Matching Items (40)

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Triangular Shape Factor for Pseudo Steady State Flow in Fractured Wells

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Pseudo-steady state (PSS) flow is a dominant time-dependent flow regime during constant rate production from a closed reservoir. Using Chen's (2016) exact analytical solution for the PSS flow of a

Pseudo-steady state (PSS) flow is a dominant time-dependent flow regime during constant rate production from a closed reservoir. Using Chen's (2016) exact analytical solution for the PSS flow of a fully-penetrated fractured vertical well with finite conductivity in an elliptical drainage area, the computational time required to solve for the PSS constant b_D,PSS is greatly reduced. This constant is the inverse of the productivity index, J_D,PSS, which is often used in modern fracture design optimization. This paper correlates the PSS flow of a fully-penetrated fractured vertical well in triangular drainage areas to Chen's solution for an elliptical drainage area using shape factors. Numerical solutions for the PSS constant are created using COMSOL, which uses a 2D model of the fractured reservoir to output time and pressure data. For equivalent reservoir properties, the numerical data for the triangular reservoir yields a PSS constant that can be directly compared to the PSS constant obtained using Chen's solution. Lack of access to the Subsurface Flow Module of COMSOL greatly limited the number of simulations that could be run, thus more simulations would significantly improve the accuracy and applicability of the triangular shape factor by making it a function of the penetration ratio through nonlinear regression methods.

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  • 2017-05

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Optimal Dimensions for Beam Power Harvester for Maximum Power Output

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In the last several years, there has been a significant growth in research in the field of power harvesting, the process of capturing the energy surrounding a system and converting

In the last several years, there has been a significant growth in research in the field of power harvesting, the process of capturing the energy surrounding a system and converting it into usable electrical energy. This concept has received particular interest in recent years with the ever-increasing production of portable and wireless electronic devices. Many of these devices that are currently in production utilize electrochemical batteries as a power source, which while effective, maintain the drawback of having a finite energy supply, thus requiring periodic replacement. The concept of power harvesting, however, works to solve these issues through electronics that are designed to capture ambient energy surrounding them convert it into usable electronic energy. The use of power harvesting in energy scavenging devices allows for the possible development of devices that are self-powered and do not require their power sources to be replaced. Several models have been developed by Soldano et al [3] and Liao et al [2] that have been proven accurate at predicting the power output of a piezoelectric power harvester in a cantileaver beam configuration. The work in this paper will expand further on the model developed by Liao et al [2], and as its main goal will use a modified form of that model to predict the optimal dimensions for a beam power harvester to achieve the maximum power output possible. The model will be updated b replacing the mode shape function used to approximate the deflection of the beam with the true defletion, which is based on the complex wavenumber that incorporates the complex Young's modulus of the material used. Other changes to account for this replacement will also be presented, along with numerical results of the final model.

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  • 2012-05

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Shape factors for pseudo-steady state flow of a fractured-well in reservoirs of square shape

Description

Pseudo-steady state (PSS) flow is a dominant time-dependent flow regime during constant rate production from a closed reservoir. Recently Chen (2016) has obtained an exact analytical solution for the PSS

Pseudo-steady state (PSS) flow is a dominant time-dependent flow regime during constant rate production from a closed reservoir. Recently Chen (2016) has obtained an exact analytical solution for the PSS flow of a fully-penetrated fractured vertical well with finite conductivity in an elliptical drainage area. The availability of this analytical solution shortens the computational time required for such a solution by several orders of magnitude. This paper correlates the PSS flow of a fully-penetrated fractured vertical well in square drainage areas to Chen’s solution for an elliptical drainage area using shape factors. Specifically such a shape factor is established by equating the dimensionless productivity index of the PSS flow in a square domain to that in an elliptical domain of identical area. The shape factor was dependent on the proppant number and fracture penetration ratio. Productivity index data for fractured wells with finite conductivity in square drainage area and no skin from Romero et al. (2003) was compared to Chen’s solution assuming equivalent drainage areas and identical proppant numbers, with the penetration ratio as a parameter. A non-linear multi-variable regression analysis results in a unified shape factor function with a correlation coefficient of 0.80 and a minimized sum of squared error of 36.1. The achieved shape factor allows the analytical solution for PSS flow of fractured well in an elliptical drainage area to be applied to square drainage areas. This generalization of the PSS flow solution is of practical significance in fracture design optimization and production rate decline analysis. Future recommendations including testing the accuracy of the shape factor in predictions of proppant numbers not used in analysis using COMSOL™, and increasing the dataset pool to increase the model accuracy.

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  • 2016-05

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TRANSIENT PRESSURE APPROXIMATION FOR AN OIL WELL IN A CLOSED CIRCULAR RESERVOIR

Description

Essential to the field of petroleum engineering, well testing is done to determine the important physical characteristics of a reservoir. In the case of a constant production rate (as opposed

Essential to the field of petroleum engineering, well testing is done to determine the important physical characteristics of a reservoir. In the case of a constant production rate (as opposed to a constant pressure), the well pressure drop is a function of both time and the formation's boundary conditions. This pressure drop goes through several distinct stages before reaching steady state or semi-steady state production. This paper focuses on the analysis of a circular well with a closed outer boundary and details the derivation of a new approximation, intended for the transient stage, from an existing steady state solution. This new approximation is then compared to the numerical solution as well as an existing approximate solution. The new approximation is accurate with a maximum 10% margin of error well into the semi-steady state phase with that error decreasing significantly as the distance to the closed external boundary increases. More accurate over a longer period of time than the existing line source approximation, the relevance and applications of this new approximate solution deserve further exploration.

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  • 2016-05

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Efficient extended finite element algorithms for strongly and weakly discontinuous entities with complex internal geometries

Description

The objective of this research is to develop robust, accurate, and adaptive algorithms in the framework of the extended finite element method (XFEM) for fracture analysis of highly heterogeneous materials

The objective of this research is to develop robust, accurate, and adaptive algorithms in the framework of the extended finite element method (XFEM) for fracture analysis of highly heterogeneous materials with complex internal geometries. A key contribution of this work is the creation of novel methods designed to automate the incorporation of high-resolution data, e.g. from X-ray tomography, that can be used to better interpret the enormous volume of data generated in modern in-situ experimental testing. Thus new algorithms were developed for automating analysis of complex microstructures characterized by segmented tomographic images.

A centrality-based geometry segmentation algorithm was developed to accurately identify discrete inclusions and particles in composite materials where limitations in imaging resolution leads to spurious connections between particles in close contact.To allow for this algorithm to successfully segment geometry independently of particle size and shape, a relative centrality metric was defined to allow for a threshold centrality criterion for removal of voxels that spuriously connect distinct geometries.

To automate incorporation of microstructural information from high-resolution images, two methods were developed that initialize signed distance fields on adaptively-refined finite element meshes. The first method utilizes a level set evolution equation that is directly solved on the finite element mesh through Galerkins method. The evolution equation is formulated to produce a signed distance field that matches geometry defined by a set of voxels segmented from tomographic images. The method achieves optimal convergence for the order of elements used. In a second approach, the fast marching method is employed to initialize a distance field on a uniform grid which is then projected by least squares onto a finite element mesh. This latter approach is shown to be superior in speed and accuracy.

Lastly, extended finite element method simulations are performed for the analysis of particle fracture in metal matrix composites with realistic particle geometries initialized from X-ray tomographic data. In the simulations, particles fracture probabilistically through a Weibull strength distribution. The model is verified through comparisons with the experimentally-measured stress-strain response of the material as well as analysis of the fracture. Further, simulations are then performed to analyze the effect of mesh sensitivity, the effect of fracture of particles on their neighbors, and the role of a particles shape on its fracture probability.

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Date Created
  • 2015

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Modeling the effect of urbanization on climate and dust generation over desert cities

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Understanding and predicting climate changes at the urban scale have been an important yet challenging problem in environmental engineering. The lack of reliable long-term observations at the urban scale makes

Understanding and predicting climate changes at the urban scale have been an important yet challenging problem in environmental engineering. The lack of reliable long-term observations at the urban scale makes it difficult to even assess past climate changes. Numerical modeling plays an important role in filling the gap of observation and predicting future changes. Numerical studies on the climatic effect of desert urbanization have focused on basic meteorological fields such as temperature and wind. For desert cities, urban expansion can lead to substantial changes in the local production of wind-blown dust, which have implications for air quality and public health. This study expands the existing framework of numerical simulation for desert urbanization to include the computation of dust generation related to urban land-use changes. This is accomplished by connecting a suite of numerical models, including a meso-scale meteorological model, a land-surface model, an urban canopy model, and a turbulence model, to produce the key parameters that control the surface fluxes of wind-blown dust. Those models generate the near-surface turbulence intensity, soil moisture, and land-surface properties, which are used to determine the dust fluxes from a set of laboratory-based empirical formulas. This framework is applied to a series of simulations for the desert city of Erbil across a period of rapid urbanization. The changes in surface dust fluxes associated with urbanization are quantified. An analysis of the model output further reveals the dependence of surface dust fluxes on local meteorological conditions. Future applications of the models to environmental prediction are discussed.

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Date Created
  • 2019

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Thermal Drainage Flow of a Viscous Gas From a Semi-Sealed Narrow Channel

Description

Drainage flow of a viscous compressible gas from a semi-sealed narrow conduit is a pore-scale model for studying the fundamental flow physics of fluid recovery from a porous reservoir without

Drainage flow of a viscous compressible gas from a semi-sealed narrow conduit is a pore-scale model for studying the fundamental flow physics of fluid recovery from a porous reservoir without using fluid injection. Thermal effect has been routinely neglected for these flows in the traditional petroleum engineering literature. Since the motion is entirely driven by volumetric expansion, temperature change always accompanies the density change. This thesis examines such thermal effects on the drainage flow.

Thermal drainage flow is first studied by simultaneously solving the linearized continuity, momentum and energy equations for adiabatic walls. It is shown that even in the absence of an imposed temperature drop, gas expansion induces a transient temperature decrease inside the channel, which slows down the drainage process compared to the isothermal model and Lighthill’s model. For a given density drop, gas drains out faster as the initial-to-final temperature ratio increases; and the transient density can undershoot the final equilibrium value. A parametric study is then carried out to explore the influence of various thermal boundary conditions on drainage flow. It is found that as the wall transitions from adiabatic to isothermal condition, the excess density changes from a plane wave solution to a non-plane wave solution and the drainage rate increases. It is shown that when the exit is also cooled and the wall is non-adiabatic, the total recovered fluid mass exceeds the amount based on the isothermal theory which is determined by the initial and final density difference alone. Finally, a full numerical simulation is conducted to mimic the channel-reservoir system using the finite volume method. The Ghost-Cell Navier-Stokes Characteristic Boundary Condition technique is applied at the far end of the truncated reservoir, which is an open boundary. The results confirm the conclusions of the linear theory.

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Date Created
  • 2020

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Numerical methods and simulations of complex multiphase flows

Description

Multiphase flows are an important part of many natural and technological phe- nomena such as ocean-air coupling (which is important for climate modeling) and the atomization of liquid fuel jets

Multiphase flows are an important part of many natural and technological phe- nomena such as ocean-air coupling (which is important for climate modeling) and the atomization of liquid fuel jets in combustion engines. The unique challenges of multiphase flow often make analytical solutions to the governing equations impos- sible and experimental investigations very difficult. Thus, high-fidelity numerical simulations can play a pivotal role in understanding these systems. This disserta- tion describes numerical methods developed for complex multiphase flows and the simulations performed using these methods. First, the issue of multiphase code verification is addressed. Code verification answers the question "Is this code solving the equations correctly?" The method of manufactured solutions (MMS) is a procedure for generating exact benchmark solutions which can test the most general capabilities of a code. The chief obstacle to applying MMS to multiphase flow lies in the discontinuous nature of the material properties at the interface. An extension of the MMS procedure to multiphase flow is presented, using an adaptive marching tetrahedron style algorithm to compute the source terms near the interface. Guidelines for the use of the MMS to help locate coding mistakes are also detailed. Three multiphase systems are then investigated: (1) the thermocapillary motion of three-dimensional and axisymmetric drops in a confined apparatus, (2) the flow of two immiscible fluids completely filling an enclosed cylinder and driven by the rotation of the bottom endwall, and (3) the atomization of a single drop subjected to a high shear turbulent flow. The systems are simulated numerically by solving the full multiphase Navier- Stokes equations coupled to the various equations of state and a level set interface tracking scheme based on the refined level set grid method. The codes have been parallelized using MPI in order to take advantage of today's very large parallel computational architectures. In the first system, the code's ability to handle surface tension and large tem- perature gradients is established. In the second system, the code's ability to sim- ulate simple interface geometries with strong shear is demonstrated. In the third system, the ability to handle extremely complex geometries and topology changes with strong shear is shown.

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Date Created
  • 2011

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Optimized vortex tube bundle for large flow rate applications

Description

ABSTRACT A vortex tube is a device of a simple structure with no moving parts that can be used to separate a compressed gas into a hot stream and a

ABSTRACT A vortex tube is a device of a simple structure with no moving parts that can be used to separate a compressed gas into a hot stream and a cold stream. Many studies have been carried out to find the mechanisms of the energy separation in the vortex tube. Recent rapid development in computational fluid dynamics is providing a powerful tool to investigate the complex flow in the vortex tube. However various issues in these numerical simulations remain, such as choosing the most suitable turbulent model, as well as the lack of systematic comparative analysis. LES model for the vortex tube simulation is hardly used in the present literatures, and the influence of parameters on the performance of the vortex tube has scarcely been studied. This study is aimed to find the influence of various parameters on the performance of the vortex tube, the best geometric value of vortex tube and the realizable method to reach the required cold out flow rate 40 kg/s . First of all, setting up an original 3-D simulation vortex tube model. By comparing experiment results reported in the literature and our simulation results, a most suitable model for the simulation of the vortex tube is obtained. Secondly, we perform simulations to optimize parameters that can deliver a set of desired output, such as cold stream pressure, temperature and flow-rate. We also discuss the use of the cold air flow for petroleum engineering applications.

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Date Created
  • 2013

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Wind farm characterization and control using coherent Doppler lidar

Description

Wind measurements are fundamental inputs for the evaluation of potential energy yield and performance of wind farms. Three-dimensional scanning coherent Doppler lidar (CDL) may provide a new basis for wind

Wind measurements are fundamental inputs for the evaluation of potential energy yield and performance of wind farms. Three-dimensional scanning coherent Doppler lidar (CDL) may provide a new basis for wind farm site selection, design, and control. In this research, CDL measurements obtained from multiple wind energy developments are analyzed and a novel wind farm control approach has been modeled. The possibility of using lidar measurements to more fully characterize the wind field is discussed, specifically, terrain effects, spatial variation of winds, power density, and the effect of shear at different layers within the rotor swept area. Various vector retrieval methods have been applied to the lidar data, and results are presented on an elevated terrain-following surface at hub height. The vector retrieval estimates are compared with tower measurements, after interpolation to the appropriate level. CDL data is used to estimate the spatial power density at hub height. Since CDL can measure winds at different vertical levels, an approach for estimating wind power density over the wind turbine rotor-swept area is explored. Sample optimized layouts of wind farm using lidar data and global optimization algorithms, accounting for wake interaction effects, have been explored. An approach to evaluate spatial wind speed and direction estimates from a standard nested Coupled Ocean and Atmosphere Mesoscale Prediction System (COAMPS) model and CDL is presented. The magnitude of spatial difference between observations and simulation for wind energy assessment is researched. Diurnal effects and ramp events as estimated by CDL and COAMPS were inter-compared. Novel wind farm control based on incoming winds and direction input from CDL's is developed. Both yaw and pitch control using scanning CDL for efficient wind farm control is analyzed. The wind farm control optimizes power production and reduces loads on wind turbines for various lidar wind speed and direction inputs, accounting for wind farm wake losses and wind speed evolution. Several wind farm control configurations were developed, for enhanced integrability into the electrical grid. Finally, the value proposition of CDL for a wind farm development, based on uncertainty reduction and return of investment is analyzed.

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Date Created
  • 2013