Ordovician Karst Water Research Articles

Hydrogeochemistry and Heat Accumulation of a Mine Geothermal System Controlled by Extensional Faults

Given the high proportion of global fossil energy consumption, the Ordovician karst water in the North China-type coalfield, as a green energy source that harnesses both water and heat, holds significant potential for mitigating environmental issues associated with fossil fuels. In this work, we collected geothermal water samples and conducted borehole temperature measurements at the Xinhu Coal Mine in the Huaibei Coalfield, analyzed the chemical composition of regional geothermal water, elucidated the characteristics of thermal storage, and explored the influence of regional structure on the karst geothermal system in the northern region. The results indicate that the geothermal water chemistry at the Xinhu Coal Mine is of the Na-K-Cl-SO4 type, with its chemical composition primarily controlled by evaporation and concentration processes. The average temperature of the Ordovician limestone thermal reservoir is 48.2 °C, and the average water circulation depth is 1153 m, suggesting karst geothermal water undergoing deep circulation. The geothermal gradient at the Xinhu Coal Mine ranges from 22 to 33 °C/km, which falls within the normal range for ground-temperature gradients. A notable jump in the geothermal gradient at well G1 suggests a strong hydraulic connection between deep strata within the mine. The heat-accumulation model of the hydrothermal mine geothermal system is influenced by strata, lithology, and fault structures. The distribution of high ground-temperature gradients in the northern region is a result of the combined effects of heat conduction from deep strata and convection of geothermal water. The Ordovician limestone and extensional faults provide a geological foundation for the abundant water and efficient heat conduction of the thermal reservoirs.

Study on the Genetic Mechanism of Carbonate Rock Type Hot Mineral Water-A Case Study of Diaozhen, Jinan.

Geothermal resources are one of the most valuable resources in renewable energy because of their advantages of green environmental protection, stability, and reliability. Carbonate rock type geothermal reservoirs have great research significance. Carbonate rock type geothermal resources are abundant in the Shandong area. In this paper, we take the carbonate-type geothermal reservoir in the Diaozhen area of Jinan City as the research object, analyze the regional geothermal geological conditions, and identify the geological structure. Through physical logging exploration, hydrochemical analysis, isotope testing, and drilling exploration, we reveal the geothermal genesis mechanism and construct the genetic model of the carbonate geothermal system. The results show that Diaozhen area belongs to a low-temperature geothermal field and weak open karst thermal reservoir and that the reservoir is mainly Ordovician Majiagou group limestone. The thermal insulation caprock is the overlying Quaternary and Neogene strata with a cumulative thickness of 1376 m. The results of geophysical exploration wells and drilling data verify that the Mingshui fracture is seen around 1630-1645m, and the diorite intrusion is seen at 1610m. The Mingshui fracture connects the deep and shallow aquifers and is a geothermal fluid migration channel. The geothermal water in the Diaozhen area is mainly from the recharge of atmospheric precipitation, with a rich ion content and easy enrichment of trace elements. The regional thermal reservoir is mainly recharged by the deep circulation lateral runoff of Ordovician karst water. After long-distance deep circulation migration, groundwater continuously absorbs heat from the surrounding rock and is heated to geothermal raw water in the deep part. Deep geothermal water rises along the water-conducting fracture and mixes with shallow cold water to form shallow, low-temperature geothermal water.

Simulation of multi-period paleotectonic stress fields and distribution prediction of natural Ordovician fractures in the Huainan coalfield, Northern China

Simulation of multi-period paleotectonic stress fields and distribution prediction of natural Ordovician fractures in the Huainan coalfield, Northern China

Characteristics of the water cycle of Jinan karst spring in northern China

Abstract Due to the multi-scale nature and complexity of the flow field, it has always been difficult for hydrogeologists to accurately grasp the water cycle characteristics of the karst water flow system. The inverse statistical model and IsoSource model were employed to calculate the spring age and the mixing ratio of spring recharge sources of the four large spring groups in Jinan. The karst hierarchical groundwater flow system was identified based on multiple factors. We found that the groundwater ages of Baotu Spring and Heihu Spring are about 6a–10a, and those of Wulongtan Spring and Pearl Spring are about 30a–35a. The main recharge sources of spring water of the four large spring groups were recognized as artificial recharge water, Ordovician karst water, and Cambrian Zhangxia Formation karst water. There were distinct differences in the recharge proportion of the four large spring groups. Three groundwater flow systems were identified according to multiple factors, which were local, intermediate, and regional. Furthermore, different levels of groundwater flow systems were recharged to the four large spring groups in different proportions. The research results provided new insights into the analysis of the hierarchical cycle and evolution of karst water.

Discriminatory analysis of spring water supply direction

In this paper,56 groups of underground water samples were collected in Baotu Spring Catchment, and a discriminant model was established to judge the recharge direction and aquifer of the four major spring groups. The results showed that Baotu Spring Group and Black Tiger Spring Group mainly recharge from southwest direction Ordovician karst water, Central south direction of Ordovician karst water respectively, and Five Dragon Pool Spring Group and Pearl Spring Group received from southwest direction and southeast direction Cambrian karst water supplement respectively. The research results are of great significance to the implementation of Jinan spring conservation and precise source replenishment measures. At the same time, it shows that the karst water system in northern China has the characteristics of uneven karst development.

Study on the genetic characteristics of spring water in four spring groups of Jinan

In order to protect the four spring groups in Jinan, it is very important to study the formation characteristics of the karst spring in Jinan. Based on the geological and hydrogeological conditions of Jinan spring group outcropping area, this paper makes a comprehensive study on the karst aquifer void type, spring water supply source, spring water gushing state, spring water flow, spring water temperature and conductivity, spring water chemistry data in the recharging area, so as to determine the genetic types of four spring groups. The results are as follows: (1) Baotu spring and Heihu spring have a similar genetic structure, their circulation depth is relatively shallower, and they are greatly affected by Ordovician karst water in the direct recharging area. Tanxi spring and Pearl spring have a similar genetic structure with a deeper circulation depth, which are greatly affected by Cambrian karst water in the indirect recharging area. Tanxi spring and Pearl spring have a similar genetic structure with a deeper circulation depth, which are greatly affected by Cambrian karst water in the indirect recharging area; (2) Baotu spring and Heihu spring are long-running cold springs recharged by confined water, which belong to erosion rising spring; Pearl spring and Wulongtan are long-running large and medium-sized cold springs recharged by pressurized water, which belong to contact rising spring. The research on the genetic characteristics of spring provides a scientific basis for spring protection in Jinan.

The identification of fault zones in deep karst aquifer of North China coal mine using parallel directional well logs

Water inrush from Ordovician karst aquifer in North China coal mine has become a key issue on underground coal mining. To address this problem, it is necessary to identify fault zones, because fault zones might connect limestone aquifers and coal seams, enabling Ordovician karst water to enter the mine. In the study area, a series of parallel directional holes were drilled along Ordovician limestone at depths between 70 and 90 m under Ordovician limestone boundary. To conveniently detect fault zones and govern mine water disasters, a series of natural gamma-ray logging while drilling (GRLWD) were undertaken. The entire detecting region can be comprehensively covered by several directional borehole groups. Then, fast Fourier transform and short-time Fourier transform approaches were employed on the basis of GRLWD data and geological data to extract faults information. A segmented identification method for deep fault zones was established in this study. This method can be used to markedly improve the identification of fault zones within Ordovician limestone or the unitary lithology formation and provide crucial information relevant for deep coal mining safety.

Evaluating the Impaction of Coal Mining on Ordovician Karst Water through Statistical Methods

This study aims to reveal karst water trend change and the variation of affecting factors in the Heilongdong spring area due to long-term coal mining. In this study, five yearly recoded data over more than 40 years were collected, including underground water level dynamics, water flow, groundwater withdrawal for industrial and agricultural production and domestic production (groundwater withdrawal), mine drainage and rainfall. On that basis, we conducted linear regression, innovative trend analysis (ITA) and the Mann–Kendall method to quantitative analyze the trend and mutation sequence of the time series of environmental hydrological parameters in the study area. To determine the correlation of different affecting parameters under coal mining, as well as the trend of the correlation, we conducted multivariate linear regression analysis and exploited wavelet coherence. The results suggest: (1) under human influence, the annual value of underground water level in the Heilongdong spring area shows an insignificant decrease of 0.42 m/a; precipitation shows a significant downward trend of 2.34 mm/a, primarily the decrease of rainstorm; the spring flow shows a significant decrease of 9.41 × 106 m3/a, and springs with different flow show a significant decrease. (2) The abrupt changes of various factors affecting spring flow in the study area were successively delayed by rainfall, mine drainage rate, industrial and agricultural water consumption and underground water level. (3) Since the year of the start of dramatic changes, under the impact of increased manual mining and mine drainage, the amount of spring overflow has decreased, the groundwater level has decreased, and the groundwater dynamics have varied from meteorological type to meteorology-artificial type. Moreover, the factors affecting the dynamic changes of groundwater have been changed to rainfall and artificial mining and drainage. (4) As the results of Wavelet coherence analysis suggest, the spring flow resonates significantly with rainfall from the period of 3a to 15a. The correlation between the original spring flow and groundwater level is more obvious than that between the original spring flow and rainfall. The correlation between residual flow and groundwater level is less obvious than that between residual flow and rainfall. The above results provide a basis for comprehensively exploiting water resources in coal mining areas and regional groundwater resources protection measures.

Water protection in the western semiarid coal mining regions of China: A case study

Water protection in the western semiarid coal mining regions of China: A case study

Research on water quality characteristics in the process of dewatering test for Ordovician limestone aquifer

Research on water quality characteristics in the process of dewatering test for Ordovician limestone aquifer

Numerical analysis of the destruction of water-resisting strata in a coal seam floor in mining above aquifers

Numerical analysis of the destruction of water-resisting strata in a coal seam floor in mining above aquifers

Water Disaster Types and Water Control Measures of Hanxing Coal Mine Area

Water Disaster Types and Water Control Measures of Hanxing Coal Mine Area

Isotope Hydrogeological Study of Karst Water in the Lu' an Mining District and the Xin' ancun Spring Basin, Shanxi

Abstract Isotope hydrogeological study has shown that the water supply exploration area in the Lu' an coal mine may be divided into four zones of hydrodynamic conditions and the Xin' ancun Spring Basin where the mine is located may be divided into three Middle Ordovician karst water systems. This paper discusses the features of recharge, runoff and discharge of karst water in various zones, and hydrogeological parameters such as the age, flow rate and natural recharge of karst water have been estimated.