1. Well Logging Course (1st Ed.)

2. 1.
2.
3.
4.
5.
6.
Well logging introduction
Wireline logging
Logging consideration
MWD vs. LWD
Properties of reservoir and logging role
Measurement techniques

4. Recent decades changes in petroleum
industry which affected Well logging
Changes in petroleum industry
hydrocarbons have become increasingly harder to
locate, quantify, and produce.
In addition, new techniques of drilling high deviation or
horizontal wells have engendered a whole new family of
measurement devices incorporated into the drilling
string that may be used routinely or in situations where
access by traditional “wireline” instruments is difficult or
impossible.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
4

5. well logging meaning
The French translation of the term well logging is carottage
´electrique,
 literally “electrical coring,” a fairly exact description of this
geophysical prospecting technique when it was invented in 1927.
 A less literal translation might be “a record of characteristics of rock
formations traversed by a measurement device in the well bore.”
However, well logging means different things to different
people.
 For a geologist,
 it is primarily a mapping technique for exploring the subsurface.
 For a petrophysicist,
 it is a means to evaluate the hydrocarbon production potential of a
reservoir.
 For a geophysicist,
 it is a source of complementary data for surface seismic analysis.
 For a reservoir engineer,
 it may simply supply values for use in a simulator.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
5

6. well logging application
The initial uses of well logging were for
correlating similar patterns of electrical conductivity from one
well to another, sometimes over large distances.
As the measuring techniques improved and multiplied,
applications began to be directed to
the quantitative evaluation of hydrocarbon-bearing
formations.
Much of the following text is directed toward the
understanding of
the measurement devices and
interpretation techniques developed for this type of
formation evaluation.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
6

7. Well logging scope
well logging grew from the specific need of the
petroleum industry to evaluate hydrocarbon
accumulations
New measurements useful for subsurface mapping
have evolved which have applications for
structural mapping,
reservoir description, and
sedimentological identification.
Identification of fractures
the formation mineralogy.
well logging is seen to require the synthesis of a
number of diverse physical sciences:
physics, chemistry, electrochemistry, geochemistry, acoustics,
and geology
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
7

8. Well logging history
birth of logging
September 5, 1927
By H. Doll and the Schlumberger brothers (and a few others)
a semicontinuous resistivity measurement
in an old field in Alsace
Using a rudimentary device (a sonde)
Connecting the device to the surface was a cable/wire
• Wireline refers to the armored cable by which the measuring devices
are lowered and retrieved from the well and, by a number of shielded
insulated wires in the interior of the cable, provide for the electrical
power of the device and a means for the transmission of data to the
surface.
More recently, the devices have been encapsulated in a
drill collar, and the transmission effected through the
mud column.
This procedure is known as logging while drilling (LWD).
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
8

10. Wireline Logging measurement
devices (Sonde)
The process of logging involves a number of
elements.
primary interest is the measurement device, or
sonde.
Currently, over fifty different types of these logging tools
exist in order to meet various information needs and
functions.
Some of them are passive measurement devices;
others exert some influence on the formation being traversed.
Their measurements are transmitted to the surface by
means of the wire line.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
10

11. Well logging Operation
The elements of well
logging:
a measurement sonde
in a borehole,
the wireline, and
a mobile laboratory
Courtesy of Schlumberger
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
11

12. Sonde dimensions
Superficially, they all resemble one another.
They are generally cylindrical devices with an
outside diameter on the order of 4 in. or less;
this is to accommodate operation in boreholes as small
as 6 in. in diameter.
Their length varies depending on the sensor array
used and the complexity of associated electronics
required.
It is possible to connect a number of devices
concurrently,
forming tool strings as long as 100 ft [30.5 m].
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
12

13. Sonde types
Some sondes are designed to be operated in a
centralized position in the borehole.
This operation is achieved by the use of bow-springs
attached to the exterior,
or by more sophisticated hydraulically actuated “arms.”
Some measurements require that the sensor
package (in this case called a pad) be in intimate
contact with the formation.
This is also achieved by the use of a hydraulically
actuated back-up arm.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
13

14. Sample sondes
Next slide illustrates the measurement portion of four
different sondes.
On the right is an example of a centralized device which uses
four actuated arms.
There is a measurement pad at the extremity of each arm.
Second from the right is a more sophisticated pad device,
showing the actuated back-up arm in its fully extended position.
Third from the right is an example of a tool which is generally
kept centered in the borehole by external bow-springs,
which are not shown in the photo.
The tool on the left is similar to the first device
but has an additional sensor pad
• which is kept in close contact with the formation being measured.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
14

15. Examples of four logging tools
 The dipmeter [on the left]
 has sensors on four actuated
arms,
 which are shown in their fully
extended position.
 Attached to the bottom of one of
its four arms is an additional
electrode array embedded in a
rubber “pad.”
 a sonic logging tool [2nd from
left]
 characterized by a slotted housing
 a density device [3rd from left]
 with its hydraulically activated
back-up arm fully extended
 another version of a dipmeter
[on the extreme right ]
 with multiple electrodes on each
pad.
Courtesy of Schlumberger
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
15

16. The truck
These specially designed instruments, which are
sensitive to one or more formation parameters of
interest, are lowered into a borehole by a surface
instrumentation truck.
This mobile laboratory provides the downhole power to
the instrument package.
It provides the cable and winch for the lowering and
raising of the sonde, and is equipped with computers for
data processing, interpretation of measurements, and
permanent storage of the data.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
16

18. Measurement speed
Most of the measurements are continuous
measurements.
They are made as the tool is slowly raised toward the surface.
The actual logging speeds vary depending on the
nature of the device.
Measurements which are subject to statistical precision errors
or require mechanical contact between sensor and formation
tend to be run more slowly, between 600 ft [183 m] and 1,800 ft/h
[549 m/h]
newer tools run as fast as 3,600 ft/h [1097 m/h]
Some acoustic and electrical devices can be withdrawn from
the well, while recording their measurements, at much
greater speeds.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
18

19. vertical resolution
The traditional sampling provides one averaged
measurement for every 6 in. [15 cm] of tool travel.
For some devices that have good vertical
resolution, the sampling interval is 1.2 in. [3 cm]
There are special devices with geological
applications (such as the determination of
depositional environment) which have a much
smaller vertical resolution;
their data are sampled so as to resolve details on the
scale of millimeters.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
19

20. logging vs.
cores, side-wall samples, and cuttings
logging is an alternate or supplement to the analysis of cores,
side-wall samples, and cuttings
Coring
 takes time, so expensive
 In soft and friable rocks,
 only possible to recover part of the interval cored
Side-wall cores
 obtained from another phase of wireline operations
 possibility of sampling at discrete depths after drilling
 Side-wall cores disadvantages:
 returning small sample sizes, the problem of discontinuous sampling
Cuttings,
 extracted from the drilling mud return,
 are one of the largest sources of subsurface sampling. However, the
reconstitution of the lithological sequence from cuttings is imprecise
due to the problem of associating a depth with any given sample.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
20

21. Well log advantages
Although well logging techniques (with the
exception of side-wall sampling) do not give direct
access to the physical rock specimens,
they do, through indirect means, supplement the
knowledge gained from the three preceding techniques
[Coring, Side-wall cores and Cuttings].
Well logs provide
continuous,
in situ measurements of parameters related to
porosity,
lithology,
presence of hydrocarbons,
and other rock properties of interest.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
21

24. measurement while drilling (MWD)
To assist drillers in the complex task of a rotary
drilling operation, a number of types of information
like
the downhole weight on bit and
the downhole torque at bit are desirable in real time.
To respond to this need, a type of service known as
measurement while drilling (MWD) began to
develop in the late 1970s.
A typical MWD system consisted of a downhole
sensor unit close to the drill bit, a power source, a
telemetry system, and equipment on the surface to
receive and display data.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
24

25. measurement while drilling (Cont.)
The telemetry system
was often a mud pulse system that used coded mud pressure
pulses to transmit (at a very slow rate of a few bits per
second) the measurements from the downhole subassembly.
The power source
was a combination of a generating turbine, deriving its power
from the mud flow, and batteries.
The measurement subassembly
evolved in complexity from measurements of the weight and
torque on bit to include the borehole pressure and
temperature, mud flow rate, a natural gamma ray (GR)
measurement, and a rudimentary resistivity measurement.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
25

26. Logging while drilling
The LWD tools are all built into heavy thick-walled drill
collars.
 Thus, like the wireline tools all the LWD resemble one another.
In next slide one particular version is shown that contains
several sensors.
 The sensors are built into the wall of the drill collar with some
protrusions.
 However, an adequate channel is provided to accommodate the
mud flow.
 the device can be run either “slick” or with an attached clamped-on
external “stabilizer.”
 This latter device centralizes the drill collar and its contained sensors.
 When the unit is run in the “slick” mode it can, in the case of a horizontal
well, certainly ride on the bottom of the hole.
 an interesting feature of LWD
 As the drill collar is rotated, data can be acquired from multiple azimuths
around the borehole, something not often achievable with a wireline.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
26

27. An LWD device
An LWD device
containing a neutron
and density
measurement.
The panel on the left
shows the tool with
clamp-on wear bands so
that the diameter is
close to that of the drill
bit.
In the right panel the
tool is shown in the
“slick” mode.
Courtesy of Schlumberger
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
27

28. difference between
LWD and wireline logging
Diameter Size
Unlike wireline tools that are generally of a standard
diameter, many of the LWD tools come in families of sizes
(e.g., 4, 6, and 8 in.).
This is to accommodate popular drilling bit sizes and collar sizes
since the LWD device must conform to the drilling string.
Another difference between LWD and wireline logging
arises from the rate of drilling which is not an entirely
controllable parameter.
Since there is no simple way to record depth as the data are
acquired, they are instead acquired in a time-driven mode.
This results in an uneven sampling rate of the data when put
on a depth scale.
Surface software has been developed to redistribute the timesampled data into equally spaced data along the length of the
well.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
28

30. Reservoir Rock
Porosity
Clay contamination (Clean or contain clay)
 The presence of clays can affect log readings as well as have a very
important impact on the permeability
Rock consolidation (consolidated or unconsolidated)
 This mechanical property will influence the acoustic measurements
made and have an impact on the stability of the borehole walls as
well as on the ability of the formation to produce flowing fluids.
formation type (homogeneous, fractured, or layered)
 The existence of fractures, natural or induced, alter the
permeability significantly.
 In layered rocks the individual layers can have widely varying
permeabilities and thicknesses that range from a fraction of an inch
to tens of feet. Identifying thin-layered rocks is a challenge.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
30

31. Reservoir Fluid
Fluid Saturation (hydrocarbons or brine)
Fluid phase (liquid or gas hydrocarbons)
This can be of considerable importance not only for the
ultimate production procedure
but also for the interpretation of seismic measurements, since gasfilled formations often produce distinct reflections.
Although the nature of the fluid is generally inferred
from indirect logging measurements,
there are wireline devices which are specifically designed to
take samples of the formation fluids and measure the fluid
pressure at interesting zones.
structural shape of the rock body
This will have an important impact on the estimates of
reserves and the subsequent drilling for production.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
31

32. Well logging roles
Well logging plays a central role in the successful
development of a hydrocarbon reservoir.
Its measurements occupy a position of central
importance in the life of a well, between two
milestones:
the surface seismic survey,
which has influenced the decision for the well location, and
the production testing.
The traditional role of wireline logging has been
limited to participation primarily in two general
domains:
formation evaluation and completion evaluation.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
32

33. The goals of formation evaluation
the presence of hydrocarbons (oil or gas)
 in formations traversed by the wellbore
The depth of formations
which contain accumulations of hydrocarbons
fractional volume available for hydrocarbon in the
formation
porosity
Saturation (hydrocarbon fraction of the fluids)
the areal extent of the bed, or geological body
falls largely beyond the range of traditional well logging
producible hydrocarbons
determination of permeability
Determination oil viscosity
often loosely referred to by its weight, as in heavy or light oil
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
33

34. Formation evaluation
A number of measurement devices and interpretation
techniques have been developed. They provide, principally,
values of porosity and hydrocarbon saturation,
 as a function of depth, using the knowledge of local geology and
fluid properties that is accumulated as a reservoir is developed.
Because of the wide variety of subsurface geological
formations, many different logging tools are needed to give
the best possible combination of measurements for the rock
type anticipated.
Despite the availability of this rather large number of
devices, each providing complementary information, the
final answers derived are mainly three:
 the location of oil-bearing and gas-bearing formations,
 an estimate of their producibility, and
 an assessment of the quantity of hydrocarbon in place in the
reservoir.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
34

35. completion evaluation
The second domain of traditional wireline logging is
completion evaluation.
This area is comprised of a diverse group of
measurements concerning
cement quality,
pipe and tubing corrosion, and
pressure measurements,
as well as a whole range of production logging services.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
35

37. Measurement types
the purpose of well logging is to provide
measurements which can be related to the volume
fraction and type of hydrocarbon present in porous
formations.
Measurement techniques are used from three
broad disciplines:
electrical,
nuclear, and
acoustic.
Usually a measurement is sensitive either to the
properties of the rock or to the pore-filling fluid.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
37

38. measurement of
electrical conductivity
The first technique developed was a measurement of electrical
conductivity.
A porous formation has an electrical conductivity which depends
upon the nature of the electrolyte filling the pore space.
 Quite simply, the rock matrix is nonconducting, and the usual saturating
fluid is a conductive brine.
 Therefore, contrasts of conductivity are produced when the brine is replaced
with nonconductive hydrocarbon.
Electrical conductivity measurements are usually made at low
frequencies.
 A d.c. measurement of spontaneous potential is made to determine the
conductivity of the brine.
Another factor which affects the conductivity of a porous
formation is its porosity.
 to correctly interpret conductivity measurements as well as to establish
the importance of a possible hydrocarbon show,
 the porosity of the formation must be known.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
38

39. nuclear measurements
A number of nuclear measurements are sensitive to the porosity
of the formation.
The first attempt at measuring formation porosity was based on
the fact that interactions between high-energy neutrons and
hydrogen reduce the neutron energy much more efficiently than
other formation elements.
a neutron-based porosity tool is sensitive to all sources of
hydrogen in a formation, not just that contained in the pore
spaces.
 This leads to complications in the presence of clay-bearing formations,
 since the hydrogen associated with the clay minerals is seen by the tool in the
same way as the hydrogen in the pore space.
As an alternative, gamma ray attenuation is used to determine the
bulk density of the formation.
 With a knowledge of the rock type, more specifically the grain density,
it is simple to convert this measurement to a fluid-filled porosity value.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
39

40. nuclear measurements (Cont.)
The capture of low-energy neutrons by elements in the formation
produces gamma rays of characteristic energies.
 By analyzing the energy of these gamma rays, a selective chemical
analysis of the formation can be made.
 This is especially useful for identifying the minerals present in the rock.
 Interaction of higher energy neutrons with the formation permit a direct
determination of the presence of hydrocarbons through the ratio of C to O
atoms.
Nuclear magnetic resonance, essentially an electrical
measurement, is sensitive to the quantity and distribution of free
protons in the formation.
 Free protons occur uniquely in the fluids, so that their quantity provides
another value for porosity.
 Their distribution, in small pores or large pores, leads to the
determination of an average pore size and hence, through various
empirical transforms, to the prediction of permeability.
 The viscosity of the fluid also affects the movement of the protons
during a resonance measurement, so that the data can be interpreted
to give viscosity.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
40

41. Acoustic measurements
 formation porosity and lithology :
 Acoustic measurements of compressional and shear velocity can be related to
formation porosity and lithology.
 formation impedance:
 In reflection mode, acoustic measurements can yield images of the borehole
shape and formation impedance;
 integrity of casing and cement:
 analysis of the casing flexural wave can be used to measure the integrity of
casing and cement.
 formation permeability:
 Using low frequency monopole transmitters, the excitation of the Stoneley wave
is one way to detect fractures or to generate a log related to formation
permeability.
 Techniques of analyzing shear waves and their dispersion provide
important geomechanical inputs regarding the near borehole stress
field. These are used in drilling programs to avoid borehole break-outs
or drilling-induced fractures.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
41

42. well logging interpretation
The one impression that should be gleaned from
the above description is that logging tools
measure parameters related to
but not the same as those actually desired.
It is for this reason that there exists a separate
domain associated with well logging known as
interpretation.
Interpretation is the process which attempts to combine
a knowledge of tool response with geology, to provide a
comprehensive picture of the variation of the important
petrophysical parameters with depth in a well.
Fall 13 H. AlamiNia
Well Logging Course: An Overview of Well Logging
42

43. 1. Ellis, Darwin V., and Julian M. Singer, eds. Well
logging for earth scientists. Springer, 2007.
Chapter 1