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I thank the discussors for their critique of the above paper. In geology there are rarely any absolute models but working hypotheses, which will be modified with new data. The paper under discussion, Charrach (Carbonates Evaporites 33:727–766, 2018a), presents a very new large data set, which is multi-disciplinary and integrated the most recent research. The critique by Möller et al. (Carbonates Evaporites 10.1007/s13146-019-00486-3, 2019) and their paper of 2018 (Int J Earth Sci 107:2409–2431, 2018), presents a computer simulation, which must be validated with field evidence and recent research in the area, and not based on assumptions, which have turned into facts over time. The discussors may be unfamiliar with the geological research that has been published over the last 20 years in the areas under consideration. Furthermore, the research on marine–non-marine evaporite formations is hardly considered in their discussion, yet much has been published. [ABSTRACT FROM AUTHOR]

This paper investigates sources of early signs of nitrate pollution in a karst aquifer and major karst spring. Te Waikoropupu Springs are the largest springs in New Zealand and amongst the largest in the Southern Hemisphere with a mean outflow of 13.4 m3/s. They discharge the clearest water ever recorded from a karst spring, but early warning of water quality deterioration is signalled by increasing nitrate concentrations. The springs discharge water from a partly artesian aquifer of 2.85 km3 volume in karstified Ordovician marble with a transmission time averaging 7.9 years. Reservoir porosity is unusually high for a crystalline carbonate rock, estimated as 6%. Water emerging at Main Spring (9.89 m3/s) and adjacent Fish Creek Springs (3.48 m3/s) is a mix of recharge from four main sources. The paper investigates by means of mass balance modelling the proportions of water coming from each source, the origins of nitrate contamination and the contribution of nitrification. Water losses into the bed of the upper Takaka River, about 17 km from the Springs, provide 13% of the mean flow at Main Spring, 34% of the flow at Fish Creek Springs, and 83% of the volume discharged at submarine springs. Infiltration from rain falling over farmed land in the middle valley is estimated to supply 10% of total outflow at Main Spring and Fish Creek Springs but to contribute 82% of the NO3-N output discharged at the springs. Nitrification accounts for 16% of the nitrate discharged. A 34% reduction of leachate concentration in the middle valley would be required to bring NO3-N values at Main Spring back to levels recorded in the 1970s. [ABSTRACT FROM AUTHOR]

With the rapid development of urbanization construction in China and the continuous growth of the real estate industry, the issue of karst collapse induced by deep foundation pit excavation in high-rise building construction has become increasingly prominent. This paper studies the impact of foundation pit excavation on groundwater and the mechanism mode of karst collapse induced by it, using the examples of karst collapse events at Wanhao foundation pit and Diaoyutai foundation pit in Guigang City, Guangxi Zhuang Autonomous Region. The study utilized ground investigation, drilling, and groundwater/gas pressure monitoring. Findings of this study helped propose the prevention and control measures. The results indicate that the geological environment conditions in the research area are fragile and characterized with underground karst features, thin overburden, and abundant groundwater. The dynamic changes in the groundwater level within cones of depression caused by foundation pit drainage and rainfall recharge are identified as key factors contributing to geological disasters of karst collapse. The large-scale extraction of groundwater over a prolonged period is a significant human-induced factor contributing to karst collapse in the research area. [ABSTRACT FROM AUTHOR]

Paleo-karst controls reservoirs in the fourth member of the Sinian Dengying formation in the Sichuan Basin. It is crucial to characterize the paleo-karst zone architecture to understand better the distribution of reservoirs controlled by the multi-stage ancient water tables. We divide vertical paleo-karst zones using cores and formation micro-scanner images based on the groundwater movement and development of pores and fractures. Then we analyze positions and variations of paleo-karst water tables according to the characteristics of different paleo-karst zones. Besides, we illustrate the distribution of underflow subzones and the development of reservoirs in each subzone. This paper reveals the relationship between paleo-karst landform relative elevation, paleo-karst zone thickness and reservoir thickness. Thus, we build the paleo-karst evolutionary pattern in the study area. Research suggests that vadose, underflow, and slow flow zones develop in the intended interval. We identify four underflow subzones in response to four paleo-karst water tables. Compared with the vadose zone, the underflow zone is thicker and holds more reservoirs, mainly distributed in the upper part of the single underflow subzone. Higher paleo-karst landform can possess a thicker vadose zone and thinner underflow zone. Besides, an excellent positive linear correlation exists between reservoir thickness and paleo-karst zone thickness. The thickness of the subzone constrains the development of reservoirs in it. The second and third underflow subzones are the most favorable intervals, owning more reservoirs. [ABSTRACT FROM AUTHOR]

Unlike the conventional approach to prevent and control water in the Ordovician limestone layer under the mine floor, which contains water. In this paper, based on the idea of “water hazard prevention and control changes from process control to source control”, innovatively determines that the study area has the basis of karst development based on the history of mine geological evolution, and analyzes the direction and area of karst development based on the fractal dimension of mine structure. According to the mineral composition and structure of Ordovician limestone, the vertical zonation of karst development is determined from the micro and macro aspects; according to the simulation of regional Ordovician limestone groundwater, it is determined that the Ordovician limestone water has cyclic alternation. Based on the comprehensive drilling data, the fracture development degree, the consumption of drilling fluid, the number of water-bearing boreholes entering the Ordovician limestone, the maximum water yield of boreholes, the number of drilled holes and the macro fracture development degree are analyzed in detail, and the horizontal and vertical development laws of the deep Ordovician limestone karst in Liangzhuang mine field are obtained. The best location for Karst development is at the north of F10 fault and 60–80 m from the top of Ordovician limestone in the study area. The correctness of the conclusion is verified by taking the 51101 working face with water inrush in Liangzhuang mine field as an example. This method is based on the combination of theoretical analysis and practical exploration, and the combination of macro analysis and micro analysis, which avoids the one-sidedness of exploring the development law of Ordovician limestone karst with single factor, and accurately predicts the development law of floor Ordovician limestone karst in detail, providing research ideas and methods for predicting the development law of deep Ordovician limestone karst in mined mines. [ABSTRACT FROM AUTHOR]

The variability of continuous hourly water temperature data and electrical conductivity measured at the Jadro karst spring was analysed for the period from January 1, 2011, to December 31, 2021. In this paper, the mean daily air temperature and daily precipitation data measured at the meteorological station Sinj, and the mean daily flow of the Jadro Spring, in the period 1995–2021 were also used. The analyses were performed on various time scales of year, month, and day. The aquifer that feds Jadro Spring has a very complex hydrogeological structure that is insufficiently explored. Jadro Spring has a limited capacity of maximum discharge. Its catchment area is not defined precisely. The relationship between water temperature and electrical conductivity is directly proportional while the relationship between water temperature and spring discharge is inversely proportional. As the flow of the spring increases, water temperature and electrical conductivity decrease. The narrow range of water temperatures and electrical conductivity indicates that the karst aquifer from which the spring is fed is not directly influenced by air temperatures and that flow does not occur through large karst conduits with a free water surface. The underground water level is located deep below the surface of the terrain, more than 100 m. [ABSTRACT FROM AUTHOR]

The current high global demand for high-quality paper, paint, adhesive/sealant, and plastic, filler industries cannot survive without unique and high-quality precipitated calcium carbonate (PCC). They are used as fillers, additives, and reinforcements. PCC is a key constituent of the modern paper and plastic industry. This article reports the effect of various organic and inorganic additives used in the synthesis of the different polymorph of calcium carbonate. The use of precipitated calcium carbonate fillers is the recommended choice in enhancing optical properties, durability, smoothness and ink adsorption in papermaking and improving the mechanical properties of plastic. PCC can best be synthesized using solid-liquid route or the gas-solid-liquid carbonation route, which consists of bubbling gaseous CO2 through a concentrated calcium hydroxide (Ca(OH)2) and/or calcium magnesium hydroxide (Ca·Mg(OH)2) slurry with suitable organic additives. The use of several organic and synthetic additives in conjunction with different reaction parameters for the synthesis of the various polymorph of precipitated calcium carbonate is reported. Depending on the desired end use, PCC polymorphs such as aragonite, vaterite and calcite are vital in the plastic and rubber industries. [ABSTRACT FROM AUTHOR]

China, being the world’s largest consumer of potassium fertilizer, faces significant challenges due to limited potassium reserves. Qarhan Salt Lake stands out as a reservoir containing 296 million tons of low-grade solid potash ore (KCl), establishing itself as the premier potassium fertilizer production base in China. The extraction of low-grade solid potash ore via liquefaction technology, leading to the generation of potassium-rich brine, emerges as a pivotal strategy for sustainable potash exploitation in the region. This approach offers a promising solution to mitigate the potassium salt shortage in China. This paper systematically examines the transformation in KCl content of solid potash ore within the Bieletan section of Qarhan Salt Lake before (2007) and after liquefaction (2022). The study employs quantitative assessments to determine liquefaction volume and efficiency. Results reveal that, at a shallow depth of 23.20m, the average KCl content of solid potash ore decreases from 2.15% before liquefaction to 1.00% after liquefaction. This observed decrease of 1.15% (53% reduction) underscores the substantial impact of liquefaction. A total of 136.94 million tons of KCl are dissolved, providing a sustainable resource for approximately 15 years or more. During the initial stages of liquefaction (2007–2008), a rapid decline in the KCl content of solid potash ore is noted, with liquefaction efficiency significantly influenced by the positioning of the brine mining channel. As liquefaction progresses, efficiency diminishes, although the overall efficiency surpasses that of the Huobuxun section at the eastern extremity of Qarhan Salt Lake. This study holds significant implications for refining the solid potash liquefaction mining strategy in Qarhan Salt Lake, providing valuable guidance for future optimization efforts. [ABSTRACT FROM AUTHOR]

The frequency of water inrush disasters severely affects tunnel construction, lives, and property. As a result, accurate forecasting of the danger of water inrush during construction is critical. This paper aims to create a progressive evaluation model for assessing water inrush risk during two stages: pre-construction and construction. The proposed model provides a static pre-construction estimation and allows dynamic updates based on previous predictions for unexcavated sections during construction. Initially, comprehensive multi-water inrush information was presented by analyzing 65 tunnel accidents of water during construction, including 12 evaluation indexes encompassing hydrogeology and excavation monitoring. Subsequently, the assessment model was constructed using a combined weighting method and non-linear attribute recognition theory. The information from dynamic monitoring on surrounding rock and seepage pressure is integrated, and feedback site data is used to dynamically modify the weighting of the indicators and update the projected predictions. This approach has been employed as a case study to evaluate the water inrush risk during the Qinling water transmission tunnel. The results demonstrate that the prediction outcomes of dynamic weights align well with on-site holes, exhibiting higher forecasting accuracy than other methods. This approach offers a novel perspective for accurately evaluating water inrush risk in tunnel construction. [ABSTRACT FROM AUTHOR]

The mineralogy of some carbonate rocks from the Abakaliki Basin has been investigated to determine the depositional environment classification and assess the suitability of the rocks for application in geotechnical construction and industrial process systems. The method of investigation included field mapping and petrographic and geochemical techniques to characterize their field characteristics, mineral types and texture and chemical contents. Mapping revealed two lithologic units of sandstone and shale that associate with the carbonates in a similar sequence. The carbonates contain fossils and are composed of calcite, quartz and rockclasts. The grains have angular to sub-rounded sphericity and are dispersed in hetereolithic groundmass. The major oxide composition shows average value of 32.30wt% SiO2, 26.37wt% CaO, 7.23wt% MgO, 6.56wt% Fe2O3, 4.38wt% Al2O3, and 3.23wt% K2O + Na2O in decreasing order of abundance. Concentrations of trace elements are significantly higher (> 100 ppm) for V, Cr, Sr, Zr, Cu, Ba, Pb and Zn and comparatively lower for Sb, Ge, Ce, Y, As, Hg, Tiand Au. The studied rocks qualify as biomicrite or wackestone and range from dolomitic, through carbonaceous to siliceous limestone deposited in a wide spectrum of environment from shallow marine to transitional setting. The rocks are marginally suitable for use as aggregates due to the presence of deleterious contents of quartz and organics. For cement production, their low content of CaO, relatively high SiO2, comparatively high LOI and elevated abundances of contaminant heavy elements are major limitations. Similarly, in paper, plastic, paint, metallurgy and pharmaceutics, the rocks are unsuitable due to the constituent minerals. [ABSTRACT FROM AUTHOR]

Determination of recharge sources for karst springs can be essential in protection against their quantity diminishment and quality deterioration but has been challenged with complexity of karst water systems. This paper discusses an innovative approach consisting of multiple lines of evidence to investigate the water and turbidity sources for a pristine karst spring (Spring #1) that is located adjacent to and downgradient of a marble quarry. The approach is based on data collected on different scales and included characterization of turbidity dynamics in the spring itself, statistical analysis on relationships between turbidity and precipitation as well as between turbidity and blasting, infiltration tests within the quarry pit, X-ray diffraction analysis of sediments samples, and dye tracing tests. Eleven dye tracing tests conducted in five phases confirmed that Spring #1 receives water from both allogenic and autogenic sources. The allogenic recharge is from four sinking streams (Sinking Streams #1 through #4) and sinkholes (Sinkhole #1 area) on the borderlands, whereas the autogenic recharge is from the karst land including the quarry pit. The groundwater flow rates estimated from the tracing tests vary from 9 to 841 m/day, indicative of presence of solution-enlarged conduits in the marble aquifer. The X-ray diffraction analysis of sediment samples collected at Spring #1, the marble quarry, and Sinking Stream #2 suggested multiple turbidity sources in Spring #1. Based on the statistical analysis of data collected over 10 years, precipitation is the most important factor impacting the turbidity in Spring #1. On average, rainfall events can raise the turbidity level by approximately 14 Nephelometric Turbidity Unit (NTU). Although the infiltration test did not identify turbidity changes in Spring #1 in response to pooling of muddy water on the quarry floor, the statistical analysis suggests that, on average, blasting in the quarry could elevate turbidity value by up to 2 NTU. The blasting impact appears to become more noticeable when blasting occurred on the lower two benches of the quarry. [ABSTRACT FROM AUTHOR]

Reliable estimates of groundwater recharge are crucial for the groundwater resources evaluating and sustainable utilization plans formulating. To protect the precious karst groundwater resources, this paper critically reviewed the previous studies on karst groundwater recharge in northern China karst regions from the perspective of diffuse recharge and focused recharge, and took Niangziguan Spring catchment as a case study. It is concluded that for the 119 karst groundwater systems, 52% occur diffuse recharge through precipitation infiltration, 48% occur both diffuse recharge through precipitation infiltration and focused recharge through surface water leakage. The mean annual precipitation, diffuse recharge and infiltration coefficient (IC, as percentage of precipitation) are 560 mm, 136 mm and 23.1%, respectively. A high correlation was observed between annual precipitation and annual diffuse recharge with a nonlinear relationship. The IC can vary substantially even with the same annual precipitation between 9.3 and 38.0%, with an evidently increasing trend eastward. This reflects a significant difference in the degree of karstification for the northern karst regions. The most commonly applied for recharge assessment in northern China karst regions is equal volume spring flow method, the chloride mass balance method is highly recommended for groundwater recharge estimation of the regions based on the case study. This work provides reference for recharge estimation, assessment and management of karst groundwater resources in northern China. [ABSTRACT FROM AUTHOR]

This paper presents a water inrush comprehensive evaluation model based on cloud model. The qualitative and quantitative transformation of water inrush evaluation indices are realized by cloud generator, applied in the water inrush risk evaluation of lead zinc ore body mining in karst aquifer. 9 factors were selected to construct the water inrush evaluation index system. The risks of water inrush were classified to five levels: risk level I, risk level II, risk level III, risk level IV and risk level V, respectively. The improved analytic hierarchy process (IAHP) and the criteria importance though intercriteria correlation (CRITIC) were adopted to determine the subjective and objective weights of the evaluation indicators, respectively. The concept of Kullback information was applied to determine the combination weight of evaluation indices. Then, the comprehensive certainty of the water inrush risk level was determined, combining the index weight and the corresponding cloud eigenvalue. In addition, combined with the water inrush risk level of the samples, the water inrush risk zoning of the study area was realized with geographic information system (GIS). This model was applied to the Maoping lead zinc mine in southwestern China to evaluate the risk of water inrush from the mining of the ore body. The results show that the combined weight method (CWM) based on the concept of Kullback information is characteristic by both subjective and objective, without weight bias; the cloud model can better convert the qualitative and quantitative between evaluation indices; the prediction accuracy of the water inrush evaluation model constructed based on the CWM is higher than that of IAHP, CRITIC and water inrush coefficient (WIC), with a better fitting effect. This work provides an innovative idea for water inrush evaluation of ore body mining in karst aquifers. [ABSTRACT FROM AUTHOR]

The karst mountainous areas of southwestern China are widely distributed and affluent in mineral resources. However, mining activities induced numerous large-scale landslides in this area, resulting in tremendous loss of lives and property to residents. As a result, it is crucial to figure out the triggering mechanism and failure modes of mining landslides for landslide prevention. In this paper, the environment characteristics and triggering mechanism of mining landslides in karst mountainous areas of southwestern China were analyzed by investigating a few mining landslides. Specifically, it can be attributed to the natural environment and human activities, which are topography, lithology, geological structure, karst hydrogeology, rainfall, and mining activities. On the other hand, a unified failure mode classification system for mining landslides in karst mountainous areas of Southwest China was established based on the international landslide classification system and different slope structures (subhorizontal bedding layered slope, bedding layered slope, anti-dip layered slope, lateral layered slope, oblique inclined bedding layered slope). In this classification system, the basic failure modes were analyzed in detail, and the mining impact mechanisms for each failure mode were revealed. The corresponding mechanical models and stability criteria for mining-induced flexural topple and planar slide were summarized. This study not only identifies and rapidly classifies mining landslides in the karst mountainous areas of southwestern China, but also further facilitates the prediction and evaluation of the stability of mining-induced unstable rock masses. [ABSTRACT FROM AUTHOR]

The main purpose of comprehensive reservoir characterization is to reliably calculate, characterize and identify petrophysical parameters including porosity, permeability, rock fabrics, pore size distribution, pore network system, saturation and capillary pressure. These essential petrophysical properties could be achieved by a combination of Nuclear Magnetic Resonance (NMR), conventional and special core analysis (CCAL/SCAL) in core laboratories. In this study, six core plug samples from the Asmari carbonate Formation in Gachsaran oilfield have been examined by the core measurements and NMR technique to evaluate and compare the petrophysical properties. Initially, the plug samples are prepared by core plugging, trimming, solvent cleaning and oven drying methods. Comparison between well Gamma ray log and core gamma ray adjust the depth to the real position of reservoir target. Basic SCAL measurements are then conducted on the prepared plugs in steps to calculate porosity, permeability, capillary pressure and fluid movements. Then the dry samples are completely saturated with brine and the basic properties are re-measured by the NMR method. The relationship between rock quality values (porosity and permeability) determined from NMR technique and core results demonstrate that by applying some adjustments on NMR modeled values, the precise results are achievable. Pore size distribution curves displayed in this paper confirm the NMR modeled pore throat curves and shows NMR could be applied as useful technique for estimating pore size distribution when they are in agreement with Mercury Injection Capillary Pressure (MICP) pore size distribution. The NMR pseudo capillary pressure curves show consistency with capillary pressure and saturation behavior of MICP tests. In addition, the lithology, rock fabric and pore shapes are checked by petrographic images of thin sections as representative of microscopic reservoir characteristics in the reservoir. In present study, applying of NMR technique to the plugs and comparison the obtained results with SCAL results demonstrate how the NMR technique can objectively and quantitatively provide petrophysical analysis for a carbonate reservoir and combination of core analysis and NMR technique could optimize reservoir quality investigation. [ABSTRACT FROM AUTHOR]

Special attention has recently been paid to the high-salt formation in Qianjiang depression as its abundant oil resources with ultra-low permeability and porosity. However, the complex pore structure characteristic of the high-salt formation has not been well understood so far because of its pore size ranging from nanometer to micrometer scale. This paper aims to investigate the complex pore structure characteristic of the target high-salt formation based on an integrated experimental approach involving X-ray diffraction (XRD), scanning electron microscope (SEM), mercury injection capillary pressure (MICP), casting lamella observation and nuclear magnetic resonance (NMR) techniques. XRD analysis results indicate that the target formation mainly includes clastic mineral, carbonate mineral and salt mineral, and the content of them are 32.16%, 36.59%, and 24.65%, respectively. The results of SEM and casting lamella observation indicate that storage space of target formation can be divided into intercrystal pores, solution pores, and fractures. Solution pores have great impact on oil production, which includes dolomite dissolved pore and glauberite dissolved pore. Based on the MICP test results, the samples can be divided into pore type and fracture-pore type. The average pore radius of pore type samples and fracture-pore type samples are 0.0144 μm and 0.40 μm, respectively. Pore size distribution (PSD) results from MICP indicate that single peaks appeared in PSD curves of pore type samples and multi-peaks appeared in PSD curves of fracture-pore type samples. Permeability contribution peaks of pore type samples range from 0.01 to 0.03 μm, and permeability contribution peaks of fracture-pore type samples range from 1 to 10 μm. Comparing the permeability contribution of pore type samples and fracture-pore type samples reveals that mesopores and macropores make the vast majority of permeability contribution of the two kind type samples. A method to get permeability contribution of pore throats from PSD results has been introduced in this paper based on T2 NMR test. Comparing the PSD results from MICP and T2 NMR test results shows that T2 NMR test can identify smaller pore throat. [ABSTRACT FROM AUTHOR]

In recent years, the rapid development of new energy vehicles and energy storage technology, driven by the new energy industry, has led to rapid growth in lithium consumption. China has abundant lithium resources, especially in salt lake brine. Zabuye salt lake is the only salt lake in Tibet that has achieved the industrial development of lithium carbonate by using the lithium extraction technique with salinity-gradient solar pond (SGSP) so far. In this paper, the stereo-crystallization process is innovated and optimized based on an enhanced SGSP with nucleation matrix. The optimal processing parameters such as the structure design of the nucleation matrix, the spatial range of underutilized heterogeneous nucleation zone (UHNZ), and the appropriate area ratio of crystallization units have been obtained by experiments. The results show that the UHNZ should be about 0.80–2.00 m from the bottom of the pond, when the total depth of water body in the solar pond is controlled within 2.80–3.30 m and the thickness of the freshwater layer is between 0.30 and 0.60 m. For the best precipitation effect of lithium carbonate, it is suggested that the height of lower nucleation matrix (LNM) in the crystallization unit should be controlled above the height of about 0.80 m from the bottom of the pond, and the area ratio of crystallization units should be about 10%, when implementing the stereo-crystallization process. In 2022, the stereo-crystallization process with the enhanced SGSP has been fully promoted and implemented in Zabuye mining area of Tibet, increasing the output and grade of lithium concentrates significantly. [ABSTRACT FROM AUTHOR]

Previous research shows that the origin and distribution of formation overpressure are governed by several dominant factors including disequilibrium compaction, hydrocarbon generation, tectonic compression and diagenesis, influenced by salt components and their concentration, but it is unclear how salts affect formation overpressure in saline lacustrine basins. This paper investigated the effect of salts on formation overpressure based on organic geochemistry, rock mineralogy, logging curve comparison and wave velocity-density cross-plot by combining the sedimentary and structural background. In the Western Qaidam Basin, the proportion of abnormally high pressures rises from the Neogene to the Paleogene. The top surface of the overpressure is between 2300 and 2500 m deep. As the subsidence and sedimentary centers of the basin moved eastward, the centers of the overpressure migrated from west to east. In the Upper Oligocene, the overpressure is developed in the deep and semi-deep lacustrine facies, and the pressure coefficient is 1.8–2.0. Disequilibrium compaction is the primary control factor with a contribution rate of more than 60% in the intersalt and subsalt strata, followed by tectonic compression with a contribution rate of 20–30%. Fracture reducing by salt filling and fluid volume expanding by gypsum dehydration increase the fluid volume in the formation, which promotes formation overpressure. The gypsum salt rocks also have strong plasticity and sealing effect, thus providing a closed environment for the formation overpressure. Through providing the primary migration driven force and sealing conditions for oil and gas, the overpressure is meaningful to petroleum accumulation and preservation in saline lacustrine formation of the Paleogene and Neogene in the Western Qaidam Basin, NW China. [ABSTRACT FROM AUTHOR]

The Zhouchang area, where the oil is mainly accumulated in Mesozoic sandstone reservoirs, is located in the Ordos Basin, China. Paleogeomorphology plays an important role in the oil accumulation of the Jurassic Yan'an Formation. Previous studies on paleogeomorphology propose that Lower Jurassic oil reservoirs are distributed in the higher units, such as the paleoslope, which is now proved to be not completely accurate in this study. The paper mainly focuses on paleogeomorphology restoration, favorable oil accumulation conditions, oil accumulation patterns, and favorable area prediction. Based on the stratigraphic division of the Lower Jurassic strata, the pre-Jurassic paleogeomorphology is precisely restored using the moldic method and is divided into secondary units. Furthermore, the controlling effects of the pre-Jurassic paleogeomorphology on oil accumulation are discussed. Results indicate that the paleogeomorphology can be divided into paleochannel, paleoslope, and paleohighland in the study area. The proved oil is distributed not only in the paleoslope but also in the lower paleochannel, which is different from previous study conclusions. Paleochannel sandbodies provide a conducive pathway and storage space for oil migration and accumulation, and the sandbodies in the paleoslope area are considered as favorable reservoir strata. Paleogeomorphology-controlled microamplitude structures are suitable traps for oil preservation. Two patterns for oil accumulation in 2D are newly established: paleochannel-braided channel-delta plain pattern and paleoslope-braided channel-delta plain pattern. The pattern for oil accumulation in 3D is also created for the first time. Through the studies above, four favorable areas for oil accumulation in Zhouchang area are predicted. [ABSTRACT FROM AUTHOR]

In order to understand the genesis of a carbonate (karst) aquifer from its initial stage to a fully developed karst system number of different methods have been developed over the last 50 years. Nevertheless, with the continued progress of new technologies developing, the groundwater genesis of the karst aquifer becoming more and more precisely defined. Still, more investigation, specific forums and scientific discussion as well as publications are necessary to improve the knowledge of groundwater genesis within carbonate aquifers, as a main step of karst groundwater protection and utilization. With increasing demands on water resources protection, water supply, urbanisation, construction of large dams, reservoirs, tunnels, railways, roads, mines, tailings and waste disposal structures also increase necessity for close co-operation of a wide spectrum of scientist in precise defining and modeling of groundwater genesis. Groundwater from carbonate aquifer as a rule have good physic-chemical characteristics, and inside of the carbonate rocks can accumulate a large quantities of groundwater, which are ideal for watersupply. On the other hand, they are characterized with high vulnerability to pollution, due to weak autopurification properties of the medium, and big variation in discharging. In order of properly using of karst natural resources, the good knowledge of the hydrogeological system genesis is necessary, meaning primarily on carbonate or evaporitic formation with well-developed dissolution porosity. In a case of defining of groundwater genesis of carbonat aquifer as well as protection, a large number of methodological approaches can be applied in order to define the recharge zone and connection between the underground and surface waters, the mean residence time, as well as groundwater interaction with the hostrock, which have influence on chemical composition and temperature regime of discharged water. This special thematic edition partly includes extended versions of the selected papers that will have been presented at the International Symposium KARST 2018, which deals with the above presented and discussed topics precisely through the works of a large number of world-renowned authors. A number of papers will be presented by invitation, and will directly refer to specific areas of karst exploration: hydrogeology, geomorphology, engineering geology, speleology, all relating to the sustainable use of karst waters as an essential natural resource. The papers will cover a wide range of recent scientific research that was carried out in karst terrains all over the world (China, USA, Canada, Russia, Iran, Peru, Turkey, Malaysia and many European countries). [ABSTRACT FROM AUTHOR]

China is one of a few countries in the world where karst is intensively developed and karst water is heavily utilized as water supply sources. Shanxi is such a Province with the largest karst distribution in places in Northern China, where 19 large karst springs and their catchments are identified to provide important sources of the water supply and ecosystem functioning in Shanxi. Over the years, many problems associated with utilization of karst springs in Shanxi cropped out, including the decrease in spring flow, decline of groundwater level, groundwater contamination and pollution, etc., which severely restrict the sustainable utilization of karst water resources in Shanxi. Through the retrieval and analysis of some 200 local and international publications, this paper critically reviews the research results of karst springs in the region from the perspective of spring flow trend, precipitation recharge and time-lag, evaluation of karst water resources, water chemistry and environmental isotopes with purposing assession, and further evaluates the integrity of the aquifer system including vulnerability, impacts of coal mining and engineering activities on karst groundwater, delineation of spring catchment sub-systems, protection and management measures. It is concluded that human activities and climate change are the primary and secondary factors negatively affecting karst springs, respectively. The impacts of human activities on karst springs are mainly facilitated by intensive development of karst water, mining drainage, engineering construction and other activities. While karst water in parts of Shanxi spring catchments is polluted to various degrees, hence it is recommended to mainstream the protection of karst spring water in the areas of strategic importance. This paper will contribute towards the establishment of sustainable development and utilization of karst water in Shanxi and even in Northern China. [ABSTRACT FROM AUTHOR]

The dolostone–evaporite co-occurring system (DECS) is widely found in Precambrian to Quaternary strata. In the eastern Sichuan Basin, DECS is mainly developed in the Cambrian Longwangmiao, Gaotai, and Xixiangchi Formations. In this paper, the controlling factors of sedimentary, sedimentary models, and main controlling factors of reservoir of the DECS of the eastern section of the Sichuan Basin were investigated, through core observations, thin section analysis, and field profiles measurement and sampling, combined with well-logging data, interpretations of geochemical analyses, and cathodoluminescence. The lithological associations of the evaporite and dolostone in the DECS include interbedded dolostone and evaporites, thick-bedded to mass evaporites above the dolomite, dolostone intercalated with evaporite, and evaporite intercalated with dolostones. The reservoir of DECS is mainly a dolomite reservoir in dolomite interbedded evaporite. The lithology mainly consists of oolitic dolomite and siliceous fine crystalline dolomite. The reservoir porosity includes dissolution porosity, porosity, and fractures. The analysis of the geochemical characteristic indicated that the formation of DECS is affected by the closed water body and high salinity (Z > 120), the hot and arid paleoclimate (T = 21.1 ℃), intense evaporation, and the continuous decline of the ancient sea level. According to the paleoenvironmental characteristic, the models of DECS include four dolomite models, evaporite pump (sabkha) dolomite diagenetic model, reflux permeable dolomite diagenesis model, diagenetic model of buried dolomite, and tectonic-age hydrothermal dolomite genesis model, and two evaporite models: Sabkha diagenetic model and underwater concentration diagenetic model. Based on previous studies, the influence of different factors on the deposition of the shoals in the DECS was evaluated. The main controlling factors for the formation of high-quality reservoir units include thermochemical sulfate reduction (TSR) and structure-controlled hydrothermal dolomitization. Sulfides and deep fluids in DECS play a constructive role in reservoirs. [ABSTRACT FROM AUTHOR]

Ooids are common and important type of carbonate rock grain, and although they have a long development history, their origin has not been determined. In recent years, increasing evidence has supported the microbial mechanism of ooids. In this paper, we used polarized microscopy, fluorescence microscopy, cathodoluminescence microscopy, and scanning electron microscopy to investigate the microbial origin of the micrites in ooids from the Cambrian Miaolingian Series, North China. Many Girvanella filaments have been preserved in the cores, and cortexes of some ooids, as well as irregular agglomerates or clots among ooids. These Girvanella fossils indicate that filamentous cyanobacteria played an important role in the formation of the micrite in ooids, especially in the cortices of giant ooids. In addition, seven types of extracellular polymeric substance mineralization fabrics (i.e., nanospherical, sheet like, lumpy, rod like, tube meshwork like, honeycomb like, and fibrous) are preserved in the micrites in ooids from the Cambrian Miaolingian Series, North China. The cyanobacterial filaments and various types of microbial mineralization fabrics indicate that the autochthonous micrites in ooids are the result of microbial mineralization of organic matter and may also provide an important evidence for the microbiological genesis of ooids. [ABSTRACT FROM AUTHOR]

As early as 2011, people have recognized the great potential of continental shale gas in the Ordos Basin and obtained commercial gas flow from some exploration wells. However, over the years, shale gas has not yet reached commercial production in this basin. The complexity of the geological conditions and the lack of understanding of the continental shale gas enrichment characteristics are the most important factors restricting shale gas from reaching commercial production capacity. Therefore, the identification and division of favorable intervals of continental shale is the key to achieving exploration breakthroughs. The Chang 7 shale of the Yanchang Formation in the Ordos Basin is the first continental shale to be targeted for shale gas exploitation in China. A large amount of drilling data and experimental analysis test data have been accumulated during exploration in recent years. Therefore, in this paper, the favorable development intervals of the Chang 7 gas shale have been divided and predicted through the analysis of multiple geological factors. The results show that two types of favorable intervals can be identified in the Chang 7 shale. One type is the thick organic-rich shale interval, in which thin sandy laminae are developed. Shale gas mainly exists in the shale as adsorbed gas and remains trapped in the interval due to the poor physical conditions. This interval can be recognized by the logging curve, characterized by a high Gr (Gr > 180 API), high resistance (Rd > 100 Ω·m), high time difference (AC > 280 μm/s), and low density (Den < 2.4 g/cm3). The other type is where sandy lamina and organic-rich shale are interbedded in a 'sandwich' arrangement, where the shale gas exists mainly in sandy lamina as free gas. This interval can be recognized by the logging response characteristics of a medium to high Gr (180 API > Gr > 120 API), high time difference (300 μm/s > AC > 250 μm/s), high resistance (Rd > 100 Ω·m), and medium–low density (2.6 g/cm3 > Den > 2.4 g/cm3). These research results can effectively explain the enrichment mechanism of the Chang 7 shale gas and guide the exploration and development of the hot gas shale. [ABSTRACT FROM AUTHOR]

The paper focuses on analyzing the water temperature of Ombla, the largest karst spring in the Dinaric Karst. Hourly measurement data were available from January 1, 2007, at 0:00 a.m. to December 31, 2021, at 11:00 p.m. It has been established that, within that period, there were two sub-periods with different characteristic (minimum, average, and maximum) water temperatures. In the first sub-period, which lasted from January 1, 2007, at 0 a.m. to January 24, 2012, at 8 a.m., the minimum, average, and maximum water temperature values were 12.5, 13.83, and 15.0 °C, respectively. In the second sub-period (January 24, 2012, at 9 a.m. to December 31, 2021, at 11 p.m.), there was a sudden drop in the characteristic temperatures, which were 10.9, 12.91, and 14.0 °C. At the same time, a strong increasing trend of the regional air temperature is noted. It has been detected that the water temperature reacts to the air temperature with a delay of about 1 month. Due to the enormous importance of this abundant karst source, it is necessary to determine the reasons that led to the sudden drop in water temperature at the end of January 2012. [ABSTRACT FROM AUTHOR]

This paper focused on analytical validation such as the amount needed, time drift, repeatability, memory effect, analytical precision and accuracy on carbon/oxygen isotopic measurement of small carbonate samples (10-80 µg) using an IsoPrime100 mass spectrometer. 10 µg of carbonate samples yielded mass 44-intensity of 2 nA. The minimum amount needed was 10 μg and the repeatability was around 0.1 ‰ (1 s.d.). Through 24-h measurement there was no temporal variation of δC, but that of δO showed variation with decreasing the amount of CO reference gas, suggesting that δO values need to conduct time drift correction. Inter-sample memory effect was not observed, indicating that IsoPrime100 mass spectrometer with CO purification system is adequately evacuated after each analysis by means of pumping system. Moreover, IAEA-CO-1 and JAMSTEC-WS values calibrated by international reference NBS19 agree within error with the reference values, demonstrating the accuracy of our analytical procedure on carbon/oxygen isotopic measurement of carbonate samples. This paper offers insights into analytical validation procedure when setting up a mass spectrometer on isotopic analyses of small carbonate samples. [ABSTRACT FROM AUTHOR]

The formation environment of continental evaporite—particularly the sedimentary environment closely related to continental evaporite deposits—has received significant research attention for several years. From this perspective, an intermountain basin exists in the inland area of Northwest China, known as the Kumishi basin. The elevation of this basin is relatively low, where a set of evaporite series strata developed during the late Quaternary. In this paper, we analysed the sedimentary environment of the Kumishi basin in terms of the sulfur isotopes combined with its paleosalinity characteristics. The results show that the δ34SV-CDT isotopic composition ranges from 6 to 11‰. The isotopic fractionation effect of the surface salt crust is significantly lower than that of the lower halite layer owing to the influence of surrounding fresh water and other chemicals. The low sulfur isotopic value is indicative of a typical continental sedimentary environment. In addition, the bacterial sulfate reduction (BSR) indicates that the sulfate formation environment is open to sulfates, and rejects H2S. This phenomenon further indicates the weak bacterial reduction environment in the Kumishi basin. In combination with its paleosalinity characteristics, we determined that the saltwater environment influenced the changes in sulfur isotope value. This can facilitate the further understanding of the sedimentary environment of evaporites in low altitude intermountain basins. [ABSTRACT FROM AUTHOR]

To characterize the polyphase palaeokarst development of Wumishan formation in Jizhong depression, the data of outcrops, cores, thin sections, SEM, core plugs, drilling relief and leakage, and carbon isotope have been analyzed in this paper. The results reveal that the polyphase palaeokarst was petrography controlled of microbial dolostone and grain dolostone, and was identified as three phases: (1) poly-period eogenetic karst during Wumishan depositional environment, (2) two-period telogenetic karst in Triassic and Cretaceous, and (3) hydrothermal karst in Paleogene. The eogenetic karst was related to high frequent sea level fluctuations with development of vugs and selective dissolution porosities which distributed at the top of microbial dolostone and grain dolostone layers. The origin of the telogenetic karst was related to Indosinian and Yanshan orogeny which formed widespread fold belts and thrust faults, and provided the endokinetic force and a strong topography difference. Each period's telogenetic karst was characteristic of one-period fracture-cave system, and the Cretaceous telogenetic karst was stronger than the Triassic telogenetic karst in karst intensity. Moreover, the karst intensity increased downward in superimposed telogenetic karst zones. Hydrothermal karst was related to volcanic activities and provided the hydrothermal environment for its formation. It was featured by solution-enlarged porosities and new forming porosities. The microbial dolostone and grain dolostone layers with three-phase palaeokarst were the best exploration targets for high-quality reservoirs. This paper rebuilds a suitable karst model to show the palaeokarst evolution process. [ABSTRACT FROM AUTHOR]

Dolomites are well-known minerals; belonging to the Infra-Cambrian Hormuz Series lies within the salt domes of southern Iran. In this paper, the origin and alteration of dolomitic rocks of Paskhand and Deh-kuyeh salt diapirs in the area of Larestan (southern Iran) are investigated. Based on petrographic (size and fabric) studies, we recognize four dolomite types that consist of very fine-to-fine crystalline dolomite (D1), neomorphic dolomite (D2), fine-to-medium crystalline euhedral-to-subhedral dolomite (D3), and pore- and fracture-filling dolomite (D4). The dolomite samples with up to 26% iron can be called ferruginous dolomites. Some igneous rock patches to gehter with hydrothermal iron veins are observable in the salt domes of Larestan. Oxygen and carbon isotope values of black and white, and altered red dolomite of Paskhand and Deh-kuyeh salt domes, are equal to − 12.35 to − 18.78 for δ18OPDB and − 5.48 to − 8.49 for δ13CPDB; values enriched δ180 with low-temperature (~ 70 °C) conditions are related to D1 dolomites and values depleted δ180 with higher temperatures (~ 270 °C) are related to D3 and D4 dolomites. The most important source for secondary dolomites is deeper hydrothermal and catchment sources, which ascended through faults during the intrusion. Meteoric waters can be mentioned as less important sources for these types of dolomites. We reported sassolite B(OH)3 mineral in Deh-kuyeh salt diapir for the first time in this paper. This mineral is only observed in the areas which have famous riftings Fumarol. Therefore, in this paper, the existence of sassolite in the studied area could be considered one of the most important the origin of the composing elements of Hormuz rocks from fumarols which are formed in an extensional regime. [ABSTRACT FROM AUTHOR]

This study is made clear expansion, depositional architecture, and sea-level change of the Seymareh Member. The Campanian carbonate sequence (Seymareh Member) of the Lurestan Zone, contains a rich macrofauna. Amid the bivalves, oysters (Lopha sp.) and echnoids are abundant and are mostly well conserved, in some beds dominating the fauna. Rich fossiliferous strata of Seymareh Member are 10–300 m and widespread in the south Lurestan Zone. A submarine canyon in the shelf is suggested for the depositional environment of the Seymareh Member which deepens to the east (Anaran and Surgah, Emam-Hasan anticline) and thins in west locations (Pasan, Soltan and Kabir-Kuh anticline). This present study is novel because few papers provide a complete overview of the frequency Seymareh canyons and out into deep water basins. The paleocanyon deposits conserved south Lurestan Zone provide an occasion for extending sequence stratigraphic ideas and thought associated with submarine canyons and deep-sea deposits. The Seymareh Member were deposited at a more toward the sea situated continental slope or outer belt region of the Late Cretaceous upwelling system and 4th order cyclic sequences in the Seymareh Member are recognised. Below these lowstand conditions, oyster shells were poured off the bioherms and deposited as large cross-bedded units on the flanks of the basins. At the same time, antecedent glauconite and phosphatic deposits were reworked and winnowed to form high-grade phosphorite. [ABSTRACT FROM AUTHOR]

Due to the cost efficiency and environmentally friendly surfactant features in enhanced oil recovery techniques, the appropriate designation of surfactant flooding should be considered. It is essential to evaluate the crucial factors that affect surfactant adsorption on rock surfaces to eliminate the total economic losses of surfactant retention and adsorption in porous media. In this paper, the considerable influence of temperature, different surfactant concentrations, and polymer addition were experimentally investigated for dolomite minerals extracted from Pabdeh formation. According to this study, higher adsorption density has occurred at lower temperatures, which implies lower kinetic energy between the surfactant molecules. For 25 ℃, the adsorption density is about 41 mg/g, and it has the lowest value of 100 ℃. It is about 17 mg/g. By the increase of surfactant concentration for different time steps, adsorption density has been increased. For the surfactant concentration of 5 Wt. %, the adsorption density is about 42 mg/g; however, it is for 0.15 Wt. % of surfactant concentration, the adsorption density is about 1 mg/g. Moreover, due to the higher stability of polymers, adsorption density has been decreased by the addition of polymer. The stopping time for each surfactant concentration is about 6.5 h for the surfactant concentration of 5 Wt. %. Consequently, the critical micelle concentration point is about 3.5 Wt. %, 4 Wt. %, and 5 Wt. % for linear alkylbenzene sulfonic acid, cetyl trimethyl ammonium bromide, and Triton X-100, respectively. This change in the conductivity is related to the start of the micelling process by increasing surfactant concentration. [ABSTRACT FROM AUTHOR]

The deep and ultra-deep oil and gas has been a prominent exploration direction in the field of petroleum industry in recent years. The deep oil and gas resources are mainly distributed in the carbonate rocks, clastic rocks and igneous rocks, of which the carbonate rock reservoirs account for about 40% of global oil and gas reserves for their superior reservoir properties. Currently, a number of large oil and gas fields have been discovered in the deep marine carbonate rocks in China, especially in the Sichuan and Tarim Basin, thus showing a broad oil and gas exploration potential in the deep marine carbonate rocks. In this paper, the genesis and source of deep natural gas in the Tarim and Sichuan Basin has been systematically studied. The results show that the natural gas in the deep marine carbonate rock reservoirs is not only sourced from the deep-source rocks, but the substantial crack of crude oil in the reservoir under the condition of high burial depth and high geotemperature can provide abundant natural gas sources for the deep reservoir. Accordingly, the contribution of gas from oil cracking should be concerned in evaluation on deep natural gas resources. [ABSTRACT FROM AUTHOR]

The spatial distribution patterns of soil organic carbon (SOC) and its relationship with various environmental factors in different topographic features are of great significance for evaluating SOC reserves and carbon pool management in karst areas. In this paper, SOC from the non-karst landforms and four typical karst landforms (karst canyon, karst peak cluster, karst plateau, and karst trough valley) was selected as the research object. The distribution patterns and the driving factors of SOC in the typical landforms were investigated from the topographical and environmental perspectives. The results showed that the average content of organic carbon in non-karst region was 9.39 g/kg, while that in karst areas was 16.31 g/kg. The vertical changes in SOC content showed different patterns in different topographic features, and each layer of the soil profile showed that SOC content in karst regions was greater than that in the non-karst one. The driving factors for SOC varied in different landforms. Specifically, in non-karst and karst peak cluster areas, slope gradient was the key factor influencing SOC. In karst canyon areas, soil thickness was the key factor influencing SOC. In karst plateau areas, land utilization was the key factor influencing superficial SOC. In karst trough valley areas, rock exposure was the major driving factor for karst SOC. These findings could provide an excellent explanation for the factors influencing SOC in karst and non-karst regions in Southwest China. [ABSTRACT FROM AUTHOR]

Geothermal activities are often associated with hydrothermal deposits and hydrothermal features that could aid in geothermal exploration. As a case study, this paper is concerned mainly with the factors controlling the hydrothermal activities and deposits in the Hammam Faraun (HF) area, Gulf of Suez rift, Egypt. In addition to dolomites, hot spring travertine deposits recorded for the first time in this area are emphasized. The proposed conceptual models illustrated that these deposits are confined to the damage zone of the Hammam Faraun fault (HFF). The main factors controlling the hydrothermal activities through time are: syn-rift volcanic activities related to shallow magma chamber bounded to the lithosphere, variable fluid conditions and nature of hydrothermal circulation through HF fault system. At rift initiation, sea water percolated along the CLB fault (a clysmic fault parallel to HFF), reached the Nubian Sandstone and Eocene Carbonate aquifers, mixed with their water, heated and arose along the HFF. The hydrothermal deposits related to fluid circulation at this time are represented by stratabound dolomite. At rift climax, the massive dolostone was formed from coastal lakes mixed water. These dolomitizing lakes occupied the topographically low area at the flank of HF relay ramp. With the beginning of post rifting time, travertine deposits were developed from fluids inside spring lakes during the Pleistocene pluvial period. This sequential development of dolomitization, travertine, and hot fluid flow in HF area would suggest continuity of geothermal activities since the rift initiation until present. Therefore, this study may be considered as a guiding model for further proper evaluation of geothermal energy resources of HF area in particular and geothermal systems in rift basins in general. [ABSTRACT FROM AUTHOR]

In this paper, we present the detailed microfacies study and geochemical characteristics of carbonate exotics (olistoliths) associated with the Eocene Disang group of Assam–Arakan Basin, Northeast India to deduct their relative age, and depositional environment. The studied carbonate rocks contain diverse fauna with the dominance of foraminiferal assemblages (planktonic and benthic). The well-preserved planktonic foraminifera, especially Globotruncana spp. and Heterohelix spp. are recorded in carbonates and age has been assigned as late Cretaceous (Maastrichtian in age). Rare earth element (REE) contents (~ 56 ppm average value) in these carbonates are high compared with the average value of typical marine carbonate (~ 28 ppm). The Post-Archean Australian Shale (PAAS)-normalized REE patterns of these carbonates exhibit seawater-like REE patterns with light rare earth elements (LREE) depletion and relatively heavy rare earth elements (HREE) enrichment with negative Ce anomalies and positive Eu anomalies. The geochemical data along with microfacies suggest that the investigated carbonate rocks might have been formed in low energy environments deposited in neritic to bathyal palaeoenvironment during Campanian–Maastrichtian age. Our study also confirmed that the investigated Disang group carbonates are similar to the adjoining carbonates exposed in the ophiolitic mélange zone of Manipur ophiolites, NE India. It is likely that the carbonate rocks were influenced by diagenetic activities at different tectonic processes during the evolution of MOC and later emplaced with the Disang group flysch-like sediments during subduction and obduction processes of the Indian plate and Myanmar plate collision. [ABSTRACT FROM AUTHOR]

Fracture evaluation is very important in the carbonate reservoirs, particularly fractured reservoir, due to the high impact of fractures on the reservoir permeability. Assessment of fracture parameters of reservoirs is necessary to optimize oil production. Image logs are regarded the best methods for this aim. This study aims to use electrical image logs in the Dalan and Kangan Formations reservoir in the Zagros Basin, SW Iran. This paper presents the new findings of analysis of the effective structures on reservoir quality of the Dalan and Kangan Formations in one of the Iranian gas fields by using FMI image logs. Formation micro-imager (FMI) was taken along with petrophysical logs from depth 4677–5253. FMI data were processed and evaluated. Through this assessment, different types of natural structures such as the fracture (open, close) and bedding planes were identified. The data analysis presented different fracture sets that have a different orientation to the anticline axis. All identified bed contacts were used to determine the structural dip. The general structural dip is interpreted to be 40 degrees toward N15E, with a corresponding strike of N75W-S75E. The total fractures encountered are in three categories: major-conductive, medium-conductive, and minor-conductive fractures. Fracture apertures with values more than 0.01 cm can be the highest value of fracture aperture with a value of more than 0.1 cm, which can be observed at 5013–5015 m, 5023 m, and 5065–5070 m. The range of fracture porosity from conductive fractures is computed to be 0–0.6%. Fractures with porosity range of more than 0.4% can be observed at 4953–4960 m, 4966 m, 4973–4980 m, 5020 m, 5113 m, and 5153 m (Lower Dalan). The highest fracture porosity can be observed at 4954 and 5020 m (close to 0.6%). The main productive zones appear to be 5160–5110 m, 5030–5000 m, 4980–4910 m, and 4830–4770 m. In this section of the reservoir, the high density, porosity, and aperture of the natural conductive/open fractures at certain intervals may indicate high productivity zones at these particular places. Considering the conductive/open fracture apertures, a production profile for a reservoir can be predicted from the fracture-enhanced permeability, with the assumption that the production of the reservoir is fracture-controlled. With the same assumption for the reservoirs within the 5.875-in. section of the well, a predictive production profile was constructed by integrating the fracture apertures. [ABSTRACT FROM AUTHOR]

The heterogeneous characteristics and their influencing factors of organic matter are still the research focuses of saline lacustrine hydrocarbon source rocks. This paper examined the heterogeneous characteristics of organic matter richness and type. The effects of tectonic activities, sedimentary facies, climate, biological sources, and preservation conditions on organic matter richness and type were examined in the Yiliping Depression, Qaidam Basin, northwestern China. Organic matter enrichment models for the Yiliping Depression were developed. Total organic carbon (TOC) content, extractable organic matter (EOM) content, and free hydrocarbon and kerogen thermal cracking hydrocarbon yield of mudstones are higher than 0.5%, 0.05% and 0.5 mg/g in the condensed sections and the early stage of high stand systems tracts while lower in other intervals. The heterogeneity of organic matter richness and type in the Pliocene is displayed. With the uplift of the A-erh-chin mountains, influenced by the Himalayan tectonic movement during the Neogene, the sedimentary facies were mainly saline lakes with braided river deltas, and their depocenters gradually migrated eastward. Climatic conditions changed from humid in the lower Pliocene to dry in the middle and upper Pliocene. Multiple water transgressive and regressive cycles formed multiple condensed sections and high stand systems tracts, where enough accommodation space, organic matter supply, favorable preservation conditions resulting from relatively deep and quiet water brought more organic matter accumulation. Mixed input of aquatic algae and terrestrial plants formed type II2 and type III kerogen in the depression, and there are more type II1 and type I hydrocarbon source rocks around lacustrine centers. The saline lacustrine evolution and organic matter accumulation models were developed, showing that the peak saline lacustrine period in the middle Pliocene was the most favorable for organic matter enrichment. The results indicate that there are active hydrocarbon source rocks (TOC content more than 0.4% and reflectance of vitrinite more than 0.5%) from the Neogene around the Jianshishan and Hongsanhan structures, and the Yikeyawuru and Taijinaier structures in the Yiliping Depression. [ABSTRACT FROM AUTHOR]

A number of techniques have been developed to detect and study fractures growth in rocks in the past few decades. Among them, the high-resolution X-ray computed tomography (CT) is a useful, rapid and nondestructive way to test and visualize the interiors of rocks in two and three dimensions. The difference in X-ray absorption between the mineral grains and the fractures can create well-contrasted CT images. In this paper, the main objective is to image the fractures in carbonated rock under uniaxial compression and rock fracturing experiments using the CT imaging technique in three dimensions. In the uniaxial compression test, the CT technology is performed to observe the macroscopic fractures in rock after failure. The 3D tomograms indicate that microcracks in rock mutually interconnect and eventually form macroscopic fractures. Then, the rock fracturing experiment is conducted to observe the geometry of induced fractures with the aid of the CT imaging. The 3D tomograms and visualized images show that the induced fracture intersects with the surface of rock sample, indicating that the CT technology can depict the induced fracture accurately. Moreover, the 3D visualized images illustrate that the macroscopic induced fracture in rock is produced with well-developed roughness. The experimental results show that the CT technique is a useful way to observe the fractures in rocks. [ABSTRACT FROM AUTHOR]

As one of the main reservoirs types in the Sichuan Basin, the granular shoal reservoirs of the Feixianguan Formation have great potential for oil and gas exploration. Therefore, it is very important to study the sedimentary evolution characteristics and the distribution of shoal deposits of the Feixianguan Formation. In this paper, the sequence stratigraphy, sedimentary characteristics and distribution characteristics of the granular shoal deposits of the southwestern section of the Kaijiang–Liangping Trough in the Sichuan Basin were investigated, through core observations, thin section analysis, and field profiles measurement and sampling, combined with well-logging data and interpretations of two and three-dimensional seismic data of the local area. According to the identification marks, three sequence boundaries (SB1, SB2, and SB3) and two third-order sequences (SQ1 and SQ2) were identified, and a transgressive systems tract (TST) and highstand systems tract (HST) were distinguished in each third-order sequence. The analysis of the Feixianguan Formation sedimentary facies indicated that this formation developed in a carbonate platform setting. In the depositional period of SQ1, the study area inherited the sedimentary pattern of the Changxing Formation and developed carbonate platform depositions. During the SQ1-HST stage, the platform margin shoals and the intra-platform shoals in the study area were relatively well developed. During the SQ2-TST period, oolitic shoals were developed in the region, but their thicknesses were smaller than those of SQ1-HST. In addition, the distribution pattern of sedimentary facies was similar to that of SQ1-HST. The platform marginal zone was relatively narrow at that time, whereas the open platform was more widely distributed, and the distribution areas of platform margin shoals and intra-platform oolitic shoals were relatively limited. During the depositional period of SQ2-TST, the sea level dropped to the lowest level of the studied interval, and limited and evaporation platform facies developed in the study area. Based on previous studies, the influence of different factors on the deposition of the shoals in the Feixianguan Formation were evaluated. The results showed that under the influence of sea level, basement faults, and hydrodynamic conditions, the platform margin area in the study area was more favorable to the development of granular shoals, and the growth model of the granular shoals was “accretion before migration”. [ABSTRACT FROM AUTHOR]

Southern Iran is one of the most significant parts of the world in terms of economic aggregation of hydrocarbons. In this paper, reservoir quality of the Cenomanian–Santonian deposits has been evaluated in southwestern Iran. According to the reservoir qualification, five particular rock types have been classified based on log responses through K-nearest neighbors (KNN) method. 1–5 are representing poor, weak, moderate, superior and non-reservoir types of rock, respectively. Rock types 3 and 4 are determined as the best types which can play a suitable reservoir role in hydrocarbon accumulation. The mentioned groups generally consist of porous limestones with low level of clay content. Rock types number 1 and 2 indicate the low porosity tight limestones and rock type 5 belongs to clays and shaly layers with high gamma radiations. Lithology of these intervals is specified using Rhomaa–Umaa and NPHI–RHOB crossplots which displayed calcite mineral is the main mineral formed both formations. SEM analysis and Th–K crossplot confirmed that Illite, Montmorillonite and Kaolinite are major clay minerals settled in these intervals that may have impact on reservoir characteristics. Interparticle and micro-porosities are considered as dominant kinds of porosities based on velocity deviation log (VDL) and it is proved by SEM results. Rock types 3 and 4 have been considered as the most productive zones which can be the best target for future perforating operation. According to petrophysical evaluation results, Ilam (Santonian) reservoir quality is enhanced toward northeast and southwest (Maximum abundance of rock type 4) of the studied area in comparison to central part. The Sarvak (Cenomanian–Turonian) Formation is in the highest level of reservoir quality in the southwest of the studied area (abundance of rock types 4 and 3). [ABSTRACT FROM AUTHOR]

Carbonate strata are widely distributed in China, which can be found in more than 30 provinces and cities, covering about 1/3 of the country’s territorial area. Affected by different geological and climatic conditions, carbonate strata in China geographically present different karst landscapes and groundwater resources. Specifically, northern China is dominated by large karst springs, while southern China is characterized by underground rivers. By determining the distribution range of carbonate strata in China, this paper pointed out the locations of large karst springs in the north and underground rivers in the south, analyzed the distribution characteristics of carbonate rocks in the north and south, the degree of karst development as well as their geological and climate genesis, and discussed the differences between karsts in northern and southern China in terms of occurrence forms of karst water and groundwater systems. [ABSTRACT FROM AUTHOR]

The coexistence of carbonates and evaporites is common for various petroliferous basins in geological periods globally. It holds much more significance to find out the interaction of these two. This paper expounds the macroscopical and microscopic relationship from petrography, facies, and geochemical analyses from core samples. The study area is dominated by successions of evaporites and carbonates, and three sulfate, five carbonates and mudstone lithofacies have been identified. And carbonates and evaporites are commonly lateral equivalents, both resulted from the similar sedimentary environment and chemical constituents. The intergrowth relationship was mainly reflected in the factors for their formation (including sea-level, evaporation, salinity, climate and so on), sedimentary cycle (including the vertical cycle and banded distribution) and the diagenetic transitions (including TSR, dolomitization, dedolomitization and dissolution). A depositional model has been developed that reveals a bull’s-eye pattern which was dominated by restricted carbonate platform and evaporitic platform with shoal and reef facies developed around the platform margins. With gypsum salts served as the caprock, favorable dolomite reservoir which largely resulted from the diagenetic transition and source of high quality can form a large reservoir. [ABSTRACT FROM AUTHOR]

Many technical problems are being encountered in roadway tunneling processes, especially at fault bundles and fault-dense zones and in vicinity of the Ordovician carbonate confined aquifers. These complicated tectonic conditions increase the difficulty of water inrush prediction and prevention. This paper takes the roadways tunneling at Jiangzhuang Coal Mine of Shandong Province, China, as a case study. The presence of fault bundles and fault-dense zones reduces the distance between roadway tunneling and the Ordovician carbonate confined aquifer and thus increases the potential risk of water inrush. Based on characteristics of the structure and water bearing formation and hydraulic conductivity in the fault zones, a trinity technique consisting of exploration, grouting, and supporting was proposed to ensure roadway safety tunneling. Underground mine seismic prediction (MSP), underground transient electromagnetic (TEM), underground drilling, numerical simulation evaluations and roadway grouting and supporting were used to understand, reduce, and mitigate the risk of poor stability and water inrush in the roadway tunneling process. Site construction has verified that the fault position was basically consistent with the results from MSP and TEM and drilling. Conclusions from risk evaluation and numerical simulation contributed to the grouting reinforcement and road supporting. Grouting reinforcement of the fracture zone reduced hydraulic conductivity, whereas the reasonable supporting was implemented for the weak part of the surrounding rock, which effectively controlled the roadway deformations. The comprehensive application of the trinity technique provided accurate and defensible geological data for roadway tunneling in this mining area, created favorable conditions for safe and efficient construction, and provided an important reference for research on similar type of roadway construction. [ABSTRACT FROM AUTHOR]

Dividing carbonate sequence with natural gamma data is the popular method, while it is not suitable for shallow platform because high gamma of mud flat represent shallow-water environment. Taking Majiagou Formation of Ordovician in Bozhong 21–22 structure of Bohai Sea as an example, a new sequence division method for shallow platform was presented based on natural gamma spectrum data, and the relationship between the sequences and reservoirs was discussed as well in this paper. The high natural gammas in Majiagou Formation of the study area are response for the weathering, uranium element enrichment in reservoirs and argillaceous sediment. The comparison result between well logging parameters and geological data shows that the ratio of Th/K is an effective parameter for sequence division, which can distinguish the origin of different high gammas effectively, even the mudstone from oxidized environment and reductive environment. Based on the ratio of Th/K, five third-order sequences were divided in Majiagou Formation of the study area; among them, all the sequences are developed in well BZ21-B-1, while SQ5 is missing in well BZ22-A-2 for denudation. The corresponding relationship between sequences and reservoirs indicates that the reservoirs of SQ4–SQ5 are dominated by structural fractures, which are mainly controlled by tectonic movement and weathering; while those of SQ1–SQ3 are dominated by dissolved pores, which may be related to the internal dissolution. [ABSTRACT FROM AUTHOR]

In the present paper, sequence stratigraphy and microfacies of the Dariyan Formation in the two sections of the Gadvan and Zana Mountains located were studied in NE and NW of Shiraz (Fars province, SW Iran). An area of 429.5 m of the Dariyan Formation sediments was studied through 187 thin sections. Also, the index microfacies were closely identified. Generally, index microfacies of the studied thin section were mudstone, wackestone, packstone, and grainstone microfacies. Received paleontological data confirm Aptian–lower Albian age of the Dariyan Formation. According to the lithostratigraphic aspect, the lower contact of Dariyan Formation with the Gadvan Formation in the Gadvan Mountain was described as a gradual type and in Zana Mountain; disconformity was found due to the sign of water withdrawal. Given the upper contact of the Dariyan Formation concerning the formation percentage, contact disconformity was observed due to the changes in the Allochem element and the situation of the entity from water and also according to the high percentage of iron nodules and Gluconate. According to the sequence, stratigraphic studies in the section of Gadvan Mountain, the lower border of the Dariyan Formation with Gadvan Formation was in the gradual form [type 2 Sequence Boundary (SB2)] and there was a disconformity in the upper border of this formation with Kazhdumi Formation [type 1 Sequence Boundary (SB1)]. Dariyan Formation included the system tracts (transgressive system tract, early highstand system tract, and late highstand system tract). There was a disconformity in its lower of the Gadvan Formation and disconformity in its upper boundary with the lower of the part Kazhdumi Formation (SB1) and it included the system tracts (highstand system tract, transgressive system tract, and lowstand system tract). Overall, lap sequence grade3 was seen in the two sections. [ABSTRACT FROM AUTHOR]

As the mining depth of North China-type coal fields increases year by year, the threat of Ordovician limestone karst water damage to coal seam mining is increasing, and the risk of floor water inrush increases gradually. To ensure safe production in coal mines and avoid casualties and economic losses, it is essential to accurately predict the risk of coal floor water inrush. The traditional approach to determine whether there is risk during the mining process is the water inrush coefficient method, which has certain limitations because it does not fully consider the water yield of the aquifer and the actual hydraulic resistance of the aquitard. Therefore, in this paper, a new method was put forward and applied for predicting the floor water inrush risk attributed to the Ordovician karst fissure confined aquifer from the Permian-age coal deposits in the Xiayukou coal field, Hancheng mining area, Shanxi, China. The influence of floor water inrush is comprehensively considered from the three aspects of the aquifer’s water yield, the hydraulic resistance characteristics of the aquitard and the tectonic development of the study area. Based on the new analytic hierarchy process-linear weighted average (AHP-LWA) method, a water abundance structure index (WASI) was created using the burial depth of the Ordovician aquifer (Dp), water abundance layer (Ly) and morphological features of the aquifer (Mf). Similarly, a hydraulic resistance structure index (HRSI) model was established using aquitard thickness (Tk), number of aquifers and aquitards (Num), sand–mud ratio (SMr) and core recovery rate (CRr); additionally, fractal dimension values were used to characterize the degree of structural development. Finally, a water inrush risk evaluation model was constructed, and a contour map was drawn using the risk index method of floor water inrush (RIWI) values and revealed three water inrush risk zones: normal mining area (0.18–0.32), medium-risk area (0.32–0.38) and high-risk area (0.38–0.52). Model verification was accomplished by the actual exposed water inrush points during the No. 3 coal seam mining work, which are all located in the high-risk area zoned by the RIWI method, and the water sources are all from the third section of the Upper Majiagou strong aquifer. The results show that the new evaluation model has high prediction accuracy, small error and wide applicability, and the model meets the basic requirements of mine production safety, provides favourable technical support for floor water inrush prediction during the Carboniferous–Permian lower coal group mining above the confined aquifer and is of great significance to ensure safe and efficient production of the coal mine. [ABSTRACT FROM AUTHOR]

Mine water damage is one of the main disasters threatening mine safety during production. The key to mine water hazard prevention and control is determining the main aquifer characteristics that threaten the mine and the hydraulic connections between aquifers and water diversion channels and proposing appropriate preventive measures. This paper focuses on the 16104 working face of the lower coal group in the Luxi coal mine of Shandong Province. The main water-filled aquifer that threatens the no. 16 coal mine is the Carboniferous no. 14 limestone thin-karst aquifer. Before adopting hydrophobic pressure-lowering measures, it is necessary to determine the water yield characteristics of the no. 14 limestone aquifer, the strength of recharging, and the hydraulic connection with the Ordovician limestone aquifer and to analyze and evaluate the feasibility of dredging. First, various geophysical exploration methods were utilized to comprehensively identify the anomalous water yield areas of the aquifer, which were verified by drilling methods. By combining these results with drilling and geophysical results, appropriate drainage and observation holes were selected. Second, a special water discharge stage and sequence were designed to carry out water discharge testing. By analyzing the change of water discharge and water pressure in dewatering test and the change of conventional ion concentration in water samples, the hydrogeological parameters were obtained, the hydrogeological situation was ascertained and the hydraulic connection with the Ordovician limestone aquifer was determined. The drainage time required for the aquifer to attain a safe water pressure and the amount of hydrophobicity were calculated. Through combination with the obtained hydrogeological parameters, the feasibility of depressurization was analyzed. The results show that the water yield property of the no. 14 limestone aquifer is not high, but the connectivity is good. There is a hydraulic connection between the no. 14 and the Ordovician limestone aquifers, but the connection is weak. The no. 14 limestone aquifer of the entire working surface was drained at a rate of 240 m3/h, indicating that the aquifer has good depressurization properties. [ABSTRACT FROM AUTHOR]

The problem of karst rocky desertification caused by soil loss is very serious in some karst areas of southwest China. The cycle process of rainwater–surface water–underground water controls the direction and trend of soil surface loss and underground leakage in karst rocky desertification areas. In this paper, Guanling–Huajiang plateau canyon rocky desertification area is the study area, and the water chemistry and stable isotopic characteristics of the karst water system in the study area were obtained by field investigation, hydrochemical and isotopic analysis of sampling water. The hydrogeological environment and lithology of karst springs' supply stratum were analyzed, and the supply elevations of main karst springs were estimated. Finally, the supply direction and scope of the main karst springs in the study area were inferred. The results reflected the characteristics of the groundwater flowing direction and the supply law of karst springs, and provided a theoretical basis for future research on the trend of soil surface loss and underground leakage in karst rocky desertification areas. [ABSTRACT FROM AUTHOR]

The mining of deep coal seams in the North China coalfields is threatened by the risk of water inrush from the Ordovician karst. As the mining depth increases, traditional methods of drainage depressurization and grouting reinforcement of the coal floor are increasingly ineffective at solving the problem of water inrush from the Ordovician karst. Grouting reinforcement of the Fengfeng Formation in the Ordovician (Ordovician top) was applied 10 years ago to solve this problem, prevalent recently, and mastering the vertical karst development is fundamental and prerequisite work. This paper carried out a study on the vertical karst development and grouting reinforcement of the Ordovician top in the Feicheng coalfield, China. Macroscopic and microscopic characteristics of the karst were researched by analysis of borehole cores and water inflow, slice identification and X-ray testing results to reveal the vertical karst development of the Ordovician top. Five layers were developed, from top to bottom: confining zone, fissure network zone, karst fissure and pore zone, karst channel zone and confining zone. Then the suitable grouting reinforcement layer was determined to be 5–45 m below the Ordovician top interface. The engineering practice of grouting reinforcement was carried out in the No. 8806 working face in the Baizhuang coal mine. The grouting technology and the evaluation of the grouting effect were analyzed comprehensively from the perspectives of the water inflow characteristics obtained from drilling and the apparent resistivity characteristics before and after grouting, which confirm the vertical karst development interpretation and good grouting effect. The study provides guidance for the prevention and control of Ordovician water disasters of the Feicheng coalfield, as well as other coal mines in North China. [ABSTRACT FROM AUTHOR]