RELIABLE QUANTIFICATION OF PORE GEOMETRY IN CARBONATE ROCKS USING NMR AND ELECTRICAL RESISTIVITY MEASUREMENTS FOR ENHANCED ASSESSMENT OF PERMEABILITY AND CAPILLARY PRESSURE

Reliable and real-time assessment of directional permeability and saturation-dependent capillary pressure are utterly important because they significantly affect the exploitation strategies. Conventional well-log-based methods (e.g., NMR-based, saturation-height analysis, resistivity-based, correlation-based) are either highly dependent on calibration efforts or rely on model parameters which are difficult to obtain in real-time and make them dependent on core measurements. Moreover, most conventional methods for assessment of directional permeability and saturation-dependent capillary pressure fail in the presence of multi-modal pore-size distribution. Recent publications suggested that integration of transverse Nuclear Magnetic Resonance (T2 NMR) and resistivity measurements enables assessment of pore-throat-size distribution as well as permeability and capillary pressure. However, the reliability of these methods is questionable in rocks with complex/multi-modal pore geometry. The objectives of this paper include (a) reliably estimating a variable constriction factor (a geometric parameter which relates the pore- and throat-size) in rocks with complex pore geometry to accurately quantify pore geometry, which is the main contribution of this work, (b) developing a new rock physics workflow for integrating NMR and electrical conductivity for assessment of permeability and capillary pressure that takes into account a variable constriction factor, and (c) verifying the reliability of the introduced workflow using core scale measurements. The proposed workflow starts with calculating pore-body-size distribution from NMR T2 distribution. Then, we combine electrical resistivity and pore-size distribution to estimate the distribution of constriction factor in the pore structure. Next, we determine pore- throat-size distribution using the estimated variable constriction factor. We then introduce a new permeability model which takes variable constriction factor into account. The inputs to the permeability model include throat-size distribution, tortuosity, and porosity. Finally, we calculate saturation-dependent capillary pressure using the estimated throat-size distribution. We successfully verified the reliability of the introduced workflow in the core-scale domain in carbonate rock samples with complex pore structure. The permeability estimates obtained by the new workflow yielded less than 7% average relative error when compared against core measurements. We also observed a good agreement between the throat-size distribution and capillary pressure estimated from the new workflow and the ones acquired from MICP (mercury injection capillary pressure) measurements. Results also confirmed that integration of a variable constriction factor improves directional permeability estimates compared to cases where an effective constriction factor was used to quantify pore-throat size distribution in rocks with multi-modal pore-size distribution.

Physicochemical Stability of Enriched Phenolic Fractions of Cyclopia genistoides and ex vivo Bi-directional Permeability of Major Xanthones and Benzophenones

Fractions of an ultrafiltered Cyclopia genistoides extract, respectively enriched in xanthones and benzophenones, were previously shown to inhibit mammalian α-glucosidase in vitro. The present study investigated ex vivo intestinal transport of these fractions, using excised porcine jejunal tissue, to determine whether the gut could be a predominant in vivo site of action. The major bioactive compounds, the xanthones (mangiferin, isomangiferin) and benzophenones (3-β-D-glucopyranosyliriflophenone, 3-β-D-glucopyranosyl-4-O-β-D-glucopyranosyliriflophenone) exhibited poor permeation in the absorptive direction with a relatively high efflux ratio (efflux ratio > 1). The efflux ratio of 3-β-D-glucopyranosyl-4-O-β-D-glucopyranosyliriflophenone (3.05) was similar to rhodamine 123 (2.99), a known substrate of intestinal P-glycoprotein 1 efflux transporters. Low epithelial membrane transport rates, coupled with efflux mechanisms, would effectively concentrate these bioactive compounds at the target site (gut lumen). Storage stability testing and moisture sorption assays of the xanthone-enriched fraction, benzophenone-enriched fraction, and ultrafiltered Cyclopia genistoides extract were performed to determine their susceptibility to physical and chemical degradation during storage. Hygroscopicity of the powders, indicated by moisture uptake, decreased in the order: benzophenone-enriched fraction (22.7%) > ultrafiltered Cyclopia genistoides extract (14.0%) > xanthone-enriched fraction (10.7%). 3-β-D-Glucopyranosylmaclurin, a minor benzophenone, was the least stable of the compounds, degrading faster in the benzophenone-enriched fraction than in ultrafiltered Cyclopia genistoides extract, suggesting that the ultrafiltered extract matrix may provide a degree of protection against chemical degradation. Compound degradation during 12 wk of storage at 40 °C in moisture-impermeable containers was best explained by first order reaction kinetics.

INVESTIGATIONS ON REPRESENTATIVE ELEMENTARY VOLUME AND DIRECTIONAL PERMEABILITY OF FRACTAL-BASED FRACTURE NETWORKS USING POLYGON SUB-MODELS

Since the directional permeability of fractured rock masses is significantly dependent on the geometric properties of fractures, in this work, a numerical study was performed to analyze the relationships between them, in which fracture length follows a fractal distribution. A method to estimate the representative elementary volume (REV) size and directional permeability ([Formula: see text] by extracting regular polygon sub-models with different orientation angles ([Formula: see text] and side lengths ([Formula: see text] from an original discrete fracture network (DFN) model was developed. The results show that the fracture number has a power law relationship with the fracture length and the evolution of the exponent agrees well with that reported in previous studies, which confirms the reliability of the proposed fractal length distribution and stochastically generated DFN models. The [Formula: see text] varies significantly due to the influence of random numbers utilized to generate fracture location, orientation and length when [Formula: see text] is small. When [Formula: see text] exceeds some certain values, [Formula: see text] holds a constant value despite of [Formula: see text], in which the model scale is regarded as the REV size and the corresponding area of DFN model is represented by [Formula: see text] (in 2D). The directional permeability contours for DFN models plotted in the polar coordinate system approximate to circles when the model size is greater than the REV size. The [Formula: see text] decreases with the increment of fractal dimension of fracture length distribution ([Formula: see text]. However, the decreasing rate of [Formula: see text] (79.5%) when [Formula: see text] increases from 1.4 to 1.5 changes more significantly than that (34.8%) when [Formula: see text] increases from 1.5 to 1.6 for regular hexagon sub-models. This indicates that the small non-persistent fractures dominate the preferential flow paths; thereafter, the flow rate distribution becomes more homogeneous when [Formula: see text] exceeds a certain value (i.e. 1.5). A larger [Formula: see text] results in a denser fracture network and a stronger conductivity.

A New Multiphysics Method for Simultaneous Assessment of Permeability and Saturation-Dependent Capillary Pressure in Hydrocarbon-Bearing Rocks

Summary Cost-effective exploitation of heterogeneous/anisotropic reservoirs (e.g., carbonate formations) relies on accurate description of pore structure, dynamic petrophysical properties (e.g., directional permeability, saturation-dependent capillary pressure), and fluid distribution. However, techniques for reliable quantification of permeability still rely on model calibration using core measurements. Furthermore, the assessment of saturation-dependent capillary pressure has been limited to experimental measurements, such as mercury injection capillary pressure (MICP). The objectives of this paper include developing a new multiphysics workflow to quantify rock-fabric features (e.g., porosity, tortuosity, and effective throat size) from integrated interpretation of nuclear magnetic resonance (NMR) and electric measurements; introducing rock-physics models that incorporate the quantified rock fabric and partial water/hydrocarbon saturation for assessment of directional permeability and saturation-dependent capillary pressure; and validating the reliability of the new workflow in the core-scale domain. To achieve these objectives, we introduce a new multiphysics workflow integrating NMR and electric measurements, honoring rock fabric, and minimizing calibration efforts. We estimate water saturation from the interpretation of dielectric measurements. Next, we develop a fluid-substitution algorithm to estimate the T2 distribution corresponding to fully water-saturated rocks from the interpretation of NMR measurements. We use the estimated T2 distribution for assessment of porosity, pore-body-size distribution, and effective pore-body size. Then, we develop a new physically meaningful resistivity model and apply it to obtain the constriction factor and, consequently, throat-size distribution from the interpretation of resistivity measurements. We estimate tortuosity from the interpretation of dielectric-permittivity measurements at 960 MHz by applying the concept of capacitive formation factor. Finally, throat-size distribution, porosity, and tortuosity are used to calculate directional permeability and saturation-dependent capillary pressure. We test the reliability of the new multiphysics workflow in the core-scale domain on rock samples at different water-saturation levels. The introduced multiphysics workflow provides accurate description of the pore structure in partially water-saturated formations with complex pore structure. Moreover, this new method enables real-time well-log-based assessment of saturation-dependent capillary pressure and directional permeability (in presence of directional electrical measurements) in reservoir conditions, which was not possible before. Quantification of capillary pressure has been limited to measurements in laboratory conditions, where the differences in stress field reduce the accuracy of the estimates. We verified that the estimates of permeability, saturation-dependent capillary pressure, and throat-size distribution obtained from the application of the new workflow agreed with those experimentally determined from core samples. We selected core samples from four different rock types, namely Edwards Yellow Limestone, Lueders Limestone, Berea Sandstone, and Texas Cream Limestone. Finally, because the new workflow relies on fundamental rock-physics principles, permeability and saturation-dependent capillary pressure can be estimated from well logs with minimum calibration efforts, which is another unique contribution of this work.

Design and Performance of a Directional Permeability Membrane

Directional permeability membranes were designed, fabricated, and tested with the potential application of facilitating drug delivery. Membranes were constructed from two porous polyimide sheets with offset pores and bonded with double sided tape with thickness values of 20 or 70 μm at the perimeter. The pores ranged in diameter from 0.25 to 1.0 mm and were cut using a laser micromachining apparatus. The pores were arranged in a square array with distance of 2 mm from center to center. The membranes were tested under pressure-driven water flow in the range of 0.01–0.10 m of H2O and flow rates were measured for two configurations: one with the thicker sheet upstream (forward direction) and one with the thinner sheet upstream (reverse direction) and the ratio of forward/reverse flow was calculated. In order to better understand membrane behavior, the maximum deflection of the thinner sheet was measured using an imaging system composed of a lens with small depth of field, digital camera, motorized linear translation stage, and a motion controller. Results show that in forward flow, by increasing hydrostatic pressure from 0.01 to 0.10 m H2O the mass flow rate increased by 40–55%. Conversely, increasing the hydrostatic pressure in the reverse direction from 0.01 to 0.10 m H2O considerably reduces the flow rate. The ratio of forward to reverse flow rate of the membrane varied in the range of 1.5 to 9529, depending on the pressure head.

Moisture safety of the construction with VCL using Hygrobrid technology

The purpouse of this work is to introduce the new patented Hygrobrid technology for moisture variable control layers. The new variable membrane has directional permeability capabilities. The tecnology ensures better safety for every construction even when the moisture levels are high during construction phase and also when the structure is subjected to extreme moisture during use. The technology minimises moisture development within the structure and maximises moisture transport out of the structure. This work is presenting the performance difference between first, second and third generation moisture variable membranes based on the computer simulation.