A study of dispersive mixing and flow based lumping/delumping in gas injection processes.

摘要

In Part I of this research project, we investigate the accuracy of the physical models that are used to describe dispersive mixing in compositional reservoir simulation. We have designed a quaternary alcohol-water-hydrocarbon analog system that exhibits two-phase liquid-liquid equilibrium behavior at room temperature and pressure. The analog system of Water -- Isooctane -- Isopropanol -- Methanol was chosen based on a favorable comparison to the phase behavior of high-pressure CO2-hydrocarbon systems. Working with this analog system allows us to perform displacement experiments at ambient conditions in the lab.;A porous medium, in the form of a packed column, was designed for the experimental component of the research project using PTFE materials (Teflon). This selection was made to have the analog oil compositions, represented by an Isooctane-rich phase, as the wetting phase while gas compositions represented by an aqueous phase be non-wetting to the PTFE materials. The PTFE column was characterized in terms of porosity, permeability and dispersivity through a series of experiments.;The interactions between the analog fluids and the porous medium were characterized by performing steady state relative permeability experiments for the immiscible pair of Water and Isooctane. The impact of the capillary number on the residual saturations was included via a study the IFT for the coexisting liquid phases.;To aid the design of lab experiments, a numerical simulator that predicts the displacement behavior in 1D was developed and tested. The simulator utilizes a comprehensive solvents phase behavior model (UNIQUAC) that accurately predicts the liquid-liquid equilibrium of the analog system. The phase behavior module was successfully tested with experimental observations for two-phase ternary and quaternary mixtures of the analog solvents. In addition, the simulator includes the effects of physical dispersion and allows us to compare the accuracy of the available physical models with experimental observations.;A set of single-phase experiments was conducted to determine the dispersivity of the column. The effluent concentrations from the displacement experiments all exhibited a moderate tailing behavior that is attributed to imperfect sweep in the system. A simulation model that captures the tailing effect from the single phase experiment was constructed by adjusting the boundary conditions to mimic mixing zones at the inlet and outlet of the column.;Two 4-component displacement experiments were designed and performed. In these experiments, the effluent compositions were analyzed by gas chromatography (GC). The results of the experiments were in agreement with existing theory of gas injection processes and represented both condensing and vaporizing segments along the displacement paths.;The displacement behavior observed in the lab was analyzed through numerical calculations and we demonstrate that the use of numerical diffusion to replace physical dispersion introduce additional artifacts to the displacement profile that are difficult to control. However, the degree of heterogeneity in the PTFE column prevented us from providing a detailed analysis and conclusions related to the dispersion phenomena in these complex multicomponent two-phase systems.;In Part II of this research project, the use of pseudo-components (lumping) for compositional simulation of a gas injection process and the related effects on accuracy and simulation time has been investigated.;Two novel flow-based lumping methods have been proposed that both integrate the displacement characteristics into the selection of component groups. The two new methods have been tested for a realistic reservoir fluid where fluid description were reduced from 15 to 7 components. The lumped fluid descriptions are demonstrated to maintaining accuracy in the prediction of displacement characteristics as well as in the prediction of available PVT experiments. The flow-based methods provide a unique answer to the problem of what components to lump depending on the relevant oil and injection gas composition.;The impact of the selected lumping scheme on the accuracy of delumped streams from 3D displacement calculations was investigated through a detailed comparison of the delumped streams from the proposed lumping schemes with other lumping methods that commonly used in the industry. Both flow based methods were demonstrated to introduce less error in the associated delumped streams. (Abstract shortened by UMI.)