In-Situ Combustion Frontal Stability Analysis

Summary Because of complex chemical reactions and multiphase flow physics, the displacement front stability for in-situ combustion (ISC) enhanced oil recovery (EOR) processes are not well understood. In this work, theory and numerical simulation validation are presented to establish an analytical frontal stability criterion for ISC processes. First, the four influencing factors for ISC displacement stability are analyzed: viscous force, heat conduction, matrix permeability changes caused by coke deposition, and gravity. A thorough analysis of the different zones and displacement fronts in a typical ISC process is conducted, and the most unstable front with the strongest tendency for gravity override is identified. Second, analytical solutions for judging the frontal stability and gravity override are established. Third, numerical reservoir simulation is performed to study the frontal stability and gravity override to validate the analytical theory. Carefully selected numerical schemes, as well as spatial and temporal discretization, are used to ensure the accuracy of these simulations. The four major zones and three displacement fronts (combustion front, leading edge of steam plateau, and oil bank leading edge) are identified in a typical 1D ISC process. The most unstable front with the largest pressure gradient contrast is the leading edge of the steam plateau. Gravity override also first takes place here with large fluid density differences across the front. By establishing material and energy balances and solving the wavy perturbation of the steam front, an analytical equation for deciding the ISC flood front stability in a 2D horizontal plane is achieved. Furthermore, the analytical solution for ISC gravity override is established. In numerical simulations, we are able to obtain results with sufficient accuracy to capture unstable ISC displacements and show fingering behavior under different conditions. The matrix permeability reduction caused by coke deposition has minimal impact on frontal stability. The simulation results are successfully validated with the analytical work for conditions in which the ISC process is stable or unstable and also for the degree of ISC gravity override. This demonstrates the predictive capability of the analytical method. In summary, a theoretical framework to analyze whether the displacement front of an ISC process is stable or not has been established. Numerical simulations confirm its predictive capability. This serves as a new reservoir engineering tool to aid the implementation and design of practical ISC projects.

Electromagnetic Enhancement of Carbon Transport in SiC Solution Growth Process: A Numerical Modeling Approach

The carbon distribution and its transport in the liquid from the source to the crystal directly affect the control of parasitic nucleation, the growth front stability, and the growth rate during SiC solution growth. Controlling the carbon transport is one of the key issues for understanding and improving the process. In this paper, numerical modeling by finite element method is used to describe the complex convective flow pattern in the melt. We focus on electromagnetic convection and investigate the effect of coil frequency, keeping a simple and technologically realistic crucible design. We show that below a critical value of frequency, the carbon transport can be controlled by the electromagnetic convection, giving rise to significant growth rate enhancement.

Experimental Study on the Influence of Pressure and Temperature on the Burning Velocity and Markstein Number of Jet A-1 Kerosene

For accurate prediction of the laminar flame front propagation the influence of the stretch effect on the burning velocity has to be considered. Thus, only burning velocity and Markstein number together give complete information about the laminar flame front behavior. The Markstein number quantifies the influence of the stretch effect on the burning velocity and accordingly, indicates the flame front stability. Due to the analogy between the laminar and the turbulent flames these two parameters, laminar burning velocity and Markstein number must be also considered as essential for describing the turbulent flame front stability [1]. Nevertheless, the experimental data of commercial liquid fuels regarding these parameters are scarce, especially at elevated pressure. Combustion characteristics (laminar burning velocity and Markstein number) of Kerosene Jet A-1 are investigated experimentally in an explosion bomb vessel. For this purpose an optical laser method is employed based on the Mie-scattering of the laser light by smoke particles. Unlike analogous experiments conducted with gaseous fuels [1], the major challenge connected with the present experiments arises from the liquid state of the investigated fuel at ambient condition. Thus, a main difficulty in the present experiments is pre-evaporation of the fuel and achieving of homogeneous gaseous fuel/air mixture prior to ignition. This is solved by mounting a heating system into the walls of the bomb vessel that provides a homogeneous temperature distribution in the vessel and therewith of the mixture itself. The experimental investigation is practically done through the following steps: heating the vessel up to the requested temperature; filling the vessel with an appropriate mixture by the partial pressure method (providing a fuel in gaseous state through the liquid fuel injection and its instantaneous evaporation due to the elevated temperature); attaining an uniform mixture by means of fans; ignition and acquisition of the data; post-processing and data analyses. Within the experimental study influence on the burning velocity and Markstein number of three crucial parameters — initial temperature, initial pressure and mixture composition — are investigated. Observed results for the burning velocity and Markstein number follow the theoretically expected tendencies resulting from the variation of the initial parameters in almost all cases. Where that was not the case the reasons for discrepancies are discussed. Impact of the results on emissions influenced by different operating modes of jet turbines is considered. Due to the common substitution of the kerosene with n-decane in numerical simulations their burning velocities are compared.