3. What is well Logging
Well log is a continuous record of measurement made
in bore hole respond to variation in some physical
properties of rocks through which the bore hole is
drilled
4. •Caliper tools measure hole size and shape.
•The simple mechanical caliper measures a vertical profile of
hole diameter.
•The more sophisticated geometry tools records two
simultaneous calipers and give an accurate borehole shape
and orientation.
Caliper Log
6. Schematic Caliper tool showing
the conversion of a mechanical
movement to an electrical signal
using a variable resistance
Function of the Tool:
•The mechanical caliper
measures variations in bore hole
diameter with depth.
• The measurements are made
by two articulated arms pushed
against the borehole wall.
•The arms are linked to the
cursor of a variable resistance.
Lateral movements of the arm is
translated into the movements of
the cursor along the resistance,
and hence variation in electrical
out put.
•The variations in output are
translated into diameter
variations after a simple
calibration.
7. •The Caliper Log is a tool for measuring the diameter and shape of
a borehole. It uses a tool which has 2, 4, or more extendable arms.
•In the 4 arm (dual caliper) tool, the two opposite pairs work together
to give the borehole diameter in two perpendicular directions.
•An example of a 4 arm tool is the Borehole Geometry Tool (BGT).
•This has 4 arms that can be opened to 30 inches (40 inches as a
special modification), and give two independent perpendicular
caliper readings.
•In the multi-arm tools, up to 30 arms are arranged around the tool
allowing the detailed shape of the borehole to be measured.
8. Various types of caliper
ƒMechanical Caliper -arm averaging
ƒUltrasonic Caliper -An Ultrasonic transducer scans around
the borehole walls, and the reflected travel time is converted
to the distance between the sonde and the wall.
Acoustic caliper – calculated from acoustic transit time and
velocity
10. 3D image of the ultrasonic caliper.
(From Schlumberger)
11. Presentation of the Caliper Logs: 1. in
ordinary format; 2. in differential
format; BS = Bit size
•The caliper log simply is a
measure of continuous value
of hole diameter with depth.
•The curve is traditionally a
dashed line.
•The horizontal scale may be
in inches of diameter or in
differential caliper, expressed
as increase or decrease in
hole diameter about a zero
defined by the bit size.
•The ordinary caliper log is
accompanied by a reference
line indicating bit size.
Caliper Log Presentation
12. •In a logging context, the greatest application of caliper data is in
environmental corrections to other logs that are sensitive to hole
size such as Natural gamma ray , Density, Neutron logs.
•Contributory information for lithological assessment.
• Indicator of good permeability and porosity zones (reservoir
rock) due to development of mudcake in association with gamma
ray log.
•Calculation of mudcake thickness, hmc = (dbit– dh)/2, where h
stands for the hole, in inches.
Uses of the Caliper log
13. •Selection of consolidated formations for wire line pressure tests,
recovery of fluid samples, for packer seating for well testing
purposes, and for determining casing setting depths.
•calipers can be used to center logging-tool strings.
•Open hole caliper data are used to estimate the volumes of gravel
and cement needed for well-completion planning.
