Page 238 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2

Formation Evaluation 207

charts available from the various service companies. In general, this tool can
be used at flow rates as low as 20 barrels per day in monophase flow situations
(usually water). Polyphase flow raises this minimum to 300 barrels per day if
gas is present (i.e., oil and water) in 5 in. casing. This tool is used in wells
with hole diameters ranging from 5 '/s to 9 5/8 in.
Continuous Flowmeter. This tool is similar to the fullbore-spinner flowmeter
except that it can be applied to hole diameters between 3 '/4 in. and 6 5/8 in. 11
has a higher flow threshold (in barrels per day) and should be restricted to use
in monophase flow situations (i.e., waterfloods, high-flow-rate gas wells, and
high-flow-rate oil wells) [221]. It can be combined with a spinner flowmeter for
better flow measurements.
Packer F/owmeter. 'This is a small spinner-flowmeter with an inflatable packer
that can be used in small-diameter tubing (1 11/16 to 2 I/s in.) . It has an operable
flow range from 10 to 1,900 barrels per day an can be applied in low-flow wells
as long as measurements are made in the tubing at a sufficient distance above
the perforations. Flow measurements are related to volume of fluid flowing the
same way found with the other spinner flowmeters.
Radioactive Tracers. Radioactive tracers axe combined with cased hole gammaray
logs to monitor:

1. Fluid velocities in monophase fluid flow situations where flow velocity is
at or near the threshold for spinner flowmeters.
2. Fluid movement behind the casing or to locate channeling in the cement.
Fluid velocity is measured by velocity-shot analysis. A shot of radioactive fluid
is injected into the flow stream above two detectors located on a stationary
mammary tool. As the radioactive pulse moves down the hole, the amount of
time required to move past the two detectors is measured. This travel time is
then related to flow rate in the casing by:

B/D
spacing(in.) x l(ft) x -(dh - d,, )(in? ) x x 256.5 -
12(m.) 4 1M( in.' ) ft "m1n
q(B/D) =
l(min)
time( sec ) x -
60( sec)
(5-124)
where q is flow rate in barrels per day, the spacing between detectors is in in.,
the time between detector responses is in seconds, d,, is the hole diameter in
in., and dhd is the tool diameter in in.
The man limitation is that slippage and water-holdup factors seriously affect
the time reading so this technique cannot be applied in production wells.
Moreover, the production of radioactive material is not desirable; therefore, use
is mainly restricted to water- or gas-injection wells [221].
Fluid movement behind the casing can be measured with a timed-run radio-
active survey. A slug of radioactive fluid is introduced at the bottom of the
tubing, and movement is then monitored by successive gamma-ray log runs.
Unwanted flow up any channels in the cement can be easily determined and
remedial action taken. Again, this technique is mainly applied to water injection
wells to monitor flood operations and injection-fluid losses. Figure 5-128 is an
example of this type of application.