June 4 13 Innovation in Water Saturation

June 4 13 Innovation in Water Saturation

6/10/2013
Schlumberger
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Horizontal Well Formation
Evaluation While Drilling,
A Case Study from Kuwait
Ahmed Elsherif, William Bryant
Contents
The Issue…
Resistivity measurements in Vertical & Horizontal wells
Shoulder Bed / Anisotropy & Polarization Effects
Petrophysical Evaluation using Sigma Σ
Time Lapse Sigma
Ultrasonic Caliper
Spectroscopy
Sourceless Density – vs – Standard Density
KOC Interpretation using Σ (By W. Bryant)
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Production from a Horizontal Well
The Main Issue
KOC has expressed a major concern regarding LWD
propagation resistivity measurements in horizontal wells.
Propagation Resistivity can be affected by:
Adjacent layer effect
Relative dip effect (anisotropy)
Polarization horn effect.
This ambiguity can affect:
The true water saturation (Sw) determination
Formation mobility for ICD design… very serious
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Resistivity in Horizontal Wells
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Introduction
Vertical wells
Horizontal wells
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Geometry Effects on Resistivity
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Polarization Horns
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Example of Resistivity Distortion
The
propagation
resistivity was
highly affected
by shoulder
bed and
polarization
horn effects
across several
intervals of the
well.
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Resistivity Response - vs - Deviation
Pilot Hole
Lateral Hole
64 Deg Dev.
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80 Deg Dev.
Courtesy of Mohamed Raffi, KOC
6/10/2013
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The Solution
A new technique was introduced to NK as a good alternative
measurement (SIGMA + Spectroscopy) to evaluate true
formation water saturation Sw in addition to standard
propagation resistivity
In addition, the tool can be run Source-less to avoid using
natural radioactive sources.
If a Gamma ray radioactive source is used for density
measurement, then density image will be available as well.
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Applications for Neutron Measurements
HI measurements (Porosity calculation)
Lithology Indicator (in conjunction with density)
Formation Sigma (Thermal neutron die-away) for water
saturation measurements (Independent of resistivity and
Archie m factor)
Lithology and clay determination (Capture gamma-ray
spectroscopy)
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Neutron Induced Gamma-Rays (Capture Σ)
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Interpretation of Σ Log
Oil
Water
Shale
Sandstone
True image of Formation Cube
containing Sandstone, Shale and
pores filled with water and Oil
Equivalent cube with the
various volumes made for
interpretation purpose
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Cased Hole Log Examples
3 Σ passes spaced 3 years apart.
Pass-2 shows a rise in the Oil / Water contact
Pass-3 shows water fingering on the top, and a further rise in the Oil/water contact
1
2
3
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Interpretation of Σ Log
Σlog
Response Equation
Σlog = Σw . φ . Sw
Water
+ Σo . φ. (1- Sw)
Oil
+ Σsh . Vsh
Shale
+ Σmatrix . (1 - φ - Vsh)
Matrix
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Saturation by Sigma – Avoids a, m, n and Rt!
Sw = n
Sw =
a Rw
.
Φm Rt
OIL-FILLED
MACROPORES
Measurementt Current is
“shorted” through the
conductive matrix
( ∑ bulk − ∑ grain ) + Φ * ( ∑ grain − ∑ HC )
WATER-FILLED
MICROPORES
Φ * ( ∑ water − ∑ HC )
Shales
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But, is Σ Good Enough to Get Accurate Sw…??
Σ has been used in the past for Sw calculations in
cased hole
The presence of casing and cement caused some
uncertainty, so most Petrophysicists will deal with Σ as
qualitative only
Open hole Σ measurement with Wireline tools was
highly affected by mud filtrate invasion
Open hole Σ with LWD does not suffer from invasion
since the formation is logged only few minutes (up to
one hour) after drilling.
It can also serve as base line Σ for future reservoir
monitoring
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Two Ways of Computing Saturation from Σ
Usual way (Sigma Response Equation)
But you need to
assume Σmatrix &
Σshale…
(∑log-∑matrix) - Ø *(∑Oil - ∑matrix) - Vsh*(∑shale-∑matrix)
Ø(∑water - ∑Oil)
From Spectroscopy Measurements
Sw =
(∑bulk − ∑grain) + Φ*(∑grain− ∑HC)
Φ*(∑water − ∑HC)
Here, Σgrain is
already measured
for you from
Spectroscopy, so
no need to guess..
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Apparent Sigma & Archie Sw vs True Sw
1.00
Sw = 90%, Fwsal = 160 kppm
Apparent Archie Sw
0.80
Sw = 80%
0.60
0.40
Sw = 40%
0.20
Sw = 20%
0.00
0.00
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20 kppm
50 kppm
100 kppm
150 kppm
200 kppm
230 kppm
100% Sw
80% Sw
60% Sw
40% Sw
20% Sw
Sw = 60%
0.20
0.40
0.60
0.80
1.00
Assumed insitu water
salinity is 230 kppm
for Sigma and Archie
Sw
Apparent Sigma Sw
Courtesy SPE
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Time Lapse Sigma
If we compare the drilling
pass Sigma with Pull out of
the hole (time lapse Σ),
then any decrease in
Sigma will be attributed to
water movement (Oil base
mud invasion).
This is a very powerful
technique to check for free
water in the reservoir,
hence ICD design.
Σ while drilling
Σ while POOH
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Time Lapse Σ in the Study Well
The Sigma time lapse showed no variation in Sigma values between
drilling pass and pulling out of the hole pass .
This Sigma can be used as a base log for future reservoir monitoring
activity (Sigma through casing)
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Another Example of Time Lapse Σ
Diesel replacing Oil
Diesel replacing water
Diesel replacing Oil
Diesel replacing Oil
Diesel replacing Oil
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Diesel replacing Oil
6/10/2013
Courtesy of Mohamed
Raffi, KOC
Neutron Induced Gamma-Rays, (Spectroscopy)
neutron
Thermal
Neutron
Formation
Element
Nucleus
Excited Nucleus
Excited
Nucleus
Stable
Nucleus
Kinetic Energy
γ
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Capture Gamma-Ray Spectroscopy
Formation nuclei emit capture gamma rays characteristic
of each element
12 Capture spectroscopy standards for EcoScope
Si, Ca, S, Fe, Ti, Gd, Tool background, H, Cl, Ba & Mg
Elemental concentrations are used for mineralogy and
matrix properties
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Gamma Ray Recorded Spectrum
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Elemental Standards for EcoScope
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Capture Gamma-Ray Spectroscopy
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Sandstone Spectroscopy Example
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GEO
2004
Carbonate Spectroscopy Example
Anhydrite
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Sulpher
GEO
2004
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Spectroscopy
Results of Study
Well
The GR was
reading high
values in areas
where Clay
content was very
low (hot Sand or
approaching
shale barrier
….???)
GR
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Vclay Vs. Vsh
MINEROLOGY
Vclay
Vsh
Spectroscopy analysis
measures Clay volume
directly.
This can be used into
permeability equation
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Courtesy of Mohamed Raffi, KOC
6/10/2013
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Ultrasonic Caliper, Time Lapse..
Reaming
Drilling
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Evolution of Density / Neutron Measurements
Neutron Porosity / Gamma Gamma Density
Sigma (thermal capture)
Lithology (spectroscopy)
Neutron Gamma Density
AmBe
CS
-22 Chemical Sources
(Retrievable)
CS
NO Chemical Sources
- 1 Chemical Source -NO
- 1 Minitron Source
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Pulsed Neutron Generator (PNG)
PNG, a switchable electronic source
1x108 Neutrons @ 14MeV
(only generated when control switch ON!)
Ion source
Controls
Control switch
HV supply
Main power
Off
Target
On
D-T Fusion:
2
1
H + 13 H → 24 He + 01 n
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PNG-Radiation -vs- Natural Source
A PNG fires around 1
x 108 neutrons/s @ 14MeV
An AmBe source fires 2 x 107 neutrons/s @ 4MeV
Never Fire the PNG on Surface
Slide 36
D&M Learning Centers
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How Bad is it to Loose a RA Source.. ?
Half life of radioactive source is
Cement
Plug
~ 400 years
Chemical powder encapsulated
in metallic cylinder
formation
water
RA
Source
Cylinder can be broken by the
attack of saline water
Become a serious HSE issue if
leaked into the reservoir
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Sourceless Density Measurement
Measurement Principle
Neutron
source
Neutron
source
Fast neutrons emitted from the
electrical source (PNG)
interact with formation nuclei,
emitting gamma rays and
creating a secondary gammaray source
Gamma rays arriving at longspaced detector exhibit
significant density sensitivity
Epithermal
neutron
detector
Neutron
detector
Secondary
γ Source
Gamma
ray
detector
Gamma ray
detector
Gamma
ray
detector
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Density Comparison…
TNPH
RHOB
RHON
source-less
Σ
GR
RHOB -vs- RHON
2.5
We have very good agreement
between Sourceless Density &
Standard Density.
Sourceless density can be used for
future wells with high confidence.
RHOB
2.4
2.3
2.2
2.1
2
2
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2.1
2.2
2.3
2.4
RHON (Source-less Density)
2.5
Σ
Water
Sigma Σ response was
also very good specially
in places where
resistivity was suffering
from noise.
Note resistivity horn
effect at the beginning
and end of the sand
body shown
Oil
Sourceless Density had
an excellent response as
shown.
Oil
Another Sourceless Exam.
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KOC Interpretation
By: William Bryant
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Offset Well
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Pilot Hole of the Study Well
Log Response Comparison
Horizontal
Pilot
Offset
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Offset Well
Used 2 equations to solve for RT
Rt = Vsh * Rsh + (1-Vsh) * Rt max
Rt - (Vsh * Rsh)
Rt max
=
(1 - Vsh)
Rt
=
1
Vsh
Rsh
+
(1 - Vsh)
Rt max
Drain Hole Interpretation
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Conclusion
Sigma (Σ) measurement has been proven to be
a good solution for resistivity ambiguity in horizontal
wells.
KOC has implemented Σ in their processing for Sw
determination from Σ.
Sourceless density has also been proven to be a
good solution to having natural sources while drilling,
this is also well received from the Drilling Department.
LWD
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