Abstract
Sealing of new wells, and the increasing need of plug
and abandonment (P&A) of old wells, has triggered
research and development of new methods for saving
time at this operation. Shale has proven to seal off the
annulus in longer well sections; however, the detection
and qualification of the sealing ability can still be
improved. As a response to this, a laboratory setup has
been built to perform pressurized measurements on
shale cores. The laboratory setup consists of a steel
casing inside a vessel, where the tool is inside the casing
and locked at a rotation board at top for steadily handling
the logging procedure. The measurements are carried
out using the pulse-echo method with a 5MHz focused
transducer, which is around 20 times lower than the
center frequency used when logging in the field. The
setup is downscaled approximately 20 times compared
to a scenario using a 9 5
8 inch casing, so the frequency
was picked to simulate a real well. The casing can be
cast with cement under pressure to differentiate good
and bad bonding, or the vessel can be filled with a rock
sample, a second casing, or any fluid.
A detailed study of this new laboratory setup has been
performed. The focusing of the transducer and the high
frequency is used to make the laboratory setup realistic
and similar as in the field, however, the high frequency
also increases the resolution for improved evaluation of
debonding and determination of the material behind the
casing. The laboratory setup has been consistently tested
with different materials behind the casing, and the
results has been compared and verified with numerical
simulations. The laboratory results and the numerical
simulations show good correlation. Further, the
sensitivity of the laboratory setup has been investigated,
and different attenuation parameters are used to develop
a model for quantifying the effect of the different
artefacts. Observations have shown how the eccentricity
of the tool, varying casing conditions, and the distance
of the transducer relative to the casing affects the
decaying reverberation ringdown.
and abandonment (P&A) of old wells, has triggered
research and development of new methods for saving
time at this operation. Shale has proven to seal off the
annulus in longer well sections; however, the detection
and qualification of the sealing ability can still be
improved. As a response to this, a laboratory setup has
been built to perform pressurized measurements on
shale cores. The laboratory setup consists of a steel
casing inside a vessel, where the tool is inside the casing
and locked at a rotation board at top for steadily handling
the logging procedure. The measurements are carried
out using the pulse-echo method with a 5MHz focused
transducer, which is around 20 times lower than the
center frequency used when logging in the field. The
setup is downscaled approximately 20 times compared
to a scenario using a 9 5
8 inch casing, so the frequency
was picked to simulate a real well. The casing can be
cast with cement under pressure to differentiate good
and bad bonding, or the vessel can be filled with a rock
sample, a second casing, or any fluid.
A detailed study of this new laboratory setup has been
performed. The focusing of the transducer and the high
frequency is used to make the laboratory setup realistic
and similar as in the field, however, the high frequency
also increases the resolution for improved evaluation of
debonding and determination of the material behind the
casing. The laboratory setup has been consistently tested
with different materials behind the casing, and the
results has been compared and verified with numerical
simulations. The laboratory results and the numerical
simulations show good correlation. Further, the
sensitivity of the laboratory setup has been investigated,
and different attenuation parameters are used to develop
a model for quantifying the effect of the different
artefacts. Observations have shown how the eccentricity
of the tool, varying casing conditions, and the distance
of the transducer relative to the casing affects the
decaying reverberation ringdown.