Vertical Conduits Research Articles

Simulating a Controlled CO2 Release Experiment in a Shallow Fault Zone in Western Australia

Geological and dynamic modelling studies are routinely performed to design and interpret field test experiments. These studies help with the planning of well location, well operations and monitoring strategies, as well as with a range of different test activities. After the test, the new interpretations of the experiment observations are then integrated with previous knowledge and reconciled with the assumption that was first tested. Often, the results of a test are significantly different from what was anticipated (hence the purpose of testing). In this work, we examine such an example and put in perspective the impact of the first modelling study on the interpretation of the test. The CSIRO In-Situ Laboratory Project (In-Situ Lab) is located at the eastern edge of the South West Hub CCS Flagship project (SW Hub) in Western Australia, which has been identified as a potential area for commercial-scale CO2 storage. A first test at the In-situ Lab has evaluated the ability to monitor and detect unwanted leakage of CO2 from a storage complex in the shallow subsurface. The In-Situ Lab is also collocated within a major fault zone. Prior to a controlled-release test, a numerical simulation study was undertaken to inform the optimal location for a monitoring well, the vertical location of the downhole instrumentation, and to ensure breakthrough of CO2 occurred within the project timeframe. Based on the likely extent of the CO2 plume for an injection volume of 40 tonnes, the observation well ISL OB-1 was located at 7 m from the injection well to maximise the likelihood the CO2 plume would be intersected. The CO2 plume was predicted to migrate vertically for at least 20 m above the injection interval. Due to the resolution of the existing seismic and limited well data, large uncertainty existed regarding the detailed fault zone geometry, and, more specifically, how disaggregation and drag has impacted the contiguity and slope of lithostratigraphic layers within the fault zone. In other words, it was not clear to what extent the relatively low-permeability paleosols would form baffles for the migration of CO2. Also, it was not known whether sub-seismic faults, if present, would act as vertical barriers or conduits to CO2 migration. During a controlled-release test, 38 tonnes of gaseous CO2 were injected in February 2019, and the gas was monitored by a wide range of downhole and surface monitoring technologies. A higher than expected bottomhole pressure was observed. CO2 reached the ISL OB-1 monitoring well after approximately 1.5 days. Observations suggest that the fault zone did not alter the CO2 migration along bedding at the scale and depth of the controlled release experiment. No vertical CO2 migration was detected beyond the perforated injection interval. The injectivity was lower than predicted from core measurements and prior modelling. Also, contrary to prior model predictions, the plume did not migrate vertically across the paleosol overlying the injection interval. Post-injection reservoir simulations calibrated to the observed pressure and CO2 distribution data confirm that (1) a vertical segregation exists just above the injection interval, and (2) local overpressure are due to a combination of wellbore damage, mud invasion at the injection well and, to a lesser extent, reservoir compartmentalisation.

Gas-liquid downward flow through narrow vertical conduits: effect of angle of entry and tube-diameter on flow patterns

Abstract The present study investigates the flow pattern characteristics of air-water co-current down-flow in millichannels. The experiments have been performed in glass tube of diameter 0.0042 and 0.008 m. The fluids are injected through Y entry the included angle between the Y arms being 45°, 90°, 135°, and 180° (T Entry). The investigation reveals that the flow patterns are function of tube-diameter, and angle of fluid entry. Interestingly, stratified flow has been observed for steeper Y entry section at low liquid flow rates.

Influence of reservoir-scale heterogeneities on the growth, evolution and migration of a CO2 plume at the Sleipner Field, Norwegian North Sea

New analysis of the baseline (pre-injection) seismic data at Sleipner has revealed large-scale, roughly north-trending, channelled ‘fairways’ at a range of stratigraphical levels in the Utsira Sand. The baseline data also reveal localised stratigraphical ‘point discontinuities’ within the reservoir, some of which show evidence of having provided vertical conduits for earlier natural gas flow. The repeat time-lapse seismic datasets, where finer details of reservoir geology are illuminated by the reflective CO2, show smaller-scale, north-trending and sometimes sinuous channels within the larger channel fairways. They also show a number of vertical CO2 pathways within the CO2 plume, corresponding to the point discontinuities seen on the baseline data.Reservoir flow models were set up with flow properties constrained only by the observed levels of CO2 accumulation in the reservoir and the arrival time of CO2 at the reservoir top just prior to the first repeat seismic survey in 1999. The initial model with laterally homogeneous sand units separated by thin semi-permeable mudstones achieved only a moderate match to the observed time-lapse seismic data. Subsequent flow models, progressively incorporating higher permeability vertical CO2 pathways through the mudstones and large-scale channel fairways within the reservoir sands, yielded a progressive and marked improvement in the history-match of key CO2 layers within the plume. Crucially, no layer-specific model calibration was employed to achieve this improvement.New geophysical measurements from Utsira Sand core have recently become available. These measurements provide important constraints on rock physics models of CO2 and brine mixtures in the Utsira Sand. An empirical Brie fluid mixing law for intermediate fluid saturations provides a good fit to the new laboratory data, allowing measurements of CO2 saturation to be converted into seismic velocity. This rock physics model was used to convert CO2 saturation distributions predicted by the most realistic reservoir model into a seismic velocity model of the CO2 plume. Synthetic seismic reflectivity profiles generated using this velocity model show a striking resemblance to the observed time-lapse seismic data, both in terms of plume layer reflectivity and also of time-shifts within and beneath the CO2 plume. This provides confidence in the fidelity of the preferred reservoir model solution.These results represent a significant breakthrough in the understanding and modelling of CO2 plume development at Sleipner. We emphasise that the improvements were brought about not by fine tuning reservoir properties to fit the observed time-lapse data, but simply by incorporating geological permeability features that can reasonably be inferred from the baseline seismic data.

A model for faults to link the Neogene reservoirs to the Paleogene organic-rich sediments in low-relief regions of the south Bohai Sea, China

Fault acts as an important vertical migration conduit for hydrocarbons in rift basins and can transport hydrocarbons from deep-buried organic-rich sediments to shallow-buried coarse-grained sequences. Such migration process is expected, but generally needs to pass through thick mudstone intervals and its controlling factors are not well understood. The low-relief regions of the south Bohai Sea in the Bohai Bay rift basin, comprising both Paleogene and Neogene hydrocarbon traps, can act as a good case study for the factors controlling the hydrocarbon transporting capacity of faults. By comparing the hydrocarbon generation potential of source rocks in different formations, we confirm that the hydrocarbons trapped in the Neogene traps mainly originate from the Eocene Shahejie Formation, and need to pass through a thick Oligocene regional caprock. Hydrocarbon fluid inclusions within the Neogene reservoir sandstones indicate two major hydrocarbon charging events in the middle Pliocene to Quaternary, based on which we chose the T02 seismic marker bed to calculate fault displacement. Seismic profiles show that Neogene hydrocarbon-charged traps are commonly linked to faults with large-amount displacement, where the regional caprock has a limited thickness. Using statistics of the Neogene charged traps in a regional 3D seismic grid, we draw the minimum fault displacement for hydrocarbon migration in the Laizhouwan Sag at 53.6 m and in the Huanghekou Sag at 56 m, and the biggest caprock thickness for hydrocarbon migration in the Laizhouwan Sag at 240.7 m and in the Huanghekou Sag at 320.2 m. These observations emphasize the coupling of fault displacement and regional caprock thickness controlling the hydrocarbon transporting capacity of faults in a rift basin.

Mathematical Modelling Of Extraction Of The Underground Fluids: Application To Peristaltic Transportation Through A Vertical Conduit Occupied With Porous Material

This paper gives a theoretical idea for extracting the underground fluids through peristalsis. Due to the similarity in aforesaid problem, peristaltic transportation of a viscous Newtonian fluid over a vertical porous conduit is studied by considering the impact of heat transfer. Presuming the long-wavelength approximation, explicit solutions are found as asymptotic expansions with reference to free convection and porosity parameters. Mathematical expressions for coefficient of heat transfer, temperature and mean flux are derived. It is experiential that for few precise values of dissimilar parameters under contemplation, the coefficient of heat transfer increases significantly as Grashof number and Eckert number increases. This narrates to optimization of heat transfer in some processes. Further, it has been observed that mean flow enhances with amplitude ratio, porosity in addition to pressure drop. This authorizes auxiliary research on the impacts of peristalsis on the flow features in vertical channels.

Mathematical Modeling of Convective Heat and Mass Transfer of a Rotating Nano-Fluid Bounded by Stretching and Stationary Walls in a Vertical Conduit

The influence of thermal emission and unvarying magnetic field of convective heat and mass transfer of a rotating nano-liquid in an upright conduit constrained by a stretching and motionless wall is studied. The temperature, concentration profile, primary and secondary velocities have been computed through similarity transformation and fourth-order Runge-Kutta shooting technique. The objective of this article is to measure the impact of emission constraint, Brownian movement constraint and Eckert number, thermophoresis constraint, Prandtl number, space, and temperature-dependent heat source constraint on velocity. The results are presented in tables and graphs. Further, various constraint impacts on the skin friction coefficient, heat and mass transfer rates are also explored. This work is pertinent to biotechnological and engineering uses, like mass and heat transfer enhancement of microfluids and design of bioconjugates.

Modeling the Matrix-Conduit Exchanges in Both the Epikarst and the Transmission Zone of Karst Systems

Usual conceptual models of karst hydrodynamics highlight the important role of unsaturated subsystems in recharge repartition. However, few of them have been compared with scarce suitable physically-based numerical models. Hybrid models that couple single continuum medium with discrete features promise an improved consideration of karst specificities. Here we evaluate their capability to properly reproduce interactions between a vertical conduit and the surrounding unsaturated matrix. We simulate the response of such a configuration to a single recharge event for various sets of parameters. We show the ability of hybrid models to reproduce the most significant behaviors described in the literature, i.e., transient storage and distribution of recharge, flow concentration towards conduits in the epikarst, and matrix-conduit exchanges varying in time and space. In addition to the explicit conduits, simulating variably saturated flows with the Richards equation and distinguishing the epikarst and the transmission zone are key elements to reproduce most processes. The contrasts between subsystems necessary to observe desired behaviors have been quantified. They are reinforced by the varying matrix saturation that causes realistic competition between matrix and explicit conduits. The study also highlights the need to deepen knowledge of the scaled medium properties we need to know to apply such models to actual cases.

Controlling factors of riverine CO2 partial pressure and CO2 outgassing in a large karst river under base flow condition

Riverine CO2 outgassing constitutes the important vertical conduit in global carbon cycle and affects climate change. In order to investigate the factors that control riverine pCO2 and CO2 diffusion rate (FCO2), river water samples were collected in the mainstream and 42 tributaries of Xijiang River, a karst river during the dry season in 2015. The pCO2 varied from 260 to 6354μatm with a mean value of 1765μatm, indicating most of the samples were oversaturated with respect to CO2 compared to atmosphere. The pH, pCO2, and HCO3− exhibited clearly spatial distribution pattern that pH and HCO3− decreased along the flow direction while the pCO2 increased along the flow direction. Theoretical calculation indicated that the water temperature fluctuation, bio-degradation/respiration, photosynthetic activities and anthropogenic acidic inputs were not the reasonable explanations. The lithologic differences essentially predominated the riverine pH, pCO2, and HCO3−, the upper reaches of Xijiang River flow through karst carbonate terrain and thus exhibited high pH, HCO3− concentrations meanwhile low pCO2, the spatial distribution of pH, pCO2, and HCO3− became visible as the continuous addition of silicate weathering products with low pH and dissolved inorganic carbon (DIC) concentrations. The mixing calculation indicated the DIC concentrations of silicate weathering should lower than 0.5 mmol/L. The calculated FCO2 of Xijiang River ranged between −38.6 and 1579.8 mmol/m2/D, with a mean value of 574.8 mmol/m2/D and median value of 410.9 mmol/m2/D. FCO2 exhibited obviously lower values in karst terrain compared that in silicate terrains, because carbonate weathering results in high pH of karst rivers, which caused the low relative proportion of pCO2 in DIC. More estimations of CO2 outgassing rate from the karst rivers are required due to the unique characteristics and geochemical process in karst landform.

Bioinspired, Mechanically Robust Chemiresistor for Inline Volatile Organic Compounds Sensing

AbstractThere are advantages to polymer/nanoparticle composite‐based volatile organic compounds (VOCs) sensors, such as high chemical and physical stability, operability under extreme conditions, flexible use in manufacturing, and low cost. Nevertheless, their lower limit of detection due to thickness‐dependent diffusion has constrained their application. Inspired by the metaxylem in vascular plants and its vertical conduits and horizontal pits that enable efficient transpiration, a polymer/nanoparticle composite‐based sensor is fabricated with a controllable, spontaneously formed, hollow core for inline VOCs transportation, and porous microstructure for radial direction diffusion. The hollow core is surrounded by an inner porous layer (thermoplastic polyurethane (TPU)), a middle sensing layer (TPU/graphene nanoplatelets/multiwalled carbon nanotubes), and an outer mechanically durable layer (TPU). This multilayered structure shows a 600% higher response rate compared to a single‐layered composite fiber sensor, with a low limit of detection (e.g., ≈15 ppm for xylene) and high selectivity based on the Flory–Huggins interaction parameter. This flexible and stretchable sensor also demonstrates a dual parameter sensing capability from VOC concentrations and uniaxial strain deformation. Via a one‐step fiber spinning procedure, this self‐induced hollow fiber offers a unique method of microstructural design, which enables the detection of low‐concentration VOCs by polymer/nanoparticle‐based sensors.

Active Volcanism Revealed from a Seismicity Conduit in the Long-resting Tatun Volcano Group of Northern Taiwan

Abundant earthquakes clustered within a particular zone often reflect an active geological feature, such as clustering seismicity along a fault zone and a huge number of volcanic-earthquakes around the erupting conduit. Herein we perform a double-difference tomographic inversion and relocate the seismicity at the long-resting Tatun volcano group (TVG) in northern Taiwan. A dramatic improvement of the earthquake location model surprisingly show that, from 2014 to 2017, two clustered seismic zones are identified in the TVG. One major group of events (>1000) persistently clustered within a ~500 m diameter vertical conduit with a ~2 km height. The clustering seismicity conduit is just located nearby Dayoukeng, one of the strongest fumaroles in the TVG, and is connected to a fracture zone characterized by low Vp/Vs in the shallow crust. The other group of events is clustered within a sphere-like zone beneath Mt. Chihsin around the depths between 0.5 km and 2 km. Both seismic zones are probably triggered by the significantly volcanic gases and fluids ascending from the deep magma reservoir. Combined with a variety of results from literature, the seismicity conduit near the strong fumarole is the evidence for an active volcano and also identifies a likely pathway for ascending magma if the TVG erupts again in the future. But possibility of developing different magma pathways at other clustered seismic zones such as beneath Mt. Chihsin may not be totally excluded.

Karstification and fluid flow in carbonate units controlled by propagation and linkage of mesoscale fractures, Jandaíra Formation, Brazil

This study examines how centimeter- to meter-long fracture sets propagate, link and form m-long structures, which are then karstified in the vadose (aerated) zone in the upper parts of exposed layered carbonate units. We characterize the fracture patterns, including both mesoscale extensional joints, veins, stylolites and macroscale faults, within the Rosario pavement, which is a 1100-m-long, 340-m-wide outcrop in the Jandaíra Formation, Potiguar Basin in semiarid Brazil. The work compares the directions of the mesoscale structures with the strikes of surface collapse dolines and cave conduits at depths of 10–20 m. The main results indicate that the background (diffuse) deformation consists mostly of bed-perpendicular, stratabound N-S-striking veins and extensional (opening mode-I) fractures and E-W- to ENE-WSW-striking stylolites, which are consistent with the same stress field. Both sets of structures are laterally continuous and are commonly traceable across the pavement. Linkage of stylolites and stratabound fractures formed via throughgoing fractures that affected several layers, as deep as 15 m. The throughgoing fractures were favorable structures for fluid pathway formation and karstification in the epigenetic environment. We conclude that sets of mesoscale structures fit with the orientations of the collapse dolines and subhorizontal cave passages, and induced hydraulic anisotropy within the vadose level. These findings indicate that the fractures, veins and stylolites grow, link and form localized vertical conduits for water percolation and karst development. These findings can constrain future models and numerical simulations of karst conduits in investigations of groundwater and oil reservoirs.

Gas-Liquid Downward Flow through Narrow Vertical Conduits: Effect of Angle of Entry and Tube-Diameter on Flow Patterns

The present study investigated the flow pattern characteristics of air-water co-current down-flow in milli-channels. The experiments have been performed on tube diameter 0.0042 and 0.008 m glass tubes with each tube diameter having four different entry sections of the included angle between the Y arms being 45ᵒ, 90ᵒ, 135ᵒ, and 180ᵒ (T Entry). The outcome of the investigation reveals that the flow patterns are a function of tube-diameter, and the angle of ejection of entry. Interestingly, Stratified flow has been observed for the Y entry section for low liquid flow rates.

Simulation of the Pneumatic System of a Seed Drill with a Vertical Flow Direction

The purpose of the work is to reveal the influence of conical directing agents on the speed and trajectory of particles movement in the vertical pneumatic conduit of the sowing machine and to establish their rational parameters. With the help of numerical modeling the particle flight trajectories in the air flow were obtained. The carried out researches have shown expediency of application of the conical directing agent, allowing to take away a longitudinal stream of particles from walls of a pneumatic conduit and to centre their trajectories of movement along an axis of a pneumatic conduit. Particles are focused to the center of the distributor when the distributor covers the area of pneumatic conduit cross-section close to 25%.

Gas-Liquid Downward Flow through Narrow Vertical Conduits: Effect of Angle of Entry and Tube-Diameter on Flow Patterns

Gas-Liquid Downward Flow through Narrow Vertical Conduits: Effect of Angle of Entry and Tube-Diameter on Flow Patterns

A Preliminary Model for the Migration of Sulfide Droplets in a Magmatic Conduit and the Significance of Volatiles

Abstract A close relationship between Ni–Cu–(PGE) sulfide deposits and magmatic conduit systems has been widely accepted, but our present understanding still rests on empirical inductions that sulfide liquids are entrained during magma ascent and aggregated at hydrodynamic traps such as the opening of a conduit into a larger magma body. In this contribution, a preliminary quantitative model for the dynamics of mm-scale sulfide droplets in a vertical magmatic conduit is developed, examining such limiting parameters as the size, transport velocity and the magmas’ maximum carrying capacity for sulfide droplets. Addition of numerous dense sulfide droplets significantly reduces magma buoyancy and rapidly increases the bulk viscosity, and the resulting pressure gradient in the propagating conduit dyke restricts the maximum volume fraction of droplets that can be carried by ascending magma. For sulfide droplets alone, the maximum carrying capacity is low, but it will be improved dramatically by the addition of volatiles which reduces the density and viscosity of silicate melt. Potential volatile degassing during decompression further facilitates sulfide entrainment by reducing bulk magma density, and the formation of buoyant compound vapour-sulfide liquid bubble drops also greatly enhances the carrying capacity. The breakdown of compound drops by detachment of parts of the vapour bubble or sulfide droplet may occur at low pressure, which liberates sulfide liquids from rising compound drops, potentially to collect in traps in the conduit system. When sulfide-laden magma flows through a widening conduit, many droplets can be captured by the re-circulation flow just downstream of the expanding section, followed by sulfide liquid accumulation and enhanced chemical interaction via diffusive exchange with the recirculating magma, potentially resulting in an economic, high-tonnage ore body. We apply our models to the emplacement of sulfide-rich magmatic suspensions at Noril’sk and show that the disseminated mineralization in intrusions could have formed when magmas carrying re-suspended sulfide liquid entrained from pre-existing sulfide accumulations in the conduit system reached their limiting sulfide carrying capacity as dictated by buoyancy and were deflected into blind sills flanking the principal conduit for flood basalt volcanism.

Three-dimensional simulations of liquid waves in isothermal vertical churn flow with OpenFOAM

Periodic liquid waves of large amplitude are one of characteristic phenomena observed in the churn flow regime of gas–liquid flow in vertical conduits, where the liquid flowing on the wall is entrained upwards by the gas flow in the core. The present work investigates the frequency of these large liquid waves. Three-dimensional simulations of isothermal churn flow of air and water in 19 and 32 mm vertical pipes were performed using the interFoam solver from the OpenFOAM library. Turbulent features in the flow are modelled using the unsteady Reynolds Averaged Navier–Stokes approach with the k–ω SST (shear stress transport) model. Interface sharpening with bounded compression was used to preserve the sharpness of gas–liquid interface by compensating the diffusive fluxes of the numerical scheme. A sensitivity study on the global amount of interface compression was performed for two flow cases taken from the literature. Mesh sensitivity study was performed using four meshes, ranging from a coarse mesh with several hundred thousand cells, to a fine mesh with several million computational cells. Results for the calculated wave frequency and wave maximum amplitude agree with measured values reported in the literature.

Seamount‐Volcanic Island Transition and Evolution From Fissural to Central Activity Inferred by the Magnetic Modeling of Salina Island (Tyrrhenian Sea)

AbstractVolcanic islands represent the later stage of an early submarine volcanic activity and show different morphologies reflecting the geometry of shallow plumbing systems, magma output rate, gravitational instability, and erosive phases. Two end‐member morphologies may be recognized: (a) rift‐like elongated edifices and ‘stellate’ volcanoes and (b) cone‐shaped, central‐type volcanoes. While the evolution from early conical shapes to stellate shapes is relatively well known, the reverse is less constrained, commonly lacking geophysical and geological data to support it. We present magnetic forward and 3‐D inverse models of the volcanic island of Salina (244‐15 ka; Aeolian Arc, Southern Tyrrhenian Sea) to characterize its shallow plumbing system. The detected magnetic sources are interpreted as the crystallized portions of dykes and vertical conduits. The dykes mainly characterize the offshore of Salina Island, whereas subcircular conduits are located onshore. The results show that the early, mainly submarine phases of Salina concentrated along dykes following weakness zones of tectonic significance. As the volcanism proceeded, the subaerial activity focused on two main cone‐shaped stratovolcanoes (Monte Fossa delle Felci and Monte dei Porri). The intersections among dykes and the progressive loading of volcanic products during the early growth of Salina are responsible for the transition from an early fissural basaltic activity to a later, basaltic to a last, more evolved central‐type volcanism. We conclude that intrusions along pre‐existing tectonic structures, dyke intersections, and loading processes related to the formation of a volcanic pile regulate the morphology and structural evolution of volcanic islands from the early, submarine phase to the later subaerial activity.

What matters for flow and recovery in carbonate gas reservoirs: Insights from the mature Central Luconia Province, offshore Sarawak, Malaysia

Miocene carbonate reservoirs in Central Luconia, offshore Sarawak, Malaysia, have been delivering gas for over 30 yr. In this paper, learnings from that period of production are used to understand the key drivers affecting flow during production and recovery optimization in existing fields as well as development decisions for new discoveries. The large data set, generated over more than 40 yr, was analyzed in a consistent manner through a holistic database, constrained by a stratigraphic framework, to allow reservoir units to be compared like-for-like (“integrated knowledge base” [IKB] concept). Carbonate reservoir heterogeneities impacting flow are grouped into “horizontal–heterogeneities”—argillaceous flooding layers and exposure-related karst—and “vertical–heterogeneities”—large-scale architectural elements, found especially along platform margins. Both types of heterogeneities control water ingress during production and influence the recovery mechanism. Argillaceous flooding layers can act as baffles, holding back water rise during production, or can form pressure compartments. Long-lived, fault-bounded reef margins, carbonate shoals, islands, and karsts can be vertical conduits for aquifer inflow. Platform shape and architecture impact column height and hence recovery efficiency. Additional drivers impacting recovery were found to be gas-column height, aquifer size and permeability, pressure connection to neighboring fields, and field development concepts. All drivers identified impact decisions throughout the field life, e.g., well count and design, intervention capabilities, evaluation and mitigation of early-water breakthrough, reservoir management, selecting enhanced recovery methods, and abandonment pressure. The IKB allowed to derive “big rules” on what matters for flow, which were used to decide on development strategies for greenfields in Central Luconia. The presented outcomes can be extrapolated to comparable carbonate systems, whereas the IKB approach can be adapted and applied to other mature basins and reservoir types where equally vast and historic data sets are awaiting to be used in the current era of digitalization.

Groundwater dynamics in fossil fractured carbonate aquifers in Eastern Arabian Peninsula: A preliminary investigation

Eastern Arabian Peninsula represents the main natural groundwater discharge area of the Arabian platform fossil aquifer system. In such settings, connections between aquifers could strongly affect the flow dynamics, water quality and availability as well as karst formation and landscape evolution. Geological structures such as folds and faults are central to aquifer connectivity, yet their role on groundwater flow is poorly understood. Herein, we perform mapping of exposed and buried structural features in the Qatar Peninsula using Landsat, Sentinel-2 and ALOS-PalSAR scenes, correlated with field, GPR and isotopic data to assess their role in aquifer connections and groundwater dynamics. Our results suggest that ENE-WSW oriented fold-related faults act as vertical conduits along which artesian upward leakages from the deep Aruma aquifer take place into the shallower main aquifer unit (i.e. Umm er Radhuma and Rus) in southern Qatar Peninsula. On the other hand, downward leakage from the freshwater lens in the Dammam aquifer take place in northern Qatar Peninsula. The deep, brackish, and gaseous-rich waters ascending along faults in south Qatar Peninsula, in addition to degrading the water quality in the main aquifer unit, enhance dissolution of carbonates and evaporites leading to strong karstification that produces abundant collapse features. Our findings suggest that structure controls can add significant complexity to recharge mechanisms and groundwater dynamics in fossil aquifers. Future large-scale radar subsurface mapping will be essential to resolve the variability of the water heads in such areas and its correlation to structural discontinuities.

Seismic hazard parameter estimation of the Mount Cameroon volcanic region (Cameroon) based on a combination of mixed catalogs

The Mount Cameroon volcanic region is one of the most seismically active areas of Cameroon, with earthquakes of duration magnitude $$M_{\text{D}}$$ ≥ 0.5 occurring at an average rate of one to three events every 3 days. The seismic hazard parameters of this region have been assessed on the basis of a procedure that combines historical events with complete instrumental data and takes into account uncertainty in the determination of the earthquake magnitude. The historical events include all felt and reported events that occurred prior to the establishment of a seismic network, whereas the complete instrumental data comprise of all instrumentally recorded events. The dataset of earthquake catalogs used in this study covers the period from 1909 to 2006. The overall seismicity pattern of the Mount Cameroon region during this period is characterized by the predominant clustering of earthquakes in four distinct regions denoted as: region A and B in the northern and southern part of the elongated axis, respectively, region C in the Douala region, and region D in the offshore area. For each region, the maximum regional magnitude $$m_{ \hbox{max} }$$ , the activity rate of seismic events $$\lambda$$ , and the b-value of the magnitude–frequency Gutenberg–Richter relation were determined. The estimated b-value during the studied timeframe ranged from a minimum of 0.81 ± 0.07 to a maximum of 1.52 ± 0.03 across the four seismic regions. The highest b-value was observed in the NE–SW seismic zone B, and the lowest b-value was found to correlate with the northern part of the elongated axis of the volcano (region A). Focal depths of seismic events from zone B (between 35 and 55 km), coupled with the anomalous high b-values obtained, confirm the existence of a vertical magma conduit as inferred from previous studies. The mean activity rates for moment magnitude $$M_{W}$$ 3.5 range from about 2 to 14 events per month across seismic zones B and C, respectively. The maximum magnitude estimate has its highest value in seismic source zone B and the lowest value in the offshore region (seismic zone D). Differences in the estimated seismic hazard parameters from zone A to zone D reflect the seismogenic complexity of the Mount Cameroon region.