Browsing by Subject "Transient"
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Item Development of a coupled wellbore-reservoir compositional simulator for horizontal wells(2010-12) Shirdel, Mahdy; Sepehrnoori, Kamy, 1951-; Ribeiro, Paulo R.Two-phase flow occurs during the production of oil and gas in the wellbores. Modeling this phenomenon is important for monitoring well productivity and designing surface facilities. Since the transient time period in the wellbore is usually shorter than reservoir time steps, stabilized flow is assumed in the wellbore. As such, semi-steady state models are used for modeling wellbore flow dynamics. However, in the case that flow variations happen in a short period of time (i.e., a gas kick during drilling) the use of a transient two-phase model is crucial. Over the last few years, a number of numerical and analytical wellbore simulators have been developed to mimic wellbore-reservoir interaction. However, some issues still remain a concern in these studies. The main issues surrounding a comprehensive wellbore model consist of fluid property calculations, such as black-oil or compositional models, governing equations, such as mechanistic or correlation-based models, effect of temperature variation and non-isothermal assumption, and methods for coupling the wellbore to the reservoir. In most cases, only standalone wellbore models for blackoil have been used to simulate reservoir and wellbore dynamic interactions. Those models are based on simplified assumptions that lead to an unrealistic estimation of pressure and temperature distributions inside the well. In addition, most reservoir simulators use rough estimates for the perforation pressure as a coupling condition between the wellbore and the reservoir, neglecting pressure drops in the horizontal section. In this study, we present an implementation of a compositional, pseudo steady-state, non-isothermal, coupled wellbore-reservoir simulator for fluid flow in wellbores with a vertical section and a horizontal section embedded on the producing reservoir. In addition, we present the implementation of a pseudo-compositional, fully implicit, transient two-fluid model for two-phase flow in wellbores. In this model, we solve gas/liquid mass balance, gas/liquid momentum balance, and two-phase energy equations in order to obtain the five primary variables: liquid velocity, gas velocity, pressure, holdup and temperature. In our simulation, we compared stratified, bubbly, intermittent flow effects on pressure and temperature distributions in either a transient or steady-state condition. We found that flow geometry variation in different regimes can significantly affect the flow parameters. We also observed that there are significant differences in flow rate prediction between a coupled wellbore-reservoir simulator and a stand-alone reservoir simulator, at the early stages of production. The outcome of this research leads to a more accurate and reliable simulation of multiphase flow in the wellbore, which can be applied to surface facility design, well performance optimization, and wellbore damage estimation.Item Identity, mobility, and marginality : counseling third culture kids in college(2012-05) Downey, Dana Leigh; Awad, Germine H.; Moore, Leslie A.The number of Americans living abroad currently is estimated at over four million, with over 37,000 matriculating into U.S. universities each year. If the social media giant Facebook were a country, it would be third largest in the world, with over 300 million users outside of America. The trajectory of our society is increasingly global. Amidst this shift, there is a unique multicultural subpopulation emerging-- Third Culture Kids (TCK), who experience a collision of cultures and form hybrid identities in the course of their development. TCKs are more specifically when a person spends a significant part of their developmental years outside their parents’ culture. The TCK takes on pieces of each culture, while never fully ‘belonging’ to any. They are most at home around others of a similar transient background. This report synthesizes research about globally mobile populations from across disciples, highlighting grief and ambiguous losses, acculturation stresses, and identity development. Potential implications for the college campus— at institutional and individual levels— will be discussed. This overview of current research and resources equips college counselors with a frame of reference for engaging this third culture in a holistic and contextualized manner.Item Pressure transient test analysis of vuggy naturally fractured carbonate reservoir: field case study(2009-06-02) Ajayi, Babatunde TolulopeWell pressure transient analysis is widely used in reservoir management to obtain reservoir information needed for reservoir simulation, damage identification, well optimization and stimulation evaluation. The main objective of this project is to analyze, interpret and categorize the pressure transient responses obtained from 22 wells in a vuggy naturally fractured carbonate reservoir in an attempt to understand the heterogeneities of the porosity system. Different modeling techniques useful in simulating well behavior in vuggy naturally fractured reservoirs were developed and categorized. The research focused on pressure transient analysis using homogeneous, radial composite, single fracture, dual porosity and triple porosity reservoir models along with conventional boundary models which show boundary limits including single and double sealing boundary, closure and constant pressure boundary. A triple porosity model was developed, and it proved to be very effective for use in the analysis of the pressure responses obtained from this field. For some wells, the need for new models to characterize the pressure responses in more complex reservoirs was highlighted as conventional models failed.Item Thermal and mechanical analysis of interconnect structures in 3D stacked packages(2010-05) Wakil, Jamil Abdul; Chen, Shaochen; Ho, Paul S.; Shapiro, Michael; Shi, Li; Sikka, KamalPhysical scaling limits of microelectronic devices and the need to improve electrical performance have driven significant research and development into 3D architecture. The development of die stacks in first level packaging is one of the more viable short-term options for improved performance. Placement of memory die above or below processors in a traditional flip chip C4 package with through-silicon vias (TSVs) has significant benefits in reducing data and power transmission paths. However, with the electrical performance benefits come great thermal and mechanical challenges. There are two key objectives for this work. The first is understanding of the die-die interface resistance, R[subscript dd], composed of the back end of line (BEOL) layers and micro-C4 interconnects. The interfacial resistance between BEOL material layers, the impact of TSVs and the impact of strain on R[subscript dd] are subtopics. The second key objective is the understanding of package thermal and mechanical behavior under operating conditions, such as local thermal disturbances. To date, these topics have not been adequately addressed in the literature. It is found that R[subscript dd] can be affected by TSVs, and that the interfacial contributions predicted by theoretical sub-continuum models can be significantly different than measurements. Using validated finite element models, the significance of the power distribution and R[subscript dd] on the temporal responses of 2D vs. 3D packages is highlighted. The results suggest local thermal hotspots can greatly exacerbate the thermal penalty due to the R[subscript dd] and that no peaks in stress arise in the transient period from power on to power off.Item Transient Lift-off Test Results for an Experimental Hybrid Bearing in Air(2011-02-22) Klooster, DavidA hybrid bearing designed for use in a next generation turbo-pump is evaluated for the performance of initial lift-off, referred to as start-transient. The radial test rig features a high-speed spindle motor capable of 20,000 rpm that drives a 718 Inconel rotor attached via a high-speed coupling. The drive end is supported by ceramic ball bearings, while the hybrid bearing supports the opposite end. A magnetic bearing delivers the applied loading along the mid-span of the rotor. Many parameters, including ramp rate [rpm/s] (drive torque), supply pressure at 15,000 rpm, magnitude of the applied load, and load orientation, are varied to simulate different start-transient scenarios. The data are recorded in .dat files for future evaluation of transient predictions. Analysis of the data includes an evaluation of hydrodynamic and hydrostatic liftoff, an assessment of rub from passing through a lightly damped critical speed, and observation of pneumatic hammer instability. Hydrodynamic lift-off occurs when the hydrodynamic pressure, resulting from the relative motion of two surfaces, overcomes the forces acting on the rotor; no indication of hydrodynamic lift-off is provided. Hydrostatic lift-off results from the external supply pressure (which for this test rig is speed dependent) overcoming the forces acting on the rotor as determined from rotor centerline plots. With 0.263 bar applied unit load in the vertical direction, hydrostatic lift-off occurs at 0 rpm and 2.08 bar supply pressure. With a much higher load of 1.53 bar, hydrostatic lift-off is at 12,337 rpm and 10.7 bar supply pressure. The required supply pressure for hydrostatic lift-off is approximately a linear function of the applied unit load. In a turbopump, hydrostatic lift-off depends on the speed because the supply pressure is proportional to the speed squared. With the load in the horizontal direction, hydrostatic lift-off occurs at lower speeds and pressures. The ramp rate did not affect the required supply pressure for hydrostatic lift-off. A lower supply pressure at 15,000 rpm lowered the required supply pressure for hydrostatic liftoff as well as the natural frequencies creating a rub. The hydrostatic lift-off speed should be minimized to avoid damage to the rotor/bearing surfaces due to contact.