Ordovician Limestone Water Research Articles

Research on a Numerical Simulation and Prediction Model of Floor Mining Failure Depth in the Chenghe Mining Area

Ordovician limestone water on the floor is a serious threat to the safety of coal mine production in the Weibei coalfield, and prediction of the floor failure depth is the key for evaluating the mining conditions under pressure. This paper combines the hydrogeological conditions of the no. 5 coal seam and uses the FLAC3D program to determine the floor failure depth under two-factor (mining depth and width) and multifactor (mining depth, width, and height) conditions via numerical calculations and analysis. We obtain the fitting formula for the floor failure depth and analyze the influence of various factors on it. The results show that when the mining width does not exceed 200 m, the mining width has the greatest influence on the floor failure depth, followed by mining depth and mining height. In this paper, the working face floor failure depths measured values of 18 flat seams in China are taken as samples for comparison with the values calculated via empirical formulas and fitting formulas, and the maximum and minimum absolute errors and relative errors are analyzed. The nonlinear fitting regression formulas offered in this paper are found to provide strong predictive value, high accuracy, and a relatively small error range. The reliability and rationality of the models are further verified, thus providing a reference for future mining operations under safe aquifer water pressure conditions in the Weibei coalfield.

Groundwater Hydrogeochemical Mechanisms and the Connectivity of Multilayer Aquifers in a Coal Mining Region

Multiple runoff connections for groundwater supply and water quality evolution mechanisms were disclosed using hydrochemistry, multivariate statistics, stable hydrogen and oxygen isotopes, and inverse hydrogeochemical modeling in a multi-layer groundwater system in a north China coal-mining district. Groundwater quality was mainly influenced by dissolution and weathering of carbonate, silicate, gypsum, halite, and fluorite, as well as cation exchange. Sulfate enrichment in the Carboniferous limestone aquifer may be due to pyrite oxidation, while gypsum dissolution and sewage contribute sulfate to the Quaternary alluvium. The Ordovician limestone groundwater is hydraulically connected to the other two aquifers. Incongruent dissolution of dolomite occurs when the Ordovician limestone water contacts the Carboniferous aquifer, while evaporation occurs when the Ordovician limestone water migrates upward through fractures to the Quaternary aquifer.

Hydro-geochemistry evolution in Ordovician limestone water induced by mountainous coal mining: A case study from North China

This research aimed to investigate the changing mechanism of hydro-geochemistry in Ordovician limestone karst (OL) water induced by mountainous coal mining activities. Thus, the hydro-geochemistry evolution of OL water over 40 years within a typical northern mountainous coal mine named Fengfeng Mine was studied by using Piper diagram, Gibbs scheme, ions correlation and Principal component analysis (PCA ) methods. Results showed that, except for HCO3-, the ions of Ca2+, Mg2+, SO42-, Na++K+, Cl- and total dissolution solids (TDS) values all increased by years as mining continues. Different hydro-geochemical characteristics in different periods can reflect different water-rock interactions. Accordingly, sulfates dissolution gradually took place of carbonates in water-rock interaction. Especially, OL water-rock interactions in different periods were all affected by rock weathering and evaporation-concentration together. At last, evaporation-concentration co-effect dominated the hydro-geochemistry evolution slowly, along with significant cations exchange over years.

Beneficial Use of Deep Ordovician Limestone Water from Mine Safety Dewatering at the Xinglongzhuang Coal Mine, North China

The use of water from mine dewatering has become increasingly important issue in northern China. Much of this water is discharged to the environment, which wastes a valuable resource and pollutes the ecosystem. To help address this, a feasibility analysis was carried on using deep Ordovician limestone water from dewatering at the Xinglongzhuang coal mine. First, a safe hydraulic pressure was estimated using the conventional water inrush coefficient method. Then, based on the results of a water release test (drilled into an artesian aquifer), a model representing the geology and hydrology of the study area was subsequently established and calibrated to existing conditions and water release test results, using the numerical simulation program FEFLOW. Finally, according to a contract signed between the mine and a local industrial water consumer, two cases of dewatering were discussed using the model to maintain a balance between mining safety and supplying water for nearby industrial operations. During the calibration and prediction analysis, the permeable faults were identified as the most important factor in water management and a key factor for balancing the aforementioned needs.

Geological Composition and Structure of the Filling Zone and Its Water-Resisting Property Evaluation on the Top of Ordovician Limestone

With the gradual increase in mining depth of coal fields in North China, the threat posed by karstic Ordovician limestone water to the safe stoping of mines is becoming increasingly prominent. Investigating the water-resisting property of the filling zone on the top of the Ordovician limestone provides the key to safe mining under pressure. This paper analyzed the formation process of the filling zone on the top of Ordovician limestone in North China, and by combining analysis results of several geological field investigations on Ordovician outcrops, the filling zone on the top of Ordovician limestone was divided into three water-resisting structures: (1) completely filled, (2) incompletely filled, and (3) nonfilled. Based on the lithological composition, logging curves, and the water inflow status of several field boreholes, various characteristics of these clay-filled zones were used to determine the mudstone content from top to bottom. Using the interbedded mudstone thickness ratio, relative argillaceous content, impermeable filling zone thickness, rock quality designation (RQD), and faulting as evaluation factors, this paper evaluated the water-resisting property of the filling zone in the study area based on feature-weighted fuzzy C-means clustering (WFCM) algorithm and determined the extent of each zone. The completely filled zone accounts for 46.9% of the total area, incompletely filled zone accounts for 23.9%, and the zone not filled with clay material accounts for 29.2%. As indicated by field investigations on the boreholes, the actual percent of each zone is similar to the theoretical results. The study results present a vital guide for Ordovician limestone water control in deep mining.

Isotope Drift Characteristics in Ordovician Limestone Karst Water Caused by Coal Mining in Northern China

Samples from different areas near the Fengfeng Mine in northern China were analyzed for 2H and 18O isotopes. In the southern areas, the 2H and 18O isotopes exhibited no significant drift off the background. However, in the eastern area, the 2H isotope drifted remarkably, although 2H and 18O both drifted in some samples. In the northern area, the 2H and 18O both obviously drifted. The 2H drift is attributed to deuterium equilibrium due to water–rock interactions between the Ordovician limestone (OL) karst water and silicate minerals. The 18O drift probably came from water–rock reactions between OL water and carbonate minerals, along with the 18O equilibrium reaction. It was demonstrated that the dual drift were connected to water–rock reactions between the OL water, carbonate, and silicate minerals. Therefore, the drift was actually due to equilibrium exchange of OL water–rock interactions during the water level descent and ascent, which was closely related to the mining activities.

Environmental behaviors of PAHs in Ordovician limestone water of Fengfeng coal mining area in China.

In this study, we collected a total of 15 Ordovician limestone (OL) water, 4 shallow groundwater, 3 mine water, 2 surface water, and 2 coal bedrock water samples, aiming to analyze the characteristics of distributions and sources of polycyclic aromatic hydrocarbons (PAHs) in OL water in a typical exploited coal mine named as Fengfeng mining area. Firstly, the PAHs behaviors and characteristics in different types of water of the mining area were investigated and summarized. And then, the hydrogen and oxygen isotopes were combined with isomer ratio method to determine the characteristics, sources, and behaviors of PAHs in OL water, respectively. Results showed that the concentration of PAHs ranged from 0.06 to 0.56ng/L in OL water of Fengfeng Mine. Among them, the dominant 2-4 cyclic PAHs, including Nap, Phe, Flt, and Flu, were detected at a low concentration level with high detection rate. Characteristic compound ratios Ant/(Ant+Phe) and Flt/(Flt+Pyr) showed that the PAHs were derived from the combustion of the coal and biomass. The results of δD/δ18O and δD/Phe testing showed that the PAHs in most OL water came from rainfall infiltration recharge with coal and biomass combustion products in exposed bedrock area at high altitude. The PAHs of some polluted areas were derived from leakage recharge of shallow groundwater, mine water, and coal bedrock water.

Bidirectional Automatic Control Waterproof Gate in Daizhuang Coal Mine

The coal mine in the area of 1160 and 2160 mining area of Daizhuang coal mine is threatened by thirteen limestone water and ordovician limestone water,coal inthe 2160 mining area need to be sent to the -580 belt conveyor system via the belt conveyor of 1160. In order to isolate the two different direction water disaster area, we decided to establish a bidirectional waterproof gate chamber.In order to close the waterproof gate quickly and effectively, decided to design the automatic control system of waterproof gate with programmable control technology, accomplish automatic control and remote control of the waterproof gate. After the completion, perform quick closing test, verify its in the 50s, quickly closed waterproof gate.

Using multi-isotopes (34S, 18O, 2H) to track local contamination of the groundwater from Hongshan-Zhaili abandoned coal mine, Zibo city, Shandong province

The Hongshan-Zhaili coal mine was extensively mined for several decades, lies in Zibo city, Shandong province. After closed in 1994, the coal strata water level raised above the Ordovician limestone water level, then led to the cross strata pollution, which greatly affected the normal use of local people. The Ordovician limestone aquifer is the important drinking water aquifer for local community which covered under the coal strata. Thirty-two domestic water wells near the former coal mine were sampled for water chemistry and stable-isotope analysis of water and dissolved SO42−. Groundwater plots close to the Global Meteoric Water Line and reveals evidence of recharging from atmospheric precipitation. The analysis of sensitive components NO3−, SO42−, 34S in groundwater shows an oxidation environment, promoting the pyrite oxidation. The result of 34S isotopes indicates that the Ordovician limestone water SO42− mainly derived from the atmospheric precipitation SO42−, and the contamination of the Ordovician limestone water from coal strata water has occurred locally in the study area, the Ordovician limestone water is enriched in SO42− and depleted 34S in sulfate.

Water Source Determination of Mine Inflow Based on Non-Linear Method and Hydrochemical Characteristics

Nonlinear methods can be used to identify inrush water rapidly. Yet to identify the mixture water must be combined with water chemistry analysis. Take 9 levels inrush water in Tangshan Mine as an example, according to routine water test data, nonlinear methods, including gray correlation analysis, stepwise distinguishing, neural network, were used to determine water supply quickly, and the results were compared. On the basis, the indicators of piper three-line graph, SI, PCO2 determine the composition of the mixed water and supply channels. The results showed that the main recharge sources of 9th levels inrush water are alluvial and Ordovician limestone water, and infiltrating surface water. Possible ways to supply water are the tectonic fracture, gob, leakage shaft, closed adverse drilling.

Research on Method of Water-resisting Coefficient for Distinguishing Floor Water Inrush Danger

The water-inrush coefficient is usually used as the gist on extracting water-prevention barrier when the coal seam suffered to floor water inrush. The method based on water-inrush coefficient shows some deficiencies in the process for change of mining depth, lithology and aquifer water-rich property. This paper adopts the water-resisting coefficient of the rock layer to evaluate the water-blocking performance of coal floor rock. And we use the water-resisting coefficient to appraise the danger of Ordovician limestone water invasion in the exploitation of lower 21# coal in Longgu Mine. The evaluation results are compared with the mining practice, and the method water-resisting coefficient is more rational than that of the method of water-inrush coefficient.

Ordovician limestone aquosity prediction using nonlinear seismic attributes: Case from the Xutuan coal mine

Ordovician limestone water is the main source of water inrush in North China coal mines. In this paper, we analyze the characteristic of three kinds of nonlinear seismic attributes, such as the largest lyapunov exponent, fractal dimension and entropy and introduce their calculation methods. Taking the 81st and 82nd coal districts in the Xutuan coal mine as examples, we extract the three seismic attributes based on the 3D prestack migration seismic data of this area, which can display the Ordovician limestone fracture distribution in the mine. We comprehensively analyzed the three nonlinear seismic attributes and compared the results with transient electromagnetic exploration results and determined the possible Ordovician limestone aquosity distribution. This demonstrated that the nonlinear seismic attributes technology is an effective approach to predict the aquosity of Ordovician limestone.