Home – Home – Jornals – Fundamental and applied issues of mining 2019 number 2

The method of rock failure stimulation in diamond drilling of deep wells is considered. To increase the rotational frequency of a rock cutting tool, a fundamentally new kinematic diagram of a sinusoidal ball rotary multiplier drill is proposed. The resulting reactive moment and the required pressing force for the braking shoe are theoretically justified. Using the rotary multiplier drill, it is possible to drill in the conditions close to optimal and increase the mechanical speed by 1.5-2.0 times. Equipping the rotary multiplier drill with special removable units allows using it in drilling wells with removable core receivers.

The method for extracting stuck pipes from a well using a special pipe unscrewing device (PUD) in drilling deep wells and overhaul is described. The main operational technical parameters of PUD are studied. To transmit the required torque, the PUD design provides a sinus-ball reversible gearbox with a braked carrier and multi-row gearing. The prototype of the developed PUD has been successfully tested under production conditions. The test results enabled to correct working technical documentation and prepare the guidelines for the implementation of the method of removing the emergency string.

The paper presents results of the experimental studies on tensile fractures formation in the geomedium with a cylindrical cavity and subjected to non-uniformly distributed compression. The hole diameter was found to have a significant effect on the local strength of the material. The new criterion proposed for quasi-brittle fracturing contains a complex parameter that characterizes the size of the pre-fracture zone and accounts not only for the material’s microstructure, but also for its plastic properties, as well as for geometry of the cavity, and loading conditions. Calculation results are in good agreement with the experimental data.

A schematic design of the pneumatic-gravitational percussion mechanism ensuring efficient driving of casing pipes in soil for degassing hole-making in coal seams, is substantiated. Using the numerical modeling method, the operating cycle dynamics of the mechanism is studied, with its rational design parameters calculated. The basic energy parameters, percussion frequency and compressed air flow depending on the compressed air pressure in the main line are determined. The comparative assessment of the weight, size and dynamic parameters of the gravitational machine and the known analogs is performed.

This paper analyzes parameters of microseismic emission signals: the number of signals accumulated over an interval of 10 s; their amplitudes and frequencies in accordance with the loading stage of the “shear stress - time” diagram when rock samples are loaded by direct shear. The experiments were carried out on intact samples from clayey weathering crust and samples from tuff sandstone with joints having different values of surface roughness. Analysis of MSE signals’ parameters and the shear deformation of rock samples revealed that the “shear stress - time” diagram can be divided into the stages which correlate with its “linear”, non-linear, and the post-peak portions. Each of these stages is associated with specific variations in of MSE signals, which therefore can be used for prediction of failure-time of rocks.

This study presents the series of experiments to determine porosity of coal samples using three methods: open porosity based on the fluid saturation (kerosene) method according to GOST 26450.1-85, surface porosity from the surface of polished section under ultraviolet light using Mineral-7 complex); and total porosity by tomographic method with the MST-05 NMR relaxometer. The porosity analysis revealed that traditional method yields essentially lower results. To correctly determine the porosity (open and total) characteristics it is necessary to use the integration of the above 3 methods, with an emphasis on one of them, depending on further applications of these characteristics.

Design solutions related to the creation of a high-speed unbalanced source of harmonic oscillations are proposed, mining and geological conditions for its application are substantiated, and flow diagrams for its operation in a productive well are proposed. Based on the modal and static analysis of design of the shaft with added mass, critical frequencies of the source, as well as stresses and strains occurring during its operation at these frequencies are determined. Technical requirements are formulated for its trouble-free operation in the well together with an electric centrifugal pump, provided that mechanical impurities are present in the produced fluid.

The influence exerted by blasting on the geomechanical state of the rock mass in mining blocks, creating compensation chambers and undercuttings is analyzed. The effect of the seismic energy of explosions on the number of shocks in mine workings and their intersections is determined. It is shown that the most of cavings occur during explosions with the energies of 10⁶ and 10⁷ J at the distances of 40-300 m or more, when the explosive weight is 300 t, their volumes are 15 m³.

This paper presents a modification of the Tarasov’s criterion for the brittleness degree considered in terms of angular coefficients inferred from the stress-strain diagram.

A non-contact method for strain measurements with virtual extensometers during the mechanical testing of rocks and equivalent geomaterials is considered. The measuring procedure is analyzed based on the geometric shape and surface of the sample.

A mathematical model of plastic deformation is constructed for initially anisotropic medium. It is assumed that the deformation process for elastic body dictating its own tensors of strain, which continue to act as eigen tensors in the states of plasticity and fracture. In the problem of indentation, the cylinder of a given length with a wedge-like tip is considered as a striker. At a given initial speed of the striker, its maximum penetration depth is determined. The influence of the medium anisotropy and parameters of the striker on the penetration depth is investigated.

The experiments were carried out to study a system with two mobile percussion masses incorporated in a common housing for steel pipes penetration into elastic-plastic environment under the action of vibro-pecrcussion. A laboratory sample of a pneumatic hammer with the pipe driving unit based on the air distribution scheme with an elastic valve in the pressurized chamber for return-stroke of the piston was fabricated and tested. The results of the study of the working cycle for different types of settings are given. Preliminary data on the possible effects of percussion actions on the duration and frequency of impact impulses are obtained.

Calculations of the design parameters of auger-type hole expansion reamer for curved wells is presented. Relationships between the magnitude of soil deformation caused by the casing of expansion reamer and its length while moving along a curved path were found during mathematical modeling. The formula for determining the maximum length of the casing of expansion reamer, depending on its diameter and parameters of the steering unit was found.

The use of sublevel caving with an upward and undercut-and-fill stoping for mining Northern ore body of the Orlovsky deposit based on the numerical simulation of the rock mass stress-strain state using the finite element method is substantiated. It is determined that undercut-and-fill stoping with a backfilling layer 8 m high is a safer option in the conditions of lower horizons of the deposit, from the viewpoint of enclosing rock stability.

Effects of external compression on the parameters of seismic waves in rock mass were investigated. The study was carried out experimentally on one-dimensional models of block-structured media under pulsed loading. It is shown that as a result of dispersion prompted by propagation of perturbations, a low-frequency pendulum wave is observed in its head part. The parameters of such wave are determined by the mass of blocks and deformability of contact zones at their interfaces. External compression enhances the rigidity of such zones thereby causing acceleration in the wave propagation speed and a change in the spectral composition of waves. A possibility of determining external compression by the spectral composition parameters of pendulum waves was investigated in the model experiments.

The paper discusses the problem of enhancement of gas well drainage productivity in coal seams using the hydraulic fracturing technology. Filling of a fracture with proppant provides a long-term increase in the well drainage performance. Results of the laboratory experiments to determine coal permeability under various stress conditions are provided. The experimental results have shown that the use of proppants significantly reduces the fracture compressibility, while permeability of the propped fracture becomes less sensitive to changes in stress conditions.