Echometer Company
Model – M Manual
Phone: (940) 767-4334
5001 Ditto Lane
Page
20
Fax: (940) 723-7507
Wichita Falls, Texas 76302, U.S.A.
E-Mail:5 - Interpretation
In an average well, the following events will be recorded on the chart: a kick will show the initial blast. A series of
small kicks will indicate the tubing collars and then the liquid level kick will be recorded. If the chart is allowed to
continue to run, another kick will often occur after the liquid level kick at twice the time of the first reflected liquid
level kick. This is a signal that corresponds to the pulse traveling from the gun to the liquid level and then to the
surface where it is reflected by the wellhead back down the well and is again reflected by the liquid interface back
to the surface. In shallow and in high pressure wells there may be numerous other reflections from the liquid level.
These are known as "multiples" of the pulse. Since all these signals have traveled the same distance at the same
speed the distance (time) from the initial blast to the first liquid level reflection will be equal to the distance (time)
between the first liquid level kick and the second reflected level kick. Multiple liquid level reflections on very
shallow liquid levels, which are 20 to 60 ft from the surface, can be misinterpreted as collar reflections.
The normal chart has a kick at the start of the trace which corresponds to the initial pressure pulse, a series of small
evenly spaced kicks indicating the collar signals and a large kick indicating the liquid level. On some charts the
collars can be distinguished from the beginning of the chart to the liquid level signal and all the collars can be
counted. The most accurate procedure is to use the eleven point dividers and to mark off groups of ten collars
directly on the chart. On other charts the collars cannot be distinguished clearly all the way from the beginning to
the liquid level reflection. In these cases it may be convenient to repeat the test trying to improve the signal to noise
ratio so as to be able to count a large percentage (better than 60%) of the collars in the well. In these cases it is
necessary to count the collars to the last discernible collar reflection signal and then extrapolate the count to the
liquid level, using the eleven point dividers set on the last collar spacing. The total number of collars counted
multiplied by the average tubing joint length results in the depth to the liquid level. This assumes that the range of
tubing joints is similar for all tubing in the well. This procedure may not be used if there are significant differences
in the lengths of tubing joints. Alternative methods to determine the depth to the fluid level are discussed in the
following section.
On both channels, the direction of kick indicates enlargements and reductions in the cross sectional area of the
annulus (or internal diameter of pipe if shooting down tubing). For an explosion signal, objects which reduce the
cross sectional area of the annulus result in compression reflections and are recorded as downward kicks when the
top of the chart is at the left of the operator. Such objects would be liners, tubing anchors, paraffin deposits or the
liquid level. Conditions that increase the area of the annulus result in rarefaction reflected waves and are recorded
as upward kicks. Such conditions include perforations, "shot" holes, parted casing, parted tubing and the end of the
tubing casing annulus. If an implosion pulse is used, then the responses will be reversed from those of an explosion
pulse.
Please refer to the appendix where several examples of traces corresponding to various wells and different cases of
signals are presented.
For the explosion pulse the liquid level is recorded as a downward kick. If the liquid level is 20 feet or so in a
"shot" hole, then the signal would first deflect upwards, then down as the sound wave is reflected from the liquid
level. Recording the liquid level below a liner will show a downward kick at the liner and a downward kick at the
liquid level then an upward kick if the recorder is still running. The upward kick corresponds to the signal
generated at the liner by the wave which was reflected at the liquid level and which is returning to the surface.
When the wave passes from the narrow liner to the larger casing a portion of the wave is converted to a rarefaction
pulse, which then travels down to the liquid level and then to the surface where it is recorded.