Effect Of Increase In Pressure Research Articles

Continuous measurement of gas permeability in non-homogeneous hydrate reservoirs under effective pressure via a novel apparatus

Gas permeability is a key physical parameter to determine the exploitation efficiency of natural gas hydrate (NGH). However, the relevant research mainly focuses on the permeability of homogeneous hydrate reservoirs, there have been no studies of non-homogeneous hydrate reservoirs. Therefore, a novel permeability measurement apparatus was designed in this study, which used two core holders in parallel to achieve the spatio-temporal continuous measurements of gas permeability for non-homogeneous reservoirs. Marine soils obtained from the South China Sea were used to remold the non-homogeneous hydrate reservoirs, including two homogeneous hydrate reservoirs with water saturation of 40% (reservoir A) and 80% (reservoir B), respectively. The constant gas flow of 0.5 ml/s and constant back pressure of 3 MPa was carried out to measure the gas permeability. The experimental results showed that the gas permeability measured in this work had similar regularities with other literature data. When the effective pressure increased from 1 MPa to 6 MPa, the permeability of reservoir A, reservoir B, and non-homogeneous hydrate reservoir decreased from 15.2 mD to 10.9 mD, 10.5 mD to 4.6 mD, and 12.5 mD to 8.5 mD, respectively. In addition, the variation in the non-homogeneous coefficient showed three stages: 1–2 MPa stage, 2–3 MPa stage, and 3–6 MPa stage. What's more, the permeability damage rate of non-homogeneous reservoirs increased by nearly 35% with the increase of effective pressure. These findings obtained by this apparatus will enhance the understanding of gas permeability in the non-homogeneous hydrate reservoirs, and guide further field exploitation of hydrate reservoirs.

Comparison of the approaches to assessing the compressibility of the pore space

Integral and differential approaches to determining the volumetric compression of rocks caused by changes in the stress state are considered. Changes in the volume of the pore space of rocks are analyzed with an increase in its all-round compression. Estimation of changes in the compressibility coefficients of reservoirs due to the development of fields is an urgent problem, since the spread in the values of compressibility factors reduces the adequacy of estimates of changes in the physical properties and subsidence of the earth's surface of developed fields and underground gas storages. This parameter is key in assessing the geodynamic consequences of the long-term development of hydrocarbon deposits and the operation of underground gas storage facilities. Approaches to the assessment differ in the use of cumulative (integral) or local (differential) changes in porosity with a change in effective pressure. It is shown that the coefficient of volumetric compressibility of pores calculated by the integral approach significantly exceeds its value calculated by the differential approach, which is due to the accumulative nature of pore compression with an increase in effective pressure. It is shown that the differential approach more accurately determines the value of the pore compressibility coefficient, since it takes into account in more detail the features of the change in effective pressure.

Pressure dependence of elastic wave velocities of unconsolidated cemented sands

We have developed lower and upper bounds for the pressure-dependent elastic wave velocities of unconsolidated cemented sands, which are due to variations in cement layer thickness and direct grain contact area with effective pressure, respectively. Investigating the factors influencing these bounds, we have found that the elastic wave (P- and S-wave) velocities increase with the effective pressure, whereas their ratio ([Formula: see text]) decreases. The elastic wave velocities and their ratio have an almost linear relationship with the effective pressure for the lower bound, whereas that for the upper bound is nonlinear. For both lower and upper bounds, the sensitivities of the elastic wave velocities and their ratio to the effective pressure increase with decreasing precompacted pressure, cement elastic moduli, and cement volume content. By comparing the theoretical predictions with ultrasonic measurements on heavy-oil sands and cemented glass beads, we have validated that the experimental data fall within the proposed lower and upper bounds. The experimental data shift from the lower bound to the upper bound as the effective pressure increases, revealing that the grain compaction pattern changes with increasing effective pressure.

Identification of preferable method for the precise estimation of coefficient of consolidation (Cv) for coal ash

The exact determination of settlement and the time required to complete that settlement is very important from the safety point of view. There are several methods available to find the rate of consolidation that is highly dependent on the settlement versus time curve. Here, it has been attempted to identify the suitable method for the determination of the rate of consolidation of coal ash. After analyzing the value of the coefficient of consolidation (Cv) estimated from various methods, the rectangular hyperbola method (RH method) is found to be in best linear correlation between the measured Cv and calculated Cv. The coal ash shows an increment in Cv with the increase in effective pressure. The Cv obtained from the RH method is higher than the Cv obtained from Taylor’s and Casagrande method that helps in close approximation with field Cv. The precise determination of Cv helps in better prediction of the time required for the consolidation settlement that will increase the performance of the structure.

Experimental Study About Water Saturation Influence on Changes in Reservoirs Petrophysical Properties

Experimental determination of the physical properties of rocks under conditions simulating in situ reservoir conditions is of great importance both for the calculation of reserves and for the interpretation of well logging data. In addition, it is also important for the preparation of hydrocarbon field development projects. The study of the processes of changes in the petrophysical properties of the reservoir under controlled conditions allows not only to determine their reliability but also to evaluate the dynamics of these changes depending on the temperature and pressure conditions of the reservoir and the water saturation of the rocks. In this work, an evaluation of the dependence of the physical properties of hydrocarbon reservoirs on their water saturation (Sw) was carried out. Residual water saturation (Swr) was created in the rocks and the properties of these rocks were compared at the states of partial (25 %) and complete water saturation (100 %). The changes in petrophysical parameters of partially water saturated rocks during the increase in effective pressure were studied and estimates of these changes were obtained. The results showed that when the effective pressure is increased, the Swr increases by an average of 6 % compared to atmospheric conditions. This is accompanied by an increase in the velocity of longitudinal (by 51.9 % on average) and lateral waves (by 37.1 % on average). As residual water saturation increases, effective permeability decreases for both standard and reservoir conditions, with, gas permeability decreasing for both dry samples (by 23 % on average) and samples with residual water saturation (effective permeability decreases by 27 % on average). HIGHLIGHTS Changes in physical properties of hydrocarbon reservoirs by determining physical properties (permeability, porosity, elastic, electrical, deformation strength) under the standard conditions and in physical modelling of reservoir conditions and processes Assessment of the effectiveness of water saturation on the physical properties of the reservoir Comparisons between the petrophysical properties of reservoir core samples in which the pore space is fully saturated with the reservoir fluid model and samples with residual water saturation Experimental determination of the physical properties of rocks under conditions simulating in situ reservoir conditions Estimation of the changes in petrophysical parameters of partial water-saturated rocks during the increase in effective formation pressure GRAPHICAL ABSTRACT

Frictional Origin of Slip Events of the Whillans Ice Stream, Antarctica

AbstractIce sheet evolution depends on subglacial conditions, with the ice‐bed interface's strength exerting an outsized role on the ice dynamics. Along fast‐flowing glaciers, this strength is often controlled by the deformation of subglacial till, making quantification of spatial variations of till strength essential for understanding ice‐sheet contribution to sea‐level. This task remains challenging due to a lack of in situ observations. We analyze continuous seismic data from the Whillans Ice Plain (WIP), West Antarctica, to uncover spatio‐temporal patterns in subglacial conditions. We exploit tidally modulated stick‐slip events as a natural source of sliding variability. We observe a significant reduction of the till seismic wave‐speed between the WIP sticky‐spots. These observations are consistent with a poroelastic model where the bed experiences relative porosity and effective pressure increases of >11% during stick‐slips. We conclude that dilatant strengthening appears to be an essential mechanism in stabilizing the rapid motion of fast‐flowing ice streams.

Effect of Effective Pressure on the Permeability of Rocks Based on Well Testing Results

During the development of oil and gas fields, the permeability of the reservoirs decreases due to a decrease in reservoir pressure and an increase in effective pressure, as a result of which significant reserves of oil and gas remain in the reservoir. To predict the rate of decrease in oil production rates during field development and to respond quickly, it is necessary to know the law of permeability decrease with an increase in effective pressure. Existing methods for describing the change in the permeability of rocks were analyzed in the paper. Numerical analysis of the results of core studies from previously published papers and the results of field well testing on the examples of the north Perm region oil fields showed that in both cases, regardless of the type of rock and the type of reservoir, the change in permeability can be described by the same equations (exponential and power-law). Obtained equations can be used to predict changes in the permeability of terrigenous reservoirs of the north Perm region oil fields. At the same time, according to the results of well testing, an intensive decrease in permeability is observed with an increase in effective pressure. Analysis of the nature of permeability changes using the Two-Part Hooke’s Model showed that significant irreversible deformations are currently taking place in the formations of the oil fields under consideration. Predicting the change in permeability from effective pressure can allow to optimize the development of oil deposits.

The effect of pressure on electrical rock typing, formation resistivity factor, and cementation factor

As a key parameter in the calculation of fluid saturation, cementation factor (m) is routinely approximated using the Archie's equation. Numerous correlations and several techniques have been proposed to determine cementation factor, one of which is electrical rock typing. Besides hydraulic rock typing, which plays a significant role in modeling and numerical simulation of reservoirs, electrical rock typing refers to categorizing rocks into distinct groups based on similarity in electrical properties of the rocks. The current study focuses on the effective pressure impact on electrical rock typing. In addition, the effect of change in effective pressure due to production on petrophysical properties, and consequently rock capacity for transmitting electricity was studied. In this paper, 39 limestone samples were studied to analyze the effect of pressure on porosity (ϕ), formation resistivity factor (F), and m. Performance of the Archie's equation under different effective pressures was further examined. Considering the fact that an increase in effective pressure causes pore and throat deformation, the pressure impact on the rock quality for transmitting electricity was scrutinized. Then, the influence of effective pressure on electrical rock typing was studied. It was discovered that due to an increase in effective pressure, F and m increase while ϕ decreases. The rock quality for transmitting electricity and the effective pressure were found to be correlated through a second-order polynomial equation. It was further concluded that the electrical rock typing was affected by the changes in electrical efficiency, and the number of electrical rock types and the presence of samples in them were influenced by variations of the effective pressure. This was a noticeable point because different rock types require the adoption of different correlations for determining the parameters of the Archie's equation; therefore, realizing that each sample belongs to which rock type is essential. The findings of this study contributed to a better understanding of the impact of the effective pressure on Archie's parameters and petrophysical properties, leading to a method for determining fluid saturation under different effective pressures during the reservoir lifespan.

Hydro-mechanical properties of a low-clay shale with supercritical CO2 imbibition

The mechanical properties and permeability of shales after supercritical carbon dioxide (SC-CO2) imbibition are vital to shale gas production and CO2 sequestration in shale reservoirs. In this study, triaxial compressive strength tests, steady state permeability tests, and CT scanning tests are performed on shale samples with 30 days of SC-CO2 imbibition. The results show that minerals dissolution and precipitation occur during SC-CO2 imbibition. The porosity calculated by the digital core increases by 19.190%. The axial stresses of samples with or without SC-CO2 imbibition increase with increasing confining pressure. When the confining pressure changes between 5 and 20 MPa, the reductions range from 6 to 13% for strength and from 11.26 to 16.47% for Young’s modulus, respectively. The strength of the samples with or without imbibition agrees well with the Mohr–Coulomb criterion. The values of cohesion and internal friction angles are very close which indicates that shale samples with SC-CO2 imbibition can still refer to the failure criterion for samples without CO2 imbibition. The permeability of the sample after SC-CO2 imbibition increases exponentially with the increase in injection pressure and decreases exponentially with an increase of effective pressure. The permeability of the sample before and after imbibition is more sensitive to the change of pore pressure than confining pressure. SC-CO2 imbibition enhances the increase of permeability. The ratio of the shale permeability after imbibition to that before imbibition varies from the minimum of 42 times to the maximum of 827 times. The reduction of strength and increasing of permeability are beneficial for shale gas recovery.

Influencing factor analysis of the elastic properties of shale with rock-physical model including pressure effects

With the continuous petroleum exploration around the world, the target of exploration is converting from conventional to deep, unconventional reservoirs. The pressure condition on those new target layers is different from the conventional reservoir, and pressure is one of the important factors affecting the elastic moduli and velocities of shale reservoirs. Therefore, it is necessary to take pressure effects into consideration in rock-physics modeling. We initially adopted a novel iterative rock-physical modeling approach on the basis of pore space stiffness theory to analyze pressure’s influence on shale. Pore space stiffness theory assumes that pores own their own stiffness like the solid matrix of rocks, which is related to the effective pressure. We have implemented plenty of numerical analysis on the effect of pressure on shale and found out the most contributive factor to the moduli and velocities of shale. Our result indicates that when the effective pressure is smaller than the critical value, the elastic moduli and elastic wave velocities of shale increase significantly with the increase of effective pressure. The elastic moduli and velocities tend to be constant when the effective pressure goes beyond that critical value. By comparison, we found that the most contributive mineral in shale is clay, and the porosity has the greatest effect on elastic moduli and velocities when the mineral composition of shale stays unchanged. The influence of pressure is not as obvious as other factors in shale reservoirs with low porosity (lower than 10%) because pores occupy a relatively small percentage of the total volume.

Influence of Effective Stress on Absolute Permeability of Ultralow-Permeability Rocks

The great potential of unconventional hydrocarbon resources in the world is realized in shale formations represented by fractured low-permeability and ultralow-permeability reservoirs. The development of shale formations in the energy depletion mode leads to an increase in effective pressure, which has a significant effect on the permeability of low-permeability and ultralow-permeability reservoirs. A laboratory estimation of the influence of effective pressure on the absolute permeability of different litological compositions rocks with permeability from 0.1 nD to 1 mD was carried out. Absolute gas permeability was determined by the pulse decay method and the modified steady-state method under pressure conditions. The results showed that an increase in the effective pressure from 7 to 45 MPa leads to a decrease in the absolute permeability of low-permeability and ultralow-permeability reservoirs by 1.8 – 100 times, depending on the initial permeability of core samples and their lithology. Reliable correlations of absolute permeability and effective pressure for reservoirs of different types have been identified. Correlations can be used to design well flow rates for the entire period of shale formations development.

Effect of Pressure Increase on Macromolecules' Adsorption in Ion Exchange Chromatography.

In this study a new method for evaluating the pressure effect on separations of oligonucleotides and proteins on an anion exchange column was developed. The pressure rise of up to 500 bar was attained by coupling restriction capillaries to the column outlet to minimize differences in pressure over the column. Using pH transient measurements it was demonstrated that no shift in ion exchange equilibria occurs due to a pressure increase. Results from isocratic and gradient separations of oligonucleotides (model compounds) were evaluated by stoichiometric displacement and linear gradient elution model, respectively. Both elution modes demonstrated that for smaller oligonucleotides the number of binding sites remained unchanged with pressure rise while an increase for large oligonucleotides was observed, indicating their alignment over the stationary phase. From the obtained model parameters and their pressure dependencies, a thermodynamic description was made and compared between the elution modes. A complementary pattern of a linear increase of partial molar volume change with a pressure rise was established. Furthermore, estimation of the pressure effect was performed for bovine serum albumin and thyroglobulin that required gradient separations. Again, a raise in binding site number was found with pressure increase. The partial molar volume changes of BSA and Tg at the maximal investigated pressure and minimal salt concentration were −31.6 and −34.4 cm3/mol, respectively, indicating a higher rigidity of Tg. The proposed approach provides an insight into the molecule deformation over a surface at high pressures under nondenaturing conditions. The information enables a more comprehensive UHPLC method development.

Characterizing the Effects of Pore Pressure Reduction and Voids using X-ray CT Scan towards Physical Changes due to Static Loading

Peat soil is widely known as soil with very low compressive strength and poor in shear strength. When loaded, it is easy to deform and visually witnessed. To understand the vital means to study the characteristic of this rupture soil material, which is of great significance in determination of soil shear strength involving peat soil settlement where pore and voids diminished when loaded especially for embankment prediction. On this basis, static triaxial test has been carried out to simulate the loading phase while pore and void elements inspected through 2D X-ray CT scan. Through the process, peat and the relationship between loading, pore and physical changes are monitored. Measurements were performed on consolidated undrained condition with strain-controlled method under monotonic loading. The 2D X-ray CT scan pattern of the sample deformation was imaged before and after loading process. Sample height is 100 mm and diameter 50 mm in cylindrical shape. Physical changes are visualized, and the data showed that, pore and voids diminished by loading factor, leading pore pressure decrease with increase of effective pressure. Pore pressure developed down-trend characteristic. From the result, there is no volume change are disclosed when loaded. From 2D CT-scan shows that, the pore between peat particles diminished in volume after static loading and parallel to static loading process.

The influence of the stress state of rocks on the matrix and fracturing Permeability in the conditions of various lithologic-facial zones of the Turn-Famen oil deposits of the Upper Kama region

A series of core experiments made it possible to establish that for fractured samples with an increase in there stressed state (increase in effective pressure), there is a sharp decrease in reservoir properties. In the future, with a decrease (or complete removal) of the stress state, the filtration-capacitive properties of fractured reservoirs are not restored. The experiments have scientific and practical importance in terms of optimizing the technological mode of operation of producing wells in fractured turn-Famennian reservoirs.

Study on mechanical characteristics and damage mechanism of the Longmaxi Formation shale in southern Sichuan Basin, China

During the development of shale gas reservoirs, the mechanical parameters of shale rocks are greatly significant to guide reservoir drilling design, reservoir stimulation, scheme design, and wellbore stability evaluation. Compared with conventional gas reservoirs, the mechanical properties of shale gas reservoir are more complex and lack of the comprehensive understanding. In this study, the uniaxial and triaxial compression experiments of the Longmaxi shale in South China were conducted to understand the mechanical characteristics and damage mechanism of shale rocks. Combined with the characteristics of shale microstructure, the effects of the mechanical properties such as mineral composition, deformation, stress–strain, and fracture damage characteristics were analyzed and discussed. The results show that the stress–strain curves of shale are two main types of elastic deformation and elastic–plastic deformation. There is a significant difference in effective pressure of yield platform in different shale post-peak deformation. The effective pressure of rigid shale is 60 MPa while that of other shales is 30 MPa. With the increase of effective pressure, the increase of peak compressive strength decreases gradually, and the effect of effective pressure on compressive strength decreases gradually with the transition from the brittleness to the ductility. The higher the effective pressure of the brittleness to the ductility is, the greater the change of compressive strength with effective pressure is, and the smaller the compressive strength under low effective pressure is, the smaller the variation with pressure is. Shale rocks with relatively high brittleness under different effective pressures are mainly characterized by brittle split fracture dominated by tensile fracture, while other shales with low brittleness are dominated by single shear fracture plane.

Application of NMR to Test Sandstone Stress Sensitivity of the Dongfang X Gas Field, China

The stress sensitivity of reservoir rocks has captured considerable attention in the field of oil and gas development. In this paper, nuclear magnetic resonance (NMR) was employed to measure the T2 spectra of sandstone samples from Dongfang X gas field under different confining pressures. According to T2 values, the pores in sandstone samples were divided into macropores (right peak of T2 spectra) and micropores (left peak of T2 spectra), and the stress sensitivity of macropores and micropores were discussed separately. The results show that the increase of net effective stress will lead to the pore deformation of rock samples, and the pore deformation characteristics of rocks in different blocks under different net effective stress can be effectively analyzed by the NMR. As the net effective pressure increases, the compression amplitudes of rock samples in different blocks are almost equal, indicating that the reservoirs in the Dongfang X gas field have good homogeneity. In addition, the study rocks have a weak stress sensitivity, the general stress sensitivity of micropores is stronger than that of macropores. For the samples with high permeability (over 80mD), the compression amplitudes of macropores and micropores are relatively small and close, and the porosity losses are almost the same.

Реологическая модель строения земной коры (модель третьего поколения)

Introduction. The ground of the rheological Earth’s crust model with a barrier zone between its upper and middle parts is given. The zone is impermeable to fluids radically changes present-day understanding of the upper part lithosphere structure. A critical generalizing review for, earlier models of the continental crust structure and geological nature of K 1 geophysical interface, which proposed by different authors, are is commited for consideration. Metods. The information regarding the middle crust watering is presented. The data on electromagnetic deep probing indicate that in the middle and lower crust and, possibly, in the upper mantle the content of free water makes up about 1% in volume. Therefore, there is some kind of block which does not allow for the whole water to squeezed up into the upper part of the Earth’s crust, where an open crack-pore space is filled with water under hydrostatic pressure. So, clearly expressed hydrodynamic zoning exists in the continental Earth’s crust. This universal continental Earth’s crust zoning now is confirmed by geophysics and super-deep drilling, but it is not yet enough realized by a great number of geologists and geophysicists. Discussion. In the upper crust the rocks become harder with deepening, as the effective pressure increases and stronger and stronger press down them. Geophysical studies mark this fact by the growth speed of seismic wave spreading and the decrease of electrical inductance. Lower of the pores and cracks closing horizon (lower of the barrier) the picture sharply changes. Effective pressure is falling and rocks lose fully their hardening, becoming even less hard than at the day surface. Consequently, lower of the hardest upper crust bottoms under a dense impenetrable zone extremely weakened water-containing rocks are located. The earth crust turns out to be sharply stratified into (zones) not only by the water-presence, but even more contrastingly - by rheological (hardening) properties. At any even miserable mechanical movements and deformations at the boundary of hard and weak storeys disruptions and motions is inevitably occured. Conclusions. The importance of suggested model of the crust structure for the tectonics, petrology, ore-formation, hydrogeology, oil geology, seismicity as well as for the nuclear wastes and others is considered.

Improving fluid flow in geothermal reservoirs by thermal and mechanical stimulation: The case of Krafla volcano, Iceland

The magmatic-hydrothermal system at Krafla Volcano, North-East Iceland, is an important source of fluids exploited for geothermal energy. Here, we employ laboratory measurements to constrain the porosity and permeability of the main lithologies forming the reservoir, and investigate the impacts of different thermal and mechanical stimulation practices to improve fluid flow.Six main rock types were identified and sampled: three basalts (a dense and a porous lava, and a surficial dyke); a hyaloclastite; an obsidian; an ignimbrite; a felsite; and a gabbro. Permeability measurements were made in a hydrostatic cell using the steady-state flow method at a range of confining pressures (1–100 MPa). The measurements show that permeability generally increases with porosity, but that permeability may vary significantly for a given porosity, depending on the presence of pore connectivity and micro-fractures. We note that an increase in effective pressure results in a decrease in permeability due to closure of pre-existing cracks, abundant in some rocks. When unloading, samples fail to recover pre-loading permeability, as cracks do not necessarily entirely reopen. To further examine the hysteresis imposed by crack closure, we cyclically loaded/unloaded a felsite sample ten times by varying pore pressure which resulted in a further nonlinear decreases in permeability with each pressurisation cycle; thus an understanding of the pressurisation path may be a requirement to constrain fluid flow variations in geothermal systems.To test the effects of thermal stimulation on fluid flow, samples of dense basalt and felsite were thermally stressed by heating to 450 °C and cooling at different rates (in air, in water and at a controlled rate of <5 °C·min−1). The results show that the permeability of originally highly fractured rocks is not affected by thermal stressing, but originally unfractured rocks show a nonlinear increase in permeability with each thermal stressing cycle, especially with the largest thermal shock imposed by quenching in water; thus thermal stimulation may not be expected to result in a similar magnitude of permeability creation along the length of a borehole.Finally, following the permeability measurements on intact rocks, the Brazilian tensile testing method was employed to impart one and two (orthogonal) macro-fractures, and permeability was measured after each step. The creation of one macro-fracture strongly enhanced the permeability of the rock (especially dense rocks), resulting in a narrower range of permeability (as a function of porosity) for the fractured rocks. Imparting a second fracture had trivial additional impact on the permeability of the rock. Yet, the presence of fine fragments and possible minor offset of fracture interfaces was found to obstruct fracture closure, which resulted in higher permeability irrespective of effective pressure; thus hydraulic fracturing may locally increase fluid flow, especially when employing proppants to obstruct fracture closure and ensure a stable permeable network in a reservoir.We discuss the implications of the findings for a first order constraint on the permeability of the reservoir rock and the potential of thermal and mechanical stimulation methods on energy production in geothermal systems nested in active volcanic fields.

Effect of pressure variation on structural, elastic, mechanical, optoelectronic and thermodynamic properties of SrNaF3 fluoroperovskite

The effect of pressure variation on structural, electronic, elastic, mechanical, optical and thermodynamic characteristics of cubic SrNaF3 fluoroperovskite have been investigated by employing first-principles method within the framework of gradient approximation (GGA). For the total energy calculations, we have used the full-potential linearized augmented plane wave (FP-LAPW) method. Thermodynamic properties are computed in terms of quasi-harmonic Debye model. The pressure effects are determined in the range of 0–25 GPa, in which mechanical stability of SrNaF3 fluoroperovskite remains valid. A prominent decrease in lattice constant and bonds length is observed with the increase in pressure from 0 to 25 GPa. The effect of increase in pressure on band structure calculations with GGA and GGA plus Tran–Blaha modified Becke–Johnson (TB-mBJ) potential reveals a predominant characteristic associated with widening of bandgap. The influence of pressure on set of isotropic elastic parameters and their related properties are numerically estimated for SrNaF3 polycrystalline aggregate. Apart of linear dependence of elastic coefficients, transition from brittle to ductile behavior is observed as pressure is increased from 0 to 25 GPa. We have successfully obtained variation of lattice constant, volume expansion, bulk modulus, Debye temperature and specific heat capacities with pressure and temperature in the range of 0–25 GPa and 0–600 K. All the calculated optical properties such as the complex dielectric function ε(ω), optical conductivity σ(ω), energy loss function L(ω), absorption coefficient α(w), refractive index n(ω), reflectivity R(ω), and effective number of electrons neff, via sum rules shift towards the higher energies under the application of pressure.

Study of pressure variation effect on structural, opto-electronic, elastic, mechanical, and thermodynamic properties of SrLiF3

The structural, electronic, elastic, optical and thermodynamic properties of cubic fluoroperovskite SrLiF3 at ambient and high-pressure are investigated by using first-principles total energy calculations within the framework of Generalized Gradient Approximation (GGA), combined with Quasi-harmonic Debye model in which the phonon effects are considered. The pressure effects are determined in the range of 0–50GPa, in which cubic stability of SrLiF3 fluoroperovskite remains valid. The computed lattice parameters agree well with experimental and previous theoretical results. Decrease in lattice constant and bonds length is observed with the increase in pressure from 0 to 50GPa. The effect of increase in pressure on electronic band structure calculations with GGA and GGA plus Tran-Blaha modified Becke–Johnson (TB-mBJ) potential reveals a predominant characteristic associated with widening of bandgap. The influence of pressure on elastic constants and their related mechanical parameters have been discussed in detail. All the calculated optical properties such as the complex dielectric function Ԑ(ω), optical conductivity σ(ω), energy loss function L(ω), absorption coefficient α(w), refractive index n (ω), reflectivity R (ω), and effective number of electrons neff, via sum rules shift towards the higher energies under the application of pressure. Moreover, important thermodynamic properties heat capacities (Cp and Cv), volume expansion coefficient (α), and Debye temperature (θD) are predicted successfully in the wide temperature and pressure ranges.