tishk international university engineering faculty

Tishk International UniversityEngineering FacultyPetroleum and Mining Department

Well Logging I

3rd Grade - Fall Semester 2021-2022

Lecture 2: Caliper Logs and Temperature Logs

Instructor: Frzan AliFrzan Ali Well Logging I 1

Content

• Caliper Tools

• Caliper Log Presentation

• Caliper Log Interpretations

• Uses of Caliper Logs

• Caliper Logging in Cased-holes

• Temperature Logs

• Uses of Temperature logs

• Borehole Temperature Corrections

• Resistivity Correction to Formation Temperature

Frzan Ali Well Logging I 2

Caliper Tool

• Caliper tools measure the size and shape of a borehole.

• It uses a tool which has 2, 4, or more extendable arms.

• The arms are linked to the cursor (indicator) of a variable resistance. The measurements are made by two articulated arms pushed against the borehole wall.

• The arms can move in and out as the tool is withdrawn from the borehole, and the movement is converted into an electrical signal by a potentiometer.

• The simple mechanical caliper measures a vertical profile of borehole diameter with depth.


Caliper Tool

• The physical movement of arms on the tool is converted to a diameter measurement through electrical circuitry.

• The arms are intended to either keep the tool CENTERED in the borehole, or to push the tool against the borehole wall (CONTACT)


Caliper log Presentation

• The caliper logs are plotted in track 1 with the drilling bit size for comparison, Or as a differential caliper reading, (caliper value minus the drill bit diameter (Fig).

• The 4 arm (or dual caliper) tools are presented together, and that they are different indicating an oval hole.


Caliper Logs

The curve is traditionally a dashed line and usually plotted in track 1.

• The hole that has the same size (diameter) as the bit which drilled it, is called on gauge, and essentially indicates good drilling technique.

• In case of caved or washed out the zone (unconsolidated shale, salt …etc.) the diameter greater than the bit size.

• Calipers may show a hole smaller than bit size.

-If the log has a smooth profile, mud cake build up is indicated permeable zone.

-But if the profile is rugose, are probably sloughed, the zones of small holes will be "tight spots" it will be these points that tools stick or the bit gets stuck while being pulled out of the hole.


Caliper Logs

Figure shows a schematic hole with caliper information


Simple Caliper Interpretation

The table describes the main influences on caliper values.


Uses of the Caliper Log

The commoner uses of the caliper log are as follows:

1. The detection of the porous and permeable zones, and the determination of the mud cake thickness

2. Open-hole caliper data are used to measurement of the hole volume in order to estimate the volumes of gravel and cement needed for well-completion and casing planning.

3. Detection of consolidated, and in gauge sections for the scaling of packers for well testing. locating seats for packers (hydraulic seals used to isolate sections of the wellbore for flow-test purposes)

4. The correction of several log types for the effect of the bore hole, and of mud cake in order to obtain a precise interpretation.

5. Calipers can be used to center or eccenter logging-tool strings.

6. A guide to lithology.


Uses of the Caliper Log

• Calculation of mud cake thickness (hmc):

hmc= (dbit–dh)/2

where h stands for the hole, in inches.

• Measurement of borehole volume (Vh):

Vh= (dh2/2)+1.2%

in liters per meter.

• Measurement of required cement volume:

V. cement = 0.5 (dh2–d2casing) + 1%

in liters per meter.


Uses of the Caliper Log to interpret borehole breakouts

• Four-arm caliper tools (such as Schlumberger’s HDT, SHDT and OBDT) are commonly run to estimate the volume of cement required for casing. However, unprocessed oriented four-arm caliper logs can also be used to interpret borehole breakouts

• Four-arm caliper tools are commonly run in the hydrocarbon industry to obtain information about the formation (primarily strike and dip of bedding)


Common types of enlarged borehole and their caliper response


Caliper Logging in cased hole

Casing Inspection Logs: There are four commonly used techniques for the inspection of casing:

1. Cased-hole calipers

2. Flux-leakage tools

3. Electromagnetic phase-shift tools

4. Ultrasonic tools.


Cased-hole Calipers

• Multi-finger calipers are used to identify changes in casing diameter as indicators of wear and corrosion.

• They are also used to monitor casing deformation. They can have up to 80 spring-loaded feelers or fingers, depending on the nominal casing diameter

• Different multi-finger caliper tools can log casing sizes from 4 to 20 in. Smaller tools are available for tubing inspection.

• Measurements are taken many times per second for each finger, giving a typical spatial sampling interval of approximately 0.15 in. as the tool travels up the borehole.


Cased-hole Calipers

• A finger extends where it encounters a pit or hole and retracts where there is scale present or there has been partial collapse.

• A potential disadvantage is that the fingers can damage the casing, although modern electronic tools have a very low finger pressure to avoid this.

• The tool also indicates which finger is the one on the highest side of the well. Moreover, fingers can be grouped azimuthally.


Temperature Logs

• The Temperature Log is a tool for measuring the borehole temperature. Temperature sensors are attached to every tool combination that is run in a well for the measurement of the maximum temperature in the bottom of the well.

• Readings from several the thermometers attached to different tool combinations and run at different times are analyzed to give the corrected temperature at the bottom of the borehole (bottom hole temperature, BHT).

• The borehole temperature is an important parameter in the analysis of resistivity logs, the detection of fluid movement, the analysis of fluid pressures and the maturity of hydrocarbons.


Uses of Temperature Logs


Temperature Logs - Theory

Temperature in the sub-surface increases with depth. (geothermal gradient ).

Subsurface temperature: formation temperature (Tf) is very important in log analysis, because the resistivity of mud, mud filtrate, and formation water change with temperature.

Y= mx+ c

while: m= geothermal gradient, x= depth and c= surface temperature

Geothermal gradient = (𝐓2−𝐓1)/ (Z2−Z1 )

T2 and T1 are measured temperatures at the two depths of Z2and Z1respectively.

The resistivity of the different fluids (Rm, Rmf, Rw) can be corrected to the formation temperature, because with changing the temperature the mentioned resistivity will change.


Borehole Temperature Corrections

The actual temperature measured is that of the drilling fluid not the formation.

The drilling mud is circulated during drilling and prior to inserting the wireline tool. The cold drilling fluid invades the formation and cools it down very efficiently.

When the circulation of the drilling mud stops (for example, in preparation for the insertion of a wireline tool), the borehole gradually regains the true formation temperature.

This process is, an equilibrium may only be attained after several months after stopping the circulation of the drilling fluid.


Borehole Temperature Corrections

Hence, temperature measurements made during drilling (MWD and LWD) consistently underestimate the formation temperature because drilling mud is being circulated.

Temperature measurements made on wireline logs sometime after the drilling fluid circulation has stopped

Measurements of temperature made by wireline logs at increasing times after fluid circulation has stopped are closer and closer to the real formation temperature.


Horner Plot

• The most common method is the Horner plot to correct the logged BHT to real formation temperatures.

• The Horner method, plots the measured temperature (at a given depth) from each of several logging runs, against log (T/(t+T).

• The parameter t represents the length of time that the borehole was subjected to the cooling effects of the fluid (circulation ), and T represents the time after circulation that the borehole has had to partially reheat (since circulation stopped).

• This plot is a straight line that intersects T/(t+T)=1 at the formation temperature.


Horner Plot

• The table below gives the drilling, logging, and bottom hole temperature data for three tool combinations that were run in a single hole one after another.


The resistivity corrected to the formation temperature

There are two methods for the resistivity correction either by equation or chart:

1. Arp’s Formula: • Rft= R. Temp* (Temp + 6.77) / (Tf. + 6.77)

• Rft: Resistivity at formation temperature.

• R. Temp: Resistivity at another temperature.

• Temp: Temperature which at resistivity is recorded.

• Tf: Formation temperature.

2. Using the chart (Temperature –Salinity –Resistivity Chart).


The resistivity corrected to the formation temperatureA water sample with 5000 ppm salinity, its resistivity equal to 1 Ω. m at 100 F°;

• What will be its Resistivity at the temperature of 150 F°?


Summary

• Caliper Tools

• Caliper Log Interpretations

• Uses of Caliper Logs

• Temperature Logs

• Uses of Temperature logs


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