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Lecture items
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Compositions of the Uphole- Downhole
Instruments.
Field Operation (Data Acquisition, Processing
and Transmission)
Log Runs
Borehole Environment opposite a Permeable
Zone.
Structure of a Log head.
Recording Format
Images logs
Basic reservoir characteristics
Compositions of the UpholeDownhole Instruments.
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Uphole Instruments include the Logging Truck and the Rig. The
logging Truck mainly consists of mechanical Winches and ordinary
driving machine.
Downhole Instruments are represented by Cables and Sondes.
Sondes differ in function from measurement to another based on the
required physical property to be measured (GR , Resistivity, Neutron,
Sonic, Density, Magnetic, Thermal, etc)
Sonde normally consists of two main parts:
Sensor: It is an electronically complicated part used for picking the
required property. It is usually shielded with fibers in the modern
tools.
Cartridge: Surrounding the sensor in the modern tools and do three
functions:
* Powering the sensor to be ON/OFF .
* Processing the acquired data (First step of processing).
* Data transmission along cables to the up-hole instruments.
Modern Cable
Complicated
Sondes
Field Operation
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Data Acquisition (by Sondes)
 Data Processing (Three steps)
 Data Transmission (Two stages)
Data Transmission
Log Runs
Borehole Environment
When a hole is drilled into a formation, the
rock and the fluids in it (rock-fluid
system) are altered in the vicinity of the
borehole. A well’s borehole and the rock
surrounding it are contaminated by the
drilling mud, which affects logging
measurements. Figure 1 is a schematic
illustration of a porous and permeable
formation which is penetrated by a
borehole filled with drilling mud.
Borehole
Environ
ment
Borehole Environment
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dh – hole diameter
di – diameter of invaded zone (inner boundary; flushed
zone)
dj – diameter of invaded zone (outer boundary; invaded
zone)
Drj – radius of invaded zone (outer boundary)
hmc – thickness of mudcake
Rm – resistivity of the drilling mud
Rmc – resistivity of the mudcake
Rmf – resistivity of mud filtrate
Rs – resistivity of shale
Rt – resistivity of uninvaded zone (true resistivity)
Rw – resistivity of formation water
Rxo – resistivity of flushed zone
Sw – water saturation of uninvaded zone
Sxo – water saturation of flushed zone
Invasion
Profile
Invasion
Profile
Invasion
Profile
Annulus zone
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An annulus profile is often recorded on a log because it
rapidly dissipates in a well. The annulus profile is detected
only by an induction log run soon after a well is drilled.
However, it is very important to a geologist because the
profile can only occur in zones which bear hydrocarbons.
As the mud filtrate invades the hydrocarbon-bearing zone,
hydrocarbons move out first. Next, formation water is
pushed out in front of the mud filtrate forming an annular
(circular) ring at the edge of the invaded zone. The
annulus effect is detected by a relatively lower resistivity
values.
Structure of
a Log Head
Recording Formats
Recording Formats
Modern Formats
Image Logs
Basic reservoir characteristics
 Porosity,φ
(Total, effective, primary,
secondary and intercrystalline)
 Permeability (K) (Absolute, relative)
 Saturation (S) (Sw, Sxo, Sh, So, Sg,
Shr, Shm) and their interrelationships.
POROUS MEDIUM
STANDARD
REALITY
Various
pore
geometries with
different effective
path length
 Water
Saturation (Sw) is the fraction of
the pore space containing water
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Sw = Vw / f
 Porosity
is the volume of pores to the total
volume of rock
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φ = Vp / VR * 100 %