Anhydrite Layers Research Articles

Cyclicity of katatectic layers in anhydrite caprocks, U.S. Gulf Coastal Region

ABSTRACT An anhydrite caprock overlies 65% of the 329 onshore salt stocks of the U.S. Gulf Coastal Region, south-central U.S. The caprock consists of a succession of katatectic (downward-building) layers of anhydrite (typically 1–4 cm thick) each overlain by an upper, black pyrite lamina (∼ 0.1 mm thick). The older (upper) katatectic layers are usually highly deformed. During four stages, these fundamental layers formed at the crest of shallow (< 1,200 m) salt stocks. Repetition of sets of the stages resulted in the cyclicity. The closed stage A flush, nearly planar contact separated mature anhydrite caprock from an underlying salt-stock crest. As the diapir elevated by a few mm/yr, it arched the caprock; it also opened conduits at the stock’s uppermost anhydrite sheath, allowing NaCl-undersaturated water from outside the diapir to contact the salt stock. The open-dynamic stage: Along the perimeter of the uppermost salt stock, a narrow, annular halite cave advanced inward and upward directly below the slightly convex base of the anhydrite caprock. The most NaCl-aggressive water rose by free convection to the highest elevations and dissolved halite. The dense, solute-enhanced water then reversed direction and, again, by free convection, flowed past the stock’s margin into country rock; NaCl-undersaturated water replaced the departing brine. A water-filled, commonly ring-shaped, planar cave up to several meters high expanded over the stock’s crest. Sparse physical supports, buoyancy, arched caprock, and high artesian water pressure prevented the cave’s collapse. The cave’s halite floor dissolved vertically downward faster than it moved diapirically upward. As the crestal halite dissolved, a small amount of residual pyrite and, typically, a layer up to ∼ 10 cm thick of residual anhydrite (generally 3–8 wt % of the stocks) accumulated on the cave floor. The open-static stage: The persistent “attack” of halite highs by the NaCl-undersaturated water eventually caused the slope of the cave’s floor to approach horizontality. The density-driven flow slowed markedly, and a static cover of NaCl-saturated brine thwarted the dissolution of the halite floor. The downward movement of the cave’s floor reversed, and it moved slowly upward via diapirism. Concurrently, an anhydrite sheath evolved around the uppermost stock. The accretionary stage The cave closed in a few thousand years, and active diapirism underplated the admixed residual minerals onto the base of the caprock. The uppermost, now compact, residual anhydrite dissolved in the high-pressure environment, leaving the discrete, topmost, thin, black pyrite lamina. With the accretion of the residual minerals, a katatectic layer formed at the base of a succession of such layers. The closed stage recurred, and a new katatectic cycle began forming. Variations of the four genetic stages probably occurred during the formation of anhydrite caprocks in other worldwide salt-dome provinces, but because of insufficient data, they are usually unrecognizable.

Geochemical Characteristics and Controlling Factors of Groundwater Chemical Composition in the Zihe River Source Area, Shandong, China

The geochemical characterization and evolution of shallow groundwater in the Zihe River source area is a key issue that needs to be addressed. In this study, a combination of traditional geochemical techniques and geochemical modeling was used to explain the geochemical processes and major ion sources in the chemical evolution of shallow groundwater in the Zihe River source area, Northeast China. Fifty-seven water samples were collected in June 2020 for chemical analysis, and the results showed that the main groundwater chemistry types in the three major aquifers are HCO3·SO4-Ca·Mg-type pore water from loose quaternary rocks, HCO3·SO4-Ca·Mg-type karstic fissure water from carbonate rocks, and HCO3·SO4-Ca-type weathered fissure water from massive rocks. Water–rock interactions in alkaline environments were the main causes of changes in groundwater chemistry. Rock weathering dominated the geochemical evolution of each aquifer. The analysis of ion concentration ratios and modeling revealed that the aquifer’s chemical components are mainly derived from the dissolution of dolomite and calcite and partly from the infiltration of pollutants containing Cl− and NO3−, as well as from the dissolution of quartz. Mg2+ is derived from the dissolution of dolomite. HCO3− is primarily derived from the co-dissolution of calcite and dolomite, and to a lesser extent, its content is also influenced by the recharge of rainfall. SO42− has two sources: it mainly originates from the dissolution of gypsum and the anhydrite layer, followed by atmospheric precipitation. The synthesis showed that the groundwater quality in the source area of Zihe River is good, all the indices reached the standard of class III groundwater quality, and the overall degree of human pollution is low. The results of this research will provide a scientific basis for the local authorities to delineate karst groundwater protection zones in the Zihe River source area and to formulate resource management strategies for the development, utilization, and protection of karst groundwater.

Profiles of δ18O and δ2H in porewater of a Mesozoic rock sequence: Regional variability and relation to large-scale transport regimes

A large drilling campaign has been conducted across sediments of the Tertiary Molasse Basin and the underlying Mesozoic in Northern Switzerland in the context of underground disposal of radioactive waste. The ~300-400 m thick Mesozoic low-permeability rock sequence of interest is located between the regional aquifers made of Malm limestone at the top and dolomite/limestone formations of the Muschelkalk at the bottom. Locally, water-conducting zones occur in Dogger marl/limestone (Hauptrogenstein) below the Malm and/or in Keuper sandstone/dolomite above the Muschelkalk aquifer. Here we report on the distribution of the natural tracers δ2H and δ18O in porewater and groundwater from eight new boreholes in three study areas. The distribution of these tracers is the result of hydrogeological processes acting in the past, and their analysis offers unique possibilities to decode large-scale transport processes. The large data set allows us to compare the variability of δ18O and δ2H vertically as well as laterally in the three areas (∼20 km apart) and in the 2–4 boreholes in each area (a few km apart). The eight isotope profiles show many similarities, but also distinct features that are related to the lateral variation of aquifer properties, tectonic setting and topography, and the geometry of the aquifer-aquitard systems. Boundaries of the profiles are typically given by groundwater in the Malm (one location in the Dogger) and Muschelkalk aquifer, and locally by water-conducting zones in the Keuper. Maximum isotope values in the central part of the profiles plot to the right of the GMWL (Global Meteoric Water Line) to different degrees, as do values in the Malm aquifer. Towards the Keuper aquifer (if present) and the Muschelkalk aquifer, the values decrease smoothly and sharply, respectively, and approach the GMWL. The sharp decrease towards the Muschelkalk aquifer indicates a change in the isotope signature in the recent past or is related to low porosity and low diffusivity values in adjacent anhydrite layers. The two tracers δ2H and δ18O show different trends in the more central parts (almost constant or decreasing with depth, respectively). These differences are very likely inherited from pre-Pleistocene processes, i.e., before the present-day signatures in the aquifers came into play. Transport simulations are used to narrow down the timing of changes in the aquifer signatures in the more recent past (10 ka to few Ma ago). The data presented here demonstrate that (1) lateral variability is limited, even though the low-permeability zones are found at different depths, meaning that transport regimes were similar over large times of the past, (2) the known lateral variability of the Keuper aquifer is confirmed by the porewater profiles, (3) diffusion can explain the observed profile shapes and (4) signatures in the central parts of the low-permeability zone are oldest in the sense that they are furthest away from the GMWL.

Investigating seismic mode conversions from an ultra-high-velocity caprock by physical modelling, numerical simulations and a Gulf of Mexico salt proximity VSP survey

SUMMARY Salt structures are widely distributed in many basins worldwide and play an important role in understanding tectonic movements, offering underground storage and sealing hydrocarbon traps. In addition to the acknowledged difficulties in mapping complex salt structures through seismic methods, when an evaporitic layer, such as anhydrite, forms over salt, it can introduce strong multimode conversions that can couple with the primary compressional wavefields and generate artefacts in resulting acoustic images. From two well-log suites from the Gulf of Mexico, we identify thin evaporitic caprocks on top of their salt bodies and analyse their elastic properties. Through controlled experiments, including physical and numerical modelling with a vertical seismic profiling survey geometry, we observe significant shear-mode conversions at the top of the ultra-high-velocity caprock, which further result in a family of prominent S and P (converted from S wave) modes across the top of the salt region. Similarly, in a field survey, we identify evident converted S waves and a multimode P wave (converted S wave in the anhydrite layer, and P wave elsewhere) following the primary P transmission inside the salt body. While separating the converted Smodes at the receiver end is more unambiguous, the multimode P waves could behave very similarly to the primary Pmodes and are more difficult to suppress. Under the common acoustic assumption of seismic velocity model building and imaging, complex mode conversions on top of the salt are generally ignored. Through controlled experiments and a field survey, we analyse the pitfalls associated with this omission. We emphasize the importance of understanding the physics of wave partitioning in the presence of a thin ultra-high-velocity layer on the top of the salt.

Hydrogen sulphide (H2S) migration in groundwater of the Zechstein strata in the Legnica-Głogów Copper Basin and its vicinity, SW Poland

Hydrogen sulphide (H2S) occurs in groundwater in various lithostratigraphic units of the Zechstein Basin in the Legnica-Głogów Copper Basin (SW Poland). This region is located in the Fore-Sudetic Monocline within which, several tens of kilometres NE of the study area, at greater depths, natural gas fields with hydrogen sulphide (H2S) occur. The Main Dolomite (Ca2), in which H2S-containing natural gas has accumulated, is younger than the Zechstein Limestone (Ca1), which is actively mined. The Ca2 and Ca1 formations are separated by a thick anhydrite succession including a wedge-shaped salt body. Hydrochemical analyses of 18 groundwater samples taken from different horizons within the Zechstein strata showed spatial variability ofH2S and chloride concentrations. A conceptual model of groundwater flow with dissolved H2S in the Zechstein formations was developed. H2S migration is associated with groundwater flow between the Ca2 and Ca1 aquifers through fissures in the anhydrite strata that separate them. Hydraulic contact through fissures in the anhydrite layers is the result of long-term exploitation of the underground copper deposit. Groundwater flow between the layers is influenced by a large change in the piezometric pressure of the groundwater in the depression cone caused by mining drainage.

Large grain-size-dependent rheology contrasts of halite at low differential stress: evidence from microstructural study of naturally deformed gneissic Zechstein 2 rock salt (Kristallbrockensalz) from the northern Netherlands

Abstract. Constitutive laws to predict long-term deformation of solution-mined caverns and radioactive-waste repositories in rock salt play an important role in the energy transition. Much of this deformation is at differential stresses of a few megapascals, while the vast majority of laboratory measurements are at much higher differential stress and require extrapolation. This can be much improved by including microstructural data of samples deformed in natural laboratories. Deformation of rock salt can occur by dislocation creep and grain-size-dependent dissolution–precipitation creep processes (pressure solution); this mechanism is not commonly included in current engineering predictions. Here we show evidence for large grain-size-dependent differences in rock salt rheology based on microstructural observations from Zechstein rock salt cores of the northern Netherlands that experienced different degrees of tectonic deformation. We studied the relatively undeformed horizontally layered Zechstein 2 (Z2) salt (Stassfurt Formation) from Barradeel and compared it with a much more strongly deformed equivalent in diapiric salt from Winschoten, Zuidwending, and Pieterburen. We used optical microscopy of thin gamma-irradiated sections for microtectonic analysis, recrystallized grain-size measurements and subgrain-size piezometry, electron microscopy with energy-dispersive X-ray spectroscopy, and X-ray diffraction analysis for second-phase mineralogy. Subgrain-size piezometry shows that this deformation took place at differential stresses between 0.5 and 2 MPa. In the undeformed, layered salt from Barradeel we find centimetre-thick layers of single crystalline halite (Kristalllagen or megacrystals) alternating with fine-grained halite and thin anhydrite layers. The domal salt samples are typical of the well-known “Kristallbrockensalz” and consist of centimetre-size tectonically disrupted megacrystals surrounded by fine-grained halite with a grain size of a few millimetres. We infer high strains in the fine-grained halite as shown by folding and boudinage of thin anhydrite layers, as compared to the megacrystals, which are internally much less deformed and develop subgrains during dislocation creep. Subgrain size shows comparable differential stresses in Kristallbrocken as in matrix salt. The fine-grained matrix salt is dynamically recrystallized to some extent and has few subgrains and microstructures, indicating deformation by solution–precipitation processes. We infer that the finer-grained halite deformed dominantly via pressure solution and the megacrystals dominantly by dislocation creep. The samples show that the fine-grained matrix salt is much weaker than Kristallbrocken because of different dominant deformation mechanisms. This is in agreement with microphysical models of pressure solution creep in which grain size has a significant effect on strain rate at low differential stress. Our results point to the importance of pressure solution creep in rock salt at low differential stresses around engineered structures but also in most salt tectonic settings. We suggest that including results of microstructural analysis can strongly improve engineering models of rock salt deformation. We recommend that this mechanism of grain-size-dependent rheology is included more consistently in the constitutive laws describing the deformation of rock salt.

Paleostress, deformation mechanisms and finite strain related to chocolate-tablet boudinage and folding of a Permian rock salt/anhydrite sequence (Morsleben site, Germany)

Polyphase chocolate-tablet boudinage of competent anhydrite layers in incompetent Permian rock salt of the Morsleben repository (Germany) developed during Triassic/Jurassic graben formation and late Cretaceous graben inversion. The competence contrast between layers and matrix is related to the deformation mechanisms of anhydrite and halite, which have been constrained in the present study using deformation microfabrics and geochemical data. Boudinage implies a finite longitudinal strain of ca. 100% in NNW-SSE direction. There is a clear impact of the layer thickness on both the deformation mechanisms and the shape of anhydrite boudins. Pervasive solution-precipitation creep is the dominant deformation mechanism in thin anhydrite layers (thickness < 15 cm), which are dominated by drawn boudins with aspect ratios ranging from 1.5 to 5.4. Deformation of thick anhydrite layers (thickness > 15 cm) was accommodated by dislocation creep succeeded by localized solution-precipitation, kinking, twinning and fracturing resulting in torn boudins with aspect ratios between 0.5 and 2.0. Halite of the incompetent rock salt matrix deformed viscously under low differential stress (2.0–3.1 MPa). The deformation mechanisms were dislocation creep in form of subgrain formation and strain-induced grain boundary migration. Moreover, close to anhydrite boudins, solution-precipitation creep of halite is indicated by decreased bromide content in halite of necks between brittle torn boudins, which should have precipitated from a fluid phase. Halite in necks of drawn boudins, on the other hand, displays a continuous decrease of bromide content, pointing to predominantly crystal plastic inflow of halite.

RESERVOIR CHARACTERIZATION OF THE PLIOCENE RED SERIES, LAM FIELD AND SURROUNDING AREAS, OFFSHORE WESTERN TURKMENISTAN

The sedimentology, petrography and reservoir potential of Pliocene sandstones within the Upper Red Series in the offshore LAM field, Western Turkmenistan, have been examined. Depositional settings are interpreted within the framework of the Red Series palaeoenvironments across the entire Turkmen sector of the Apsheron‐Prebalkhan uplift zone, including its onshore extension to the east.Examination of 81 m of core from three separate intervals suggests that the Red Series in the LAM field is the product of a fluvial‐dominated delta system with associated floodplain deposits, periodically flooded by the saline waters of the South Caspian Lake. Relatively thick sandstones, up to around 5 m thick, are interpreted as channel and point‐bar deposits of a meandering river system, with thinner and finer‐grained sandstones and siltstones inferred to be crevasse‐splay and interdistributary floodplain deposits. Floodplain mudstones display signs of desiccation, soil formation, plant rootlets and occasional thin layers of anhydrite. Intervals with marine trace‐fossil assemblages record incursions of saline‐lake waters. Conglomeratic layers at the base of thicker mudstone intervals may be associated with abrupt transgressions of the lake. The best reservoir qualities are associated with the fluvial channel and point‐bar sandstones. Crevasse‐splay and other overbank sandstones are of poorer quality, while intercalated floodplain to lacustrine claystone/siltstone units may constitute local seals.Eighteen sandstone plug samples from the cored intervals were examined in thin‐section and by XRD and SEM to assess how mineralogy, grain size and diagenesis affect reservoir quality. The samples consist predominantly of lithic arkoses and feldspathic litharenites; higher porosities, and therefore better reservoir potential, are associated with the feldspathic litharenites. Primary controls on porosity include compaction, clay‐matrix content and calcite cementation. XRD data reveal the presence of illite, illite‐smectite and chlorite. The presence of swelling clays has been the main cause of formation damage in the field.The interpretation of meandering fluvial channels here is thought to represent the first published account of such channels within Pliocene reservoir rocks in the north of the South Caspian Basin. Previous accounts of the Red Series sandstones deposited onshore to the east have indicated deposition within braided channels of the palaeo‐Amu Darya river delta plain, and alluvial‐fan deposits sourced from uplands to the north. Deposition of the equivalent Productive Series by the palaeo‐Volga in the Azerbaijan sector to the west has also been interpreted as having taken place within braided systems, although mixed or suspended‐load fluvial channels ascribed to the contemporary Kura delta farther south may have been associated with a meandering system. Two palaeogeographic maps are presented to illustrate depositional environments for the Red Series during relative high‐ and low‐stands of the South Caspian Lake. The maps cover the area where the Productive Series of Azerbaijan passes into the Red Series of Western Turkmenistan.

Hydro-mechanical behavior of heated bentonite buffer for geologic disposal of high-level radioactive waste: A bench-scale X-ray computed tomography investigation

The behavior of heated bentonite buffer is critical for the security and long-term performance of a geological repository for high-level radioactive waste (HLW). While laboratory column experiments have been conducted to investigate compacted bentonite and coupled THMC (thermal-hydro-mechanical and chemical) processes for a moderate temperature range of up to 100 °C, data for a higher temperature range are limited. Understanding bentonite behavior and coupled THMC processes under higher temperatures (e.g., up to 200 °C) could allow for a more economic repository design and would expand the data and knowledge base for more reliable modeling. In this study, a bench-scale experiment was conducted in a compacted bentonite column experiencing both heating up to 200 °C in the center and hydration from a sand-clay boundary surrounding the column. During the experiment run for 1.5 years, frequent X-ray computed tomography (CT) scanning of bentonite provided insights into the spatiotemporal evolution of (1) hydration/dehydration, (2) clay swelling/shrinkage, (3) displacement, and (4) mineral precipitation. After the experiment, a comprehensive post-dismantling characterization of bentonite samples was conducted. Results showed that the bentonite hydration was axi-symmetrical despite the initial heterogeneity due to packing, confirming the ability of bentonite to seal fast flow/transport paths. Compared to a non-heated control experiment, the heated column showed greater CT density variations along the radial distance, indicating that homogenization of bentonite might be more difficult if a temperature gradient is maintained in the repository. Precipitation of an anhydrite layer occurred in the inner hot zone, pointing to potential concerns about salt precipitation causing canister corrosion. Ultimately, the experiments provided a high-resolution window into the strongly dynamic and coupled behavior of bentonite exposed to heating, hydration and swelling, which will be valuable for improving modeling of coupled processes, especially for the early state of a HLW repository.

Imaging gypsum–anhydrite interface by a structure‐based conceptual resistivity model: A case study from Bala (Turkey) gypsum deposits

AbstractPrincipal calcium sulphate rocks, such as gypsum and anhydrite, originate from evaporitic processes. Gypsum is considered an industrial raw material with high economic value, but anhydrite has no economic interest. Therefore, delineating the interface between sedimentary cover and gypsum, and differentiating gypsum from anhydrite has significant importance in the production planning of open pits. An electrical resistivity tomography study was carried out in the Bala gypsum formation (Central Anatolia, Turkey) to map the gypsum–anhydrite interface. Because open‐pit mining is economical up to a certain depth due to the cost of excavation, delineation of the upper boundary of gypsum is also necessary. As the survey's primary purpose is to delineate the interfaces of the sedimentary cover–gypsum and gypsum–anhydrite layers in shallow depths (50 m), a structure‐based model search scheme that includes a sequential use of global and local search methods has been applied for the derivation of the subsurface resistivity model. The conventional cell‐based conceptual model using the damped least‐squares inversion method is also used for comparison purposes. The strong resistivity contrast leads to an easy identification of cover and gypsum for both conceptual models. However, only the structure‐based conceptual model delineates the interface between gypsum and anhydrite. The estimated interfaces derived from the structure‐based model are consistent with the borehole data. This case history for gypsum investigation indicates the value of selecting an appropriate conceptual model for a specific exploration problem.

Leaky waveguides in hydrocarbon reservoirs and their implications for oil banks detection

The presence of naturally occurring subsurface waveguides for electromagnetic (EM) waves has been previously documented. In particular, the mining industry recognized that a coal seam bounded by layers of conductive rock acts as a leaky waveguide. Consequently, the attenuation constant and phase shift of EM signals propagating through the coal layer are modulated by the thickness of the coal and the EM properties of the three layers forming the leaky waveguide. The radio imaging method was developed based on this discovery to characterize coal deposits. Recent studies have determined that guided waves can provide useful information about the subsurface. Structures with similar dimensions and EM properties are found in oil fields in the form of layers of evaporite (e.g., anhydrite) bounded by hydrocarbon reservoirs. To the best of our knowledge, the feasibility of exploiting such structures to characterize the interwell region has not been investigated extensively. We have conducted a theoretical analysis and 3D numerical simulations in the time and frequency domains to demonstrate that layered structures in oil fields can act as leaky waveguides and efficiently guide EM waves. Our results suggest that such structures substantially enhance the propagation of megahertz EM signals. Among multiple parameters evaluated, the conductivity of the layers has the most significant effect on signal attenuation, and thus its range of propagation. We estimated that EM signals of approximately 10 MHz can propagate several hundreds of meters through a layer of anhydrite in the presence of conductive bounding reservoirs. The received signals are not only affected by the properties of the anhydrite layer, but also by the properties of the bounding reservoirs, conferring sensitivity to changes in reservoir saturation. We conclude that this approach could be further developed to infer fluid saturation and especially to identify the presence of oil banks in water-flooded hydrocarbon reservoirs.

New discoveries on the first petroleum scientific drilling (QK-1) of the Qiangtang Basin, Tibetan Plateau

<p indent=0mm>QK-1 is the first scientific drilling designed to solve the key problems in petroleum geology in the Qiangtang Basin on the northern Tibetan Plateau. Its altitude is <sc>5030 m,</sc> and the well depth is <sc>4696.2 m.</sc> It is also the highest-altitude scientific drilling on the globe, and is located in the Lake Bandaohu area in the northern Qiangtang Basin. By performing the QK-1 and its affiliated shallow drillings, a series of new discoveries has been made in regard to high-quality regional seals, source rocks, petroleum displays and the Jurassic strata succession. (1) Two sets of caprocks, which could be regional high-quality seals, were discovered through drilling, i.e., an anhydrite layer in the Quemoco Formation (J_1-2<italic>q</italic>) <sc>(354–365 m</sc> thick) and a gypsum-bearing mudstone in the Xiali Formation (J₂<italic>x</italic>) <sc>(230–252 m</sc> thick). Comprehensive analyses of drilling and seismic data show that the distribution of these caprocks is regionally continuous and stable. Moreover, petroleum displays and well logging data reveal that these two caprocks are characterized by low porosity, good permeability (the mean permeability is <sc>0.265×10⁻³ μm²,</sc> and the mean breakthrough capillary pressure is <sc>9.0 MPa),</sc> and good sealing. (2) The northern Qiangtang Basin contains high-quality hydrocarbon source rocks in Upper Triassic deltaic facies. The affiliated shallow drillings reveal a good Upper Triassic hydrocarbon source rock in a coastal swamp-deltaic plain facies on the northern Qiangtang Basin margin. The two mudstone source rock members have a thickness of <sc>36.0 m</sc> and total organic carbon (TOC) values of 2.0%–3.6%, and a thickness of <sc>61.0 m</sc> and TOC values of > 1.0%, respectively. The organic matter type is II₁-, II₂- and III-type kerogen with high to over-thermal maturation. Well logging, seismic data and facies analyses indicate that the pro-deltaic to shelf mudstones in the covered area in the central northern Qiangtang Basin are better source rocks than those in the deltaic plain on the basin margin. (3) Well logging petroleum displays provide important insights for petroleum reservoir formation and destruction. Based on petroleum displays and evidences of gas release in 250 outcrops, the QK-1 scientific drilling has also discovered 14 petroleum anomalies in the Eocene Suonahu Formation, Middle Jurassic Buqu Formation and the Upper Triassic Nadigangri Formation. One anomaly is oil-bearing, while thirteen anomalies are gas-bearing. The total hydrocarbon value of gas logging is 10%, and is mainly methane in composition. The petroleum displays of well logging occurred after drilling through the Xiali or Quemoco formations which are caprocks, while outcrop petroleum displays are mainly distributed on the basin margin or central uplift which are strong tectonic deformation zones. The widespread petroleum displays indicate good hydrocarbon-generation conditions and petroleum reservoir formation/destruction processes, while the distribution characteristics of petroleum displays indicate that the high-quality regional-seals-covered area in central basin could be favorable plays of petroleum reservoirs. (4) The QK-1 drilling cut through a sedimentary succession from the Upper Jurassic to Upper Triassic, i.e., from the upper to the bottom, the Upper Jurassic Suowa Formation (J₃<italic>s</italic>), Middle Jurassic Xiali (J₂<italic>x</italic>) and Buqu Formations (J₂<italic>b</italic>), Middle-Lower Jurassic Quemoco Formation (J_1-2<italic>q</italic>) and Upper Triassic Nadigangri Formation (T₃<italic>nd</italic>), in which the whole Jurassic strata is completely continuous. The Jurassic sedimentary succession shows a transition from alluvial facies to shore, shallow shelf and carbonate platform facies up section. This finding breaks the previous view that suggests a lack of Lower Jurassic strata, and provides new basics for Qiangtang Basin analysis. Overall, the discovery of two regional high-quality seals in the Jurassic Quemoco and Xiali formations in the Qiangtang Basin refutes the previous traditional perception, which suggests poor petroleum preservation conditions. The northern Qiangtang Basin contains high-quality source rocks with great hydrocarbon generation potential in the Upper Triassic deltaic facies. Petroleum display anomalies and distribution characteristics reveal that the Qiangtang Basin not only underwent large-scale hydrocarbon generation, reservoir formation/destruction processes, but also developed favorable display of petroleum preservation. The establishment of a continuous Jurassic strata succession provides a new evidence and valid framework for petroliferous basin analysis of the Qiangtang Basin.

Paleoproterozoic Rajapalot Au-Co system associated with evaporites: Chemical composition and boron isotope geochemistry of tourmaline, and sulfur isotopes of sulfates, Peräpohja belt, northern Finland

The Raja Au-Co mineralization in the Paleoproterozoic Peräpohja belt in northern Finland is part of the wider Rompas-Rajapalot mineralized area with several known Au-Co occurrences. The area is characterized by distinct tourmaline occurrences, spatially associated with Au-Co mineralization. Four texturally distinct tourmaline types were identified although all analysed tourmalines belong to the alkali-group and are classified as dravite. δ 11B values and fractionation modelling indicates that at least two distinct fluids were responsible for the tourmaline formation with initial end member δ11B values of the fluids at −8‰ and −1‰. Possible sources for boron rich fluids are Svecofennian orogeny related (ca. < 1.9 Ga) metamorphic fluids and magmatic-hydrothermal fluids related to the late-orogenic ca. 1.78 Ga granitoids. Structural data from the quartz-tourmaline veins outlines a strong linear trend towards the Raja high-grade mineralization trend. This is interpreted as evidence for structural control of the Raja mineralization, which possibly is contained in shear-zones or within the hinge regions of local high degree folding.A distinctive rock unit with bright purple anhydrite layers and white gypsum veins has been intersected by drilling. While the sulfate-rich unit is unmineralized, the mineralogy and regional geological setting suggests an evaporitic origin. Anhydrite has δ34S values in a narrow range from 8.1 to 9.8 ‰. Gypsum has slightly heavier δ34S from 10.6 to 12.2 ‰. Together with isotope fractionation constraints, textural evidence suggests the authigenic formation of gypsum with SO42- sourced from anhydrite. Significant similarities in textures and sulfur isotope values to well-known evaporite successions of the Onega basin, western Russia, further supports the presence of evaporitic strata within the Peräpohja belt.

Characteristics of Natural Background Radiation in the Polkowice-Sieroszowice Mine, Poland

Natural radioactivity in underground locations is the main parameter for the safety of work (occupational hazards) and for the success of experiments in physics or biology requiring unique conditions. The characterization of natural prominence was carried out in the Conceptual Lab development in one of KGHM deep copper mines co-ordinated by KGHM Cuprum R&amp;D. Natural radioactivity studies were performed and included in situ gamma spectrometry, neutron flux measurements, radon concentration, and alpha and gamma laboratory spectrometry measurements of rock samples. At a depth of 1014.4 m (2941.8 m w.e.) within the anhydrite layer, a neutron flux of 2.0 ± 0.2 × 10−6 cm−2 s−1, a gamma-ray dose of 0.008 ± 0.001 μSv/h, a photon flux density of 0.64 ± 0.20 cm−2 s−1, and a radon concentration of 6.6 Bq/m3 were determined. Laboratory analyses of 226,228Ra, 40K, and 238,234U concentrations in collected rock samples showed low values. The exceptionally low level of natural radioactivity in the Polkowice-Sieroszowice mine makes this location a unique place for scientific research.

Velocity model building for single-offset VSP data via deformable-layer tomography: A Texas salt dome example

We have applied multiscale deformable-layer tomography (DLT) to build a laterally varying velocity model, using a single-offset vertical seismic profile (VSP) data set acquired for a salt proximity survey in southern Texas. The purpose of the VSP survey is to delineate the 2D salt flank using the P-wave reflections. Previous study has identified an anhydrate layer as the cap rock of the salt dome. The large impedance contrasts of this anhydrite layer generate strong downgoing P (sediment)-S (anhydrite)-P (salt) waves recorded by downhole geophones. Incidentally, the P-S-P-waves have traveltimes similar to those of the P-wave salt flank reflections, thus contaminating the imaging of the salt flank. Identifying shear-mode contamination requires an accurate velocity model of anhydrite. However, the extremely poor coverage of the single-offset VSP greatly challenges tomographic techniques to determine the lateral velocity variation. We tackle this problem using multiscale DLT, which characterizes the velocity field by a set of deformable layers. We constrain the layer velocities using the check-shot data and invert for the geometric variation. The inverted model indicates that the anhydrite layer has a “thick-thin-thick” lateral variation with offset, and the S-wave in the anhydrite layer helps in imaging the P-S-P-waves along the well track. The estimated anhydrite layer geometry is validated by the kinematic accuracies of P-waves in the data domain and P-S-P-waves in the image domain. Some in-salt dipping structures are determined by multiscale DLT as well. This field data example indicates that multiscale DLT is feasible for estimating velocities using VSP data of the single-offset situation. An accurate velocity model is the key for modeling and adaptive subtraction of the shear-mode contamination related to the salt geometry.

Rare Occurrence of Mirabilite in the Thirteenth-Century Historic Salt Mine in Bochnia (Poland): Characterisation, Preservation, and Geotourism

The small stalactites found on the ceiling at level I near the Sutoris shaft in the thirteenth-century historic salt mine in Bochnia, Poland, are mainly composed of mirabilite (Na2SO4·10H2O) followed by blödite (Na2Mg(SO4)2·4H2O). The unique presence of these two minerals in only one location in this old underground mine is attributed to contemporary precipitation from percolating solutions. This can be caused by a combination of at least two factors: a specific and stable microclimate (characterised by a low temperature, high humidity, and relatively strong air circulation which accelerates the processes of evaporation and crystallisation) and the specific chemical composition of the leaking solution (contains a low carbonate and high sulphate content, and characterised by acidic pH (4.8) and intermediate-mineralisation (174,308 mg/L)). The microclimate specified above can be linked to the long distance from the ventilation shaft that pumps the air from the surface to the mine, while the composition of the leaking solution as well as the hydrochemical modelling results obtained with PHREEQC can be directly related to the top anhydrite layer and the overlying secondary cap consisting mainly of claystone, anhydrite, and gypsum. In this study, the challenges underlying the preservation of mirabilite in the underground environment of the salt mine are discussed, in terms of both nature and mining law. Based on the results of detailed geological, mineralogical, and chemical research, appropriate solutions that can be practically applied for the management, preservation, and protection of the mirabilite efflorescence are proposed. The presence of this intriguing mineral, with appropriate protection, can be another geological attraction for tourists visiting this thirteenth-century UNESCO-recognised salt mine.

Reversible emulsion fluids with a high internal phase ratio (HIPR)

Invert muds are the most commonly used oil-based drilling muds. The oil to water phase ratio in invert drilling muds ranges from 65/35 up to 90/10, with the most common ones ranging from 70/30 to 80/20. At these oil to water phase ratios, the drilling mud is characterized with high stability and appropriate rheological and structural parameters allowing to adjust drilling mud density in a wide range. One of the disadvantages of invert muds is their cost (due to oil content) and environmental problems associated with waste and management of oily drill cuttings. Taking into account the properties of oil-based muds, the article presents laboratory tests aimed at developing the composition of an invert mud with a limited oil phase content and high internal phase ratio (HIPR). Drilling muds with an o/w ratio less or equal to 50/50 vary from conventional inversion muds in terms of their composition and properties. Due to the higher concentration of the dispersed inner phase, muds have reduced stability and high rheological and structural parameters. Maintaining the appropriate rheological and structural parameters of the drilling mud and its high stability is possible only through the use of appropriate chemicals adapted to the emulsion system with a specific oil to water phase ratio. In the drilling muds of this type it is also possible, due to the higher concentration of the internal phase, to partially adjust the density of the mud with the water phase, such as salt solutions, thus limiting the solids content (weighting agents) in the mud. The developed mud system should be more economical, have a reduced toxicity, while maintaining the operational advantages of invert mud. These types of muds can be used during the drilling of reactive shale formations, salt layers, gypsum and anhydrite layers, as well as for drilling productive horizons and for reconstruction works carried out in oil and gas wells.

FORMATION EVALUATION FOR JERIBE FORMATION IN THE JARIA PIKA GAS FIELD

The Jaria Pika Gas field is a domal anticlinal structure in the northeast of Iraq NW trending, about 3.6 km long and 1.9 km wide. The 55 m thick gas bearing Jeribe Formation is the main reservoir. This study intends to well log interpretation to determine the petrophysical properties of the Jeribe Formation in the Jaria Pika Gas Field. Total porosity, effect porosity, and secondary porosity have been calculated from neutron, density, and sonic logs. Porosity is fair to good in the Jeribe formation. From RHOB-NPHI and N/M cross plot, the Jeribe Formation is composed mainly of dolomite, limestone with nodules of anhydrite. The Fatha Formation contains considerable amounts of anhydrite layers, so it's represented the cap rocks for the Jeribe Reservoir which is recognized based on the reading of Gamma-ray log, Density log, Neutron log, and Sonic log. The Jaria Pika is considered as gas field as the Jeribe reservoir rocks are gas saturated ones.

Simulation of Mosul Dam Break Using Finite Volume Method

Mosul dam is an earth-fill embankment located north of Iraq on the Tigris River forming a reservoir with 11.11 km3 water storage capacity which is the largest dam in the country. The dam is built on a rock bed foundation, in which the dissolution process is dynamic in the zone where gypsum and anhydrite layers present. During the construction development seepage locations were found in the dam foundation and the grouting process is in progress until now to control this problem. Therefore, the possibility of the Mosul dam break is highlighted by previous studies. In this research, a FORTRAN code based on the finite volume method is modified to solve the two-dimensional shallow water equations and simulating the Mosul dam break. The computational domain discretized using unstructured triangular mesh. The solver applied Harten lax van leer with contact (HLLC) wave approximate Riemann solver to calculate the cell interface fluxes, and the semi-implicit scheme employed to solve the friction source term. The numerical scheme applied to two benchmark test cases, and the results showed that the presented model was robust and accurate especially in handling wet/dry beds, mixed flow regimes, discontinuities, negative water depths, and complex topography. The results of this study demonstrate that flood waves may reach the center of Mosul city in &lt; 6 h and water depth may rise to 34 m after 7 h of Mosul dam breaking. Finally, the simulation results of the Mosul dam break were used to prepare an emergency action plan.

THE SILURIAN OF LOWER PRIDNESTROVIE, THE PROBLEMS OF STUDY, PROSPECTS, PRACTICAL SIGNIFICANCE

Problem Statement and Purpose. In Lower Pridnestrovie, the Silurian system rocks are widely distributed, well stratified, and composed of thick mainly limestone-do­lomite strata with thin layers of anhydrite, reaching 243-400 m in the southern part. The last geological survey works were carried out in the study area in the early 1990s. Reinterpretation of the received factual material of previous years can give more ac­curate ideas about the stratigraphy of the pre-Mesozoic sediments of the region.Data &amp; Methods. For the article, the deep drilling data for 28 wells crossing the Si­lurian served as material. While processing the actual material, modern GIS methods were used. The actual material on the well columns was compiled in the database "Mane base" created in the software product K-MINE.Results. The article shows the comparison of Silurian stratigraphical schemes of re­search area of different authors as well as the contradictions are examined. The first campaigns of geological exploration of the territory were conducted in the 1960s (Bukatchuk et al., 1967). Following the chronology of the Lower Palaeozoic of Po­dillya of that time, accordingly, the Moldavian horizons and strata were assigned to older epochs and ages of the Silurian. The refinement in the 1970s of the stratigraph­ical scheme of the Silurian of Western Ukraine allowed Moldavian geologists in the 1980s to redistribute the intervals in earlier drilled (1960s) exploration wells to new local formations and members of corresponding age (Bukatchuk et al., 1985). The last survey campaigns in the region in the late 1980s-early 1990s used this revised stratigraphical scheme (Zakharov et al., 1987; Pozdnyakov et al., 1992). As the result of research carried out the data on Silurian formations were collected and system­atized, lithological characteristics were described, and characteristic faunal elements were identified for objective geochronological dating of stratigraphic divisions. As the main outcome of the work, the local stratigraphic scheme was presented. Eight for­mations were assigned: Morosesti and Step-Soci Formations (Llandovery), Balti For­mation and Lower Puhoi Subformation (Wenlock), Upper Puhoi Subformation, Ichel Formation and lower parts of Chisinau Formation (Ludlow), upper parts of Chisinau Formation, Rashkiv and Zvenyhorod Formations (Pridoli).