SU189164A1 - ACOUSTIC INSULATOR - Google Patents

Description

In ultrasonic (acoustic) logging of wells, one of the necessary elements in the wellbore is the acoustic isolator, which serves to absorb elastic signals propagating from the radiator to the receivers directly along the material of the probe. The lack of effectiveness of the isolator can lead to the appearance of false signals in the first entries, which makes it impossible to perform well without any logging.

The basic requirements for an acoustic isolator are as follows: 1) the isolator must have a low velocity of propagation of elastic waves (at least less than the velocity of the waves in the drilling fluid, i.e. less than 1500 m / s; 2) the insulator must have a high absorption coefficient of elastic waves in order to attenuate as much as possible all the waves passing through the probe.

Various insulator constructions are known both in the Soviet Union and abroad. Various types of rubber insulators, insulators in the form of curved metal plates, insulators of chain connections, insulators with metal filter weights, etc. are used. Most of these insulators have a flexible or semi-rigid construction, and all of them give

the ability to place inside only a few electrical conductors necessary to transmit various signals from the probe elements, separated by an insulator. Therefore, such insulators have the following disadvantages:

1) the semi-rigid structure creates the possibility of the probe bending in the well, which results in erroneous values of the measured values (for example, elastic wave velocities);

2) a similar result is caused by stretching the insulator under the proper weight of the probe and the weight of the weight-weight of the gel, as well as the insulator under high pressure, which changes the distance between the transducers, in this case the errors are systematic;

3) sufficiently strong bends of the probe during operation and transportation cause damage to the current-carrying conductors passing inside the insulator.

4) to accommodate the electronic circuit it is necessary to have a special container,

which significantly increases the size and weight of the probe; 3 6) the flexible probe creates inconvenience in handling and requires the use of special devices for its non-transport and storage. In order to increase the coefficient of waveform, reduce the rate of unrau-5 wave propagation and ensure rigidity of the structure, the isolator is made in the form of a metal pipe having internal and external grooves located at certain intervals on the outer and inner sides, and covered with a layer of material with high coefficients {) by the absorption of ultrasound. FIG. 1 shows an acoustic isolator; in fig. 2 shows a diagram of Kaiiav's rationalization in the pipe and shows the path of the acoustic wave-15; in fig. 3 - records of acoustic waves. In connection with the basic features of ultrasound logging, the distance between the transmitter and the receivers in the baseline 20 should be about 1-3 meters. The design of the isolator allows the spacer to use this space for the electrical circuit or other necessary devices. , 25 whereas in existing zoids this distance is occupied by an acoustic insulator. The insulator is a metal pipe / with a thin transverse 30 caia 2, located on the outer and inner surface along the entire length of the pipe through certain intervals. From above, the pipe is covered with a layer of rubber or other soft material 3. Each of these 35 elements in the insulator performs certain functions in the insulator. The metal tube gives the zoid sufficient rigidity and allows the necessary elements of electronic circuits or other devices to be positioned externally.40 Each slit in the tube is the boundary of reflection and scattering. It causes part of the elastic energy to be reflected back, and the other part to bypass the slot in the form of a diffracted wave. Such a process is repeated many-five times over a BceiM set of slots. which leads to a significant attenuation of the wave. The rubber covering the pipe performs 50, the role of an absorber both as direct volpas that propagate through the pipe from the radiator and as waves that are reflected on each of the slits. Different muds of the will can spread across the insulator: longitudinal, 55 transverse, surface, bending, etc. The insulator must absorb all these waves well. It is especially important that the speed of the longitudinal will was sufficiently small. The fact that in the present isolator a pro-60 longitudinal wave bypasses its path along each of the slots leads to an increase in the propagation of waves along the probe. Such an apparent propagation speed (V) of the longitudinal wave along the zoid can be calculated by the following approximate formula y - (- -. I where A is the depth of the slots, /, is the distance between the slots, V is the velocity of the elastic wave in the metal It can be seen from the formula that it is easy to reduce the wave propagation speed along the metal pipe by even 3-4 times. Thus, if the pipe is made of steel, the speed of a longitudinal wolf in which is 5500 m1s, then the speed of propagation of the longitudinal wave of the probe can easily be reduced to 1200 -1500 w / ce / s, in addition, so and the system (rugged rubber-coated pipe) is a low frequency filter. Thus, the spectrum of the will passing through the insulator is found in the low-frequency region, where it can be easily suppressed by frequency filtering in amplifiers. In Fig. 3, a , b illustrates the effect of reducing the speed of the wave along the probe by simulating an aluminum plate with a length of 35 / mJ, a width of 5 cm and a thickness of 7 mm was taken as a model. At one end, the plastium was reinforced with a segateta salt emitter, and a similar receiver moved along the surface of the model with an air gap 2 cm. In FIG. 3, and the records made when moving the receiver on a continuous nlastin are given. The first phase of the longitudinal wave shows a speed of 5580 m / s. It can be seen that the damping of the waves is practically absent, FIG. 3, b are shown below along the profile, which was passed through a model with slits 2.5 mm deep, propylene with mm sutures. The first phase of iris follows this at a speed of 2350 m / s, i.e., almost 2.5 times slower. FIG. 3 (e) illustrates the effectiveness of the described type of insulator, which is compared with the efficiency of a pure rubber insulator, which is currently considered the best. FIG. 3, the records of the waves along the profile traversed along the surface of the plastia cut from soft vacuum rubber are presented. Clearly noticeable strong damping of all these waves. At the same time, the most intense of all waves decreases in amplitude by a factor of 7 at a distance of 30 cm. In FIG. 3, a similar profile is shown in the case when there is a solid aluminum plate under the rubber (imitation of a whole pipe). Acoustic contact between the rubber and the metal was created by castor oil. In this case (with the same initial wave amplitude), a rather intense high-velocity wave propagating to the metal, which slowly decays, is recorded in the first entries. FIG. 3, e shows the profile when under the same rubber there is a similar aluminum plate having slots 2.5 mm deep at intervals of 5 mm. As can be seen, the wave attenuation is 7 times, which occurs in rubber after 30 cm (see Fig. 5, b), here it is reached only in 8 cm, i.e. almost 4 times faster. At a distance of 30 cm but compared with FIG. 5, 8 and 5 g are practically absent here. 5 10 Subject of the Invention Acoustic isolator for an ultrasonic logging well borehole, characterized in that, in order to increase the coefficient of extrusion, reduce the speed of propagation of elastic waves and ensure the rigidity of the structure, it is made in the form of a metal pipe having transverse grooves with and the inner sides, spaced at regular intervals, and covered with a layer of material with a high absorption coefficient of ultrasound.

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