RRT Technical Presentation

Dr Paul Basan, Director, RRT

NMR large, often complex topic in the detail

The overview is not so big or complex

Will focus on the fundamentals• The data (what it looks like)

• The applications

• The “tool box”

• Theory overview

WHAT ARCHIE SAID MORE THAN 60 YEARS

AGO

A tool that could measure pore sizeand fluid distribution continuouslywould provide significant answers forformation evaluation

Pore-size increasing

Area under the curve = Total Porosity

“Effective Porosity”

Forward model assumes system is water-wet and distribution = pore size.Assumes all water bound in small pores is immobile at a give Pc.

Total bound fluid

NMR petrophysical data is a waveform that has the magnitude of total porosity.We can partition the distribution into components parts that make up totalporosity.

Area under curve below cutoff =Clay-bound water ormicroporosity

3%

Area under curvebetween cutoff =Capillary bound water

5%

Area underthe curve> cutoff =Free fluid

15%

Remember, NMR is not just a numberlike 20% or 50mD and instead adistribution of the parts that comprisethe number. A distribution means wecan evaluate porosity and permeabilityby how fluid or pore size is distributedin a core plug or depth sample.

Core DataSet waveform distributionsfrom individual core plugs

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.1 1 10 100 1000 10000

Norm

alised

Poro

sit

y(P

U)

T2 Relaxation Time (ms)

Stacked Amplitudes from 15 samples

Log DataContinuous waveformsthroughout thesequence

Nearly 1000 ft Stacked Amplitudes

NMR is like other FE tools• Acquires information about rock and fluid properties• Differs in data acquisition from other tools Records fluid confined to pore space without influence of

matrix (i.e. Independent of matrix corrections) Non-Archie

About things you already know• Porosity• Permeability• Sw• Rock (pore) types

NMR part of the portfolio that completes the FE story• Validate conventional log interpretation Basic information should match

• Augment interpretation if questions arise Provides a means to interrogate differences

• Information an independent realisation of rock properties(reduce uncertainty)

The “Perfect” formation-evaluation technology:• No need for matrix corrections

• Applications for: Complex lithologies (e.g. volcaniclastics and mixed

carbonates)

Uncertain Rw/fresh water

Low-resistivity/low-contrast conditions

Shaly

Silty

Thin bedded

High Swirr

• Routine applications for: “Sourceless” porosity

Quick permeability estimations

Irreducible water saturation

Rock typing

NMR Core Analysers• Laboratory instrumentation

Three primary instruments on the market

Maran 2 Ultra (GeoSpec2)

Magritek

AMR Core Analyser

NMR Logging Tools

• Shallow DOI (1”-4”)

• 5 different wirelinetools + 1 indevelopment

• 3 different LWD tools

GeoSpecAMR R2

AMR R4 Research

Magritek

MR

Sca

nn

er

(MR

X)

MR

EX

MR

ILX

L

CMR PlusPad tool

Eccentred toolsMRIL PrimeCentralised tool

Method to observe static and dynamicbehaviour of nuclear magnetism

• Refers to nucleus and not radiation

Principles• Nuclei with odd atomic numbers have

magnetic moment

Examples: Na11, F9, H1

We use H1 for NMR petrophysics because:• Present in all reservoir fluids• Has a large magnetic moment (align and precess in

the direction of the magnetic field)• Required to record in a borehole environment

Diagram of NMR CPMG ExperimentT1 Build-up

Wait Time (TW)

95% polarisation=3 x max T1

Natural alignmentin earth’s magneticfield Aligned to tool

magnet andprecess in directionof magnetic field

T1 Build-upT2 Decay

Decay time (T2)

RF coil flips molecules;molecules precess (spin)in the 900 plane

B1

RF coil pulses to keepspinning molecules inphase

B1

Molecules eventuallylose phase andrealign to B0 field

All mechanisms commonlyparticipate to some degree,although one normallypredominates:

)..(

:

113

2

2

diametergeLength

factorScaling

Where

V

S

T

The simple equation is the key for understanding NMR because peaks have a unique position in the distribution dependingthe fluid and in turn the relaxation mechanism that characterises the fluid.

• Surface relaxation predominatesin water

• Pore size

• Bulk relaxation predominatesin oil

• Pore size and oil

• Diffusion predominates ingas

• Pore size and gas

T2 surface =pore-size dependentT2 bulk =fluid dependentT2diffusion =fluid and measurement dependent

DiffusionSurfaceBulkTTTT 2222

1111

Bulk Response

DiffusionResponse

SurfaceResponse

f

End Product

Fastest timeClay-boundwater

~3+ms ~33ms

Sandstone Distribution

Sh

ort

time

Pc

-bo

un

dw

ate

r

Slowest timeFree fluid

T2 Relaxation Time (ms)

Fastest timeMicroporosity

~3+ms~100+ms

Carbonate Distribution

Sh

ort

time

Pc

-bo

un

dw

ate

r

Slowest timeFree fluid

Raw Data

Processed Data

Filtered Data

Distribution of noise

Continuous butvariable T2distribution inwater leg=water-filled poresNMR por=Denspor

Increasedamplitude atlong T2’s=lightoilNMR por=denspor

Upper peak shifts toshorter T2’s with lossof amplitude=gasNMR por<Dens PorIncreased X-over onD/N

Notice how the predominantrelaxation mechanism alters thedistribution shape and position

D

T1

Gas

Water

Limitations• Shallow DOI (flushed zone)• Native fluids diluted• Low SNR• Moving tool, etc., etc.

Courtesy of Schlumberger

NMR creates a magnetic field either inside (lab)or outside (field) a volume of rock• CPMG experiment measures the volume and

distribution of fluid residing within a pore system• Processing produces a spectrum that reflects pore

size and/or the distribution of a fluid confined withinthe system Partitioning the spectrum shows the component parts of the

pore system

NMR an independent realisation of porosity andhow it is distributed (not just a value)• Requires no matrix correction• Validates rock properties from other sources• Provides resource for evaluating differences• Provides a resource for obtaining continuous

distribution of rock (pore) types

Visit:http://www.esandaengineering.com/Esanda-training-courses/course-schedule.html

and find out about the London NMR Petrophysics course scheduled for 9th to 13th May 2016.

Visit:http://www.esandaengineering.com/Esanda-training-courses/course-schedule.html

and find out about the London NMR Petrophysics course scheduled for 9th to 13th May 2016.