SYSTEM AND METHOD FOR ULTRASONICALLY TREATING LIQUIDS IN WELLS AND CORRESPONDING USE OF SAID SYSTEM

Use of an ultrasonic transducer and a system and method for treating liquids in wells

The invention relates to the use of an ultrasonic transducer, to a system for treating liquids in wells and to a method for treating liquids in such wells according to the preamble of the independent patent claims.

It is known to treat liquids in wells such as gas, oil or water wells with ultrasonic energy in order to reduce the viscosity of the liquid without the use of chemical reagents or steam genera^¬ tors. Such use of ultrasonic energy e.g. has been disclosed in WO 2005/090746A1, WO 93/11338 or US 6 973 972. The effect of re^¬ duction of viscosity is due to cavitation effects induced in the liquid by ultrasonic vibrations.

All these known solutions, however, have certain drawbacks. In particular, there are problems in context with transmission of ultrasonic energy to bore wells over relatively high distances which typically may be greater than several kilometres. Also, known devices have a poor efficiency.

It is therefore an object of the present invention to overcome the drawbacks of the prior art, in particular to provide a sys^¬ tem and a method for treating liquids in gas, oil or water wells which can be used also in deep wells and which has a high effi^¬ ciency for treating the liquid, in particular for reducing its viscosity .

According to the invention, these and other objects are solved with the use of an ultrasonic transducer, a system and a method for treating liquids according to the independent patent claims. It has been found that the use of an ultrasonic transducer with a resonator connected thereto where at least one end of the resonator is connected to a front surface of the transducer at the point of longitudinal oscillation maximum and where the length of the resonator is tuned to an integral multiple of a half acoustic length of the longitudinal oscillation of the transducer is particularly efficient for treatment of liquids in wells such as gas, oil or water wells. Such resonators are known per se in the art e.g. as shown in EP 44 800 A2, the content of which is incorporated herein by reference.

According to a preferred embodiment the resonator is tubular or a solid round rod. It is, however, also conceivable to have non tubular resonators such as resonators with a polygonal cross section or - depending on the shape and size of the well to be treated - resonators with an overall conical shape or resonators with a wave like outer shape. However, care should be taken that the resonator is properly tuned to the resonance frequency of the transducer.

In particular, an ultrasonic transducer with a resonator is used, where the transducer is additionally provided with a means for adapting the power to the impedance, in particular an impedance matching transformer for up converting the voltage of an incoming ultrasonic signal. In case of transmission of ultra^¬ sonic energy over relatively large distances, e.g. over cables having a length of more than 3km, high losses will occur in the cable. With this matching transformer the energy supplied to the transducer is maximum by adaptation to the impedance of the cable and the device formed by the transducer with the resonator.

Accordingly a further aspect of the invention is directed to a system for treating liquids in gas, oil or water wells. The sys- tern comprises an ultrasonic treatment device. The ultrasonic treatment device has a transducer with a resonator connected thereto. At least one end of the resonator is connected to a front surface of the transducer at the point of longitudinal os^¬ cillation maximum. The length of the resonator is tuned to an integral multiple of half an acoustic length of the longitudinal oscillation fed from the transducer to the resonator. According to the invention, the system comprises a generator for generating ultrasonic power. The signal are generated at a —relatively high voltage. The system further comprises a long cable for connecting the generator to the treatment device. The device fur^¬ ther comprises means for adapting the generator to the impedance of the cable, the transducer and the resonator, in particular a matching network transformer to transfer a maximum of generator power to the transducer in the well. In a preferred embodiment the resonator is tubular. Other shapes are possible depending on the use.

According to a further preferred embodiment the transformer or the matching impedance network adapting means is directly at^¬ tached to the tubular resonator. Therewith, one integral device can be formed which easily can be placed in a well, e.g. by at^¬ taching it to a mechanical cable. The matching transformer is integrated in the device so that there is no need for additional connectors or cables which could be damaged during use. Typi^¬ cally the cable has a length of more than 3km, preferably around 6 to 8km.

Preferably, an ultrasonic frequency of 5 to 25kHz with a voltage of upto 2kV will lead to the transducer in the well.

According to a further preferred embodiment of the invention, there is provided a set of different resonators having different shapes which can be chosen depending from the geometry of the well or depending from the composition of the liquid to be treated. Typically, the set comprises at least two resonators having a different shape, preferably around eight different sizes and/or shapes.

The invention will now be explained in more detail with reference to the drawings which show:

Figure 1 a schematic overview of a device according to the in^¬ vention,

Figure 2 an enlarged view of the treatment device as shown in figure 1 and

Figure 3 a set with three treatment devices having different shapes .

Figure 1 schematically shows an ultrasonic treating device 1 ar^¬ ranged in a bore well B. The ultrasonic treatment device 1 sub^¬ stantially consists of a resonator 2, a transducer 9 and a matching transformer 10. The transducer 9 is attached to one end of the resonator. The transformer 10 is integrally attached to the resonator 2 e.g. by welding or through screw connections. A long cable 11 is connecting the treatment device 1 and in par^¬ ticular its transformer 10 with an ultrasonic generator 5. The ultrasonic generator 5 is a generator basically known to a skilled person and generating ultrasonic energy with a frequency of approx. 20kHz and with a maximum voltage/amplitude of 2kV. The cable 11 typically has a length up to 7km. In view of the high length of the cable, the transformer 10 is used to up con^¬ vert the amplitude of the incoming signal. The transformer is designed in such a way as to adapt the vibrating amplitude in the transducer to create a high cavitation on device 1 for the treatment .

The treatment device 1 is shown in more detail in figure 2. The treatment device 1 has a tubular resonator 2. The open ends of the tubular resonator 2 are closed with an acoustic transformer 3 and an acoustic transformer piece 4. Attached to the front end formed by the transformer piece 4 there is arranged a piezoelec^¬ tric transducer 9. These parts of the treatment device are formed substantially identically as the one shown in EP 44 800 A2. In particular, the length of the device is adapted to the wave length of operation and to the resonance frequency of the transducer 9. Typically, the length of the resonator corresponds to an integer multiple of half a wave length (λ/:2) .

The transformer 10 is arranged in a metal casing which is at^¬ tached to the resonator 2 through mechanical connections such as welds or screws. In operation, the resonator 2 is generating ultrasonic waves which are radially distributed around the resona^¬ tor. Because of cavitation in the fluid, the viscosity of the fluid, in particular of oil is reduced.

Depending on the specific circumstances, other resonators may be used. In particular, the resonator may be formed of a rod (not hollow) or may have a rectangular or other polygonal cross section. Also, it is possible to use two transducers arranged on both sides (seen in the axial direction) of the resonator in order to have a "push-pull" operation. As schematically shown in figure 3, depending on the specific requirements, other shapes of resonators 2 can be used e.g. conically shaped resonators or resonators having a wave like outer surface. In the embodiment as shown in figure 3, all resonators have a round cross section in plane perpendicular to the axis.