The document provides an overview of well logging analysis methods used in petroleum geology, including various techniques for measuring physical properties in boreholes. It covers different classifications of logging methods such as electric, nuclear, and acoustic techniques. Additionally, it details specific logging tools and their applications, emphasizing the importance of these methods in identifying reservoir characteristics and fluid content.

1. WELL LOGGING ANALYSIS
METHODS AND INTERPRETATION
PETROLEUM GEOLOGY II – WS 2013/14
CRISTIANO ASCOLANI

2. 2
Well Logging
“The product of a survey operation, also called a survey, consisting of one or
more curves. Provides a permanent record of one or more physical
measurements as a function of depth in a well bore. Well logs are used to identify
and correlate underground rocks, and to determine the mineralogy and physical
properties of potential reservoir rocks and the nature of the fluids they contain.”
(SPWLA - Society of Petrophysicists and Well Log Analysts, online glossary, last
modified 2010/03/02)
LOGGING AND CORE ANALYSIS - PETROLEUM GEOLOGY II – WS 2013/14
• Downhole
Sondes lowered into the well bore by a
survey
• On surface
Core logs, mud sample logs,
hydrocarbon well logs, etc.

3. 3
Well Logging
Commonly classified by the kind of energy that is input (active systems) or
received (passive systems):
1. Electric Logging Techniques
• Spontaneus Potential Log
• Resistance Log
• Microlog
• Induction Log
2. Nuclear Radiation Logging
Techniques
• Gamma Ray (Natural Gamma)
Log
• Natural Gamma Spectral Log
• Density or Gamma-Gamma Log
• Neutron Log
• Neutrino Log
3. Acoustic/Seismic Logging
Technique
• Sonic/Acoustic Log
• Acoustic Borehole Imaging Log
• Cross-Hole Seismic Test
• Seismic Tomography
• Borehole Optical Systems
• Borehole Image Processing
• System (BIPS)
4. Other Wireline System
• Borehole Caliper Log
• Directional Surveys
• Borehole Fluid Temperature Log
• Borehole Gravity Log
• Magnetic Log
• Flowmeter Log
LOGGING AND CORE ANALYSIS - PETROLEUM GEOLOGY II – WS 2013/14

4. 4
Electric Log
Spontaneus Potential
Log
It records the difference in potential
in millivolts between a fixed
electrode at the surface and an
electrode in a borehole
• Clays and shales generate one
charge, permeable formations such
as sandstone will generate an
opposite one
• SPs occur when two aqueous
solutions with different ionic
concentrations are placed in contact
(brime-mud, fresh water-mud)
• Hydrocarbon suppression: SP log
response is reduced
Resistivity Log (SP)
Characterization of the rock or
sediment in a borehole by measuring
its electrical resistivity.
• Most rock materials: non-conductor
• Enclosed fluids (water based):
conductor
• Hydrocarbon fluids: almost infinitely
resistive
LOGGING AND CORE ANALYSIS - PETROLEUM GEOLOGY II – WS 2013/14

5. 5
Electric Log
(CRCLEME, 2002) (Technical Service Center, Bureau of Reclamation, 2002)
LOGGING AND CORE ANALYSIS - PETROLEUM GEOLOGY II – WS 2013/14

6. 6
Gamma Ray Log
The simplest radioactive method in geophysical well logging is the natural
gamma log. These logging tools record the level of naturally occurring gamma
ray emissions from the rocks around a borehole.
Different types of rock emit different amounts and different spectra of natural gamma
radiation
• Shales usually emit more gamma rays than other sedimentary rocks: potassium is a
common component in their clay content, and because the cation exchange capacity
of clay causes them to adsorb uranium and thorium.
• Sandstones/carbonate rocks usually do not generate so much gamma rays.
• BE CAREFUL: sometimes non-shales also have elevated levels of gamma radiation:
sandstone can contain uranium mineralization, coal and dolomite may contain
absorbed uranium etc..
LOGGING AND CORE ANALYSIS - PETROLEUM GEOLOGY II – WS 2013/14

7. 7
Bulk Density Log
Radioactive source and detector
are lowered down the borehole and
the source emits medium-energy
gamma rays into the formation.
Big elements rate: gamma rays rapidly
loose energy
Neutron Porosity Log
Radioactive source and detector are
lowered down the borehole and the
source emits neutrons into the
formation.
High H rate: neutrons rapidly loose
energy
𝐵𝑢𝑙𝑘 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 𝐿𝑜𝑔 ∝
1
𝑁𝑒𝑢𝑡𝑟𝑜𝑛 𝐿𝑜𝑔
LOGGING AND CORE ANALYSIS - PETROLEUM GEOLOGY II – WS 2013/14

8. 8
Acoustic/Sonic Log
They provide a formation’s interval transit time, designated as ∆t, which is a
measure of a formation’s capacity to transmit seismic waves.
The velocity is calculated by measuring
the travel time from the piezoelectric
transmitter to the receiver
∆ 𝑡= 𝑡𝑓𝑎𝑟 − 𝑡 𝑛𝑒𝑎𝑟
Calculation of porosity: Wyllie’s time
averaged equation
1
𝑉
=
∅
𝑉𝑓
+
1 − ∅
𝑉 𝑚𝑎𝑡
(Wikipedia.org)
LOGGING AND CORE ANALYSIS - PETROLEUM GEOLOGY II – WS 2013/14

9. 9
Acoustic/Sonic Log
The velocities and corresponding travel times of the rock and matrix are:
(Petrocenter.com)
LOGGING AND CORE ANALYSIS - PETROLEUM GEOLOGY II – WS 2013/14

10. 10
Caliper Log
Well logging tool that provides a continuous measurement of the size and shape
of a borehole along its depth.
The caliper tool measures the variation in
borehole diameter as it is withdrawn from
the bottom of the hole, using two or more
articulated arms that push against the
borehole wall
(Wikipedia.org)Multi-finger Caliper, MFC model (Landau
Petroleum Technology Co.).
LOGGING AND CORE ANALYSIS - PETROLEUM GEOLOGY II – WS 2013/14

11. 11
Wireline Logging: example
Basic Log (Schlumberger, 2011)
LOGGING AND CORE ANALYSIS - PETROLEUM GEOLOGY II – WS 2013/14

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References
• Oilfield Review Spring 2011: 23, no.1, Schlumberger, 2011
• Oilfield Review Autumn 2012: 24, no.3, Schlumberger, 2012
• In Papp, É. (Editor), 2002, Geophysical and Remote Sensing
Methods for Regolith Exploration, CRCLEME Open File Report 144,
pp 105-115.
• Engineering Geology Field Manual, Second Edition, Volume II; U.S.
Department of the Interior Bureau of Reclamation, 2001
• Wikipedia.org
LOGGING AND CORE ANALYSIS - PETROLEUM GEOLOGY II – WS 2013/14