Use of the permeability test of Carboniferous rocks in the underground coal mines located in the Upper Silesian Coal Basin Iwona Augustyniak1, Katarzyna Niedbalska1, Przemysław Bukowski1

1Central Mining Institute, Laboratory of Mining and Environmental Hydrogeology, Plac Gwarków 1, 40-166 Katowice, Poland, [email protected], [email protected], [email protected]

Abstract Carboniferous rock permeability tests can be used both for documenting hydrogeological and gas conditions, as well as for predicting the possibility of pre- exploitation demethanation of seams and rock mass surrounding mining excavations. The article describes the research process of rarely performed non-destructive profiling of permeability of hard rocks in different directions (x, y, z) using a PDPK- 400 permeameter created by Micrometrics. The solution can be applied in mining hydrogeology, and in particular in the assessment of the water hazard in mines located close to reservoirs in flooded mine, evaluation of water filtration through safety pillars and in determining zones with increased permeability, among others for the migration of mine gases to demethanize the deposits, e.g. through holes from the surface. Keywords: permeability, hydrogeological properties, USCB, rock mass, rocks

Introduction methane out of flooded excavations). Mining Extraction of hard coal generates various exploitation carried out at ever greater depths interdependent hydrogeological phenomena. records lower values of water inflow to mine The restructuring of hard coal mining workings, but increases methane emission conducted since 1990 in USCB have led to the from coal seams, which is associated with abandoning of some mines and coexistence known regularities in the geological structure of active and flooded mines. Mining activity of USCB and variability of porosity. The negatively affects on water environment and methane capture in the CBM, CMM and results in drainage of aquifers and discharge AMM process is increasingly difficult to plan of large amounts of contaminated minewater due to the constantly decreasing porosity and to surface watercourses. Lack of activities permeability of rocks in the vertical profile. aimed at dewatering of mine workings of The difficulty in determining the conditions decommissioned mines causes them to be of water and gas circulation in mining filled by the water from the natural inflow. The excavations and rock mass and the difficulty in water level in the flooded excavations increases establishing plans for draining the rock mass gradually until a hydrodynamic equilibrium is and its demethanation is often caused by the obtained with the aquifers in the surrounding lack of knowledge of the variability of the rock Carboniferous rock mass. Conditions for the and rock mass permeability distribution in the formation of hydrodynamic equilibrium may vertical profile. occur in border regions with active mines The permeability of rocks is relatively as a result of filtration of water that leaks or rarely investigated in mining hydrogeology escapes from the decommissioned mine’s in the areas of hard coal mines. The tests reservoirs to the workings of an active mine. are carried out on rock material taken from In the area between the flooded and active mine workings as solid samples or on cores mines, there are conditions for hazards related from holes made at the bottom of the mine. to the flow and accumulation of water and Commonly used methods of researching gases in the rock mass. This may determine hard rocks include specially prepared rock the possibility of a water hazard (disruption samples, tested in one direction, generally in a of the safety and effect pillars) and methane direction parallel to the axis of the core sample hazard in active mines and surfaces (pushing and perpendicular to the stratification. Such

Wolkersdorfer, Ch.; Khayrulina, E.; Polyakova, S.; Bogush, A. (Editors) 559 IMWA 2019 “Mine Water: Technological and Ecological Challenges” standard tests allow obtaining the test result a wide measurement range from 0.001 mD at least by an order of magnitude smaller to 30 D. The time of determination of the than in the case of a test made perpendicular permeability at one measuring point varies to the core axis and parallel to the bedding from 2 to 35 seconds. The permeameter of rocks. The test result is obtained in a time- enables testing of drill cores of various consuming manner and after preparation diameters, but not less than 2.5 cm, and of any of the core and selection of test samples. In length of the drill core tested in measuring addition, it replicates the filtration process, cycles from 2.5 cm to 3 m in one measuring which is closer to the inter-layer filtration cycle. It conducts measurements in an process. The research process of profiling extremely precise, fast and efficient manner, the filtration coefficient in the direction giving the possibility of non-destructive perpendicular to the axis of the core sample, profiling of permeability of drilling cores in i.e. parallel to the stratification using the the direction of parallel flow to the stagnation. PDPK-400 device created by Micrometric, is The device also allows to conduct tests of described below. permeability on individual samples (2.5-20 Characteristics of the test method cm) cut out from the core or on rectangular with the application of PDPK-400 cube samples used in geomechanical studies with height or thickness below 20 cm. Then permeameter the measurements are made in three planes, The PDPK-400 permeameter is used for perpendicular to the axis of the sample in non-destructive drill core permeability the XY system and parallel to the axis in the profiling. This device gives the possibility of Z-system (photo 1B), i.e. in a parallel and precise measurement of the permeability of perpendicular direction to the strangulation. one-meter rock samples cut from the core The device is fully integrated with the perpendicular to its axis, in two planes, in control unit equipped with the PROPERM the XY system (photo 1A). The markings are software, giving the possibility of the carried out using gases, mainly nitrogen class current registration of the test. Based on the 5.0 or 6.0. The device allows to determine the obtained data, it is possible to create graphs heterogeneity of samples thanks to the tested of variability of permeability as a function filtration properties, in order to identify the of depth, taking into account the entire ranges of high and low permeability of the lithostratigraphic profile of drilled layers and examined rock layers. The device is equipped determination of fragments with increased with a built-in sensor that indicates the exact and reduced permeability. location of the measurement sites, and also The principle of measuring permeability has the option of selecting any interval of the is to determine the time curve of nitrogen core to be tested and planning frequency of pressure drop in the main tank, which measurements.The test is carried out with is connected to the probe injecting the

Photo 1. PDPK-400 permeameter A – profiling of permeability on rock cores; B – testing of individual rock samples

560 Wolkersdorfer, Ch.; Khayrulina, E.; Polyakova, S.; Bogush, A. (Editors) IMWA 2019 “Mine Water: Technological and Ecological Challenges” medium into the sample under test. The • CSS from 5.0 10-9 m/s to 3.3 10-4 m/s, permeameter allows measurements of • MS from 9.6 10-10 m/s to 5.0 10-4 m/s, sample permeability including corrections • USSS from 4.0ˑ 10-11 m/s to 2.5ˑ 10-5 m/s, for the gas slip effect (Klinkenberg • PS from 8.5 ˑ10-9 m/s to 8.4 10-6ˑ m/s. correction), so that even at low speeds, In the north-easternˑ part of theˑ USCB, the gas flowing through the porous rock permeability studiesˑ give the ˑopportunity behaves in accordance with Darcy’s law. to assess the inflows, flows and filtration of In the case of samples where intense water (the course of the study should reflect gas flows occur in fissures with high the flow directions perpendicular to the core permeability and small width, linear axis, i.e. parallel to the rock stratification). flow velocities are characterized by high For gas, these studies are of less importance. values. Under these conditions, the flow The permeability of rocks examined in the becomes turbulent and there is additional direction perpendicular to the stratification flow resistance due to inertia effects. becomes more important in the case of Permeability measurements performed by assessing the vulnerability of groundwater the PDPK 400 can therefore also be carried to contaminants (Bukowski, Bromek, out under conditions of high inertia of the Augustyniak 2006). It can also be a relevant sample, even with relatively low differences element in the assessment of the common in applied pressures. Hence, the analysis hazard associated with the accumulation includes the Forchheimer correction. The and pushing of mine gases from mining inertial resistance virtually disappears for excavations of abandoned mines, as a result samples with a permeability <0.1 mD for of flooding. This part of the basin is located initial pressures <10 psig. in the hydrogeologically exposed subregion, where the Carboniferous rock mass is not Possibilities of application of effectively isolated, and thus it is easily permeability in mining recharged into the infiltration water from the Permeability is an important parameter surface and shallow deposits of aquifers that describing fluid filtration processes (gas, build the deposit overburden. The flooding water). In the area of USCB, the inflow of Carboniferous forms is mainly related to intensity and chemical composition of the occurrence of the complex of the Cracow water entering active and abandoned mines and Upper Silesian Sandstone Series, in depend on the degree of the Carboniferous which permeable compositions predominate hydrogeological structure “opening” and (Figure 1). lithology of the Carboniferous series in which However, in the south-western part of the the mine is located. Due to the conditions USCB, the main problem in mines is not so of supplying the Carboniferous region, much related to the flow and filtration of water the USCB area is divided into an exposed as to the migration of mine gases, mainly and covered hydrogeological subregion. In methane. It is recommended here to perform contrast, a different lithological formation permeability tests in each direction in relation differentiates hydrogeological properties in to the stratification of rocks, i.e. parallel and particular lithostratigraphic series. In the perpendicular to the axis of the drill cores. productive carbon, four lithostratigraphic The filtration coefficient determined for water series were separated, differing essentially in in this region is more important only locally permeability and the ability to store and release for safety and boundary pillars from water free water. Starting from the oldest, these are: reservoirs in mining excavations. In this the parallel series (PS), the Upper Silesian part of the basin there is a hydrogeologically Sandstone Series (USSS), the mudstone series covered subregion, which is characterized by (MS) and the Cracow Sandstone Series (CSS). the presence of deep impermeable formation For individual lithostratigraphic series, the isolating Carboniferous deposits. Mines permeability, in field studies, expressed by the located in this part of the USCB conduct coal filtration coefficient shows a high variability exploitation mostly within the mudstone (Różkowski, ed. 2004) for: and parallel series, in which there are less

Wolkersdorfer, Ch.; Khayrulina, E.; Polyakova, S.; Bogush, A. (Editors) 561 IMWA 2019 “Mine Water: Technological and Ecological Challenges” favourable conditions for recharging the gases and contaminants and insulating rock mass with water, and the coal seams are zones, etc. The tests in the parallel lining characterized by high methane capacity. to lamination indicate the conditions of Below are exemplary tests using the PDPK- filtration of the fluid in the layer, and in the 400 permeameter made on the core of the perpendicular direction show the possibility Carboniferous rock from the USCB. The tests of its percolation. Therefore, the PDPK 400 included 33 m of the rock core with a diameter device gives complete data on the basis of 8.0 cm that was profiled. The studied core of which the conditions of filtration and fragment included works of the Upper Silesian percolation of water in any tasks of mining Sandstone Series from the depth interval of hydrogeology and general hydrogeology can 355.00 ÷ 388.00 m. The measurements were be determined. The obtained results can be carried out in the XY plane with a stage of a solid base for studying model filtration approximately 5 cm. An exemplary graph of processes and in rock mass composed of permeability variability of these formations as compact rocks. They can also be a tool for a function of depth is presented in Fig. 2. assessing the rock mass permeability in methane prevention prior to commencing Conclusions mining exploitation. The PDPK-400 permeameter allows quick identification of high and low permeability Acknowledgements ranges of the rock layers. It allows to Article is the result of the work carried out in obtain an accurate profile of changes in Methenergy Plus + project funding from the rock mass permeability with a depth and Research Fund for Coal and Steel (UE) under to a relatively accurate separation of zones the grant agreement No 754077, with use of or layers with features characteristic for equipment maintained as part of the PANDA privileged water flow paths, migration of project

Figure 1. A sketch of a geological map of the Carboniferous layer (according to Kotas 1982) with the range of subregions I and II (Różkowski 2003): 1 – country borders, 2 – range of USCB, 3 – mining areas, 4 – CSS, 5 – USSS, 6 – MS, 7 – PS, 8 – range of subregions

562 Wolkersdorfer, Ch.; Khayrulina, E.; Polyakova, S.; Bogush, A. (Editors) IMWA 2019 “Mine Water: Technological and Ecological Challenges”

References Warszawa, s. 45-72. Bukowski P., Bromek T., Augustyniak I. (2006) Us- Różkowski A. (2003) Budowa geologiczna i wa- ing the DRASTIC system to assess the vulner- runki hydrogeologiczne w GZW. W: Hydrogeo- ability of groundwater to pollution in mined ar- logia polskich złóż kopalin i problemy wodne eas of the Upper Silesian Coal Basin. Mine and górnictwa, część 1. Praca zbiorowa pod red. Z. the Environment. Journal of the International Wilka. Kraków, Wydaw. Naukowo-Dydaktyczne Mine water Association (IMWA). Vol. 25, nr 1. AGH, Kraków, s, 42-145. Kotas A. (1982) Zarys budowy geologicznej Różkowski A. (2004) Środowisko hydrochemic- Górnośląskiego Zagłębia Węglowego. W: Prze- zne karbonu produktywnego górnośląskiego wodnik 54. Zjazdu Naukowego PTG. Red. Zagłębia Węglowego. Wydaw. Uniwersytety Różkowski, Ślósarz. Wydawnictwa Geologiczne, Śląskiego. Katowice.

Figure 2. Variability of permeability within the borehole profile

Wolkersdorfer, Ch.; Khayrulina, E.; Polyakova, S.; Bogush, A. (Editors) 563