© Rider-French

Subsurface Geological Interpretation

of

Well Logs

Welcome
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Folder A 04/07J

Contents…

Tools

Interpretation

1
 The Very Beginning

Pechelbronn
Alsace 1927

Characteristics of Logs

• Graph of a physical property against

depth.
• Measurements are made at regular
depth increments.
• Measurements are averages over a
more or less constant volume.

2
 3
CORES

3/3-3

North Sea
discovery
0.3

Well 3/3-
an early
0.25

Old Style Analogue Composite Log

0.2
0.15 Raw
poro

whole core
0.1
core plug
0.05
0
0 2 4 6 8 10
-0.05
depth
0.3
0.25
0.2
Raw
0.15
poro

log
0.1
log values
0.05
0
0 2 4 6 8 10
-0.05
depth
LOGS
 Repeatability:
A good check that the tool is working properly

…but there may be good reasons why the logs do not repeat

Modern Computer Logging

Unit allows Repeat and Main
Logs to be plotted on top
of each other.

4
A Modern Digital Composite Log

1936

5
 a logging truck 1936

a logging truck 1985

6
 offshore
floating
platform

without logs we
would have a very
poor record of the
subsurface

7
Wireline Logging Setup

Log recorded
from the
bottom up

A Modern Logging Tool

8
 Tool Electronics

The Logging Heptacable

cable armour

9
When wireline logs are ‘run’

Logs run

Logs run

TD
Final logging

Signal Flow

10
 LWD or FEWD
Logging While Drilling

MWD
Measurements While Drilling

Direction

Vibration

Resistivity
Gamma ray

Inclination

LWD/MWD tools

11
Data Transmission

• LWD transmits to surface using

pressure pulses in the mud.
• Continuous (Real-
(Real-Time)
Transmission as long as pumps
are running.
– Tx rate ca 10bit/s.
– Cf wireline >100000bit/s
• Data is also stored down-
down-hole.
– 200 hour battery life
– GByte memory
– 45000 data points.
• Wired Pipe allows realtime Tx at
wireline rates.

bottom hole assembly

for horizontal drilling

12
 LWD vs Wireline

In this example from

a vertical well the measurements
agree well.

The LWD curves are 3m deep wrt

wireline at the top of the section
and 3m shallow at the base
which is only 50m deeper.

The hole is in good condition

with no significant overpulls
seen on the wireline.

Real-
Real-time vs Recorded Data

Real
Time

Recorded

1. Data gaps
2. Fewer curves

13
 Real Time LWD Log Plot

The March of MWD/LWD/FEWD

Generatio 1988-1992
1988- 1993-
1993-1996 1997-
1997-2000 2001-
2001-2006
n

LWD Resistivity Quadrant Density Images

MWD Gamma ray density images Array sonic
Density Sonic Porosity NMR
Seismic tool Pressure

MAIN Formation Geosteerin Real time Real time

NEW Evaluation g FE images
USES while F.E while decisions Pressure
drilling drilling Sweet-
Sweet-spot while
steering drilling

FAX INTERNET

14
 Well Logs Today

• WIRELINE
– Open hole
• Formation Evaluation
• Pressure Tests and Fluid Sampling
• Rock Samples
– Cased Hole
• Production/Reservoir Monitoring
• Perforating
– Pipe-Conveyed – high angle wells
– Tractor-Conveyed

• LWD
– Open-hole
• Formation evaluation
• Pressure tests
• Drilling

• Through-
Through-Bit

Complex Drilling/Time Curve

Vertical hole Deviated/horizontal hole

15
END

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