Edge Of Chamber Research Articles

ANALYSIS AND CHOICE OF DESCRIPTION METHODS FOR PROCESSES OF FATIGUE, CREEP AND LONG TERM STRENGTH FORECASTING FOR HIGH-SPEED FORCED DIESELS PISTONS

The work is devoted to the analysis and choice of description methods for processes of fatigue, creep and long-term strength forecasting of high-speed forced diesel pistons at the initial design stages. The existing description methods for the process of the combustion chamber parts fatigue of high-speed diesel engine are analyzed from the point of view of their use efficiency, especially at the initial design stages. The description methods are also considered for creep process in the material of high-speed engine combustion chamber parts. A method is proposed for estimating of accumulated damage in a piston material under conditions of low-frequency cyclic creep action. The forecasting method is presented for the long-term strength of the piston combustion chamber edge based on the operating model of a high-speed diesel engine, which takes into account the combined effect of low-frequency fatigue and creep on the damage accumulation process. It is proved that it is advisable to use the deformation criteria of fatigue strength to predict durability in the field of low-cycle fatigue.

Oil-Rate Prediction Model for the Ramp-Up Phase of a Steam-Assisted-Gravity-Drainage Process: Stability Approach

Summary In a steam-assisted-gravity-drainage (SAGD) process, the steam chamber starts to develop in three stages: ramp up, lateral spreading, and wind down. Although the physics of ramp up (or the rising phase) is completely different from that of lateral spreading, the current theoretical analyses of SAGD use a similar approach for modeling lateral spreading to calculate the ramp-up oil rate. The oil rate at the ramp-up phase is highly dependent upon the upward growth of the steam chamber, which is controlled by the frontal instability of the steam-condensate front into the heated bitumen. In this study, the evolution of disturbance (spatial-growth rate) was explored by solving the initial value problem governing the linear stability of the pressure and water-phase velocity normal to the edge of the steam chamber found in the SAGD process. To investigate the interaction of the steam chamber/reservoir zones, a new model was formulated that coupled the pressure diffusion equations and condensate leakoff into a reservoir beyond the chamber. The results suggested that the steam interface in the SAGD process was unstable if it moved faster than the critical velocity. In the ramp-up phase, the velocity at the chamber interface increased until it reached the instability velocity. Once it was reached, the instability caused extensive mixing and convection that reduced the temperature at the interface, thus causing the interface velocity to reduce to the instability velocity. As a result, the interface grew at the equilibrium velocity of minimum instability velocity (or critical velocity). The vertical/horizontal permeability ratio (Ωk) of the reservoir is a controlling parameter of instability. The calculated oil-production rate at ramp up increases linearly with time (i.e., qo∝t), which contradicts Butler's ramp-up formula that states that the rate is correlated to the cubic root of time (i.e., qo∝t1/3). Another key finding was that the suggested ramp-up-rate formula was highly dependent upon the reservoir-water mobility, which was supported by field operations in reservoirs with high water mobility such as Suncor/Firebag and Nexen/Long Lake, where the ramp-up time was significantly less than that in reservoirs with low water mobility, such as those in the MacKay River Field.

Models of steam-assisted gravity drainage (SAGD) steam chamber expanding velocity in double horizontal wells and its application

The development of steam chamber can be used to evaluate steam-assisted gravity drainage (SAGD) performance. The velocity of steam chamber expanding is the key parameter for evaluating the development of steam chamber. Based on SAGD technology theory and heat transfer theory, two calculation model methods, observation well temperature method and steam chamber edge method for estimating the horizontal expanding velocity of steam chamber, were presented. Through analyzing the monitoring data and numerical simulation results of a typical super heavy oil block developed by SAGD in Fengcheng oilfield in Xinjiang, NW China, the development patterns of steam chamber and temperature variation law in the observation well at different stages are determined. The observed temperature data was used to calculate steam chamber expanding velocity. The calculated chamber velocity at different time was applied to predict the temperature distribution of oil drainage zone at the edge of steam chamber and SAGD oil rate. The results indicate that temperature function of high temperature zone in the observation well temperature curve has a linear relationship with measuring depth. The characteristic section can be used to calculate key parameters such as the angle of the drainage interface, expanding edge and velocity of steam chamber. The field production data verify that the results of the two proposed methods of steam chamber growth are reliable and practical, which can provide theoretical support for the efficient development of SAGD.

Three-dimensional CFD simulation of a circular OWC with a nonlinear power-takeoff: Model validation and a discussion on resonant sloshing inside the pneumatic chamber

This study presents a three-dimensional numerical simulation of a circular bottom-sitting OWC device for wave energy extraction. The numerical model is based on Reynolds-Averaged Navier-Stokes equations with a modified k-ω turbulence model and a Volume-of-Fluid method to track the air-water surface. The numerical model and setup are validated against a set of wave-flume experimental results. The numerical simulation provides detailed flow-field information, which allows for an analysis of the spatial non-uniformity inside the OWC chamber and the measurement error associated with it. New numerical results show that vortex shedding at the sharp edge of the OWC chamber enhances the spatial non-uniformity inside the OWC chamber through a resonant sloshing mechanism. The enhanced spatial non-uniformity can affect the accuracy of the experimentally-determined quantities such as the extraction efficiency of the OWC chamber and the characteristics of the power take-off device; Suggestions are also provided to improve the accuracy of the experimentally-determined quantities that may be affected by the spatial non-uniformity inside the OWC chamber.

Determination of binary diffusion coefficients between hot liquid solvents and bitumen with X-ray CT

Abstract The Steam Assisted Gravity Drainage (SAGD) process has been used for in-situ thermal bitumen recovery in Canada. Nevertheless, there are several drawbacks that could impair the SAGD performance. One of the main drawbacks of SAGD is nontrivial consumption of energy to generate steam. To curtail the consumption of steam, many SAGD variants have been proposed. For example, Vapor Extraction (VAPEX) was proposed as a solvent-based cold production method and Solvent-Assisted SAGD (SA-SAGD) was proposed as a solvent-assisted hybrid method. In those solvent-based/assisted methods, the dissolution of solvents in bitumen enhances the in-situ oil mobility. The speed of the mixing between solvents and bitumen in solvent-based/assisted recovery processes is dictated by dispersive mass flux which is proportional to the transverse dispersion coefficient. Diffusion coefficient, tortuosity and transverse dispersivity should be quantified to characterize the transverse dispersion coefficient. In this research, the diffusion coefficients of solvents in Athabasca bitumen were determined with X-ray computed tomography (CT). A medical X-ray CT scanner was used to capture the diffusion phenomenon occurring between fresh liquid solvents and bitumen. The experiments were designed to reproduce the in-situ high pressure, high temperature condition (3.5 MPa, 135C) where solvent and bitumen actually interact at the vapor chamber edge in the SA-SAGD process. Using our new °experimental system, we successfully measured molecular diffusion coefficients at the condition of the vapor chamber edge for the first time. In conclusion, the binary diffusion coefficients between solvents and bitumen were successfully measured at the condition where the mixing of solvents and bitumen actually occurs in the SA-SAGD process. The characterized diffusion coefficients will be input parameters for the reservoir simulation and semi-analytical models.

INFLUENCE OF A TYPE OF CONTROLLING FUNCTIONS OF NON-STATIONARY PROBLEM OF THERMAL CONDUCTING ON THE RESOURCE STRENGTH OF THE PISTON

The analysis of calculation and experimental data of the temperature and thermo-stressed state of the piston in the transient processes of the engine is performed. The control functions are determined in the zone of the first and second porous rings. The results of the temperature state of the piston have been obtained taking into account certain control functions. The obtained results coincide with the experimental data with an error in the admissible mediums. A one-step change in control functions is considered in comparison with the obtained type of control functions. The influence of the type of control functions of the non-stationary heat conduction problem on the temperature and thermo-stressed state of the edge of the combustion chamber of the piston is shown. The simplified variants of control functions are offered on the basis of one-step change of the type of control functions. The estimation of the resource strength of the piston is taken into account taking into account the peculiarities of the change of simplified control functions. A simplified version of control functions is defined, which corresponds to the concept of guaranteed maintenance of the resource of the edge of the combustion chamber of the piston.

New Solubility and Viscosity Measurements for Methane–, Ethane–, Propane–, and Butane–Athabasca Bitumen Systems at High Temperatures up to 260 °C

One of the important mechanisms in solvent-aided thermal recovery processes is viscosity reduction due to dissolution of solvent in the bitumen. This dissolution occurs either with the condensed solvent at the edge of the steam chamber or with direct contact of gaseous solvent and bitumen. Therefore, it is essential to determine the solubility and viscosity of solvent in bitumen for reservoir simulation of solvent-aided thermal recovery processes. We report new experimental viscosity and solubility data of methane–, ethane–, propane–, and butane–Athabasca bitumen systems at high temperatures (up to 260 °C). The experimental measurements have been conducted under liquid–vapor equilibrium conditions. Peng–Robinson Equation of State (PR-EoS) was employed to model the solubility data. The tuned PR-EoS represented the experimental solubility data of methane, ethane, propane, and n-butane in bitumen with absolute average relative deviations of 5.7, 4.1, 7.8, and 4.9%, respectively. The reported data find applic...

Development of Process for Fast Plasma-Chemical Through Etching of Single-Crystal Quartz in SF6/O2 Gas Mixture

Process for deep plasma-chemical etching of single-crystal quartz plates in a SF6/O2 gas mixture was developed. The method of scientific experiment design based on the Taguchi matrix technique was used to rank basic technological parameters (bias voltage applied to the substrate holder, output power of the high-frequency generator, oxygen flow rate, and position of the substrate holder relative to the lower edge of the discharge chamber) as regards their influence on the etching rate. The ranking results were used to optimize the plasma-chemical etching process and perform a control experiment on through etching of windows with large linear dimensions (3 × 10 mm) in a single-crystal quartz plate (z-cut) with thickness of 369 μm.

Steam-Oil Ratio in Steam-Solvent Coinjection Simulation for Homogeneous and Heterogeneous Bitumen Reservoirs

This research presents a mechanistic analysis of expanding-solvent steam-assisted gravity drainage (ES-SAGD) for heterogeneous reservoirs in terms of cumulative steam-oil ratio (SOR) as a function of cumulative bitumen production. Simulation case studies for SAGD and ES-SAGD with normal hexane at 35 bars are conducted for geostatistical realizations of two types of heterogeneous Athabasca-bitumen reservoirs. For the first type, low-permeability mudstone barriers are oriented horizontally. For the second type, they are inclined and more representative of the middle McMurray member. The solubility of water in the oleic phase at elevated temperatures is properly modeled to ensure reliable comparison between steam-assisted gravity drainage (SAGD) and ES-SAGD. Simulation results show that ES-SAGD is less sensitive to heterogeneity than SAGD in terms of cumulative SOR. On average, the reduction in SOR due to steam-solvent coinjection is simulated to be greater under heterogeneity. The reduction in SOR is greater for reservoir models with inclined mudstone barriers than in those with horizontal mudstone barriers. Analysis of simulation results indicates that the injected solvent tends to accumulate more significantly under heterogeneity, which enhances the mechanisms of ES-SAGD, such as dilution of bitumen by solvent and reduced thermal losses to the overburden. Tortuous hydraulic paths and slower gravity drainage under heterogeneity enhance the mixing between solvent and bitumen in the transverse direction along the edge of a steam chamber. Then, a larger amount of the accumulated solvent tends to facilitate lower temperatures near the chamber edge.

Mechanistic simulation study of expanding-solvent steam-assisted gravity drainage under reservoir heterogeneity

Expanding-solvent steam-assisted gravity drainage (ES-SAGD) is a potential method to reduce steam-oil ratio (SOR) of SAGD, which is a critical concern especially for highly-heterogeneous reservoirs. The main objective of this research is to investigate the flow characteristics of heterogeneous reservoirs in which solvent is more likely to lower SOR of SAGD.SAGD and ES-SAGD with normal hexane are simulated for fifty geostatistical realizations consisting of clean sand and shale, qualitatively representative of the middle member of the McMurray formation. Thermodynamic models are calibrated with experimental phase behavior data for reliable comparison between SAGD and ES-SAGD, including the water solubility in oil at elevated temperatures.Results show that the SOR reduction by steam-solvent coinjection is positively correlated with the increase in SAGD's SOR due to heterogeneity. Enhancement of bitumen flow by dilution is more important for lowering SOR for those reservoirs in which the permeability variation makes slow-flow regions during SAGD.Simulation results show that a larger amount of bitumen tends to be diluted by solvent in those reservoirs for which SAGD exhibits slow production of bitumen. Then, the observed results are analyzed by use of SAGD analytical equations that clarify several influential factors for bitumen flow beyond the edge of a steam chamber. It is shown that dilution of bitumen by solvent in steam-solvent coinjection becomes more significant where flow barriers limit the local bitumen flow under SAGD even at high temperatures. In such slow-flow regions, the bitumen flow rate can be substantially increased by accumulation of solvent in ES-SAGD, which reduces the oleic-phase viscosity and increases the oleic-phase saturation and, therefore, relative permeability. Solvent accumulation within a steam chamber can also reduce thermal losses because of lower operating-chamber temperatures.

Performance of Solvent-Assisted Thermal Drainage process and its relationship to injection parameters: A comprehensive modeling

The addition of hydrocarbon solvents to the steam injection, known as Solvent-Assisted Thermal Gravity Drainage (SA-SAGD), has recently been proven to be a more energy saving and environmentally friendly method for heavy oil recovery. Nevertheless, the relationship between injection parameters and heavy oil production in conventional SAGD were always introduced to analysis the performance of SA-SAGD, which makes many confusing in the interpretation. In this paper, the heat lost to the cap rock of the reservoir is determined by taking into account not only the chamber-edge velocity, but also the temperature and mass distributions inside the chamber. Besides, by implicitly characterizing the chamber-edge shape and considering heat and solvent diffusion beyond the chamber edge, the oil rate is calculated. Then, the model couples heat and mass balance equations in the whole oil sand dynamically by considering the effect of liquid pool. This comprehensive method enables us to clearly examine the relationship between the Production-Injection Ratio (PIR) and the height of liquid pool. Lastly, the new model is verified by comparing predicted results with that of numerical simulation. The results show that, the oil rate of SA-SAGD is improved by both of the diluting effect of solvent on bitumen viscosity and a more reasonable chamber shape formed by co-injection solvent with steam. In addition, although heat-loss rate of SA-SAGD is generally smaller than that of conventional SAGD, the Steam-Oil Ratio (SOR) of SA-SAGD may even higher than that of SAGD in the late period of the process if the liquid level is extremely high. Moreover, the liquid-pool height for SA-SAGD is more sensitive to the PIR than for SAGD. Accordingly, when the effect of liquid pool on the production is considered, the PIR of SA-SAGD must be selected carefully.

A Semianalytical Model for Simulating Combined Electromagnetic Heating and Solvent-Assisted Gravity Drainage

Summary Solvent/thermal hybrid methods have been proposed recently to enhance heavy-oil recovery and to overcome the shortcomings that are encountered when either method is solely applied. One of the methods for this hybridization is to combine electromagnetic (EM) heating and solvent injection to facilitate heavy-oil production by gravity drainage. This approach has several advantages including reduced CO2 emissions, decreased water consumption, and appropriateness for water-hostile reservoirs. We are currently lacking any mathematical model for better understanding, designing, and optimizing this hybrid technique, which is partly attributed to this technique still being in its infancy. We propose a semianalytical model to predict the oil-flow rate resulting from the combined EM heating and solvent-assisted gravity drainage. The model first calculates the temperature distribution within the EM-excited zone caused by the radiation-dominated EM heating. Using different attenuation coefficients within and beyond the vapor chamber, the model can properly describe the corresponding temperature responses in these regions. Next, an average temperature of the chamber edge contributed by EM heating is used to estimate the temperature-dependent properties, such as vapor/liquid equilibrium ratios (K-values), heavy-oil/solvent-mixture viscosity, and solvent diffusivity. Subsequently, a 1D diffusion equation is used to calculate the solvent-concentration distribution ahead of the chamber edge. Eventually, the oil-flow rate is evaluated with the calculated temperature and solvent distributions ahead of the chamber edge. The proposed model is validated against the experimental results obtained in our previous study, and the predicted oil-flow rate agrees reasonably well with the experimental data. The proposed model can efficiently predict the oil-flow rate of this hybrid process. We conduct sensitivity analyses to examine the effect of major influential factors on the performance of this hybrid technique, including EM heating powers, solvent types, solvent-injection pressures, and initial reservoir temperatures. The modeling results demonstrate that a higher EM heating power, a heavier solvent, and a higher solvent-injection pressure could accelerate the oil-recovery rate, but tend to lower the net present value (NPV) and increase the energy consumption. In summary, the newly proposed model provides an efficient tool to understand, design, and optimize the combined technique of EM heating and solvent-assisted gravity drainage.

On the Effect of the Surface State and Geometry of the Discharge- Chamber Edges and Sizes of Morozov’s Stationary Plasma Thruster upon its Long-Term Operation

The results of long-term tests of Morozov’s stationary plasma thrusters are presented. It is revealed how the surface state and geometry of the discharge chamber’s edges influence the thruster’s parameters. It is shown that, during the ground tests of thrusters with cylindrical geometry of the acceleration channel under initial stage of operation, material sputtered from the discharge chambers’ walls is deposited onto the nearanode segment of the walls. Films of deposited material fail during thruster operation causing fragment formation, which jut out towards the discharge volume and disturb the motion of drifting electrons in the area of their acceleration. As a result the thruster reactive force and specific impulse decrease. The way in which the forming fragments influence thruster performance and operation is examined. It is shown that it decreases under long-term operation and significant channel widening since the ion flux to the wall and the quantity of the sputtered material decrease, and since the profile of the walls changes due to their wear and cleaning effect of the discharge. As a result the thruster’s parameters are restored to a level close to the initial one. It is shown that the dynamics of thruster parameters variation in space and during ground tests is different. This means that it is necessary to simulate more properly the conditions of thruster operation in space when conducting ground development tests. Thrusters with a long lifetime should be designed with widening of the acceleration channel beyond the loop which surrounds the magnetic system so that areas of acceleration and the erosion of walls are located in the widened part of the channel.

Dimethyl Ether as an Additive to Steam for Improved Steam-Assisted Gravity Drainage

Summary Coinjection of solvent with steam results in lower chamber-edge temperatures than those in steam-assisted gravity drainage (SAGD), which enables the decrease of heat losses to the overlying formation rocks. However, use of highly volatile solvents, such as propane, can yield significantly slow bitumen production because of low chamber-edge temperatures. The suitability of alkane solvents for SAGD in terms of phase behavior has been reported to increase with increasing carbon number and tends to level off at a certain carbon number, which is approximately C6 for Athabasca bitumen reservoirs. The main objective of this research is to investigate the potential of dimethyl ether (DME), a water-soluble solvent, as an additive to steam for reducing steam/oil ratio (SOR) while keeping SAGD-like rates of bitumen production. The chamber-edge temperature for a given overall composition and operating pressure is defined as the temperature at which the vapor phase completely condenses with decreasing temperature. Thermodynamic predictions show that the chamber-edge temperature so defined will increase substantially if the solvent can partition into the aqueous phase at chamber-edge conditions. This is confirmed in numerical-reservoir simulation for coinjection of steam with DME, as a water-soluble solvent, for Athabasca bitumen. In simulation case studies, coinjection of steam with DME (DME-SAGD) is compared with SAGD and coinjection of steam with C4 (C4-SAGD), in terms of SOR, bitumen production, local displacement efficiency, and solvent recovery. The steam-injection pressure is 35 bar for all cases, and 2 mol% of solvent is coinjected in solvent-SAGD simulations until the steam chamber reaches the side boundary of a 2D homogeneous reservoir model. Because the DME volatility is between C3 and C4, C4 is selected as the alkane counterpart in this simulation study to see the effect of the solvent solubility in water on oil recovery in solvent-SAGD. DME is more volatile and less soluble in bitumen than C4 at their corresponding chamber-edge conditions. However, results show that DME-SAGD results in 35% lower SOR than SAGD while being able to increase bitumen-production rates of SAGD. Analysis of simulation results indicates that the solubility of DME in water not only makes the chamber-edge temperature higher than that of C4-SAGD, but also yields 15% higher solvent-recovery factor than C4-SAGD. The main reason for the latter observation is that a much-smaller fraction of the injected solvent is present in the vapor phase in DME-SAGD than in C4-SAGD. Also, DME dissolves in both water and bitumen, which results in the aqueous and oleic phases of nearly equal density within the gravity-drainage zone near the edge of a steam chamber. This is the neutral regime of oil/water two-phase flow along the chamber edge between the two extreme cases: SAGD and C4-SAGD. Unlike in C4-SAGD, the reduced gravity segregation in DME-SAGD is expected to facilitate the mixing of condensed solvent with bitumen near the edge of a steam chamber.

Evolution characteristics of SAGD steam chamber and its impacts on heavy oil production and heat consumption

Currently, Steam-Assisted Gravity Drainage (SAGD) is the most successful commercialized method used to produce bitumen from oil sands and heavy oil reservoirs. Precise description of the steam chamber evolution is important for evaluating the economic effectiveness and Greenhouse Gas (GHG) emission of the SAGD process. In this study, the properties of MacKay River Oil Sands were used in laboratory experiments to compare the chamber evolution and production performance of SAGD under different permeability distributions. Then, a mathematical model was established to predict the steam chamber evolution and the closely related oil production and heat consumption in a heterogeneous formation. Next, the calculated production performance and steam chamber evolution were compared with measured experimental data to verify the accuracy of the model. Finally, the chamber evolution characteristics and their impacts on SAGD oil production and heat consumption are discussed in this paper for formations with different permeability distributions. The results indicate that horizontal permeability controls the evolution of steam chamber such that higher horizontal permeability may cause an obvious convex shape of the chamber edge, whereas vertical permeability has little effect on the chamber shape despite significant influence on the oil production in the early stage of SAGD. Moreover, a convex-shaped chamber interface indicates a higher production rate in the spreading stage and a lower rate in the depleting stage. In addition, this study shows that to minimize the heat consumption of the SAGD process, so that GHG emission can be curbed, a concave-like chamber shape is favorable in the early spreading stage, whereas a convex shape is better in the late spreading stage and depleting stage.

Analytical solution for steam-assisted gravity drainage with consideration of temperature variation along the edge of a steam chamber

Steam-assisted gravity drainage (SAGD) is a widely-used method for heavy-oil and bitumen recovery. Analytical SAGD models presented in the literature often overestimate bitumen-production rate substantially. Although bitumen-production rate and steam-oil ratio (SOR) depend significantly on temperature near the steam-chamber edge in SAGD, previous analytical models assumed the injected-steam temperature to uniformly distribute along the edge of a steam chamber. The main objective of this research is to develop the first analytical SAGD model that takes into account temperature variation along the edge of a steam chamber.Local material balance and Darcy’s law are applied to each cross section perpendicular to the edge of a steam chamber. Then, they are coupled with the global material balance for the chamber geometry that is an inverted triangle. New analytical equations are presented for bitumen-production rate and SOR, in addition to associated variables as functions of elevation from the production well, such as oil-flow rate and temperature along a linear chamber edge. Bitumen-production rate and SOR can be calculated for a representative chamber-edge temperature at a certain elevation from the production well.Comparison of the analytical model with numerical simulations shows that bitumen-production rate and SOR can be accurately estimated when the new model is used with the temperature taken from the midpoint of the edge of a steam chamber. The chamber-edge temperature used for the new analytical model that gives accurate results can be up to 100 Kelvin lower than the injected steam temperature for a given operating pressure in the cases tested. The previous assumption of the injected-steam temperature at the chamber edge gives overestimated oil-production rates for SAGD. The constant temperature along the edge of a steam chamber gives Butler’s concave interface of a steam chamber that is detached from the production well. For a chamber to exhibit a linear interface, temperature must vary along the chamber edge, which occurs in reality mainly because of heat losses to the over- and under-burden formations.

In–Situ Dilation Affects Solvent–Assisted Steam–Assisted–Gravity–Drainage Performance: The Case of a Shallow Athabasca–Type Oil–Sands Reservoir

Summary It is generally accepted that solvent/steam injection in heavy-oil/bitumen reservoirs outperforms steam-only injection in terms of oil-recovery rate, ultimate oil recovery, and steam/oil ratio (SOR). Important parameters in the design of solvent-assisted steam-assisted-gravity-drainage (SA-SAGD) are solvent selection, injection strategy, and solvent retention in situ. The role of geomechanics in optimal application of SA-SAGD, however, remains largely unexplored. Recent studies suggest that solvent transport, solvent-dilution effect, and the temperature distribution around the edge of the steam chamber have major control over SA-SAGD performance. In SA-SAGD, elevated temperature and solvent concentrations within a few meters of the steam-chamber edge reduce the virgin-oil viscosity, causing oil drainage. However, this is the same region where geomechanically induced volume changes alter porosity, permeability, and relative permeability profiles. These alterations could improve the convective-heat transfer and solvent dispersion into the cold bitumen zone, and could also enhance the drainage rate. Consequently, the solvent/oil-phase behavior, steam-chamber growth, and solvent retention and distribution will be affected. This chain of events could have an effect on optimal solvent selection and solvent/steam-injection scenarios. These geomechanical considerations are of particular interest for bitumen deposits, both oil sands and carbonates, where chemical, thermal, and fluid pressures can impose significant volume changes within the reservoir, especially in shallower, lower-confining-stress settings. The role of geomechanics in SA-SAGD was explored numerically by use of a sequentially coupled modeling approach with STARS (CMG 2015a) and FLAC (Itasca 2016). A 2D shallow-depth homogeneous-oil-sands-reservoir geomodel, with properties similar to the Underground Test Facility (UTF) Phase A project, was constructed (Edmunds et al. 1994). Studies were conducted at two scales: the edge of the steam chamber and the reservoir scale including underburden and overburden. The results of these numerical studies revealed that geomechanics considerations directly affect the optimal solvent-type selection and injection strategy during a high-pressure SA-SAGD process. These studies provide valuable direction for further detailed mechanistic studies (both numerically and experimentally) and provide valuable input to the challenges of optimizing SA-SAGD processes in oil sands.

Hybrid steam/solvent wellbore design for an optimal operation

To have an efficient oil recovery in hybrid steam-solvent injection, the solvent must condense at the steam chamber edge. Thus, the injection well must deliver the solvent near its dew point at the sand face. This paper presents a sensitivity analysis to study how different operational parameters and well design affect the behaviour of steam and solvent along the wellbore before reaching the perforation intervals. This study highlights the importance of wellbore modelling in the solvent assisted steam injection process. Results show that with some specific operational parameters and solvent composition, up to 23% of the solvent condense along the wellbore before reaching the sand face, meaning that only 77% of the solvent mixture effectively is used for the heavy oil recovery. Also, in a case study, it was shown that using 2 7/8 inch tubing instead of a 3 1/2 inch leads to a temperature improvement of 54°F. [Received: December 16, 2016; Accepted: June 18, 2017]

Cornea and anterior eye assessment with placido-disc keratoscopy, slit scanning evaluation topography and scheimpflug imaging tomography.

Current corneal assessment technologies make the process of corneal evaluation extremely fast and simple and several devices and technologies allow to explore and to manage patients. The purpose of this special issue is to present and also to update in the evaluation of cornea and ocular surface and this second part, reviews a description of the corneal topography and tomography techniques, providing updated information of the clinical recommendations of these techniques in eye care practice. Placido-based topographers started an exciting anterior corneal surface analysis that allows the development of current corneal tomographers that provide a full three-dimensional reconstruction of the cornea including elevation, curvature, and pachymetry data of anterior and posterior corneal surfaces. Although, there is not an accepted reference standard technology for corneal topography description and it is not possible to determine which device produces the most accurate topographic measurements, placido-based topographers are a valuable technology to be used in primary eye care and corneal tomograhers expanding the possibilities to explore cornea and anterior eye facilitating diagnosis and follow-up in several situations, raising patient follow-up, and improving the knowledge regarding to the corneal anatomy. Main disadvantages of placido-based topographers include the absence of information about the posterior corneal surface and limited corneal surface coverage without data from the para-central and/or peripheral corneal surface. However, corneal tomographers show repeatable anterior and posterior corneal surfaces measurements, providing full corneal thickness data improving cornea, and anterior surface assessment. However, differences between devices suggest that they are not interchangeable in clinical practice.

Hybrid steam/solvent wellbore design for an optimal operation

To have an efficient oil recovery in hybrid steam-solvent injection, the solvent must condense at the steam chamber edge. Thus, the injection well must deliver the solvent near its dew point at the sand face. This paper presents a sensitivity analysis to study how different operational parameters and well design affect the behaviour of steam and solvent along the wellbore before reaching the perforation intervals. This study highlights the importance of wellbore modelling in the solvent assisted steam injection process. Results show that with some specific operational parameters and solvent composition, up to 23% of the solvent condense along the wellbore before reaching the sand face, meaning that only 77% of the solvent mixture effectively is used for the heavy oil recovery. Also, in a case study, it was shown that using 2 7/8 inch tubing instead of a 3 1/2 inch leads to a temperature improvement of 54°F. [Received: December 16, 2016; Accepted: June 18, 2017]