Large Increase In Permeability Research Articles

Numerical modelling of earthquake sequences involving valving and pumping of fluids

SUMMARY Faults in the upper crust are sometimes thought to act as self-sealing valves, episodically releasing highly overpressured fluids trapped at greater depth during earthquakes. They are also often considered to be capable of actively pumping fluids into or out of faults in response to coseismic volumetric strain, thermal pressurization or other mechanisms. In this study, we investigate how these different types of behaviour (i.e. valve versus pump) are manifested in earthquakes. We do this using a 2-D plane strain model where frictional sliding on a thrust fault that is fed by a fluid source at its base is coupled to porous flow, thermal pressurization and strong variations in permeability. Our results show that thermal pressurization leads to dramatic dynamic weakening that produces earthquakes that propagate as slip pulses producing large stress drop, large slip and high slip velocities. On the other hand, valve-type behaviour typically produces smaller, less energetic earthquakes that commonly arrest before rupturing the entire fault. In some valve models, we observe complex compound ruptures and swarm activity, which is linked to the ascent of a propagating fluid pressure pulse driven by a large increase in permeability during sliding. Both pump and valve mechanisms can produce anomalously weak faults, though they are each associated with distinctly different fluid pressure and strength evolution over the seismic cycle and during rupture. Our models highlight the complex way in which fluids may interact with earthquakes, especially if valve and pump models coexist.

Experimental Study on the Effect and Mechanism of Chemical Stimulation on Deep High-Temperature Granite

Chemical stimulation has been increasingly applied to improve the performance of geothermal reservoirs since early 1980s. The potential for the successful application of this technique to high-temperature reservoirs hosted in granitic rocks is still uncertain, and one of the keys to assess this potential is to investigate experimentally the geochemical reactivity induced via chemical stimulation on relevant rock specimens. On this premise, we combined high-temperature and high-pressure dynamic simulation and static corrosion experiments to explore the effect of different chemical stimulants on the permeability of granite samples from the Baimiao formation (Hebei Province, China). Experimental results show that NaOH-dominated alkaline stimulants cause only weak dissolution patterns on primary feldspar and quartz, and they do not sensitively affect the original amount of chlorite. The overall effect is a negligible enhancement of the original permeability of all the granite specimens analyzed. Conversely, a large increase in permeability is observed when an acid mixture of 10wt% HCl + 1.5wt% HF is used as a stimulant, with an observed maximum magnifying effect of about 27 times, due to the effective dissolution of feldspar and chlorite. Though quartz appears not to be affected by dissolution, a relatively large amount of secondary neo-formed amorphous silica is also documented.

Investigating Fracture Network Deformation Using Noble Gas Release

We investigate deformation mechanics of fracture networks in unsaturated fractured rocks from subsurface conventional detonation using dynamic noble gas measurements and changes in air permeability. We dynamically measured the noble gas isotopic composition and helium exhalation of downhole gas before and after a large subsurface conventional detonation. These noble gas measurements were combined with measurements of the subsurface permeability field from 64 discrete sampling intervals before and after the detonation and subsurface mapping of fractures in borehole walls before well completion. We saw no observable increase in radiogenic noble gas release from either an isotopic composition or a helium exhalation point of view. Large increases in permeability were observed in 13 of 64 discrete sampling intervals. Of the sampling intervals which saw large increases in flow, only two locations did not have preexisting fractures mapped at the site. Given the lack of noble gas release and a clear increase in permeability, we infer that most of the strain accommodation of the fractured media occurred along previously existing fractures, rather than the creation of new fractures, even for a high strain rate event. These results have significant implications for how we conceptualize the deformation of rocks with fracture networks above the percolation threshold, with application to a variety of geologic and geological engineering problems.

The effect of offset on fracture permeability of rocks from the Southern Andes Volcanic Zone, Chile

The Southern Andes Volcanic Zone (SVZ) represents one of the largest undeveloped geothermal provinces in the world. Development of the geothermal potential requires a detailed understanding of fluid transport properties of its main lithologies. The permeability of SVZ rocks is altered by the presence of fracture damage zones produced by the Liquiñe-Ofqui Fault System (LOFS) and the Andean Transverse Faults (ATF). We have therefore measured the permeability of four representative lithologies from the volcanic basement in this area: crystalline tuff, andesitic dike, altered andesite and granodiorite. For comparative purposes, we have also measured the permeability of samples of Seljadalur basalt, an Icelandic rock with widely studied and reported hydraulic properties. Specifically, we present the results of a systematic study of the effect of fractures and fracture offsets on permeability as a function of increasing effective pressure. Baseline measurements on intact samples of SVZ rocks show that the granodiorite has a permeability (10−18 m2), two orders of magnitude higher than that of the volcanic rocks (10−20 m2). The presence of throughgoing mated macro-fractures increases permeability by between four and six orders of magnitude, with the highest permeability recorded for the crystalline tuff. Increasing fracture offset to produce unmated fractures results in large increases in permeability up to some characteristic value of offset, beyond which permeability changes only marginally. The increase in permeability with offset appears to depend on fracture roughness and aperture, and these are different for each lithology. Overall, fractured SVZ rocks with finite offsets record permeability values consistent with those commonly found in geothermal reservoirs (>10−16 m2), which potentially allow convective/advective flow to develop. Hence, our results demonstrate that the fracture damage zones developed within the SVZ produce permeable regions, especially within the transtensional NE-striking fault zones, that have major importance for geothermal energy resource potential.

Systemic Treatment with a miR-146a Mimic Suppresses Endotoxin Sensitivity and Partially Protects Mice from the Progression of Acute Graft-versus-Host Disease.

Acute GVHD (aGVHD) is driven by interactions between the allogenic T cell response, inflammation, tissue injury and microbial products that enter the circulation when protective barriers such as the intestinal epithelium become compromised. Mice with aGVHD become hypersensitive to LPS, secreting large quantities of inflammatory mediators that exacerbate tissue injury. We hypothesized that microRNA (miR) modulators could be used in vivo to mitigate LPS hypersensitivity, altering the course of aGVHD. Using the C57BL/6 → (C57BL/6 × DBA/2)F1 -hybrid model of aGVHD, we measured intestinal permeability over time and used a qPCR array to detect concomitant changes in the expression levels of certain microRNAs (miRs) in the intestine. Large increases in permeability were seen on day 15, when endotoxemia becomes detectable and GVHD-associated histopathological lesions develop. Amongst the miRs with altered expression levels were some that regulate sensitivity to endotoxin. We chose to focus on miR-146a and treated recipient mice systemically with a miR-146a mimic early in the GVH reaction. This led to a reduction in the burst of IFNγ that likely plays a priming role in the mechanism underlying heightened sensitivity to endotoxin. LPS-induced TNFα release and GVHD-associated weight loss were also diminished and survival was prolonged. In summary, systemic treatment with a miR-146a mimic dampens the heightened sensitivity to LPS that occurs concomitantly with increased intestinal permeability and provides partial protection from the progression of acute GVHD.

Implications of stress re-distribution and rock failure with continued gas depletion in coalbed methane reservoirs

Significant increases in permeability of coal with continued production of coalbed methane (CBM) is a well-accepted phenomenon, particularly in the San Juan basin in the US and Surat basin in Australia. Modeling this increase is either based on the resulting increase in fracture porosity of coal or the associated changes in stresses as a result of the sorption-induced strain. This paper combines the experimental results of a study that measured sorption-induced coal matrix volumetric strain with depletion and a model proposed to estimate the associated changes in stress. The overall changes in stress, resulting from the combined effect of the poro-mechanical behavior and sorption-induced strain, were estimated by introducing a Biot-like coefficient. Plotting the stress path followed during depletion along with the failure envelope for the coal-type clearly showed that shear failure of coal is possible due to anisotropic loading resulting from a large reduction in the horizontal stresses. This would explain the large increases in permeability, typically observed in CBM operations. Finally, a permeability model was developed using the Biot-like coefficient, and assuming transversely isotropic behavior of coal. A comparison of the experimental and modeled permeability results showed that the model works well as long as coal does not fail. However, it demonstrates that a permeability model, incorporating failure of coal, is warranted for reliable prediction of permeability variation.

Synthesis and properties of poly(arylene ether)s based on 3‐pentadecyl 4,4'‐biphenol

AbstractA new biphenol, 3‐pentadecyl 4,4′‐biphenol, was synthesized starting from 3‐pentadecylphenol and was polycondensed with 4,4′‐difluorobenzophenone, 1,3‐bis(4‐fluorobenzoyl)benzene and bis(4‐fluorophenyl)sulfone to obtain poly(arylene ether)s with biphenylene linkages in the backbone and pendent pentadecyl chains. Inherent viscosities and number‐average molecular weights (Mn) of the poly(arylene ether)s were in the range 0.50 − 0.81 dL g−1 and 2.2 × 104 − 8.3 × 104, respectively. Detailed NMR spectroscopic studies of the poly(arylene ether)s indicated the presence of constitutional isomerism which existed because of the non‐symmetrical structure of 3‐pentadecyl 4,4′‐biphenol. The poly(arylene ether)s readily dissolved in common organic solvents such as dichloromethane, chloroform and tetrahydrofuran and could be cast into tough, transparent and flexible films from their chloroform solutions. The poly(arylene ether)s exhibited Tg values in the range 35–60 °C which are lower than that of reference poly(arylene ether)s without pentadecyl chains. The 10% decomposition temperatures (T10) of the poly(arylene ether)s were in the range 410–455 °C indicating their good thermal stability. A gas permeation study of poly(ether sulfone) containing pendent pentadecyl chains revealed a moderate increase in permeability for helium, hydrogen and oxygen. However, there was a large increase in permeability for carbon dioxide which could be attributed to the internal plasticization effect of pendent pentadecyl chains. © 2016 Society of Chemical Industry

Alterations of Fractures in Carbonate Rocks by CO2-Acidified Brines.

Fractures in geological formations may enable migration of environmentally relevant fluids, as in leakage of CO2 through caprocks in geologic carbon sequestration. We investigated geochemically induced alterations of fracture geometry in Indiana Limestone specimens. Experiments were the first of their kind, with periodic high-resolution imaging using X-ray computed tomography (xCT) scanning while maintaining high pore pressure (100 bar). We studied two CO2-acidified brines having the same pH (3.3) and comparable thermodynamic disequilibrium but different equilibrated pressures of CO2 (PCO2 values of 12 and 77 bar). High-PCO2 brine has a faster calcite dissolution kinetic rate because of the accelerating effect of carbonic acid. Contrary to expectations, dissolution extents were comparable in the two experiments. However, progressive xCT images revealed extensive channelization for high PCO2, explained by strong positive feedback between ongoing flow and reaction. The pronounced channel increasingly directed flow to a small region of the fracture, which explains why the overall dissolution was lower than expected. Despite this, flow simulations revealed large increases in permeability in the high-PCO2 experiment. This study shows that the permeability evolution of dissolving fractures will be larger for faster-reacting fluids. The overall mechanism is not because more rock dissolves, as would be commonly assumed, but because of accelerated fracture channelization.

Recent advances in time-lapse, laboratory rock physics for the characterization and monitoring of fluid-rock interactions

Monitoring thermo-chemo-mechanical processes geophysically — e.g., fluid disposal or storage, thermal and chemical stimulation of reservoirs, or natural fluids simply entering a new system — raises numerous concerns because of the likelihood of fluid-rock chemical interactions and our limited ability to decipher the geophysical signature of coupled processes. One of the missing links is understanding the evolution of seismic properties together with reactive transport because rock properties evolve as a result of chemical reactions and vice versa. Capturing this coupling experimentally is one of the missing elements in the existing literature. This paper describes recent advances in rock-physics experiments to understand the effects of dissolution-induced compaction on acoustic velocity, porosity, and permeability. This paper has a dual aim: understanding the mechanisms underlying permanent modifications to the rock microstructure and providing a richer set of experimental information to inform the formulation of new simulations and rock modeling. Data observation included time-lapse experiments and imaging tracking transport and elastic properties, the rock microstructure, and the pH and chemical composition of the fluid permeating the rock. Results show that the removal of high surface area, mineral phases such as microcrystalline calcite and clay appears to be mostly responsible for dissolution-induced compaction. Nevertheless, it was the original rock microstructure and its response to stress that ultimately defined how solution-transfer and rock compaction feed back upon each other. The change in pore volume to the applied stress, the permeability characterizing the formation, and the reactive transport of phases characterized by a high surface area were strongly coupled during injection, controlling how velocity evolved. In less stiff rocks, rock-fluid interactions led to grain-slip-driven compaction and a consequent decrease in velocity. In tight and stiff rocks, rock-fluid interactions led to minimal compaction, a larger increase in permeability, and crack opening. Nevertheless, the change in velocity of these tight rocks was almost negligible.

The effects of inflammatory cytokines on lymphatic endothelial barrier function

Proper lymphatic function is necessary for the transport of fluids, macromolecules, antigens and immune cells out of the interstitium. The lymphatic endothelium plays important roles in the modulation of lymphatic contractile activity and lymph transport, but it's role as a barrier between the lymph and interstitial compartments is less well understood. Alterations in lymphatic function have long been associated with edema and inflammation although the integrity of the lymphatic endothelial barrier during inflammation is not well-defined. In this paper we evaluated the integrity of the lymphatic barrier in response to inflammatory stimuli commonly associated with increased blood endothelial permeability. We utilized in vitro assays of lymphatic endothelial cell (LEC) monolayer barrier function after treatment with different inflammatory cytokines and signaling molecules including TNF-α, IL-6, IL-1β, IFN-γ and LPS. Moderate increases in an index of monolayer barrier dysfunction were noted with all treatments (20-60% increase) except IFN-γ which caused a greater than 2.5-fold increase. Cytokine-induced barrier dysfunction was blocked or reduced by the addition of LNAME, except for IL-1β and LPS treatments, suggesting a regulatory role for nitric oxide. The decreased LEC barrier was associated with modulation of both intercellular adhesion and intracellular cytoskeletal activation. Cytokine treatments reduced the expression of VE-cadherin and increased scavenging of β-catenin in the LECs and this was partially reversed by LNAME. Likewise the phosphorylation of myosin light chain 20 at the regulatory serine 19 site, which accompanied the elevated monolayer barrier dysfunction in response to cytokine treatment, was also blunted by LNAME application. This suggests that the lymphatic barrier is regulated during inflammation and that certain inflammatory signals may induce large increases in permeability.

Pervaporative Separation of Aromatic/Aliphatic Mixtures with Poly(Siloxane-co-Imide) and Poly(Ether-co-Imide) Membranes

Aromatic random copolyimides were synthesized and tested as membrane materials for the separation of a mixture of aromatic and aliphatic hydrocarbons by pervaporation. The polymers were synthesized by a two-step polycondensation route with a total of 4 aromatic dianhydrides, 4 aromatic diamines, and 3 diamino-terminated aliphatic oligomers containing either ether or siloxane units. Pervaporation experiments were conducted at two temperatures with toluene/n-heptane and benzene/n-heptane mixtures as feed streams. All polymers were selective toward the aromatic hydrocarbon. Introduction of siloxane units in the polymer generally led to very high hydrocarbon permeability coefficients, but caused a reduction in selectivity relative to that of the aromatic homopolyimide. Incorporation of ether units, on the other hand, did not generally cause such large increases in permeability, nor large decreases in selectivity. The performance of these materials was compared with previous results reported in the literature for other polymers.

Instabilities in the dissolution of a porous matrix

[1] A reactive fluid dissolving the surrounding rock matrix can trigger an instability in the dissolution front, leading to spontaneous formation of pronounced channels or wormholes. Theoretical investigations of this instability have typically focused on a steadily propagating dissolution front that separates regions of high and low porosity. In this paper we show that this is not the only possible dissolutional instability in porous rocks; there is another instability that operates instantaneously on any initial porosity field, including an entirely uniform one. The relative importance of the two mechanisms depends on the ratio of the porosity increase to the initial porosity. We show that the “inlet” instability is likely to be important in limestone formations where the initial porosity is small and there is the possibility of a large increase in permeability. In quartz-rich sandstones, where the proportion of easily soluble material (e.g., carbonate cements) is small, the instability in the steady-state equations is dominant.

Permanent carbon dioxide storage in deep-sea sediments.

Stabilizing the concentration of atmospheric CO(2) may require storing enormous quantities of captured anthropogenic CO(2) in near-permanent geologic reservoirs. Because of the subsurface temperature profile of terrestrial storage sites, CO(2) stored in these reservoirs is buoyant. As a result, a portion of the injected CO(2) can escape if the reservoir is not appropriately sealed. We show that injecting CO(2) into deep-sea sediments below [corrected] 3,000-m water depth and a few hundred meters of sediment provides permanent geologic storage even with large geomechanical perturbations. At the high pressures and low temperatures common in deep-sea sediments, CO(2) resides in its liquid phase and can be denser than the overlying pore fluid, causing the injected CO(2) to be gravitationally stable. Additionally, CO(2) hydrate formation will impede the flow of CO(2)(l) and serve as a second cap on the system. The evolution of the CO(2) plume is described qualitatively from the injection to the formation of CO(2) hydrates and finally to the dilution of the CO(2)(aq) solution by diffusion. If calcareous sediments are chosen, then the dissolution of carbonate host rock by the CO(2)(aq) solution will slightly increase porosity, which may cause large increases in permeability. Karst formation, however, is unlikely because total dissolution is limited to only a few percent of the rock volume. The total CO(2) storage capacity within the 200-mile economic zone of the U.S. coastline is enormous, capable of storing thousands of years of current U.S. CO(2) emissions.

Effects of CO 2 exposure and physical aging on the gas permeability of thin 6FDA-based polyimide membranes : Part 1. Without crosslinking

The changes in permeability of He, O 2, N 2, CH 4 and CO 2 through thin films (∼350 nm) of 6FDA-based polyimides with and without DABA units in the chain were monitored as a function of aging time at 35 °C using different methodologies that varied the exposure of these films to CO 2. A pulse of CO 2 exposure after aging causes the permeability of each gas to increase; the change is greater the larger the probe gas molecule. Continuous exposure to CO 2 over 100 h leads to a larger increase in permeability than periodic CO 2 exposure over the same period, but the trends are basically similar for the two cases. After a CO 2 pulse, the permeability relaxes and approaches the aging response established prior to CO 2 exposure. The change in refractive index for CO 2 exposed films is consistent with the change in gas permeability in most regards; however, the recovery of refractive index following CO 2 exposure is somewhat less than observed by permeability. Periodic exposure to CO 2 during aging seems to retard the decline in gas permeability with the effect being greater for larger probe molecules. An increase in CO 2/CH 4 and O 2/N 2 selectivities with aging was observed for thin films that were never exposed to CO 2 while these selectivities decrease with aging when periodic exposure to CO 2 was imposed.

Measurement of Gas Diffusion Capacity of Cigarette Papers

Abstract Apparatus suitable for measuring gas diffusion capacity of cigarette paper was assembled and evaluated. The apparatus provides semi-automated means for measuring the concentration of carbon dioxide diffusing through a small area of the paper, and computation of a paper thickness-dependent diffusion capacity of the sample. Measurements are rapid and can be made in about 30 s. Diffusion capacity measurements were repeatable and reproducible to within about 1%. Variability of the diffusion capacity values was much lower than that observed for permeability measurements. For these reasons, the apparatus is useful for quality assessment and research applications. Diffusion capacity was measured for cigarette papers of inherent permeability ranging from 6 to 62 cm/min. As expected from prevailing theory, the diffusion capacity values generally increased with permeability. The diffusion capacity measured for electrostatically perforated papers was only slightly higher (about 6-11%) than the unperforated base paper despite large increases in permeability. This result indicates that diffusion capacity is governed by small pores in the paper. The apparatus is capable of measuring banded areas of papers designed for reduced ignition propensity. Diffusion capacity values for banded areas were lower than those of non-banded paper of similar permeability, suggesting that the band material preferentially occludes small pores in the paper.

Knockdown of occludin expression leads to diverse phenotypic alterations in epithelial cells

The function of occludin (Occ) in the tight junction is undefined. To gain insight into its role in epithelial cell biology, occludin levels in Madin-Darby canine kidney II cells were suppressed by stably expressing short interfering RNA. Suppression of occludin was associated with a decrease in claudins-1 and -7 and an increase in claudins-3 and -4. Claudin-2 levels were unaffected. The tight junction "fence" function was not impaired in suppressed Occ (Occ-) clones, as determined by BODIPY-sphingomyelin diffusion in the membrane. The most striking changes were those related to control of the cytoskeleton and the "gate" function of tight junctions. A reduced ability of Occ- clones to extrude apoptotic cells from the monolayers suggested that neighbors of apoptotic cells either failed to sense their presence or were unable to coordinate cytoskeletal activity necessary for their extrusion. To further test the extent to which actin cytoskeletal activity depends on the presence of occludin, Occ- and Occ+ monolayers were depleted of cholesterol. Previous studies showed that cholesterol depletion is associated with reorganization of the actin cytoskeleton and a fall in transepithelial electrical resistance. In contrast to control Occ (Occ+) cells, transepithelial electrical resistance did not fall significantly in cholesterol-depleted Occ- monolayers and they failed to generate Rho-GTP, one of the signaling molecules involved in regulating the actin cytoskeleton. While steady-state transepithelial electrical resistance was similar in all clones, tight junction permeability to mono- and divalent inorganic cations was increased in Occ- monolayers. In addition, there was a disproportionately large increase in permeability to monovalent organic cations, up to 6.96 A in diameter. Chloride permeability was unaffected and there was little change in mannitol flux. The data suggest that occludin transduces external (apoptotic cells) and intramembrane (rapid cholesterol depletion) signals via a Rho signaling pathway that, in turn, elicits reorganization of the actin cytoskeleton. Impaired signaling in the absence of occludin may also alter the dynamic behavior of tight junction strands, as reflected by an increase in permeability to large organic cations; the permeability of ion pores formed of claudins, however, is less affected.

Spermine increases the active and passive transport across the alveolar epithelium in situ: effect of thiol reagents.

An intact alveolar epithelial barrier is thought to be important for alveolar liquid absorption. However, polycations increase alveolar permeability without affecting alveolar liquid absorption (Saumon et al., Am J Physiol 1995: 269:L185-L194). We have reconsidered this issue using polyamines. The polyamine spermine (10(-3) mol/l) produced a large (up to 20-fold), sustained increase in the permeability of the alveolar barrier to mannitol (PAMan) and in alveolar liquid absorption (Jw, twofold) in isolated rat lungs. These increases were inhibited by 5 x 10(-3) mol/l putrescine and 2 x 10(-3) mol/l spermidine. Because spermine is known to affect the phosphoinositide/Ca2+ signalling pathway, we evaluated the effects of thiol reagents known to interfere with this pathway in different ways. Thimerosal, a thiol reagent which sensitizes the inositol 1,4,5-trisphosphate (IP3) receptor, inhibited the spermine-induced increase in PA(Man) and, to a lesser extent, that of Jw. Mersalyl, a thiol reagent which blocks IP3-gated Ca2+ channels, enhanced spermine's effect, whereas N-ethylmaleimide, a non-specific thiol reagent, had no effect. These observations show that large increases in permeability may coexist with increases in Jw. They also suggest that the phosphoinositide/Ca2+ second messenger pathway is involved in modulating the tightness of the alveolar barrier and alveolar liquid absorption.

Gas sorption and transport in poly(tertiary-butyl methacrylate)

Gas sorption and transport properties of poly(tertiary-butyl methacrylate) (PtBMA) have been measured at 35°C and are compared with prior results for poly(methyl acrylate) (PMA), poly(methyl methacrylate) (PMMA), and poly(ethyl methacrylate) (PEMA). The t-butyl substitution increases the gas permeability as a result of increases in both diffusivity and solubility coefficients; however, the ideal selectivity for a given gas pair may increase or decrease depending upon the methacrylate polymer to which it is compared. Poly(t-butyl methacrylate) does not show plasticization by CO 2 up to 10 atm of CO 2. The effect of t-butyl substitution on gas permeability observed here for the methacrylate polymer is compared to that reported in the literature for other polymer types. This substitution causes a larger increase in permeability the smaller the repeat unit of the base polymer since this results in a greater modification in structure and subsequent greater decrease in efficiency of chain packing.

Influence of crystal plastic deformation on dilatancy and permeability development in synthetic salt rock

While the fluid transport properties of rocks are well understood under hydrostatic conditions, little is known regarding these properties in rocks undergoing plastic deformation. In this study the influence of macroscopic plastic deformation on permeability has been investigated experimentally using synthetic salt rock. Dilatometric triaxial deformation experiments performed on this material, at room temperature, confining pressures (Pc) in the range 5–20 MPa and strain rates of ∼ 4 × 10−5 s−1 to total strains of ∼ 15%, exhibited work hardening behaviour with minor amounts of dilatancy at Pc < 18 MPa. Microstructural observations confirmed that deformation occurred by dislocation glide, with grain boundary microcracking in the dilatant field. At the lowest pressures, deformation-induced dilatancy of only 0.1–0.2 vol.% produced extremely rapid initial increases in permeability (from ≤ 10−21 m2 to ∼ 2 × 10−16 m2), suggesting critical behaviour of the type described by percolation theory. This rapid permeability development with dilatancy is well described by crack linkage models based on percolation theory, provided a broad range of fluid conductance is incorporated. The study has shown that minor dilatancy (< 0.2 vol.%) during plastic deformation of salt rock can lead to very large increases in permeability. This is of direct interest with regard to the behaviour of salt rock in waste disposal and storage systems, and may have important implications for the transport of fluids through, and the interaction of fluids with, crystalline rocks undergoing crystal plastic deformation in nature.

Gas separation properties of aromatic polyamides containing hexafluoroisopropylidene groups

The synthesis and gas transport properties of aromatic polyisophthalamides (PIPAs), based on isophthaloyl chloride derivatives bearing pendent groups and hexafluoroisopropylidene (6F) linkages in the main chain, are reported and compared with properties of a similar series of PIPAs containing sulfonyl (SO 2) rather than 6F in the main chain. All of those polymers exhibit high glass transitions temperatures. The polymers containing 6F groups were markedly more permeable and somewhat less selective than their sulfonyl analogs. Polymers containing a t-butyl pendent group at the 5 position of the isophthaloyl linkage were much more permeable than those bearing only a hydrogen atom at this position, although a strong decrease in permselectivity accompanied the large increase in permeability. CO 2/CH 4 solubility selectivity values of the 6F-containing polymers were similar to values reported for other polymetric and non-polymeric organic materials with similar concentrations of polar carbonyl linkages. In contrast, the CO 2/CH 4 solubility selectivity in SO 2-containing variants of these polymers was substantially lower than expected based on total polar group concentration. The low CO 2/CH 4 solubility selectivity is believed to be related to the extremely efficient chain packing in the SO 2-containing polymers, which may lead to strong amide-amide linkage interaction, thereby inhibiting carbonyl groups in the amide linkage from interactions with CO 2 molecules to increase CO 2/CH 4 solubility selectivity.