Transient Permeability Research Articles

Numerical simulation of kinetically-controlled calc-silicate reactions and fluid flow with transient permeability around crystallizing plutons

Numerical simulations were performed to examine the relationships between variable contact-aureole permeability, the kinetics of calc-silicate reactions, and the fluxes of mixed CO 2 -H 2 O fluids around a crystallizing granite laccolith. The role of magmatic water was explicitly considered. The Notch Peak contact-metamor- phic aureole in Utah was used to define the stratigraphy of the model domain and rock compositions. Reactions that were considered include the major isograd-defining reactions that occurred in the Notch Peak aureole. The half-space model domain had the laccolith, 2 km thick at the middle apex. Only 1-phase fluid flow was considered. Results show that the evolution of the fluid flow-field is highly dependent on the pressure (P) boundary condition at the top of the model domain. When P at the top boundary is allowed to increase, P in most of the top half of the domain eventually exceeds the lithostatic pressure plus the assumed tensile strength of rocks of 15 MPa. This boundary condition simulates an unvented flow-system. A more realistic boundary condition, one that simulates a system that is able to vent to the surface, is when Pat the top boundary is held at a hydrostatic pressure. In this case, the flow-field is determined largely by pressure gradients between the overpressured magmatic fluid exsolving from the pluton and the lower pressures at the domain boundaries. Fracturing is predicted to occur early after pluton emplacement as the pore fluid is heated and metamorphic reactions produce CO 2 . Although fracturing and reaction-enhanced porosity and permeability influence the local flow-field, the domain-scale flow-field is controlled by long-distance pressure gradients. The domain-scale flow-field and tem- perature distribution impose the largest control on the distribution of major mineral assemblages in the metamorphic aureole. Transient changes in permeability due to fracturing and volume changes in the solid matrix that accompany reactions have a smaller control on the distribution of minerals. The simulations predict significant overstepping and coeval progress of metamorphic reactions. Reaction rates range from 5x 10 -10 to 10 -14 kmol/m 2 /sec, depending on the actual P-T-XCO 2 f conditions and the abundance of the rate-controlling mineral. Throughout the metamorphic aureole, XCO 2 f approaches 1 as CO 2 evolved by reactions displaces H 2 0. High pore pressures prevent magmatic H 2 O from infiltrating the aureole until pressures drop when reactions are approaching completion. Consequently, only in the inner aureole, which is eventually infiltrated by magmatic H 2 O, can minerals such as wollastonite and vesuvianite be produced. An integrated H 2 O flux of 3×10 4 kmol/m 2 is required to produce the width of the model wollastonite zone by 20 ky. Because of pressure gradients, CO 2 that is produced in the inner aureole flows outward into colder rocks even before these rocks are heated. The T-XCO 2 f paths in outer aureole rocks cut across the H 2 O-CO 2 solvus, which predicts that in nature H 2 O and CO 2 should unmix and behave as two separate fluid phases. The average yearly CO 2 flux at the top of the model domain, 2.3 × 10 3 mol/m 2 /y, is comparable to fluxes of metamorphic carbonic fluids in active geothermal fields.

Hydrogen peroxide protects myocardium from ischemia/reperfusion injury through transient mitochondrial permeability transition pore opening

Hydrogen peroxide protects myocardium from ischemia/reperfusion injury through transient mitochondrial permeability transition pore opening

FSI-Analysis of the MMC-Thixoforging Process Regarding the Rheology of the Aluminiumcast-Alloy AlSi7Mg0,3

This paper illustrates investigations regarding the infiltration process of the thixotropic cast-alloy AlSi7Mg0,3 into laminated fibre woven fabrics by Fluid-Structure Interaction Analysis (FSI). As results of such FSI-Analysis on the one hand the kinematical behaviour of the reinforcement due to the infiltration process on the macroscopic and microscopic level on the other hand fluiddynamical effects of the regarded alloy are achieved. Thus in the run-up to timeconsuming and cost-intensive experiments, informative bases like fluidic optimizing of the cavity or the configuration and insertion of the reinforcement component can be numerically developed. Furthermore a reliable prediction of transient permeability of the fibre fabric is possible, which effects the infiltration process significantly. Numerical input data such as rheological parameters characterizing the behaviour of partial solidified alloys have been conducted. Therefor basic rheological tests of the aluminium cast-alloy AlSi7Mg0,3, like `HYSTERESIS TESTS´, `SHEAR RATE JUMP TESTS´ and detection of `STATIC´ and `DYNAMIC YIELD POINTS´ and the `DIFFERENTIAL STRUCTURAL PARAMETER´ have been conducted. Furthermore `EVOLUTION OF VISCOSITY´ has been correlated with thermodynamical calculations using ThermoCalc®. Finally the infiltration of a textile semi-finished part (carbon fibre fabric / canvas bonding) by A356 is discussed as an example to demonstrate the feasibility of FSI-Analysis, taking into account a two-way coupling between the interacting CSM- and CFD-Codes.

L. Lonergan, R. J. H. Jolly, K. Rawnsley & D. J. Sanderson (eds) 2007. Fractured Reservoirs. Geological Society Special Publication no. 270. viii + 285 pp. London, Bath: Geological Society of London. Price £80.00, US $160.00; GSL members' price £40.00, US $80.00; AAPG/SEPM/GSA/RAS/EFG/PESGB members' price £48.00, US $96.00 (hard covers). ISBN 9781 86239 213 7.

This book contains seventeen papers arising from a Petroleum Group conference in November 2004, a somewhat lengthy gestation but ultimately worth while. The content is subdivided into four sections. The first, outcrop studies, comprises papers on economically critical fold-related fracturing in the Asmari reservoirs of the Zagros Mountains, transient fracture permeability and diagenetic resealing in the Dent Fault (UK) and factors affecting the potentially very variable transmissibility of relay ramps in sandstones based on data from Utah. Notable in the value of outcrop studies is the detail and insights now available from satellite imagery. The second, geophysics, …

IFN-β Increases Listeriolysin O-Induced Membrane Permeabilization and Death of Macrophages

Type I IFN (IFN-I) signaling is detrimental to cells and mice infected with Listeria monocytogenes. In this study, we investigate the impact of IFN-I on the activity of listeriolysin O (LLO), a pore-forming toxin and virulence protein released by L. monocytogenes. Treatment of macrophages with IFN-beta increased the ability of sublytic LLO concentrations to cause transient permeability of the plasma membrane. At higher LLO concentrations, IFN-beta enhanced the complete breakdown of membrane integrity and cell death. This activity of IFN-beta required Stat1. Perturbation of the plasma membrane by LLO resulted in activation of the p38MAPK pathway. IFN-beta pretreatment enhanced LLO-mediated signaling through this pathway, consistent with its ability to increase membrane damage. p38MAPK activation in response to LLO was independent of TLR4, a putative LLO receptor, and inhibition of p38MAPK neither enhanced nor prevented LLO-induced death. IFN-beta caused cells to express increased amounts of caspase 1 and to produce a detectable caspase 1 cleavage product after LLO treatment. Contrasting recent reports with another pore-forming toxin, this pathway did not aid cell survival as caspase 1-deficient cells were equally sensitive to lysis by LLO. Key lipogenesis enzymes were suppressed in IFN-beta-treated cells, which may exacerbate the membrane damage caused by LLO.

The inclusion record of fluid evolution, crack healing and trapping from a heterogeneous system during rapid cooling of pegmatitic veins (Dronning Maud Land; Antarctica)

AbstractGranitoid (pegmatite and aplite) veins in metamorphic rocks and intrusive syenites of central Dronning Maud Land, Antarctica, are flanked by conspicuous light‐coloured alteration halos, which represent the damage zone of fracture propagation. The damage zone is characterized by a high density of sealed or healed microcracks, about 1 order of magnitude above background. Fluid inclusions along healed microcracks in quartz of both pegmatite and alteration halos are inspected by optical and scanning electron microscopy, and their composition is analysed by microthermometry and quadrupole mass spectrometry. The similar inclusion record in the granitoid vein and in the damaged host rock indicates the derivation of the fluids from the hydrous melt phase. The aqueous inclusions bear abundant daughter crystals, mainly silicates, and may represent a hydrous melt. The volatile composition is variable in the system H2O–CO2, with mostly subordinate amounts of N2. Phase separation with partitioning of CO2 into the fluid phase coexisting with the hydrous melt, and possibly immiscibility in the subsolidus range, govern fluid evolution during cooling. The variable CO2/N2 ratio suggests mixing with fluids from an external source in the host rock and vigorous circulation at an early stage of high transient permeability. Experiments have shown that healing of microcracks at high temperatures is a matter of hours to weeks, hence similar in time scale to the cooling of the cm‐ to dm‐thick granitoid veins. In this case, rapid cooling and concomitant crack healing in a system undergoing phase separation causes a broad compositional variability of the inclusions due to necking down, and the underpressure developing in closed compartments precludes a meaningful thermobarometric interpretation.

Transient permeability and reseal hardening in fault zones: evidence from dilation breccia textures

Abstract It is well established that earthquake faulting can create permeability along a fault zone in high competence rocks - by mismatch of the fault walls and by secondary fracture in a surrounding damage zone - and that this permeability is created repeatedly during successive earthquake cycles. Less well proven is that such permeability is transient, being episodically reduced by precipitation of cements in the fracture porosity. The textures of carbonate dilation breccias, formed at around 1.7 km depth on the Dent Fault zone (NW England), lend support to this economically important concept of transient fracture permeability. The key observation is that many breccias reflect only a single episode of brecciation and reseal. A generally applicable explanation of such single-phase breccias is that they were resealed in the interval between major earthquakes, that this reseal made the breccia stronger that the intact rock, and that subsequent brecciation in the same rock volume was inhibited. This reseal-hardening model implies that transient permeability in fault zones may last no longer than the recurrence times of large earthquakes, and that the permeability conduits will change position in the damage zone with time, unless focused at a major fault jog or termination.

3D numerical modelling of fluid flow in the Val-d’Or orogenic gold district: major crustal shear zones drain fluids from overpressured vein fields

Fluid flow patterns have been determined using oxygen isotope isopleths in the Val-d’Or orogenic gold district. 3D numerical modelling of fluid flow and oxygen isotope exchange in the vein field shows that the fluid flow patterns can be reproduced if the lower boundary of the model is permeable, which represents middle or lower crustal rocks that are infiltrated by a metamorphic fluid generated at deeper levels. This boundary condition implies that the major crustal faults so conspicuous in vein fields do not act as the only major channel for upward fluid flow. The upper model boundary is impermeable except along the trace of major crustal faults where fluids are allowed to drain out of the vein field. This upper impermeable boundary condition represents a low-permeability layer in the crust that separates the overpressured fluid from the overlying hydrostatic fluid pressure regime. We propose that the role of major crustal faults in overpressured vein fields, independent of tectonic setting, is to drain hydrothermal fluids out of the vein field along a breach across an impermeable layer higher in the crust and above the vein field. This breach is crucial to allow flow out of the vein field and accumulation of metals in the fractures, and this breach has major implications for exploration for mineral resources. We propose that tectonic events that cause episodic metamorphic dehydration create a short-lived pulse of metamorphic fluid to rise along zones of transient permeability. This results in a fluid wave that propagates upward carrying metals to the mineralized area. Earthquakes along crustal shear zones cause dilation near jogs that draw fluids and deposit metals in an interconnected network of subsidiary shear zones. Fluid flow is arrested by an impermeable barrier separating the hydrostatic and lithostatic fluid pressure regimes. Fluids flow through the evolving and interconnected network of shear zones and by advection through the rock matrix. Episodic breaches in the impermeable barrier along the crustal shear zones allow fluid flow out of the vein field.

Transient permeability induced by alkyl derivatives of amphotericin B in lipid membranes

Individual ionic channels were shown to be formed in the brain cholesterol containing phospholipid membranes by two-sided addition of the amphotericin B alkyl derivatives. At concentrations between 10 −8 and 10 −7 M, the resulting conductance appeared to be transient. Existence of different antibiotic assemblies was justified by the kinetic analysis of the membrane conductance decline following the antibiotic washing out. In order to account for the transient characteristics of the induced conductance, it was proposed that the antibiotic oligomers incorporate into the membrane from the aqueous phase, form channels aggregating with cholesterol, and then dissociate in the bilayer into non-active degraded oligomeric or monomeric forms.

A simulation of the hydrothermal response to the Chesapeake Bay bolide impact

AbstractGroundwater more saline than seawater has been discovered in the tsunami breccia of the Chesapeake Bay Impact Crater. One hypothesis for the origin of this brine is that it may be a liquid residual following steam separation in a hydrothermal system that evolved following the impact. Initial scoping calculations have demonstrated that it is feasible such a residual brine could have remained in the crater for the 35 million years since impact. Numerical simulations have been conducted using the code HYDROTHERM to test whether or not conditions were suitable in the millennia following the impact for the development of a steam phase in the hydrothermal system. Hydraulic and thermal parameters were estimated for the bedrock underlying the crater and the tsunami breccia that fills the crater. Simulations at three different breccia permeabilities suggest that the type of hydrothermal system that might have developed would have been very sensitive to the permeability. A relatively low breccia permeability (1 × 10−16 m2) results in a system partitioned into a shallow water phase and a deeper superheated steam phase. A moderate breccia permeability (1 × 10−15 m2) results in a system with regionally extensive multiphase conditions. A relatively high breccia permeability (1 × 10−14 m2) results in a system dominated by warm‐water convection cells. The permeability of the crater breccia could have had any of these values at given depths and times during the hydrothermal system evolution as the sediments compacted. The simulations were not able to take into account transient permeability conditions, or equations of state that account for the salt content of seawater. Results suggest, however, that it is likely that steam conditions existed at some time in the system following impact, providing additional evidence that is consistent with a hydrothermal origin for the crater brine.

Determining the Rate Constant of Diffusion-Controlled Oxygen Scavenging Reaction in Polymer Membranes by Transient Permeability Measurements

A new method for determining the effective rate constant of diffusion-controlled oxygen scavenging reactions in reactive polymer membranes with finite reactive capacity is proposed. The method is based on rapid homogeneous scavenger activation throughout the membrane and measurement of transient oxygen flux through the membrane with fixed boundary conditions according to standardized testing procedures. After the steady state flux is established across the initially passive membrane the reactive species are activated throughout the membrane thickness by an external source. The transient permeability tests are separately performed on two activated reactive films with preselected different thicknesses, scavenger loadings, and/or scavenger activities, and the minimum transient fluxes through the films are compared. The ratio of these fluxes is related to the reaction rate constant using the analytical results for the effective flux through the catalytic reactive membrane. To account for noninstantaneous and potentially inhomogeneous scavenger activation, the asymptotic behavior of the effective flux growth around the activation time is analyzed in two limiting cases. On the basis of the derived asymptotic expressions, the correction procedures for adjusting the measured minimum fluxes are proposed. The method validity is supported by numerical simulations that demonstrated excellent agreement between the analytical and numerical results for a variety of scavenger activation mechanisms.

An Experimental Study of Saturated and Unsaturated Permeabilities in Resin Transfer Molding Based on Unidirectional Flow Measurements

Resin transfer molding (RTM) is a manufacturing process of composite parts that consists of injecting a fluid resin through a fibrous reinforcement. Permeability of the fiber bed is a key parameter that governs the flow, together with the viscosity of the resin. In this paper, the saturated and unsaturated permeabilities of a glass-woven fabric are studied for different injection pressures and porosities of the fibrous reinforcement. Unidirectional injection experiments are carried out to evaluate the unsaturated permeability of the reinforcement during the injection and the saturated permeability that governs the permanent flow established after filling of the cavity. The unsaturated permeability is evaluated by a linear regression in function of the position of the resin front during transient flow experiments performed at constant injection pressure. For each position of the resin front in the test mold, a transient permeability can be calculated by application of Darcy’s law. This transient permeability depends on the injection pressure, position of the resin front in the mold, and porosity of the reinforcement. After a certain flow length called the convergence length, the transient permeability converges to a value that is independent of the flow rate and of the injection pressure. This limit value is called here the unsaturated permeability. The convergence length is related to a maximum flow rate or average particle velocity below which Darcy’s law holds. The saturated permeability is measured after all air bubbles have been evacuated from the cavity. As a result of this experimental investigation, three parameters can be identified that are characteristic of the pore structure of the fibrous reinforcement: (1) a maximum average resin velocity can be identified below which the transient permeability remains constant; (2) the saturated and unsaturated permeabilities differ by a value that remains constant within the injection pressure range used in this study and that is independent of the fiber volume content; (3) the new notion of convergence length proposed here, namely the flow length necessary to ensure convergence of the transient permeability, depends on the two-scale pore structure of the fibrous reinforcement. This study corroborates the findings of several other investigators, who have shown that the saturated permeability is always higher than the unsaturated permeability. The difference between these two permeability values is also related to the pore structure of the fiber bed. It is hoped that this work will contribute to define a much-needed standard on permeability measurements.

Measurement of the permeability and resealing time constant of the electroporated mammalian cell membranes

In this study a new method is presented for measuring the transient permeability of mammalian cell membranes to sugar and electrolyte molecules based on the volumetric response of cells subjected to electroporation. The time constant of membrane resealing was determined independently by flow cytometry using a fluorescent dye as the reporter molecule. The volumetric and dye uptake data were analyzed with a model relating the cell volume changes to the solute transport across the reversibly permeabilized cell membrane. The experimental approach developed here might be useful for estimating the amount of electroinjected molecules, which are difficult to measure directly.

Transient permeability leak of nuclear envelope induced by aldosterone.

The mineralocorticoid hormone aldosterone controls fluid and electrolyte transport in target cells of the kidney and the cardiovascular system. Classic genomic aldosterone action involves the activation of cytosolic mineralocorticoid receptors and translocation into the cell nucleus where specific transcription processes are initiated. A key barrier of the intracellular signalling pathway is the nuclear envelope, which physically separates the nucleoplasm from the cytoplasm. It was shown recently that aldosterone changes ion conductivity of the nuclear envelope mediated by nuclear pore complexes. The latter are supramolecular nanomachines responsible for import and export of inorganic ions and macromolecules. The aim of the present study was to test whether aldosterone changes the macromolecule permeability of the nuclear envelope. Aldosterone-responsive Xenopus laevis oocytes were used as a model system. We isolated the cell nuclei at defined times after hormone injection. By means of confocal fluorescence microscopy and fluorescence-labelled dextrans we evaluated passive macromolecule import and export in isolated nuclei. 10 minutes after aldosterone injection nuclear envelope permeability of 10 kD dextran was found sharply increased. At the same time cell nuclei were found swollen by about 28%. Changes in nuclear volume and nuclear envelope permeability lasted 5 to 15 minutes and could be inhibited by the mineralocorticoid receptor blocker spironolactone. We conclude that aldosterone transiently changes the barrier function of the nuclear envelope. This short-lasting permeability change signals the start of a sustained transcription process that follows in response to steroids.

Bleomycin--electrical pulse delivery: electroporation therapy-bleomycin--Genetronics; MedPulser-bleomycin--Genetronics.

Bleomycin--electrical pulse delivery: electroporation therapy-bleomycin--Genetronics; MedPulser-bleomycin--Genetronics.

A theoretical model for reverse water-level fluctuations induced by transient permeability in thrust fault zones

A numerical model was applied to simulate the poroelastic response to changes in fault permeability as a result of earthquakes. The ‘fault valve’ model describes faults as impermeable barriers for fluids except immediately after earthquakes, when fault zones are damaged and transient pathways for fluids are created. In this case the fault is viewed as a discharging well, draining fluids from the surrounding rock. The reverse water-level effect is characterized by the increase of water level in adjacent aquifers and aquitards, resulting from withdrawing fluids through a well. Theoretical calculations suggest that the reverse water-level effect exists also in earthquake cycling and is in the same order of magnitude as the co-seismic hydraulic head change. A significant rise of the hydraulic head (>1 m) occurs within the country rock from both sides of the fault. The rise of the water level takes months to years to occur, and perhaps that is why it cannot be easily distinguished from seasonal hydrologic changes observed in the field. The reverse water-level effect also propagates away from the fault at a rate of hundreds of meters per year, depending on the permeability of the country rock. In deep formations where the permeability is low, the propagation takes years. The magnitude of the reverse water-level effect is greater when the fault efficiently drains fluids, when it is highly permeable and slow to reseal.

Therapeutic ultrasound: Surgery and drug delivery

The field of therapeutic ultrasound is emerging with strong potential and broad medical applications. Characterized by its ability to penetrate at depth inside the body without harming intervening tissue, ultrasound has posed the basis for a new array of noninvasive therapies. Al low intensities, important interactions occur in the tissue; wound healing is accelerated, functional recovery is enhanced, and bone growth is more rapid. At moderate intensities, cellular membranes show transient permeability, blood clots dissolution is increased, and gene-transfection is accomplished. At higher intensities, ultrasound produces lesions and stops bleeding by heating the tissue beyond its protein denaturalization threshold and thus provides a noninvasive, bloodless alternative to conventional surgery. This article presents a review of moderate and high intensity applications, including their mechanisms of action and the imaging modalities used for guidance and monitoring.

An exhumed palaeo‐hydrocarbon migration fairway in a faulted carrier system, Entrada Sandstone of SE Utah, USA

AbstractThe Moab Anticline, east‐central Utah, is an exhumed hydrocarbon palaeo‐reservoir which was supplied by hydrocarbons that migrated from the Moab Fault up‐dip towards the crest of the structure beneath the regional seal of the Tidwell mudstone. Iron oxide reduction in porous, high permeability aeolian sandstones records the secondary migration of hydrocarbons, filling of traps against small sealing faults and spill pathways through the Middle Jurassic Entrada Sandstone. Hydrocarbons entered the Entrada Sandstone carrier system from bends and other leak points on the Moab Fault producing discrete zones of reduction that extend for up to 400 m from these leak points. They then migrated in focused stringers, 2–5 m in height, to produce accumulations on the crest of the anticline. Normal faults on the anticline were transient permeability barriers to hydrocarbon migration producing a series of small compartmentalized accumulations. Exsolution of CO2 as local fault seals were breached resulted in calcite cementation on the up‐dip side of faults.Field observations on the distribution of iron oxide reduction and calcite cements within the anticline indicate that the advancing reduction fronts were affected neither by individual slip bands in damage zones around faults nor by small faults with sand: sand juxtapositions. Faults with larger throws produced either sand: mudstone juxtapositions or sand: sand contacts and fault zones with shale smears. Shale‐smeared fault zones provided seals to the reducing fluid which filled the structural traps to spill points.

Heat and fluid flow in contact metamorphic aureoles with layered and transient permeability, with application to the Notch Peak aureole, Utah

We have investigated the control of layered and transient permeability structures on fluid flow and thermal evolution in contact metamorphic aureoles using two‐dimensional numerical modeling with petrological and geochemical constraints from the Notch Peak aureole, Utah. The model includes interbedded aquitard and aquifer lithologies on the scale of formations and transient enhancement of permeability due to devolatilization reactions. The results show that a layered permeability structure causes focusing of fluids into aquifer layers, resulting in flow pattern that is strongly time‐dependent and significantly different from the predicted simple convection cells in aureoles with homogeneous permeability. The model predicts temporal development of three distinctive flow regimes: (1) early radial down‐temperature flow due to release of magmatic fluid, (2) small flat convection cells near the pluton‐aquifer contacts during peak metamorphism, (3) late unidirectional down‐temperature flow in the upper aureole and up‐temperature flow in the middle to lower aureole. When the bulk permeability of host rocks is >10−16 m2, heat advection by flowing fluids is significant. At lower bulk permeability, heat conduction dominates, and the effects of detailed permeability structure on the thermal field become negligible. Metamorphic reactions enhance permeability within the inner aureole, localizing fluid convection and increasing fluid flux. The observed spatial distribution of mineral assemblages and oxygen isotopic shifts in the upper part of the Notch Peak aureole is consistent with the predicted time‐integrated fluid flux, which over duration of metamorphism is dominated by the down‐temperature flow of a large amount of water from the pluton into the wall rocks.

Hydraulic fracturing during the formation and deformation of a basin: A factor in the dewatering of low-permeability sediments

The geological expression of hydraulic fracturing is varied and is controlled primarily by the magnitude of the differential stress and the intrinsic properties of the rock. The orientation and type of fractures that develop within a basin are determined by the state of stress, which in turn is controlled by the geological boundary conditions. During the early stages of burial and diagenesis the formation of hydraulic fractures is thought to be an important factor in the movement of fluids through and out of low-permeability, semilithified sediments. Unfortunately, these fractures are not generally preserved and are presumed to heal once the fluid pressure is relieved. The low-permeability Mercia Mudstones of the Bristol Channel Basin, southwest England, however, contain bodies of sand that, during the opening of the basin, were injected along some of the hydraulic fractures in the mudstones, preserving them as sedimentary dikes and sills. Field observations indicate that fluid pressures within the Mercia Mudstones were also very high during basin inversion and that hydraulic fracturing provided a transient permeability that relieved this excess pressure. The fractures are not visible in most of the mudstones but have been preserved within evaporite-rich horizons as a network of satin spar veins. Thus, the chance preservation of the sedimentary dikes and satin spar veins shows that at different times during the evolution of the basin, fluids migrated through low-permeability units along transient networks of hydraulic fractures. In addition, the orientation and spatial organization of these fractures reflect the boundary conditions operating at various stages in the basin history.