log interpretation in non-hydrocarbon environments - methods and applications -.pdf
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8/10/2019 Log Interpretation in Non-Hydrocarbon Environments - Methods and Applications -.pdf
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ICDP International Continental Drilling Program
Log Interpretation in
Non-Hydrocarbon Environments
- Methods and Applications -
Dr. Renate Pechnig
Aachen University of Technology
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Log data for lithology prediction
Enhanced interpetration for lithology reconstruction is
required if:
information on lithology is available only from cuttings
e.g . KTB main ho le
core recovery is very low and cuttings are not available
e.g. ODP hole in oceanic crust (504B)
core recovery is high, but information on petrophysical
characteristics of the drilled rocks are also required
e.g HSDP2, Hawaii
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KTB
Examples from the KTB boreholes
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Overview KTB boreholes
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Motivation for KTB
The KTB main hole has reached a depth of 9101 m.
Drilling strategy was targeted to avoid expensive coring.
The total core available from the main hole is only about
85 m.In contrast, the KTB pilot hole was completely cored down to
4000 m.
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Target
Transfer of log data into lithological information
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Strategy
Calibration of log responses in the fully
cored 4 km deep KTB pilot hole
Transfer of knowledge to the more than
9 km deep main hole and
predict lithology from logging data.
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Data Compilation and Calibration
Selection of calibration
intervals
Compilation of all
available core, cuttings
and log data
Comparing of core and
log data and
classification ofelectrofacies
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Identification of Electrofacies
1) Manual identification by examining the shape
of the various log curves and by relating log
boundaires to core stratigraphy.
2) Cross-plot techniques to identify and separate
the different rock types by their log responses.
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Grouping of electrofacies in the pilot hole
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Training and transfer to uncored sections
Learn stage:
Storing the specific
information of each
electrofacies into a
multidimensional data baseby using e.g. neural
networks, discriminance
analysis.
Transfer of the
electrofacies data base to
uncored sections –>
level by level lithology
prediction.
Result:
a synthetic lithological
profile, theEFA LOG
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Example KTB – Paragneisses pilot hole
EFA-Log versus core profile of a paragneiss section in a calibration section inthe pilot hole. Core recovery in this depth section is almost 100%.
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Example KTB – Metabasites pilot hole
EFA-Log versus core profile of a metabasites section in the pilot hole.Core recovery in this depth section is almost 100%.
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Example KTB – Metabasites main hole
EFA - Log constructed from logs in the main hole compared to the cuttings
profile. Resolution of the log derived profile is much higher!
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ODP
Examples from ODP Hole 504B
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American Plate
504B896A
Mid- AtlanicRidge
CostaRica
Rift
Nazca Plate
CocosPlate
PacificPlate
Drilling Location of Holes 504B and 896A
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Motivation in ODP Hole 504B
Need for lithology reconstruction in ODP Hole 504B
504B is the deepest hole drilled in oceanic crust
core recovery is extremely low < 20 %
lithostratigraphic information from core is not complete
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Simplified log responses of pillows and lavaflows
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504B 896A
10 100
electrical resistivity
(Ω
m)
10 100
electrical resistivity
(Ω
m)
0
5
10
t o t a l
g a m m a r a y ( A P I )
massive units
thin flowspillow basalts
0
5
10
t o t a l
g a m m a r a y ( A P I )
Cross plots: resistivity versus gamma ray
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Cross plots: resistivity versus velocity
504B 896A
10 100
electrical resistivity
(Ω
m)
10 100
electrical resistivity
(Ω
m)
2
3
4
5
6
7
V P ( k m / s )
massive units
thin flowspillow basalts
2
3
4
5
6
7
V P ( k m / s )
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high electrical resistivity
high velocitylow gamma ray
slightly alteredslightly fractured
low electrical resistivitieslow velocity
high gamma ray
highly altered
strongly fractured
intermediate resistivitiesintermediate velocityintermediate gamma ray
intermediate alterationintermediate fracturing
massive units
thin flows
pillow basalts
Results of cross plot analysis
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Lithology Reconstruction
300310320330340350 d e p t ( b s )
c o e e c o e yLitho-str atigr aphy(Adamson1985)c alibr atio ndiscr iminantanalysisE FA-LogNPHI(%)LLD(ohmm)VP(km /s)R HOB(g /cm)302 04060
110100 2.03.0
246<1m
pr obablynotcor edpr obablynotcor edLegend:
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250
300
350
400
450
500
500
550
600
650
700
750
Core Core
EFA-Log EFA-Log
C o r e r e c
o v e r y
C o r e r e c
o v e r y
D e p t h ( m b s f )
D e p t h ( m b s f )
LLD
( m)Ω
1 500
LLD
( m)Ω
1 500
massive units
dikes (core only)
thin flows
pillow basalt
EFA-LOG of Hole 504B
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ICDP
Examples from HSDP2, Hawaii
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AaPahoehoe
Pillow
Massive
Transitional
Hyaloclastite
Legend
0
500
1000
1500
2000
2500
3000
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
Depth
(mbsl)
Core
Recovery[%]
Depth
(ftbsl)
Core
Lithology
L
O
G
G
I
N
G
I
N
T
ER
V
A
L
Final depth: 3110 mbsf
Core recovery: 95%
Lithology of HSDP2
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Bitsize
T E M
P
C a l i p e r
I n c l i n a t i o n
D T S
S o
n i c
R e
s i s t i v i t y
M a g n
e t o m e t e r
γ
S p e c t r u m
G R
B H
T V
412 ft/126 m
1981 ft/604 m
6007 ft/1831 m
8930 ft/2723 m
HSDP 2 Logging Sections
performed byUSGS GFZ Uni Göt-Uni Hawaii Potsdam tingen
1st Run:
July 1999
2nd Run:
December 1999
Logging Program
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Objective:
Reveal the internal structure of Mauna Kea and constrain
the understanding of volcano hydrogeology.
Understanding of volcano hydrogeology requires
information on porosity and permeability
Only few petrophysical measurements were made on cores
Log data provides the only continuous information for
porosity prediction
Porosity prediction form logs needs a prior understandingof in-situ petrophysics and rock characteristics
Motivation for log analysis
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Discrimance
Analysis
Core Lithology
Resistivity medium(Ohmm), logTotal Gamma Ray
(API)Depth(mbsl)
1 10 100 5 10 15
Fr
acs
Vesic
les
Alter ation
815
820
825
830
835
840
845
850
855
C o r
e I n
f o r m
a t i o n
Calibration
Result
700
705
710
715
720
725
730
735
740
745
750
755
760
765
770
775
780
785
790
795
800
700
705
710
715
720
725
730
735
740
745
750
755
760
765
770
775
780
785
790
795
800
U119
U120
U121
U123
U124
U125
U126
U127
U128
U130
U129
U131
U133
U132
U119c
U119d
U120a
U120b
U120c
U120dU120e
U121aU121b
U124a
U124b
U125a
U125b
U126a
U126b
U127a
U127b
U127c
U127d
U127e
U127f
U128a
U120f
CoreLithology
CoreRecovery
(%)
Lava FlowSuccession
??
Lithology reconstruction in the subaerial stage
L i bilit i th b i t
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Low resistivity‚ high GR
(a) Borehole data, measured by GFZ-Potsdam, Operation Support Group (July 1999)(b) Borehole data, measured by University of Goettingen, Institute of Geophysics (July 1999)
3600
3800
4000
4200
4400
4600
4800
5000
5200
5400
5600
5800
6000
LU 2
LU 3
LU 4
Depth[ftbsl]
Resistivity
deep[Ohmm]
(a)Total
Gamma Ray[API]
(a)
Depth[mbsl]
Total Field
[nT]
(b)
Changes in Total Field= Magnetic Anomaly
Log Unit Boundary
Low resistivity‚ low GR,
strong magnetic anomalies
High resistivity‚ high GR
Log variability in the submarine stage
Rocks described from
core as hyaloclastites
show significantdifferences with depth
L lith l d i t l t t f M K
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Aa-, Pahoehoe Lava widely brecciated partly low potassium
Aa-, Pahoehoe Lava predominantly massive
Hyaloclastite, polymict/monolithologic high matrix content, weak consolidation
Hyaloclastite, ,
polymict/monolithologichigh matrix content, strong consolidation
Hyaloclastite, monolithologic few matrix content, weak consolidation
Massive units ,weakly fractured
Pillow units, massive to strongly fractured
volcanoclastic apronlow consolidation
volcanoclastic apronhigh consolidation
landslide - debris flow?
transition from pillow core
complex to volcanoclasticapron
subaerial flows
TotalGamma Ray
[API]
Resistivitydeep
[Ohmm]
Depth[mbsl]
600
1000
1500
2000
2500
LU1
LU2
LU3
LU6
LU5
LU4
LU7
LU8
LU9
1 4 1510,000
meteoricalteration
Log lithology and internal structure of Mauna Kea
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