PROCEEDINGS
OF THE TOMSK ORDER OF THE RED BANNER OF LABOR POLYTECHNIC
INSTITUTE named after S. M. KIROV

Volume 165　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　1969

SOME QUESTIONS OF METHODS FOR EXPLORING DEEP HORIZONS OF COAL DEPOSITS IN THE KUZBASS

V. Ya. Koudelny

(Presented by Professor A. M. Kuzmin)

The principal supplier of coking coals is the Kuzbass. Prospecting work has evaluated almost all areas of the basin that are promising for identifying coals of grades K and Zh. The upper horizons of many deposits have either already been mined out or are in the process of being mined. The question of developing the deep horizons of deposits with such coals is being placed on the agenda.

In carrying out exploration work, a whole series of difficulties of a methodological and technical nature arises, as is also emphasized by the geologists of the Donbass [4]. Let us consider several questions of the exploration of deep (lower) horizons where coal seams have been mined out at the upper horizons. This is all the more necessary because an almost complete absence of work at this stage of exploration is noted.

It is known that the tasks of detailed exploration, preparing a mine field for industrial development, are the study of the structural elements of the deposit that determine the mining-geological conditions of operation, the persistence of the structure and thickness of the coal seams, and also the quality of the coal—the specific objects of exploitation. At this stage of exploration, when determining the density of the exploration network, the regularities of the geological structure of the fields are taken into account; the analogy method is applied, which makes it possible, guided by the principle of equal reliability of exploration, to create an exploration network in accordance with the differing complexity of various parts of the field. Despite the fact that the analogy method is of great importance, at this stage of exploration it nevertheless receives limited application because of the need for careful substantiation by factual data. In many cases there are insufficient materials for this because of the fragmentary nature of the preliminary exploration data and because of the absence of syntheses of materials on the deposits. The analogy method itself has many shortcomings, which significantly hinder its application at the detailed-exploration stage.

It is a different matter in the exploration of deep horizons. When beginning their exploration, coal prospectors, on the basis of materials from detailed exploration and from the mining of coal seams at the upper horizons, know the structural type of the deposit and the detailed characteristics of the structures present in the mine field, the thickness classes and the degree of persistence of the thickness and structure of the coal seams, and the grade composition of the coals.

Thus, if the task set for detailed exploration is to establish the geological regularities and features of the structure of the mine—

of the field, then before the stage of prospecting deep horizons there stands a narrower task—the checking and tracing of regularities established by detailed exploration and exploitation. This circumstance may serve as a basis for thinning the exploration network when prospecting deep horizons.

Analogy and forecasting of the geological structure at this stage are more fully justified and, undoubtedly, should find wider application than at the stage of detailed exploration.

As an example one may consider the materials obtained by us in the Prokopyevsk–Kiselevsk district of the Kuzbass in summarizing the documents of the exploration and mine geological services and in compiling a summary on the geology of the deep horizons of the district. Taking into account that the leading factor determining the density of the exploration network here is tectonics, we shall consider only the materials on the tectonics of the deep horizons of the district.

The district is characterized by large, linearly elongated brachyfolds with steep angles of dip of the limbs and by a large number of fault disturbances with displacement amplitudes of hundreds and thousands of meters, breaking the folds into a series of narrow tectonic slices thrust over one another. The limbs of the folds are often complicated by additional folds of higher orders, which, in combination with diverse tectonic faults, makes the structure still more complicated. It is no accident that in schemes of tectonic zoning of the Kuzbass the district under consideration is assigned to the Salair zone of complex linear folds and faults [1]. We have attempted to refine the regularities of the district’s tectonics and to resolve the question of the possibility of extending them to deep horizons.

For this purpose, throughout all mine fields of the district, materials characterizing the tectonics of worked-out areas were studied. On seam maps of working horizons and on structural maps of coal seams at scales of 1:2000 and 1:5000, tectonic elements were shown, indicating areas with different conditions for carrying out mining operations. In particular, areas with reserves written off because of tectonic conditions were noted, as were areas where mining workings had proved a very complex structure, as well as areas with multivariant correlation of coal seams and places with a complex structure established by exploration boreholes. The results of this work were compiled on seam maps at a scale of 1:25000 for a series of horizons and on geological sections at a scale of 1:5000, specially constructed for this purpose and covering the deep horizons. This approach made it possible, by analyzing the tectonics of individual mine fields and of the district as a whole, to refine its regularities and to give a more substantiated forecast of the disturbance of rocks and coals with depth.

On the maps and sections, ten main zones and a number of smaller zones with difficult conditions for mining coal seams stood out clearly, caused by substantial complication of plicative structures and by the wide development of numerous and varied small tectonic faults. The amplitude of such faults is very diverse. Here one may encounter faults with amplitudes from a few centimeters to tens and the first hundreds of meters. Often they are concentrated in individual areas, creating conditions so complex that extraction of the seams becomes impossible.

Study of the regularities in the manifestation of medium- and small-amplitude faults shows that, according to the conditions of formation, these faults may be subdivided into three groups.

The first group includes faults arising in the limbs of large

faults, where they, often being feathering and having different orientations, create a dense network—the zone of influence of a major fault.

The second group is formed by faults that arose at various stages in the formation of the principal and subsidiary folds and are genetically connected with them. Most often such faults affect the hinges of folds, as well as areas of sharp bends in fold axes, where additional folding is very often observed.

The third group includes faults that arose as a result of intra- and interstratal movements. They are often concentrated in a definite part of the coal seam (near the floor, the roof, less often in the middle part), turning the coal into a structureless coal mass with all possible pinches and swellings.

All these faults are highly varied in form even within a single mine field: conformable and nonconformable reverse faults, thrusts and upthrusts, and more rarely strike-slip faults. In contrast to large-amplitude faults, which usually produce duplication of seams, small-amplitude faults more often form gaps. Thus, of all the faults (more than 500) studied in 17 mines of the district, approximately 80% are faults with gaps, and only 20% are faults with duplication of coal seams; moreover, reverse faults and thrusts account for about 50%, upthrusts for about 30%, and underthrusts for about 20%.

The overwhelming majority of medium- and small-amplitude faults belong to the diagonal type. Longitudinal (not bedding-parallel) and especially transverse faults are less widespread. Among the longitudinal faults the predominant forms are reverse faults, thrusts, and upthrusts; transverse faults form strike-slip faults or reverse strike-slip faults. For diagonal forms of faults, reverse strike-slip faults are most characteristic, both with gaps and with duplication of seams.

In view of the fact that these faults exert an enormous influence on the conduct of preparatory and stoping operations, the regularities in their disposition are of special interest. Some of them were noted in the work of A. A. Belitskii [2]. They have been confirmed by our investigations as well.

1. The spatial and genetic connection of numerous small tectonic faults with major ones. Study of this connection shows that the development and localization of small faults forming zones of crushing along the flanks of large faults depend on a whole series of factors [9].

2. The connection of small tectonic faults with certain elements of folds. Within the Prokop’evsk-Kiselevsk district, well-preserved hinges of comparatively large anticlines are rare. Usually they are affected by major faults. In other cases major faults are absent, but minor ones are widely developed, which, together with plicative dislocations, often creates hinges of very peculiar configurations.

3. The connection of small tectonic faults with certain subsidiary folds. This connection is especially characteristic of subsidiary folds formed in areas of bending of the axes of the principal folds, where bedding-parallel displacements of the type of conformable reverse strike-slip faults became widespread.

4. A certain regularity is also established in the distribution of particular forms of small faults. On opposite limbs of folds there are faults of different form and other characteristic complications. Thus, on the limbs of folds dipping to the SW, conformable reverse faults and thrusts are predominantly developed, while on those dipping to the NE—nonconformable reverse faults and upthrusts.

5. The connection of small tectonic faults with the jointing of rocks and coal. Sometimes faults were accommodated to one system of frac-

fractures, and then a series of unidirectional parallel ruptures was formed. In other cases the ruptures developed along conjugate systems of fractures, which led to the formation of “wedge structures.” There are also cases in which ruptures developed along several systems of fractures with the formation of small-block structures. In the general case, the intensity of fracturing and the degree of its expression may serve as an indicator of the complexity of the tectonics.

All these regularities have been confirmed in a number of other districts of Kuzbass [8, 9], and we do not doubt that, to one degree or another, they will hold true for the entire basin.

This makes it possible to use them in assessing the tectonics of deep horizons. In specific cases the possibility will be predetermined by the persistence of the principal structural elements and their features, behavior, and morphology at depth. In the Prokopyevsk–Kiselevsk district, complex zones are expected in those parts of the deep horizons whose structure is in its principal features analogous to the structure of complex areas in the upper horizons. The accuracy of prognostic constructions depends on the reliability of the complex zones identified in the upper horizons and on the accuracy of extrapolation of the principal structural elements to depth.

To check the prognostic constructions and to resolve the question of whether the tectonics becomes simpler in the deep horizons, a comparison was made of the structure of fields in the upper and lower horizons opened by mine workings. In addition, about 200 deep boreholes have been drilled in the district; for some of them, core material and logging diagrams were studied in detail. All these investigations give grounds to consider the tectonics of the deep horizons to be as complex as in the upper horizons.

Taking into account the different tasks of detailed exploration and of exploration of the deep horizons of mine fields, and also bearing in mind the different possibilities of prediction and analogy in this connection, we may expect a change in the role of the factors that determine the methodology of exploration work at these stages. The number of factors determining the methodology of exploration of deep horizons is, in the general case, reduced. The principal factors remain:

1. The tectonics of the mine field and the conditions of occurrence of the coal seams.
2. The persistence of the seams in terms of their thickness, structure, and quality.

Of special importance is the fact that, within the limits of one and the same seam, the degree of metamorphism, and consequently the rank composition of the coal, often changes with depth; together with the persistence of thickness and the structure of the seam, this strengthens this factor in exploration of the horizons.

1. The overall degree of study of the deposit, the experience of exploration and mining of the upper horizons, and the availability and quality of the geological documentation of mine workings driven during exploitation.

The role of other factors, which sometimes have a decisive importance for the methodology of exploration of the upper horizons, becomes insignificant. At the same time, new factors appear, such as the depth of mining, the displacement of rocks above the mined-out space, and others, which determine the possibility and advisability of carrying out exploration work from the surface or from underground mine workings, as well as the use of directed multi-bottomhole drilling of boreholes.

The accumulated practical experience of exploration in Kuzbass, verified by mining operations, shows that, in undisturbed or weakly disturbed occurrence of the coal-bearing strata, for reliable establishment of the synonymy of coal seams and for solving other problems of detailed

the distances between exploration intersections must be fully determined and lie within the limits indicated by E. M. Pakhom and E. M. Senderson [10]. For such deposits it is possible to plan in advance the exploration grid for detailed exploration, proceeding from the degree of persistence of the coal seams and the need to obtain a definite degree of exploration of the upper horizons. Of course, in the course of exploration the grid must be refined, taking into account the geological features revealed by previous work; however, no substantial changes occur in it as a result.

This applies fully also to the exploration of the deep horizons of such deposits. Taking into account the objectives of their exploration, as well as the possibilities of using the established regularities of the geological structure of the field, with undisturbed and weakly disturbed occurrence of coal seams the exploration grid may be considerably thinned out. In fields of semi-closed and closed types, where in the preceding stages of exploration the grid was tightened in order to trace the outcrops of coal seams beneath overburden, the thinning may be greater than in fields of the open type. The task here consists in correctly determining, under the specific conditions of the field and taking into account its features, degree of exploration, and development, the optimal grid for exploration of the deep horizons and for the allocation of reserves of various categories, including categories $A+B$.

An entirely different situation obtains in highly dislocated mine fields. We have already shown [3, 6, 7] that, under the conditions of the Kuzbass, detailed exploration of such fields must be carried out with due regard for the features of the geological, especially tectonic, structure. The exploration grid undergoes considerable changes and, within the limits of the field, proves to be extremely uneven. Cases are not rare in which the reserve categories also undergo substantial changes. Many geological sections, as detailing proceeds, become multivariant. In exploring these fields it becomes especially important to point out that “the system of placing exploration workings, the distances between them, and the depths must be substantiated by the specific geological features of the deposit” [5]. Exploration of the deep horizons also proves to be more complex here. It too must be carried out with a thinned-out grid of workings. The degree of thinning of the grid depends on the complexity of the particular structures and on the reliability of the particular constructions. It is clear that the grid cannot be fully definite, as is the case in simple deposits. The complexity of the structure of the deep horizons makes it possible to raise the question also of the unjustified allocation of reserves of high categories explored by a sparser exploration grid.

Agreement of the exploration project for the lower horizons with the geological-surveying service of the mine assumes special importance. The project must set out specific exploration tasks and indicate the ways of solving them, up to the agreement of the locations for laying down exploration boreholes and for cutting individual seams. Only such joint consideration of all questions of exploration of the deep horizons will make it possible more fully to take into account the features of the structure of the field and its regularities refined by mining operations, and to reduce the expenditure of time and funds on exploration.

The principal technical means of exploring deep horizons is core drilling. Already in the exploration of the upper horizons in coal deposits, the exploration grid is characterized by a lower density than in the exploration of many mineral resources. At deep horizons it proves still sparser. This imposes very high requirements on the reliability of the data obtained from boreholes, especially since the boreholes are deep and costly. Along with serious geological substantiation of the density of the exploration grid, at present

by which time a number of directions for reducing the cost and increasing the reliability of exploration had become apparent in Kuzbass.

1. The use of underground drilling boreholes for solving problems of exploration of deep horizons. All possible combinations of structures in Kuzbass, especially in complexly dislocated fields, often make it possible, for exploration of the lower horizons, to drill boreholes from underground mine workings, which leads to a significant reduction in the volume of exploratory drilling and eliminates the need to drill boreholes through worked-out areas and zones of displacement of the rocks.

2. Drilling of directional and multibranch boreholes. In the course of exploration of deep horizons there often arises the need to tighten the exploration grid (outlining areas with nonworking seam thickness, clarifying tectonic faults and the boundaries of coal grades, etc.). The work of the team of geologists under the direction of S. S. Sulakshin in Kuzbass has shown that, under certain conditions, grid tightening can be achieved by drilling directional and multibranch boreholes, with a considerable saving in borehole meterage.

3. Core-metric investigations. A detailed investigation of the cores of boreholes in a number of coal deposits, and comparison of the results obtained with data from mining operations, show that core material makes it possible to characterize the section under study with great accuracy and to provide important information on the mining-engineering conditions of exploitation, including the stability of the roof and floor of coal seams. Numerous direct and indirect indications of plicative and rupture disturbances are observed in borehole cores, including small-amplitude ones, which cause especially great difficulties during subsequent exploitation. The jointing of rocks also receives a fairly complete characterization. The value of studying small structural forms increases because, in combination with logging, it makes it possible to verify the regularities established for the upper horizons, and thus the forecast receives additional confirmation.

4. Re-drilling of the upper horizons by the coreless method and the application of a broad set of geophysical methods in borehole logging.

LITERATURE

1. A. A. Belitskii, E. M. Pakh. Regularities of the tectonic structure of the Kuznetsk Basin. In: Basic Ideas of M. A. Usov in Geology, Publishing House of the Academy of Sciences of the Kazakh SSR, Alma-Ata, 1960.

2. A. A. Belitskii. On the development of a methodology for forecasting the disturbance of mine fields in Kuzbass. In: Problems of the Geology of Kuzbass, vol. 2. TSU Publishing House, Tomsk, 1959.

3. A. A. Belitskii, V. Ya. Koudelnyi. On the reliability of calculated reserves of high-category coals in complexly dislocated regions of Kuzbass. Exploration and Protection of Mineral Resources, No. 6, 1958.

4. Yu. V. Butsik, V. F. Temnikov. Some problems of exploration of deep horizons in Donbass. Exploration and Protection of Mineral Resources, No. 5, 1964.

5. Instruction on the application of the reserve classification to deposits of coals and combustible shales. Gosgeoltekhizdat, 1961.

6. V. Ya. Koudelnyi. Analysis of the methodology of exploration of mine fields in the Prokopievsk-Kiselevsk district of Kuzbass. Proceedings of TSU, 1958.

7. V. Ya. Koudelnyi. Some questions of the methodology of exploration of mine fields in the Anzhero-Sudzhensk district. In: Problems of the Geology of Kuzbass, vol. 2, TSU Publishing House, 1960.

8. V. Ya. Koudelnyi, Yu. N. Popov. On the methodology of forecasting the disturbance of mine fields in the Leninsk-Kuznetsk district of Kuzbass. In: Materials on Geology and Mineral Resources. West Siberian Branch, TSU Publishing House, 1964.

9. V. Ya. Koudelnyi. Accounting for coal reserves in the flanks of tectonic faults. Proceedings of TPI, vol. 167, TSU Publishing House, 1964.

10. E. M. Pakh, E. M. Senderzon. The density of the detailed exploration grid and the testing of coal deposits in Kuzbass. In: Problems of the Geology of Kuzbass, vol. 2. TSU Publishing House, 1959.