SU1425324A1 - Method of monitoring crack border in rock specimens - Google Patents

Abstract

This invention relates to the mining industry. The purpose of the invention is to expand the functionality of the method by defining the gap of an arbitrary shape. Cracks are created in the sample by hydraulic fracturing with an electrically conductive fluid, which produces electrical insulation. An electrode is introduced into the liquid; a source of alternating voltage is connected to it; a bias current sensor is installed on the sample surface. The latter is moved along the surface of the sample and the current IMQKC is measured with the source turned on and the value of IMMM when the source is turned off. The crack boundary is determined when the source is turned on by a line in which the current is equal to 1 °, corresponding to the arithmetic average of the currents IMQKC and. To implement this method, only standard commercially available measuring equipment is required, and, additionally, there is no need to build the dependence of the bias current on the position of the receiving plate relative to the axis of the hole. 2 Il. F (L

Description

I.cho "1pP" refers to the mountain 11p (1mipigein (sty and is intended for AND {: next don. Nn cracking in rock samples. 2

The aim of the invention is to extend the functionality of the method by defining the slot boundary of an arbitrary shape.

FIG. Figure 1 shows a scheme for the formation of cracks in a specimen; in fig. 2 shows a scheme for determining the crack boundary in a specimen.

The method is carried out as follows.

For the formation of cracks in sample 1 of rocks, a hole 2 is drilled, in the downhole part of which a germinal gap 3 is cut through a special device. In hole 2, a device consisting of a body 4 in the form 2 is installed and fixed with an adhesive substance. pipe, on the end of which the cup 5 is fixed, having a central hole with a thread, 25 where the screw 6 is screwed in with the handle 7. The screw 6 through the ball 8 interacts with the pin 9 of the dielectric. The internal cavity of the device and the germinal gap fill the electric wire with 30 liquid. Rotate the handle 7 to move the piston hole to the bottom hole, which leads to an increase in the fluid pressure to the value at which the rock breaks with 35 forming a crack 10.

To control the change of the crack boundary, the device case is electrically isolated from the liquid by a special dielectric coating. An electrode 11 is introduced into the liquid through a piston 9 and connected with a shielded cable 12 to an alternating voltage generator 13. On the surface of the block move the plate 14 (displacement current sensor). FIG. 2, three zones are marked (I, II, III) by vertical dashed lines; Zone I corresponds to the area in which the crack is located. Zone II is limited to the area immediately adjacent to the border of the crack, Zone III corresponds to the region in which there is no crack.

FIG. Figure 2 shows the dependencies of the DC current of the bias (b) and the gradient of the bias current (c) on the location of the receiving plate (bias current sensor) relative to the axis of the hole in the sample.

If the plate 14 is in the socket 1, then its surface together with the surface of the liquid in the crack forms a capacitor C. A current flows through this capacitor (IMR.C) measured by the current meter 15 through this capacitor.

If plate 14 is in zone III, no capacitor is formed and, of course, no current flows through the plate from generator 13.

With the passage of the plate 14 of the II zone, for example from I to III, the current through the plate decreases to a certain minimum value. The width of zone II (the zone in which the current varies) is determined mainly by the distance of the crack to the surface of the sample.

If the plate is turned off when the plate is on the sample surface, then the measured current will drop not to zero, but to some value (indicated in the application as) determined by the field of other sources of electromagnetic energy.

It was established experimentally that the projection of the crack boundary onto the sample surface is located at the point where the value of the measured current is

+ I

T

min

the current IQ is the value of the current on the isolines, A.

melon slit. BUT;

IMUH is the current value when the AC source is turned off. BUT,

To find the projections of the border. cracks on the surface of the block, it is enough to measure the bias current once in the I zone (the zone of the germinal gap), then turn off the generator and measure IMWHJ to calculate the arithmetic average of the measured currents 1o, turn on the generator and determine the isoline on the sample surface in which the current is 1o generator). In this case, the standard commercially available measuring equipment is required and there is no need to build the dependences of the bias current and the bias current gradient on the position of the receiving plate relative to the axis of the hole.

P

9

1

Editor G. Volkova

Compiled by I. Fomichev

Tehred L. Oliynyk Proofreader E. Lonchakova

Order 4749/29

Circulation 459

VNIIPI USSR State Committee for Inventions and Discoveries 113035, Moscow, Zh-35, 4/5 Raushsk nab.

Production and printing company, Uzhgorod, st. Project, 4

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Claims (1)

Claim A method of controlling the boundary of a crack in rock samples, including creating a fracture in a fracture sample using an electrically conductive fluid, electrically isolating the fluid, introducing an electrode into it, connecting a voltage source to it, moving the electrode in the fluid and determining the boundary by changing the voltage across the electrode cracks, characterized in that, in order to expand the functional capabilities of the method by determining the boundary of a slot of arbitrary shape, a bias current sensor is installed on the surface of the sample, to A variable-voltage source is connected to the electrode, a bias current sensor is moved along the sample surface, and a current value of 1max ^P R is measured ^and the source is switched on and 1 _MMN with the source _turned off, and the crack boundary is determined with the source turned on, along a line in which the current is 1 “, Corresponding to the average 5 arithmetic currents 1mkshs. ^and . FIG. 1