Permeability Measurements Research Articles

Enhancing Bioequivalence Predictions with PAMPA Dissolution Using Formulations of Telmisartan

Traditionally, the pilot bioequivalence study is a generalpractice for generic drug development. However, due to its difficulty in differentiating the variation between subject and drug formulation for bioequivalence results. A new instrument called PAMPA Dissolution is proposed in this study to improve the correlation between in vitro and in vivo absorption forbioequivalence study. PAMPA Dissolution allows for the simultaneous measurement of drug dissolution (Cb) and permeation (Pe), two key parameters in oral drug absorption according to the validated equation F (drug absorbed) = Cb*Pe*Area. The use of Parallel Artificial Membrane Permeability Assay (PAMPA) eliminates the concern of subject variation. Biorelevant media further allows this device to simulate in vivo conditions closely. Brand and generic formulations of 40 mg telmisartan tablets were used in various studies to demonstrate the potential of PAMPA Dissolution in generic drug development. Bioequivalence predictions between brand and generic telmisartan from PAMPA Dissolution produced avalue（test/reference）for Cmax of 86.3% and a value for AUC of 91.4%, indicating that PAMPA Dissolution predictions conform with bioequivalence requirements. Other parameters such as stirring at different speeds and phospholipids concentrations for PAMPA are also included for optimal performance of the system. Based on these data, the PAMPA Dissolution system is reproducible, precise, and can therefore be applied in predicting bioequivalence study.

Enhancement of coercivity, permeability, and dielectric properties of Co0.2Zn0.3Ni0.5EuxFe2–xO4 ferrites for memory and high frequency devices

Spinel cubic ferrites have huge applications in memory and high frequency devices. For the improvement of these modern devices, the magnetic coercivity, permeability, and dielectric properties of a ferrite are the important issues. This article focuses on improving the magnetic coercivity, magnetic permeability, and dielectric properties of Co0.2Zn0.3Ni0.5EuxFe2–xO4 ferrites, where x = 0.00, 0.06, and 0.10. The X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX), vibrating sample magnetometer (VSM), and an impedance analyzer were used to characterize the structural, magnetic, and dielectric properties of the samples. The XRD patterns indicate the formation of spinel cubic structure of the samples with a secondary peak (EuFeO3) for Eu doped samples. The densities and porosities of the samples follow an inverse trend, where the doped samples’ lattice parameters are increased with the increment of rare earth Eu concentration. The FTIR analysis also proves the spinel cubic phase of the samples. The average grain size of the ferrites is obtained via FESEM images, and it is increased from 121 to 198 nm. VSM analysis confirms that doping of the Eu content also changes other hysteresis loop properties of Co0.2Zn0.3-Ni0.5EuxFe2–xO4 ferrites. Particularly, the coercivity of the Eu doped samples is greater than that of the mother alloy (x = 0.00). The EDX study shows that there is no impurity contamination in the ferrites. The permeability and dielectric measurements show an improved quality factor of the Eu-doped samples with low magnetic and dielectric losses. Frequency dependent resistivity and impedance analysis also show the improved nature. From the observed properties of the samples, all the investigated ferrites might be strong candidates for potential applications in memory devices, magnetic sensors, and high frequency applications.

Characterizations of Middle–Lower Triassic Reservoir Quality and Gas Accumulations in the Northeastern Margin of the Ordos Basin, China

New Middle–Lower Triassic gas reservoirs were found in the eastern margin of the Ordos Basin, which provides new possibilities for gas exploration in the Ordos Basin. However, there are few relevant studies on these gas reservoirs. In this study, we use porosity–permeability measurements, optical light microscopy, scanning electron microscopy, mercury intrusion capillary pressure experiments, core-scale low-field nuclear magnetic resonance experiments, fluid inclusion analysis, burial history reconstruction, organic geochemistry data, and wireline log data to systematically investigate the reservoir quality and accumulation pattern of Middle–Lower Triassic gas reservoirs. The Middle–Lower Triassic sandstones are mostly lithic arkose, with a small amount of feldspathic litharenite. In comparison to the upper Paleozoic tight sandstone, the Middle–Lower Triassic sandstones exhibit a superior pore structure and increased porosity and permeability. A significant portion of the Middle–Lower Triassic sandstones can be referred to as “conventional sandstones” (porosities >12% and permeabilities >1 mD). The source rocks of the Middle–Lower Triassic gas reservoirs are most likely the upper Paleozoic coal and organic-rich mudstone, and the accumulation of natural gas occurred in the Early Jurassic to Late Cretaceous. The gas accumulation in the sandstones of the Middle–Lower Triassic reservoirs was mainly driven by buoyancy. The initiation and extension of vertical faults with small displacement in the northeast margin of the Ordos Basin enabled gas to move through the faults from the deep upper Paleozoic source rocks to the Middle–Lower Triassic reservoirs. Since gas accumulation relies on buoyancy, conventional sandstone layers with good reservoir properties are more likely to reach high gas saturation and are the primary targets for exploration and development.

Permeability and fabric compaction in forming of fiber metal laminates

Significant fluid–structure interaction is present in fiber metal laminate forming with a low viscous matrix. A modular, process-inspired test setup is presented for one-dimensional saturated and unsaturated infiltration experiments for fiber metal laminates. Permeability measurements for different fabric orientations, fabric layers, and fiber volume contents show low scatter and good repeatability for fiber volume contents up to 65%. Fiber metal laminate specimens were formed by exchanging the mid-segment of the test setup with a punch and die. The stiffness differences between metal and fabric lead to remarkably high compactions in the bending radii, significantly reducing the flow during infiltration. Contrary to resin transfer molding processes, no formation of resin-rich zones along bending edges occurs due to the high normal pressures from metal forming. A numerical forming simulation was developed to predict the local fiber volume content. Comparing the experimental results with the numerical simulation shows that the high fiber volume content in the radii almost exclusively impacts the overall permeability. Implications for fiber metal laminate processing and modeling are outlined.

Straw management in small grain cereal crop production – The long-term effects on soil carbon and soil pore characteristics

Intensive tillage, non-diversified crop rotations and reduction in the return of organic residues to soil imply decreasing levels of soil organic carbon (SOC). Straw removal for (bio)energy production may increase in the future, given the attempts to phase out fossil energy sources. The decreasing SOC contents may deteriorate soil structure with adverse effects on soil ecosystem services. In this study, the long-term (28–36 years) effect of repeated experimentation with removal, burning or incorporation of straw was quantified at a coarse sandy and two sandy loam soils. At the end of experimentation, remolded soil was sampled and analyzed for SOC and a range of other chemical characteristics. Undisturbed soil cores were collected in the plough layer (10 cm depth) and the upper subsoil (30 cm depth). The cores were drained to a range of matric potentials (ψ), and air permeability measured at ψ = -30 and ψ = -100 hPa. At all three locations, incorporation of straw increased SOC by ∼ 13% and ∼ 15% relative to removal and burning, respectively. Leaving straw in the field (chopped or burned) increased exchangeable potassium found in the soil layer 0–80 cm depth with approximately 110–400 kg per hectare, highest for the most clay-holding soil. Addition of straw decreased soil dry bulk density and increased the volume of soil pores holding water available for plants (0.2–30 µm), while no significant effect was found for pores>30 µm. For the two sandy loam soils, air permeability tended to be highest for soil with incorporation of straw. For one of the sandy loam soils, the effect was significant when normalized to unit volume of air-filled pore volume. No effects of straw management were found on the volume of soil pore fractions in the subsoil. However, the measurements of air permeability indicated more continuous pores for straw-amended soil in the generally dense plough pan layer. The long-term effects of straw may affect important soil functions and ecosystem services.

Combining multimodal magnetic resonance brain imaging and machine learning to unravel neurocognitive function in non-neuropsychiatric systemic lupus erythematosus.

To study whether multimodal brain MRI comprising permeability and perfusion measures coupled with machine learning can predict neurocognitive function in young patients with SLE without neuropsychiatric manifestations. SLE patients and healthy controls (HCs) (≤40 years of age) underwent multimodal structural brain MRI that comprised voxel-based morphometry (VBM), magnetization transfer ratio (MTR) and dynamic contrast-enhanced (DCE) MRI in this cross-sectional study. Neurocognitive function assessed by Automated Neuropsychological Assessment Metrics was reported as the total throughput score (TTS). Olfactory function was assessed. A machine learning-based model (i.e. glmnet) was constructed to predict TTS. Thirty SLE patients and 10 HCs were studied. Both groups had comparable VBM, MTR, olfactory bulb volume (OBV), olfactory function and TTS. While after correction for multiple comparisons the uncorrected increase in the blood-brain barrier (BBB) permeability parameters compared with HCs did not remain evident in SLE patients, DCE-MRI perfusion parameters, notably an increase in right amygdala perfusion, was positively correlated with TTS in SLE patients (r = 0.636, false discovery rate P < 0.05). A machine learning-trained multimodal MRI model comprising alterations of VBM, MTR, OBV and DCE-MRI parameters mainly in the limbic system regions predicted TTS in SLE patients (r = 0.644, P < 0.0005). Multimodal brain MRI demonstrated increased right amygdala perfusion that was associated with better neurocognitive performance in young SLE patients without statistically significant BBB leakage and microstructural abnormalities. A machine learning-constructed multimodal model comprising microstructural, perfusion and permeability parameters accurately predicted neurocognitive performance in SLE patients.

CO2/Brine/Rock Interactions in the Cedar Keys-Lawson Formation

It has been reported that among the various geologic storage options, deep saline aquifers have the largest estimated capacity for CO2 storage. Obtaining knowledge of possible artificially geochemically induced changes to the permeability and porosity of host CO2 storage deposits will enable us to gain insight on long-term reservoir behavior under CO2 storage conditions. An experimental study of the interaction of CO2/brine/rock on saline formations was conducted in a static system under CO2 storage conditions. Chemical interactions in the Cedar Keys-Lawson Formation carbonate during exposure to CO2 and brine under sequestration conditions were studied. Samples were exposed to the simulated in-situ reaction conditions for one and six months. The samples were exposed to a model brine at 55 °C and CO2 pressure of 23.8 MPa (3,500 psig). Computed tomography (CT), x-ray diffraction (XRD), scanning electron microscopy (SEM)-energy dispersive x-ray spectroscopy (EDS), brine composition, core porosity, and core permeability analyses were conducted prior to and after the exposure experiments. Preliminary permeability measurements obtained from the core samples showed changes after they were exposed to CO2-saturated brine for one and six months. This observation suggests that mineral dissolution and mineral precipitation could occur in the host deposit altering its characteristics for CO2 storage over time. The 3D images of the pore space clearly illustrate the degree of dissolution that occurred during exposure. It is noted that the dissolution that occurred during the six-month exposure could have enhanced the connectivity between voids. This may contribute the increase of permeability after the CO2/brine exposure. In addition, the primary minerals comprising the core are dolomite and gypsum. Both minerals could dissolve in the CO2/brine environment resulting in the increase of permeability after the six-month exposure.

Measurement of solute permeability in the mouse spinal cord

BackgroundSensory perception and motor dexterity is coordinated by the spinal cord, which remains effective due to maintenance of neuronal homeostasis. This is stringently controlled by the blood spinal cord barrier. Therefore, the function of the spinal cord is susceptible to alterations in the microvessel integrity (e.g. vascular leakage) and/or perfusion (e.g. changes in blood flow). New MethodSpinal cord solute permeability was measured in anaesthetised mice. The lumbar spinal cord vertebra were stabilised and a coverslip secured to allow fluorescent tracers of vascular function and anatomy to be visualised in the vascular network. Fluorescence microscopy allowed real time measurements of vascular leakage and capillary perfusion within the spinal cord. ResultsCapillaries were identified through fluorescent labelling of the endothelial luminal glycocalyx (wheat germ agglutin 555). Real time estimation of vascular permeability through visualisation of sodium fluorescein transport was recorded from identified microvessels in the lumbar dorsal horn of the spinal cord. Comparison with existing method(s)Current approaches have used histological and/or tracer based in-vivo assays alongside cell culture to determine endothelium integrity and/or function. These only provide a snapshot of the developing vasculopathy, restricting the understanding of physiological function or disease progression over time. ConclusionsThese techniques allow for direct visualisation of cellular and/or mechanistic influences upon vascular function and integrity, which can be applied to rodent models including disease, transgenic and/or viral approaches. This combination of attributes allows for real time understanding of the function of the vascular network within the spinal cord.

An impedance based microfluidic sensor for evaluation of individual red blood cell solute permeability

—In this paper, we investigate a microfluidic based sensing device for cell membrane permeability measurements in real time with applications in rapid assessment of red blood cell (RBC) quality at the individual cell level. The microfluidic chip was designed with unique abilities to line up the RBCs in the centerline of the microchannel using positive dielectrophoresis (p-DEP) forces, rapid mixing of RBCs with various media (e.g. containing permeating or nonpermeating solutes) injected from different inlets to achieve high mixing efficiency. The chip detects the impedance values of the RBCs within 0.19 s from the start of mixing with other media, at ten electrodes along the length of the channel and enables time series measurements of volume change of individual cell caused by cell osmosis in anisosmotic fluids over a 0.8 s postmixing timespan. This technique enables estimating water permeability of individual cell accurately. Here we first present confirmation of a linear voltage-diameter relationship in polystyrene bead standards. Next, we show that under equilibrium conditions, the voltage-volume relationship in rat red blood cells (RBCs) is linear, corresponding to previously published Boyle van ‘t Hoff plots. Using rat cells as a model for human, we present the first measurement of water permeability in individual red blood cells and confirm that these data align with previously published population level values for human RBC. Finally, we present preliminary evidence for possible application of our device to identify individual RBCs infected with Plasmodium falciparum malaria parasites. Future developments using this device will address the use of whole blood with non-homogenous cell populations, a task currently performed by clinical Coulter counters.

Influence of Equation Nonlinearity on Pulse-Decay Permeability Measurements of Tight Porous Media

Influence of Equation Nonlinearity on Pulse-Decay Permeability Measurements of Tight Porous Media

Electromagnetic Performance of NiMgCuZn Ferrite for Hyperthermia Application in Cancer Treatment.

Ferrite with high permeability, high magnetic loss, and a low Curie temperature is a highly promising material for hyperthermia applications in cancer treatment. In this work, Ni(0.29-x)MgxCu0.14Zn0.60Fe1.94O3.94 (NiMgCuZn) ferrites were prepared at different Mg ion concentrations. The dependence of the Mg ion contents on the crystal structure, magnetic, and permeability properties of NiMgCuZn ferrite was investigated. Structural characterization showed a high crystallinity of the materials and an increase in the lattice constant with the Mg ion content. The magnetic hysteresis loops revealed that the saturation magnetization decreased with an increasing Mg content. Furthermore, the permeability measurements showed an increase in permeability and magnetic loss with the doping of Mg. More importantly, the Curie temperature of the NiMgCuZn ferrite decreases with the Mg ion content and reaches 42.37 °C for x = 0.26 as well as a real permeability of ∼797.88@1 MHz and a magnetic loss of 0.316@1 MHz, which meet the requirements of tumor hyperthermia.

The Effect of Stereoregularity and Adding Irganox 1076 on the Physical Aging Behavior of Poly(1-trimetylsilyl-1-propyne).

The effect of the stereoregularity of poly(1-trimethylsilyl-1-propyne) [PTMSP] (cis-content from 50 to 90%) on physical aging was investigated by measurement of the gas permeability. Films from pure PTMSP as well as those with the addition of the antioxidant Irganox 1076 were exposed to the air. The permeability of pure PTMSP films increases with an increase in cis-stereoregularity and correlates with an increase in interchain distances (according to X-ray analysis). For pure PTMSP films, the most significant aging (up to 50% of permeability drop) was observed for polymers with mixed microstructure, and the slowest aging (10-30% of permeability drop) was observed for polymers with cis-regular structure. For PTMSP films with added Irganox 1076, some decrease in permeability with time is also observed. The addition of Irganox 1076 to PTMSP in mixed as well as cis-enriched configurations visibly slows down aging. In the case of cis-regular PTMSP with a slow aging rate, the introduction of an antioxidant does not provide any advantages. The high stability of cis-regular PTMSP demonstrates the possibility of obtaining more stable membrane materials with the highest equilibrium state of the polymer selective layer prepared by casting solution.

Quantification of the impact of pore pressure on relative permeability curves utilizing coreflood unit with gamma ray scanning capability

Physics of multiphase flow in porous media at Darcy scale heavily relies on the concept of relative permeability. Moreover, relative permeability is an important input parameter for numerical reservoir simulation for multiphase flow in porous media. Often fixed set of relative permeability curves is applied for the entire complex large-scale reservoir models whilst the pressure typically declines during a field’s production. In this study, we are experimentally focusing on investigating the effect of high pressures on relative permeability curves.We use a state-of-the-art custom-made relative permeability steady-state flow system with integrated gamma-ray scanning. We limit the fluids to a model oil, brine, and rock to avoid any secondary effects of fluid-rock interactions, such as wettability alteration, asphaltenes, and gas-dissolution, miscibility, and interaction of phase behavior and flow. We run the relative permeability scans at a fixed temperature (isotherm) and at several pore pressure values (isobars), such as 2000, 4000, 6000, and 8000 psi with fixed and variable net confining pressures. To be able to perform the analysis more diligently, we observe the in-situ phase saturations via two methods: mass balance and gamma-ray scanning. The resulting relative permeability curves are then compared to each other to examine the impact of pressure. We did not observe significant pressure effect on relative permeability measurements in simple model system used in this work, where minimal fluid-fluid and fluid-rock interactions occur. However, the outcome of this work should not be extended to more complex systems where strong fluid-fluid and rock-fluid interactions take place, such as gas flooding with strong solubility effects, and chemical flooding.Systematic analysis of the pressure effect on relative permeability is extremely scarce in the literature, even though the pressure varies significantly in the reservoir during the lifetime of the field. Therefore, it is essential to understand pressure effect on relative permeability under well controlled laboratory conditions. The outcomes of this paper may help engineers to improve their model predictions during field development and therefore decision-making processes.

Analysis of PFAS in Locally Acquired Food Containers

The measurement of intestinal permeability is important for diagnoses of diseases of the gastrointestinal tract, such as Crohn’s disease. The gold standard for measurement of intestinal permeability is the dual sugar absorption test, which measures the urinary or blood concentrations of two orally administered sugars, a monosaccharide and a disaccharide, over a period of time. The lining of the small intestine allows monosaccharides to cross into the bloodstream, but the larger disaccharide is not permitted to cross the intestine unless the barrier is compromised. The permeability of the lining is measured by a ratio between select monosaccharides and disaccharides, and this indicates the overall status of the small intestine. In order to study the effects of resistance exercise on intestinal permeability in human subjects, we developed a liquid chromatography tandem mass spectrometry (LC–MS/MS) method for the analysis of saccharides in blood plasma. The analytes included rhamnose, a monosaccharide not commonly found in food, and lactulose, a disaccharide. A trisaccharide, raffinose, was used as an internal standard. The method was robust, and had consistent reliability.

Investigating the contribution of cytokinesis to population-based measurements of epithelial Leak Pathway permeability

The mechanism mediating the paracellular movement of macromolecules across epithelial cell layers, the Leak Pathway, remains poorly understood. Two recent studies have demonstrated that epithelial cell cytokinesis allows the transient paracellular passage of macromolecules (Stephenson et al. 2019. Dev Cell 48:445-459, Richter et al. 2022. Ann NY Acad Sci 1516:151- 161). It is unclear, however, if this cytokinesis-mediated transepithelial passage of macromolecules can contribute significantly to the Leak Pathway permeability measured in a post-confluent epithelial cell population. The renal epithelial cell line, Madin Darby Canine Kidney (MDCK II), develops tight junctions and forms a typical paracellular permeability barrier upon reaching a confluent density. MDCK II cells have been reported to maintain a basal rate of cell proliferation, even in post-confluent cell populations. To investigate the role of cytokinesis in contributing to population-based measurements of Leak Pathway permeability, we examined the effect of arresting and releasing cytokinesis in post-confluent populations of MDCK II cells on Leak Pathway permeability. We confirmed that post-confluent populations of MDCK II cells exhibit a low level of cell proliferative activity. Leak Pathway permeability was determined by measuring the flux of 20 kDa fluorescein-dextran across post-confluent populations of MDCK II cells grown on permeable membrane filters. Inhibiting cytokinesis of MDCK II cells by overnight treatment with RO-3306, a CDK-1 inhibitor, decreased modestly the paracellular flux of 20 kDa fluorescein-dextran compared to untreated cell populations. Washing out RO-3306 1 hour prior to the flux assay produced an increase in paracellular flux of 20 kDa fluorescein-dextran to a level higher than that observed in untreated cell populations. Our results support the working hypothesis that cytokinesis can contribute to Leak Pathway permeability measured in epithelial cell populations. They suggest that more proliferative epithelial cell populations will exhibit higher rates of Leak Pathway permeability compared to epithelial cell populations with very low levels of proliferative activity. The significant Leak Pathway permeability measured in MDCK II cell populations maintained in the presence of RO-3306 suggests that cytokinesis is not the sole mechanism mediating Leak Pathway permeability across epithelial cell populations. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Differentiating between fresh and frozen-thawed fish fillets by muscle fibre permeability measurement

There is no comprehensive method for differentiating between fresh and frozen-thawed fish fillets. This is an ongoing problem, particularly in relation to regulations. In this study, we showed the relevance of using the properties of mitochondria to discriminate fresh fish fillets from frozen-thawed fish fillets. The use of red muscle fibres of Gilthead sea bream allowed us to leave mitochondria in their physiological environment and to avoid possible alterations of mitochondrial membranes during isolation steps. The impact of freezing on fillets was evaluated by measuring the permeability of fibres and mitochondrial membranes to nicotinamide adenine dinucleotide + hydrogen (NADH). NADH permeability of fresh fillet fibres stored at 4 °C was compared to the permeability of fibres extracted from frozen-thawed fillets. Two approaches were used to measure permeability changes: a spectrophotometric method that measured consumption of NADH by complex I, and an oxygraphic approach that measured stimulation of O2 consumption by NADH. Fibres from frozen-thawed fillets were more permeable to NADH and were less sensitive to the permeabilizer alamethicin. The sensitivity of this method allowed us to clearly detect red muscle fibres from frozen-thawed fish versus fresh fish fillets.

Robust reservoir identification by multi-well cluster analysis of wireline logging data

A novel clustering method is applied to well logs for improved rock type identification in hydrocarbon formations. For grouping the objects in the multi-dimensional data space, we propose a Most Frequent Value (MFV) based clustering technique applied to natural gamma ray, bulk density, sonic, photoelectric index, and resistivity logs. The MFV method is a robust estimator, which assists in finding the cluster centers more reliably than a more noise sensitive K-means clustering approach. The result of K-means cluster analysis highly depends on the choose of the initial centroids. To reduce the risk of inappropriately chosen starting values, we apply a histogram-based selection method to give the best position of the initial cluster centers. We assure the robustness of the solution by calculating the centroid as the MFV of the cluster elements and defining the overall deviation of cluster elements from the center by a weighted Euclidean (Steiner-) distance. The proposed workflow relies on a fully automated weighting of the cluster elements, which does not require a constraint on the statistical distribution of the observed variables. The processing of synthetic data shows high noise rejection capability and efficient cluster recognition even beside considerable amount of outlying and missing data; the accuracy is measured by the difference between the estimated and the exactly known distribution of cluster numbers. The clustering tool is first applied to single borehole data, then the procedure is extended to multi-well logging datasets to reconstruct the multi-dimensional spatial distributions of clusters revealing the lithological and petrophysical characteristics of the studied formations. A large in situ dataset acquired from several boreholes traversing Hungarian gas-bearing clastic reservoirs of Miocene age is analyzed. The accuracy of the field results is confirmed by core permeability measurements, independent well log analysis and a gradient metrics characterizing the noise rejection capability of the clustering method.

Water Permeability Measurements by Steady-State and Pulse Decay Methods on the Callovo-Oxfordian Claystone and Impact on its Mechanical Properties

Water Permeability Measurements by Steady-State and Pulse Decay Methods on the Callovo-Oxfordian Claystone and Impact on its Mechanical Properties

UV-curable polyimide/layered silicate films with improved barrier properties for the protection of semiconductor chips

Polyimide/layered silicate films can be used to protect semiconductor chips against gas and moisture permeation to prevent corrosion followed by failure of the electronic chip. The layered silicates in these films are used as barrier pigment to extend the diffusion pathway and to improve the barrier properties. However, the exfoliation of the silicates has an essential impact on the quality of the barrier. Films prepared from polyimide matrix with layered silicates were investigated as well as the distribution and orientation of silicate particles in the UV-cured film and the correlative mechanisms while hardening. The films were characterized by a variety of methods including SEM, FTIR, TGA, water vapor diffusion (WVD) and oxygen permeation measurement. The prepared films using polyimide / layered silicates nanocomposites showed a reduction of WVD and oxygen permeation of 30% and 80%, respectively. Results demonstrated that polyimide/layered silicate nanocomposite could be used as barrier coating to reduce the permeation of moisture and gases.

“Double sweet spot” identification method via cluster analysis of petrophysical properties from well logg data: A case study of a tight sandstone reservoir

In recent years, interest in unconventional resource plays has grown substantially due to horizontal drilling and hydraulic fracturing techniques. However, the high cost of drilling, choosing the right locations for perforation intervals during hydraulic fracturing is a crucial issue. Therefore, identifying so called “sweet spot” with high potential for hydrocarbon production plays an important role in oil and gas industry. In this study a new “double sweet spot” identification method using cluster analysis of well-logged petrophysical properties of facies is presented. Firstly, an engineering sweet spot identification method based on geophysical responses parameters (brittleness index and permeability) is introduced to classify the target zone. Triaxial compression tests are performed to obtain the static Young's modulus and Poisson's ratio of the rock samples. To calculate dynamic Young's modulus and Poisson's ratio, a novel model for determining interval transit time of S-wave is proposed based on the multiple linear regression theory according to well logging data. By performing the cluster analysis, an intersection diagram of permeability and calculated normalized Rickman's brittleness is built and then engineering sweet spots in target zone are characterized based on well-logged petrophysical properties of facies. By plotting the intersection diagram of porosity and oil saturation based on the cluster analysis theory, geological sweet spots in target zone were characterized and four types of rock petrophysical facies are divided: Sandstone A (So＞48%, 8＜φ＜19%); Sandstone B (31＜So＜48%, 6＜φ＜18%); Sandstone C (18＜So＜31%, 8＜φ＜20%) and Sandstone D (0＜So＜18%, 8＜φ＜17%). Secondly, target formation classification is carried out using a proposed geological sweet spot identification method based on reservoir physical parameters (oil saturation and porosity). The relationship between core electrical resistivity and water saturation is determined by traditional Archie's formula and then an oil saturation prediction model in target reservoir is established. Based on the experimental porosity and permeability measurements of 47 core samples and well logging data, a porosity interpretation model is proposed. By plotting the intersection diagram of porosity and oil saturation based on the cluster analysis theory, geological sweet spots in target formation are characterized and four types of rock petrophysical facies are given: Sandstone A (K＞0.1mD, BI＞38); Sandstone B (K＞0.1mD, 33＜BI＜38); Sandstone C (K＞0.1mD, BI＜33) and Sandstone D (0.01＜K＜0.1mD, 10＜BI＜60). The integrated “double sweet spot” identification results of Well 1 in Daqing tight sandstone oil reservoir are given. Rock AA is the most favorable type of petrophysical rock facies and rock DD is the worst favorable type of petrophysical rock facies. Finally, an integrated “double sweet spot” identification method proposed in this study was applied to screen proper interval candidates during refracturing operation in a tight sandstone oil reservoir in China. After refracturing operation a gradually increase of average oil production in well group was found from 1.10 t/d to 5.63 t/d. This novel “double sweet spot” identification method has applicability in other tight oil reservoirs around the world.