Echometer Company
Model – H Manual
Phone: (940) 767-4334
5001 Ditto Lane
Page 68
Fax: (940) 723-7507
Wichita Falls, Texas 76302, U.S.A.
E-Mail:
Acoustic Record 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 acoustic record 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 records the collars can be distinguished from the beginning of the shot to the liquid level signal and all the
collars can be counted. On other records 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 the
software extrapolates the count to the liquid level. 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.
The direction of kick of an echo signal, indicates enlargements and reductions in the cross sectional area of the
annulus (or internal diameter of pipe if shooting down tubing). Objects which reduce the cross sectional area of
the annulus result in compression reflections and are recorded as downward kicks. 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. It is important to select the correct
mode of pulse generation (Implosion or Explosion) by pressing the corresponding soft key, so that the displayed
polarity of the echoes will be consistent with the above description.
Please refer to the appendix where several examples of traces corresponding to various wells and different
cases of signals are presented.
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 record time is sufficiently long. 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.
Calculation of Bottomhole Pressures
Bottomhole pressure calculation in static and producing wells is described in technical papers and is facilitated
by the use of software, which is supplied with the Echometer Model H. Details of the calculation methods used
by the software are found in technical papers on the internet at
www.echometer.com
.
The BHP calculation program AWP2000 requires one of the following: Windows 9x, ME, NT, 2000 and XP, and
can be downloaded for free from the Echometer Web page,
www.echometer.com
.