nmr a refresher nfes stravanger 2013 · obmf or gas. proportion of signal on t2 ‘moves’ to left...

Nuclear Magnetic Resonance

A Refresher !

NFES Monthly Meeting

9/01/13

By

Edmund Smith

Baker NMR GeoScience Contacts:edmund.smith@bakerhughes.com (Aberdeen, UK)roman.mirzwinski@bakerhughes.com (Tananger, Norway)

Outline

• Introduction

• Field Print(s): a starting point

• NMR Porosity & Permeability

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• Controls on ‘relaxation’

• Differing spectra & interpretation

• 2D NMR:• Fluid typing for gas• Fluid typing for oil

NMR Field Prints

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Standard NMR Print – A revision

A fundemental ‘corner-stone’ ofNMR is the:

• Relaxation spectrum• The area underneath the

spectrum indicates porosity.• The position of the peaks from

left to right indicates the timetaken for that porosity to ‘relax’.

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taken for that porosity to ‘relax’.• Generally the spectrum has been

optimised for porositydetermination.

There are other types of spectra –check what type you are viewing

Spectra can be generated from subsetsof the recorded NMR data.

Spectra interpretation varies betweenlow-gradient and high-gradient tools

Standard MREX Field Print (PoroPorm + )

• CBW, BVI, BVM, fe, ft and kNMR

• Bound water field print will NOT show;BVM, fe, ft and kNMR

• Porosity distribution based on chosencutoffs such as:

CBW 3 ms and BVI/BVM 33 ms

• kNMR based on Coates equation with

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• kNMR based on Coates equation withchosen c, m and n

(use as a relative permeability indicator)

• Underestimation of BVM, fe, ft

and kNMR in oil/gas zones if HI effect issignificant

- to account for HI by phase we need toanalyze the NMR data for fluid contentvia 2D-NMR techniques.

CBW, BVI, BVM, fe, ft, and kNMR

Porosity distribution based on

chosen cutoffs such as:

CBW 3 ms and BVI 33 ms

kNMR based on Coates equation

with chosen C, m, and n

Underestimation of BVM, f , f

PoroPerm + Gas Field DeliverablePoroPerm + Gas Field Deliverable

Underestimation of BVM, fe, ft

and kNMR in gas zones if HI effect is

significant

T2 spectra for long and short TW

and the differential spectrum– Highlights intervals with gas in the

flushed zone due to insufficientpolarization of gas with short TW

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NMR Porosity & Permeability Models

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Conductive Fluids

dryclay-

mobilecapillary

Magnetic Resonance Porosity ModelMagnetic Resonance Porosity Model

BVMBVI

feffective

ftotal

matrixdryclay

clay-boundwater

mobilewater

capillaryboundwater

hydrocarbon

CBWBVM – Bulk Volume MovableBVI – Bulk Volume IrreducibleCBW – Clay Bound Water Volume

MR Permeability - kNMR

Two models in use

CoatesCoates--Timur Model :Timur Model :

nf mNMR

BVIBVM

CkNMR =

SDR Model:

Where assumed default parameters are: C =10, m = 4 & n = 2

Note: kNMR is an estimate of permeability based on a model.For accuracy kNMR should be calibrated to local reservoirdata.

SDR Model:

a nCkNMR T2 Geo. Mean= NMRf

m

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T2 Cutoff = 80 ms kk ==1.731.73

BVIBVI

BVMBVM44

10.9110.91

NMRNMR

ff

Core Calibrated MR Analysis ResultsCross-Well Prediction – Well B

Calibrated UncalibratedPermeability

Core-Calibrated Un-Calibrated

GammaRay

T2

Spectra

Calibrated UncalibratedPorosity

BVI Core-Calibrated Un-Cal’

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NMR Controls on relaxation

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MR Relaxation

• 2 types of MR relaxation

–T1 relaxation – longitudinal relaxation

•Time constant for the net magnetization toalign with the static magnetic field

–T2 relaxation – transverse relaxation- T2 decayrate

•Time constant for the echo train to decay

• T1 & T2 contain information on pore sizes and fluidproperties

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Ech

oA

mplit

ude

25

20

Wetting Phase Relaxivity Non-wetting Phase Relaxivity

1

T= r +S

V+ 1

T1

T

Controls on Relaxation - T2 DecayControls on Relaxation - T2 Decay

Ech

oA

mplit

ude

0 45 15015 13512010590756030

Time (ms)

15

10

5

2,appT= +

V+

T2DT2b

Kenyon, 1992, Klienberg etal 1994, & Coates et al1999 (and referencestherein)

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Controls on Relaxation - T2 Decay

1

2,appT= r +S

V+ 1

T2D

1T2b

TT2,D2,D –– This is called the ‘diffusion’This is called the ‘diffusion’ TT22,,and occurs in the presence of aand occurs in the presence of amagnetic gradient.magnetic gradient. This is a propertyThis is a propertyof the free fluid thatof the free fluid that maymay bebemanipulated by the MR acquisitionmanipulated by the MR acquisitionsequence.sequence.DiffusionDiffusion –– the ability of the moleculethe ability of the moleculeto move.to move.

TT2,app2,app = T= T2,log2,log –– This is the TThis is the T22 that is measured bythat is measured bythe logging tool. Historically is was referred to asthe logging tool. Historically is was referred to assimply Tsimply T22. With the latest generation of MR tools. With the latest generation of MR toolsit is good practice to the subscript ‘app’ or ‘log’ forit is good practice to the subscript ‘app’ or ‘log’ forclarity.clarity.

TT2,b2,b = T= T2,bulk2,bulk = T= T2,int2,int –– This is called the ‘bulk’ orThis is called the ‘bulk’ or‘intrinsic’ T‘intrinsic’ T22. This is. This is an inherentan inherent property of the freeproperty of the freefluid and it is used to identify and quantify the fluidfluid and it is used to identify and quantify the fluidtype and volume.type and volume.

to move.to move.

SurfaceSurface relaxivityrelaxivity; a; afunction of porefunction of pore--size andsize andgrain surface.grain surface.

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Controls on Relaxation - Gradient

2,appT= r +S

V+ 1

2D

1T

1

2b T

T2 apparent is recorded bygradient NMR tools e.g. MReX tool.

It is NOT recorded by the gradient-less tools e.g. MagTrak, which doesnot employ a gradient. Thus cannotdetermine T2D.

2,intT= r +S

V+ 1

2D

1T

1

2b T

Low gradient/No gradient tools e.g.

MagTrak measures T2 intrinsic.

MReX also measures T2,int and canmanipulate the magnetic gradient todetermine properties of the fluids.

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NMR Properties of Typical Reservoir Fluids

Fluid T1 (ms) T2,a (ms)*

Typical

T1/T2,a Viscosity (cp)

D ∙ 10-9

(m2/s)

Brine 1 – 2,000 1 – 500 2 0.2 – 0.8 1.8 – 7

Oil 1 – 3,000 1 – 2,000 2 0.2 – 1000 0.0015 – 7.6

Gas 3,000 – 4,000 30 – 500 16 0.011 – 0.014 80 - 100

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* Gradient tool

NMR Differing Spectra

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Differing Spectra Types T1 and T2

2 32 512ms 2 32 512ms

Two types of spectra arecommonly displayed:

T1 – spectrumT2 – spectrum

(of which there are severaltypes)

Other spectra:

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Other spectra:T2 TWST2 TWLDifferential spectraDiffusion spectra

Comparing spectra canprovide valuableinformation: for instance theexample opposite indicatesthe presence of gas.

T2 Spectra: Gradient control ~ which type isyours?

High Gradient Low Gradient

3

4

Pa

rtia

lPo

rosi

ty

T2 cutoffs

3

4

Pa

rtia

lPo

rosi

ty

T2 cutoffs

Diffusion Effect No Diffusion Effect

0

1

2

0.1

Pa

rtia

lPo

rosi

ty

1 10 100 1000

T2 (ms)

0

1

2

0.1

Pa

rtia

lPo

rosi

ty

1 10 100 1000

T2 (ms)

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Note the diffusion effect is greatest for gas, but can also occur to a lesserextent in light oil and rarer water.

TWShort TWLong

NM

RP

oro

sity

Po

rosity

Po

rosi

ty

Long Recovery Time (TWLONG)

Short Recovery Time (TWSHORT)

Differing Spectra: Differential SpectrumDiffering Spectra: Differential Spectrum

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TW (sec)1.5

T1 Buildup

NM

RP

oro

sity

8

T2 Time (ms)1 10 100 1,000 10,000

Po

rosi

tyP

oro

sity Differential Spectrum

Water Gas Oil

CBW, BVI, BVM, fe, ft, and kNMR

Porosity distribution based on

chosen cutoffs such as:

CBW 3 ms and BVI 33 ms

kNMR based on Coates equation

with chosen C, m, and n

Underestimation of BVM, f , f

Gas IdentificationGas Identification

Underestimation of BVM, fe, ft

and kNMR in gas zones if HI effect is

significant

T2 spectra for long and short TW

and the differential spectrum– Highlights intervals with gas in the

flushed zone due to insufficientpolarization of gas with short TW

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Answers?

Gas Identification: T1 and T2 comparison2 32 512ms 2 32 512ms

1) Is the reservoir gasbearing & why?

2) If so does the gas occurthroughout?

3) Is there moveable water?4) Compare the MReX

porosities versus thedensity measurement,what do you observe,why may this occur?

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2 32 512ms 2 32 512msT1 and T2 spectra comparison

On T1 spectrum slowrelaxing componentscould represent Oil,OBMF or Gas.

Proportion of signal onT2 ‘moves’ to left andoccupies 30 – 500msportion of spectrumcompared to T1,therefore Gas.Gas T1 >> T2

‘Short’ T1 signal notcharacteristic of thegas or oil so faridentified. In theabsence of any heavyoil phases; probable

Reservoir has limitedclay bound water

Reservoir hascommon irreduciblefluids

Correspondingreduction of late T2

signal

Limited change (T1 =T2)No Gas in lowersandstone.

oil phases; probablemoveable water.Signal decreases inabundance upwards.

T1 and T2 spectra areNOT Hydrogen Indexcorrected. Thus in thepresence of lighthydrocarbondepending on thereservoir temperatureand pressure, NMRporosities will‘undercall’density/neutronmeasurements

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Example of a T2 spectrum: Quiz

What can youidentify?

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Oil identification - Simple Analysis of MagTrakT2

Oil identification - Simple Analysis of MagTrakT2

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Simple Analysis of MagTrak T2Simple Analysis of MagTrak T2

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Fluid Identification: T2 Analysis Challenges

Bound HBound H22OO

Free HFree H22OO

GasGas

OilOil

Po

rosit

y

Gas

Gas position controlledby diffusion effect

100 10000 T2 (ms)

Po

rosit

y

1 100010

Viscous Oil

Po

rosit

y

Light Oil

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2D NMR

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2D NMR Fluid Identification: D -T2 & R-T2

R-T2

Used for Gas

2,a

pp

16

Clay bound water

Irreducible water

Moveable water

2,a

pp

16

Clay bound water

Irreducible water

Moveable water

2,a

pp

16

Clay bound water

Irreducible water

Moveable water

Clay bound water

Irreducible water

Moveable water

D-T2

Used for Oil & Gas

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2 8 32 128 512

T2,app (ms)

T1/T

2,a

pp

4

1

Moveable water

Light oil/OBM filtrate

Viscous oil

Gas

2 8 32 128 512

T2,app (ms)

T1/T

2,a

pp

4

1

Moveable water

Light oil/OBM filtrate

Viscous oil

Gas

2 8 32 128 512

T2,app (ms)

T1/T

2,a

pp

4

1

Moveable water

Light oil/OBM filtrate

Viscous oil

Gas

Moveable water

Light oil/OBM filtrate

Viscous oil

Gas

2D R-T2 NMR Video

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2D NMR Fluid Identification: D -T2 & R-T2

R-T2

Used for Gas

2,a

pp

16

Clay bound water

Irreducible water

Moveable water

2,a

pp

16

Clay bound water

Irreducible water

Moveable water

2,a

pp

16

Clay bound water

Irreducible water

Moveable water

Clay bound water

Irreducible water

Moveable water

D-T2

Used for Oil & Gas

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2 8 32 128 512

T2,app (ms)

T1/T

2,a

pp

4

1

Moveable water

Light oil/OBM filtrate

Viscous oil

Gas

2 8 32 128 512

T2,app (ms)

T1/T

2,a

pp

4

1

Moveable water

Light oil/OBM filtrate

Viscous oil

Gas

2 8 32 128 512

T2,app (ms)

T1/T

2,a

pp

4

1

Moveable water

Light oil/OBM filtrate

Viscous oil

Gas

Moveable water

Light oil/OBM filtrate

Viscous oil

Gas

D-T2 animation

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Example illustratingMREX 2NMR techniquesacross OWC in alaminated reservoir

- Saturationdeterminations were

OILOIL ?

Oil Reservoir &WBM

determinations weremade using 2DNMRtechniques

- Water based mud filtrateinvasion is responsible formoveable water shown inupper (oil) section

OIL

H2O

OIL

H2O

H2O

H2O

OIL?

OIL?

???

H2O

H2O

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Summary

• NMR can provide multiple spectra types.

• Differing Spectra provide differing and usefulinformation.

• Understand how the spectra was acquired,before starting to interpret them.before starting to interpret them.

• Confirmation of visual interpretation of thespectra by 2D NMR fluid typing or other sourcesof information.

• Permeability is calculated not measured.

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