Summary
Ultrasound or a high-frequency (20 kHz to 100 kHz) pressure wave has been
used in diagnosis and treatments in different areas, such as: medicine,
dentistry, civil engineering, and many other industrial applications. In the
oil industry, there are applications (i.e., pipeline inspections, fluid
velocity measurements, etc.), but to the present, these applications in
formation stimulation have been incipient, and only a few lab and field test
experiences have been reported. Stimulation with ultrasound is not a common
operation offered by oil service companies. To visualize the real potential of
ultrasound in oil well stimulation, it is necessary to understand the wave
phenomenon, its properties, the parameters that define its behavior, and its
interaction with the propagation media. This basic knowledge and the
understanding of the different formation damage mechanisms are the keys to
comprehend the real potential and application window of the ultrasound in oil
well stimulation. This paper presents the theoretical basis of ultrasound and
wave phenomena that must be considered when considering stimulation with
ultrasound. Finally, some suggestions about the application window of this
technology are given.
Introduction
Ultrasound has been applied in many areas, such as diagnosis, quality
control, inspections, cleaning, etc. Industrial cleaning is achieved by flaking
out the particles with a mechanical action of the pressure waves (Fig. 1).
Usually, the piece is submerged in fluids inside a container with walls that
have ultrasonic sources. Clearly, there is a great difference with an
application for oil well stimulation, in which the source is running inside the
hole, and the cleaning area is around the source.
Each application has a particular frequency and power associated according
to the sample dimensions and the purpose. For example, the power and frequency
used for control echography in pregnant mothers are different than ones used in
muscular therapeutic treatments. In the first case, it is enough to detect an
echo with high resolution (higher frequencies). In the second case, energy is
required to be transferred to the tissue, but high resolution is not required
(lower frequencies). It is clear that the purpose and the propagation media
affect the ultrasound parameters, highlighting the importance to understand
which are the damage mechanisms in which ultrasound can be applied and vice
versa.
The advantage of applying ultrasound comparing with conventional stimulation
is that no invasion or external fluids are required. Ttherefore, fluid/rock
interaction analysis is avoided, and the placement as well as the associated
equipment and risky operation of handling high pressures at the wellhead is
also avoided. Additionally, ultrasound allows underbalance treatments without
shutting in the well.
Ultrasound cleaning is not a common tool offered by service companies in the
field. Only field tests in China and Russia have been reported with more
qualitative than quantitative information making these tests inconclusive.
Recent references about lab experiences and tool prototypes suggest the
potential of this technology. However, ultrasonic stimulation has little
understanding of the phenomena taking place in the porous media, and how the
waves are interacting with the matrix and the trapped particles. The parameters
for suitable cleaning with ultrasonic treatment are not well defined, and how
these parameters change while the wave is propagating in the porous media is
also not clear.
Power requirements for stimulation and effective penetration depend on the
elastic media (matrix), the radial geometry, and completion (i.e., either open,
gravel packed, or case hole). Wave phenomena as reflection,
transmission-refraction, diffraction, and interference must be considered;
otherwise, a successful application in Russia can be a failure in other places,
because change in one or more parameters considerably affects the wave.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
17 January 2007
- Meeting paper published:
15 April 2007
- Revised manuscript received:
10 April 2008
- Manuscript approved:
7 May 2008
- Published online:
2 March 2009
- Version of record:
26 February 2009
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