Echometer Company
Model – M Manual
Phone: (940) 767-4334
5001 Ditto Lane
Page
40
Fax: (940) 723-7507
Wichita Falls, Texas 76302, U.S.A.
E-Mail:USE OF RATE OF FILL-UP INFORMATION
If a well is shut down for ten minutes for surface connection work prior to a liquid level shot and the initial fill-up rate is
only 1.3 feet per minute, then the maximum error would be only 13 feet due to the shut-in time. However, if the fill-up rate
is 35 feet per minute, the maximum error could be as high as 350 feet.
The fill-up rate found in the chart is the initial rate at which liquid will fill the casing annulus. This rate decreases as the
pressure in the well bore approaches the static reservoir pressure. For example, if the static reservoir pressure is 1000 PSI,
the reservoir pressure will support approximately 2500 feet of liquid (assuming low casing pressure), so the fill-up rate
found on the chart would be within 10
o
/
o
for the first 600 feet or so. However, if the static reservoir pressure would support
only 900 feet of liquid, then the fill-up rate would be reduced to one-half by the time the well had filled with 600 feet of
liquid.
The rate of fill-up graph can be used to estimate the production rate of a well. A first fluid level depth measurement is
performed while the well is at normal producing conditions. Then, the well is shut down and the liquid level in the casing
annulus is allowed to rise. The height that the liquid rose and the amount of shut-in time is recorded. This data is used in
conjunction with the casing and tubing sizes to determine the production rate of a well. This procedure is more accurate in
wells that produce small amounts of gas up the casing annulus.
If the well is producing gas up the casing annulus, the rate of fill-up is not as predictable. Also, using the rate of fill-up to
estimate the production rate is not as accurate. A casing pressure build-up rate in excess of 1 PSI in three minutes indicates
that the casing annulus liquid contains a substantial amount of free gas and the fill-up data should be used with caution.