Analytical Model Analysis Research Articles

Dynamic Model of the DC Fault Clearing Process of a Hybrid Modular Multilevel Converter Considering Commutations of the Fault Current

Hybrid modular multilevel converter that consists of a combination of half-bridge submodules and full-bridge submodules (FBSMs) can block dc fault current. However, in the case of distant bulk power transmission, the large excess energy that stored in the long-distance line will greatly affect the fault clearing time and FBSM capacitor overvoltage. During the fault clearing process, several commutations of the fault current from one arm to another may occur during the fault clearing process. A dynamic model, in which the commutations of the fault current are considered, is proposed to describe the fault clearing process after converter blocking in precise detail. The fault clearing time and FBSM overvoltage can be exactly estimated. The analytical analysis model is verified by the simulation and experimental results.

3-D Analytical Magnetic Field Analysis of the Eddy Current Coupling With Halbach Magnets

In this article, a simple and accurate 3-D analytical model is presented to compute the magnetic-field distribution and the torque of eddy current coupling with Halbach magnets. By employing a group of H-formulations in the conductor region and Laplacian equations with magnetic scalar potential in other regions, the analytical magnetic distribution and electromagnetic torque of the coupling are predicted in the Cartesian coordinate system. The calculated results for a 300 kW coupling are compared with the numerical simulation results by using 3-D finite-element models and experimental results. The comparison verifies the low computational time and good accuracy of the proposed 3-D analytical analysis model.

Rate-Transient Analysis in Multifractured Horizontal Wells of Tight Oil Reservoir

SummaryMultifractured horizontal wells (MFHWs) have become the most commonly used technology for developing unconventional oil and gas reservoirs. Because unconventional reservoirs are currently the focus of exploration and exploitation around the world, a growing number of researchers and scholars are concentrating on production-performance evaluation of unconventional MFHWs to obtain the stimulated reservoir volume (SRV) or hydraulic-fracture properties, which are usually obtained from expensive reservoir tests or production logs. Rate-transient-analysis (RTA) techniques that use continuous-production and flowing-pressure data have proved to be convenient and applicable approaches to estimate the reservoir parameters and hydraulic-fracture properties. Although many cases or work flows of RTA have been previously studied, most of those works were performed for shale-gas or conventional reservoirs. Few studies on RTA have been conducted for MFHWs completed in tight oil reservoirs, particularly for actual field cases in which the usually scattered production data significantly increase the difficulty in analyzing the production performance.In this research, the authors focus on using convenient and economical methods (RTA techniques) to obtain the SRV parameters and hydraulic-fracture properties that characterize the fracturing-treatment effectiveness of an actual MFHW in a tight oil reservoir, which many engineers and technical personnel expect to achieve. A comprehensive work flow [including production-data filtering, flow-regime diagnosis, straight-line analysis, type-curve matching (TCM), analytical-model analysis (AMA), numerical-model analysis (NMA), and uncertainty and nonuniqueness analysis] has been developed to perform a production-performance analysis of an MFHW completed in a tight oil reservoir. In particular, two approaches for calculating the permeability of SRV (kSRV) and effective half-length of hydraulic fracture (Xf) have been introduced. Moreover, the dual permeability parameters, the storativity ratio, and the interporosity coefficient (ω and λ, respectively), have been derived to enter into the AMA model to improve the accuracy of history matching. With the combination of AMA and NMA, the estimated ultimate recovery (EUR) of an actual MFHW completed in a tight oil reservoir can be predicted. Considering the uncertainty and nonuniqueness of the original reservoir parameters or nature of the adopted methods, a probabilistic analysis using Monte Carlo simulation has been performed to address the uncertainty of the analysis results. In addition, a simplified application of the developed method has been introduced. To demonstrate the feasibility and practicability of the developed work flow, two field cases from an actual tight oil reservoir have been analyzed. The consistent analysis results for field cases validate the developed work flow and proposed methods.

Thermodynamic Analysis of Thermal Responses in Horizontal Wellbores

Wellbore models are required for integrated reservoir management studies as well as optimization of production operations. Distributed temperature sensing (DTS) is a smart well technology deployed for permanent downhole monitoring. It measures temperature via fiber optic sensors installed along horizontal wellbores. Correct interpretation of DTS surveys has thus become of utmost importance and analytical models for analysis of temperature distribution behavior are critical. In this study, we first show how thermodynamic analysis can describe in detail the physical changes in terms of pressure and temperature behavior from the simplest cases of “leaky tank” to the horizontal wellbore itself. Subsequently, rigorous single-phase thermodynamic models for energy, entropy, and enthalpy changes in horizontal wellbores are derived starting from 1D conservative mass, momentum, and energy balance equations and a generalized thermal models, along with their steady-state temperature profile subsets, are presented. Steady-state applications are presented and discussed. The analysis presents the factors controlling horizontal wellbore steady-state temperature responses and demonstrates that wellbore thermal responses are neither isentropic nor isenthalpic and that the isentropic expansion-driven models and Joule–Thompson-coefficient (JTC) driven may be used interchangeably to analysis horizontal wellbore thermal responses.

Analytical model for analysis and design of V-shaped thermal microactuators

An analytical solution of the thermoelastic bending/buckling problem of thermal microactuators is presented. V-shaped beam actuators are modeled using the theory of beam-column buckling. Axial (longitudinal) deformations including first-order nonlinear strain-displacement relations and thermal strains are included. The resulting nonlinear transcendental equations for the reaction forces are solved numerically and the solutions are compared with a nonlinear finite element (FE) model. A test actuator has also been fabricated and characterized. The obtained accuracy of the prediction is within 1.1% of the nonlinear FE solution and agrees well with the experimental data. A corresponding one-dimensional (1-D) heat transfer model has also been developed and validated against experimental i-V measurements at various temperatures. The developed analytical models are then used to analyze maximum stress and the heat transfer paths. It has been confirmed that the heat flux toward the substrate is a dominant heat dissipation route in sacrificially released devices.