Echometer Company
Model – M Manual
Phone: (940) 767-4334
5001 Ditto Lane
Page
6
Fax: (940) 723-7507
Wichita Falls, Texas 76302, U.S.A.
E-Mail:Depth Calculation
In most cases, once a strip chart record has been obtained and the liquid level signal has been identified, the
operator must count the number of tubing collar reflections from the surface to the liquid level in order to calculate
its depth. The corresponding number of tubing joints, multiplied by the average joint length yields the distance to
the liquid level.
Other techniques are available for determining the liquid level depth. When other signals are identified on the
chart, such as those generated by gas lift mandrels, liner tops, tubing anchors or perforations, the known depth of
these anomalies can be used to calculate the depth to the deeper liquid level by the ratio of chart distance or
elapsed time. When the lengths of tubing joints vary considerably, so that an average joint length is not
representative, some operators placed an over-sized tubing collar (marker) to serve as a depth reference.
When the specific gravity or the composition of the gas in the annulus is known with some accuracy, then the
velocity of sound in the gas can be calculated. The acoustic wave round-trip travel time from the initial pulse to
the liquid level reflection is read directly from the strip chart, which displays timing marks. The round-trip travel
time is divided by two and multiplied by the acoustic velocity to calculate the depth to the liquid level.
Still another technique involves measuring the acoustic velocity of the gas by sampling the casing gun into a tube
of sufficient length to measure the velocity of sound in the gas by pulse testing. This technique is applicable only if
the well continuously vents gas from the annulus so that a representative sample of the gas sample obtained at the
top of the well will not be representative of the gas in the well.
The most common application of an acoustic liquid level instrument is to measure the distance to the liquid level in
the casing annulus of a well. However, it can also be applied to measurements inside tubing. Other applications
include determination of the distance to the mud or kill liquid level during drilling and work-overs. The acoustic
instruments can be used to measure the distance to any change in cross-sectional area inside pipe or in the annulus.