Pressure Derivative Research Articles

Theories of complicated identifications exchange

The main objective of this study is to determine the pressure derivatives diagnoses for the infinite-conductivity horizontal well flow regimes identification which are not well studied so far in literature. The pressure derivatives diagnoses for the uniform-flux horizontal well flow regimes identification are fully studied in literature and presented here for comparison purposes only. The horizontal well flow regimes: early-radial, early-linear, late-radial, late-linear, and pseudo-steady state (PSS) are being identified. The identifications of flow regimes which have characteristic trends on log-log graph of pressure derivatives versus time represent unique technique in reservoir characterization. Five pressure derivatives are studied in detail: primary pressure derivative (PPD) (i.e., PPD=∂PD/∂tDA), Slope of PPD, PPD ×tDA, Bourdet derivative (i.e., tDA × PPD), and Slope of Bourdet derivative. For the first time, the pressure derivatives have been computed at high-resolution to diagnose the five infinite-conductivity horizontal well flow regimes identifications (i.e., the wellbore is discretized into twenty thousand of segments). In field application, synthetic pressure drawdown test data for infinite-conductivity horizontal well are analyzed by using type-curve matching technique.The novelties in this study are the following:1.The identifications of infinite-conductivity early-radial and early-linear flow regimes by Slope of Bourdet derivative are equal to −0.5 and 0 respectively which are different to their uniform-flux counterparts 0 and 0.5 respectively. Therefore, the pressure derivatives diagnoses are unique for a certain wellbore condition and there is a complicated identifications exchange between uniform-flux and infinite-conductivity flow regimes. The identification of infinite-conductivity early-radial flow regime is used for uniform-flux spherical flow regime and vice versa, and the identification of infinite-conductivity early-linear flow regime is used for uniform-flux early-radial and late-radial-flow regimes and vice versa.2.Theories of developing infinite-conductivity early-radial flow regime by multi aligned and merged uniform-flux spherical flow regimes and developing infinite-conductivity early-linear flow regime by multi aligned uniform-flux early-radial flow regimes are presented. The new theories prove the existence of the complex identifications exchange between uniform-flux and infinite-conductivity flow regimes.3.Without type-curve matching technique, downhole flow or pressure profile measurement, or presence of uniform-flux early-linear flow regime, or determination of mt at late-radial, late-linear, or PSS flow regime are crucial to distinguish if the wellbore is under uniform-flux or infinite-conductivity condition for correct horizontal well test analysis, mt = segments number of the half-length wellbore.4.At infinite-conductivity late-linear flow regime, qD distribution over the wellbore is uniform for any well and reservoir configuration as at infinite-conductivity PSS flow regime, qD = dimensionless inflow rate.

Dynamical Mechanical Analysis and Micromechanics Simulations of Spin-Crossover@Polymer Particulate Composites: Toward Soft Actuator Devices

We investigated the interplay between the thermomechanical and spin-crossover (SCO) properties of a series of stimuli-responsive polymer composites consisting of [Fe(NH2trz)3]SO4 and [Fe(Htrz)(trz)2]BF4 particles (trz = 1,2,4-triazolato) embedded in thermoplastic polyurethane, TPU, and poly(vinylidene fluoride–trifluoroethylene), P(VDF-TrFE), matrices. The effective thermoelastic coefficients and transformation stress and strain in the composites were assessed utilizing dynamical mechanical analysis (DMA), differential scanning calorimetry (DSC), thermal expansion, and thermal stress measurements. Remarkably, the composites display a characteristic elastic softening and increased mechanical damping around the spin transition temperature, which arise from the significant spin state–volume strain coupling in the particles and scale semiquantitatively with the pressure derivative of the low spin fraction (∂n∂P)T. Crucially, for a given particle volume fraction, the transformation strain (respectively stress) substantially increases (respectively decreases) in soft matrices, which was rationalized by micromechanical simulations. The results provide a fundamental understanding and a quantitative guideline for the design of SCO@polymer composites for applications in mechanical transducers.

A characteristic nonlinear distortion length for broadband Gaussian noise

The nonlinear evolution of high-amplitude broadband noise is important to the psychoacoustic perception, usually annoyance, of high-speed jet noise. One method to characterize the nonlinear evolution of such noise is to consider a characteristic nonlinear waveform distortion length for the signal. A common length scale for this analysis is the shock formation distance of an initially sinusoidal signal. However, application of this length scale to broadband noise, even with the amplitude and source frequency replaced with characteristic values, may lead to underestimates of the overall nonlinear waveform distortion of the noise as indicated by the skewness of the time derivative of the acoustic pressure (or derivative skewness). This paper provides an alternative length scale derived directly from the evolution of the derivative skewness of Gaussian noise that may be more appropriate when analyzing the nonlinear evolution of broadband noise signals. This Gaussian-based length scale is shown to be a useful metric for its relative consistency and its physical interpretation. Various analytical predictions of the evolution of the derivative skewness for an ensemble of numerical simulations of noise propagation are used to highlight various aspects of this new length scale definition.

Cavitation Modeling Using Lumped Parameter Approach Accounting for Bubble Dynamics and Mass Transport Through the Bubble Interface

AbstractVaporous and gaseous cavitation cause several physical phenomena which are typically undesirable, such as reduction in compressibility and material damage. Therefore, the ability to capture these effects in simulation is highly valued. In the fluid power field, lumped parameter modeling technique has proven effective for analyzing components and systems, allowing for fast simulations. Past efforts in modeling cavitation using lumped parameter approach have assumed dependence of fluid properties such as bulk modulus, density, and viscosity directly to pressure and temperature. This cannot be considered as the fluid mixture is composed of different phases of matter. Some other formulations account for gaseous cavitation based on the equations that are derived from vaporous cavitation. This paper illustrates a better approach that combines the two cavitation effects by considering that both vapor and undissolved gas co-occupy a spherical bubble. The size of the spherical bubble is solved using the Rayleigh–Plesset equation, and the transfer of gas through the bubble interface is solved using Henry's law and diffusion of the dissolved gas in the liquid. These equations are coupled with a novel pressure derivative equation. To show the validity of the proposed approach, the instantaneous pressure of a closed fluid volume undergoing expansion/compression is compared with multiple experimental sources, showing an improvement in accuracy when compared to existing models. Integrating this modeling technique with current displacement chamber simulation can further improve the understanding of cavitation in hydraulic systems.

On the Transition-State theory approach to the Jones-Dole’s viscosity B-coefficient: A novel molecular-based interpretation, assessment of its implications, and experimental evidence

We report a novel statistical mechanics interpretation of the frequently invoked Feakins’ transition-state theory approach to the Jones − Dole’s Bi- coefficient, and its temperature–pressure derivatives, in the context of their suitability as structure-making/breaking markers for the behavior of solutes in dilute electrolyte solutions. We provide additional rigorous molecular-based thermodynamic evidence to highlight the non-uniqueness of the Bi- and ∂Bi/∂TP- responses to the solute–solvent intermolecular asymmetries in these systems, and to illustrate the resulting outcomes according to a fundamental structure-making/breaking function involving the available experimental data for aqueous electrolyte solutions. Finally, we discuss the implications of our findings while providing a cautionary outlook on the pervasive use of the viscosity-based structural markers.

Modelling of the structural, electronic, magnetic properties and magnetocaloric effect of Cr2Ge2Te6 and Cr2Si2Te6 compounds: DFT combined with the Monte Carlo method

ABSTRACT In the following work, we are mainly focused on the study of the structural, magnetic and electronic properties of Cr2Ge2Te6 and Cr2Si2Te6 compounds using DFT combined with the Monte-Carlo simulation method. We have used the Generalized Gradient Approximation of Perdew, Burke and Ernzerhof (GGA-PBE) for modeling the exchange-correlation potential.The results obtained for the density of states and the band structure reveal that our compounds have a semiconductors character. The structural properties of both compounds are given for the lattice constants and the bulk moduli and their pressure derivatives. In addition, we have been studying the effect of the external magnetic field on the magnetic phase transitions, critical temperature, magnetization, susceptibility and hysteresis cycles of these materials. The magnetic entropy, the specific heat capacity and the relative cooling power for different external magnetic fields are obtained around the critical temperature.

Automated Classification of Well Test Responses in Naturally Fractured Reservoirs Using Unsupervised Machine Learning

Understanding the impact of fractures on fluid flow is fundamental for developing geoenergy reservoirs. Pressure transient analysis could play a key role for fracture characterization purposes if better links can be established between the pressure derivative responses (p′) and the fracture properties. However, pressure transient analysis is particularly challenging in the presence of fractures because they can manifest themselves in many different p′ curves. In this work, we aim to provide a proof-of-concept machine learning approach that allows us to effectively handle the diversity in fracture-related p′ curves by automatically classifying them and identifying the characteristic fracture patterns. We created a synthetic dataset from numerical simulation that comprised 2560 p′ curves that represent a wide range of fracture network properties. We developed an unsupervised machine learning approach that can distinguish the temporal variations in the p′ curves by combining dynamic time warping with k-medoids clustering. Our results suggest that the approach is effective at recognizing similar shapes in the p′ curves if the second pressure derivatives are used as the classification variable. Our analysis indicated that 12 clusters were appropriate to describe the full collection of p′ curves in this particular dataset. The classification exercise also allowed us to identify the key geological features that influence the p′ curves in this particular dataset, namely (1) the distance from the wellbore to the closest fracture(s), (2) the local/global fracture connectivity, and (3) the local/global fracture intensity. With additional training data to account for a broader range of fracture network properties, the proposed classification method could be expanded to other naturally fractured reservoirs and eventually serve as an interpretation framework for understanding how complex fracture network properties impact pressure transient behaviour.

Theoretical prediction of Grüneisen Parameter for γ-Fe2O3

The application of nanomaterials in modern technologies requires the study of its Grüneisen parameter. For this purpose, we have theoretically calculated the pressure, bulk modulus, and first order pressure derivative of bulk modulus at different compression ratios (V/V0). Further, we have tried to predict the variation of Grüneisen parameter with respect to compression ratio (V/V0) for ɣ-Fe2O3 nanomaterial. The Grüneisen parameter was calculated using the Borton and Stacey model at compressions up to V/V0 = 0.64. We have used three different equations of state: Birch- Murnaghan EOS, Brennan-Stacey EOS, and Vinet-Rydberg.

Sound velocities and single-crystal elasticity of hydrous Fo90 olivine to 12 GPa

Nominally anhydrous minerals (NAMs) may contain significant amounts of water and constitute an important reservoir for mantle hydrogen. The colloquial term ‘water’ in NAMs is related to the presence of hydroxyl-bearing (OH−) point defects in their crystal structure, where hydrogen is bonded to lattice oxygen and is charge-balanced by cation vacancies. This hydrous component may therefore have substantial effects on the thermoelastic parameters of NAMs, comparable to other major crystal-chemical substitutions (e.g., Fe, Al). Assessment of water concentrations in natural minerals from mantle xenoliths indicates that olivine commonly stores ∼0–200 ppm of water. However, the lack of samples originating from depths exceeding ∼250 km coupled with the rapid diffusion of hydrogen in olivine at magmatic temperatures makes the determination of the olivine water content in the upper mantle challenging. On the other hand, numerous experimental data show that, at pressures and temperatures corresponding to deep upper mantle conditions, the water storage capacity of olivine increases to 0.2–0.5 wt%. Therefore, determining the elastic properties of olivine samples with more realistic water contents for deep upper mantle conditions may help in interpreting both seismic velocity anomalies in potentially hydrous regions of Earth's mantle as well as the observed seismic velocity and density contrasts across the 410-km discontinuity.Here, we report simultaneous single-crystal X-ray diffraction and Brillouin scattering experiments at room temperature up to 11.96(2) GPa on hydrous [0.20(3) wt% H2O] Fo90 olivine to assess its full elastic tensor, and complement these results with a careful re-analysis of all the available single-crystal elasticity data from the literature for anhydrous Fo90 olivine. While the bulk (K) and shear (G) moduli of hydrous Fo90 olivine are virtually identical to those of the corresponding anhydrous phase, their pressure derivatives K′ and G′ are slightly larger, although consistent within mutual uncertainties. We then defined linear relations between the water concentration in Fo90 olivine, the elastic moduli and their pressure derivatives, which were then used to compute the sound velocities of Fo90 olivine with higher degrees of hydration. Even for water concentrations as high as 0.5 wt%, the sound wave velocities of hydrous and anhydrous olivines were found to be identical within uncertainties at pressures corresponding to the base of the upper mantle. Contrary to previous claims, our data suggest that water in olivine is not seismically detectable, at least for contents consistent with deep upper mantle conditions. In addition to that, our data reveal that the hydration of olivine is unlikely to be a key factor in reconciling seismic velocity and density contrasts across the 410-km discontinuity with a pyrolitic mantle.

In-doped Aluminum antimonide alloy for optoelectronic applications

First-Principles calculations are made to study the structural electronic and optical properties for indium doped aluminum antimonide. The most appropriate method of density functional theory (DFT) naming Full Potential Linearized Augmented Plane Wave (FP-LAPW) is used. The structural properties like Lattice constant (a), pressure derivative, bulk modulus (B) examined by Local density approximation (LDA) along with generalized gradient approximation (GGA). Generalized gradient approximation along with TB-mBJ is used to determine electronic parameters like band structure along and density of states. According to the computed results the binary compound AlSb is optically inactive and exhibits an indirect (Γ -L) band gap. By increasing the concentration of indium with different percentages, the indirect band gape shifted to direct (Γ – Γ) band gap which shows material is optically active. The optical properties of material including dielectric (Real and imaginary part) constant, reflectivity, refractive index, energy loss, absorption coefficient, and optical conductivity have changed significantly. Electronic and optical properties are modified by (TB-mBJ) approach. The results obtained are examined with experimental data and utilized as a starting point to propose that the material is the superlative choice for optoelectronic devices/applications.

DFT-continuum characterization of third-order elasticity of sI methane hydrates under pressure

Methane gas hydrates (GHs) are polyhedral crystalline guest-host materials found under high pressure and low-temperature conditions, which can serve as an energy source. Previous work on methane GH material physics was limited to simple linear models, which only involves second-order elasticity. However, this is not fully suited to high-stress load conditions in technological applications and fundamental material physics. For other material systems, it has been demonstrated that third-order elasticity and pressure derivatives of second-order elasticity have a strong and hence significant correlation. To narrow a critical theory-simulation gap in gas hydrates materials research, in this work we expand prior work from second-order elastic constants (SOECs) to third-order elastic constants (TOECs). By using the open-source Python tool Elastic3rd and the DFT calculation software Vienna Ab initio Simulation Package (VASP), we found that the non-linear fitting involving TOECs gave a better overall prediction and a smaller root-mean-square deviation on pressure-strain evaluation when compared with linear fitting. In addition, the non-linear fitting provides robust results on the piezo-effect on the shear constant C44 and the ductile-to-brittle transition (P = −0.5 GPa). These results are not achievable from previous work based on a linear model and these findings prove that non-linear models, including TOECs, are needed under high pressures. In addition, this research includes a detailed analysis of the calculation of TOECs and mechanical properties to study pressure stability limits and ductile-brittle transitions. Together the results, findings, and analyses from this work are a novel and significant contribution to the material physics knowledge of gas hydrates and hydrogen-bonded crystalline materials.

Transient Flow Performance of a Vertical Well With Multiple Varying Conductivity Fractures in a Tight Oil Reservoir

Summary Due to uneven proppant distribution and varied proppant sizes during hydraulic fracturing, artificial fractures of varying length, asymmetry, and varying conductivity are easily formed near the wellbore. The principal focus of this work is to investigate the pressure transient performance of a vertical well penetrated by multiple asymmetrical fractures with varying lengths and varying conductivities in a tight oil reservoir. A novel fracture flow equation was developed specifically to describe the flow behavior inside the complex artificial fractures mentioned above. By combining with the point source solution of the tight oil reservoir, a semianalytical solution was further obtained to analyze the pressure transient behavior of a vertical well with multiple varying-conductivity fractures in a tight oil reservoir. The accuracy and reliability of the newly-developed solution were verified by comparing with the result of a numerical model. With this new solution, fracture flux distribution for different conductivity modes, namely, linearly declining mode, exponentially declining mode, and elliptically declining mode, shows that the near-wellbore fracture flux of the exponential mode is greater than that of the other two modes, but the flux distribution near the fracture tips is on the contrary. Meanwhile, the transient flow characteristics under the above varying conductivity modes indicate that the exponentially varying conductivity has a significant influence on the early linear flow regimes, while the linear and elliptical mode only has a slight influence on the bilinear flow regime under high conductivity. Parameter sensitivity analysis reveals that the obvious inversion point occurring in the pressure derivative curves of uniform conductivity fractures disappears on the pressure derivative curves of varying conductivity fractures, and a weaker asymmetry, a greater adjacent fracture angle, and a larger fracture number and fracture length ratio are conducive to improve the fracturing stimulation effect. This study deepens our understanding of the transient flow performance of vertically fractured wells and helps to estimate artificial fracture properties and evaluate hydraulic fracturing performance.

Thermophysical and lattice vibrational study of thorium telluride (ThTe) by use of three-body force shell model

In this paper, a complete lattice study of thorium telluride (ThTe) in the effects of three-body interaction (TBI) in the framework of RIM and RSM models is reported. By use of the present model, I have theoretically reported elastic constants, pressure derivatives, dispersion relation curve, specific heat curve, combined density of states (CDS) and equation of state of the ThTe compound. The achieved results are good with experimentally reported results and have given very important information about this compound for further investigation.

High-Pressure Structural and Thermodynamic Properties of Cerium Orthosilicates (CeSiO4)

Pressure-induced phase transitions from the zircon structure-type (I41/amd) to the scheelite structure type (I41/a) are known for many ternary oxides systems (ABO4). In this work, we present the first high-pressure study on synthetic stetindite (CeSiO4) by a combination of in situ high-pressure synchrotron powder X-ray diffraction up to 36 GPa, implemented with and without dual sided laser heating, and in situ high-pressure Raman spectroscopy up to 43 GPa. Two phase transitions were identified: zircon to a high-pressure low-symmetry (HPLS) phase at 15 GPa and then to a scheelite at 18 GPa. The latter from HPLS scheelite phase was found irreversible; i.e., scheelite is fully quenchable at ambient conditions, as in other zircon-type phases. The bulk moduli (K0) of stetindite, HPLS, and high-pressure scheelite phases were determined, respectively, as 171(5), 105(4), and 221(40) GPa by fitting to a second-order Birch–Murnaghan equation of state. The pressure derivatives of vibrational modes and Grüneisen parameters of the zircon-structured polymorph are similar to those of other orthosilicate minerals. Due to the larger ionic radii of Ce4+, with respect to Zr4+, stetindite was found to possess a softer bulk modulus and undergo the phase transitions at a lower pressure than zircon (ZrSiO4), such observations are consistent with what were found in coffinite (USiO4).

DETERMINATION OF A SIMPLE AND ROBUST METHOD TO CALCULATE IGNITION DELAY IN COMPRESSION IGNITION ENGINES: APPLICATION TO DIESEL-BIODIESEL-ETHANOL BLENDS

Today, the automobile industry is under increasing pressure from governments and environmental organizations to lower their carbon footprint. Car manufacturers release new models that follow modern and severe norms of pollutant emissions using eco-friendly technologies. Their strategy follows two main pathways: decarbonization and increase of efficiency. In order to achieve the aforementioned objective, the replacement of fossil fuels with renewable biofuels with lower carbon footprints, such as biodiesel and/or ethanol, contribute to the decarbonization of current internal combustion engines. However, changes in the fuel composition also imply some adjustments in the injection and combustion settings to optimize the engine operation. An important parameter to assess the combustion process in a compression ignition (CI) engine is the ignition delay (ID), defined as the duration between the start of fuel injection (SOI) and the start of combustion (SOC). Different direct and indirect approaches are reported in the literature to measure or calculate the ID. This study investigates two indirect methods based on the measurement of the indicated pressure inside the combustion chamber, throughout the displacement of the piston. These measurements are based on the position of the maximum of the third-order derivative of pressure as a function of the crank angle and the subjective shift from a polytropic compression process, respectively. The objective of the present work is to define an objective criterion to quantify this shift in order to allow a unique determination of the ID, independently of the adopted method. Thus, data of six different fuel blends of diesel-biodiesel-ethanol in a four-stroke CI engine from tests performed at PUC Rio’s Vehicular Engineering Laboratory for different loads and engine speeds were analyzed using the software Matlab. As observed in previous literature, the results show that the addition of biodiesel and ethanol concentration in the blends slightly increases the ID. Moreover, the difference between the experimental pressure with combustion and the calculated pressure in the polytropic compression process at the SOC position is lower as engine load increases and/or engine speed decreases and seems independent of the fuel blend composition. Nonetheless, the variation of the pressure difference at the SOC stays moderate, allowing the determination of a unique value to directly read the ID from the indicated pressure profile, without requiring the smoothing process of the third-order derivative of the pressure.

Effects of dispersion corrections on the theoretical description of bulk metals

The addition of a London dispersion correction to standard Kohn-Sham density-functional theory is essential for an accurate description of noncovalent interactions. While several dispersion-corrected density functionals (DC-DFs) have shown excellent performance for hard solids at ambient conditions, their transferability to metallic systems at ambient conditions or under isotropic compression has not been systematically examined. In this study, we assess the ability of selected DC-DFs to describe the equations of state (EOSs) of selected elemental metals and intermetallic compounds up to several gigapascals of pressure. EOS-derived properties, such as the unit-cell volume, the bulk modulus, and its pressure derivative, were then evaluated with and without thermal effects and the results compared with experimental reference data. We also assess the ability of the DC-DFs to predict the phase-transition pressures for a set of intermetallic compounds. The results of this study establish that London dispersion physics, and even dispersion contributions from the core electrons, is important in the description of bulk metals.

Precision in Defining Diagnostic Plots Optimizes Well-Test Results

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 206108, “Diagnostic Plots of Pressure-Transient, Rate-Transient, and Diagnostic Fracture Injection/Falloff Tests,” by David Craig, SPE, Occidental, and Thomas Blasingame, SPE, Texas A&M University. The paper has not been peer reviewed. _ All transient-test interpretation methods use diagnostic plots for the identification of wellbore or fracture storage distortion, flow regimes, and other parameters. The associated diagnostic plots are not interchangeable between such tests. The objective of this work is to clearly define the appropriate diagnostic plots for each type of transient test. Introduction In the complete paper, the authors review constant-rate drawdown solutions for a few specific cases of interest and the plotting function used to match buildup data to the drawdown solutions. They extend their review to the cases of buildup or falloff analysis following short flow periods and illustrate the differences between analysis of buildup or falloffs following short and long flow periods. After covering pressure-transient testing, they discuss rate-transient diagnostic plots and the ambiguity observed during analysis of multifractured horizontal well diagnostic plots and the uncertainty of analyst straight lines. Finally, they discuss and demonstrate the correct plotting functions and flow-regime interpretation for diagnostic fracture injection and falloff tests. Multiple examples from the literature are included as part of the discussion. Pressure-Transient Diagnostic Plots Pressure-transient-testing diagnostic plots evolved from the solutions to constant-rate drawdown problems. The authors’ intent is to review infinite-acting solutions for radial flow with wellbore storage and skin and flow through an infinite-conductivity fracture. On a log-log plot, the characteristic slopes, detailed in the complete paper, are unit slope, ½ slope, and zero slope. Many authors have proposed plotting functions for overlaying the observed pressure response from transient tests other than a constant-rate drawdown on the drawdown solutions. In many cases, the slopes identifying storage distortion and flow regimes from drawdown solutions will match and can be used to identify storage and flow regimes from pressure-buildup tests. A situation in which pressure-buildup or falloff test plotting functions fail to match the drawdown solution is when the flow period before shut-in is short. Short-flow transient tests have been reviewed by multiple authors. In lower-permeability reservoirs, pressure-transient tests with short flow periods are very common, and, in unconventional reservoirs, short-flow transient tests are the most-common transient test. Diagnostic plots constructed based on the characteristic shapes of the dimensionless pressure and the dimensionless pressure derivative with respect to the natural logarithm of dimensionless time for constant-rate drawdown solutions cannot be applied in the same manner for short-flow transient tests. With short-flow transient tests, the observed derivative of pressure difference with respect to the natural logarithm of time matches the negative product of dimensionless time and the second derivative of dimensionless pressure with respect to dimensionless time. Additionally, the commonly known impulse derivative, which is defined as the product of time and the derivative of pressure difference with respect to the natural logarithm of time, will match the negative product of dimensionless time squared and the second derivative of dimensionless pressure with respect to dimensionless time.

High-pressure equations of state and elastic properties of the hcp-Iron

The present study deals with the elastic properties at different pressure of hcp-iron have been carried out. By exerting pressure on the cubic body of n-th power of edge length, we have used a new equation of state based on Eulerian finite theory. We have computed the bulk modulus and their pressure derivative from this formulated equation of state. The results from the proposed equation of state (EOS) show the better agreement with available experimental data. Thus, the derived expressions are able to predict the elastic properties of hcp-iron under high pressures.

Transient pressure analysis of polymer flooding fractured wells with oil-water two-phase flow

The oil-water two-phase flow pressure-transient analysis model for polymer flooding fractured well is established by considering the comprehensive effects of polymer shear thinning, shear thickening, convection, diffusion, adsorption retention, inaccessible pore volume and effective permeability reduction. The finite volume difference and Newton iteration methods are applied to solve the model, and the effects of fracture conductivity coefficient, injected polymer mass concentration, initial polymer mass concentration and water saturation on the well-test type curves of polymer flooding fractured wells are discussed. The results show that with the increase of fracture conductivity coefficient, the pressure conduction becomes faster and the pressure drop becomes smaller, so the pressure curve of transitional flow goes downward, the duration of bilinear flow becomes shorter, and the linear flow appears earlier and lasts longer. As the injected polymer mass concentration increases, the effective water phase viscosity increases, and the pressure loss increases, so the pressure and pressure derivative curves go upward, and the bilinear flow segment becomes shorter. As the initial polymer mass concentration increases, the effective water phase viscosity increases, so the pressure curve after the wellbore storage segment moves upward as a whole. As the water saturation increases, the relative permeability of water increases, the relative permeability of oil decreases, the total oil-water two-phase mobility becomes larger, and the pressure loss is reduced, so the pressure curve after the wellbore storage segment moves downward as a whole. The reliability and practicability of this new model are verified by the comparison of the results from simplified model and commercial well test software, and the actual well test data.

A new semi-analytical flow model for multi-branch well testing in natural gas hydrates

This paper presents a new semi-analytical solution and the related methodology to analyze the pressure behavior of multi-branch wells produced from natural gas hydrates. For constant bottom-hole pressure production, the transient flow solution is obtained by Laplace transforms. The interference among various branches is investigated using the superposition principle. A simplified form of the proposed model is validated using published analytical solutions. The complete flow profile can be divided into nine distinct regimes: wellbore storage and skin, vertical radial flow, linear flow, pseudo-radial flow, composite flow, dissociated flow, transitional flow, improvement flow and stress-sensitive flow. A well’s multi-branch structure governs the vertical radial and the linear flow regimes. In our model, a dynamic interface divides the natural gas hydrates deposit into dissociated and non-dissociated regions. Natural gas hydrates formation properties govern the compositeeffect, dissociated, transitional, and improvement flow regimes. A dissociation coefficient governs the difference in flow resistance between dissociated and non-dissociated natural gas hydrates regions. The dissociated-zone radius affects the timing of these flow regimes. Conversion of natural gas hydrates to natural gas becomes instantaneous as the dissociation coefficient increases. The pressure derivative exhibits the same features as a homogeneous formation. The natural gas hydrates parameter values in the Shenhu area of the South China Sea cause the prominent dissociated flow regime to conceal the later transitional and improvement flow regimes. Due to the maximum practical well-test duration limitation, the first five flow regimes (through composite flow) are more likely to appear in practice than later flow regimes. Cited as: Chu, H., Zhang, J., Zhang, L., Ma, T, Gao Y., Lee, W. J. A new semi-analytical flow model for multi-branch well testing in natural gas hydrates. Advances in Geo-Energy Research, 2023, 7(3): 176-188. https://doi.org/10.46690/ager.2023.03.04