1. CGE 674
FORMATION EVALUATION
BY:
TENGKU AMRAN TENGKU MOHD

2. 1 Introduction

3. Outline
Logging History
Openhole Logging Acquisition
Principles of Openhole Logging Tools –
GR, SP, Neutron-Density, Resistivity,
Sonic

4. Objectives
After completing this chapter, you should be
able to:
- Understand the basic principle of formation
evaluation and well logging
- Describe the surface and downhole
equipments/ tools to conduct a logging
operation
- Describe the principle and log response of
each of logging tool.

5. Overview
WHAT ARE FORMATION
EVALUATION AND WELL
LOGGING???

6. Overview
Formation Evaluation…
Process/method to determine or identify if a
potential oil or gas field is commercially
viable by using all available data (e.g. well
log data, core data, mud log, RFT data etc.)
for interpretation of reservoir formation

7. Overview
Well Logging…
A method or in situ measurement or
recordings (vs depth) to determine the
physical, chemical and petrophysical
properties of the reservoir rocks and fluids.

8. Overview
HOW ABOUT LOGGING WHILE
DRILLING (LWD)???

9. Overview
Logging While Drilling…
Advanced logging operation allowing acquisition of log data
via tools placed in the actual drilling assembly, which
transmit the data to the surface on a real-time basis or store
the data in a downhole memory from which it may be
downloaded when the assembly is brought back to the
surface.
Their use may be justified when:
– real time information is required for operational reason, e.g.
steering a well
– acquiring data prior to the hole washing out or invasion
occurring
– safeguarding information if there is a risk of losing the hole
– the trajectory where wireline acquisition is difficult

10. Overview
EVALUATION SEQUENCE
Rock
Hydrocarbons Gas Evaluate
Reservoir
Water Oil Evaluate
Non Reservoir
Locate the Detect Differentiate
Reservoir Hydrocarbons Between gas/oil

11. What subsurface information is important?
• Hydrocarbon thickness
What is value of hydrocarbon in place? • Porosity
(Potential value) • Saturation
• Area
• Hydrocarbon type
How easily can the hydrocarbon flow
• Permeability
out the well?
• Pressure
How easy is it to drill to the reservoir? • Lithology
(Cost of drilling, completing…) • Depth, pressure, temperature

12. Formation evaluation is critical to
understanding the reservoir
What is value of hydrocarbon in place?
(Potential value)
How easily can the hydrocarbon flow
out the well?
How easy is it to drill to the reservoir?
(Cost of drilling, completing…)

13. Logging History
Electrical Logging
Year Description
1927 • First electrical log was recorded in a well in the small oil field of Pechelbronn, in Alsace, a
province of north-eastern france.
• Single graph of electrical resistivity of rock formations was recorded by “station” method.
• “sonde” was stopped at periodic intervals in borehole, measurements made, and calculated
resistivity was hand-plotted on a graph – this procedures was carried out from station to
station until entire log was recorded.
• Resistivity log was used to detect HC present in the formation.
1929 • Electrical resistivity logging was introduced on a commercial basis in Venuzuela, US, Russia
and Dutch East Indies.
• Usefulness: for well to well correlation and identification of potential HC-bearing strata.
1931 • Include SP measurement with Resistivity curve on electrical log.
• Schlumberger brothers (Marcel & Conrad) perfected a method of continuous recording
1936 • Photographic-film recorder was introduced
• Electrical log consisted of SP curve, short normal, long normal & long lateral resistivity
curves, was predominant in logging activity from 1936 to late 1950’s (curves were recorded
simultaneously after about 1946).

14. Logging History
Dipmeter Log
Year Description
1930’s • The development of dipmeter began with the anisotropy dipmeter tool.
1943 • Three-arm dipmeter device, with an associated photoclinometer was introduced – permitted
both direction and angle of formation dip to be determined (SP sensor at each arm).
1946 • SP sensors were replaced by short resistivity devices – made dip measurements possible
in wells where SP had little correlatable detail.
Mid- • First continuously recording electrical dipmeter sonde (used 3 microresistivity arrays and
1950’s contained a fluxgate compass) was introduced.
Today • A 4-arm dipmeter tool records 10 microresistivity curves simultaneously, and a triaxial
accelerometer and magnetometers provide highly accurate info on tool and deviation
azimuth.
• Processing data done exclusively with electronic computers.

15. Logging History
GR and Neutron Tools (first use of radioactive properties in well logging)
Year Description
1941 • Neutron log was first described by Pontecovo.
• In combination with GR log, neutron log enhanced lithological interpretations and well-to-well
stratigraphic correlations.
1949 • Attention to neutron log as a porosity indicator.
1962 • SNP sidewall neutron porosity tool was introduced.
1936 • CNL* compensated neutron tool was introduced.
• Dual Porosity neutron tool combines those 2 neutron measurements into a single tool.

16. Logging History
Early Porosity Determination & Microresistivity Measurement
Year Description
1950’s • Microlog tool was introduced – used a miniature linear array of 3 electrodes imbedded in the
face of an insulating pad, which is applied to the borehole wall.
• Microlog recording is also useful to delineate permeable beds, and other microresistivity
devices help establish resistivity profile from the invaded zone near the borehole to the non-
invaded virgin formation.
1951 • Laterolog tool was introduced (the first focused deep-investigating resistivity device) –
focused resistivity logs are well adapted for investigating of thin beds drilled with low-
resistivity muds (eg. Salt muds & highly resistive formations)
1953 • Microlaterolog tool was developed for salt muds.
• The MicroProximity log and MicroSFL* log have followed.
Today • DLL* dual lateral log tool (deep laterolog and shallow laterolog measurements) is the
standard.
• Usually run with a MicroSFL device as well

17. Logging History
Induction Log (replace original electrical log in freshwater muds)
Year Description
1949 • Induction log was developed, as an outgrowth of wartime work with mine detectors, for use in
oil-based mud.
• However, its superiority over electrical log in freshwater muds was soon recognized.
1956 • Combine a five-coil induction device with SP curve and a 16-in normal to make induction
electrical tool.
1959 • Five-coil device was replaced by one with a six-coil array with deeper investigation.
1963 • DIL* dual induction log was introduced, now is the standard – deep induction, medium
induction, and shallow resistivity-measurements.
• The shallow resistivity-measuring device is now a focused resistivity device – a Laterolog 8
on the 1963 tool and an SFL device on current tools
• A new dual induction log, the Phasor* induction, provides improved thin-bed response,
deeper depth of investigation, and greater dynamic resistivity range.

18. Logging History
Sonic Log
Year Description
Since • Logging cables have been used to lower geophones into wells to measure long-interval
1930 acoustic travel times from sound sources at the surface.
Late • Sonic log was accepted as a reliable porosity logs – its measurement responds primarily to
1950’s porosity and is essentially independent of saturation.
• Sonic log, coupled with focused resistivity logs (laterolog and induction) – made possible
modern formation evaluation from well logs.
• Sonic log – measure porosity; focused resistivity logs – measure true resistivity of non-
invaded virgin formation.
• Subsequent improvements in sonic logging – BHC borehole compensated sonic, LLS*
long-space sonic, and the Array-sonic* tools.

19. Logging History
Density Log
Year Description
Early • Logging of formation bulk density (measurement of formation porosity), was commercially
1960’s introduced.
1964 • An FDC* compensated formation density log (compensated for the mudcake), was
quickly followed.
1981 • Litho-Density* log provided an improved bulk density measurement and a lithology-sensitive
photoelectric absorption cross section measurement.

20. Logging History
Recovery of Physical Rock Samples & Formation Fluid Samples with Wireline Tools
Year Description
1937 • Sidewall coring, using a hollow, cylindrical “bullet” shot into formation and retrieved by pulling
it out, has existed since 1937.
1957 • A formation tester was introduced – recovered a sample of formation fluids and pore presure
was measured during the sampling process.
• FIT formation interval tester and RFT* repeat formation tester have followed (RFT tool
can make unlimited number of pressure measurements and recover two fluid samples per
trip.
1978 • Dielectric measurements have been developed to handle formation with freshwater
& formation, or varies in salinity, or in which salinity is unknown.
1985 • EPT* electromagnetic propagation log was introduced in 1978
• DPT* deep propagation log was followed in 1985.

21. Wireline Logging
Introduction
Well logs or wireline logs are continuous recordings of well depth versus
different petrophysical characteristics of the rocks through which the well is
drilled. There are many types of well logs, depending upon the characteristics
of the rock being measured.
Logging Objectives
The main purpose of well logging is:
- to provide data for evaluating petroleum reservoirs.
- to aid in testing, completion and repairing of the well.
To calculate the oil reserve in an oil pool we need to know the following.
• Thickness of the oil bearing formation.
• Porosity of the formation.
• Oil saturation.
• Lateral extent of the pool.
Logs should always be calibrated with core data to improve
interpretations.

22. Wireline Logging
• In situ meas. (vs. depth) of
– Rock properties
– Fluid properties
• When
– Openhole (before casing) Casing
• While drilling (LWD / MWD).
• After drilling (wireline).
– Cased hole (C/O, sigma)
• Interpretation for: Open hole
– Geological properties.
– Petrophysical properties.
– Production properties.

23. Types of Well Logging
Well logging is classified into three broad
categories:
Open Hole Logging
Cased Hole Logging
Production Logging

24. Open Hole Logging
Logging surveys taken before the hole is cased are called open
hole logs. The logs included in this group are:
Electrical surveys (induction, laterolog and microlog logs).
Sonic logs.
Caliper Logs.
Dipmeter Logs.
SP logs
Radioactive surveys (density, neutron and gamma ray logs).

25. Electrical Logs
Electrical logs (Induction, laterolog, and microlog)
measure the electrical properties of the formation
alongwith the formation fluids.
Sonic/ Acoustic Logs
Sonic logs measure the elastic or (sound) wave
properties of the formation.
Caliper Logs
Caliper logs measure the size or geometry of the hole.

26. Dipmeter Logs
Dipmeter logs measure dip of the formations.
SP Logs
SP logs measure potential different between a shale-sand or
shale-carbonate due to difference salinity of formation water
and mud filtrate.
Radioactive Logs
Gamma ray & neutron logs measure radioactive and neutron
absorption properties. Density logs measure electron density of
the formation which is related to formation density.

27. OPEN HOLE LOGGING MEASUREMENTS
LOGGING TOOL
27

28. Cased Hole Logging
Logging surveys taken after the casing is lowered are usually
categorized as cased hole logs. The surveys included in this group are:
Gamma Ray
Neutron
Temperature
Pulsed Neutron
Cement Bond Log
C/O and sigma Log
Some of these surveys like the gamma ray, neutron and temperature
logs can be run in both open and cased hole wells.

29. CASED HOLE LOGGING MEASUREMENTS

30. Production Logging
Well logging surveys taken to improve production or repair the well are
termed as production logs. Surveys included in this category are:
Flowmeter
Pressure
Temperature
Fluid Density

31. VALUE AND LIMITATIONS OF WELL LOG DATA
Strengths
• Provides remotely sensed values of reservoir properties and fluids.
• Among the most abundant reservoir data.
• Presentation results fairly well standardized.
• Allows evaluation of lateral (map) and vertical (cross section)
changes in reservoir properties and fluids.
Limitations
• Indirect measurements.
• Vertical resolution.
• Depth of investigation.

32. Petrophysical Logging Tools - Primary
Log Type Tool Type Physical Derived Interpreted
Measurement Parameter Parameter
Resistivity
-Induction Array Voltage (V) Rt Sw
-Laterolog Array V and Current (I) Rt Sw
-Micro laterolog Pad Current Rxo Sxo
Acoustic
- Sonic Array Transit Time PHIs Lithology
Nuclear
-GR (Density) Pad Gamma Ray RHOB, PHID Lithology
- Neutron Mandrel Neutron RHON Lithology
Auxiliary
-Natural GR Mandrel Gamma Ray None Vsh
-SP Electrode mV None Vsh
-Caliper (*various) Dh, Volume
32

33. SOME QUESTIONS ADDRESSED BY
LOG INTERPRETATION
• Geophysicist / Geologist • Reservoir Engineer
– How thick is the pay zone?
– Are the tops as predicted?
– How homogeneous is the zone?
– Are potential zones porous?
– Porosity?
– Formation intervals?
– Permeability?
– Lithology?
– Hydrocarbons? • Production Engineer
– What type of hydrocarbons? – Which zone(s) to complete?
– Commercial quantities? – What production rates?
– Any water production?
– Is zone hydraulically isolated?
– Will well need stimulation?
– What stimulation would be best?

34. Fig. 3.1: A Logging Truck

35. WIRELINE
LOGGING
EQUIPMENT

36. Computerized Logging Units
Computer-based units offer the following features:
Computer control of the data allows logs to be recorded
either logging up or down with all curves on depth.
Calibration are performed under programme control and can
be performed more quickly, consistently and accurately.
Logs can be played back from the data tapes on many
different formats.
Basic wellsite, processing/analysis of data is available.

38. DETAILS OF WIRELINE LOGGING RIGUP

39. LOGGING CABLE
39

40. Log Presentation
• Heading.
• Curves related to some physical property of rock/casing
surrounding the wellbore.

41. LOG PRESENTATION - THE HEADING
• Well location
• Depth references
• Date of log
• Well depth
• Casing shoe depth
• Bit size
• Mud data
– Type
– Properties
– Resistivities
• Max. Temperature
41

42. LOG PRESENTATION

43. LOG PRESENTATION - LINEAR GRID
Depth
Track 1 track Track 2 Track 3
43

44. LOG PRESENTATION - COMMON DEPTH SCALES
44

45. TYPES OF LOGS TO BE RUN
• Logging suites generally include one resistivity and one
porosity device.
• The logging string will also have other tools like the gamma
ray, SP and caliper tools.
• However, logging suites usually have two porosity devices to
give more information about rock type, hydrocarbon type and
porosity.
• Other considerations – to estimate permeability or to take
fluid samples – require other special tools like the formation
testers.

46. MUD FILTRATE INVASION
Uninvaded
Zone
(Rt)
Invaded
Zone
(Rxo)
Wellbore
Mud
(Rm)
Uninvaded Mud Cake
Zone (Rmc)
(Rt)

47. MUD FILTRATE INVASION

48. COMMON TERMINOLOGY
Borehole
Rm : Borehole mud resistivity
Rmc : Mudcake resistivity
Invaded zone
Rmf : Mud filtrate resistivity
Rxo : Invaded zone resistivity
Sxo : Invaded zone water saturation
Uninvaded zone
Rw : Interstitial water resistivity
Rt : Uninvaded zone resistivity
Sw : Uninvaded zone water saturation

49. Radial Fluid and Resistivity
Distribution
Rx0 Rt Rx0 Rt
Resistivity
Resistivity
Rxo
Rxo Rt
Rt
Water Based Muds
Qualitative Distribution of Resistivity (Rmf > Rw)

50. Fresh mud, salt water zone
Salty mud, Hydrocarbon zone

51. NOMENCLATURE FOR ZONES IN
AND AROUND THE BOREHOLE

52. Sources of subsurface data
Data collected during drilling Penetration rate
Drill cuttings analysis
Drill mud analysis
Mud gains/losses
Shows of gas/oil/water
Core analysis Lithology
Presence of shows
Porosity
Permeability
Special core analysis
Wireline log analysis Electric logs
Acoustic logs
Radioactivity logs
Pressure measurements
Special logs
Productivity tests Formation tester
Drill stem test
Production test

53. Sources of subsurface data
Data needed: Data source:
Hydrocarbon thickness
Porosity
Saturation Cuttings, Mud log
Area Coring
Hydrocarbon type Logging
• LWD – Logging while drilling
Permeability • WL – Wireline (usually open hole)
Pressure
Lithology

54. Mud Log
• Immediate interpretation of what the drill bit has
penetrated and whether there are any hydrocarbons
present (a show).
• Making maps of the subsurface geology.

55. Sources of data – Mud log

56. Mud log

58. Sources of subsurface data
Data needed: Data source:
Hydrocarbon thickness
Porosity
Saturation Cuttings, Mud log
Area Coring
Hydrocarbon type Logging
• LWD – Logging while drilling
Permeability • WL – Wireline (usually open hole)
Pressure
Lithology

59. Coring - Conventional
• Taking a core requires that the regular drill bit
be removed from the hole. It is replaced with a
"core bit", which is capable of grinding out and
retrieving the heavy cylinder of rock.
• The core bit is usually coated with small, sharp
diamonds that can grind through the hardest
rock. A core bit cuts very slowly.
• A core is a solid cylinder of rock about 4-5
inches in diameter, and a single core will
usually be about 30 feet long.

60. Coring - Conventional
Whole Core Slab Core

61. Sources of data – Core

62. Coring - Sidewall
• This method is cheaper than the
conventional coring.
• Cores can be taken in hours, instead of
days.
• In sidewall coring, a slim wireline coring tool
is run into the hole. The tool may be of two
general types; either "rotary sidewall" or
"percussion".
• Typically, cores about 1" in diameter and 1"
to 2" long can be retrieved with this method.

63. Coring - Sidewall

64. Sources of subsurface data
Data needed: Data source:
Hydrocarbon thickness
Porosity
Saturation Cuttings, Mud log
Area Coring
Hydrocarbon type Logging
• LWD – Logging while drilling
Permeability • WL – Wireline (usually open hole)
Pressure
Lithology

65. Sources of data – Logs