Phase Redistribution Research Articles

Stability and Heat Resistance of Silicide Coatings on Refractory Metals. Part 3. Stability of Silicide Coatings on Niobium Heated in Air at 1500-1800°C

The kinetics of phase redistribution in the (Mo, W)Si2 ― Nb system at 1500-1800°C was investigated. The kinetic parameters for growth of the lower silicides (Mo, W, Nb) 5Si3 + Nb5Si3 and decrease in the layer thickness of the higher silicide (Mo, W)Si2 as function of the oxidation temperature were determined. It was established that the stability of the multiphase and multicomponent system was more than twice that of the system MoSi2 ― Nb, and 15-18 times that of MoSi2 ― Mo.

STEAM-WATER STRATIFIED FLOW IN T-JUNCTIONS – EXPERIMENTS AND MODELLING

Experimental data on dividing steam-water two-phase stratified flow in T-junctions with horizontal inlet and both horizontally and vertically downward branches are presented in this paper. The measurements included inlet liquid level and run and branch fully developed void fraction. These measurements were used to describe the effects of the inlet flow conditions and junction geometry (relative branch diameter and orientation) on phase redistribution. The data covered the range of inlet steam and water superficial velocities from 1.5 to 5.0 m/s and 0.05 to 0.09 m/s respectively. Under these conditions, which have not been previously examined, the extent of phase redistribution was greatly affected by the inlet superficial gas velocity (uGS), and the junction geometry. The effect of inlet superficial water velocity (uLS) on the redistribution characteristics was less significant for the range of data tested. A model for the phase redistribution of stratified flow in T-junctions is developed. It consists of...

Detection of pressure buildup data dominated by wellbore phase redistribution effects

This paper presents a new diagnostic technique that detects the presence of any type of phase redistribution pressure response and determines the true beginning of the semilog straight line for conventional analysis techniques. The method can also be used to predict the end of any wellbore effects. This greatly enhances the conventional analyses and yields more accurate estimation of the reservoir parameters. The technique is based upon existing analytical solutions for radial flow in homogenous reservoirs. The proposed method is simple and straightforward. It does not require manual or automatic type curve matching and it does not use complicated nonlinear optimization or history matching as some other methods necessitate. The applicability and accuracy of the proposed method are demonstrated through the analysis of three simulated cases and two field examples.

Stability and Heat Resistance of Silicide Coatings on Refractory Metals. Part 1. Effect of Subsurface Layer on Process of Phase Redistribution in System WSi2 ― W

The effect of a subsurface layer of metal silicide on the phase composition stability of high-temperature MeSi2-type coatings on refractory metals was investigated. Using the system WSi2 ― W as a prototype it was experimentally determined that a subsurface layer of the tungsten disilicide, and the distribution profile of silicon in the diffusion zone upon high-temperature heating have a substantial effect on the formation of a barrier layer of lower silicide which determines the stability of the system as a whole. It is proposed that the search for more stable silicide coatings on refractory metals should be directed toward the creation of diffusion barriers on not only the inner interface MeSi2 ― Me, but also the external surface of the coating. The process of coating formation must be accompanied by the formation of a metal silicide on the external surface with the highest possible concentration of silicon.

Role of magma pressure, tectonic stress and crystallization progress in the emplacement of syntectonic granites. The A-type Estrela Granite Complex (Carajás Mineral Province, Brazil)

The Archaean, syntectonic, A-type Estrela Granite Complex (Carajás Mineral Province, Brazil) consists of three plutons emplaced in a greenstone sequence under low-pressure conditions (180< P<310 MPa). It is composed mainly of annite-, ferropargasite (±hedenbergite)- and ilmenite-bearing monzogranites. The contact aureole is affected by a subvertical penetrative schistosity conformable with the limits of the plutons. Meso- to microstructures and mineral reactions in the granites indicate that deformation occurred in a continuum from above-solidus to low- T subsolidus conditions. Two distinct planar structures are observed: (i) a concentrical primary foliation (S 0) corresponding to rhythmic, isomodal, phase layering associated with a faint grain shape fabric; it is horizontal in the centre and vertical towards the edges of the plutons; and (ii) a steep to subvertical foliation (S 1) associated with the deformation of S 0 and accompanied with emplacement of synplutonic dykes and veins of leucocratic granites and pegmatites. Emplacement, differentiation and consolidation of the Estrela Granite Complex are considered to result from a continuous evolution under decreasing temperatures in a single-stage strained crust (transpression), with two main periods. (1) The first period is controlled by body forces, and it corresponds to inflation with magma ponding. As long as the rheology is melt dominated, magma pressure is the critical parameter and almost no strain is recorded. With decreasing T, magmas crystallize and differentiate leading to a concentrical magmatic phase layering. The growing magmatic bodies are mechanically decoupled from the country rocks and their evolution depends on internal magma chamber processes. (2) For higher amount of crystallization (residual melt fraction F<0.5), the role of magma pressure becomes insignificant. Establishment of a continuous crystal framework leads to the coupling of plutons with their surroundings, and deformation in response to tectonic stress. Most of the strain is recorded during this period which starts from the rigid percolation threshold, and extends to subsolidus low-grade conditions. This leads to deformation of the partially crystallized volume and redistribution of fluid-enriched differentiated melts. The amount of crystallization through the rheological thresholds appears as the critical parameter determining the transition from magma-controlled processes (inflation and differentiation of the magma chamber, with development of a phase layering) to tectonic-controlled processes (deformation of the phase layering and redistribution of residual melts). This accounts for the fact that syntectonic plutons commonly display intermingled, boudinaged layers with distinct modal compositions and in some cases well-preserved rhythmic layering.

Field Data Demonstrate Thermal Effects Important in Gas Well Pressure Buildup Tests

Abstract Thermal effects become an important factor in gas well pressure buildup tests with a surface shut-in. Welltest data from Western Canada demonstrate that, due to the PVT relationship, temperature changes of wellbore fluids can cause thermal-storage effects that can be misinterpreted as complex reservoir characteristics by unexplained pressure transient response or nonunique pressure response. Understanding the duration of thermalffects can improve the interpretation of buildup tests to allow enough time for observation of true reservoir pressure transient responses. Temperature effects can be significant and extended, depending on many in situ and imposed factors. Thermal effects can be important, even when pressure recorders are placed at the midpoint of the producing interval, due to Joule-Thompson effects. Field observations demonstrate that Joule-Thompson cooling exists in many gas wells. Cooling effects were observed to extend 50 m in the formation, suggesting that significantly long time periods are required for formation fluids to reach thermal equilibrium after shut-in. Implications of not understanding the thermal effects in a buildup test analysis can result in "heterogeneities" being interpreted when there are none and skin calculations indicating an improved wellbore condition when the well has only been perforated. It is the purpose of this paper to show how temperature data diagnostics can be used to aid the welltest engineer in distinguishing between general wellbore effects and reservoir behaviour in the pressure transient data. In this paper, we have adopted the acronym PTTA for (P)ressure (T)emperature (T)ransient (A)nalysis. Introduction Use of pressure transient tests has become an established practice to determine reservoir parameters, potential reserves and near wellbore conditions. It is widely recognized that wellbore and near wellbore effects can distort and mask true reservoir responses, specially in the early stages of a buildup test. Both analytical and practical efforts have been developed to quantify and evaluate these effects by using concepts of skin, wellbore storage and phase redistribution(1–5). In addition, wellbore dynamics beyond wellbore storage and phase redistribution, such as liquid influx/efflux, wellbore (and near wellbore) clean-up, plugging, recorder effects, etc., have been discussed in the past decade(6–8). However, theoretical and numerical analyses of thermal effects have only been addressed recently(9–12). Implicit assumptions that require well test data to reflect information from an isothermal condition in both wellbore and reservoir are generally made in interpretation models. Such assumptions hold only if the pressure and temperature recorders are placed at the middle of the perforation interval, and neither Joule- Thompson cooling or heating occurs. Although various aspects of heat transfer between a wellbore and the formation have been studied, most of them are steady-state models, which assume that fluid properties and flow rate are not functions of time in theellbore(9). Thermal effects are more pronounced in gas wells because gas properties are strong functions of pressure and temperature. Observations demonstrate that gas well pressure buildup tests often exhibit complex reservoir pressure behaviours. These models, such as narrow channels, double porosity, or multiple nearby boundaries, often did not agree with the actual reservoir system and, consequently, resulted in incorrect interpretation of well and formation parameters(12).

Well Test Analysis of Horizontal Wells In Bounded Naturally Fractured Reservoirs

Abstract Using the source function approach and the method of images, we generated the pressure response of a horizontal well in a bounded homogeneous reservoir. Then we converted the homogeneous solution to the case of a dual-porosity system by means of Laplace Transform. Furthermore we introduce skin and wellbore storage in the solution. Use of the technique is illustrated with the case of a horizontal well in a naturally fractured reservoir. Introduction Mathematical modelling of horizontal wells, though abundant in the literature, seldom pays much attention to computational efficiency. Only recently do a couple of papers appear to deal with the situation(1–2). They use the method of images for early time and Fourier Series for late time. Ohaeri and Vo(1), using Laplace Transform, handle wellbore storage effects, skin and phase redistribution. Thompson et al.(2), on the other hand, deal with double porosity reservoirs, also through Laplace Transform. They appear to be both faster than Daviau's approach(11) or Ozkan's approach(6). Our main interests lie in naturally fractured reservoirs. Therefore we follow closely the schemes of Thompson et al.(2), although Carvalho and Rosa(3–4) present yet another way of generating pressure response of horizontal wells in naturally fractured reservoirs. Most of these solutions use source functions, Fourier Series, Boundary Element Methods(4) or even Fourier Transform Methods(5). Theory We define the following Dimensionless Pressure Drop: Equation 1–13 (available in full papper) Thompson et al.(2) indicated that they were not successful in finding an approximate (polynomial) expression which reproduces the error function with sufficient accuracy. In the Appendices, we give two subroutines to calculate the error function. These subroutines give good graphical accuracy. The above formulation is efficient computationally. The one thing to watch out for is the definition of the point of evaluation, (XD, YD, ZD) in space. Ozkan and Raghavan(6) give a very detailed discussion on this point. Since we are using a line source, and it is not possible to compute pressure drop on the source, one has to decide on a point away from the well-axis, to account for the radius of the actual well. Dual Porosity System Once we obtain PD from the above formulation we use a scheme given in Houze, Home, and Ramey(7) to generate double porosity solutions. The approach involves the following steps:Find the Homogeneous SolutionLaplace TransformMultiply by sChange s to s F (s)Divide by sStehfest InversionDouble Porosity Solution where s is the Laplace parameter Equation 14–21 (available in full papper) Model Verification Figure 1 was generated using data from Table 1 of Reference (5). Stars are data of Reference (5) and the solid line is simulated with the equations presented in this paper. They agree very well [(See Figure 9 of Reference (5)]. Figure 2 was generated using data from Table 2 of Reference (5). In this case the reservoir is anisotropic. The comparison between the data presented in Reference (5) and the plot (Figure 2) developed using the equations presented in this paper is good.

Analysis of Short Transient Tests Affected by Changing Wellbore Storage

Summary It is well known that wellbore storage and phase redistribution have a direct influence over well-testing data, mainly on those recorded at early times of the test. After this early time period, such influence disappears, and the pressure response is dominated by the reservoir and the skin zone properties. However, sometimes the effects of wellbore dynamics last long enough to completely disguise the reservoir response. This situation frequently constrains the use of such analysis procedures as type-curve matching, especially if the test did not last long enough to reach radial-flow conditions. Some tests are uninterpretable because of the duration of these wellbore effects. By means of two classical models related to well test affected by changing wellbore storage, this work introduces a new method of analysis for those tests with insufficient duration to reach radial-flow conditions. The methodology proposed in this work is illustrated with synthetic examples and a field case. For some synthetic cases the type-curve-matching procedure may yield completely erroneous values for the parameters, whereas, with the suggested method, reasonable estimates are obtained.

Modelling of phase redistribution of horizontal annular flow divided in T‐junctions

AbstractA phase redistribution model for annular flow divided in T‐junctions is developed. The model consists of two sub‐models accounting for phase distribution in the inlet to the junction and phase redistribution in the junction, respectively. In modelling phase redistribution in the junction, the dividing streamlines for each phase were determined separately assuming that the phenomena is mainly governed by the fluid inertia and pressure distribution in the junction. The overall model is capable of predicting phase redistribution in T‐junctions having horizontal inlet and any branch orientation. The predictions of this model and those of other available models are compared with experimental data. The predictions of the present model were found to be in better agreement with the experimental data than other available models and correlations.

Prediction of PCDD and PCDF emissions from municipal solid waste (MSW) incinerators

A procedure has been developed for predicting PCDD/F formation in and emission from incinerator off-gas plant. Calculations are based on rates of static and in-flight formation, and take account of electrostatic enhancement and phase redistribution in electrostatic precipitators. Application to operating data from two incinerators gave good estimates of PCDD levels within an order of magnitude, while PCDF levels were overestimated by a considerable margin. The discrepancy is believed to arise mainly from the use of an overestimated in-flight formation rate, and homologue distribution data that over-represents the proportion of furans. The results suggest different formation routes for dioxins and furans, and underline the need for more reliable data as a basis for prediction.

Inhibitory effect of ursolic acid on B16 proliferation through cell cycle arrest.

The effects of ursolic acid on the proliferation of B16, a mouse melanoma cell line, were studied. During investigations of the anti-proliferative effects of this triterpene, we observed that MTT colorimetric and colony forming assays show that ursolic acid is a potent inhibitor of B16 cell growth. Cell cycle analysis was performed by propidium iodide staining and flow cytometry technique. This triterpene exerts an early effect on cell cycle at G1, which explains its anti-proliferative activity. These results suggest that alterations in cell cycle phase redistribution of B16, by ursolic acid, may significantly influence the proliferation of B16, melanoma cells.

Automated Analysis of Pressure Build up Tests Affected by Phase Redistribution

Analytical Solutions and type curves for the constant rate radial flow of fluid in both conventional and naturally fractured reservoirs including the effect of wellbore phase redistribution are presented. An automated procedure for non-linear least square minimization using the analytical solutions and their derivatives with respect to the unknown parameters developed to analyze the pressure build up data affected by phase redistribution. Field examples and analysis are also presented.

Generalization of Wellbore Effects in Pressure-Transient Analysis

Summary Wellbore effects have been recognized as being important in the analysis of pressure-transient tests for many years. Other works have evaluated the effects of wellbore storage and phase redistribution on pressure-transient response, and analysis methods that account for these effects are well known. It is also known, however, that other wellbore phenomena may affect pressure-transient response, but little has been presented that evaluates or generalizes wellbore phenomena in common pressure-transient tests. This paper presents an analysis of generalized wellbore phenomena, including both mass-related and momentum effects, shows how these are incorporated into general solutions of the diffusivity equation, and provides general guidelines for recognizing these effects in pressure-transient data. In addition, it is shown that the phase redistribution formulation for pressure-transient analysis is actually a special case of wellbore mass-related phenomena, which has much wider applicability than previously realized. Besides general methods for accounting for wellbore phenomena, analytical pressure solutions are also presented for several situations, including heating or cooling of wellbore fluids, phase changes in the wellbore, and inertial effects owing to rapid acceleration or deceleration of wellbore fluids.

Modeling and Analyzing Pressure Buildup Data Affected by Phase Redistribution in the Weilbore

Abstract This work describes the development of a simple mechanistic model to predict the effect that the transient two-phase flow of oil and gas has on pressure buildup data. Results from the model provide an improved physical understanding of the phase segregation process and how it influences buildup pressure data. The model is applied to obtain new physical insights into the variable wellbore storage models applied previously in pressure transient analysis.

Effect of Branch Orientation on Annular Two-Phase Flow in T-Junctions

Experimental data on dividing steam-water two-phase annular flow in T-junctions with horizontal inlet and downwardly inclined branches were obtained. The experiments were performed under experimental conditions which have not been examined before. The branch orientation was found to be a significant parameter affecting phase redistribution in the junction. Increasing the downward inclination of the branch was found to reduce the degree of phase separation in the junction under the present test conditions. This is caused by the nonuniform distribution of the liquid film thickness associated with the horizontal inlet annular flow. The phase redistribution data were compared with available models. The need for additional modelling studies was evident. The pressure changes of two-phase flow in the junction were closely correlated with the phase redistribution phenomenon. The data on pressure changes in the junction were correlated using simple models based on momentum and mechanical energy balances.

The impact of late Cenozoic uplift and erosion on hydrocarbon exploration: offshore Norway and some other uplifted basins

Uplift and erosion of sedimentary basins can have a wide range of effects, both positive and negative, on hydrocarbon prospectivity. These phenomena are discussed with special reference to the Norwegian Continental Shelf. Late Cenozoic uplift and erosion have affected large expanses of the shelf, and in particular the Barents Sea. Up to 3000 m of sedimentary overburden have been removed from the Barents shelf, and this process is widely held to be responsible for disappointing results in petroleum exploration. Negative effects identified include spillage of hydrocarbons from accumulations, expansion of gas and evacuation of structures, potential for seal failure and cooling of source rocks. We argue, however, that these aspects have been overstated based on a limited database. Many of the world's hydrocarbon basins (and most of the world's petroleum reserves) lie on land. Most of these basins must have been recently uplifted in order to be above sea level today. Using some of these examples, we show that in other areas with a similar magnitude of uplift and erosion to the Barents Sea sealing capacity (particularly that of evaporites) has been preserved. Hydrocarbon systems have remained intact despite phase changes and redistribution of hydrocarbons. Several enhancing effects of the uplift are documented, including the development of fracture permeability in reservoirs, the remigration of hydrocarbons to shallower subsurface levels and the exsolution of light oil (retrograde condensate). Looking to a future in which natural gas may have increased value, potential exists in uplifted basins such as the Barents Sea for vast volumes of methane formed by exsolution from formation brines. We stress the importance of studying such worldwide analogues in order to throw new light on Norwegian shelf problems. Attention is drawn to some striking similarities between the hydrocarbon systems of the Western Canada Basin and those of the Barents Sea. Examination of the massive databases in the Western Canada Basin and other analogous provinces, rather than a continuing locally-centred approach, will probably help to focus exploration directions in the Barents Sea and may help to distinguish between the effects of uplift and erosion per se and those of more specific, local phenomena such as ice loading and rapid deglaciation.

An electrothermodynamic model with distributed properties for effective permittivities of sea ice

This paper presents a model to calculate the temperature dependence of effective permittivities for sea ice, a heterogeneous medium containing multiphase scatterers. With the strong permittivity fluctuation approach the model accounts for the electrodynamic scattering effect together with the quasi‐static characteristics of multiple species and subspecies of inhomogeneities with distributed orientations, sizes, and shapes. Because of a preferential direction in the orientation distribution, the medium is effectively anisotropic. The size distribution is described with a probability density function in terms of normalized volumetric sizes. Scatterer shapes are nonuniform and have a general ellipsoidal form characterized by arbitrary axial ratios of correlation lengths which are related to physical geometries of the scatterers. In this formulation, sea ice consisting of solid ice, liquid brine, and gaseous inclusions is modeled to derive effective permittivities with thermodynamic phase redistribution and structural metamorphism. Theoretical results are in good agreement with experimental data at the C band frequency of 4.8 GHz for saline ice undergoing warming and cooling cycles. A competitive effect between the increase of liquid brine and the shape rounding of ellipsoidal scatterers at increasing temperatures explains the trend observed in measured data. Sensitivities of effective permittivities to structural and physical parameters characterizing sea ice are also studied.

Post-dryout dispersed flow in circular bends

The effect of curvature on the post-dryout dispersed flow in 90-degree circular bends is investigated theoretically and experimentally. The theoretical study concentrates on two basic aspects of the flow, i.e. bulk vapor flow and droplet dynamics. The former is analyzed by solving the conservation equations of the vapor phase whereas the latter is studied by a Lagrangian droplet trajectory model considering both thermal and turbulence effects. The experimental study deals with phase distribution of the flow by measuring local liquid fraction with an impedance probe. The results indicate that the curvature induced centrifugal force and the secondary flow significantly change the behavior of droplet dynamics and phase distribution. Droplets in the vapor stream reveal a general trend of centrifugal migration towards the outside of the bend and may even impinge directly on the wall. The effects of the secondary flow and turbulent dispersion are found to bring about a better circumferential transportation of liquid. Depending on the heat transfer condition, two different patterns of phase distribution are found. The first associated with film boiling is mainly dominated by phase separation. The second connected with the rewetting phenomenon is governed firstly by phase separation and then phase redistribution in the form of liquid inward reversal.

Radiation Effects on S-Phase Duration, Labelling Index, Potential Doubling Time and DNA Distribution in Head and Neck Cancer Xenografts

The effect of irradiation on S-phase duration (Ts), labelling index (LI), potential doubling time (Tpot), and cell cycle phase distributions was determined by DNA flow cytometry in xenografted human squamous cell carcinoma of the head and neck (SCCHN). Tumours were treated with a single dose of 3 Gy, and excised at intervals over a 90-h period. Six hours before each excision the tumours were labelled in vivo with bromodeoxyuridine (BrdUrd). Although the growth rate of irradiated tumours was comparable with that of untreated controls, analysis of BrdUrd uptake revealed a transient reduction of LI and a prolongation of Ts in irradiated tumours. Maximum mean Tpot was 931 days in irradiated tumours as compared to 13 days in untreated controls. The variations in Ts, LI and Tpot all occurred within the first hours after irradiation; during the remainder of the observation time, the values of the variables did not differ from those of untreated controls. In irradiated tumours the distribution of cells according to DNA content changed significantly on three occasions during the observation period: 1) Parallel to the initial lowering of LI and prolongation of Ts there was a transient increase in the proportion of cells in G0/G1 and a decrease in the proportion of cells in S and G2; 2) At 18 h, the most pronounced cell cycle phase redistribution occurred when the G0/G1 fraction decreased and the S and G2 phase fractions increased; 3) At 66 h (i.e., approximately one cell cycle later), the pattern was the same as that after 18 h. The findings suggest that the transient prolongation of DNA replication seen in SCCHN cells immediately after a single radiation dose is a symptom of DNA damage inflicted during late G1 or early S-phase, and that this disturbance in DNA synthesis is associated with the subsequent accumulation of cells in G2 phase.

Modeling Changing Storage During a Shut-In Test

Summary Phase redistribution has been observed to occur in oil, gas, and steam-injection wells during a shut-in test. Two empirical approaches—involving exponential and error functions—are currently available to analyze field data. However, these methods do not have any mechanistic basis and may lead to erroneous estimates of reservoir parameters, such as skin. More importantly, these methods cannot be used in a forward mode to predict the reservoir and/or well conditions that would cause changing wellbore storage situations. Such predictions are desirable for deciding on the need for expensive downhole shut-in or flow measurement. Phase redistribution is a consequence of the higher relative velocity of the gas phase in a well's production string after shut-in at the surface. The resulting segregation of phases caused by buoyancy of the gas phase may cause wellbore pressure buildup to be quite different from normally expected response before the onset of the middle-time period. Under one scenario, the bubbles may segregate rapidly to the top of the wellbore leading to an increasing storage situation. Conversely, the bubbles may travel slowly without reaching the top to precipitate a decreasing storage situation. In either event, the commonly used constant-storage model cannot be used for test interpretation. A mechanistic approach, based on the physics of migration of a swarm of bubbles, is developed that explains the changing storage phenomenon by incorporating continually decreasing afterflow from the reservoir after shut-in, the variation of void distribution within the wellbore with depth and time, and the combined effect of afterflow and bubble migration on the wellhead and bottomhole pressures (BHP's). The model is used to develop a simulator, and a few cases are examined to illustrate the simulator's capabilities.