SU1610004A1 - Method of determining hazardous stress concentration in coal seams - Google Patents

Abstract

The invention relates to mining. The goal is to increase accuracy. Using a drilling tool, elastic oscillations are excited in the array and the intensity of the received acoustic signal is determined while drilling holes. The excitation and reception of elastic vibrations are carried out from opposite sides of the coal seam in the host rocks. The minimum value U _{0 of} the signal intensity, which is taken as the reference, is measured. The relative gradient V of the signal intensity is determined intervalwise. The interval at which V≥3 is selected. Starting from this interval, a relative increase in A signal intensity is determined. The values of V and A are determined by the formulas V = U ₂ -U ₁ / U ₀ ΔL

A = U _max -U _p / U ₀ , where U ₁ , U ₂ - signal intensity at the beginning and at the end of the interval

ΔL - interval value

U _max - the greatest IP obtained in the process of drilling

U _p - the intensity of the signal in the interval, starting with a short V≥3. If A≥10, stress concentration is considered dangerous. 1 hp ff, 1 ill.

Description

oscillations are performed from opposite sides of the formation in the host rocks, i.e. the source of oscillations is placed in the roof of the reservoir, and the receiver in the soil, or vice versa. The intensity of the detected acoustic signal is determined along the length of the hole and focuses the minimum value of the intensity Uo, which is taken as the reference. The decrease in the intensity of the acoustic signal is due to the entry of the drilling tool into the zone of increased fracturing, beyond which there is an area of increased stress in which the signal intensity increases again. Therefore, a change in the intensity of the acoustic signal reflects the stress state of the coal seam. To assess the stress state by the intensity of the acoustic signal, the relative gradient V of the intensity change is determined from the expression

U2-U1

(one)

THDG

where Ui, U2 signal intensity, respectively, at the beginning and at the end of the interval,

Do is the reference intensity value;

D is the interval value.

The value of the interval D1 is determined by the required detail in determining the desired areas, but, as a rule, does not exceed 1 m.

By changing the relative gradient of V, an interval is selected, starting from which an accelerated increase in the intensity U is observed. The criterion for the transition to an accelerated increase in intensity is condition V 3. For the selected and subsequent intervals, the relative increase in the signal is determined by the formula

whether p

2

where Umaks - the greatest intensity of the acoustic signal recorded during the drilling process:

Un is the signal intensity at the transition interval of the relative gradient to the value of V 3.

When the value of the relative increase in the signal AJ; 10 stress concentration is considered dangerous.

This method makes it possible to increase the accuracy of determining zones with a dangerous concentration of stresses and thereby reduce the cost of

blowout preventive measures.

Claims (2)

Claim 1. Method for determining hazardous stress concentration zones in coal seams, including excitation of elastic vibrations in an array using a drilling tool, their continuous recording during the drilling of holes and determination of changes in the intensity of an acoustic signal along the length of development, by which stress concentration zones are distinguished, characterized in that, in order to increase accuracy, the minimum value of Do intensity is determined, the relative the gradient V changes in intensity and highlights the interval over which V 3, the relative increase in Aj is determined further; signal and at 10 the stress concentration is considered dangerous, and the relative gradient V and the relative increase in A of the Signal are determined by the formulas X, - and 2 - and 1. d and max and p Vs 51 WOD and, where DI, U2 - the intensity of the acoustic signal, respectively, at the beginning and end of the interval; Uo - minimum intensity value; D1 is the value of the interval for determining the relative intensity gradient; UMBKC - the highest intensity of the acoustic signal recorded during the drilling process; Un is the signal intensity at the transition interval of the relative gradient to the value. 2. A method according to claim 1, characterized in that, in order to increase safety, the excitation and recording of elastic vibrations are carried out on opposite sides of the coal seam in the host rocks. iU (dS2