Dynamic Modeling of the Gas Discharge of a Mine in the Karaganda Coal Basin Under High Uncertainty Using a Multiple Realization Approach

The current work is intended to show the application of a multiple realization approach to produce a strategic development plan for one of the mines in Karaganda coal basin. The presented workflow suggests using a comprehensive reservoir simulator for a history matching process of a coal pillars on a detailed 3D grid and application of sensitivity and uncertainty analyses to produce probabilistic forecast. The suggested workflow significantly differs from the standard approaches previously implemented in the Karaganda Basin. First, a dynamic model has been constructed based on integrated algorithm of petrophysical interpretation and full cycle of geological modeling. Secondly, for the first time in the region, dynamic modeling has been performed via a combination of history matching to the observed degassing data and multiple realization uncertainty analysis. Thirdly, the described model parameters with defined range of uncertainty has been incorporated into the forecasting of degassing efficiency in the mine using different well completion technology. From the hydrodynamic modeling point of view, the coal seam gas (CSG) reservoir is presented as a dual porosity medium: a coal matrix containing adsorbed gas and a network of natural fractures (cleats), which are initially saturated with water. This approach has allowed the proper description of dynamic processes occurring in CSG reservoirs. The gas production from a coal is subject to gas diffusion in coal micropores, the degree of fracture intensity and fracture permeability. By tuning these parameters within reasonable ranges, we have been able to history match our model to the observed data. Moreover, application of an uncertainty analysis has resulted in a range of output parameters (P10, P50, and P90) that were historically observed. Performed full cycle of CSG dynamic modelling including history matching, sensitivity, and uncertainty analyses has been performed to create a robust model with the predictive power. Based on the obtained results, different optimization technologies have been simulated for fast and efficient degassing through a multiple realization probabilistic approach. The coal reservoir presented in this work is characterized by very low effective permeability and final degassing efficiency depends on well-reservoir contact surface. The decrease of the well spacing led to a proportional increase of gas recovery which is very similar to unconventional reservoirs. Therefore, vertical and horizontal wells with hydraulic fractures have been concluded the most efficient way to develop coal seams with low effective permeability in a secondary medium.

Features of the Working Area Aerogasdynamics with the Direct-Flow Ventilation Scheme

To control rock pressure in the Karaganda coal basin, various technological schemes are used for mining and developing coal seams. At the same time, in order to form healthy and safe working conditions at workplaces in coal mines in the course of mining operations, it is necessary to ensure effective ventilation of the development and breakage faces. When solving the problem of aeration of stopes, the authors of the article propose to take into account air leaks through the collapsed coal-rock mass of the goaf when controlling gas emission of an working area. For this purpose, the gas-dynamic state of the goaf has been studied under various conditions of ventilation: when isolating the longwall face goaf, when demolishing the supported ventilation working, when the amount of air supplied to the longwall face is changed and for refreshing, as well as a combination of these options. Experimental studies have been carried out in the mines of the Karaganda coal basin. This article took into account the features of the working area aerogasdynamics with the direct-flow ventilation scheme. As a result of the study, a quasi-network model of the working area and an algorithm of calculating air leaks through the collapsed goaf massif have been developed.

APPLICATION OF SEISMOTOMOGRAPHY METHODS FOR SOLVING VARIOUS PROBLEMS IN THE MINING AND GEOLOGICAL DIRECTION

The Karaganda coal basin is characterized by a complex structure. The presence of geological inconsistencies such as tectonic disturbances, washouts, variable reservoir hypsometry, etc. makes it difficult to conduct underground mining operations. Currently, in the world practice, mine seismic exploration is widely used for the purpose of studying the geological structure and solving various mining problems. Safe and productive operation of treatment faces in underground coal mining requires a timely and reliable forecast of the mining and geological conditions of the structure and condition of the coal-bearing mass from the mine workings. The most accurate and reliable picture of the tectonic structure of the Carboniferous massif can be obtained using methods of mine seismic exploration to study the geological structure and conditions of the coal bed and host rocks. The main goal of implementing modern methods of mine seismic exploration was to conduct mathematical modeling to assess the possibility of identifying tectonic disturbances with an offset amplitude of the order of magnitude and higher than the reservoir capacity using various methods of underground seismic exploration - the seismic transmission method (STM) and the reflected wave method (RWM). For this purpose, physical models of sections of the Carboniferous massif were developed, including a geometric description of geological structures, the distribution of rock densities, velocities, wave propagation and their influence on compression, and the shift of the mountain range. One of the models corresponded to a section of the formation without geological disturbances, and the second one - to a section with tectonic disturbances with displacement amplitudes from 5 to 15 m. The results obtained can be used in the development of modern effective methods for predicting the state of the mountain range in complex mining and geological conditions of both the Karaganda coal basin and other coal basins with a complex geological structure. Initially, seismic surveys were performed using the method of reflected waves using the common depth point method. However, the problem of obtaining an objective image of the geological environment is still relevant, due to the peculiarities of elastic wave excitation in mine conditions (features of the generated wave field, patterns of its propagation, the direction of the source). The method of mine seismic survey based on channel and boundary waves registration was developed and applied. This method allows obtaining a detailed geological and geophysical model of the field site. Due to the processing of both types of waves, the resolution of the method is increased to obtain information about both the coal bed and the host rocks, and, in particular, the state of the roof of the formation. The method of measurements in mine conditions is presented, the results of testing the method of performing field work in mine conditions are shown, and seismic characteristics with high contrast and clear traceability of reflecting boundaries are obtained.

The efficiency analysis of the SH-25A ball drum mill when grinding industrial products of fossil fuels

The working characteristics of a laboratory ball drum mill during grinding of Karaganda coal products were studied in order to apply the results obtained to industrial installations. The performed analysis shows that the most complicated and energy-intensive stage of preparation of coal dust is the grinding of fuel. The operational characteristics of the mill productivity, consumed electric power and specific energy consumption in terms of the relative rotational speed of the drum as well as the optimal values of the relative velocity determining the qualitative grinding of the fuel have been determined. The performance of the processed drum mill reaches its maximum at a relative speed of rotation of the drum 0.71 ensuring a waterfall mode of grinding of fuel related to the high-speed mode of a coal-grinding mill. The estimated specific energy consumption for fuel grinding varies in the range from 0.11 kWh/kg up to 0.23 kWh/kg at fuel milling coefficient of Kl = 1.2.