Laboratory%20MR%20Measurements%20and%20MRIL

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Laboratory MR Measurements and MRIL
Integration by Dave Marschall
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Crucial Formation Evaluation Questions

• What is the storage capacity (?e and ?t ) in a
  Complex Lithology Environment ?
• Are there hydrocarbons,
• what types of hydrocarbons and,
• how are they distributed?
• What is the permeability (deliverability)?
• Will the formation produce water free? (what is
  irreducible saturation (BVI))

MRIL answers them all
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Magnetic Dipole
NMR works with Protons - Hydrogen -gt H2O and
CxHy
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Random Orientation in Natural State
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Magnetization Buildup
Bo
BoExternal Field MBulk Net Magnetization
t 0.75 sec
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Buildup at 95 polarization
Bo
BoExternal Field MBulk Net Magnetization
t 6.0 sec
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Oilfield MRI(Relaxation Time Spectrum)
Fluids
Solids.invisible to MRI
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T1 build-up and T2 decay
T1 characterizes the rate at which longitudinal
magnetization builds up T2 characterizes the
rate at which transverse magnetization decays
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NMR Experiment Timing
Mo
T1 400 msec
M to Bo (longitudinal component)
0
TW
Mo
T2 250 msec
M to Bo (transverse component)
0
TE
TX
B1
RF field
0
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
time, seconds
adapted from Murphy, D.P., World Oil, April 1995
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MRIL-Prime is Fast
4X Fluid Volume 4X Speed
ã NUMAR Corp., 1995
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Measured signal decay
Amplitude Porosity
Amplitude (pu)
Decay rate (1 / T2) gt rock fluid information
time (ms)
TE
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3 Relaxation Mechanisms
Echo Amplitude vs Time
Effect of Each Mechanism is Additive
Bulk Relaxation - T2B Intrinsic Property of fluid
Amplitude
Diffusion - T2D Molecular Movement
Surface Relaxation - T2S Pore-walls cause rapid
dephasing
Time, msec.
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Pore Size and T2 (Water)
T2
time
T2
time
T2 relaxation time constant.
time
T2
S surface area of the pore.
T2
V volume of the pore.
time
?2 relaxation rate constant.
T2
time
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Data Processing - Inversion
T2i are pre-selected T2i 4, 8, 16, 32, 64,
128, 256, 512, 1024...
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MRIL Permeability

• MPERM ((MPHI/10)2 (MFFI/MBVI))2
• MPHI - MRIL Porosity (porosity units)
• MBVI - MRIL Bulk Volume Irreducible
• MFFI - MRIL Free Fluid Index
• MPERM - Permeability (millidarcies)

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Density Porosity
0
0
Neutron Porosity
0
8
0
-100
Effective Porosity
0
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Laboratory MRI - Textural Properties
Relaxation Time (T2), msec.
0.1
1
10
100
1000
10000
Relaxation Time (T2), msec.
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NMR - Porosity Model
Neutron ?
Density ?
Resistivity ?Sw
capillary bound water BVI
clay matrix
movable water
clay bound water
rock matrix
hydrocarbons
NMR BVI
NMR FFI
Integration of MR Log and Resistivity Log
Interpretation
MR porosity (effective)
MR porosity (total short TE)
Producible hydrocarbon
nonmovable water
will produce some water
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Suitable Sample Types

• Rock Sample
• Conventional Core
• Rotary Sidewall
• Cuttings
• Percussion Sidewall
• Fluid Samples
• Oils
• Gas/Condensate
• Brines

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Example Lab Program
Pre-clean and dry
Fresh State -OB mud
Sample Preparation Trim, clean, and dry
Sample Preparation Trim, measure bulk volume
Determine Routine Properties, K, Por., Grain
Density
MRI on Fresh sample
Dean Stark for Swi
Resaturate Sample to 100 Sw
Clean and dry the sample, measure routine
properties, K, Por., and Grain Density
Lab MRI _at_ 100 Sw
Desaturate the sample to a capillary
pressure that non movable saturation
Optional
Lab MRI _at_ Swi
Develop Interpretation Model
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Porosity ComparisonLab MRI (MPHI) vs Core
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Standard Method to Determine BVI
Bulk Volume Irreducible (BVI)
Free Fluid Index (FFI)
Relaxation time distribution
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Effect of Air/Brine Desaturation on T2
Distributions
Dominated by Surface Relaxation Mechanism
After air/brine 100 psi
100 Brine saturated
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Lab Determination of Cutoff T2
Cutoff T2
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Variation in T2 Cutoff Values
T2 - Cutoff
1
10
100
0
5
10
Sample Number
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20
25
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T2, Cutoff T2 and Pore Size
MRI Relaxation Time (T2) Surface to Volume Ratio
1/T2 ?2 S/V
Capillary Pressure (Pc) Pore Throat Radius (r)
Pc ??cos? 2/r
Since S/V of a capillary tube 2/r then
1/T2 ? ?2 2/r

• Since T2 is related to Pore Size S/V
• then T2 is directly proportional to K,
• and T2 is inversely proportional to Swi

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T2 Cutoff Related to Pc
Free Water Level
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Spectral BVI Model
SBVI Model a step function
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SBVI Model Linked to Permeability Equations
Given K1/2 100f 2 (FFI/BVI) K1/2 4f
2 T2GM
Equating the two equations gives
Substituting f (1-SWIRR) for FFI f SWIRR
for BVI
The empirical form is
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Lab Method to Determine SBVI

• Correlate Core Swi and T2

• Compute fraction for each
• T2 Bin

Bin T2 time BVI Fraction 1 2 0.919 2 4 0.849
3 8 0.738 4 16 0.585 5 32 0.414 6 64 0.261 7 1
28 0.150 8 256 0.081 9 512 0.042 10 1024 0.022
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BVI Model Comparison
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SBVI Determination for Cotton Valley
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NMR Adds Surface Area
Ability to Determine Swir

• Three Mechanisms Control Transverse Relaxation
  Time (T2)
• Bulk Relaxation
• Diffusion
• Surface Relaxation
• Surface Relaxation
• It is the dominating mechanism in porous media
  (for the wetting fluid - assumed to be water)
• Controlled by surface area and pore structure

where r2 relaxivity, m/sec. S/V surface
area to pore volume ratio
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Predicting K with NMR
The surface relaxation mechanism provides the
relationship of T2 to radius and K
From Kozeny estimates of kzSp are given by T2 as
follows
However, this model is representative of pores
with a single fluid.
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Predicting K with NMR

For the linear function y mxb where
Increasing C with increasing pore
structure complexity
(FFI/BVI)0.5
C 9.32 r2 0.91
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Predicting K with NMR
BVI bulk volume irreducible
FFI free fluid in dex
T2 and K are directly proportional
K and T2 are inversely proportional to Swir
0.1 1.0 10 100
1000 10000
Where C is similar to KZ in the Kozeny equation
and is a function of the pore geometry.
Relaxation Time (T2), msec
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Predicting K with NMR
Pores with two nonmiscible fluids

• For Two Fluids
• Geometric mean values are influenced by the
  nonwetting fluid.
• Model is not correct
• The wetting fluid is dominated by Surface
  Relaxation
• the wetting fluid has short T2 times, thus cutoff
  T2s can be used to estimate BVI

Non- wetting fluid
100 brine
air/brine
crude oil/brine
Geometric mean 100 brine
Geometric mean oil/brine
Relaxation Time Cutoff Determines Swir or BVI
0.1 1.0 10 100
1000 10000
Relaxation Time (T2), msec
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Lab Evaluation Permeability Model
Free Fluid (Coates) Model
C is a variable and can be represented as a line
function
The equation becomes
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Coates Model for a Tight Gas Sand
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T2Sb K Model Tight Gas Sand
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How Do the Models Work?
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Combining K, f and Swir
Predicting K
0.5
0.4
Where C 250 Also - Timur Equation
0.3
Porosity
(f x Swir) increases
0.2
0.1
K, md
0
0
0.2
0.4
0.6
0.8
1
Swir
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Predicting K using Swir
Predicting Swir from f
Known Swir
Predicted K, md
Measured K, md
Measured K, md
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X600
X500
0
6
GR
CALI
200
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0.2
0.2
0.2
LLD
LLS
MSFL
Cooper Basin Low Porosity Example
2000
2000
2000
0.01
0.01
0.01
PMRI
MPERM
PMRIC
1000
1000
1000
0
30
30
30
30
30
30
PDSS
PNSS
SBVI
MPHI
CBVI
CBVWE
BVID
10
0
0
0
0
0
0