Edge Of Chamber Research Articles

Abstract ID: 53 Impact of the true sensitive volume on ion chamber response in magnetic fields

Development of magnetic resonance guided radiation therapy (MRgRT) has sparked interest in evaluating the performance of ion chambers in the presence of magnetic fields. The effect of the field on electron trajectories alters ion chamber response [1] . In most Monte Carlo (MC) simulations, the geometric sensitive volume, often beginning at the edge of chamber’s stem, is used instead of the potentially unknown true collection volume [2] . This work evaluates the sensitivity of chamber response in the presence of magnetic fields to the collection volume used in the MC calculation. The egs_chamber application of the EGSnrc system is used with a recently validated magnetic field transport algorithm [3] to simulate the response of several ion chambers. The chambers are simulated in a PMMA phantom with an incident Co-60 photon beam and magnetic fields between 0 and 2 T, perpendicular to both the incoming photon field and the long axis of the ion chamber. The dose, normalized to 0 T, is calculated in the geometric sensitive volume with either the first 0, 0.5, or 1.0 mm of the volume away from the stem excluded. Increases in chamber response with a maximum of 1.77 ± 0.03% and 3.33 ± 0.03% are observed for a reduction in the length of the collection volume by 0.5 mm and 1.0 mm, respectively. For four chambers, the reduced volumes generally give better agreement with experimental results [4] . Various chamber orientations are under investigation to minimize the effect. This is an important effect that must be addressed to ensure proper calibration of MRgRT machines.

FEATURES OF THE DETERMINATION OF BORDER CONDITIONS OF NON-STATIONARY PROBLEMS OF HEAT CONDUCTIVITY OF DIESEL PISTON

The stationary and non-stationary models of the operation of transport engines have been analyzed by using the example of a third-class tractor diesel. The estimation of the resource strength of the edge of the combustion chamber of the piston is made taking into account the change in the rotational speed of the crankshaft. The control functions of the boundary conditions of the thermal conductivity of the piston in the zone of piston rings are determined, which are necessary for modelling the main transient processes of the non-stationary model of diesel operation. The work is performed on the example of a diesel engine 4ЧН12/14.

Unified model of heat transfer in the multiphase flow in Steam Assisted Gravity Drainage process

Steam assisted gravity drainage (SAGD) is an effective method for bitumen and heavy oil reservoirs. In SAGD process, steam is injected into the reservoir with a high pressure from the upper horizontal well, and the injected steam will heat the surrounding oil sands through a conduction and convection heat transfer process. In this paper, a novel unified model is developed to investigate the heat transfer mechanism in SAGD process. Typically, the multiphase flow assumption at the edge of steam chamber is introduced in our model. And the effect of both the conduction and convection heat transfer in steam chamber are considered. Especially, in this model, the convective heat transfer process caused by pressure difference and gravity is studied. Then the simulation results are compared against the UTF field data to confirm the accuracy of our model. Results indicate that our model can match the UTF field data very well, and it can be used to investigate the heat transfer process in SAGD process. It is found that the oil production rate decreases as the interface velocity increases. The optimal interface velocity is about 1.5–2.5 cm/d. In this range, the oil production rate is about 0.4 m3/(m·d) and oil cut is approximately 31%. The variations of condensate liquid mobility and density lead to that oil production will decrease as the pressure difference increases. Finally, it can be concluded that a suitable injection pressure should be chosen to guarantee the optimal interface velocity in SAGD process. This new model will benefit to understanding the convective heat transfer mechanism and guiding the field production behavior in SAGD process.

A Phase-Behavior Study for n-Hexane/Bitumen and n-Octane/Bitumen Mixtures

Summary Steam/solvent coinjection has been studied as a potential method to improve the efficiency of conventional steam-assisted gravity drainage (SAGD) for bitumen recovery. This research is part of an experimental program for phase behavior of Athabasca-bitumen/solvent mixtures. This paper presents a new set of experimental data for phase equilibrium, viscosity, density, and asphaltene precipitation for 11 mixtures of Athabasca bitumen with n-hexane and 10 mixtures of the same bitumen with n-octane. Phase-boundary measurements were conducted at temperatures up to 160°C and pressures up to 10 MPa. The bitumen sample used in this research was studied in our previous research, in which the same bitumen was not effectively diluted by n-butane because of the coexistence of a butane-rich liquid with a bitumen-rich liquid phase. In this research, the liquid/liquid separation of hydrocarbons was not observed for n-hexane/bitumen (HB) and n-octane/bitumen (OB) mixtures for the range of temperatures and pressures tested, even at solvent concentrations higher than 90 mol%. This observation indicates that the amount of solvent available near the edge of a steam chamber is expected to be entirely used for bitumen dilution beyond the chamber edge in coinjection of steam with heavier hydrocarbon solvents, such as n-hexane and n-octane. Experiments for asphaltene precipitation at atmospheric pressure showed a larger amount of precipitates with n-hexane than with n-octane at a given solvent concentration higher than 50 wt%. For solvent concentrations less than 50 wt%, no asphaltene precipitation was observed for both solvents with the bitumen sample tested in this research.

Development of a system for organizing a modular design and technological preparation for the production of cast iron pistons for internal combustion engines

Modern engine building requires a significant increase in power, fuel efficiency and ensuring high environmental performance of internal combustion engines (ICE). When forcing the operating modes of diesel engines, one of the most loaded engine parts becomes a piston, due to a significant increase in mechanical and thermal stresses. With increasing load on the piston, the difficulty of meeting the high demands for them increases. When creating modern ICE and improving the quality of existing ones, special attention is paid to the design and technological preparation of the production of pistons, which is the object of research. Pistons determine the reliability and life of the engine as a whole.To solve this problem, all the main works related to the design and manufacture of cast-iron pistons are proposed to divide into separate modules, performed simultaneously in three areas: organizational, design and technological. These modules are integral sectors of a single modular system for organizing design and technological preparation for production of cast iron pistons. Modeling of the stressed-strain state of monolithic cast-iron pistons is considered for an example of implementation of one of the modules. The results of calculations of the stress-strain state and the temperature distribution field in the body of the piston are presented. The results show that the maximum temperature is 315 °C and concentrated on the edge of the combustion chamber. The stress does not exceed 617 MPa.

Analysis of adaptive grid refinement technique for simulations of ES-SAGD in heavy oil reservoirs

The intrinsic advantages of hybrid steam-solvent or solvent-based thermal recovery methods for heavy oil include faster oil production, higher ultimate recovery factor, reduction of energy, and water treatment expenses, better control of GHG emission. Light hydrocarbon injection implies improved heavy oil mobilization, steam and solvent condensation, solvent to oil mixing, and oil viscosity effect at moderate temperature. Typically, field-scale reservoir simulation models are built on numerical grids with cell sizes making practically difficult accurate description of heat and mass transport at the edge of the gas chamber. Outside this zone, this typical grid can be acceptable. The adaptive grid refinement may offer a compromise solution if the numerical model accepts the necessary degree of refinement. In our current work, we present a methodology of large-scale numerical simulations for so-called expanding solvent SAGD (ES-SAGD) processes using adaptive dynamic gridding at different degrees of the refinement. The adaptive grid refinement is a Cartesian grid amalgamation process based on threshold values of predefined trigger variables. Comparison is performed between oil production mechanism interactions for typical Athabasca bitumen and illustrated with temperature and solvent concentration fields for different discretization sizes. Good adaptive grid refinement results have been obtained for the models based on adaptive implicit approach with high refinement degree, in heterogeneous reservoir (at relatively small correlation length) in vertical 2D cross-section. The numerical performance aspects including the CPU time analysis with and without the use of dynamic gridding are presented in some detail.

Multiple optical diagnostics on effect of fuel stratification degree on reactivity controlled compression ignition

Reactivity controlled compression ignition (RCCI) was investigated on a light-duty optical engine under different fuel stratification degrees, using multiple laser diagnostic techniques. The engine was run at a speed of 1200rpm and under a load of about 7bar gross IMEP. To form different fuel stratification degrees, the direct-injection timings of n-heptane were changed, while the port-injection timings of iso-octane was kept constant. The fuel/air equivalence ratio and primary reference fuel (PRF) number were quantified by the fuel-tracer planar laser-induced fluorescence (PLIF) under non-combusting condition. The results indicated that with retarding n-heptane injection timing from −90° CA ATDC (RCCI-90 case) to −10°CA ATDC (RCCI-10 case), regions of higher fuel concentration and reactivity moved downstream to the edge of combustion chamber before high-temperature heat release (HTHR) phase. Time-resolved natural combustion luminosity imaging and single-shot OH PLIF imaging indicated that RCCI-10 case presented a staged combustion process that an auto-ignition first happened in the region of high reactivity around the combustion chamber and then another auto-ignition process took place in the region of low reactivity in the central part of the combustion chamber. The staged combustion feature involved in RCCI combustion could result in lower combustion pressure-rise rate. PLIF images of formaldehyde showed that formaldehyde first formed during low-temperature heat release (LTHR) phase in the regions where n-heptane resided. With retarding n-heptane injection timings, both formaldehyde and OH PLIF images presented more stratified distribution, and the consumption of formaldehyde and formation of OH processes got slower. OH PLIF images indicated that HTHR phase of RCCI could extend to the central part of combustion chamber. In the low-load LTC conceptual model proposed by Musculus et al. (2013), no HTHR happened and UHC formed in the central part of combustion chamber. This meant that RCCI could have less UHC emission than LTC in theory.

The Palatal Interpterygoid Vacuities of Temnospondyls and the Implications for the Associated Eye- and Jaw Musculature.

A diagnostic feature of temnospondyls is the presence of an open palate with large interpterygoid vacuities, unlike the closed palate of most other early tetrapods, in which the vacuities are either slit-like or completely absent. Attachment sites on neurocranium and palatal bones in temnospondyls allow the reconstruction of a powerful m. retractor bulbi and a large, sheet-like m. levator bulbi that formed the elastic floor of the orbit. This muscle arrangement indicates that temnospondyls were able to retract the eyeballs through the interpterygoid vacuities into the buccal cavity, like extant frogs and salamanders. In contrast, attachment sites on palate and neurocranium suggest a rather sauropsid-like arrangement of these muscles in stem-tetrapods and stem-amniotes. However, the anteriorly enlarged, huge interpterygoid vacuities of long-snouted stereospondyls suggest that eye retraction was not the only function of the vacuities here, since the eye-muscles filled only the posterior part of the vacuities. We propose an association of the vacuities in temnospondyls with a long, preorbital part of the m. adductor mandibulae internus (AMIa). The trochlea-like, anterior edge of the adductor chamber suggests that a tendon of the AMIa was redirected in an anteromedial direction in the preorbital skull and dorsal to the pterygoids. This tendon then unfolded into a wide aponeurosis bearing the flattened AMIa that filled almost the complete interpterygoid vacuities anterior to the orbits. Our muscle reconstructions permit comprehensive insights to the comparative soft tissue anatomy of early tetrapods and provide the basis for a biomechanic analysis of biting performances in the future. Anat Rec, 300:1240-1269, 2017. © 2017 Wiley Periodicals, Inc.

Analysis of methods for improvement of thermal stability of pistons of tractor diesel engines

The article considers the applied methods for improving the thermal strength of pistons of internal combustion engines. Tractor diesels with combustion chamber in the piston have the greatest rate of temperature change at load rise and release, as well as the highest values of temperature gradients. The highest thermal loads occur in pistons with a semi-open combustion chamber. Periodic thermal loads with high value of temperature gradient lead to thermal fatigue fractures. Such fractures may begin with the appearance of cracks on the edge of combustion chamber. The presence even of a small crack on the edge of combustion chamber leads to its further growth, which can cause the destruction of piston. The main causes of cracks formation on the edge of combustion chamber are the alternating stresses induced from alternating gas pressure in cylinder during the working cycle; the low-frequency oscillations of the piston temperature arising from the changing of operation modes of engine; the high-frequency cyclical thermal oscillations caused by the temperature change of material in the surface layer of combustion chamber for each working cycle. The most common design and technology solutions improving the thermal strength of pistons are the following ones: the change of the edge radius of combustion chamber throat; the reinforcement of combustion chamber edge with more heat-resistant materials; the use of materials with high thermal stability for manufacture of pistons; the artificial heat insulation of piston or its cooling by oil. The disadvantage of use of cooling oil gallery is the acceleration of oil aging process. The alternative solution is to limit the heat supply to the walls of combustion chamber by means of heat protection coating applied by gas-flame, detonation or electric-arc way. The easiest way to improve the thermal strength of diesel piston with a semi-open combustion chamber is the design change.

A Model to Estimate Heat Efficiency in Steam-Assisted Gravity Drainage by Condensate and Initial Water Flow in Oil Sands

Steam-assisted gravity drainage (SAGD) is one of the most popular approaches for oil sands recovery. In this study, an accurate and simple heat efficiency calculation model is presented by modeling transient heat transfer involving the flow of both hot condensate and mobile initial water in oil sands. A 2-D numerical simulation procedure is proposed to calculate temperature distribution ahead of the steam chamber edge in SAGD. A new heat efficiency model is proposed to estimate heat efficiency in SAGD by using the temperature distribution obtained from the 2-D numerical simulation. Results indicate that convection dominates the heat transfer ahead of the steam chamber edge which is induced by condensate and initial water flow in oil sands. On the basis of these studies, abundant analysis shows that the heat efficiency of SAGD can be improved by using moderate steam injection pressures for the reservoir scenarios from 1 to 10 darcy permeability.

Failure criteria of heat-stressed parts of piston engines and the review of methods for assessment of pistons durability

During designing, calculation and further development of an engine it is necessary to take into account all the values that define its lifetime. In variable modes of tractor diesel engine, the stress level of piston changes over time, which leads to the appearance of cracks on the edge of combustion chamber. It especially applies to the semi-open combustion chambers. The appearance and growth of crack to a critical length often leads to failure of the combustion chamber edge. In this regard, the selection of failure criteria of pistons in operation is an urgent task. The durability assessment should be made on the criteria of the thermal fatigue strength that could be divided into three groups: the deformation criteria, the deformation and kinetic criteria, the energy criteria. Deformation criteria is the most widely used. Taking into account the active loading in conditions of uniaxial tension, the damage accumulation related to the material plastic deformation, or the peak deformation criterion is determined. Along with experimental methods consuming time and money, the other reliability assessment methods based on the numerical calculations, such as finite element method become common use. The fatigue material properties when loading a small number of cycles are determined by the Coffin-Manson equations in the form introduced by J. Morrow for the amplitudes of elastic and plastic deformations, depending on the number of cycles to failure. The analysis of the works of various authors shows that the crack growth process is not fully considered. The lack of theoretical approach to determining the remaining lifetime demands the improvement of calculation method which should take into account the temperature difference on the surface of piston, gas pressure and piston geometric dimensions affecting the stress concentration.

Analysis of thermal temperature fields and thermal stress under steady temperature field of diesel engine piston

With the improvement of the diesel engine power and performance, the piston in the combustion chamber is subjected to higher thermal load and the thermal stress decreases its working life. Therefore, it is necessary to analyze the subsequent thermal stress on the piston during design process to reach the optimum one. This paper tries to present a new calculation method for the theoretical design of the piston. In this study, the 3D solid model of piston in 16V280 diesel engine was developed and the simulation calculation of the steady-state and the transient-state temperature field is carried out. Based on calculation results, the maximum temperature fluctuation of the piston temperature field is less than 20°, so the steady-state temperature field was used as boundary condition for the thermal stress calculation and the thermal mechanical decoupling method was used to calculate the thermal stress caused only by the uneven temperature distribution. The results show that the maximum temperature is 354°C, which appears at the edge of the combustion chamber. The steady-state temperature field of finite element simulation shows a good agreement with the experimental results. The thermal stress obtained from thermal mechanical decoupling method was within the allowable range, since the maximum value is 270MPa. Danger zone appears at the combustion chamber throat, the contact area of piston head and skirt.

An Experimental Study of Multiphase Behavior for n-Butane/Bitumen/Water Mixtures

Summary Steam/solvent coinjection has been studied and pilot tested as a potential method to improve steam-assisted gravity drainage (SAGD) for bitumen recovery. Reliable design of coinjection requires reliable pressure/volume/temperature (PVT) data for bitumen/solvent/water mixtures, which are scarce and fragmentary in the literature. The main objective of this research was to present a new set of PVT and multiphase data for n-butane/Athabasca-bitumen/water mixtures at pressures up to 10 MPa and temperatures up to 160°C. Experiments were conducted with a conventional PVT apparatus. The data presented include multiphase equilibria up to four coexisting phases and liquid densities for 100% bitumen, two mixtures of n-butane/bitumen, and one mixture of n-butane/bitumen/water. Liquid/liquid separation of hydrocarbons was experimentally observed at the n-butane concentration of 97 mol% in the n-butane/bitumen system with/without water, for a wide range of temperatures at operating pressures for expanding-solvent SAGD (ES-SAGD). This may indicate the limited solubility of n-butane in bitumen even when a high level of accumulation of n-butane takes place near a chamber edge in ES-SAGD for Athabasca bitumen. The multiphase transition that involves appearance/disappearance of the vapor phase was observed to occur near the vapor pressure of n-butane or its extension. Such phase transition occurs at a higher pressure in the presence of water, because of its vapor pressure, than in the absence of water at a given temperature. This is the first time four coexisting phases are reported for n-butane/Athabasca-bitumen/water mixtures at temperature/pressure conditions relevant to ES-SAGD.

Loading conditions of pistons of internal combustion engines and causes of crack formation on combustion chamber edge

In order to develop the methods for assessment of durability of pistons of tractor diesel engines, it is necessary to conduct the research of causes of failures in their operation, in particular crack formation on the edge of combustion chamber. Tractor engines operate in transient regimes due to periodic changes of control organ position and resisting moment when tractor performs agricultural, logging and other works. In transient regimes, the stress-strain state of piston varies in time, which leads to the formation of fatigue cracks on the edge of combustion chamber. The paper reviews the studies on regularities of change in the rate of propagation of fatigue cracks on the edge of combustion chamber of tractor diesel engine. The peak values of heat flows passing through the heat-absorbing surface of piston head in transient regimes exceed by 2.5 times the same values in steady-state regimes. According to the researches, for the 4ChN 11/12.5 tractor diesel engine stress intensity on the edge of combustion chamber caused by temperature gradients equals to 92-98 MPa, and exceeds more than by 2 times the stresses caused by gas pressure forces in cylinder (38-42 MPa). With the increase of engine forcing, the edge of combustion chamber becomes a local concentrator of thermal stresses, that leads to elastic-plastic deformations of cyclical pattern and microdefects. Stresses appearing on the edge of combustion chamber under rapid change of loading modes typically exceed the values of yield stress of piston material. This leads to the appearance of plastic deformations on the edge of combustion chamber. The analysis of causes of crack formation on the edge of combustion chamber of piston of a tractor diesel engine shows that when assessing the durability of piston, the whole range of indicators and parameters of the engine should be taken into account.

PERFECTION OF METHODICAL SOFTWARE CAD PISTON ICE

In work the analysis of known approaches and schemes to support the automated design of internal combustion engines with a view of improving the efficiency of the design process. Notable features are considered passing piston combustion engine project in CAD. Based on the analysis of constructions of Pistons of diesel engines, their conditions of heat transfer from the combustion chamber and the effect of Thermo-Stressed State on the degradation process of the edge of the combustion chamber of a piston refined analysis stages of constructions of pistons and the manner of their passing in a multi-stage CAD taking into account the diversity of detail of source data.

Compositional Mechanisms in Steam-Assisted Gravity Drainage and Expanding-Solvent Steam-Assisted Gravity Drainage With Consideration of Water Solubility in Oil

Summary Experimental data have shown that the solubility of water in the oleic (L) phase (xwL) can be significant at elevated temperatures. However, xwL was not properly considered in prior studies of steam-assisted gravity drainage (SAGD) and expanding-solvent (ES)-SAGD. The main objective of this research is to present a detailed study of compositional mechanisms in SAGD and ES-SAGD simulation by considering xwL. The phase-behavior models used in this research are carefully created on the basis of experimental studies presented in the literature. Mechanistic simulation studies are then conducted for SAGD and ES-SAGD. Coinjectants used in ES-SAGD simulations range from propane through n-decane. Results show that xwL enhances bitumen production in both SAGD and ES-SAGD, mainly because xwL results in reduction of L-phase viscosity. The enhancement is more significant when the chamber-edge temperature is higher, because xwL increases with temperature. The enhancement of bitumen production observed in the case studies is 7.66% for SAGD, 4.08% for n-C6-SAGD, and 4.85% for n-C8-SAGD for a fixed period of operation at 35 bar. It is important to consider xwL in SAGD and ES-SAGD simulations, because the performance of ES-SAGD relative to SAGD tends to be overestimated without considering xwL. A guideline is presented to leverage xwL to improve bitumen production in ES-SAGD. As discussed in our prior research, solvent becomes effective in diluting bitumen and reducing the steam requirement only when it sufficiently accumulates near the chamber edge. New results show that water can act as a diluting agent until solvent sufficiently accumulates near the chamber edge.

Study of commercial detector responses in non-equilibrium small photon fields of a 1000 MU/min CyberKnife system

PurposeThe purpose of this study was to analyze the detector responses in non-equilibrium small photon fields. MethodsFive detectors (PTW 31014 ionization chamber, PTW 60016, PTW 60017 and Sun Nuclear EDGE diodes and PTW 60003 diamond detector) and one passive dosimeter (Harshaw micro-LiF) as well as a 1000MU/min CyberKnife were modeled with the PENELOPE Monte Carlo code. Field factors, ΩQclin,Qmsrfclin,fmsr were calculated and perturbations due to volume averaging effect, active material effect and coating effect were quantified for the five detectors and passive dosimeter. ResultsThe PTW 31014 ionization chamber under-response is mainly due to the fluence perturbation caused by the presence of air as detecting material. Regarding diodes, the high density materials used in their active volume and in their coating is responsible for their over-response. Regarding the PTW 60003 diamond, its under-response for the 5mm field size is due to a large volume averaging effect whereas for largest field sizes a nearly perfect compensation between the volume averaging effect and the material effect due to the diamond density occurs. Despite its small size, a volume averaging effect was observed for the micro-LiF for the 5mm field size. ConclusionPerturbations due to volume averaging effect, active material effect and coating effect were investigated and quantified for five active detectors. Since these perturbations can cause opposite effects, wrong conclusions may be drawn regarding the radiological water-equivalence of detectors. Thus, we recommend performing such a study for each novel detector available on the market.

A Methodological Analysis of the Mechanisms Associated With Steam/Solvent Coinjection Processes Using Dynamic Gridding

Summary Hybrid steam-solvent processes have gained importance as a thermal-recovery process for heavy oils in recent years. Numerous pilot projects during the last decade indicate the increasing interest in this technology. The steam/solvent coinjection process aims to accelerate oil production, increase ultimate oil recovery, reduce energy and water-disposal requirements, and diminish the volume of emitted greenhouse gases compared with the steam-assisted-gravity-drainage (SAGD) process. Among the identified physical mechanisms that play a role during the hybrid steam/solvent processes are the heat-transfer phenomena, the gravity drainage and viscous flow, the solvent mass transfer, and the mass diffusion/dispersion phenomena. The major consequence of this complex interplay is the improvement of oil-phase mobility that is controlled by the reduction in the oil-phase viscosity at the edge of the steam chamber. It follows that a detailed representation of this narrow zone is necessary to capture the involved physical phenomena. In this work, a study of sensitivity to grid size was carried out to define the appropriate grid necessary to represent the near-edge zone of the steam/solvent chamber. Our results for the steam/solvent coinjection process in a homogeneous synthetic reservoir indicate that a decimetric scale is required to represent with a good precision the heat and mass-transfer processes taking place at the edge of the steam chamber. In addition, we present some numerical results of the adaptive dynamic gridding application. Comparison was performed between the SAGD process and steam/solvent coinjection after the characterization and analysis of the mechanisms that govern oil production under typical Athabasca oil-sand conditions. Finally, in the framework of the proposed numerical methodology, the effect of solvent type and injection conditions on the oil-recovery efficiency is quantitatively illustrated. Published data for similar applications are also discussed. It is expected that this work will provide some insight for the simulation community about methodological aspects to be taken into account when hybrid steam/solvent processes would be modeled.

Analytical Modeling of Emulsion Flow at the Edge of a Steam Chamber During a Steam-Assisted-Gravity-Drainage Process

Summary Recently, different models were proposed to describe two- and three-phase flow at the edge of a steam chamber developed during a steam-assisted-gravity-drainage (SAGD) process. However, 2D-scaled SAGD experiments and recent micromodel visualizations demonstrate that steam condensate is primarily in the form of microbubbles dispersed in the oil phase (water-in-oil emulsion). Therefore, the challenging question is: Can the multiphase Darcy equation be used to describe the transport of water as a discontinuous phase? Furthermore, the physical impact of water as a continuous phase or as microbubbles on oil flow can be different. Water microbubbles increase the apparent oil viscosity, whereas a continuous water phase decreases the oil relative permeability. Investigating the impact of these two phenomena on oil mobility at the steam-chamber edge and on overall oil-production rate during an SAGD process requires development of relevant mathematical models, which is the focus of this paper. In this paper, we develop an analytical model for lateral expansion of the steam chamber that accounts for formation and transport of water-in-oil emulsion. It is assumed that emulsion is generated as a result of condensation of steam, which penetrates into the heated bitumen. The emulsion concentration decreases from a maximum value at the chamber interface to zero far from the interface. The oil viscosity is affected by both temperature gradient caused by heat conduction and microbubble concentration gradient resulting from emulsification. We conduct a sensitivity analysis with the measured data from scaled SAGD experiments. The sensitivity analysis shows that, by increasing the value of m (temperature viscosity parameter), the effect of emulsification on oil-flow rate decreases. It also shows that the effect of temperature on oil mobility is much stronger than that of emulsion. We also compare the model predictions with field production data from several SAGD operations. Butler's model overestimates oil-production rate caused by the single-phase assumption, whereas the proposed model presents more-accurate oil-flow rate, supporting the fact that one should include emulsification effect in the SAGD analysis.

Drained/Undrained-Zones Boundary in Steam-Assisted-Gravity-Drainage Process

Summary Li et al. (2004) described three zones at the edge of steam chambers on the basis of drainage conditions: drained, partially drained, and undrained. In the drained zone, the pore pressure is controlled by injection pressure, and fluid mobility within this region is sufficient to drain additional pore pressures because of shear dilation and pore-fluid thermal expansion. The undrained zone lies beyond the partially drained zone and extends to virgin reservoir far beyond the chamber. In this zone shearing behaves under undrained conditions; by this, Li et al. (2004) mean no volume change occurs but shear lead to changes in pore pressure. Li et al. (2004) proposed that the boundaries of these zones are dependent on bitumen viscosity, which relates to the temperature distribution beyond the steam interface. Because drained/undrained conditions affect the geomechanics at the edge of the chamber, we investigate whether the assumption of Li et al. (2004) that there is no volume change within the sheared zone is correct and is supported by field data. Here, we establish the physics associated with the undrained zone at the edge of steam-assisted gravity-drainage steam chamber and explore the pressure front vs. temperature front of different oil-sand field projects. The results reveal that the drained zone governed by pressure-front advancement is greater in extent than the sheared zone. The thermodynamics of the undrained zone are discussed to derive a new theory for mechanothermal phenomena at the edge of the chamber. The results from the theory show that the drained zone extends beyond the temperature front and thus, from a geomechanical point of view, the system solely consists of the drained and partially drained zones.