Development of a Rational Methodology for the Exploration of Simple Coal Deposits (Using the Baidaevsky District of Kuzbass as an Example)
Abstract Generated abstract
This paper develops a methodology for improving detailed exploration of simple coal deposits, using eleven explored areas of the Baidaevsky district in Kuzbass as a case study. It analyzes drilling expenditure per reserve unit, reserve-category ratios, geological complexity, coal-bearing productivity, and exploration block size, and uses nomograms and grid-thinning comparisons to evaluate the efficiency of existing exploration practice. The study distinguishes subtypes of areas within deposits previously treated as uniformly simple, identifies cases of excessive drilling and underexploration, and proposes optimal ranges for exploration efficiency and reserve-category targets. It also recommends borehole grid densities and calculation formulas that vary with area size, seam stability, and site shape, arguing that detailed exploration can often be conducted with a wider grid than formerly applied.
Full Text
DEVELOPMENT OF A RATIONAL METHODOLOGY FOR THE EXPLORATION OF SIMPLE COAL DEPOSITS
(case study of the Baidaevsky district, Kuzbass)
L. M. PETROVSKII
(Presented by the scientific seminar of the departments of mineralogy, petrography and geology, and exploration of mineral deposits)
The principal ways of improving the methodology and increasing the efficiency of exploration of coal deposits should be:
1) detailed geological-industrial typification of areas;
2) operational analysis of the methodology and efficiency of the exploration work being carried out;
3) substantiation of the possibility of conducting detailed exploration at simple coal deposits using an exploration grid that is more widely spaced than the one actually being applied, and development of a rational methodology for determining the density of such a grid.
Analysis of exploration efficiency
At present, in the Baidaevsky district, 11 areas have been explored in detail; in six of them additional exploration has been carried out and operating mines are located (Table 1). An analysis of the costs of borehole meterage per 1000 tons of reserves of categories $A + B$ (the index $\mu$), taking into account the ratio of reserve categories, confirms the subdivision of the areas by exploration complexity on the basis of the study of their tectonics: areas 1–7 are of simple structure, with values of $\mu$ up to 0.25 m, and areas of more complex structure have $\mu$ values greater than 0.25 m. At the same time, areas 3 and 4 of the group of simple structure have $\mu$ values greater than 0.25 m. The high specific costs in these areas, as will be shown below, are caused by excessive borehole expenditure there in connection with additional exploration; by their position on the comparison diagram, the areas themselves should belong to group I, although according to the data on actual costs they tend toward group II (Fig. 1).
The analysis of the comparative efficiency of exploration of the areas of the Baidaevsky district was based on the methodology proposed by V. Ya. Koudelnyi [3] for estimating the optimal limit of detailed exploration of coal deposits, which provides for comparison of the ratios of high reserve categories with the specific costs of boreholes (the index $\mu$). This methodology for analyzing the efficiency of detailed exploration of areas takes into account the influence of geological-methodological factors; the specific costs calculated by it do not depend on organizational and technical factors. The latter becomes an invaluable advantage when analyzing long-duration exploration work in areas, or when it is impossible to establish cost expenditures for individual periods of such work. Both circumstances occur in a number of areas of the district, explo—
that were extracted in the prewar and war years. Therefore, costs in monetary terms are not included in the present analysis.
The use of the values of the indicator \(\mu\) in the general characterization of the degree of exploration of areas was described above. However, the change in the indicator \(\mu\) for areas identical in tectonics depends not only on the achieved degree of exploration of the coal seams and on the size of the areas, but also on the conditions of occurrence of the seams, the constancy of their thickness, and the degree of coal content of the part of the section being explored. Such a dependence can be expressed by means of the proposed nomogram,
Table 1
Technical-and-economic indicators of exploration of areas of the Baidaevsky district
| No.—name of areas of detailed exploration and supplementary explorationx (operating mines) | Drilling volume, thousand m | Number of borehole meters per 1 km² | Indicator \(\mu\), m | \(\dfrac{A+B}{A+B+C_1}\), % | Reduced size of a unit exploration block \((l\cdot b)\), m |
|---|---|---|---|---|---|
| 1x — Baidaevsky 1—2 (Baidaevskaya 1—2) | 16,7 | 1670 | 0,19 | 83 | 155000 (610×250) |
| 2x — Zyryanovsky (Zyryanovskaya) | 7,7 | 1000 | 0,24 | 64 | 157000 (630×250) |
| 3x — Abashevsky 1—2 (Abashevskaya 1—2) | 14,6 | 2470 | 0,37 | 70 | 58500 (235×250) |
| 4x — Abashevsky 3—4 (Abashevskaya 3—4) | 26,7 | 1900 | 0,38 | 58 | 79000 (320×250) |
| 5x — Baidaevsky 3—4 (Baidaevskaya 3—4) | 28,6 | 2350 | 0,18 | 84 | 90000 (360×250) |
| 6x — Esaulsky 1—2 | 17,7 | 1170 | 0,21 | 80 | 155000 (610×250) |
| 7 — Baidaevsky eastern 1—2—3 | 27,4 | 1140 | 0,11 | 88 | 210000 (840×250) |
| 8 — Esaulsky 3—4 | 37,7 | 1880 | 0,43 | 76 | 98000 (400×250) |
| 9 — Antonovsky 1—2 | 33,6 | 1050 | 0,31 | 60 | 148000 (600×250) |
| 10 — Esaulsky 5 | 26,8 | 1200 | 0,47 | 85 | 111000 (440×250) |
| 11 — Antonovsky 3 | 21,4 | 980 | 0,27 | 61 | 178000 (700×250) |
in which reserves of categories \(A+B\) are plotted on the abscissa axis, and the total footage of core drilling on the ordinate axis (Fig. 2). The corresponding values of the abscissa and ordinate axes determine the position of points on the lines of equal values of the indicator \(\mu\) (0.1; 0.15, etc.). With the aid of auxiliary upper abscissa axes, expressing total industrial reserves and shifted relative to the main abscissa axis of the nomogram in the order corresponding to a definite ratio of reserves (35, 55%, etc.), the level of the degree of exploration of the areas is shown.
The arrangement of the areas on the nomogram shows that areas 5, 7, and 11 are characterized by the best exploration effect in their groups. At the same time, with an increase in the area of the areas, all other conditions being equal, the exploration effect increases.
The further comparative analysis of exploration efficiency is based on expressing the dependence of the character of exploration on the degree of workable coal content, i.e., on the number, thickness, and constancy of the workable coal seams and the thickness of the part of the section being explored. For this purpose, lines of equal workable coal content are plotted on the nomogram, in ob-
from which the values of the index $\mu$ are obtained. In this connection, taking into account the regular increase in drilling-meterage costs as the exploration target becomes smaller, the origin of the lines of working coal-bearing capacity is shifted upward from the common origin of the nomogram coordinates by the meterage of the average number of boreholes in one exploration line of the sector (2000 m for sectors of type I of the district). The lines of working coal-bearing capacity are tied to the most representative sector (No. 5 for type I). To determine the scale at which the coal-bearing-capacity lines are to be laid out, the premise used is that, in the exploration of sectors with different working coal-bearing capacity but, other conditions being equal (area, conditions of occurrence of the seams, etc.), the meterage costs for a given degree of exploration will be the same.
Fig. 1. Comparison of specific meterage costs (the index $\mu$) and the degree of exploration of sectors of detailed exploration and supplementary exploration: 1—sectors of simple geological structure and the comparison curve for them; 2—the same for sectors of complex geological structure; 3—values of the average working coal-bearing capacity
Having obtained, at the point of intersection (point C) of any of the horizontal lines with the coal-bearing-capacity line of the representative sector (3.1%), the corresponding reserves of categories $A+B$ (120 million tons), we determine the position of the remaining lines of working coal-bearing capacity.
A new optimal position of the sectors is found at the intersection of the perpendiculars to the axis of reserves of categories $A+B$, passing through the points of the sectors on the principal axes of the nomogram, and the lines of their working coal-bearing capacity, from whose ordinate one can determine the optimal drilling-meterage costs for them. Comparison of the actual final costs with the optimal costs thus obtained for detailed exploration of type-I sectors shows that there is an overexpenditure of meterage in all supplementary-exploration sectors except sectors 2 and the “standard” sector 5; the overexpenditure is greatest in sectors 4, 3, and 1. In addition, the optimal costs for detailed exploration exceed, by different amounts, the actual costs for it in sectors that have undergone supplementary exploration...
Fig. 2. Nomogram for determining the comparative effectiveness of detailed exploration of tracts:
1 — actual position of tracts according to detailed-exploration data (a) and allowing for supplementary exploration (b);
2 — optimum position of tracts and the amount of excess drilling footage;
3 — position of tracts on the lines of the corresponding ratio of reserves of categories \(A+B\) in detailed exploration (a) and allowing for supplementary exploration (b).
Visible labels and annotations in the figure:
- \(T\), thousand m.
- Reserves, categories \(A+B+C_1\) (at \(35\%\ A+B+C_1\)), million tons.
- Reserves, category \(A+B\), million tons.
- Reserves, category \(A+B\), million tons.
- Reserves, category \(A+B\), million tons.
- \(A+B\), million tons.
- \(m = 0.10\)
- \(m = 0.25\)
- \(m = 0.30\)
- \(m = 0.40\)
- \(m = 0.10\) according to Panford formula
- Reserves, category \(A+B\), million tons.
- \(a\), \(b_1\)
- \(a)\), \(b_1\)
- \(a)\), \(b_1\), \(b_2\), \(b_3\)
exploration. On this basis it became possible to conclude that, on the one hand, in areas with follow-up exploration there indeed remained underexploration after detailed exploration had been carried out on them; on the other hand, the magnitude and character of this underexploration were different for areas with different conditions of seam occurrence, exploration depth, and area.
The obtained values of excess expenditure and of the optimum costs of borehole meterage in areas of type I may be regarded as entirely objective. Then the optimum efficiency of detailed exploration of areas of this type, taking into account differences in working coal content, the area of the objects, and the tasks of exploration, should be characterized by values of \(\mu\) within the limits from \(0.12\) to \(0.2\) m. The optimum efficiency of detailed exploration of areas of type II should be determined by values of \(\mu\) within the limits \(0.2\)—\(0.45\) m. It is inadvisable to explore areas of simple structure (type I) to a degree of exploration exceeding 75%, and those of complex structure (type II)—65%.
Detailed geological-industrial typification of areas
An important prerequisite for highly efficient exploration of coal deposits is their detailed geological-industrial classification. The known geological-industrial classifications of Kuzbass deposits are based exclusively on statistical accounting, mainly of their morphological features (Vasil'ev P. V., 1960; Pakh E. M. and Senderzon E. M., 1959), and more rarely of the technical-economic indicators of exploration (Burtsev D. N., 1962; Senderzon E. M., 1962). These classifications have the shortcoming that, in almost every one of the distinguished types of deposits, there are areas with exploration conditions of different complexity. The use of such classifications has often encountered well-known difficulties already at the stage of preliminary exploration of deposits.
We set ourselves the task of developing a quantitative methodology for geological-industrial typification of areas on the basis of analysis of geological and technical-economic exploration data. Along with calculating the values of the costs of borehole meterage per 1000 t of reserves of categories \(A + B\) (indicator \(\mu\)) and per 1 km\(^2\) of area of the sites (Table 1), a determination was made of the so-called geological complexity of areas (the size of the unit exploration block \(l \cdot b\)) according to the conditions of their exploration, using the formula:
\[ \mu = \frac{10^5 hS}{lbKd \sum ms} \quad \text{or} \quad l \cdot b = \frac{10^5 hS}{\mu Kd \sum ms}, \]
where \(l\) and \(b\) are the average distances between exploration lines and the boreholes on them, determining the dimensions of the sides of a unit block, m;
\(h\)—average depth of boreholes in the area, m;
\(S\)—area of the site, m\(^2\);
\(\mu\)—specific costs of borehole meterage per 1000 t of reserves of categories \(A + B\), m/t;
\[ K \text{—degree of exploration } \left(\frac{A+B}{A+B+C_1}\right), \%; \]
\(s, m, d\)—the occupied area, average thickness, and volume weight of the coal of individual seams.
The magnitude of the expression \(\sum ms\) entering the formula depends to a considerable extent on the level of vertical and areal productivity of the suite of working coal seams in the area. Therefore the absolute dimensions of the blocks determined must be corrected by coefficients,
balancing each given productivity condition to the unit conditions adopted for some sector (Baydaevsky 1–2 in our case). Analysis of the reduced sizes of unit exploration blocks obtained in this way made it possible to distinguish a group of sectors 1, 2, 6, 7, 9, 11 with large block sizes and a group of sectors 3, 4, 5, 8, 10—with relatively small sizes (Table 1). Both groups of sectors, with the exception of sectors 6 and 5, are determined by their location on the western and eastern limbs of the Baydaevskaya syncline. The excessively small sizes of exploration blocks in sectors 3, 4, 5 compelled the assumption that wells had been over-sited there, which was also confirmed by subsequent analysis of the explored state of the mine fields. After accounting for the over-siting of wells in sectors 1–5 (by the method of network thinning and with the aid of the special nomogram proposed for analyzing exploration efficiency), among the two groups or types it proved possible to distinguish sectors of the southern and northern subgroups with the following sizes of exploration blocks (Table 2).
Table 2
Typification of sectors by reduced sizes of unit exploration blocks
| Western limb of the Baydaevskaya syncline | Eastern limb of the Baydaevskaya syncline | |
|---|---|---|
| Northern part (type II) |
Sectors 9, 11 (subgroup 3) $(600—700 \times 250)\ \text{m}$ |
Sectors 8, 10 (subgroup 4) $(400—500 \times 250)\ \text{m}$ |
| Southern part (type I) |
Sectors 1, 2, 5, 7 (subgroup 1) $(800—900 \times 250)\ \text{m}$ |
Sectors 3, 4, 6 (subgroup 2) $(600—700 \times 250)\ \text{m}$ |
Note: these block sizes are necessary and sufficient for outlining category A reserves.
It is evident from Table 2 that, for detailed exploration of sectors in the northeastern part of the area, a network of wells is required whose density is twice that for sectors in the southwestern part. Thus, the explored area of the district, characterized under the existing general classifications by simple conditions for detailed exploration, has been differentiated by us from this standpoint into 3 subgroups of sectors.
Selection and substantiation of the optimal density of the well network at the detailed exploration stage
For relatively persistent coal seams, using sector 4 as an example, the determination and comparison of exploration density was carried out by the methods of analogy (2, 4, 5), thinning, and comparison with production data, Bogatsky V. V. [1] and Prokin V. A. [7]. The analysis showed that:
- Reliable performance of detailed exploration of medium-sized sectors of simple structure [type I] is ensured by a well network of $300—400 \times 700—1400\ \text{m}$, thinned by a factor of 1.5–2 relative to that actually used for categories A and B. Such thinning of the principal well network is possible only with detailed tracing of coal seams at their outcrops beneath the cover, with the distance between intersections along the outcrop not exceeding $200\ \text{m}$.
-
The exploration grid recommended on the basis of analogy methods corresponds to the optimal density (according to grid-thinning data) only for particular cases of variability in the characteristics of the deposit and in the size of the areas of its sectors.
-
The exploration grid calculated by Bogatskii’s method for medium and large objects is larger than the optimal grid; only on small objects does it correspond to the latter (Table 3).
-
The distances between boreholes determined by Prokin’s method on medium and large objects are closer to the optimal ones than on small objects (Table 3).
Table 3
Calculated borehole grids
| Area of sector, km² | By V. A. Prokin: exploration grid, m, A | By V. A. Prokin: exploration grid, m, B | By V. A. Prokin: number of unit blocks, A | By V. A. Prokin: number of unit blocks, B | By V. V. Bogatskii: number of unit blocks, A | By V. V. Bogatskii: number of unit blocks, B | By V. V. Bogatskii: exploration grid, m, A | By V. V. Bogatskii: exploration grid, m, B | According to the author: number of unit blocks, A | According to the author: number of unit blocks, B | According to the author: exploration grid, m, A | According to the author: exploration grid, m, B |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 2 | 660×1200 | 890×1600 | 3 | 2 | 14 | 8 | 270×540 | 350×700 | 7 | 4 | 350×700 | 500×1000 |
| 5 | ″ | ″ | 7 | 4 | ″ | ″ | 400×800 | 550×1100 | 14 | 8 | 400×800 | 550×1100 |
| 7 | ″ | ″ | 9 | 5 | ″ | ″ | 500×1000 | 650×1300 | 14 | 8 | 500×1000 | 650×1300 |
| 14 | ″ | ″ | 18 | 10 | ″ | ″ | 700×1400 | 950×1900 | 30 | 18 | 500×1000 | 650×1300 |
| 21 | ″ | ″ | 27 | 15 | ″ | ″ | 850×1700 | 1150×2300 | 30 | 18 | 600×1200 | 750×1500 |
The proposed methodology for calculating the density of the grid, based on the formulas of V. V. Bogatskii and V. A. Prokin, rests on accounting for the regularity of change in the required number of blocks and in the distances between boreholes as a function of the area of the objects, with the aid of the derived correction coefficient [6]. It is evident from Table 3 that the exploration grid calculated by the proposed methodology differs advantageously from the other grids; it is closest to the results of the grid-thinning performed. On the basis of the calculated grid obtained, taking into account the need to ensure its multiplicity, the following optimal borehole grid is recommended for detailed exploration of relatively stable seams in simple coal deposits (Table 4).
Table 4
Recommended optimal borehole grid for sectors of simple structure
| Reserve categories | Area of sector, sq km: 2 | Area of sector, sq km: 5 | Area of sector, sq km: 7 | Area of sector, sq km: 14 | Area of sector, sq km: 21 |
|---|---|---|---|---|---|
| A | 350×700 | 350×900 | 350×1100 | 400×1200 | 450×1300 |
| B | 350×1400 (700×700) |
350×1800 (700×900) |
350×2200 (700×1100) |
400×2400 (800×1200) |
450×2600 (900×1300) |
After selecting the optimal distances between intersections of coal seams for each reserves category, it is proposed that the optimal total number of unit blocks \(N\) on a site in detailed exploration be calculated by the formula:
\[ N = 0.3 \frac{S}{S_A} + 0.3 \frac{S}{S_B} + 0.4 \frac{S}{S_C}, \]
where \(S\) is the area of the site being explored;
\(S_{A,B,C}\) is the area of the unit exploration blocks within the contour of reserves of categories \(A\), \(B\), and \(C_1\);
\(0.3\) and \(0.4\) are indicators of the ratio of the areas of reserves of categories \(A\), \(B\), and \(C_1\), corresponding to the requirement of the GKZ instruction for obtaining 30% of reserves in categories \(A\) and \(B\) and 40% in \(C_1\).
Then the optimal number of boreholes \(C\) for sites with different shapes of their area may be determined: for a square-shaped site as
\[ C = \left(\sqrt{N}+1\right)\left(\sqrt{N}+1\right); \]
for a rectangular shape with a ratio of its sides of \(1:2\), as
\[ C = \left(\sqrt{\frac{N}{2}}+1\right)\left(2\sqrt{\frac{N}{2}}+1\right); \]
the same for a side ratio of \(1:3\), as
\[ C = \left(\sqrt{\frac{N}{3}}+1\right)\left(3\sqrt{\frac{N}{3}}+1\right), \]
and so on.
The maximum number of boreholes on sites that are extremely elongated in shape is determined by the formula \((N+1)(1+1)\), or \(2(N+1)\), which we recommended for steeply dipping seams in simple coal deposits [6].
When determining the optimal density of the exploration grid in the final (detailed) stage of exploration, it is necessary to take into account the regularities of the geological-tectonic structure of the fields; this makes it possible, using the method of analogy and guided by the principle of equal reliability, to develop the exploration grid in accordance with the varying complexity of the sites.
Fig. 3. Rational exploration scheme for a group of interbedded stable and relatively stable coal seams, using site No. 4 as an example: 1—prospecting borehole lines; 2—borehole lines in preliminary exploration; 3—the same in detailed exploration. (The scheme does not show workings and boreholes driven to trace the outcrops of seams beneath overburden and to take large coal samples.)
The analysis carried out of exploration of type I sites in the Baidaevsky district makes it possible to recommend, for analogous open sites of simple structure, the following rational scheme of detailed exploration (Fig. 3). It is based on the provision that boreholes of the detailed-exploration period should not be laid out on the former exploration lines, which, when exploring a multi-seam sequence, will make it possible to avoid drilling deep boreholes close to boreholes previously drilled during preliminary exploration.
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