Permeability Trends Research Articles

A New Cleat Volume Compressibility Determination Method and Corresponding Modification to Coal Permeability Model

Coal is known as a dual-porosity media composed of cleat and matrix pore. Methane can be stored in the cleats or adsorbed on the inner surface of matrix pore. While fluid mobility is mainly controlled by the developed cleat network, methane desorption has a significant effect on cleat deformation. In the process of coalbed methane recovery, both reservoir compaction and matrix shrinkage will occur and have opposite effects on permeability evolutions. A variety of analytical permeability models have been developed to describe the transient characteristics of permeability in coals. In this study, three common permeability models are first revisited and evaluated against the experimental data under uniaxial strain condition. Shi–Durucan (S&D) model demonstrates the best performance among these models. However, constant cleat volume compressibility was used to assume for S&D model, and the generalization of S&D model is significantly limited. For ease of generalization, the relation between cleat volume compressibility and effective horizontal stress is re-derived and introduced to the derivation of permeability model. Since coal reservoirs usually demonstrate strong anisotropy and heterogeneity, the influences of elastic and adsorption properties are further tested to reveal the overall trend of permeability. The results show that S&D model and its modification with the main variable of effective horizontal stress have the best performances in matching the experimental data under uniaxial strain. The relationship between cleat volume compressibility and effective horizontal stress can be better reflected by the inverse proportional function. In addition, the strengths of reservoir compaction effect relative to matrix shrinkage effect in different models only vary with Poisson’s ratio, while their magnitudes are also affected by Young’s modulus. For a typical coal reservoir, the C&B and P&M models will observe a stronger permeability decline at the initial, while the improved P&M model will receive an earlier and more rapid rebound than the S&D and W&Z models.

An ichnological-assemblage approach to reservoir heterogeneity assessment in bioturbated strata: Insights from the Lower Cretaceous Viking Formation, Alberta, Canada

Facies-scale trends in porosity and permeability are commonly mapped for reservoir models and flow simulation; however, these trends are too broad to capture bed and bed-set heterogeneity, and there is a need to up-scale detailed, bed-scale observations, especially in low-permeability reservoir intervals. Here we utilize sedimentology and ichnology at the bed- and bedset-scale to constrain the range of porosity and permeability that can be expected within facies of the Lower Cretaceous Viking Formation of south-central, Alberta, Canada.Three main facies were recognized, representing deposition from the middle shoreface to the upper offshore. Amalgamated, hummocky cross-stratified sandstone facies (Facies SHCS) consist of alternations between intensely bioturbated beds and sparsely bioturbated/laminated beds. Trace fossil assemblages in bioturbated beds of Facies SHCS are attributable to the archetypal Skolithos Ichnofacies, and are morphologically characterized by vertical, sand-filled shafts (VSS). Bioturbated beds show poor reservoir properties (max: 10% porosity, mean: 85.1 mD) compared to laminated beds (max 20% porosity, mean: 186 mD). Bioturbated muddy sandstone facies (Facies SB) represent trace fossil assemblages primarily attributable to the proximal expression of the Cruziana Ichnofacies. Four ichnological assemblages occur in varying proportions, namely sediment-churning assemblages (SC), horizontal sand-filled tube assemblages (HSF), VSS assemblages, and mud-filled, lined, or with spreiten (MLS) assemblages. Ichnological assemblages containing horizontal (max: 30% porosity, mean: 1.28 mD) or vertical sand-filled burrows (max: 10% porosity, mean: 2.2 mD) generally have better reservoir properties than laminated beds (max: 20% porosity, mean: 0.98 mD). Conversely, ichnological assemblages that consist of muddy trace fossils have lower porosity and permeability (max 10% porosity, mean: 0.89 mD). Highly bioturbated, sediment churned fabrics have only slightly higher porosity and permeability overall (max: 15% porosity, mean: 1.29 mD). Bioturbated sandy mudstone facies (Facies MB) contain ichnofossils representing an archetypal expression of the Cruziana Ichnofacies. Four ichnological assemblages occur throughout Facies MB that are similar to Facies SB; SC, HSF, VSS, and MLS assemblages. The SC (max: 15% porosity, mean: 21.67 mD), HSF (max: 20% porosity, mean: 3.79 mD), and VSS (max: 25% porosity, mean: 7.35 mD) ichnological assemblages have similar or slightly lower values than the laminated beds (max: 20% porosity, mean: 10.7 mD). However, MLS assemblages have substantially lower reservoir quality (max: 10% porosity, mean: 0.66 mD).Our results indicate that the most likely occurrence of good reservoir characteristics in bioturbated strata exists in sand-filled ichnological assemblages. This is especially true within the muddy upper offshore to lower shoreface, where vertically-oriented trace fossils can interconnect otherwise hydraulically isolated laminated sandstone beds; this improves vertical fluid transmission. The results of this work largely corroborate previous findings about ichnological impacts on reservoir properties. Unlike previous studies, however, we demonstrate that the characteristics of the ichnological assemblage, such as burrow form and the nature of burrow fill, also play an important role in determining reservoir characteristics. It follows that not all bioturbated intervals (attributed to the same facies) should be treated equally. When upscaling bed-scale observations to the reservoir, a range of possible permeability-porosity values can be tested for model sensitivity and to help determine an appropriate representative elementary volume.

Description of gas transport in perfluoropolymer/SAPO-34 mixed matrix membranes using four-resistance model

Abstract Mixed matrix membranes (MMMs) are considered a viable solution for coupling the outstanding gas separation performances of inorganic porous materials with the ease of fabrication of polymeric membranes. It is known that the heterogeneous system may include a polymer shell of modified permeability surrounding the filler particles. In addition to that, modifications of the filler were evidenced from the comparison of the permeability of selective perfluoropolymer/SAPO-34 MMMs with existing extended Maxwell-like model calculations. This is in agreement with experimental and theoretical evidences of the presence of barriers to gas transport in the filler. A 4-phase approach for the transport of gas through MMMs is proposed here to quantitatively describe the modified layers, both within the Maxwell model and by finite element analysis. The four phases are: bulk and modified polymer and bulk and modified filler. The latter explicitly accounts for the barriers to mass transport. The changes in the modified layers are quantitatively determined by numerical optimization procedures based on Maxwell’s effective medium analytical formula and a finite element solution of the transport differential equations. The new approach is applied to the minimization of the residuals between each model and an extensive set of experimental permeability data (He, H 2 , CO 2 , N 2 ) through Hyflon AD60X/SAPO-34 MMMs, including different filler particle sizes (0.2, 1.5 and 2 μm), aspect ratios (2, 3 and 9) and loadings (20, 30, 35 and 44 vol%). A MMM subset containing impermeable fillers gives information on the transport properties of the sole matrix. Both the effective medium and the microscopic 4-phase approaches yield physically sound descriptions of the permeability trends, but FEM simulations also provide spatially resolved gas flows and concentrations throughout the systems. The focus on the real physical phenomena makes the four-phase approach a powerful tool for understanding the MMM transport and improving membrane design.

Characterizing convective heat transfer coefficients in membrane distillation cassettes

Accurate characterization of conductive heat transfer in membrane distillation (MD) is essential for determining membrane permeability, calculating thermal efficiency, and describing the effects of process parameters on permeate flux. This work demonstrates the effect of convective heat transfer on common MD performance metrics, reviews existing methods to model and measure convective heat transfer in MD cassettes, and proposes a novel experimental method to validate and or correct estimated convective heat transfer coefficients. This simple method compares trends in experimental permeability to those of theoretical permeability over a series of driving forces and/or flow conditions. We first validate this method using experimental data collected from two cassettes using a single membrane. After correcting the heat transfer coefficients for each cassette, the permeability of a single membrane is consistent across two different cassettes. We then validate this method for a single cassette using two different membranes, finding that the experimentally determined cassette correction factor is consistent within the cassette. Consistent and accurate reporting of cassette heat transfer coefficients will promote direct comparison of membrane and module performance across different MD systems.

Investigation on the Permeability Evolution of Gypsum Interlayer Under High Temperature and Triaxial Pressure

The permeability of the surrounding rock is a critical parameter for the designing and assessment of radioactive waste disposal repositories in the rock salt. Generally, in the locations that are chosen for radioactive waste storage, the bedded rock salt is a sedimentary rock that contains NaCl and Na2SO4. Most likely, there are also layers of gypsum \(( {\text{CaSO}}_{ 4} \cdot 2 {\text{H}}_{ 2} {\text{O)}}\) present in the salt deposit. Radioactive wastes emit a large amount of heat and hydrogen during the process of disposal, which may result in thermal damage of the surrounding rocks and cause a great change in their permeability and tightness. Therefore, it is necessary to investigate the permeability evolution of the gypsum interlayer under high temperature and high pressure in order to evaluate the tightness and security of the nuclear waste repositories in bedded rock salt. In this study, a self-designed rock triaxial testing system by which high temperature and pressure can be applied is used; the μCT225kVFCB micro-CT system is also employed to investigate the permeability and microstructure of gypsum specimens under a constant hydrostatic pressure of 25 MPa, an increasing temperature (ranging from 20 to 650 °C), and a variable inlet gas pressure (1, 2, 4, 6 MPa). The experimental results show: (a) the maximum permeability measured during the whole experiment is less than 10−17 m2, which indicates that the gypsum interlayer has low permeability under high temperature and pressure that meet the requirements for radioactive waste repository. (b) Under the same temperature, the permeability of the gypsum specimen decreases at the beginning and then increases as the pore pressure elevates. When the inlet gas pressure is between 0 and 2 MPa, the Klinkenberg effect is very pronounced. Then, as the pore pressure increases, the movement behavior of gas molecules gradually changes from free motion to forced directional motion. So the role of free movement of gas molecules gradually reduced, which eventually leads to a decrease in permeability. When the inlet gas pressure is between 2 and 6 MPa, the Klinkenberg effect dribbles away, and the gas flow gradually obeys to the Darcy’s law. Hence, the permeability increased with the increase in inlet gas pressure. (c) The curve of permeability versus temperature is divided into five stages based on its gradient. In the temperature range of 20–100 °C, the permeability of gypsum decreased slowly when the temperature decreased. From 100 to 200 °C, the permeability of gypsum increased dramatically when the temperature increased. However, a dramatic increase in permeability was observed from 200 to 450 °C. Subsequently, in the temperature range of 450–550 °C, due to closure of pores and fractures, the permeability of the specimens slowly lessened when the temperature increased. From 550 to 650 °C, the permeability of gypsum slightly increased when the temperature increased; (d) the micro-cracks and porosity obtained from the CT images show a high degree of consistency to the permeability evolution; (e) when compared to the permeability evolutions of sandstone, granite, and lignite, gypsum exhibits a stable evolution trend of permeability and has a much greater threshold temperature when its permeability increases sharply. The results of the paper may provide essential and valuable references for the design and construction of high-level radioactive wastes repository in bedded salt rock containing gypsum interlayers.

Synthesis and characterization of ionic liquid based mixed matrix membrane for acid gas separation

This work evaluates the potential of a mixed matrix membrane synthesized with 1-ethyl-3-methylimmidazolium-ethylsulphate [EMIM][EtSO4] a common ionic liquid (IL) blended with poly (ether-block-amide) (PEBA) elastomer to separate either hydrogen sulphide (H2S) or carbon dioxide (CO2) or both acid gasses (H2S and CO2) from its streams. Layer-by-layer deposition method was used to synthesize the defect-free blended membrane. The prepared membranes were characterized by field emission scanning electron microscopy (FESEM), fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) for physical and thermal properties. Several experiments were conducted by varying pressure and ionic liquid concentration at normal temperature for pure gases (H2S/CO2/CH4/Air). The presence of ionic liquid (5 wt%) shows higher H2S permeability of 540 barrer and a comparatively low CO2 permeability of 55 barrer at pressure of 7 kg/cm2 through the blended membrane due to higher H2S solubility (1.5 times more than CO2) in the same IL. The trend of permeability for different single gases was observed in the pattern following: H2S > CO2>Air > CH4. Ideal selectivity was 66.0 for H2S/CH4 and 24.0 for H2S/Air which is much higher than those for CO2 binary mixture such as CO2/CH4 (4.6) and CO2/Air (2.4). The addition of ionic liquid in the membrane matrix enhances the permeability of acid gases compared to pure PEBA membrane. Robeson’s diagram also shows the promising trends for the experimental points either crossing the upper bound line or getting nearer which highlight the pivotal role of IL in blended membrane.

Laboratory Investigation of Coal Deformation Behavior and Its Influence on Permeability Evolution During Methane Displacement by CO2

Geological sequestration of CO2 in coal seams is of significant interest to both academia and industry. A thorough laboratory investigation of mechanical and flow behaviors is crucial for understanding the complex response of coalbeds to CO2 injection-enhanced coalbed methane recovery (CO2-ECBM) operation. In this work, systematic experiments were carried out on cylindrical coal core specimens under different uniform confining stresses. The coal deformation caused by variations in effective stress as well as the sorption-induced matrix swelling/shrinkage was monitored. The competitive gas sorption characteristics and permeability evolution during the process of methane displacement by CO2 were also investigated. The measured volumetric strain results indicate that sorption-induced strain is the dominant factor in the coal deformation. The relationship between the volumetric strain and the adsorbed gas volume has been revealed to be a linear function. Experimental results obtained under different stress conditions suggest that higher confining stress suppresses the increase in both volumetric strain and the adsorbed gas volume. Furthermore, both methane displacement and CO2 injection are reduced when applying higher confining stresses. In addition, the permeability enhancement is heavily suppressed at higher confining stress. At a certain confining stress, a characteristic “U-shaped” trend of permeability is presented as a function of decreasing pore pressure. This study contributes to the understanding of coal deformation and its impact on permeability evolution under uniformly stressed condition, which has practical significance for CO2 sequestration and CO2-ECBM operation in the Qinshui basin.

Experimental Study of Drilling Fluid's Filtration and Mud Cake Evolution in Sandstone Formations

In real time drilling, the complexity of drilling fluid filtration is majorly attributed to changing mud rheology, formation permeability, mud particle size distribution (PSD), filter cake plastering effects, and geochemical reaction of particles at geothermal conditions. This paper focuses on quantifying the major effects as well as revealing their contribution toward effective wellbore stabilization in sandstone formations. We conducted an extensive experimental and analytical study on this subject at different levels. First, we used field application and the results as guides for our experiments. We have considered both oil-based mud and water-based mud. Next, we optimized the mud particle size distribution (PSD) by carefully varying the type, size, and concentration of wellbore strengthening material (WSM). Laboratory high pressure high temperature fluid loss tests were carried out on Michigan and Bandera Brown sandstones. The results from these tests identify the formation heterogeneity and permeability in successful wellbore stabilization. Filter cake permeability calculations, using the analytical model for linear systems, were consistent with filtration rates, and the expected trend of permeability declines with time. Finally, we investigated the evolution of internal filter cake and plastering mechanism, using scanning electron microscopic (SEM) analysis. The test results revealed a significant difference in the formation permeability impairment for the optimal mud PSD and WSM blend.

A Hierarchical Sampling for Capturing Permeability Trend in Rock Physics

Among all properties of reservoir rocks, permeability is an important parameter which is typically measured from core samples in the laboratory. Due to limitations of core drilling all over a reservoir, simulation of rock porous media is demanded to explore more scenarios not seen in the available data. One of the most accurate methods is cross correlation based simulation (CCSIM) which recently has broadly applied in geoscience and porous media. The purpose of this study is producing realizations with the same permeability trend to a real sample. Berea sandstone sample is selected for this aim. Permeability results, extracted from smaller sub-samples of the original sample, showed that classic Kozeny–Carman permeability trend is not suitable for this sample. One reason can be due to lack of including geometrical and fractal properties of pore-space distribution in this equation. Thus, a general trend based on fractal dimensions of pore-space and tortuosity of the Berea sample is applied in this paper. Results show that direct 3D stochastic modeling of porous media preserves porous structure and fractal behavior of rock. On the other hand, using only 2D images for constructing the 3D pore structures does not reproduce the measured experimental permeability. For this aim, a hierarchical sampling is implemented in two and three steps using both 2D and 3D stochastic modeling. Results showed that two-step sampling is not suitable enough, while the utilized three-step sampling occurs to be show excellent performance by which different models of porous media with the same permeability trend as the Berea sandstone sample can be generated.

Optimized pressure pulse-decay method for laboratory estimation of gas permeability of sorptive reservoirs: Part 2 - Experimental study

Since pressure measurements can be made more conveniently and accurately compared to fluid flowrate, the pressure transient technique is considered an advanced method for laboratory permeability measurement of unconventional gas reservoir rocks, specifically, gas shales, tight gas sand, and highly-stressed coalbed methane (CBM) reservoirs. However, two major factors, compressive storage and sorption effect, can lead to enormous error when testing sorptive rocks using the pulse-decay method (PDM). In order to overcome these, an optimized PDM experimental design of the transient technique for permeability testing of unconventional gas reservoir rocks was introduced in Part 1 of this two-part series. A modified mathematical model, describing one-dimensional fluid flow in porous media and best representing the optimized PDM design, was then presented to numerically investigate the fluid flow behavior and theoretically verify the applicability of Brace et al.’s solution in permeability calculation of sorptive rocks.To experimentally illustrate and verify the applicability of the optimized experimental design under best replicated in situ stress/strain conditions, a core of coal from San Juan basin was tested under triaxial stress. The experimental results showed that accurate and time-saving measurement can be achieved by choosing appropriate fluid reservoir volumes. Based on characterization of the pressure pulse decay plots, it was concluded that the effect of compressive storage on pressure variation in the up-/down-stream reservoirs and permeability calculation can be avoided when applying the optimized PDM.CO2 was used as the test fluid to investigate the effect of sorption on pressure variation due to its higher affinity towards coal than methane. The experimental results showed that sorption effect was eliminated, leading to accurate permeability values. A similar permeability trend with pressure drawdown, as previously measured for San Juan basin coal, was established. Also, comparison of the measured pressure decay plots and those obtained from computer simulation exhibited perfect matches, indicating that Brace et al.’s solution can be used for permeability estimation of sorptive rocks by adopting the optimized transient technique.

Controls on reservoir quality in exhumed basins – an example from the Ordovician sandstone, Illizi Basin, Algeria

Petroleum exploration in many North African intracratonic basins targets Early Paleozoic sandstones as the primary reservoir objective. These sandstones are often characterized by highly variable reservoir quality (0.0001–1000 mD), and the ability to predict and selectively target areas of enhanced porosity and permeability is crucial to unlock the hydrocarbon potential. The objective of this study is to characterize the primary controls on reservoir quality in an Ordovician field in the Illizi Basin of Algeria through detailed core and petrographic analysis, and establish if variations in thermal history across the field have a material impact on reservoir quality. The best reservoir quality is observed in facies where primary intergranular porosity has been preserved in fine to coarse grained quartzarenites with less than 1% fibrous illite. These lithologies are most commonly found within the high-energy, tidally reworked, post-glacial facies sandstones of the uppermost Ordovician succession. Observed differences in quartz cement volume within compositionally and texturally similar samples from the southern and northern parts of the field are interpreted to reflect variations in thermal exposure due to deeper burial. This interpretation is supported by field-wide numerical modelling of sandstone diagenesis. This study indicates that subtle variations in thermal history can have a material impact on the spatial trends in reservoir permeability. Thermal history, therefore, is an important consideration in reservoir quality studies in exhumed basins where variations in present-day burial depth will be a poor guide for evaluating reservoir quality risk across a basin or play.

Evaluation of Various Pulse-Decay Laboratory Permeability Measurement Techniques for Highly Stressed Coals

The transient technique for laboratory permeability measurement, proposed by Brace et al. (J Geophys Res 73:2225–2236, 1968) and widely used for conventional gas reservoir rocks, is the preferred method when testing low-permeability rocks in the laboratory. However, Brace et al.’s solution leads to considerable errors since it does not take into account compressive storage and sorption effect when applied to sorptive rocks, such as, coals and shales. To verify the applicability of this solution when used to characterize fluid flow behavior of coal, an in-depth investigation of permeability evolution for flow of helium and methane depletion was conducted for San Juan coals using the pressure pulse-decay method under best replicated in situ conditions. Three permeability solutions, Brace et al.’s (1968), Dicker and Smits’s (International meeting on petroleum engineering, Society of Petroleum Engineers, 1988) and Cui et al.’s (Geofluids 9:208–223, 2009), were utilized to establish the permeability trends. Both helium and methane permeability results exhibited very small difference between the Brace et al.’s solution and Dicker and Smits’s solution, indicating that the effect of compressive storage is negligible. However, methane permeability enhancement at low pressures due to coal matrix shrinkage resulting from gas desorption can be significant and this was observed in pressure response plots and the estimated permeability values using Cui et al.’s solution only. Therefore, it is recommended that Cui et al.’s solution be employed to correctly include the sorption effect when testing coal permeability using the transient technique. A series of experiments were also carried out to establish the stress-dependent permeability trend under constant effective stress condition, and then quantify the sole contribution of the sorption effect on permeability variation. By comparison with the laboratory data obtained under in situ stress/strain condition, it was verified that accelerated CBM production can be achieved by reducing the horizontal stresses.

Predicting permeability of low-enthalpy geothermal reservoirs: A case study from the Upper Triassic – Lower Jurassic Gassum Formation, Norwegian–Danish Basin

This paper aims at improving the predictability of permeability in low enthalpy geothermal reservoirs by investigating the effect of diagenesis on sandstone permeability. Applying the best fitted porosity–permeability trend lines, obtained from conventional core analysis, to log-interpreted porosity, is crucial in estimating reservoir permeability from logs. Petrographical analysis of sandstones from the Gassum Formation reveals lithological and diagenetic controls on plug permeability and porosity. Porosity–permeability trend lines vary with grain size for the shallowly buried sandstones (<2500m). Deeply buried sandstones (>2500m) from a steeply sloping porosity–permeability trend line since the pore-throat diminution due to quartz, ankerite and illite precipitation affects the permeability more than porosity, as evident from mercury injection curves. Permeabilities lower than the general trend for each grain-size group are caused by early diagenetic siderite cement, late diagenetic illitic clays and/or detrital clays. Permeabilities of sandstones deposited under humid well-vegetated conditions in marine and paralic environments, such as the Gassum Formation, are primarily dependent on burial history (maximum burial depth) and depositional environment.

Influence of Numerical Cementation on Multiphase Displacement in Rough Fractures

We present an application of 3D X-ray computed microtomography for studying the influence of numerical cementation on flow in a cement-lined rough-walled fracture. The imaged fracture geometry serves as input for flow modeling using a combination of the level set and the lattice Boltzmann methods to characterize the capillary-dominated fluid displacement properties and the relative permeability of the naturally cemented fracture. We further numerically add cement to the naturally cement-lined fracture to quantify the effect of increasing cement thickness and diminishing aperture on flow properties. Pore space geometric tortuosity and capillary pressure as a function of water saturation both increase with the numerically increased fracture cement thickness. The creation of unevenly distributed apertures and cement contact points during numerical cement growth causes the wetting and non-wetting fluids to impede each other, with no consistent trends in relative permeability with increasing saturation. Tortuosity of wetting and non-wetting fluid phases exhibits none to poor correlation with relative permeability and thus cannot be used to predict it, contrary to previous findings in smoother fractures.

Simulation of water impregnation through vertically aligned CNT forests using a molecular dynamics method.

The flow rate of water through carbon nanotube (CNT) membranes is considerably large. Hence, CNT membranes can be used in nanofluidic applications. In this work, we performed a molecular dynamics (MD) simulation of the introduction of water into CNTs in the CNT membranes, especially in vertically aligned CNT forests. The results showed that the Knudsen number (Kn) increased with an increasing volume fraction of CNT (VC) and was greater than 10−3 for each VC. Beyond this value, the flow became a slip flow. Further, the permeability increased as VC increased in the actual state calculated by the MD simulation, whereas the permeability in the no-slip state predicted by the Hagen–Poiseuille relationship decreased. Thus, a clear divergence in the permeability trend existed between the states. Finally, the flow enhancement ranged from 0.1 to 23,800, and the results show that water easily permeates as VC increases.

General Gas Permeability Model for Porous Media: Bridging the Gaps Between Conventional and Unconventional Natural Gas Reservoirs

Many field observations have indicated that permeabilities of both conventional and unconventional gas reservoirs are not constant when gas pressure drops. For conventional reservoirs, permeability will decrease while for unconventional gas rocks, the apparent permeability may increase as gas pressure decreases to a lower magnitude. Evolution trends of permeability for different natural gas reservoirs are distinct. These differences are observed by laboratory experiments of sandstones, coals, or shales. In this study, we present a general permeability model to bridge the gaps between conventional and unconventional gas reservoirs. This model coupled three critical factors namely effective stress, adsorption, and flow regimes to reflect dynamic performances of permeability. On the basis of specific reservoirs properties, the model degenerates into four reduced types. The first reduced model is applicable for reservoirs with lower adsorption capacity. The second reduced model is adopted by unconventional re...

Conditional reconstruction: An alternative strategy in digital rock physics

Digital rock physics (DRP) is a newly developed method based on imaging and digitizing of 3D pore and mineral structure of actual rock and numerically computing rock physical properties, such as permeability, elastic moduli, and formation factor. Modern high-resolution microcomputed tomography scanners are used for imaging, but these devices are not widely available, and 3D imaging is also costly and it is a time-consuming procedure. However, recent improvements of 3D reconstruction algorithms such as crosscorrelation-based simulation and, on the other side, the concept of rock physical trends have provided some new avenues in DRP. We have developed a modified work flow using higher order statistical methods. First, a high-resolution 2D image is divided into smaller subimages. Then, different stochastic subsamples are generated based on the provided 2D subimages. Eventually, various rock physical parameters are calculated. Using several subsamples allows extracting rock physical trends and better capturing the heterogeneity and variability. We implemented our work flow on two DRP benchmark data (Berea sandstone and Grosmont carbonate) and a thin-section image from the Grosmont carbonate formation. Results of realization models, pore network modeling, and autocorrelation functions for the real and reconstructed subsamples reveal the validity of the reconstructed models. Furthermore, the agreement between static and dynamic methods indicates that subsamples are representative volume elements. Average values of the subsamples’ properties follow the reference trends of the rock sample. Permeability trends pass the actual results of the benchmark samples; however, elastic moduli trends find higher values. The latter can be due to image resolution and voxel size, which are generated by imaging tools and reconstruction algorithms. According to the obtained results, this strategy can be introduced as a valid and accurate method where an alternative method for standard DRP is needed.

Integrated On-Chip Solenoid Inductors With Nanogranular Magnetic Cores

On-chip integrated solenoid inductors with nanogranular FeCoTiO magnetic cores have been fabricated. Both single-layered and multilayered magnetic cores with different geometries were studied. An inductance of 14.2 nH was achieved when using a multilayered core structure and keeping the device area of 0.14 mm2. The inductance of the magnetic core inductor is $\sim 14$ times that of the air core inductor, and the quality factor is 7.5. The permeability trends calculated from inductance were compared with the permeability spectra of the patterned FeCoTiO films measured by an improved shorted microstrip transmission line perturbation method. Consistent results have been obtained after considering the demagnetization effect of the magnetic core with high permeability.

A pilot study using dynamic contrast enhanced-MRI as a response biomarker of the radioprotective effect of memantine in patients receiving whole brain radiotherapy.

PurposeThis pilot prospective study sought to determine whether dynamic contrast enhanced MRI (DCE-MRI) could be used as a clinical imaging biomarker of tissue toxicity from whole brain radiotherapy (WBRT).Method14 patients who received WBRT were imaged using dynamic contrast enhanced DCE-MRI prior to and at 8-weeks, 16-weeks and 24-weeks after the initiation of WBRT. Twelve of the patients were also enrolled in the RTOG 0614 trial, which randomized patients to the use of placebo or memantine. After the unblinding of the treatments received by RTOG 0614 patients, DCE-MRI measures of tumor tissue and normal appearing white matter (NAWM) vascular permeability (Initial Area Under the Curve (AUC) Blood Adjusted) was analyzed. Cognitive, quality-of-life (QOL) assessment and blood samples were collected according to the patient's ability to tolerate the exams. Circulating endothelial cells (CEC) were measured using flow cytometry.ResultsFollowing WBRT, there was an increasing trend in the vascular permeability of tumors (p=0.09) and NAWM (p=0.06) with time. Memantine significantly (p=0.01) reduced NAWM AUC changes following radiotherapy. Patients on memantine retained (COWA p= 0.03) better cognitive functions than those on placebo. No association was observed between the level of CEC and DCE-MRI changes, time from radiotherapy or memantine use.ConclusionsDCE-MRI can detect vascular damage secondary to WBRT. Our data suggests that memantine reduces WBRT-induced brain vasculature damages.

Atomistic Hydrodynamics and the Dynamical Hydrophobic Effect in Porous Graphene.

Mirroring their role in electrical and optical physics, two-dimensional crystals are emerging as novel platforms for fluid separations and water desalination, which are hydrodynamic processes that occur in nanoscale environments. For numerical simulation to play a predictive and descriptive role, one must have theoretically sound methods that span orders of magnitude in physical scales, from the atomistic motions of particles inside the channels to the large-scale hydrodynamic gradients that drive transport. Here, we use constraint dynamics to derive a nonequilibrium molecular dynamics method for simulating steady-state mass flow of a fluid moving through the nanoscopic spaces of a porous solid. After validating our method on a model system, we use it to study the hydrophobic effect of water moving through pores of electrically doped single-layer graphene. The trend in permeability that we calculate does not follow the hydrophobicity of the membrane but is instead governed by a crossover between two competing molecular transport mechanisms.