

Q F

C

Ternary w/symbols

Quartz Feldspar

Clay Relaxivity/Roughness

(um/s)


•• ••• •• •

••••

•

••

••

•

••• •

•

• ••

•

•

••

Q F

C

Ternary w/symbols

•• ••• •• •

••••

•

••

••

•

••• •

•

• ••

•

•

••

Q F

C

Ternary w/symbols

Accounting for Cementation

A

B

Porosity (p.u.)

36.9

8.7

9.3

12.5 +

1.4

5 p.u.

Overgrowth: 5%

(increase of radius)

Effective porosity

(dry clay)

CBW


Log Example

XX

40

XX

50

XX

40

XX

50

Clean unconsolidated

sandstone example


Lab GSD

Case Study: Application to Well Completion

• Sand control – Stand alone screens

– gravel packs

• Grain size (D90, D50)

Cased Hole Gravel Pack

Open Hole Gravel Pack

Screen

Gravel

Perforation

Screen

Gravel

Perforation

Screen

Gravel

Perforation

Stand Alone Screens

D90

D50

D (microns)

Cu

mu

lati

ve P

w (D

)


Grain Size for Sand Control


Conclusions

• NMR log, with the aid of MSRM, may provide grain size distribution

– Methodology and procedure are presented

– More logging data, such as mineralogy, saturation, can improve the robustness

• MSRM is a new log integration method addressing – Hydrocarbon effect on NMR prediction of grain sizes

– Lithology/mineralogy variation and diagenesis effects

• Log-based grain size distribution has advantage over core-based analysis

– Continuous grain size distributions capture the variations of grain size -- Important for varying lithology formation


Acknowledgments

• With thanks to Baker Hughes Staff (Past & Present):

– Mehmet Altunbay

– Songhua Chen

– Jiansheng Chen

– Guodong Jin

– Evgeny Tyurin

• Based in part upon SPE Paper:

– 128011

21 © 2012 Baker Hughes Incorporated. All Rights Reserved.

afes nmr seminar 25th april · afes nmr seminar 25th april snr geoscientist edmund smith grain-size...

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