Carbonate Karst Research Articles

Experimental study on petrophysical parameters of deep carbonate karst geothermal reservoir in China's Xiong’an New Area

The relationship of P- and S-wave velocities, density, and P-wave velocity provides a physical basis for the interpretation, inversion, and prediction of the well-logging and geophysical data of the carbonate reservoir, which is of great significance for deep geothermal exploration and exploitation. This paper takes the carbonate karst geothermal reservoir in the Niutuozhen geothermal field in North China as the research object, based on the physical property parameters such as P-wave velocity, S-wave velocity, and density obtained by petrophysical experiment and the geophysical exploration data of two-dimensional seismic and well-logging. The change rule of P- and S-wave velocities with temperature and pressure increases in carbonate rock is studied using mathematical statistics. The results show that the P-wave velocity of carbonate rocks increases with the increase in temperature below 50 °C, decreases with the rise in temperature above 50 °C, and tends to be stable above 100 °C. The change rule of S-wave velocity with temperature increasing is not apparent. Both P- and S-wave velocities increase with the increase in surrounding pressure, with the most extensive increase range of 10–15 MPa. At the same time, mathematical models of the P-S wave velocity relation and density-P-wave velocity relation applicable to the study area were also established. The density of the Wumishan formation of the Jixian System in borehole D15 was predicted under the constraint of well-logging. The results were in good agreement with the measured data, which proved the applicability of the constructed petrophysical model in the study area. It helps improve the accuracy and reliability of geophysical exploration data interpretation and reservoir prediction, and it has important practical application and theoretical value.

Matese Mts. and Caserta District Karst Bauxites (Campania Region, Southern Italy): Insights on Geochemistry, Paleoclimate, Paleoenvironment, and Parental Affinity

In the Campania region (Southern Italy), in the Matese Mts. (Albian to Turonian/Coniacian) and Caserta district (Albian to Cenomanian), two karst bauxite deposits outcrop, consisting of flat lenses over shallow karst carbonate. Although the mineralogy and geochemistry of Campania bauxite deposits have been widely studied in recent years, new major and trace elements relationships were provided to highlight paleoclimatic and paleoenvironmental conditions that occurred during their formation. The purpose of this research is to provide for the first time information on the paleoclimatic and paleoenvironmental conditions that affected the bauxites of Campania. These deposits formed during different periods since the Matese deposit formed during intense weathering processes with more abundant precipitation while the Caserta district deposit experienced a more long-lasting exposure event. During the formation of the studied bauxites, the drier conditions favored the replacement of kaolinite by boehmite. R-mode factor analysis showed geochemical affinity among Al2O3, TiO2, and Nb. REEs minerals are mainly associated with the bauxite matrix while Zr, Hf, and V were mainly concentrated in detrital minerals during the later stages of bauxitization. Parental affinity indices (Eu/Eu* vs. Sm/Nd; Eu/Eu* vs. TiO2/Al2O3) assessed the origin of the protolith of the Campania bauxites by rejecting the hypothesis of the dissolution of the bedrock carbonate. The results confirmed the eolian transport of parental material with an Upper Continental Crust and an intermediate to mafic magmatic composition.

Isotopic study for evaluating complex groundwater circulation patterns, hydrogeological zoning, and water-rock interaction in a Mediterranean coastal karst environment

In this study groundwater provenance, circulation, and rock interaction processes have been assessed by cross processing the spatial distribution of chemical and isotopic signatures in freshwater with the hydrogeological features of the coastal karst carbonate aquifer of Murgia, located in the southeastern end of Italy, along the Adriatic Sea. Thanks to widespread groundwater quality monitoring (major, minor, and trace-element analyses) and multi-isotopic measures of O, H, Sr, and B, some assumptions about complex groundwater circulation patterns, hydrogeological zoning, and water-rock interaction have been drawn. Three sectors have been distinguished into the Adriatic side of the Murgia aquifer all fed by two main recharge areas located on the most elevated, inner side of the aquifer. Each sector is characterized by different groundwater circulation patterns, residence time, and hydrogeochemical features. The water samples collected into the western sector evidence a certain degree of water-rock interaction, which allows us to assume long groundwater flow paths and residence time. On the contrary, the eastern sector of Murgia has been proven to be characterized by short residence times and a possible direct freshwater contribution even in the downstream course due to the massive presence of karst forms. Herein, the isotopic analysis of the water samples does not provide evidence of water-rock interaction. Finally, in the third, central sector, water infiltrated at different locations mixes flowing through relatively long paths even though not sufficient to allow groundwater to gain the rock's isotopic signature.

Groundwater resilience, security, and safety in the four largest cities in Denmark

Denmark's complete reliance on groundwater for water supply presents a unique case study in management of natural resources, urban planning, and water resilience in the face of climate change. This paper examines the groundwater management strategies in Denmark in general, focusing on Denmark's four largest cities—Copenhagen, Aarhus, Odense, and Aalborg— each facing distinct challenges due to their demographic, geographical, hydrogeological, and economic characteristics. Through analysis of these cities' approaches to groundwater management, this research contributes to the global discourse on sustainable urban water supply systems. As coastal groundwater cities (CGC), these urban areas must navigate the complexities of sustaining growing populations, mitigating climate change impacts, and coastal processes while ensuring the long-term viability of their groundwater resources. Copenhagen and Aalborg, built atop semi-confined fractured and locally karstic carbonate rocks, highlights the specific challenges associated with karstic groundwater systems, while, Aarhus, and Odense built on glaciofluvial aquifers faces different issues. The different groundwater challenges in these cities underscores the importance of integrating urban development with water resource management and environmental sustainability, offering valuable insights and lessons learned for other regions facing similar challenges. This study, thus not only sheds light on Denmark's groundwater management practices, but also emphasizes the need for innovative solutions to ensure the resilience of urban water supply systems in a changing climate and increasing pressures of emerging organic contaminants and elevated concentrations of geogenic elements induced by water abstraction and fluctuating water tables. Advanced Danish monitoring and modelling tools applied to support decision-making and innovation within the water sector are continuously developed and improved to support resilient and sustainable management of the available water resources.

Improving Fault Zones Hydrodynamic Characterization and Simulation in Karstified Carbonate Environments with GLM and IES Invers Methods

Improving Fault Zones Hydrodynamic Characterization and Simulation in Karstified Carbonate Environments with GLM and IES Invers Methods

Morphogenesis of a new landform responsive to superimposed sulphate and carbonate buried karsts in western Canada

AbstractThis case study documents the morphogenesis of a new karstic landform consisting of a calcareous tufa mound with a gypsum caprock that developed at La Saline Lake, an oxbow of the Athabasca River in northeast Alberta, Canada. The development of this novel tiered carbonate‐sulphate mound architecture resulted from emplacement above the largest known buried salt dissolution collapse‐subsidence karst system, which was superimposed by an overlying buried carbonate karst. Dissolution of halite‐anhydrite beds of the Middle Devonian Prairie Evaporite, 200 m below, resulted in extensive subsidence and brecciation of the overlying Upper Devonian carbonate karst. The development of the calcareous tufa mound resulted from meteoric‐driven groundwater mixed with glacial meltwater directed along the shallowly buried karstic carbonate terrain of Middle‐Upper Devonian limestone, which floors the McMurray Formation, the main reservoir unit of the Lower Cretaceous Athabasca Oil Sands. The flow of the carbonate‐saturated groundwater responsible for the emplacement of the tufa mound at the surface was abruptly redirected along a deeper pathway in response to dissolution collapse‐subsidence adjustments within the buried salt karst of the Prairie Evaporite. The redirected groundwater flow deeper encountered an anhydrite‐dominated segment of the salt dissolution trend within the Prairie Evaporite Formation, 200 m below. The migration up‐section of sulphate‐saturated brine onto the surface of the previously formed tufa mound resulted in the emplacement of a gypsum caprock as a new landform.

Characteristics of Psychrotolerant Bacteria Isolated from Clay Organogenic Deposits of Mramorny Cave (Primorsky Territory)

A cultivated community of bacteria of the genus Pseudomonas was researched in clayey organogenic deposits of the Mramorny Cave (Primorsky Territory). The bacterial strains studied in this work are eurythermal and psychrotolerant. Their phylogenetic affiliation was found by high throughput sequencing of 16S rRNA gene fragments. It is known that bacteria of the genus Pseudomonas represent all the Earth ecological niches and, accordingly, have a wide range of adaptive functions. Using microscopy methods, a change in the nature of mobility and the cell size stability with changes in the temperatures of cultivating bacteria were established. The studied strains are of scientific and practical interest due to the enzymatic activity detection to several substrates simultaneously at different temperatures (25 and 4℃), as well as the ability to secrete cold active pectinase, protease and lipase. However, phosphate-solubilizing activity both at 4 and at 25℃ became preferable for the strains. The Mramorny Cave is karst and is characterized by carbonate karst, which explains the preference for the studied strains in calcium phosphate. An analysis of the obtained data shows that the collection of cultivated bacteria obtained by us includes both typical psychrotolerant ones, which exhibit enzymatic activity under conditions of optimal growth temperature, and unique ones, capable of synthesizing a wide range of enzymes under conditions not characteristic of its optimum growth.

Геохимическая характеристика озера Чваниха, памятника природы Кировской области

The article presents characteristics of the abiotic components (water and bottom sediments) of the karst Lake Chvanikha. The lake is located in the Nolinsky district of the Kirov region and has the status of the hydrological natural monument of regional significance. The results are based on precision analytic data (obtained by ICP-MS, X-ray fluorescence analysis, chemical methods, photometry, etc.) and on thermodynamic calculations (Visual-MINTEQ. ver. 3.1). The composition of the waters indirectly indicates to the development of carbonate karst (mainly the dissolution of dolomite) in the upper rock strata at the base of the lake basin and to the presence of minor gypsum interlayers at depth. The concentrations of dissolved forms of trace elements do not exceed the MPCs of harmful substances in the waters of fishery basins and generally corresponds to the average contents in the rivers of the world. The base forms of trace elements in water are their free ions (for Sr, Ba, Fe, Mn, Zn, Ni, Co, Cd) and carbonate complexes (for Pb and Cu). The bottom sediments are represented of fine quartz sands, which overlap the karst rocks. In the absence of a significant technogenic impact, the poor grade of sand’s ferruginization determines low contents of potential pollutants (Cu, Zn, Pb, Cd, As, Mo, Ni, Cr, V), typical for quartz sands.

Fault system dynamics and their impact on ordovician carbonate karst reservoirs: Outcrop analogs and 3D seismic analysis in the Tabei region, Tarim Basin, NW China

Fault system dynamics and their impact on ordovician carbonate karst reservoirs: Outcrop analogs and 3D seismic analysis in the Tabei region, Tarim Basin, NW China

Low Bacterial Diversity and Nitrate Levels in Cores from Deep Boreholes in Pristine Karst.

This study investigates the nitrate gradients within the deep biosphere of karst carbonate rocks and their resident microbiota. Samples were taken from borehole cores at depths down to 350 m below the surface, collected during geological site investigations for proposed railway tunnels and analysed using 16S rRNA amplicon sequencing. 16S rRNA amplicon sequencing analysis revealed relatively low microbial diversity, which can serve as a reliable indicator of the pristine nature of deep karst. However, some local hotspots of diversity are independent of depth. Pseudomonadota dominated the samples, with Gammaproteobacteria dominating at the class level. The low nitrate content in deep karst, in contrast to higher values closer to the surface, serves as an additional marker of its undisturbed and unpolluted status. Based on the prediction of functional profiles from 16S rRNA sequencing data, nitrates remain low due to indigenous microbial denitrification and assimilatory nitrate reduction. Pathways related to nitrogen fixation, ammonia assimilation, and nitrification were not confirmed. When elevated nitrate levels are observed in karst, they are most probably related to anthropogenic activities. Environmental factors other than depth and nitrate content play an important role in shaping bacterial communities.

Groundwater flow modelling in Neoproterozoic carbonate karst based on dye tracer pathways

Groundwater flow modelling in Neoproterozoic carbonate karst based on dye tracer pathways

Real-time karst groundwater monitoring and bacterial analysis as early warning strategies for drinking water supply contamination

Karst aquifers have been globally exploited as a reliable source of drinking water but their intrinsic characteristics (concentrated recharge, high groundwater flow velocities, etc.) and the increase of anthropogenic pressures makes them highly vulnerable to pollution. Continuous monitoring of karst springs constitutes an effective approach for identifying episodic groundwater contamination and assuring safety conditions in drinking water supply systems. This study aims to improve groundwater protection insights through an integrated methodological approach based on real-time measurements of continuous water parameters coupled to bacterial analysis for the characterization of contamination events in a carbonate karst aquifer of a mountainous and rural area in S Spain. For this purpose, environmental, hydrodynamic and physico-chemical data in addition to bacterial activity (Escherichia coli) analysis were gathered from the analysis of eight flooding events at the two main outlets. In these karst springs, partially captured for drinking water supply, the recurrent turbid groundwater episodes suppose an important limitation for groundwater exploitation during several days, but also a concerning human health risk. The results revealed the different flow and sediment dynamics and mixing processes which determine the impact of faecal contamination derived from human activities on the karst groundwater drained by each spring. The described processes control the variable influence of allogenic recharge, which provokes notable differences regarding response times and maximum values of turbidity and associated bacterial activity in the investigated outlets. The outcomes of this work highlight the usefulness of the applied methodological framework to set the bases for an efficient implementation of early-warning strategies to prevent public health issues worldwide.

Dynamics and a Hydraulic-Soil Mechanical Model for Pockmarks in a Mud-draped Lake: Lake Sünnet (NW Anatolia)

The scarcity of bathymetric studies in most Turkish lakes does not allow the documentation and the potential causes of lake bottom irregularities. In this study, relatively high-resolution bathymetric data from Lake Sünnet (NW Anatolia) revealed five deep (5.7 to 9.2m) and narrow (10 to 20m) depressions located along the boundary between the lake bottom and the steep lake margins. Analysis of lake level data belonging to dry seasons hints no leakage through these depressions. However, the negative conical shape and weakly developed levees around the holes suggest an upward episodic groundwater discharge for which direct evidence has been absent up to date. A combined hydraulic and soil mechanical model successfully explains the pockmark activity due to the flow of water through conduits in karstic carbonate bedrock. According to sedimentation rates and average depth of pockmarks in Lake Sünnet, and available regional paleoclimate studies, the onset of pockmark activity might coincide with the transition from the Near East Aridification Phase to the humid Beyşehir Occupation Phase around 300 BCE in SW and NW Anatolia.

Karst of Sterlitamak (BASHKIR) Shikhans and Their Surroundings in Southern Pre-Ural Area

Abstract—Shikhans, or lone mountains, is the local name for island mountains in the flat foothills of the Southern Urals. The shikhans are denudation remnants, sometimes with preserved residuals of Miocene-Pliocene planation surface on their tops, which allows estimating the total time of development of karst processes at least 5 million years. Despite more than 200 years of research on the shikhans, karst and its manifestations have received little attention to date. A map of karst in the shikhan territory was drawn up according to the standard methodology of karstological survey. Widespread and quite rare forms of carbonate karst of the shikhans and sulphate karst of their close vicinities were characterised. It was established that along with widespread and known in temperate latitudes karstic features, very rare corrosion wells are developed in the gypsum of the Kungurian Stage in the study area, forming karst fields with the highest density of karst forms known in the East European Plain. Gypsum caves at various stages of formation, as well as semi-blind karst-erosion gullies not typical for the lowland sulphate karst of the region were recorded. For the carbonate karst of the Shikhans in the limestones of the Sakmarian Stage, the highest location of karst caves in the foothills of the Southern Urals and the oldest (earky Middle Pleistocene) age of their foundation were established. The main peculiarity of distribution of both surface and underground karst-holes is a clearly expressed dependence of forms and frequency of their occurrence on the course of formation of relief elements in the Neogene-Quaternary time. The presence in a small area of two types of karst by composition of karst rocks with very rare karst forms predetermines the high scientific, practical and educational significance of the shikhans and their surroundings.

Residual carbonate karst reservoir reconstructed by karst planation: A case study of Ordovician paleokarst reservoir characterization in Ordos Basin, North China

Residual carbonate karst reservoir reconstructed by karst planation: A case study of Ordovician paleokarst reservoir characterization in Ordos Basin, North China

Formation mechanisms and resource potential of carbonate geothermal reservoirs in the Beijing-Tianjin-Hebei plain

Formation mechanisms and resource potential of carbonate geothermal reservoirs in the Beijing-Tianjin-Hebei plain

Structural attributes, evolution and petroleum geological significances of the Tongnan negative structure in the central Sichuan Basin, SW China

Structural attributes, evolution and petroleum geological significances of the Tongnan negative structure in the central Sichuan Basin, SW China

Karst architecture characterization of deep carbonate reservoir using image logs in Tarim Basin, West China

This paper has conducted a high‐resolution characterization of a deeply buried carbonate karst in the Tarim Basin of China by utilizing the FMI (Full‐bore Formation Micro Image) method integrated with seismic data, drilling cores and thin sections. It was found that the type and scale of wellbore karst architecture are mainly controlled by karst paleogeomorphology and vertical faults. The karst highlands and slopes, respectively, develop vadose karst and phreatic karst, with different compositions of karst elements. In terms of the karst thickness in the wellbore, the vertical fault development zone is almost twice that of the non‐development zone, both for the vadose karst and phreatic karst. Furthermore, the vertical fault is also able to promote the development of mixing karst. The mixing zone is located 55 m below the water table, with a strata thickness of approximately 25 m, a net reservoir thickness of 5–15 m, and an average porosity of 4%–8%, which serves as an effective hydrocarbon reservoir in the Yingshan Formation. The results will provide insights into the vertical division of karst reservoir and help predict reservoirs using well logs.

Sensitivity Analysis of Mechanical Parameters of Collapse Roof of Carbonate Rock Deep Buried Oilfield

Carbonate rock oilfields account for two-thirds of proven marine carbonate oilfield reserves, which are the primary way to increase future oil and gas energy reserves. Cave collapses occur during the process of oil reservoir development, seriously affecting oil production. In order to reveal the collapse failure mechanism of carbonate karst caves and predict whether the fracture cave type oil reservoir will collapse before drilling, a binary depth reduction method for determining the critical collapse depth of karst caves is proposed based on the Tahe fracture cave type oil reservoir. The sensitivity of karst cave collapses to multiple factors is analyzed, and a prediction formula for the critical collapse depth of karst caves with changes in the deformation modulus, the internal friction angle, and the cohesion is established through multiple regression analysis. By calculating and analyzing the numerical values of a large number of operating conditions under different mechanical parameters, the failure process, failure mode, and the change law of collapse depth during the Tahe oilfield destruction process were obtained. We used the established formula for predicting the collapse depth of karst caves to predict and analyze the actual distribution of karst caves in the Tahe oilfield. The calculation and analysis results showed that in the karst cave failure mode characterized by vertical shear failure, the cohesive force is the most sensitive factor affecting cave collapse, followed by the internal friction angle. The deformation modulus is hardly sensitive to the influence of the karst collapse. Through the geomechanical model test, the result verified the accuracy and reliability of the calculation results. The research results will provide necessary theoretical support for the large-scale safe extraction of deep petroleum resources, increase oil production in China, and have important theoretical significance and engineering application value.

Numerical Simulation of Ground Subsidence Response Conditional on Geothermal Exploitation in a Karst Reservoir Area of North China

Carbonate karst geothermal resources are widely distributed and have large reserves in North China. Currently, the scale of exploitation and utilization of the carbonate karst geothermal resources is gradually increasing. In this work, a geothermal exploitation area where the karst geothermal reservoirs are exploited on a large scale is selected as the study area, and methods including experiment and numerical simulation are used to study the exploitation-induced ground subsidence problems based on the long-term water level monitoring data of the geothermal reservoir. Through analyses of ground subsidence caused by water level changes in the geothermal reservoir, the following conclusions were obtained. The water level drawdown of different types of geothermal reservoirs had different effects on ground subsidence. The maximum ground subsidence of the study area caused by the water level decline of the Jxw carbonate geothermal reservoir was only 0.29 mm/a from 1983 to 2019, which is generally insignificant. In contrast, the same water level change of the Nm sandstone geothermal reservoir was predicted to cause 8.9 mm/a ground subsidence. To slow down or even prevent the ground subsidence, balanced production and reinjection are required. From the result of this work, it can be concluded that the decline of the water level of the Jxw carbonate geothermal reservoir caused by current large-scale geothermal exploitation will not cause serious ground subsidence.