Low Intrinsic Permeability Research Articles

Visual Laboratory Tests: Effect of Operational Parameters on Proppant Transport in a 3D Printed Vertical Hydraulic Fracture with Two-Sided Rough Surfaces

Summary Hydraulic fracturing technology is an effective measure that can improve oil and gas production and achieve enormous economic benefits owing to it phenomenally increasing the oil recovery from the low intrinsic permeability of the compact rock. Good placement and distribution of the proppant in the hydraulic fractures can provide successful stimulation for a well, which is essential for applying the hydraulic fracturing process. Previous studies extensively explored proppant placement, distribution, and operational factors in simplified smooth surface fracture models. However, the operational factors such as pump rate, proppant concentration, proppant size, fluid viscosity, and inlet condition (pulse time) involved in proppant placement and distribution in realistic rough surfaces of fractures are not clearly understood. In particular, the law of proppant transport in a two-sided rough surface of fracture with changes in the aforementioned operational factors was unclear. Hence, in this study, we investigated the effect of these operational factors on proppant placement and transport in both the smooth surface fracture model and the two-sided rough surface fracture model. The results suggested that the traditional law of proppant transport drawn on the smooth surface fracture model did not apply to the two-sided rough surface model. It is suggested that selecting corresponding variables was needed to reduce the risk of proppant bridging and offer a better channel ratio.

Unraveling the complex pressure propagation of two-time depressurization production in Shenhu hydrate reservoir: Insights for long-term exploitation

Depressurization serves as the primary method for exploiting marine hydrate reservoirs, and understanding the long-term pressure propagation efficiency and identifying the potential limiting factors are crucial for enhancing and optimizing this approach. In this study, we employed numerical modeling to simulate two-time depressurization exploitation in the Shenhu hydrate reservoir, aiming to predict the long-term gas production and pressure propagation efficiency under various depressurization schemes. Our simulation results indicate: 1) The pressure propagates rapidly near the wellhead and gradually decelerates with distance due to the impeding influence of the reservoir's low intrinsic permeability and groundwater seepage in the covering strata. 2) Pressure propagation in single-well systems exhibits substantial variation among sublayers, resulting in limited areas of hydrate dissociation. Long-term gas production depends on the hydrate dissociation. Consequently, the total 5-year gas production for single-vertical-well and single-horizontal-well systems are only 3.59 × 106 m3 and 5.04 × 106 m3, respectively. 3) Multi-horizontal-well systems can significantly extend pressure propagation, but the maximum increase in gas production is only 47.0%. This is due to the reservoir's low permeability (2.3 mD), which severely hampers hydrate dissociation pressure, limiting it to 8 MPa. Therefore, optimizing depressurization requires reservoir modifications to enhance reservoir permeability.

Physical property characterization of the Waipapa greywacke: an important geothermal reservoir basement rock in New Zealand

Greywacke basement rocks in New Zealand host conventional geothermal reservoirs and may supply important hotter and deeper geothermal energy resources in the future. This work combines petrological analyses and physical property measurements of Waipapa greywacke, a basement unit hosting New Zealand geothermal reservoirs, in order to understand better how structurally controlled flow networks develop and channel geothermal fluids within it. Results show intact Waipapa greywacke has high tensile and triaxial compressive strengths, and low intrinsic permeability (~ 10–21 m2). Permeability of intact Waipapa greywacke does not increase significantly during triaxial loading to failure and is accompanied by minimal changes ultrasonic wave velocities. These data taken together suggest that microcrack development during brittle deformation is very limited. Upon failure, the permeability increases by two orders of magnitude and shows similar permeability to tests performed on synthetic, single, mode I fractures in intact Waipapa greywacke. Permeability persists in Waipapa greywacke fractures under confining pressures of at least 150 MPa. It is concluded that Waipapa greywacke rocks will not allow fluid flow through the matrix of the rock and that substantial geothermal fluid flow will only occur through macrofracture networks.

Recent Advances in Mixed-Matrix Membranes for Light Hydrocarbon (C1-C3) Separation.

Light hydrocarbons, obtained through the petroleum refining process, are used in numerous applications. The separation of the various light hydrocarbons is challenging and expensive due to their similar melting and boiling points. Alternative methods have been investigated to supplement cryogenic distillation, which is energy intensive. Membrane technology, on the other hand, can be an attractive alternative in light hydrocarbon separation as a phase change that is known to be energy-intensive is not required during the separation. In this regard, this study focuses on recent advances in mixed-matrix membranes (MMMs) for light hydrocarbon (C1–C3) separation based on gas permeability and selectivity. Moreover, the future research and development direction of MMMs in light hydrocarbon separation is discussed, considering the low intrinsic gas permeability of polymeric membranes.

Factors Influencing Luciferase-Based Bioluminescent Imaging in Preclinical Models of Brain Tumor.

Bioluminescent imaging (BLI) is a powerful tool in biomedical research to measure gene expression and tumor growth. The current study examined factors that influence the BLI signal, specifically focusing on the tissue distribution of two luciferase substrates, D-luciferin and CycLuc1. D-luciferin, a natural substrate of firefly luciferase, has been reported to have limited brain distribution, possibly due to the efflux transporter, breast cancer resistance protein (Bcrp), at the blood-brain barrier. CycLuc1, a synthetic analog of D-luciferin, has a greater BLI signal at lower doses than D-luciferin, especially in the brain. Our results indicate that limited brain distribution of D-luciferin and CycLuc1 is predominantly dictated by their low intrinsic permeability across the cell membrane, where the efflux transporter, Bcrp, plays a relatively minor role. Both genetic ablation and pharmacological inhibition of Bcrp decreased the systemic clearance of both luciferase substrates, significantly increasing exposure in the blood and, hence, in organs and tissues. These data also indicate that the biodistribution of luciferase substrates can be differentially influenced in luciferase-bearing tissues, leading to a "tissue-dependent" BLI signal. The results of this study point to the need to consider multiple mechanisms that influence the distribution of luciferase substrates. SIGNIFICANCE STATEMENT: Bioluminescence is used to monitor many biological processes, including tumor growth. This study examined the pharmacokinetics, brain distribution, and the role of active efflux transporters on the luciferase substrates D-luciferin and CycLuc1. CycLuc1 has a more sustained systemic circulation time (longer half-life) that can provide an advantage for the superior imaging outcome of CycLuc1 over D-luciferin. The disparity in imaging intensities between brain and peripheral sites is due to low intrinsic permeability of these luciferase substrates across the blood-brain barrier.

Hydrothermal alteration and sealing at Turrialba volcano, Costa Rica, as a mechanism for phreatic eruption triggering

Turrialba is a basaltic to andesitic Holocene stratovolcano that after decades of quiescence re-activated in 1996 and has been highly active ever since. Turrialba is characterized by a highly active magmatic-hydrothermal system, and we propose that hydrothermal sealing and volatile accumulation are the mechanisms responsible for the reactivation and persistent phreatic activity at Turrialba since 2010. Evidence of sealing is found in pyroclastic breccias from phreatic eruptions as high concentrations of hydrothermal minerals coupled with low intrinsic permeability. The suite of volcanic breccias studied herein erupted from the main vent between 2014 and 2019 and has an alteration mineral assemblage of SiO2 polymorphs ± gypsum ± natroalunite ± pyrite. The mineral assemblage is indicative of acid sulphate alteration within the advanced-argillic alteration facies characterized by temperatures of approximately 200–350 °C as indicated by the presence of gypsum and natroalunite, the high temperature endmember of the alunite series. Acid sulphate alteration is the result of extreme base leaching by acidic fluids (pH <4) with a high sulphate content. Measurements of permeability and porosity yielded variable porosity and very low to non-existent permeability in all hydrothermal breccia samples. Back-scatter electron (BSE) images reveal nano-, micro- and macro-scale fracture networks discontinuously filled with hydrothermal gypsum and pyrite which are responsible for diminished permeability, supporting the conclusion that hydrothermal sealing is active at Turrialba. Diminished permeability associated with the formation of a seal inhibits the escape of gases, causing them to accumulate below the seal and pressurize the system. Eventual seal failure due to overpressure results in the frequent phreatic eruptions seen at Turrialba.

Enhancing the gas production efficiency of depressurization-induced methane hydrate exploitation via fracturing

Most of the existing field tests of gas recovery from hydrate-bearing sediments suffer from the difficulty in pressure propagation, leading to a low productivity and energy efficiency. Fracturing has shown enormous potential in the shale gas production; thus in this study, we introduced this technique into the laboratory-scale gas hydrate production. The performance of gas production was investigated through numerically analyzing the gas hydrate dissociation behavior under different fracturing patterns. The results indicate that fracturing can significantly facilitate the pressure propagation in the hydrate sediments with a low intrinsic permeability during depressurization, thereby contributing to a better gas production performance. Fracture depth plays a critical role in promoting the gas production efficiency; the maximal enhancement ratio of average production rate by fracturing could attain 13.1%. Moreover, the contribution of reservoir’s sensible heat in hydrate dissociation is limited in the core with a low permeability; timely and sufficient heat supply is thus important for the successive gas production. The findings of this study illustrate the effects of fracturing on enhancing the gas production efficiency of depressurization-induced gas hydrate exploitation; this will provide important guidance for its potential application in the field test of marine and permafrost hydrate reservoir where low permeability is commonly encountered and an enhancing technique is much required.

Discovery of a Gut-Restricted JAK Inhibitor for the Treatment of Inflammatory Bowel Disease

To identify Janus kinase (JAK) inhibitors that selectively target gastrointestinal tissues with limited systemic exposures, a class of imidazopyrrolopyridines with a range of physical properties was prepared and evaluated. We identified compounds with low intrinsic permeability and determined a correlation between permeability and physicochemical properties, clogP and tPSA, for a subset of compounds. This low intrinsic permeability translated into compounds displaying high colonic exposure and low systemic exposure after oral dosing at 25 mg/kg in mouse. In a mouse PK/PD model, oral dosing of lead compound 2 demonstrated dose-dependent inhibition of pSTAT phosphorylation in colonic explants post-oral dose but low systemic exposure and no measurable systemic pharmacodynamic activity. We thus demonstrate the utility of JAK inhibitors with low intrinsic permeability as a feasible approach to develop gut-restricted, pharmacologically active molecules with a potential advantage over systemically available compounds that are limited by systemic on-target adverse events.

Numerical modeling for drilling fluid invasion into hydrate-bearing sediments and effects of permeability

Drilling fluid invasion into hydrate-bearing sediments could induce hydrate dissociation and complicate heat and mass transfer around wellbore, and further affect mechanical strength of hydrate-bearing sediments and accurateness of wellbore logging interpretations. In this study, a cylindrical numerical model was established to study the characteristics of drilling fluid invasion into hydrate-bearing sediments and the effects of permeability on this process. The distributions of temperature, pressure, saturation, and salinity of pore water around wellbore at different time were obtained. The pressure and temperature around wellbore gradually increase, and the hydrate around wellbore dissociates with the high-temperature drilling fluid invasion. Meantime, water and gas generated from hydrate dissociation gradually migrate outward and then form ‘secondary hydrate’ in some areas outside wellbore. Dissociation and formation of hydrate can sharply change the salinity of pore water around wellbore. The drilling fluid invasion and hydrate dissociation ranges become larger when the intrinsic permeability is higher. The salinity in sediments decreases sharply while the dilution range is narrow when drilling fluid invasion into hydrate-bearing sediments with low permeability. In addition, the permeability decline exponent of the Masuda model has a significant influence on drilling fluid invasion. However, the Corey exponents of the relative permeability model only have a limited influence on drilling fluid invasion into hydrate-bearing sediments with low intrinsic permeability (e.g., 5.5 mD), while they have a noticeable influence on hydrate-bearing sediments with high intrinsic permeability (e.g., 75 mD).

Molecular and Functional Characterization of Grapevine NIPs through Heterologous Expression in aqy-Null Saccharomyces cerevisiae.

Plant Nodulin 26-like Intrinsic Proteins (NIPs) are multifunctional membrane channels of the Major Intrinsic Protein (MIP) family. Unlike other homologs, they have low intrinsic water permeability. NIPs possess diverse substrate selectivity, ranging from water to glycerol and to other small solutes, depending on the group-specific amino acid composition at aromatic/Arg (ar/R) constriction. We cloned three NIPs (NIP1;1, NIP5;1, and NIP6;1) from grapevine (cv. Touriga Nacional). Their expression in the membrane of aqy-null Saccharomyces cerevisiae enabled their functional characterization for water and glycerol transport through stopped-flow spectroscopy. VvTnNIP1;1 demonstrated high water as well as glycerol permeability, whereas VvTnNIP6;1 was impermeable to water but presented high glycerol permeability. Their transport activities were declined by cytosolic acidification, implying that internal-pH can regulate NIPs gating. Furthermore, an extension of C-terminal in VvTnNIP6;1M homolog, led to improved channel activity, suggesting that NIPs gating is putatively regulated by C-terminal. Yeast growth assays in the presence of diverse substrates suggest that the transmembrane flux of metalloids (As, B, and Se) and the heavy metal (Cd) are facilitated through grapevine NIPs. This is the first molecular and functional characterization of grapevine NIPs, providing crucial insights into understanding their role for uptake and translocation of small solutes, and extrusion of toxic compounds in grapevine.

Enhanced selectivity in mixed matrix membranes for CO2 capture through efficient dispersion of amine-functionalized MOF nanoparticles

Mixed matrix membranes (MMMs) for gas separation applications have enhanced selectivity when compared with the pure polymer matrix, but are commonly reported with low intrinsic permeability, which has major cost implications for implementation of membrane technologies in large-scale carbon capture projects. High-permeability polymers rarely generate sufficient selectivity for energy-efficient CO2 capture. Here we report substantial selectivity enhancements within high-permeability polymers as a result of the efficient dispersion of amine-functionalized, nanosized metal–organic framework (MOF) additives. The enhancement effects under optimal mixing conditions occur with minimal loss in overall permeability. Nanosizing of the MOF enhances its dispersion within the polymer matrix to minimize non-selective microvoid formation around the particles. Amination of such MOFs increases their interaction with thepolymer matrix, resulting in a measured rigidification and enhanced selectivity of the overall composite. The optimal MOF MMM performance was verified in three different polymer systems, and also over pressure and temperature ranges suitable for carbon capture. Mixed matrix membranes can separate CO2 from flue gas mixtures but increasing selectivity without sacrificing permeability remains challenging. Selectivity can be increased with little loss in permeability by using nanoparticulate, amine-functionalized metal–organic framework fillers.

Blends of a Polymer of Intrinsic Microporosity and Partially Sulfonated Polyphenylenesulfone for Gas Separation.

Polyphenylenesulfone (PPSU) and sulfonated polyphenylenesulfone (sPPSU) are widely used for liquid separations in the medical and food industries. However, their potential applications for gas separation have not been studied extensively owing to their low intrinsic gas permeability. We report here for the first time that blending with sPPSU can significantly improve the gas separation performance of highly permeable polymers of intrinsic microporosity (PIMs), specifically PIM-1, because of the strong molecular interactions of the sulfonic acid groups of sPPSU with CO2 and O2 . In addition, a novel co-solvent system has been discovered to overcome the immiscibility of these polymers. The presence of a higher degree of sulfonation in sPPSU results in better gas separation performance of the blend membranes close to or above the Robeson upper bound lines for O2 /N2 , CO2 /N2 and CO2 /CH4 separations. Interestingly, the blend membranes have comparable gas selectivity to sPPSU even though their sPPSU content is only 5-20 wt %. Moreover, they also display improved anti-plasticization properties up to 30 atm (3 MPa) using a binary CO2 /CH4 feed gas. The newly developed PIM-1/sPPSU membranes are potential candidates for air separation, natural gas separation, and CO2 capture.

Auto-Adhesion Potential of Extraocular Aqp0 during Teleost Development.

AQP0 water channels are the most abundant proteins expressed in the mammalian lens fiber membranes where they are essential for lens development and transparency. Unlike other aquaporin paralogs, mammalian AQP0 has a low intrinsic water permeability, but can form cell-to-cell junctions between the lens fibers. It is not known whether the adhesive properties of AQP0 is a derived feature found only in mammals, or exists as a conserved ancestral trait in non-mammalian vertebrates. Here we show that a tetraploid teleost, the Atlantic salmon, expresses four Aqp0 paralogs in the developing lens, but also expresses significant levels of aqp0 mRNAs and proteins in the epithelia of the pronephros, presumptive enterocytes, gill filament and epidermis. Quantitative PCR reveals that aqp0 mRNA titres increase by three orders of magnitude between the onset of somitogenesis and pigmentation of the eye. Using in situ hybridization and specific antisera, we show that at least two of the channels (Aqp0a1, -0b1 and/or -0b2) are localized in the extraocular basolateral and apical membranes, while Aqp0a2 is lens-specific. Heterologous expression of the Aqp0 paralogs in adhesion-deficient mouse fibolast L-cells reveals that, as for human AQP0, each intact salmon channel retains cell-to-cell adhesive properties. The strongest Aqp0 interactions are auto-adhesion, suggesting that homo-octamers likely form the intercellular junctions of the developing lens and epithelial tissues. The present data are thus the first to show the adhesion potential of Aqp0 channels in a non-mammalian vertebrate, and further uncover a novel extraocular role of the channels during vertebrate development.

Accelerated curing regimes for polymer-modified cement

Polymer-modified materials provide numerable enhancements to cementitious composites. However, the curing/hardening conditions for cementitious and polymeric materials differ significantly, although they are mixed to form a single entity. Cement requires a moist environment for the hydration process to occur, while polymers require a hot and dry environment. Consequently, the polymer-modified composite exhibits lower compressive strength than the ordinary cementitious product. The objective of the present study was to resolve this issue by using accelerated curing regimens, following the fundamental concept that the dominant contribution to the toughness of the composite matrix is from the cement system, while polymer films refine the microstructure. Hygrothermal treatment for plain mortar was first developed in order to achieve 100% of the 28-day strength after treatment is completed. The hot + dry treatment required for the formation of polymer film was studied in the second phase of this study, together with an investigation of the microstructure using scanning electron microscopy. The results show that, after being subjected to the hygrothermal and hot + dry treatment, polymer-modified mortar can achieve low intrinsic permeability without compromising the compressive strength. A 15% polymer loading in styrene–butadiene rubber- and epoxy-modified mortar led to 46% and 18% higher compressive strengths, and 660% and 460% lower intrinsic permeabilities, compared with unmodified mortar, respectively.

Slip-corrected liquid permeability and its effect on hydraulic fracturing and fluid loss in shale

Pore diameter in shale strata ranges from a few to hundreds of nanometers, whereas in conventional reservoirs the range is 3 orders of magnitude greater. In spite of the small size of the pores—which would be expected to cause very low intrinsic permeability—field reports document unusually high loss of hydraulic fracturing fluid (as much as 90%) in shale reservoirs. The lost fluid remains in induced fractures and also leaks off into the shale matrix. Liquid flow in tiny pores is different from the flow in large pores. To compensate for this difference, the traditional liquid flow model needs a correction parameter called liquid slip length. We measured slip length of brine and pores in shale by using an atomic force microscope (AFM). Our measurements suggest a slip length of 250nm in organic pores. We used measured slip length in a stochastic permeability model to calculate apparent liquid permeability (ALP) in the shale matrix. When corrected for slip length, the ALP in shale can be much greater than intrinsic Darcy permeability. We then used ALP in a coupled flow–geomechanical simulator to study the effects of slip-corrected matrix permeability on the induced fracture network and fluid loss during hydraulic fracturing. The results show the dramatic effects of the slip parameter on the fracture network and explain the high fluid loss during hydraulic fracturing.

Nanoscale simulation of shale transport properties using the lattice Boltzmann method: permeability and diffusivity.

Porous structures of shales are reconstructed using the markov chain monte carlo (MCMC) method based on scanning electron microscopy (SEM) images of shale samples from Sichuan Basin, China. Characterization analysis of the reconstructed shales is performed, including porosity, pore size distribution, specific surface area and pore connectivity. The lattice Boltzmann method (LBM) is adopted to simulate fluid flow and Knudsen diffusion within the reconstructed shales. Simulation results reveal that the tortuosity of the shales is much higher than that commonly employed in the Bruggeman equation, and such high tortuosity leads to extremely low intrinsic permeability. Correction of the intrinsic permeability is performed based on the dusty gas model (DGM) by considering the contribution of Knudsen diffusion to the total flow flux, resulting in apparent permeability. The correction factor over a range of Knudsen number and pressure is estimated and compared with empirical correlations in the literature. For the wide pressure range investigated, the correction factor is always greater than 1, indicating Knudsen diffusion always plays a role on shale gas transport mechanisms in the reconstructed shales. Specifically, we found that most of the values of correction factor fall in the slip and transition regime, with no Darcy flow regime observed.

Transient Porosity Resulting from Fluid–Mineral Interaction and its Consequences

The term porosity is very widely used in geosciences and normally refers to the spaces between the mineral grains or organic material in a rock, measured as a fraction of the total volume. These spaces may be filled with gas or fluids, and so the most common context for a discussion of porosity is in hydrogeology and petroleum geology of sedimentary rocks. While porosity is a measure of the ability of a rock to include a fluid phase, permeability is a measure of the ability for fluids to flow through the rock, and so depends on the extent to which the pore spaces are interconnected, the distribution of pores and pore neck size, as well as on the pressure driving the flow. This chapter will be primarily concerned with how reactive fluids can move through ‘tight rocks’ which have a very low intrinsic permeability and how secondary porosity is generated by fluid–mineral reactions. A few words about the meaning of the title will help to explain the scope of the chapter: 1. “Fluid–mineral interaction”: When a mineral is out of equilibrium with a fluid, it will tend to dissolve until the fluid is saturated with respect to the solid mineral. We will consider fluids to be aqueous solutions, although many of the principles described here also apply to melts. The generation of porosity by simply dissolving some minerals in a rock is one obvious way to enhance fluid flow. Dissolution of carbonates by low pH solutions to produce vugs and even caves would be one example. However, when considering the role of fluid–mineral reaction during metamorphism the fluid provides mechanisms that enable re-equilibration of the rock, i.e., by replacing one assemblage of minerals by a more stable assemblage. This not only involves the dissolution of the parent mineral phases, but the …

Plug Design for Deep Borehole Disposal of High-Level Nuclear Waste

This paper focuses on the improvement of the longevity and robustness of materials for sealing and plugging the upper portion of a deep borehole used for permanent isolation of high-level nuclear waste. Analytical models of porous and laminar flows show that even when materials have low intrinsic permeability, micron-sized cracks and gaps between the plug and rock (formed via chemical reaction, shrinkage, osmotic consolidation, etc.) significantly diminish the plug’s sealing properties. On this basis, materials such as asphalt, traditional cements, and pure bentonite—which crack or shrink under certain conditions—are unfavorable. An ongoing test program has formulated expanding cement mixtures containing MgO to prevent such bypass flow. Furthermore, these findings support using stable, malleable, and low-permeability plug material (k ≤ 10-16 m2), such as a crushed rock (70%) and bentonite (30%) mixture. Alternative clays such as sepiolite could be blended with the bentonite to further reduce the potential negative effects of salinity on bentonite permeability. A bounding and analytical model of a scenario where radionuclide escape is determined by advection through the plug (and assuming a large and constant driving pressure) shows that a plug permeability of 10-16 m2 is sufficiently low to prevent advective transport of radionuclides from a depth of 2 to 3 km to the surface within the timescale of interest (~1 million yr). Purely diffusive transport over the same distance, whether through the plug or host rock, is conservatively estimated to be significant only for a time >850 000 yr.

Physicochemical factors impacting CO2 sequestration in depleted shale formations: The case of the Utica shale

Abstract Fractured shale formations could serve as an attractive target formation for geologic carbon sequestration once they have been depleted of hydrocarbons. The low intrinsic permeability of the shale matrix could reduce the CO 2 leakage potential, the kerogen in the shale would provide a matrix within which the CO 2 can be permanently sorbed, and the infrastructure in place at gas production sites could all be leveraged to minimize costs. Here, a modeling framework previously developed by the authors to estimate the sequestration capacity of shale formations is extended to better capture the physicochemical realities associated with injecting CO 2 into fractured shale formations. The model uses CH 4 production data to fit key parameters about the formation and applies those to a unipore diffusion model to characterize the controlling gas transport processes. A number of parameters, including the gas diffusion coefficient, the ratio of adsorbed gas to free phase gas, water saturation and gas adsorption isotherms are considered and their effect on modeling estimates is explored. The model is found to be most sensitive to the ratio of adsorbed gas to the total gas which includes both adsorbed and free phase gas. The equilibrium adsorption parameters of CH 4 and CO 2 also have significant influence largely because published estimates for these parameters vary considerably. The effect of pore collapse following production was explored in terms of its effect on characteristic diffusion length. The results indicate that increasing this characteristics length by an order of five would triple the time it takes to complete the injection of CO 2 into the formation. Similarly, an increase in water content in the formation or in the ratio of free CH 4 to sorbed CH 4 would decrease the sequestration potential of the formation. Based on this improved constitutive understanding of the modeling inputs and the estimates, the CO 2 sequestration capacity of the Utica Shale was calculated and the results were compared with those from Marcellus Shale. The differences could be understood in terms of the distinct petrophysical properties of those two shale formations. This analysis provides recommendations about experimental directions that could be very useful for improving the accuracy of sequestration capacity models.

Effect of low pH exposure on Na+ regulation in two cichlid fish species of the Amazon

We evaluated the effects of acute exposure to low pH on Na+ regulation in two Amazon cichlids collected from natural ion-poor “blackwaters”, angelfish (Pterophyllum scalare) and discus (Symphysodon discus). Na+ uptake kinetic parameters, unidirectional Na+ fluxes, and net Cl− fluxes were determined at pH6.0 and 3.6. At pH6.0, both species presented low unidirectional Na+ flux rates, with kinetics showing a relatively low affinity for Na+ (angelfish Km=79, discus Km=268μmolL−1), with similar maximum transport capacities (Jmax~535nmolg−1h−1). Overall, there appeared to be high sensitivity to inhibition by low pH, yet low intrinsic branchial permeability limiting diffusive ion effluxes, resulting in relatively low net loss rates of Na+, the same strategy as seen previously in other blackwater cichlids, and very different from the strategy of blackwater characids. At low pH, Na+ uptake in angelfish was inhibited competitively (increased Km=166μmolL−1) and non-competitively (decreased Jmax=106nmolg−1h−1), whereas in discus, only a decrease in Jmax (112nmolg−1h−1) was statistically significant. An acute reduction in H+-ATPase activity, but not in Na+/K+-ATPase activity, in the gills of angelfish suggests a possible mechanism for this non-competitive inhibition at low pH. Discus fish were more tolerant to low pH than angelfish, as seen by lesser effects of exposure to pH3.6 on unidirectional Na+ uptake and efflux rates and net Na+ and Cl− loss rates. Overall, discus are better than angelfish in maintaining ionic balance under acidic, ion-poor conditions.