Pore Fluid Research Articles

MINING OF BIOMECHANICAL AND GEOMETRY DATA OF INTERVERTEBRAL DISC FINITE ELEMENT SIMULATIONS

This study investigates the relationships between Intervertebral Disc (IVD) morphology and biomechanics using patient-specific (PS) finite element (FE) models and poromechanical simulations.169 3D lumbar IVD shapes from the European project MySpine (FP7-269909), spanning healthy to Pfirrmann grade 4 degeneration, were obtained from MRIs. A Bayesian Coherent Point Drift algorithm aligned meshes to a previously validated structural FE mesh of the IVD. After mesh quality analyses and Hausdorff distance measurements, mechanical simulations were performed: 8 and 16 hours of sleep and daytime, respectively, applying 0.11 and 0.54 MPa of pressure on the upper cartilage endplate (CEP). Simulation results were extracted from the anterior (ATZ) and posterior regions (PTZ) and the center of the nucleus pulposus (CNP). Data mining was performed using Linear Regression, Support Vector Machine, and eXtreme Gradient Boosting techniques. Mechanical variables of interest in DD, such as pore fluid velocity (FLVEL), water content, and swelling pressure, were examined. The morphological variables of the simulated discs were used as input features.Local morphological variables significantly impacted the local mechanical response. The local disc heights, respectively in the mid (mh), anterior (ah), and posterior (ph) regions, were key factors in general. Additionally, fluid transport, reflected by FLVEL, was greatly influenced (r2 0.69) by the shape of the upper and lower cartilage endplates (CEPs).This study suggests that disc morphology affects Mechanical variables of interest in DD. Attention should be paid to the antero-posterior distribution and local effects of disc heights. Surprisingly, the CEP morphology remotely affected the fluid transport in NP volumes around mid-height, and mechanobiological implications shall be explored. In conclusion, patient-specific IVD modeling has strong potential to unravel important correlations between IVD phenotypes and local tissue regulation.Acknowledgments: European Commission: Disc4All-MSCA-2020-ITN-ETN GA: 955735; O-Health-ERC-CoG-2021-101044828

EFFECT ON INCLINED STRETCHING PLATE UNDER SLIP CONDITION DUE TO NON-NEWTONIAN FLUID IN POROUS MEDIUM FOR MAGNETOHYDRODYNAMIC FLOW OF UNSTEADY NATURE

An analytical probe is executed for evaluating the impact of unsteady flow pertaining to non-Newtonian fluid of magnetohydrodynamic nature on a stretching inclined porous plate, built in porous medium. Electrically conducting unsteady flow facing applied magnetic force with applied slip condition are the other factors utilized for the study of convective heat transfer. For converting governing equations to nonlinear differential equations, the similarity transformation method has been deployed. MATLAB was also used. Ordinary differential equations were solved numerically with the help of the Newton iterative method as well as the shooting method. Results for velocity and temperature were derived for a wide range of unsteady and other parameters including magnetic, source/sink, Grashof number, Prandtl number, Deborah number, and angle of inclination. Graphs and tables were used for compiling and computing values of skin friction and heat transfer rate. Results derived in the present analysis have been compared to those available in the previous literature, and parity has been formed to ascertain the accuracy of the current analytical exercise.

Clogging and Unclogging of Fine Particles in Porous Media: Micromechanical Insights From an Analog Pore System

AbstractPore clogging and unclogging in porous media are ubiquitous in subsurface hydrologic processes, which have been studied extensively at various scales ranging from a single pore to porous‐medium samples. However, it remains unclear how fluid flow, particle rearrangement, and the arching effect typical of cone‐shaped pore geometry interact and how they are captured by a pressure drop model at the macroscopic scale. Here, we investigate the pore‐scale feedback mechanisms between fluid flow and pore clogging and unclogging using a fully resolved fluid‐particle coupling approach (lattice Boltzmann method‐discrete element method). We first propose to use a truncated‐cone pore to represent realistic pore geometries revealed by X‐ray images of prepared sand packing. Then, our simulations indicate that the pore cone angle significantly influences the pressure drop associated with the clogging process by enhancing particle contacts due to arching. A modified Ergun equation is developed to consider this geometric effect. At the microscale, clogging can be explained by the interparticle force statistics; a few particles in an arch (or a dome) take the majority of hydrodynamic pressure. The maximum interparticle force is positively proportional to the particle Reynolds number and negatively associated with the tangent of the pore cone angle. Finally, a formula is established utilizing fluid characteristics and pore cone angle to compute the maximal interparticle force. Our findings, especially a modified pressure drop model that accounts for pore geometry resistance, provide guidance for applying pore‐scale models of clogging and unclogging to large‐scale subsurface fines transportation issues, including seepage‐induced landslides, stream bank failure, and groundwater recharge.

Volume viscosity of inhomogeneous fluids: a Maxwell relaxation model

Volume viscosity is one of the most important and fundamental parameters in hydrodynamics. It measures the momentum loss caused by a volume deformation rather than shape deformation. So it is closely related to numerous phenomena in fluid dynamics. However, most of the existing related researches focus on the bulk fluids, but there is still a lack of in-depth understanding of the bulk viscosity of inhomogeneous fluids. In this work, a novel theoretical method is proposed for the inhomogeneous volume viscosity in the framework of Maxwell viscoelastic theory. In this proposal, the local relaxation time is calculated by using the viscous and elastic properties of the bulk fluids. Accordingly, the inhomogeneous volume viscosity can be obtained by combining the calculations of the local relaxation time and the local relaxation modulus. It is advantageous in the theoretical sense over the conventional LADM, because it takes into account the underlying correlation much better. On the one hand, the local infinite-frequency modulus is more accurate. On the other hand, by using an appropriate weight function to calculate the weight, the correlation effect can be better considered . As an application, the volume viscosity of the confined Lennard-Jones fluid in slit pore is investigated, and the influences of bulk density, temperature, pore width and adsorption strength are calculated and analyzed. The results indicate that these factors can significantly modulate the volume viscosity of the confined fluid. Specifically, the positive correlation between the volume viscosity and the local density leads to the oscillation of viscosity profile in the pore. Besides, the occurrence of capillary condensation in the cases of lower density and lower temperature makes the inhomogeneous viscosity rather different from that of bulk gaseous phase. Further, this study shows that the inhomogeneous volume viscosity usually increases with temperature decreasing, or with adsorption strength increasing. This is again the result of its dependence on the fluid structure in the pore. Furthermore, the influence of pore width on the inhomogeneous volume viscosity indicates that the excluded volume plays a decisive role. This can be attributed to the fact that it exerts a direct influence on the deformation of the fluid. Moreover, comparison between the volume and shear viscosity is also conducted and analyzed. In general, this study can be beneficial to deepening the understanding of volume viscosity in the confined fluids, and can provide reliable theoretical support for studying related issues in hydrodynamics.

Frozen soil properties modification in the context of climate change

One of the expected effects of global warming is the gradual melting of permanently frozen ground, known as permafrost. The melting of permafrost will significantly impact soil material properties and (pore) fluid flow, potentially causing instability of infrastructures and triggering natural hazards such as landslides, rock falls, or debris flows. The overall objective of this research is to experimentally quantify the effect of thawing on the geomechanical strength of a reconstituted soil. More specifically, it is intended to qualify the initial frozen state and compare it to the state after thawing. The proposed experimental study was carried out in three steps. Firstly, soil samples were identified by the usual parameters such as water content, bulk density, solid particle density, triaxial test etc. Permafrost temperatures recorded by PERMOS and PermaFrance in the Alps (Swiss and French) are of the order of -3 to -4.5°C at a depth of -10m. This is why, for the second step, the shear tests were carried out at a slightly lower temperature than that recorded in situ. Artificial samples were sheared at a temperature of -5°C in our temperature controlled triaxial press in order to determine the soil’s strength parameters (cohesion and internal angle of friction). Thirdly, same tests were carried out at a temperature of +5°C in order to thaw the soil completely before the shearing. In total, three tests for each temperature were compared and discussed. The expected results aim at a better understanding and quantification of soil strength reduction after the thawing phase. As many infrastructures are now built on permafrost, such as roads, ski infrastructures, power lines or alpine chalets, they will be affected by this phenomenon in the near future. A better understanding of (geo)mechanical consequences might facilitate risk analysis, evaluation and mitigation.

IMPACTS OF USING POROUS CORNER PARTITIONS AND BLADE SHAPED NANOPARTICLES IN BASE FLUID ON THE PERFORMANCE IMPROVEMENT OF THERMOELECTRIC GENERATOR MOUNTED VENTED CAVITIES AND INTERFACE TEMPERATURE ESTIMATION WITH PROPER ORTHOGONAL DECOMPOSITION

Numerous technical applications, such as solar power, refrigeration, waste heat recovery, thermal management, and many more, employ thermoelectric devices because of the numerous advantages they offer. Techniques are required to improve their effectiveness in usage. In this study, a unique technique for improving the performance of a thermoelectric generator (TEG) positioned between vented cavities is proposed. The method combines the effects of blade-shaped nanoparticles in the base fluid and corner porous partitions. A numerical study using the finite element method is conducted for different values of Darcy number of upper and lower cavity (10<sup>-6</sup> ≤ Da<sub>1</sub> ≤ 10<sup>-2</sup>, 10<sup>-6</sup> ≤ Da<sub>2</sub> ≤ 10<sup>-2</sup>), opening ratio (SR between 0.5 and 2.5), and nanoparticle loading amount (SVF between 0 and 0.03). By adjusting the permeability of the partitions and opening ratio of the cavities, significant changes in the flow field can be obtained. TEG power increases with greater opening ratios and lower partition permeabilities. By changing the permeability, the TEG power can increase by up to 27.5 percent, while increasing the opening ratio from SR = 0.5 to SR = 1 can increase the TEG power by up to 140 percent. Using blade-shaped nanoparticles results in additional improvements, with values of 32.7% at SR = 0.5 and 20.26% at SR = 2.5. Using 180 parametric computational fluid dynamics cases, a POD-based low-cost reconstruction model is created for the interface temperatures at the hot and cold sides using five-POD modes. The method may be used for other complicated geometries where 3-D computations are costly and allows for the rapid computation of coupled TEG-vented cavity systems with corner partitions.

IMPACT OF POROUS AND MAGNETIC DISSIPATION ON DISSIPATIVE FLUID FLOW AND HEAT TRANSFER IN THE PRESENCE OF DARCY-BRINKMAN POROUS MEDIUM

In this article, the boundary layer flow of an electrically-conducting fluid through a porous medium attached with a radiative permeable stretching sheet is analyzed. Following the Brinkman theory, an extended Darcy model (Darcy-Brinkman model) is utilized for the model momentum equation. Heat transfer analysis is also performed in the presence of viscous and Joule dissipation. Moreover, in the modeling of the energy equation, the effects of internal heating resulting from the mechanical effort required to squeeze out the fluid through the porous medium are also included in porous dissipation. Suitable dimensionless variables are introduced to convert the governing boundary layer equations into a dimensionless form, which are then converted into self-similar, nonlinear ordinary differential equations by utilizing similarity transformations. The exact solution of the nonlinear self-similar momentum equation is obtained in the form of the exponential function. In contrast, the solution of the energy equation is computed through the Laplace transform technique in the form of Kummer confluent hypergeometric functions. Effects of involved physical parameters on the momentum boundary layer (MBL), thermal boundary layer (TBL), wall shear stress, and local Nusselt number are explored through graphs and tables. Moreover, the slope linear regression (SLR) technique is used to calculate the rate of decrease/increase in shear stress and the rate of heat transfer at the boundary. The velocity and momentum boundary layer decreases for large values of porosity parameter and increases by increasing the viscosity ratio. The shear stress increases by increasing the porosity parameter, Hartman number, and suction parameter, while the opposite effect is examined with increasing values of viscosity ratio parameter. Heat transfer rate also enhances by increasing the Brinkman viscosity ratio parameter and wall suction velocity.

Heitt Mjölnir: a heated miniature triaxial apparatus for 4D synchrotron microtomography.

Third- and fourth-generation synchrotron light sources with high fluxes and beam energies enable the use of innovative X-ray translucent experimental apparatus. These experimental devices access geologically relevant conditions whilst enabling in situ characterization using the spatial and temporal resolutions accessible at imaging beamlines. Here, Heitt Mjölnir is introduced, a heated miniature triaxial rig based on the design of Mjölnir, but covering a wider temperature range and larger sample volume at similar pressure capacities. This device is designed to investigate coupled thermal, chemical, hydraulic and mechanical processes from grain to centimetre scales using cylindrical samples of 10 mm × 20 mm (diameter × length). Heitt Mjölnir can simultaneously reach confining (hydraulic) pressures of 30 MPa and 500 MPa of axial stress with independently controlled sample pore fluid pressure < 30 MPa. This internally heated apparatus operates to temperatures up to 573 K with a minimal vertical thermal gradient in the sample of <0.3 K mm-1. This new apparatus has been deployed in operando studies at the TOMCAT (Swiss Light Source), I12 JEEP (Diamond Light Source) and PSICHÉ (Synchrotron SOLEIL) beamlines for 4D X-ray microtomography with scan intervals of a few minutes. Heitt Mjölnir is portable and modular, allowing a wide range of 4D characterizations of low-grade metamorphism and deformational processes. It enables spatially and temporally resolved fluid-rock interaction studies at conditions of crustal reservoirs and is suitable for characterization of material properties in geothermal, carbonation or subsurface gas storage applications. Technical drawings and an operation guide are included in this publication.

Effect of the Microorganisms Dynamics on the Base Subsidence of the Solid Household Waste Storage During Consolidation

The effect of the dynamics of the development of the microorganism biomass on the subsidence of the surface of the mass of the porous medium at the base of the storage of solid household waste was studied using mathematical and computer modeling methods. The repository of solid household waste is considered a source of the spread of organic pollutants that contribute to the development of the biomass of microorganisms. The subsidence model is considered from the theory of filtration consolidation of porous media. For this purpose, a corresponding boundary value problem in the domain with a free-moving boundary is formed. The classical equation of filtration consolidation is modified for the case of variable porosity due to biomass change. The finite element method allowed for solving the resulting mathematical model numerically in the form of a boundary value problem for the system of parabolic equations in the variable domain. Based on the developed algorithms, a software package for numerical experiments was created where the effect of microorganisms on the subsidence dynamics of a porous medium was investigated. Numerical experiments on a model example showed that the presence of microorganisms in soil pores slows the dissipation of excess pressure. However, this does not lead to a slowdown in subsidence but, on the contrary, to a particular increase of up to 18 % compared to the case of neglecting bioprocesses. From the point of view of the physics of the processes, this is explained by the increase in biomass, which leads to an increase in pressure, thus increasing the volume of filtered pore fluid and, hence, increasing subsidence.

Depositional and diagenetic controls on hydrocarbon generation of mudstones through clay–organic matter interactions: A comparative study of the Dongpu Depression, Bohai Bay Basin, China

Although the hydrocarbon generation of mudstones is greatly affected by depositional and diagenetic environments, how they affect the integrated theoretical framework of organic matter (OM) preservation, mudstone formation, and OM diagenetic conversion remains unresolved. Therefore, we addressed this issue from the perspective of clay–OM interactions during mudstone formation and diagenetic evolution. The northern and southern Dongpu Depressions represent two endmembers of depositional (weak vs. strong hydrodynamics and abundant vs. limited terrigenous input) and diagenetic (saline vs. freshwater pore fluid) environments. Results highlighted that the protection of clay minerals on OM preservation was more affected by the depositional fabric than mineral content. For the northern Depression mudstones, the predominance of laminated mudstones and remarkable enrichment of high-hydrogen index OM in the clay-sized fractions indicated the intimate clay-OM associations during mudstone formation, which led to better OM preservation and a higher hydrocarbon generation potential. For the southern Depression mudstones, the scattered distribution of OM particles and inconspicuous OM enrichment in the clay-sized fractions coincided with lower hydrocarbon generation potential. Additionally, the faster smectite illitization accelerated by the saline environment of the northern Depression led to OM desorption. Thus, OM lost the protection of clay minerals and the mineral reactive sites were liberated, both of which were beneficial to hydrocarbon generation. Generally, deposition controlled the material premise and diagenesis determined the hydrocarbon generation impetus. These findings provide a theoretical reference for shale oil accumulation in saline lacustrine systems and can potentially serve as a guide for future oil–gas exploration and development.

Geophysical exploration methods on bauxite reservoirs in L gasfield, Ordos Basin

Introduction: The L gasfield on the eastern edge of the Ordos Basin mainly focuses on the exploration and development of coalbed methane and tight sandstone gas. As the overlying strata of Majiagou Formation of Lower Ordovician in Lower Paleozoic, bauxite has always been considered a regional cap rock and has not been widely followed with interest. The drilled wells has revealed that bauxite can be used as a unconventional reservoir with good reservoir properties. In the future, it will become a new natural gas exploration target in the L region. This article is dedicated to the comprehensive study of geophysical methods for the bauxite exploration in the L region.Methods: Firstly, we use seismic data to restore paleo-geomorphology of the Lower Paleozoic. Secondly, we analyze the well log data of different paleo-geomorphic unit. Then, we establish a mineral model based on the logging data to calculate the lithological composition and porosity, and use imaging logging to evaluate the pore structure and fluid type.Result and Discussion: Finally, we obtained favorable reservoir development zones for bauxite, guiding exploration and evaluation of bauxite.

Simulation Study on the Mechanical Effect of CO2 Geological Storage in Ordos Demonstration Area

In order to understand the long-term process of CO2 storage and demonstrate its safety, multi-field coupled numerical simulation is considered a crucial technology in the field of geological CO2 storage. This study establishes a site-specific homogeneous thermo-hydro-mechanical coupling model based on TOUGH-FLAC3D coupling program using actual stratigraphic data from the Ordos demonstration area. The analysis investigates the transport behavior of CO2 within the formation considering pore permeability homogeneity, incorporates redistribution of effective stress and rock deformation, and provides a mechanical evaluation of the effectiveness of CO2 sequestration at this specific site. The findings indicate that: (1) the sealing effect of the cap rock depends on the difference of permeability between the reservoirs. The greater the permeability difference, the better the sealing effect. (2) High pore fluid pressure can lead to a decrease in the effective stress of rocks, causing deformation. After simulation calculations, the maximum deformation of rocks can reach 7.79 mm within a decade of CO2 injection. (3) Under the condition of continuous CO2 injection, the pore pressure will not be able to dissipate quickly and will continue to rise, and eventually shear failure will occur in the rock layer, but it is mainly concentrated in the lower part of the cap rock.

Local thermal conductivity of inhomogeneous nano-fluidic films: A density functional theory perspective

Combining the mean field Pozhar–Gubbins (PG) theory and the weighted density approximation, a novel method for local thermal conductivity of inhomogeneous fluids is proposed. The correlation effect that is beyond the mean field treatment is taken into account by the simulation-based empirical correlations. The application of this method to confined argon in slit pore shows that its prediction agrees well with the simulation results, and that it performs better than the original PG theory as well as the local averaged density model (LADM). In its further application to the nano-fluidic films, the influences of fluid parameters and pore parameters on the thermal conductivity are calculated and investigated. It is found that both the local thermal conductivity and the overall thermal conductivity can be significantly modulated by these parameters. Specifically, in the supercritical states, the thermal conductivity of the confined fluid shows positive correlation to the bulk density as well as the temperature. However, when the bulk density is small, the thermal conductivity exhibits a decrease-increase transition as the temperature is increased. This is also the case in which the temperature is low. In fact, the decrease–increase transition in both the small-bulk-density and low-temperature cases arises from the capillary condensation in the pore. Furthermore, smaller pore width and/or stronger adsorption potential can raise the critical temperature for condensation, and then are beneficial to the enhancement of the thermal conductivity. These modulation behaviors of the local thermal conductivity lead immediately to the significant difference of the overall thermal conductivity in different phase regions.

Sensitivity Analysis of Wellbore Mud Pressure towards Anisotropic Shale Properties, Pore Fluid Pressure and Far Field Stresses

The paper investigates the mud pressure to maintain the stability of wellbores drilled in transversely isotropic shale through sensitivity analyses, carried out with analytical and numerical modeling (FLAC). To this end, we interpreted the anisotropic strength of the Tournemire shale with the Weakness Plane Model (WPM) and the modified Hoek–Brown criterion (HBm). The sensitivity analyses of synthetic case studies indicated a different trend in mud pressure for the two criteria. In some cases, the WPM predicts mud pressures higher than those predicted by the HBm and vice versa. The mud pressures predicted by the HBm resulted in being more sensitive to the increase in the anisotropy of the far field stresses for all the inclinations of the weakness planes. In this context, the WPM predicts some anomalous low mud pressures in a wide range of inclinations of the weak planes. The change in the frictional component of strength decreases with an increase in the pore fluid pressure for both criteria. The mud pressure predicted by the WPM resulted in being more sensitive to the change in frictional strength. The change in trend of the two criteria with change in input data suggests caution in the “a priori” selection of the strength criterion. A simple solution is proposed to predict a safe and reliable mud pressure with a small number of lab tests.

Authigenic mineralization in Surtsey basaltic tuff deposits at 50 years after eruption

Alteration of basaltic glass and in situ mineral growth are fundamental processes that influence the chemical and material properties of Earth’s oceanic crust. These processes have evolved at the basaltic island of Surtsey (SW Iceland) since eruptions terminated in 1967. Here, subaerial and submarine lapilli tuff samples from a 192 m-deep borehole drilled in 2017 (SE-02b) are characterized through petrographic studies, X-ray powder diffraction analyses, and SEM–EDS imaging and chemical analyses. The integrated results reveal (i) multi-stage palagonitization processes in basaltic glass and precipitation of secondary minerals from matrix pore fluids, (ii) multi-stage crystallization of secondary phillipsite, analcime and Al-tobermorite in the vesicles of basaltic pyroclasts and (iii) variations in palagonitization processes as a function of thermal and hydrological domains. Although temperature appears to be an important factor in controlling rates of secondary mineralization, the chemistry of original basaltic components and interstitial fluids also influences reaction pathways in the young pyroclastic deposits. The integration of systematic mineralogical analyses of the 50-year-old tuff from one of the most carefully monitored volcanic sites on Earth, together with temperature monitoring in boreholes since 1980, provide a reference framework for evaluating mineralogical evolution in other Surtseyan-type volcanoes worldwide.

The Effect of Slickwater on Shale Properties and Main Influencing Factors in Hydraulic Fracturing

As shale gas reservoirs have low porosity and low permeability, hydraulic fracturing is a necessary means for industrial exploitation of shale gas. In this study, aiming at the problem of reservoir damage in the process of hydraulic fracturing of shale gas reservoir, a physical simulation method of slickwater fracturing fluid flow in shale core has been established. The change laws of physical parameters of the shale were quantified after slickwater fracturing fluid filtrating into it. The main factors affecting physical parameters of shale matrix around fractures were found out in the process of fracturing, shut-in, and flowback of slickwater fracturing fluid. The results show that after treated by slickwater fracturing fluid, the wettability of shale becomes more uniform in distribution (the water contact angles from 43° to 48°). In the fracturing filtration zone, the damage rate of fracturing fluid to shale porosity is 6.4%-42.0%. Low differential pressure flowback can reduce the damage of the shale, and prolonging the time of shut-in has no obvious effect on the damage to porosity. After 0.3 d (imbibition stability time), the damage of fracturing fluid to shale permeability is basically stable (55.9%). Permeability damage is mainly caused by residue of the fracturing fluid in large pores and bound water in small pores. Analysis of weights of all fracturing parameters shows that flowback differential pressure has the largest influence weight on shale porosity (51.4%), and well shut-in time has the largest influence weight on shale permeability (62.7%). Therefore, in the production process, it is suggested to properly reduce the backflow differential pressure and moderately shorten the well shut-in time.

Seismicity near Mayotte explained by interacting magma bodies: Insights from numerical modeling

Mayotte island experienced a large volcanic eruption 50 km offshore in 2018–2021, creating the submarine volcano “Fani Maoré”. The eruption was accompanied by intense seismicity at mantle depths (20–45 km), divided into a “proximal” and a “distal” cluster centered 10 and 30 km east from the island, respectively. Previous studies suggest that two separate magma reservoirs may lie at the top and bottom of the proximal cluster. Here, we assess whether two reservoirs are a mechanically viable explanation for the proximal cluster's truncated conical shape. We developed finite-element models of pressurized magma reservoirs in a 2D axisymmetric domain, modeling the reservoirs as compliant elastic ellipsoids embedded in an elastoplastic host rock. We find that, at these depths, extremely low friction is required to generate failure at realistically low reservoir pressures. This implies in turn that mechanical weakening must occur at these depths. The weakening could be induced by fractures or pore fluid overpressure in the volcanic system. We find that two superimposed reservoirs can generate a plastic domain between them, if they are spatially close enough. Several reservoir geometries (from spherical to sill-like) are plausible. A conical fracture domain is more likely to appear for reservoirs with opposite pressure loads (i.e. one inflating, one deflating). Given the geometrical match with the proximal seismicity cluster at Mayotte, we suggest that the shallower (Moho-depth) reservoir is inflating, creating a potential hazard for Mayotte island.

Effect of cyclic thermal stimulation on the pore structure and fluid space of coal and inspiration for coalbed methane production

Based on the modified programmed temperature-raising system, cyclic thermal stimulation with different temperature gradients was carried out for lignite, bituminous and anthracite coal, and each group of coal samples after thermal stimulation cycle was subjected to nuclear magnetic resonance (NMR) testing. The NMR T1-T2 spectra and the fractal dimensions of coals in different ranks during thermal simulation quantitatively described the dynamic evolution of the pore fluid storage space of coals. The variation of T2 distribution and pore throat were used to reflect the pore development process of coals. The results shows that the pores and pore throat of lignite developed the best among the three coal ranks and the structure of the pore is complete after the cyclic thermal simulation; the T1-T2 signal peaks increased from 17.05 at 30 °C to 163.00 at 180 °C; the seepage of lignite increased from 6.54 % to 12.43 %; total pore fractal dimension DT has a decreasing trend, indicating reduced inhomogeneity of pores. This indicates that the cyclic thermal stimulation treatment can promote the growth of seepage pores to a greater extent, improve the seepage space, and enhance the connectivity of the pores in the coal samples.

Revisiting the relationship between the pore water carbon isotope gradient and bottom water oxygen concentrations

Reconstructing the oxygen content at the ocean floor provides insight into ocean circulation, ventilation, and carbon storage in the deep sea. The microbial breakdown of organic carbon within marine sediment through aerobic respiration consumes oxygen in the pore fluid and releases dissolved inorganic carbon. The offset in the carbon isotopic composition, δ13C, of epifaunal and infaunal foraminifera, Δδ13C, is considered to reflect the aerobic respiration of organic carbon and can be used to reconstruct the oxygen content of the bottom water. Previous work provided an empirical calibration that was suggested to be valid for oxygen reconstructions between 55 and 235 μmol kg−1. In this study, we apply a biogeochemical reactive transport model (RTM) to extend and update this calibration, allowing for the reconstruction of oxygen concentrations ([O2]) up to ∼300 μmol kg−1. Using the RTM and new bottom water [O2] and pore fluid measurements from Iberian Margin sediment cores, we also demonstrate that the calibration between the Δδ13C and bottom water [O2] must account for the coupled changes in the carbon system due to the respiration of organic carbon in the overlying ocean including the concentration and carbon isotopic composition of the dissolved inorganic carbon, and the δ13C of the organic carbon within the sediment column. We apply the improved calibration to reconstruct the changes in oxygen content at International Ocean Discovery Program (IODP) Site U1385 in the deep North Atlantic over the past 1.5 Myr.

Spatial evolution and temporal stability of hydrothermal processes at sediment-covered spreading centers: Constraints from Guaymas Basin, Gulf of California

The Guaymas Basin, Gulf of California is a hydrothermally active sediment-covered oceanic spreading center in the early stages of rifting. Hot-spring fluids were collected from its southern trough in 1998, 2003, and 2008 and analyzed for the concentration and isotopic composition of organic and inorganic aqueous species to assess subseafloor geochemical processes. Fluids discharged from the seafloor through hydrothermal edifices with measured temperatures of 91 to 317 °C. In general, fluids exiting larger structures were characterized by higher temperatures than fluids venting from smaller structures. Measured pH (25 °C) ranged from 5.7 to 7.1. Endmember fluids were characterized by near-zero concentrations of Mg and SO4, depletions in Na, and enrichments in K, Ca, and Cl relative to seawater, reflecting extensive interaction with sediment during circulation. Thermal maturation of sedimentary organic matter resulted in the addition of abundant ΣNH4+, ΣCO2, CH4, short-chain n-alkanes, and carboxylic acids to solution. Organic compounds added to fluids during recharge pass through high temperature deep-seated reaction zones and reach high levels of thermal maturity while others may be added by entrainment of lower temperature sedimentary pore fluids in hydrothermal upflow zones.The relative abundance of many organic compounds mobilized during hydrothermal alteration is consistent with metastable states of thermodynamic equilibrium that likely record subseafloor temperature conditions. The isotope composition of low molecular weight hydrocarbons and elevated concentrations of dissolved Cl suggest that temperatures may have exceeded the two-phase boundary for seawater and subsequently cooled before discharging at the seafloor. Periods of high temperature fluid-sediment or fluid-rock interaction followed by cooling may provide a mechanism for the aqueous mobilization and concentration of sulfide-forming metals in subseafloor mineral deposits. Fluid compositions have remained constant at the southern trough of Guaymas Basin for at least 26 years, indicating decadal stability in the physical and chemical conditions in subseafloor environments as well as the km-scale regional recharge zones containing unaltered sediment.