Shallow Fluid Research Articles

Major and trace element geochemistry of CO2-rich groundwater in the volcanic aquifer system of the Eastern Sikhote-Alin (Russia)

The largest CO2-rich mineral water resource in the Sikhote-Alin ridge of Eastern Russia at Gornovodnoe village was studied. The high-pCO2 groundwaters are cold (5.8–10 °C) with pH 5.9–6.5, TDS varied from 1.2 to 2.7 g/l and belong to Ca–Mg (Ca–Na)–HCO3 type. New data on geology, mineralogy, hydrogeology and hydrogeochemistry, in conjunction with isotope data of water and gas phases, have provided a much better understanding of the origin of this distinctive groundwater. It was found that this water is of meteoric origin, but its unusual chemical composition is controlled by interactions of CO2-rich groundwater and the aquifer materials. The dissolved CO2 gas makes the water slightly acidic (at about pH 6.2) which increased the leaching of many trace elements from host volcanic rocks typically considered immobile at these pH values. 3He/4He ratios and δ13C indicate that mantle degassing is important as a source of deep exogenic fluids. The cold CO2-rich groundwater of the Eastern Sikhote-Alin ridge is the result of interactions between fresh groundwater of meteoric origin, mantle gases and the host volcanic rocks. It thus highlights connectivity between deep and shallow fluids along with deep fractures related to ancient terrane boundaries.

Well-Posedness and input-output stability for a system modelling rigid structures floating in a viscous fluid

We study a PDE based linearized model for the vertical motion of a solid floating at the free surface of a shallow viscous fluid. The solid is controlled by a vertical force exerted via an actuator. This force is the input of the system, whereas the output is the distance from the solid to the bottom. The first novelty we bring in is that we prove that the governing equations define a well-posed linear system. This is done by considering adequate function spaces and convenient operators between them. Another contribution of this work is establishing that the system is input-output stable. To this aim, we give an explicit form of the transfer function and we show that it lies in the Hardy space H∞ of the right-half plane.

Evaluating the sealing potential of young and thin mass-transport deposits: Lake Villarrica, Chile

Abstract Subaqueous mass-transport deposits (MTDs) can be important elements in hydrocarbon systems, forming potential reservoirs or seals. Most research has targeted outcrops or moderately to deeply buried MTDs and, therefore, the petrophysical properties of near-seafloor MTDs, and their influence in the trapping and release of shallow fluids, is poorly studied. Here, we investigate shallow MTDs in Lake Villarrica (Chile) by combining sub-bottom profiles, free-fall penetrometer data, pore pressure dissipation tests and geotechnical properties of sediment cores. Low undrained shear strength under a surficial MTD indicates underconsolidation caused by sudden loading and rapid sealing. Larger, buried MTDs show acoustic signatures of free gas at their base, indicating effective sealing. This is supported by degassing core gaps just below MTDs and by excess pore pressure ratios c . 30–70% within MTDs. Acoustic windows below rafted blocks suggest local fluid escape. MTDs exhibit elevated undrained shear strength and reduced porosity compared to surrounding sediments, but are comparable to upslope source sequences. This suggests that MTD sealing capacity in Villarrica relates to the apparently overconsolidated nature of the slope sequence, leaving a minor role for shear densification. This study shows that shallow MTDs can form a relatively rapid seal for fluid migration, locally degraded by rafted blocks.

Fault-controlled deep hydrothermal flow in a back-arc tectonic setting, SE Tyrrhenian Sea

Understanding magmatic systems and deep hydrothermal circulation beneath arc-volcanoes provides insights into deep processes associated with slab-subduction and mantle-wedge partial melting. Here we analyze hydrothermal flow below a structural high (Capo Vaticano Ridge, CVR) located offshore Capo Vaticano (western Calabria) and affected by magmatic intrusions generated from above the Ionian subducting-slab. In order to explain observations, we combine geophysical and numerical modelling results. Fluid-flow modelling shows that temperature distribution and geothermal gradient are controlled mainly by hydrothermal circulation, in turn affected by heat source, fault pattern, rock permeability, basement topography and sediment thickness. Two main faults, shaping the structural high and fracturing intensely the continental crust, enable deep hydrothermal circulation and shallow fluid discharge. Distribution of seismicity at depth supports the hypothesis of a slab below Capo Vaticano, deep enough to enable mantle-wedge partial melting above the subduction zone. Melt migration at shallow levels forms the magmatic intrusions inferred by magnetic anomalies and by δ3He enrichment in the discharged fluids at the CVR summit. Our results add new insights on the southern Tyrrhenian Sea arc-related magmatism and on the Calabrian inner-arc tectonic setting dissected by seismogenic faults able to trigger high-destructive earthquakes.

Coexistence of the solitary and periodic waves in convecting shallow water fluid

The existence of a solitary wave for the shallow water model in convecting circumstance was established in previous works. It is still unknown that whether there exist periodic waves. In this paper, we prove that the models possess periodic waves with a fixed range of wave speed. The amplitude and wave speed are explicitly given. Moreover, the coexistence of the solitary wave and one periodic wave is established.

Geological setting and hydrogeothermal characteristics of the Kapong non-volcanic hot spring area in Southern Thailand

Thailand is well known for its hot springs, altogether more than 112; all of them are related to non-volcanic geological settings. Currently most hot springs are used as spas; however, for any further development a better understanding of the subsurface geological settings and hydrogeothermal characteristics is. The Kapong hot spring system, located in the northwestern part of Southern Thailand with exit temperatures of maximal 78 °C and flow rates of 1.5–2.0 L/s, is presented here as an example and as a case study for similar investigations in Thailand and for countries having non-volcanic geothermal systems. Geological investigations were combined with aeromagnetic data for the delineation of Mesozoic igneous bodies. Shallower (1D, 2D) and deeper (magnetotelluric) resistivity surveys, down to 2000 m, were carried out for the characterization of shallow aquifers and fluid pathways. Geochemical water analyses, isotope studies, and geothermometer calculations provided evidence for the source and pathways of the hot spring waters, as well for the geothermal reservoir temperature. Results show that meteoric water is flows downwards and heats up by radioactive decay in the igneous bodies. Intersections of fractures and faults related to a nearby major fault zone provide the main pathways for the meteoric water to descend downwards and particularly for hot water to flow upwards. Further steps will be taken to identify the potential of the Kapong hot spring site for electricity generation via low enthalpy technology; possible demand sides are less than 50 km in the west with international tourist destinations along the Andaman coastline.

O, H, and Sr isotope evidence for origin and mixing processes of the Gudui geothermal system, Himalayas, China

The Gudui geothermal field records the highest temperature at equivalent borehole depths among the mainland hydrothermal systems in mainland China. Located about 150 ​km southeast of Lhasa City, the capital of Tibet, the Gudui geothermal field belongs to the Sangri–Cuona rift belt, also known as the Sangri–Cuona geothermal belt, and is representative of the non-volcanic geothermal systems in the Himalayas. In this study, oxygen-18 and deuterium isotope compositions as well as 87Sr/86Sr ratios of water samples collected from the Gudui geothermal field were characterized to understand the origin and mixing processes of the geothermal fluids at Gudui. Hydrogen and oxygen isotope plots show both, deep and shallow reservoirs in the Gudui geothermal field. Deep geothermal fluids are the mixing product of magmatic and infiltrating snow-melt water. Calculations show that the magma fluid component of the deep geothermal fluids account for about 21.10%–24.04%; magma fluids may also be a contributing source of lithium. The linear relationship of the 87Sr/86Sr isotopic ratio versus the 1/Sr plot indicates that shallow geothermal fluids form from the mixing of deep geothermal fluids with cold groundwater. Using a binary mixing model with deep geothermal fluid and cold groundwater as two end-members, the mixing ratios of the latter in most surface hot springs samples were calculated to be between 5% and 10%. Combined with basic geological characteristics, hydrogen and oxygen isotope characteristics, strontium concentration, 87Sr/86Sr ratios, and the binary mixing model, we infer the 6th-Class Reservoirs Evolution Conceptual Model (6-CRECM) for the Gudui geothermal system. This model represents an idealized summary of the characteristics of the Gudui geothermal field based on our comprehensive understanding of the origin and mixing processes of the geothermal fluid in Gudui. This study may aid in identifying the geothermal and geochemical origin of the Gudui high-temperature hydrothermal systems in remote Tibet of China, whose potential for geothermal development and utilization is enormous and untapped.

Breather wave solutions for the Kadomtsev‐Petviashvili equation with variable coefficients in a fluid based on the variable‐coefficient three‐wave approach

Herein, the Kadomtsev‐Petviashvili equation with variable coefficients is investigated, which describes the long waves with small amplitude and slow dependence on the transverse coordinate in a single‐layer shallow fluid. Breather wave solutions are obtained based on a variable‐coefficient three‐wave approach. The dynamical behaviors of the obtained solutions are graphically discussed for different choices of the free parameters in these solutions.

Structural controls on shallow fluid flow and associated pockmark fields in the East Breaks area, northern Gulf of Mexico

Three-dimensional (3D) seismic data, combined with semi-automated mapping methods in ArcGIS, were used to analyse the morphology and distribution of 720 pockmarks and 62 mud volcanoes in the northern Gulf of Mexico. The relationship amongst salt bodies, faults and the distribution of pockmarks and mud volcanoes stresses the significance of these structures in focusing fluid flow on continental margins. The pockmarks were classified according to their structural setting and depth of source, and later correlated with seep data from the Bureau of Ocean Energy Management (BOEM). Key findings include: a) half of the pockmarks are located within faults rooted on the top of salt diapirs, whilst 96% of the pockmarks are associated with salt diapirs – emphasising the importance of salt and crestal faults in focusing fluid flow to the sea floor; b) diffusion flow through the salt minibasins is evident due to the presence of soft amplitude anomalies (indicating fluids) and pockmarks located far from salt or faults; c) oil and gas are actively leaking to the sea floor; d) a higher density of fluid flow features are found in areas with steeper minibasin dips and greater catchment areas. While no clear correlation is evident between the morphological attributes and depth of source, the shallow plumbing system is dominated by pockmarks whereas mud volcanoes are sourced from the deeper parts of the salt minibasins. In summary, this study uses a novel approach to analyse the plumbing system in a salt-rich basin based on the surface fluid flow features. The importance of characterising the fluid flow features and associated structures to reduce risk and uncertainty is stressed in terms of both shallow gas hazards and hydrocarbon leakage from deeper reservoirs.

Dispersive and propagation of shallow water waves as a higher order nonlinear Boussinesq-like dynamical wave equations

The propagation of small amplitude long capillary–gravity waves on the surface of shallow water described by the higher order nonlinear Boussinesq type wave equation. This model is arising in mathematical physics, shallow water waves, fluid dynamics and fluid flow. We applied the modified Jacobi elliptic function expansion method to obtained exact solutions in the type of solitary wave and elliptic functions solutions. These solutions helps the mathematicians and physicians to understand the physical phenomena of this model. This technique can be utilized on other models to launch further exclusively novel solutions for other categories of nonlinear PDEs occurring in mathematical Physics.

Chemical and isotopic signature of groundwater in the Santa Ninfa karst system and possible inferences on neotectonics

The Santa Ninfa karst system is an area strongly controlled by tectonics, whose intense fracturing gave rise to the formation of a large number of cavities that foster the drainage of water. The hydrogeochemical characters of groundwater circulating in this aquifer, together with its isotopic signature, were investigated in detail. The chemistry of groundwater reflects the nature of the rocks hosting the aquifers, constituted by primary and diagenetic selenitic gypsum, salts, and gypsum- arenite, whose dissolution is responsible of the geochemical fingerprint of the quasi-totality of the samples. A single site (CAM) is characterised by a different chemical composition, indicating a mixing between Ca-sulphate, Ca-bicarbonate and a NaCl-rich water. From the chemical point of view, no evidence of interaction between shallow groundwater and deep fluids has been detected. Conversely, isotopic fluctuations highlight mixing processes between surficial (evaporated) runoff and groundwater. Different mixing proportion among these endmembers can be reflected in variations of the chemical character of the sampled springs. Changes in mixing proportions can be the effect of differential permeability variations, in turn produced by local stress field changes during seismogenic processes. In this scenario the geochemical monitoring of the Santa Ninfa karst aquifer could be of relevant interest in the study of seismogenic processes in this area, with particular reference to the relationship between seismic and geochemical transients.

Waves of complicated structure in nonlinear dispersive media

A semi-analytical asymptotic model for large amplitude solitary internal waves in shallow fluids is presented. These solitary waves only exist for large amplitudes beyond the limit of applicability of the KdV/mKdV equations. The theory describes complicated structures including multi humped waves and waves with algebraic asymptotes. All these effects lead to drastically different wave structures even for almost identical density profiles. Trapped core inside the wave prevents appearance of such multiple scales within the core area. The structural stability of waves of large amplitude is investigated using the approach presented earlier in the literature. Multiscaled waves without vortex core are shown to be structurally unstable. It is anticipated that complicated multiscaling phenomena could exist for solitary waves in various geophysical situations.

Acoustic and biological characteristics of seafloor depressions in the North Yellow Sea Basin of China: Active fluid seepage in shallow water seafloor

High resolution multibeam bathymetry revealed the occurrence of numerous craterlike depressions, so-called pockmarks, in the sea floor of the North Yellow Sea Basin (NYSB). To investigate whether these pockmarks are related to any type of fluid flow or gas seepage from subsurface stratum, acoustic survey and box samplings were conducted in a selected area containing several typical pockmarks. This allowed for an integrated analysis of the morphology, distribution, and subsurface strata as well as a direct comparison of seafloor characteristics among different areas inside and outside of a pockmark. Additionally, surface sediments were analyzed for particle structure and grain size. Based on the combination of multibeam bathymetry and backscatter intensity data, 282 seafloor depressions were accurately identified. Moreover, the formation of pockmark can be attributed to existence of gas chimneys and other shallow gases revealed by shallow seismic profile records in the subsurface strata. Sediments inside and outside the pockmark showed remarkable discrepancies in terms of grain size, and benthic fauna. Additionally, strong internal reflection area was observed inside the depressions where benthic habitats are abundant and sediments contain strawberry pyrite and carbonate cementation. Side scan sonar also recorded sediment plumes in the water column, which indicates that the pockmarks are still active. Several “pearl-string-like” accumulations of pockmark were found in the study area, which well agree with the distribution of buried channels and lakes. These results thus provide new insights in interpreting shallow water fluid seepage, with implications for our current knowledge of overall sedimentation process in offshore continental shelves.

Jupiter's Turbulent Power Spectra From Hubble Space Telescope

AbstractTurbulence in Jupiter's atmosphere was investigated with archival and ongoing observations from the Hubble Space Telescope. Data sets that include one full rotation (360° longitude coverage) were used to produce complete maps of the planet's upper cloud layer. The global maps were analyzed to generate the passive tracer power spectrum of cloud features for single rotation observations, while successive rotations produced pairs of maps such that zonal winds were calculated. An atmosphere's dimensionality and dynamics are reflected in the slopes of such turbulent power spectra. Many of the retrieved passive tracer power spectra have a shallow spectral index over wave numbers k∼1 − 30 and transition to the well‐known Kolmogorov k−5/3 relation at smaller scales between wave numbers k∼30 − 1,000. The transition scale is similar to the number of jets in Jupiter's zonal wind profile and is related to the Rhines scale and the beta effect induced anisotropy scale. We also report on differences found in anticyclonic and cyclonic shear region power spectra and how they correlate to latitudinal changes in the zonal wind profile. We found that properties of Jupiter's power spectra are consistent with quasi‐geostrophic turbulence for shallow fluids.

Geochemical evidence for seabed fluid flow linked to the subsea permafrost outer border in the South Kara Sea

Driven by rising bottom water temperatures, the thawing of subsea permafrost leads to an increase in fluid flow intensity in shallow marine sediments and results in the emission of methane into the water column. Limiting the release of permafrost-related gas hydrates and permafrost- sequestered methane into the global carbon cycle are of primary importance to the prevention of future Arctic Ocean acidification. Previous studies in the South Kara Sea showed that abundant hydro-acoustic anomalies (gas flares) induced by seafloor gas discharge into the water column occur in water whose depth is ≥20 m. This distribution of gas flares could indicate the outer extent to which continuous permafrost restricts upward fluid flow. This paper reports on a geochemical analysis of a 1.1 m long sediment core located in an area of shallow fluid flow off of the Yamal Peninsula coast (South Kara Sea) using high-resolution seismic data. Our results reveal a thin zone of Anaerobic Oxidation of Methane (AOM), a sharp shallow sulfate-methane transition (SMT) located at a sub-bottom depth of 0.3 m, and significant temporal variation in methane discharge confirmed by the pyrite (FeS2) distribution in the core sample. A concave up pore water chloride profile depicts upward fresh/brakish water advection in subsurface sediments. The terrestrial/fresh water genesis of methane from the sampled core is deduced from the stable isotopic signatures (δ13 C and δD). We propose two mechanisms for the observed fluid flow: i) convection of thaw water from subsea permafrost; and/or ii) lateral sub-permafrost ground water discharge marking the outer extent of continuous permafrost off of the central Yamal Peninsula coast at ˜45 m water depth.

Brief communication: Modulation instability of internal waves in a smoothly stratified shallow fluid with a constant buoyancy frequency

Abstract. Unexpectedly large displacements in the interior of the oceans are studied through the dynamics of packets of internal waves, where the evolution of these displacements is governed by the nonlinear Schrödinger equation. In cases with a constant buoyancy frequency, analytical treatment can be performed. While modulation instability in surface wave packets only arises for sufficiently deep water, “rogue” internal waves may occur in shallow water and intermediate depth regimes. A dependence on the stratification parameter and the choice of internal modes can be demonstrated explicitly. The spontaneous generation of rogue waves is tested here via numerical simulation.

On the regularity of the Green–Naghdi equations for a rotating shallow fluid layer

The Green–Naghdi equations are an extension of the shallow-water equations that capture the effects of finite fluid depth at arbitrary order in the characteristic height to width aspect ratio $H/L$. The shallow-water equations capture these effects to first order only, resulting in a relatively simple two-dimensional fluid-dynamical model for the layer horizontal velocity and depth. The Green–Naghdi equations, like the shallow-water equations, are two-dimensional fluid equations expressing momentum and mass conservation. There are different ‘levels’ of the Green–Naghdi equations of rapidly increasing complexity. In the present paper we focus on the behaviour of the lowest-level Green–Naghdi equations for a rotating shallow fluid layer, paying close attention to the flow structure at small spatial scales. We compare directly with the shallow-water equations and study the differences arising in their solutions. By recasting the equations into a form which both explicitly conserves Rossby–Ertel potential vorticity and represents the leading-order departure from geostrophic–hydrostatic balance, we are able to accurately describe both the ‘slow’ predominantly sub-inertial balanced dynamics and the ‘fast’ residual imbalanced dynamics. This decomposition has proved fruitful in studies of shallow-water dynamics but appears not to have been used before in studies of Green–Naghdi dynamics. Importantly, we find that this decomposition exposes a fundamental inconsistency in the Green–Naghdi equations for horizontal scales less than the mean fluid depth, scales for which the Green–Naghdi equations are supposed to more accurately model. Such scales exhibit pronounced activity compared to the shallow-water equations, and in particular spectra for certain fields like the divergence are flat or rising at high wavenumbers. This indicates a lack of convergence at small scales, and is also consistent with the poor convergence of total energy with resolution compared to the shallow-water equations. We suggest a mathematical reformulation of the Green–Naghdi equations which may improve convergence at small scales.

A Petrov–Galerkin multilayer discretization to second order elliptic boundary value problems

We study in this paper a multilayer discretization of second order elliptic problems, aimed at providing reliable multilayer discretizations of shallow fluid flow problems with diffusive effects. This discretization is based upon the formulation by transposition of the equations. It is a Petrov–Galerkin discretization in which the trial functions are piecewise constant per horizontal layers, while the test functions are continuous piecewise linear, on a vertically shifted grid.We prove the well posedness and optimal error order estimates for this discretization in natural norms, based upon specific inf–sup conditions.We present some numerical tests with parallel computing of the solution based upon the multilayer structure of the discretization, for academic problems with smooth solutions, with results in full agreement with the theory developed.

Geological Controls on Fluid Flow and Gas Hydrate Pingo Development on the Barents Sea Margin

AbstractIn 2014, the discovery of seafloor mounds leaking methane gas into the water column in the northwestern Barents Sea became the first to document the existence of nonpermafrost‐related gas hydrate pingos (GHPs) on the Eurasian Arctic shelf. The discovered site is given attention because the gas hydrates occur close to the upper limit of the gas hydrate stability, thus may be vulnerable to climatic forcing. In addition, this site lies on the regional Hornsund Fault Zone marking a transition between the oceanic and continental crust. The Hornsund Fault Zone is known to coincide with an extensive seafloor gas seepage area; however, until now lack of seismic data prevented connecting deep structural elements to shallow seepages. Here we use high‐resolution P‐Cable 3‐D seismic data to study the subsurface architecture of GHPs and underlying glacial and preglacial deposits. The data show gas hydrates, authigenic carbonates, and free gas within the GHPs on top of gas chimneys piercing a thin section of low‐permeability glacial sediments. The chimneys connect to faults within the underlying tilted and folded fluid and gas‐hydrate‐bearing sedimentary rocks. Correlation of our data with regional 2‐D seismic surveys shows a spatial connection between the shallow subsurface fluid flow system and the deep‐seated regional fault zone. We suggest that fault‐controlled Paleocene hydrocarbon reservoirs inject methane into the low‐permeability glacial deposits and near‐seabed sediments, forming the GHPs. This conceptual model explains the existence of climate‐sensitive gas hydrate inventories and extensive seabed methane release observed along the Svalbard‐Barents Sea margin.

Investigating the contour dynamics of the vortex eye on the laboratory model of a differentially rotating fluid

This article studies the contour dynamics of the vortex eye based on the results of laboratory experiments with a differentially rotating shallow fluid. This paper also describes the analysis of the energy processes inside the vortex center with variations in the velocity shift between the center of the system and the periphery in the framework of the instability representations due to the presence of inflection points on the velocity profile. Moreover, it is shown that the conditions for the development of instability arise only at fully determined values of the velocity shift to the width ratio of the shear zone. Finally, articles states that the formation of polygonal configurations of vortex contours with velocity shift is associated with energy transfer.