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.