Page 233 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2

202 Reservoir Engineering

1. Casing collars.
2. Areas of corroded pipe.
3. Perforations.
4. Breaks or cracks in the pipe.

This tool only records if corrosion has occurred on the pipe, not whether it
is currently taking place. It does give an indication of casing quality and integrity
without removing the pipe from the hole. The principle behind this tool is the
same as the magna flux device used to detect flaws in metals in a machine shop.

Electrical Potential Logs. Similar in some respects to an SP log, this tool
measures the potential gradient of a DC current circulating through a string of
casing. This current is applied to provide the casing with cathodic protection
thereby preventing casing corrosion; any deviation from a negative field suggests
that the pipe is not receiving proper protection and is probably being corroded.
Combined with an electromagnetic inspection log, areas currently undergoing
corrosion as well as having a relative amount of damage can be determined
with ease.

Borehole Televiewers. This tool incorporates an array of transmitters and
receivers to scan the inside of the casing. The signals are sent to the surface
where they are analyzed and recorded in a format that gives a picture of the
inside of the casing. Any irregularities or cracks in the pipe are clearly visible
on the log presentation. This allows engineers to fully scan older pipe and get
an idea of the kind and extent of damage that might not otherwise be readable
from multifinger caliper, electromagnetic inspection, or electrical potential logs.
The main drawback to this device is that it must be run in a liquid-filled hole
to be effective.

Production Logs. Production logs are those devices used to measure the nature
and behavior of fluids in a well during production or injection. A Schlumberger
manual [221] summarizes the potential benefits of this information:

1. Early evaluation of completion efficiency.
2. Early detection of disturbances which are not revealed by surface measure-
ments (i.e., thief zones, channeled cement, plugged perforations, etc.).
3. Detailed information on which zones are producing or accepting fluid.
4. More positive monitoring of reservoir production.
5. Positive identification of encroachment, breakthrough, coring, and mechan-
ical leaks.
6. Positive evaluation of injection efficiency.
7. Essential guidance for remedial workover and secondary or tertiary recovery
projects.

The reader is referred to the Schlumberger volume [221] on production log
interpretation for examples of various cased-hole-log situations. It is still free
upon request .
The types of logs run include:

1. Temperature
2. Manometer and gradiomanometer
3. Flow meters
4. Radioactive tracers