SU1111118A1 - Acoustic insulator - Google Patents

Abstract

ACOUSTIC INSULATOR FOR. acoustic logging devices made in the form of a steel helix, characterized in that, in order to increase its efficiency, as well as to simplify the design and manufacturing technology, the coils of the helix are interconnected by jumpers installed with a pitch chosen from a series of 2/3, 2 / 5, 2/7,. ,, turnover of spirogs. (/}

Description

; The invention relates to geophysical instruments designed for well testing using acoustic logging. An acoustic insulator made of two pipes is known, the pipe is also in black, with well-defined transverse grooves arranged in a checkerboard pattern, while the gap between the pipes and the grooves in them is filled with rubber C1. However, such an insulator practically does not attenuate and works towards the delay line. An acoustic insulator is also known. It consists of a steel cylindrical helix, inside of which sealed steel discs with an air cavity inside are located at a certain distance. These disks are bonded to each other and to a cylindrical helix of an elocride or silicon organic resin with a filler. In the insulator, the metal coil is made of a solid profile of rectangular section 2. However, the section area of the coil of such an insulator must be sufficiently large to provide the required axial rigidity, which leads to a decrease in acoustic attenuation. Acoustic waves propagate in the insulator along the epoxy resin with a filler at a speed of 24003500 m / s, which also impairs its sound insulation properties. The closest to the present invention is an acoustic isolator for downhole acoustic instruments, logging, made in the form of a steel helix with flat oval section. However, this insulator has a significant cross section of the helix, as a result of which its acoustic attenuation is small and equal to 24 dB / m. To increase the efficiency of the insulator, metal sleeves, separated by sound insulating sleeves, are put on it. The isolator has an axial strength of 200 kgf, which is insufficient for use in downhole tools. It is recommended to insert a cable into it. Its axial rigidity is very small, kgf / mm. With such a small axial stiffness, the measuring base and the transducer spacing can vary in the probe, which leads to unacceptable measurement errors of the time and amplitude parameters of the received signals. Such an insulator with a small axial stiffness on the acoustic carriage, necessary for the probes, of 2 m length, has practically no transverse rigidity and does not allow the instrument to be centered in the well. Flat-oval section, bushes, jTpoc and its fastenings complicate insulators and their manufacturing technology. Insulators tl, C 2 also have a complex structure and are not technological in production. The purpose of the invention is to increase the effectiveness of the acoustic isolator, simplifying the design and technology of its manufacture. The goal is achieved by the fact that in the acoustic insulator, made in the form of a steel spiral, the turns of the spiral are interconnected by jumpers installed with a step selected from a series of 2/3, 2/5, 2/7, ... turns of the helix. The drawing shows an isolator. In the isolator, the turns of helix 1 are connected by jumpers 2-4, installed through 2/3 turns of the helix. Acoustic isolator works as follows. The action of the acoustic isolator is based on the principle of elongation of the path of the elastic wave in a metal pipe. The elastic wave propagates along the turns of the spiral, which leads to an increase in the time of its run along the insulator. With the helix pitch h, the length of insulator 1, the average diameter dc, the increase in the path length of the acoustic insulator is expressed as (Jrdc) + h and the apparent speed of the propagating waves is determined by the expression: TTdc V.) + hz from where i / Vi - V where Vo is the wave propagation velocity in the material of the isolator; The 3-empirical coefficient takes into account that the elastic wave propagates through the turns of the spiral not along a helical line, but by multiple reflections from the spiral walls forming the turns of a cylindrical helix, which also causes the wave to attenuate in the insulator. With an average insulator diameter of 70 mm, an elastic wave propagation velocity in the insulator V 1200 m / s and an elastic wave velocity in the material of the insulator Vo 5500 m / s, the pitch of the turns of the cylindrical helix is 64 mm. The minimum width of bridges connecting the turns of the helix is chosen from the conditions of the axial strength of the insulator

b

(2)

n. t rrf ™

me b - jumper width, in mm;

P is the maximum axial force applied to the insulator, kgf; t is the wall thickness of the helix from. l torus, mm; , - yield strength, which

for alloy steels, 50 kgf / mm can be used; n is the number of jumpers per helix rotation, when jumpers are installed after 2/3 of the helix rotation n 1.5.

For an insulator made of a steel pipe t of 5.5 mm according to the drawing, with P 2000 kgf, we have b = 4.85 mm. Since the propagation velocity of the elastic wave in steel Vo 5500 m / s and the upper frequency limit of the transducers (for example for devices such as SPLK, LCN) does not exceed 30 kHz, elastic waves with a minimum length of 110 mm propagate along the insulator. For such waves, based on the known transparency effect of half-wave screens, the jumper 4.85 mm wide is much less than 1/4.

The jumpers in the isolator must be installed in 2/3, 2/5, 2/7, .. turn of the helix.

The tests of insulator samples in air in a pulsed mode close to that used in devices like SPAK with the device UK-10P have the following indicators.

For insulators with a 2/3 turn of the helix, the expression (1) is completely true.,

Sample 1 of an insulator made of steel pipe 36 X 4 with a pitch of 15 mm and a spiral groove width of 2 mm, with a jumper 1 and a width of 4 mm, installed through 2/3 of a turn, a spiral at a frequency of 25 kHz has an elastic wave propagation speed of the first entry 1085 m / s and the maximum amplitude attenuation of the full wave signal is 184 dB / m.

In insulators with jumper spacing through 2/5 of the helix rotation and less along with elastic and waves, defined by the expression (1), the waves propagate along a shorter path with greater speed through the jumpers, but the attenuation of all types of waves the propagation of the sphc over the insulator, measured over the maximum and the amplitude of the full pulsed wave signal, remains high.

Samples of insulators 2 and 3 with jumper pitch, respectively, through 2/5 and 2/7 helix turn from steel pipe 73 x 5.5 mm, pitch

spirals 48 mm, spiral groove width 5 mm, 10 mm width grinders have an elastic wave propagation velocity over the first entry and a maximum amplitude attenuation in a full pulsed wave signal at different frequencies in accordance with the table.

Sample 3 has excessive strength and in it it is possible to reduce the walls of the initial pipe to 2.5-3 mm, which will increase its efficiency.

When a 10 kgf force is applied along the axis of the sample 2, a change in its length on the base of a 100 mm bar can not be detected.

Further studies show that, although the insulators (with a step of 2/5 of a turn of a spiral and less) propagate through the insulators at high speeds, the high efficiency of the insulators is their high efficiency and they can be used in measuring instruments sound speeds and in a few hundred meters.

five

Testing prototypes of the device LK1-841 with probe dimensions And 1.5 P1 0.5 P2 (in which insulators with sample parameters 2 are installed) in an open pond, in wells with a diameter from

0 120 mm to 400 mm and metrological tests at the UPAK-1 unit show that the elastic waves do not propagate through the insulator body and provide a high acoustic output of the radiator from the receivers. The ratio of the maximum amplitude of various kinds of interference and noise to the maximum amplitude of the maximum useful signal under well conditions is more than 100 dB. Most

0 technology of analogs is the isolator tn

Production and testing of prototypes of AK1-841 devices show that

5, these acoustic insulators with respect to axial and lateral strength are the same from 11, but much better than 37 with respect to manufacturability (they are made on a conventional milling machine.

0 have more than an order of magnitude, the complexity of the). The proposed insulator is much simpler in construction as compared to the known ones, it has less metal and material consumption and

5 weight and greater efficiency due to the smaller wall thickness of the cylindrical rectangular cross section of the helix, which is ensured by the strength of the insulator, obtained by

0 placement of the shredders between the turns, spirals.

The isolator is characterized by high thermo oil and gas resistance, since it is a simple metric construction.

five

. Insulator tests show that they have sufficient lateral strength to ensure good centering of the instruments in the well and have elastic flexibility, which improves the permeability of the instruments in the well, especially with bends.

The square 1 with jumpers over 2/3 turns of the helix has much more flexibility than sample 3 with jumpers over 2/7 turns of the helix. Therefore, insulators with jumpers over a 2/3 turn of the helix are preferably used in small-diameter devices to ensure good permeability in curved pipes with a diameter of less than 40 mm, and with jumpers through 2/5 turns of the helix and less in devices with a diameter of more than 50 mm which requires greater transverse strength.

Claims (1)

ACOUSTIC INSULATOR FOR. acoustic logging tools made in the form of a steel spiral, characterized in that, in order to increase its efficiency, as well as simplify the design and manufacturing technology, the spiral coils are interconnected by gears installed in increments selected from a number of 2/3, 2 / 5, 2/7,. ,, spiral rotation.