RU2056640C1 - Method of excitation of seismic vibrations - Google Patents

Abstract

FIELD: seismic prospecting. SUBSTANCE: blast dispersing of fuel is carried out. For this purpose dispersing charge with mass equal to 3-5% of mass of fuel is positioned under bottom of vessel with fuel Vessel is put deep into ground or into safe-guarding acreen to depth of up to 0.3 height of vessel or on to specified screen. Screen is made of noncombusticble material and its thickness is chosen with allowance for mass of fuel, density of material of screen and its surface area contacting vessel when it is put into ground. EFFECT: enhanced efficiency of method. 10 dwg

Description

 The invention relates to the field of geophysical engineering, in particular to techniques for seismological exploration, and in particular to methods of exciting seismic vibrations based on the use of explosives (BB), and can be used in seismological exploration.

 There are many ways to excite seismic vibrations [1] in which the explosion of a condensed explosive is widely used as a source of oscillation, and also for this purpose, the detonation of fuel-air explosive mixtures (TWF) can be effectively used.

A known method of exciting seismic vibrations in the soil by feeding into the well a gaseous explosive mixture or liquid explosive and their subsequent detonation [2]
Its disadvantage is that, due to the limited volume in which fuel assemblies are formed and blown up, the excited seismic signals are low-power and do not allow probing massive subsurface masses.

 This method allows the formation of a space charge in open space and, compared with blasting in the borehole or in the blast chamber, significantly increase the mass of the blown fuel assembly and, therefore, the power of the resulting seismic vibrations. Compared with methods that use large quantities of condensed explosives to be detonated, this method is simpler; it does not require drilling wells and the consumption of large quantities of condensed explosives, which significantly reduces the cost of work. In addition, the surface of the earth remains practically without destruction, i.e. significant environmental benefits.

 However, despite its relative simplicity and cheapness, this method is not very convenient in practical implementation, since the tank with fuel and dispersing charge has to be placed quite high above the surface of the earth. If the height of the container is reduced, the explosion power of the forming cloud of the fuel assemblies drops sharply, since part of the fuel during the formation of the cloud is on the ground and does not participate in the formation of the fuel assemblies and the lower the capacity, the greater the loss.

 The aim of the invention is to increase the reliability of the excitation of seismic vibrations, increase safety and reduce labor costs when implementing the method.

где ρ плотность материала экрана;
S площадь поверхности экрана, контактирующей с емкостью при ее заглублении на 0,3 высоты емкости, а заряды для инициирования топливно-воздушной смеси размещают на расстоянии от вертикальной оси, проходящей через центр емкости, и на высоте от поверхности грунта, выбираемой по данным опытных подрывов.The goal is achieved by the fact that by the method of exciting seismic vibrations, including placing a container with fuel above the soil surface, explosive dispersion of fuel in air and the subsequent initiation of the fuel-air mixture formed above the soil surface to disperse the fuel, a dispersing charge weighing 3-9% of mass M of fuel, placed under the center of the bottom of the tank close to it, the tank is buried in the ground or in the safety screen to a depth of 0.3 height of the tank or placed on the surface soil (or screen), while the screen is made of non-combustible material and a thickness of at least δ determined from the ratio
δ

where ρ is the density of the screen material;
S is the surface area of the screen in contact with the container when it is deepened by 0.3 of the tank height, and the charges for initiating the fuel-air mixture are placed at a distance from the vertical axis passing through the center of the tank and at a height from the soil surface, selected according to experimental detonations .

 In FIG. 1 schematically depicts elements of a device that implements the proposed method; in FIG. 2-10 depict a number of options for placing a tank with fuel and a dispersing charge of a condensed explosive in various forms of execution of the safety screen.

 The method is as follows (Fig. 1). A tank 1 with fuel, for example a thin-walled metal barrel, is installed above the ground, for example, on a low stand 2 or directly on the surface on which work is carried out. The lower part of the tank is placed to a depth h in the safety screen 4 made of some non-combustible material, in particular of the surface material (earth, sand, ice, water, etc.). The surface itself can be used as a screen, while the container is buried into it to a depth of h. Dispersing charge 5 should be located under the center of the bottom of the tank close to it. The mass of the dispersing charge should be 3-9% by weight of the fuel used. The charge of the condensed explosive is undermined, the capacity is destroyed, and the fuel is dispersed in air and, mixed with it, forms an aerosol cloud 6 of the fuel assembly. After that, with a certain delay in time, the charges 7 of the condensed explosive, one or several, located in advance around the tank, which initiate detonation of the cloud, are detonated. The fuel-air mixture explodes and excites seismic vibrations in the soil.

 In FIG. 2-10 show examples of the execution of the safety screen of a container having a cylindrical shape (barrel shape). The container can be placed both vertically (Fig. 2, 3, 5, 6, 7, 9), and horizontally (Fig. 4, 8, 10). In the manufacture of the screen (Fig. 2-5), various suitable materials of natural or artificial origin can be used as the screen material, not burning or difficult to burn, preferably dense (lead, steel, earth, sand, shell water, etc. ) It is more convenient to use improvised materials. But situations are possible, for example, when working on water or on rocky ground, when it is easier to specially make materials for the screen or even make a screen in advance.

 The dispersing charge of the condensed explosive should fit snugly both on the bottom of the tank and on the screen. In this case, options are possible when either a hole is made in the screen for setting the charge (Fig. 2, 3), or the screen fits tightly around both the lower part of the tank and the dispersing charge (Fig. 4, 5). The depth of placement of the lower part of the tank in the screen can vary from 30% of the tank height (Fig. 2) to zero (Fig. 1) depending on the conditions of detonation and requirements for it.

 As a protective screen, you can use the surface on which work is carried out (Fig. 6-8), as well as a combination of this surface with an embankment of this material (Fig. 9, 10).

 Numerous experiments have shown that it is possible to avoid ignition of the fuel assembly cloud if for some time after detonation of the dispersing charge contact of the oxygen in the air with those places where hot detonation products come into contact with the fuel is excluded. Without oxygen, fuel does not ignite. After a short time (tens of microseconds), the detonation products, having expanded, cool down so much that the fuel, after touching the air, no longer ignites. Thus, you need some kind of screen, eliminating for some time after undermining the simultaneous contact of air, fuel and detonation products of the dispersing charge. In particular, such a screen can be the earth, if the fuel tank is deepened into the ground, and the charge of the condensed explosive is placed under the tank. In this case, the hot detonation products at the initial stage of dispersion do not ignite the fuel, since the air is blocked by the ground. After the detonation products, having expanded, reach air, they cool down so much that they are not able to set fire to fuel.

 In some cases, for example, in places where the soil is strong and difficult to dig (frozen ground, rocky soil), the tank can not be buried, it can be installed on the surface and an embankment made of any material around the bottom of the tank (earth, sand, small stones, ice, etc.). In this case, the charge of the condensed explosive is buried under the capacitance. And in this case, the surface and the embankment play the role of a screen, and the cloud of the fuel assembly does not light up during formation. You can generally use only the working surface of the soil as a screen, deepening the dispersing charge into it and installing a container on it. But it’s better to deepen the tank a little in the ground, this will allow more directional fuel throwing up and eliminate small losses of fuel on the ground, which are possible if the tank is installed on the surface. It is not advisable to deepen the capacity by more than 30% of its height, since the formed fuel assembly cloud will be stretched upward, has the shape of a column, and this leads to a decrease in the fraction of the explosion energy converted to seismic vibrations due to the small area of contact between the cloud and the ground.

Экспериментально показано, что минимальная масса применяемого экрана M $\genfrac{}{}{0ex}{}{\text{мин}}{\text{э}}$ при максимальном заглублении емкости в экран на величину 0,3 высоты емкости равна половине массы используемого топлива:
М $\genfrac{}{}{0ex}{}{\text{мин}}{\text{э}}$ 0,5 М
Принимая М $\genfrac{}{}{0ex}{}{\text{мин}}{\text{э}}$ ρ S δ получают для минимальной толщины экрана уже известное выражение
δ

Такая толщина экрана надежно предохраняет топливо от возгорания при подрыве и обеспечивает направленное метание топлива в верхнюю полусферу. Меньшая толщина (или меньшая масса) экрана снижает направленность формирования облака, увеличивая потери топлива на земле, а также приводит к возможности разрыва экрана на ранних стадиях расширения продуктов взрыва диспергирующего заряда, прорыва сквозь него воздуха и возгорания разлетающегося топлива. Это подтверждается рядом проведенных экспериментов.The thickness of the screen should be at least δ which is determined from the formula
δ

It is experimentally shown that the minimum mass of the applied screen M $\genfrac{}{}{0ex}{}{\text{min}}{\text{uh}}$ at the maximum depth of the tank into the screen by a value of 0.3 the height of the tank is equal to half the mass of fuel used:
M $\genfrac{}{}{0ex}{}{\text{min}}{\text{uh}}$ 0.5 m
Taking M $\genfrac{}{}{0ex}{}{\text{min}}{\text{uh}}$ ρ S δ get the already known expression for the minimum screen thickness
δ

This screen thickness reliably protects the fuel from ignition in the event of an explosion and provides directional throwing of fuel into the upper hemisphere. A smaller thickness (or less mass) of the screen reduces the direction of cloud formation, increasing fuel loss on the ground, and also leads to the possibility of a screen rupture in the early stages of expansion of the products of the explosion of a dispersing charge, breakthrough air and ignition of expanding fuel. This is confirmed by a number of experiments.

 An increase in the thickness (and mass) of the screen does not lead to any significant changes in the process of formation of the fuel assembly cloud. In particular, a screen with practically infinite thickness and mass values can be used (in the case of using the earth's surface as a screen).

 The mass of the dispersing charge of the condensed explosive should be 3-9% by weight of the fuel used. If the mass of the charge of the condensed explosive is less than 3%, then the cloud is formed smaller than required, the mixture contains excess fuel. As a result, either during the explosion, not all fuel burns out and the power of the fuel assembly explosion is reduced, or the mixture cannot detonate at all. An increase in the charge mass of more than 9% leads to the ignition of the forming fuel assemblies or the formation of a cloud of large fuel assemblies with a low fuel concentration in it, as a result of which the cloud cannot detonate.

The location of the initiating charges, one or more (the height of the _IS and the distance from the vertical axis of the tank is the _IS , is determined by empirical data from the data of previous explosions. For this, the formation of the fuel assembly cloud is organized, using the filming, fix the shape of the cloud at any given time and determine the standard values H and l _{IZ IZ} providing accommodation initiating charge in the cloud. Then, organizing cloud formation and subsequent undermining initiating charge, can find the optimal placement of series, moving them and achieving the maximum power of the explosion.

 The mass of initiating charges must be such as to reliably excite detonation in the resulting mixture. It is different for different fuels, and its value can be determined either from reference data or experimentally. For most fuels, detonation of fuel assemblies is sufficient to detonate several kilograms of concentrated explosive in the cloud.

 The value of the time delay between the detonation of the dispersing and initiating charges of the condensed explosive is also determined by empirical data. At short delay times, the mixture is not prepared for detonation; the cloud is not formed; the fuel is not sufficiently mixed with air. With a significant increase in the delay time, cloud dispersion is possible, especially in strong winds. The amount of time delay depends on the mass and type of fuel. For actual fuel masses, the delay is fractions of a second. The optimal delay time is determined for each design of the tank and the dispersing charge with special test explosions for the highest explosive action of the explosion.

 As a fuel, almost any liquid hydrocarbon can be used whose gas-droplet-air mixtures can detonate (gasolines, acetone, hexane, alcohols, etc.).

 The conditions for the preparation and implementation of the excitation of seismic vibrations by the proposed method is much simpler than in the prototype method. This is due primarily to the fact that work at a height is excluded (in the prototype method, the capacity should be installed at a height of 2-4 m). It is not required to construct and deliver to the place of work a heavy stand, staircase, railing. You do not need to prepare an empty container, cut out the top cover to install the dispersing charge, raise the container to the stand, strengthen the dispersing charge in the container, and then fill it with fuel, while raising the fuel to a height of several meters. In addition, it is not necessary to carefully isolate the dispersing charge from the fuel, since now it was placed outside the tank. Preparation for undermining with the proposed method is much faster (3-4 times) in time. At the same time, the safety of the work itself is increased, since there is no need to work with explosives and with flammable fuels at a height.

 In addition to the above advantages, the proposed method increases the reliability of processing the device. This is due to the fact that the dispersing charge of the condensed explosive is now located outside the tank with fuel, as a result, the probability that the fuel would leak into the charge of the condensed explosive and the detonation in it disappears exists in the prototype.

 Compared to the large explosions of condensed explosives that are being used now, the annual economic effect of the proposed method can be much larger than when using the prototype method, while having undoubted environmental benefits.

 Currently, the method is tested in the conditions of the experimental station of NPO Altai. The question of the application of the method in practice is considered by organizations involved in geophysical exploration of the earth's interior.

Claims (1)

METHOD FOR EXCITING SEISMIC OSCILLATIONS, including placing a container with fuel in a medium, explosive dispersion of fuel in air and subsequent initiation of a fuel-air mixture formed above the soil surface, characterized in that, in order to increase the reliability of excitation of seismic vibrations, increase safety and reduce labor costs during implementation of the method for dispersing fuel a dispersing charge with a mass equal to 3 - 9% of the mass M of fuel is placed under the center of the bottom of the tank close to it, and the container is buried in the ground or in the safety screen to a depth of up to 0.3 the height of the container or placed on the surface or on the specified screen, while the latter is made of non-combustible material and a thickness of at least δ, chosen from the ratio

where ρ is the density of the screen material;
S is the surface area of the screen in contact with the container when it is deepened by 0.3 of the tank height, and the initiating charges are placed at a distance from the vertical axis passing through the center of the tank and at a height from the soil surface, selected according to experimental explosions.

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