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



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



KTB

Examples from the KTB boreholes



Overview KTB boreholes



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.



Target

Transfer of log data into lithological information



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.



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





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.



Grouping of electrofacies in the pilot hole



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



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%.



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%.



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!



ODP

Examples from ODP Hole 504B



American Plate

504B896A

Mid- AtlanicRidge

CostaRica

Rift

Nazca Plate

CocosPlate

PacificPlate

Drilling Location of Holes 504B and 896A



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



Simplified log responses of pillows and lavaflows



504B 896A

10 100

electrical resistivity

(Ω

m)

10 100


(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



Cross plots: resistivity versus velocity

504B 896A

10 100


(Ω

m)

10 100


(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 )



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



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:



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



ICDP

Examples from HSDP2, Hawaii





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



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



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



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



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



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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Log Interpretation in Non-Hydrocarbon Environments - Methods and Applications -.pdf

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