Contribution of gravity gliding in salt-bearing rift basins – a new experimental setup for simulating salt tectonics under the influence of sub-salt extension and tilting

Basin-scale salt flow and the evolution of salt structures in rift basins is mainly driven by sub- and supra-salt faulting and sedimentary loading. Crustal extension is often accompanied and followed by thermal subsidence leading to tilting of the graben flanks, which might induce an additional basinward-directed driver for salt tectonics. We designed a new experimental analogue apparatus capable of integrating the processes of sub-salt graben extension and tilting of the flanks, such that the overlapping effects on the deformation of a viscous substratum and the brittle overburden can be simulated. The presented experimental study was performed to demonstrate the main functionality of the experimental procedure and setup, demonstrating the main differences in structural evolution between conditions of pure extension, pure tilting, and extension combined with tilting. Digital image correlation of top-view stereoscopic images was applied to reveal the 3D displacement and strain patterns. The results of these experiments suggest that in salt basins affected by sub-salt extension and flank inclination, the salt flow and downward movement of overburden affects the entire flanks of the basin. Supra-salt extension occurring close to the graben centre is overprinted by the downward movement; i.e. the amount of extension is reduced or extensional faults zones are shortened. At the basin margins, thin-skinned extensional faults developed as a result of gravity gliding. A comparison with natural examples reveals that such fault zones can also be observed at the margins of many salt-bearing rift basins indicating that gravity gliding played a role in these basins.

The Application of a Sonic Probe Extensometer for the Detection of Rock Salt Flow Field in Underground Convergence Monitoring

Special regulations have been laid down to establish the principles and requirements for the safety and serviceability of old mining workings which are adapted for tourism. To comply with these regulations the measurements were taken in the Bochnia Salt Mine, which has been in use for 800 years. The presented work demonstrates the use of a sonic probe extensometer in connection with the obtained results of displacement measurements in intact rocks surrounding the gallery. There were also test measurements carried out for determination of the real accuracy of the instrument. The presented study of deformations detected by electromagnetic extensometer measurements is presumed to be the first time that research has been made in salt mines operating in rock mass affected by tectonic stress. The paper presents the process of rock salt flow into the gallery observed over a period of 3 years. It is an unprecedented depiction of salt deformation subjected to natural stresses. One of the more surprising results presented here is the discovery of the occurrence of a specific distribution of strain around the measured gallery. The results of measurements showed that the southern part of the intact rock mass surrounding the passage is more compressed (strain rate 3.6 mm/m/year) than the northern one (strain rate 1.6 mm/m/year). This illustrates the presence and influence of additional tectonic effects resulting from the Carpathian push. These observations represent a new kind of research into tectonic stress and tectonic activity in underground measurements.

THE INFLUENCE OF NaCl SOLUTION FLOW RATE ON ION ABSORPTION OF CAPACITIVE ELECTRIC CARBON PLATE

Research on desalination technology in seawater is being developed. This is because sea water has not been used optimally to meet community needs. One of the rapidly developing desalination systems is desalination technology using a capacitive carbon plate. The development of this desalination system technology is carried out using electrode plates made of carbon. These plates are capable of absorbing salt ions through the porous surface. The amount of ion absorbed is determined by the pore surface structure of the plate, the salt flow rate, the number of plates used, the applied voltage and other factors. The salt flow rate between the carbon plates determines the speed of the salt ions to reach the smallest pores on each plate surface. For this reason, this article has conducted research by testing the variation in the flow rate of NaCl solution to the amount of salt ions absorbed on the carbon plate.

A new experimental approach to assess the influence of gravity gliding on salt tectonics in rift basins

<p>Salt flow in rift basins is mainly driven by sub- and supra-salt extension imposing shear stresses and differential loading on the salt layer. In many rift basins, the graben flanks are tilted as a result of thermal subsidence and sediment load. Such tilt induces additional basin-ward directed stresses potentially causing downward directed salt flow and gravity gliding of the supra-salt overburden. However, sediment loading in extensional basins is usually largest in the basin centre, which would lead to an upward directed salt expulsion and might act as an effective buttress resisting downward gliding.</p><p>Our aim is to investigate the opposing influence of sub-salt extension, sedimentary loading and tilting on deformation patterns in the viscous salt and the brittle overburden. We try to assess under which geological configurations (e.g. minimum basin slope or topographic gradient) upward directed salt flow and downward directed gravity gliding are the dominating deformation processes in extensional basins. Therefore, we developed a new analogue modelling apparatus enabling to simulate the processes of tectonic extension of a graben structure and the gradual tilting of the graben flanks, acting either simultaneously or separately. Using digital image correlation technique, temporal and spatial changes of the displacement and strain patterns can be analysed. Cross sections through the final experiments enable to identify structures characteristic for specific driving processes.</p><p>Here, we present results of a preliminary experimental study in which the basic influence of flank tilting and syn-kinematic sedimentation on salt tectonics in rift basins is examined. In case that the graben flanks remain flat during extension, widespread extensional fault zones develop on the footwall sides near the graben faults. In case that the flanks are tilted simultaneously with basal extension, additional extensional fault zones evolve at the upslope basin margins resulting from downward gliding of the overburden. In the downslope basin centre, this peripheral extension is balanced by reduced amounts of extension near the graben and later by shortening above the graben bounding faults and the hanging wall graben centre. If syn-kinematic sedimentation is introduced, downslope gravity gliding is significantly reduced and extensional fault zones are rather localized. Peripheral extensional structures observed in the experiments resemble typical thin-skinned extensional structures occurring at the flanks of many salt-bearing rift basins, e.g. the Polish Basin and Norwegian-Danish Basin. Thus, such structures might serve as diagnostic indicators for the occurrence of gravity gliding in rift basins.</p>

Contribution of gravity gliding in salt-bearing rift basins – A new experimental setup for simulating salt tectonics under the influence of sub-salt extension and tilting

Basin-scale salt flow and the evolution of salt structures in rift basin is mainly driven by sub- and supra-salt faulting and sedimentary loading. Crustal extension is often accompanied and followed by thermal subsidence leading to tilting of the graben flanks, which might induce an additional basinward directed driver for salt tectonics. We designed a new experimental analog apparatus capable of integrating the processes of sub-salt graben extension and tilting of the flanks, such that the overlapping effects on the deformation of a viscous substratum and the brittle overburden can be simulated. The presented experimental study was performed to demonstrate the main functionality of the experimental procedure and setup demonstrating the main differences in structural evolution between conditions of pure extension, pure tilting and extension combined with tilting. Digital image correlation of top view stereoscopic images was applied to reveal the 3D displacement and strain patterns. Results of these experiments suggest that in salt basins affected by sub-salt extension and flank inclination, the salt flow and downward movement of overburden affects the entire flanks of the basin. Supra-salt extension occurring close to the graben centre is overprinted by the downward movement, i.e. amount of extension is reduced or extensional faults zones are shortened. At the basin margins, thin-skinned extensional fault developed, which resemble fault zones observed on basin flanks offset from the central graben zone.

Thermal Stress and Deformation of Hollow Paddle-Shaft Components with Internal High Temperature Molten Salt Flow

Excessive thermal stress and deformation are important reasons causing disservice of high temperature heat exchangers. This paper presents thermal stress and expansion analysis of single-leaf type hollow paddle-shaft components with internal high temperature molten salt flow based on three-dimensional numerical simulations. The results show that the hollow paddles enhance the heat transfer and decrease the maximum thermal stress simultaneously with the expense of a much higher pressure drop than that of solid paddles. The cumulative von Mises stress distribution curve shows that the stress distribution of the component with hollow paddles is more uniform than that with solid paddles. The radial and axial deformations do not differ much for the components with hollow and solid paddles. A larger volume of the fluid space in the hollow paddles leads to stronger heat transfer, smaller maximum thermal stress, and more uniform stress distribution. The effects of the paddle height, the diameter and number of flow holes, the molten salt flow rate, and the material-side heat transfer coefficient are identified. The advantages of hollow paddle designs in both heat transfer and thermal stress (local and overall) performance are revealed. The work in this study can provide a reference for the design and optimization of hollow paddle heat exchangers with high temperature molten salt as working fluid.

Monitoring surface deformation of deep salt mining in Vauvert (France), combining InSAR and levelling data for multi-sources inversion

The salt mining industrial exploitation located in Vauvert (France) has been injecting water at high pressure in wells to dissolve salt layers at depth. The extracted brine is used in chemical industry for more than thirty years, inducing a subsidence of the surface. Yearly levelling surveys monitor the deformation since the 1996. This dataset is supplemented by synthetic aperture radar images, and since 2015, GNSS data are also continuously measuring the deformation. New wells are regularly drilled to carry on with the exploitation of the salt layer, maintaining the subsidence. We make use of this careful monitoring by inverting the geodetic data to constrain a model of deformation. As InSAR and levelling are characterized by different strengths (spatial and temporal coverage for InSAR, accuracy for levelling) and weaknesses (various biases for InSAR, notably atmospheric, very limited spatial and temporal coverage for levelling), we choose to combine SAR images with levelling data, to produce a 3-D velocity field of the deformation. To do so, we develop a two-step methodology which consists first by estimating the 3-D velocity from images in ascending and descending acquisition of Sentinel 1 between 2015 and 2017, and second by applying a weighted regression kriging to improve the vertical component of the velocity in the areas where levelling data are available. GNSS data are used to control the resulting velocity field. We design an analytical model based on the geological and geophysical data. The model is made of 21 planes of dislocation with fixed position and geometry. We invert the combined geodetic dataset to estimate the slip and tensile motions of each plane. The results of the inversion highlight two behaviours of the salt layer: a major collapse of the salt layer beneath the extracting wells and a salt flow from the deepest and most external zones towards the centre of the exploitation.

Base-salt Relief Controls Salt-related Contractional Styles in the Translational Domain of the Outer Kwanza Basin, offshore Angola

<p>Salt-bearing passive margins are typically characterized by thin-skinned, gravity-driven deformation above a salt detachment, resulting in kinematically-linked domains of updip extension and downdip contraction. These domains are commonly connected by a mid-slope translational domain in which salt-related structures accommodate local extensional and contractional strains associated with salt flow across base-salt relief. Despite a general understanding of these salt-tectonic processes and products, little is still known about the detailed geometric and kinematic evolution of mid-slope contractional structures.</p><p>We use a high-quality, depth-migrated three-dimensional seismic reflection dataset located in the mid-slope translational domain of the Outer Kwanza Basin, offshore Angola. We analysed the seismic-stratigraphic architecture of the Aptian salt and its immediate Albian overburden to reveal the distribution of local, salt-related contractional structures above varying geometries of base-salt relief.</p><p>Our analysis reveals two types of salt-related contractional structures, variably distributed in terms of their trend relative to underlying ramps that trend NW or N. The first type is represented by salt-cored anticlines, the limbs of which may be dissected by salt-detached thrusts. The folds trend parallel to the NW- or N-trending ramps, being located either updip or directly above the underlying ramp. These folds increase in amplitude and decrease in wavelength basinward, and are also locally polyharmonic; showing an upwards increase in wavelength, but a decrease in amplitude. The second type of structure is represented by two sub-types of salt walls: (i) reactive salt walls, and (ii) squeezed salt walls. These salt walls trend broadly parallel to, and are located above or downdip of NW-trending, basinward- and landward-facing ramps. The salt-cored anticlines are formed by local contraction associated with salt flow deceleration above ramp-updip. This process of local contraction also locally induces active rise and overburden piercement as salt walls translate over local base-salt structural highs. Still, other salt walls are locally contracted on the basinward-facing ramp during salt flow seaward, resulting in the squeezed salt wall.</p><p>We show that careful seismic-stratigraphic analysis of salt and overburden deformation, in the context of the underlying base-salt geometry, reveals complex patterns of salt structure evolution during seaward translation across the midslope translational domain. The results are applicable along salt-bearing passive margin worldwide and may provide an important insight in identifying potential plays along the midslope translational domain, where major deepwater oilfields reside.</p>