STOCHASTIC INTERPOLATION OF AQUIFER PROPERTIES OF HETEROGENEOUS GEOLOGIC MEDIA USING FRACTAL PROCESSES

The relevance of the work is conditioned by the need to use random processes based on Levi-distribution in describing the process of filtration of fluid flow in oil reservoirs and groundwater. These processes describe the filtration process more accurately than the fractal Brownian motion (fBm) and fractal Gaussian noise (fGn), especially with sharp changes in the geological environment. The purpose of the work is to show the advantages of using stochastic interpolation methods in geostatistics as compared to deterministic methods (in particular, the creaking method). Research methodology: theoretical analysis and experimental study of methods for probabilistic modeling of aquifer properties of geological media under conditions of uncertainty and limited availability of information on permeability and porosity of reservoirs. Results. It is shown that stochastic interpolation is most suitable for modeling dispersion characteristics of heterogeneous geological formations. The use of the assumption of Gaussian distribution in describing the process of fluid filtration is unreasonable. It is especially unreasonable in the presence of abrupt changes inherent in geological stratifications. Such changes are more adequately described by fractal Levi-motion (fLm). Stable Levidistribution of increments of the studied filtration characteristics of oil-saturated deposits showed a good coincidence with empirical data of numerous physical changes of geological structures in a wide range of spatial variables vertically and horizontally. Conclusions. The use of fLm – models represents a fundamentally new approach in geostatistics. The presence of heavy tails of the Levi-distribution of increments of the filtration characteristics of the layers and scaling the distribution parameters of this distribution allows us to react to sudden and sharp changes in rock properties. This effectively reproduces the strata and sedimentary deposits on the reservoir surface and characterizes heterogeneity in a wide range of distribution of spatial variables

High-pressure NMR spectroscopy in studies of the conformational composition of small molecules in supercritical carbon dioxide

© 2020 Elsevier B.V. An experimental approach in conducting NMR measurements at supercritical parameters of state is discussed. A novel design of the high-pressure NMR cell was developed which allowed eliminating the field inhomogeneity and, thus, increasing the sensitivity of the experiment at the supercritical state. Analysis of the MD simulations and NMR data showed that two conformers of ibuprofen dominate in the solution in supercritical CO2 along the critical isochore 1.3 ρcr(CO2). Conformer populations calculated from MD simulations and from NMR spectra agree with each other

Investigation of the Spatial Structure of Flufenamic Acid in Supercritical Carbon Dioxide Media via 2D NOESY

The search for new forms of already known drug compounds is an urgent problem of high relevance as more potent drugs with fewer side effects are needed. The trifluoromethyl group in flufenamic acid renders its chemical structure differently from other fenamates. This modification is responsible for a large number of conformational polymorphs. Therefore, flufenamic acid is a promising structural modification of well-known drug molecules. An effective approach in this field is micronization, employing “green” supercritical fluid technologies. This research raises some key questions to be answered on how to control polymorphic forms during the micronization of drug compounds. The results presented in this work demonstrate the ability of two-dimensional nuclear Overhauser effect spectroscopy to determine conformational preferences of small molecular weight drug compounds in solutions and fluids, which can be used to predict the polymorphic form during the micronization. Quantitative analysis was carried out to identify the conformational preferences of flufenamic acid molecules in dimethyl sulfoxide-d6 medium at 25 °C and 0.1 MPa, and in mixed solvent medium containing supercritical carbon dioxide at 45 °C and 9 MPa. The data presented allows predictions of the flufenamic acid conformational preferences of poorly soluble drug compounds to obtain new micronized forms

The Role of Hidden Conformers in Determination of Conformational Preferences of Mefenamic Acid by NOESY Spectroscopy

Mefenamic acid has been used as a non-steroidal anti-inflammatory drug for a long time. However, its practical use is quite limited due to a number of side effects on the intestinal organs. Conformational polymorphism provides mefenamic acid with unique properties regarding possible modifications obtained during the micronization process, which can improve pharmacokinetics and minimize side effects. Micronization can be performed by decompression of supercritical fluids; methods such as rapid expansion of the supercritical solution have proven their efficiency. However, this group of methods is poorly applicable for compounds with low solubility, and the modification of the method using a pharmaceutically suitable co-solvent may be useful. In our case, addition of only 2 mol% dimethyl sulfoxide increased the solubility remarkably. Information on the conformational state may be critically important for carrying out micronization. In this work, structural analysis and estimate of conformational preferences of mefenamic acid in dimethyl sulfoxide-d6 (at 25 °C and 0.1 MPa) and in a mixed solvent supercritical carbon dioxide + dimethyl sulfoxide-d6 (45 °C, 9 MPa) were performed based on nuclear Overhauser effect spectroscopy. Results show changes in the conformation fractions depending on the medium used. The importance of allowing for hidden conformers in estimating the conformational state was demonstrated in the analysis. Obtained results may be useful for improving micronization parameters

Dispersion of single-walled carbon nanotubes in alcohol-cholic acid mixtures

A procedure for dispersing single-walled carbon nanotubes (SWNTs) for the preparation of suspensions with high concentrations of individual nanotubes in various solvents was described. The most stable suspensions were obtained from a mixture of ethanol with cholic acid at an acid concentration of 0.018 mol/kg

Molecular Dynamics and Nuclear Magnetic Resonance Studies of Supercritical CO₂ Sorption in Poly(Methyl Methacrylate)

The study of supercritical carbon dioxide sorption processes is an important and urgent task in the field of “green” chemistry and for the selection of conditions for new polymer material formation. However, at the moment, the research of these processes is very limited, and it is necessary to select the methodology for each polymer material separately. In this paper, the principal possibility to study the powder sorption processes using 13C nuclear magnetic resonance spectroscopy, relaxation-relaxation correlation spectroscopy and molecular dynamic modeling methods will be demonstrated based on the example of polymethylmethacrylate and supercritical carbon dioxide. It was found that in the first nanoseconds and seconds during the sorption process, most of the carbon dioxide, about 75%, is sorbed into polymethylmethacrylate, while on the clock scale the remaining 25% is sorbed. The methodology presented in this paper makes it possible to select optimal conditions for technological processes associated with the production of new polymer materials based on supercritical fluids