RU2467171C1 - Method of diagnosing dangerous situations in deep mining and forecasting parameters of fissuring zones formed by fracturing - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: set of inventions relates to safe deep mining of solid hydrocarbons. Proposed method proceeds from continuous ground monitoring of geodynamic state of massif and seismic activity of bed roof and bed working on surface area covering bed headway in real time by passive prospecting seismology methods. Obtained results are automatically processed to isolate zones with abnormally-high seismic energy emission, define their area and depth coordinates so that map of anomalies of seismic emission. Maximum magnitudes of seismic emission are used to define coordinates of slope ratio of coal bed fracturing well. Development of main cracks is forecast from the well by the method of double refraction of transverse waves from surface excitation source. After fissuring, direction of main crack development in face bulk is controlled. Area is drilled from surface in directions of main crack development to pump methane out from the wells. With seismic emission decreasing, possibility to extract coal is forecast.

EFFECT: higher safety and intensity of coal extraction.

3 cl, 3 dwg

Description

The invention relates to technologies for the safe underground mining of solid hydrocarbons by a mine method. The proposed method can be used in the construction of new underground workings and open pits in order to extract minerals to the surface and predict the occurrence of dangerous situations in mines and quarries that have been in operation for a long time.

The method of coal mining by the mine method, based on the extraction of minerals to the surface of the earth using a system of underground workings, has long been known. The volume of underground workings in mines reaches tens of millions of tons. The depths of coal mining in this way reach 1.3-1.5 km. The length of underground workings is tens of kilometers. In the technological schemes of the mining enterprise, the mine solves the problems of rational breaking and extraction of coal from the rock mass, laying the mined-out space, securing the bottom-hole space, controlling rock pressure, ventilation, drainage and environmental protection. A constant increase in the intensity of technogenic impact on the geomedium during mining and an increase in the depth of penetration into the earth's thickness and the corresponding complication of the geological and tectonic structure of the massif determine the activation of energy exchange and deformation processes in rock structures. The high level of tension arising in the rock mass during its excavation leads to the release of the accumulated potential energy of deformation in the form of rapidly occurring dynamic processes (rock impacts, gas-dynamic phenomena and large-scale rock collapse at depth). The problem of creating monitoring systems focused on predicting catastrophic natural and technological events is especially relevant when developing deposits located in geodynamically active regions with a high concentration of mines and mines.

Existing forecast methods are based on the analysis of signs characterizing the main factors that determine these phenomena: rock pressure, gas enclosed in coal, physical and mechanical properties of the reservoir and the rocks enclosing it. The methods for predicting sudden emissions of coal, gas, wringes and caving, as well as the forecast of rock blows are most developed and found practical application.

According to its purpose, the forecast is divided into: regional, before the discovery of layers, local and current. The regional forecast is carried out at the stage of exploration. The forecast before opening the strata is to determine the critical depth, upon reaching which conditions arise for the appearance of rock blows.

A known method for the current forecast of outburst hazard according to the initial gas release rate and drill hole output (Device for predicting outburst hazard of formations. USSR author's certificate No. 1245715, BI No. 27, 1986) [1]. This forecasting method has been used in coal mines for about 30 years. However, this method cannot be considered reliable, since it has the following disadvantages:

1) the initial gas release rate is ambiguously associated with the outburst hazard, since it simultaneously characterizes the gas content of the bottom of the formation and its permeability, which cannot be applied to the entire coal seam; in the case of high gas permeability, it is possible to obtain critical values of the initial gas release rate in a low-gas-bearing formation or section; in the case of low gas permeability, non-hazardous values of the gas release rate on the high-gas reservoir are obtained, which, ultimately, leads to accidents;

2) emissions of coal and gas occur in the process of coal mining or mining, that is, emissions are formed in the active phase of the mining cycle, which is also not taken into account by the forecast for the initial gas release rate;

3) the forecast of the danger zone of the formation depends on the operator, is not amenable to automation and is subjective.

There is a method for predicting mountain impacts according to the parameters of the phase-physical state (FFS) of the formation, prone to brittle fracture rapidly (Method for determining the outburst hazard of the formations. Auth. Certificate. USSR No. 1384789, BI No. 12, 1988) [2]. The essence of the method lies in the fact that the coal seam is considered as a three-phase system (solid part - water-saturated part - gaseous part), in which three characteristic indicators are distinguished with respect to the liquid phase: maximum hygroscopic humidity W _mg , characterizing the sorption pore volume of coal; the pore space structure index G _{m g} , corresponding to the fraction of the sorption volume in the total porosity of the coal seam; natural humidity W _in and the index of natural water saturation G _in . The measurement of these four indicators is carried out on coal samples taken in the mine, in laboratory conditions. The criteria by which the outburst hazard of coal seams is determined are the following relationships: at W _in ≤W _mg or G _in ≤C _{mg, the} seams are considered prone to mountain impacts. At G _e ≤0.5 and W _e ≤W _mg, coal seams are considered prone to sudden emissions.

The main disadvantages of the method are its complexity and discreteness of the measured parameters and the discrepancy between the conditions of occurrence of coal samples in the lava and those conditions under which the measurements of the predicted characteristics are made. Therefore, the forecast for such indicators is not reliable.

A known method for assessing seismic hazard in mines, including measuring the time and energy distributions of a number of seismic events - precursors of strong shocks (Acoustic forecast method for outburst hazard of coal seams. Auth. Svid. USSR No. 1222853, BI No. 13, 1986) [3]. To carry out the forecast, the directional coefficient of the time trend of recorded seismic events, the rms value of the variance of the events, and the statistical coefficient of seismic diffusion are used.

The main disadvantages of the method is its complexity and noise caused by technogenic interference from mechanisms operating in the lava. However, this method does not answer the question: why do gas emissions occur in mines, producing underground fires and deaths due to poisoning by gas and coal products of combustion. It is impossible to manage with seismic hazard assessment methods alone in these severe cases, since they show the behavior of the roof of the workings and have no relation to the gas saturation of the lava.

There is a method of acoustic forecasting the outburst hazard of coal seams and a device for its implementation (A method for forecasting outburst hazard in a treatment or preparatory face. Auth. Certificate. USSR No. 1696729, BI No. 45, 1991) [4]. The method is based on recording events of seismic acoustic emission (SAE), in which the forecast is carried out by exceeding the amplitudes of the signals of a given amplitude threshold for a certain time interval. The obtained activity value is compared with a critical level established experimentally for a specific lava in the field.

The main disadvantage of this method is the variety of critical levels for which it is necessary to conduct experimental studies of each coal seam each time, since the regional dependence of the informative parameters of acoustic emission at the stage of preparation for an outburst hazardous mine, where the conditions of occurrence of coal seams, is not established.

A known method of seismic diagnostics of the geodynamic state of a rock mass. The method is based on the use of seismic waves that shine through the main roof in the area of mine cleaning, and seismic registration results in building models of the rock mass, which takes into account the distribution of physical parameters of rocks depending on the type of tectonic disturbances and anomalous changes in elastic characteristics in the zones their influence (Device for automatic control of the outburst hazard of a formation during its excavation. Auth. St. USSR No. 1359205, BI No. 15.1990) [5].

The method has a number of significant disadvantages: low noise immunity from noise of mining equipment; individual layers have a weak level of seismic activity, which requires a large number of accumulations to increase the useful signal-to-noise ratio; the controlled activity of seismic emission characterizes not the residual stability resource of the array, but the intensity of crack opening; control of seismic activity of the reservoir does not allow to estimate the gas factor of outburst hazard.

Known adaptive automated system for monitoring and forecasting gas occurrences in coal mines. The system is designed for continuous monitoring of methane mobility, soufflare and outburst hazard of mine workings, faces and a comprehensive forecast of all types of gas occurrences. The system includes: a methodology and a program for assessing carbon resources in mountain blocks; methane abundance of preparatory workings and excavation sites; control of the gasdynamic hazard of the bottom of the formation; Estimation of methane resources in waste fields; cumulative packer fracturing devices. The main directions of modernization in the extraction of coal are associated with the widespread use of computer technology and new methods for processing large amounts of information, which is built as information-measuring and diagnostic systems of coal mines

At the same time, this adaptive system is not without significant drawbacks, mainly due to the fact that this system works in a mine, where there are continuous technological processes for developing coal seams and so on. The collection and processing of information requires additional signal filtering procedures to reduce interference, which leads to shaking of sensors and processing technical systems. Filtration procedures require additional and quite considerable time, therefore the system, although it provides, does not provide real-time monitoring and forecasting of dangerous situations.

A known method of controlling gas during the development of a coal seam suite. The method is as follows. The formations in the formation are worked out in a descending order with long columns along strike along with the discharge of the emitted gas by the outgoing stream of the extraction section, a gas collection tank is created, which is used as the worked out space of the formation or a network of drainage workings and the gas flows from the underlying formation into the gas collecting tank are filtered. Gas filtration paths are created by drilling wells through inter-layers or by drilling into inter-layers, with the subsequent formation of directed cracks emerging into the gas collection tank and the collapse zone of the roof of the underlying formation. The methane-air mixture is collected in the upper part of the roof collapse arch and, due to the pressure drop, the gas is filtered through the wells in a natural way through hydraulic fractures into a gas collection tank on an overlying formation, from where it is removed by gas-suction plants. Method for seismic-acoustic diagnostics of the geodynamic state of a coal seam in a treatment mine. Patent of Ukraine No. 25374, BI No. 12, 2007 [6].

The disadvantages of the gas emission control method include the following features:

1) to control gas evolution in the method, a gas collection container is arranged, which is the worked out space in the mine, where the mixture of methane and air is collected, which is an explosive mixture;

2) to remove this mixture, it is necessary to carry out operations to drill additional wells and arrange hydraulic fracturing with the direction of cracks in the gas reservoir capacity;

3) the gas pressure in the mined-out space of the mine, increased compared to atmospheric, so the gas must be forced into this tank, and not naturally, through cracks, where the flow rate is associated with the filtration flows of methane through the cracks, which can be low. For this reason, gas in most of its volume will not remain in the gas collection tank, but in the coal seam, which does not eliminate the danger of its release along with the rock.

The objective of the invention is to provide a method that is very likely to diagnose and prevent the occurrence of dangerous situations during underground mining of solid fuels, thereby ensuring safe underground mining of solid hydrocarbons by the mine method.

The purpose of the invention is to increase the information content of the forecast of dangerous situations in the mine method of coal mining.

The problem is solved in that in an automated method for diagnosing dangerous situations that occur during coal mining, ground-based seismic monitoring of the geodynamic state of the rock mass using observations of the seismic activity of the roof of the formation and its production, which are conducted on the surface of the earth on an area that overlaps the formation, is used in real-time continuous mode using passive seismic exploration. The resulting material is automatically processed, selecting zones of abnormally high energy of seismic emission on the observation area, determine their areal and depth coordinates using the seismic tomography algorithm and build a map of the distribution of seismic emission anomalies on the observation area; the maximum values of the energy of seismic emission determine the coordinates of the well for hydraulic fracturing of a coal seam. From a well using a hardware-software complex (for example, "Probe"), which has an independent orientation of geophones located orthogonally in each downhole tool, the development of main cracks by the method of birefringence of transverse waves from a surface excitation source is predicted. After hydraulic fracturing, the directions of development of main cracks in the volume of lava are monitored by microseismic activity (MSA), the area is drilled from the surface along the directions of development of main cracks, and methane gas is pumped from wells.

After the seismic emission reaches a lower level, which determines the non-hazardous concentration of the gas remaining in the reservoir, the possibility of extraction of coal is predicted, while continuing to record the seismic emission generated by the coal seam and the roof of the overburden by the MSA method, including continuous processing of the obtained material by the identification of subsequent zones of abnormally high energy of seismic noise.

The technical result of the invention is as follows:

firstly, along with coal, a gas component (methane) is produced, which can be used for energy needs instead of natural gas and for the chemical industry, since the price of methane is much lower than the cost of natural gas, due to the fact that wells are drilled for its production shallow depths;

secondly, safe mining of coal is ensured due to the elimination of the main danger for personnel working in mines with a high concentration of methane in high-grade coals;

thirdly, it is possible to increase the intensity of coal mining in lavas through the use of more productive techniques for the sinking and extraction of coal.

All these measures lead to a significant increase in the productivity of the mine, as a separate mining enterprise, and the industry as a whole.

The method is as follows.

Passive seismic surveys using MSA technology are carried out on the area of development of coal deposits that have not yet been developed, that is, seismic emission on this area is observed in real time by the arrangement of three-component geophones. Processing the observation data in the SAN-MCS package, determining the velocity characteristics of the scattered waves within the coal seam and the depth of the seismic emission sources, and finding objects saturated with gas (B.P. Dyakonov, O.L. Kuznetsov, O.G. .Raevsky, I. S. Fayzullin, I. A. Chirkin, S. I. Shlenkin. Method of seismic exploration of rocks. RF patent No. 2008697) [7].

Then, along these distinguished anomalous zones, a conventional seismic survey is carried out on a group of linear profiles with a distance between them of 500 m. The length of each profile is at least 1.5 km. The distance between the geophones is not more than 10 m.

Next, these profiles are processed, determining the position of the structural boundaries at the sites of detected anomalies in the intensity of seismic emission.

Next, geological models of fractured media are built and the elastic moduli of the section are determined by the propagation velocities of longitudinal and transverse waves and their ratio (Poisson's ratio). A model of the distribution of the stress state of rocks at a depth of coal seams is built. These two models determine the coordinates of the well for hydraulic fracturing of coal seams and carry out hydraulic fracturing.

After hydraulic fracturing, the directions of development of main cracks in the volume of lava are monitored by the MSA method, the area is drilled from the surface along the directions of development of main cracks and methane gas is pumped from wells. After the seismic emission reaches a lower level, which determines the non-hazardous concentration of the gas remaining in the reservoir, the possibility of extraction of coal is predicted, while continuing to record the seismic emission generated by the coal seam and the roof of the overburden by the MSA method, including continuous processing of the obtained material by the identification of subsequent zones of abnormally high energy of seismic noise.

Method for predicting the parameters of fracture zones formed by hydraulic fracturing

The physical basis of the new forecasting technique is the Doppler law, which establishes the dependence of the dynamic parameters of the wave pulse on the speed and direction of movement of the radiation source and receiver. In this case, the front of the main cracks is considered as a radiation source, which propagates along the strike of the reservoir from the injection well. Since the fracture front propagates through the rock at a speed much lower than the velocity of a longitudinal seismic wave, the emission of elastic waves into the near-wellbore space will occur from a moving source. On seismograms, this movement will be displayed as a change in the shape of the hodograph. If we fix the hodograph of a longitudinal wave first from a stationary source located within the thickness of the formation subjected to hydraulic fracturing, and then the same hodograph from the movement of the fracture front, then the difference in the coordinates of the geophones, which record the minimum time, will show the distance from the injection well to the stop of the fracture front. In the future, spectral analysis of the seismic wave on the hodograph branches, the centers of which lie on the axis of the injection well, in accordance with the Doppler effect, will show that the prevailing frequency of the elastic wave radiation when the source (crack) moves from the well towards the increasing pickets of the profile will increase, and vice versa decrease on the opposite branch of the hodograph. This frequency variation is proportional to the ratio of the velocity of propagation of the crack front and the elastic longitudinal wave emitted by the crumbling rock.

ν = ν ₀ (1-cosφv _and / c _p ) / (1-cosφv _c / c _p ),

where ν is the observed frequency of the signal; ν ₀ is the frequency of the signal from a fixed source; φ is the angle between the arrangement of the geophones and the direction of motion of the source; v _and , _with - the speed of the relative motion of the source and the geophone; with _p is the velocity of propagation of the longitudinal wave in the investigated non-destroyed medium.

Under the conditions of hydraulic fracturing technology, geophones do not change their spatial coordinates, i.e. v _c = 0. From the formula above it follows that when moving away from the well v _and = -v ₀ , φ = π,

ν ₁ = ν ₀ / (1 + v ₀ / s _p );

and when approaching the recording sensors: v _and = v ₀ , and φ = 0, i.e.

ν ₂ = ν ₀ / (1-v ₀ / c _p ).

When comparing the dominant frequencies on two branches of the hodograph, either for each channel or averaged over the entire length of half the arrangement, we will have:

Δν = ν ₂ -ν ₁ = ν ₀ / (1 + v ₀ / c _p ) -ν ₀ / (1-v ₀ / c _p ) = 2ν ₀ (v ₀ / c _p ).

Thus, regardless of the state of the rock at a depth in the presence of a source moving at a speed less than the movement of the elastic wave front per unit time, the geophones will record the oscillatory process of a successively changing frequency with distance from the injection well. In this case, two cases are possible: the first is the propagation of the discontinuity front in an initially isotropic medium, and the second, respectively, in an azimuthally anisotropic medium.

For the first case, Δν = ν ₂ -ν ₁ = 0, which indicates the removal of the fracture front from the center of the well at a constant speed regardless of direction. However

ν ₁ = ν ₂ = ν ₀ / (1 + v ₀ / c _p ), for any direction and geophones, the spatial coordinates of which are the same relative to the axis of the injection well.

In the second case, Δν = ν ₂ −ν ₁ > 0 in some directions, where ¹ v ₀ ≠ ² v ₀ . The rupture front tends to spread in those directions where ¹ c _p < ² c _p , transforming from cylindrical to ellipsoidal. The eccentricity of such an ellipse characterizes the anisotropy of the formation, and the frequency difference of the Doppler effect, which will be observed, will be in this case:

Δν = ν ₂ = ν ₁ -ν ₀ / (1- v ^{2 _0/2} c _p) -ν ₀ / (1 + v ^{1 _0/1} c _p) = 2ν ₀ (v ₀ ^2/2 c _p) ( 1-Δc _p / ² c _p ) [1 + ξ (1 + η / 2],

where ² v ₀ , ² c _p are the minimum values of the propagation of the velocities of the fracture front and the elastic wave, respectively; η = ( ¹ v ₀ - ² v ₀ ) / ² v ₀ is the anisotropy index of the propagation velocity of the fracture front in the formation; ξ = Δс _p / ² c _p is the anisotropy index of the propagation velocity of longitudinal waves in the reservoir. The last formulas are obtained by expanding the function (1 ± v / s) ^-1 in a bin with retention of the first terms, provided that (v / s) <1.

Thus, an elementary analysis of the situation with hydraulic fracturing shows that, using the entire arsenal of seismic methods and technologies for recording elastic seismic waves, it is possible to predict fractured zones in the dynamics of their development based on the use of the Doppler effect. However, for a more or less reliable forecast, it is necessary to have available data on the velocity characteristics of the section and its anisotropic properties based on polarized seismic profiling of the wells. The parameters of the geological and geophysical reservoir model, based on well log data and polarized seismic profiling of wells (PSPS), will make it possible to use the method of calculating the stress state before and after hydraulic fracturing to accurately predict the parameters of the fractured zone, and, ultimately, to control the technology for increasing the productivity of low-yield methane gas deposits.

The main effect, on which the forecast of the development of the main fracturing during hydraulic fracturing is based, is based on the principles of birefringence of PS exchange waves (transverse Sv).

Ha Fig. 1 shows fragments of field records of the birefringence effect of the transverse exchange PS wave on the roof of the Vendian shear wave Sh.

This effect can only be observed with downhole tools that have a gyroscopic orientation, which does not depend on the properties of geological rocks that make up the borehole space.

Fig. 2 shows a copy of the seismograms of the well PSPD with the distribution of the longitudinal and transverse wave propagation velocities in depth, obtained by the hardware-software complex of digital sounding equipment with gyroscopic orientation “ZOND”. The depth interval 43-86 m is characterized by sharp anisotropy and the manifestation of the effect of birefringence of the transverse wave on fast Sv and slow Sh.

Using these data, with high accuracy, the rock velocity characteristics are determined for the subsequent calculation of the stress state.

Figure 3 shows a map of the distribution of reservoir pressure (MPa) in the reservoir.

The capabilities of the seismic survey technique and technology are primarily associated with the latest domestic developments in the field of telemetric systems for collecting seismic information that do not have the current channel limitations and memory volumes. The cordless data collection systems developed by FSUE SNIIGGiMS allow virtually round-the-clock recording of seismic events regardless of the area of work. This method is crucial in predicting hydraulic fracturing parameters, since it provides real-time monitoring of the dynamics of fracture fronts development, for example, using the Rosa-A four-channel field module operating in stand-alone mode without operator intervention. The equipment is synchronized by the turn-on time of each recorder relative to the time zone of the Greenwich meridian.

Information sources

1. Device for predicting outburst hazard. Auth. Testimonial. USSR No. 1245715, BI No. 27, 1986.

2. A method for determining the outburst hazard of formations. Auth. Testimonial. USSR No. 1384789, BI No. 12, 1988.

3. The method of acoustic forecasting the outburst hazard of coal seams. Auth. Testimonial. USSR No. 1222853, BI No. 13, 1986.

4. A method for predicting outburst hazard in a treatment or preparatory face. Auth. Testimonial. USSR No. 1696729, BI No. 45, 1991.

5. The device automatically controls the outburst hazard of the formation when it is removed. Auth. Testimonial. USSR No. 1559205, BI No. 15, 1990.

6. A method for seismic-acoustic diagnostics of the geodynamic state of a coal seam in a treatment mine. Patent of Ukraine No. 25374, BI No. 12, 2007.

7. B.P. Dyakonov, O.L. Kuznetsov, O.G. Raevsky, I.S. Fayzullin, I.A. Chirkin, S.I. Shlenkin. Method for seismic exploration of rocks. RF patent No. 2008697.

8. A method for seismic diagnostics of the geodynamic state of a rock mass. Patent of Ukraine No. 26538, BI No. 1, 2007.

Claims (3)

1. A method for diagnosing dangerous situations in underground mining of coal, including ground-based seismic monitoring of the geodynamic state of the rock mass, automatic processing of the data with the allocation of zones of abnormally high energy of seismic emission in the observation area, the construction of geological models, characterized in that the seismic monitoring of the geodynamic state of the rock the massif is carried out by the method of passive seismic exploration; the maximum values of the energy of seismic emission determine the ordinates of the hole for fracturing a coal seam from wells predict the development of main cracks by the method of birefringence of shear waves from a surface source of excitation and their reception using a hardware-software complex that has independent orientation of geophones located orthogonally in each downhole tool, after hydraulic fracturing control of the directions of development of main cracks in the volume of lava by microseismic activity for subsequent gas extraction process, the area is drilled from the surface along the directions of development of the main cracks and the methane gas is pumped out from the wells, after the seismic emission reaches a lower level, which determines the non-hazardous concentration of the gas remaining in the reservoir, the possibility of coal recovery is predicted, while continuing to record the method of microseismic activity of seismic emission generated by the coal seam and the roof of the overburden, including continuous processing of the obtained material to identify subsequent zones of abnormally high energy of seismic noise. 2. The methodology for predicting the parameters of fracture zones formed by hydraulic fracturing, used in the method according to claim 1, based on the dependence of the dynamic parameters of the wave pulse on the speed and direction of movement of the radiation source and receiver, which consists in recording the hodograph of the longitudinal wave first from the stationary a source located within the thickness of the formation subjected to hydraulic fracturing, and then of the same travel time curve from the movement of the fracture front, and by the difference in the coordinates of the geophones, on oryh recorded minimum time determined distance from the injection well to stop the front gap. 3. The method according to claim 2, characterized in that the distribution pattern of cracks in the formation is built according to the anisotropy of the propagation of longitudinal waves in the coal seam.

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