Echometer Company
Model – M Manual
Phone: (940) 767-4334
5001 Ditto Lane
Page
21
Fax: (940) 723-7507
Wichita Falls, Texas 76302, U.S.A.
E-Mail:6 - Problem Wells
Obtaining a good record is made more difficult by excessive surface vibrations, excessive down-hole noise from gaseous
liquid columns, improper wellhead connections, dirty microphone and electrical connections, or low casing pressure.
Excessive surface vibrations and downhole noise should be reduced as much as possible. The gain controls permit an actual
measure of extraneous noise as described in Section 4.
Any well venting gas to the atmosphere, venting gas to the flow line or using casing gas to operate an engine, will have a
gaseous liquid column if liquid exists above the pump or formation. The amount of liquid present in a gaseous liquid
column can be determined by a casing pressure build-up test. Another technique is compression of the gaseous column with
casing pressure to determine the gaseous column gradient. Additional information is presented in the papers "Producing
Bottom Hole Pressures" and "Acoustic Foam Depression" in the appendix. Gaseous columns caused by gas bubbling
through oil cause excessive down-hole noise and can be a problem in obtaining clear records of deep collars and liquid
levels. Increasing the casing pressure by closing the flow line-casing valve will generally result in much improved signals.
The pressure in the gas gun volume chamber may have to be increased to the maximum so as to increase the signal to noise
ratio.
Whenever there are doubts that the correct liquid level signal has been identified the best way to differentiate it from other
signals (such as signals from liners, paraffin rings, or liquid influx from perforations) is to cause the liquid level to move.
The liquid level signal is the only signal that can move in a well and such movement identifies the liquid level. A high fluid
level can be depressed by increasing the casing pressure. An increase of 10-psi in the casing pressure will depress a gas-free
liquid level by approximately 30 feet. The liquid level will rise when a producing well is shut down. The rate of fill-up will
vary with the productivity of the well and the annular volume. A Rate of Fill-up chart is presented in the appendix and may
be used to estimate the amount of time required for liquid level rise. Note also that this chart may be used to estimate the
production rate from a well by shutting in the well and measuring the change in fluid level as a function of time, then using
the chart to estimate the production rate.
If a chart shows numerous "kicks" which are difficult to interpret, the shot should be repeated and the new chart compared
with the first recording. All "kicks" should be duplicated on each chart. Signals that are not duplicated correspond to stray
noises and other random signals. The source of these noises should be identified so as to eliminate them as described above.
The effect of casing pressure on signal quality is very important. Stronger signals are returned in high-pressure wells. It is
especially difficult to obtain good recordings in deep wells with the casing pressure near or below atmospheric pressure.
On rare occasions, paraffin deposits, scaling, dirty tubing or other conditions can result in additional down-hole signals,
which make it difficult to count collars or to determine the fluid level depth. In extreme cases it may be necessary to clean
the tubing and casing to remove the foreign material.