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Development of More-Efficient Gas Flooding Applicable to Shallow Reservoirs Progress Report

Description: The objective of this research is to widen the applicability of gas flooding to shallow oil reservoirs by reducing the pressure required for miscibility using gas enrichment and increasing sweep efficiency with foam. Task 1 examines the potential for improved oil recovery with enriched gases. Subtask 1.1 examines the effect of dispersion processes on oil recovery and the extent of enrichment needed in the presence of dispersion. Subtask 1.2 develops a fast, efficient method to predict the extent of enrichment needed for crude oils at a given pressure. Task 2 develops improved foam processes to increase sweep efficiency in gas flooding. Subtask 2.1 comprises mechanistic experimental studies of foams with N{sub 2} gas. Subtask 2.2 conducts experiments with CO{sub 2} foam. Subtask 2.3 develops and applies a simulator for foam processes in field application. Regarding Task 1, several very important results were achieved this period for subtask 1.2. In particular, we successfully developed a robust Windows-based code to calculate MMP and MME for fluid characterizations that consist of any number of pseudocomponents. We also were successful in developing a new technique to quantify the displacement mechanism of a gas flood--that is, to determine the fraction of a displacement that is vaporizing or condensing. These new technologies will be very important to develop new correlations and to determine important parameters for the design of gas injection floods. Regarding Task 2, several results were achieved: (1) A detailed study of the accuracy of foam simulation validates the model with fits to analytical fractional-flow solutions. It shows that there is no way to represent surfactant-concentration effects on foam without some numerical artifacts. (2) New results on capillary crossflow with foam show that this is much less detrimental than earlier studies had argued. (3) It was shown that the extremely useful model of Stone ...
Date: January 28, 2003
Creator: Rossen, William R.; Johns, Russell T. & Pope, Gary A.

Development of More-Efficient Gas Flooding Applicable to Shallow Reservoirs Progress Report

Description: The objective of this research is to widen the applicability of gas flooding to shallow oil reservoirs by reducing the pressure required for miscibility using gas enrichment and increasing sweep efficiency with foam. Task 1 examines the potential for improved oil recovery with enriched gases. Subtask 1.1 examines the effect of dispersion processes on oil recovery and the extent of enrichment needed in the presence of dispersion. Subtask 1.2 develops a fast, efficient method to predict the extent of enrichment needed for crude oils at a given pressure. Task 2 develops improved foam processes to increase sweep efficiency in gas flooding. Subtask 2.1 comprises mechanistic experimental studies of foams with N{sup 2} gas. Subtask 2.2 conducts experiments with CO{sup 2} foam. Subtask 2.3 develops and applies a simulator for foam processes in field application. Regarding Task 1, several results related to subtask 1.1 are given. In this period, most of our research centered on how to estimate the dispersivity at the field scale. Simulation studies (Solano et al. 2001) show that oil recovery for enriched gas drives depends on the amount of dispersion in reservoir media. But the true value of dispersion, expressed as dispersivity, at the field scale, is unknown. This research investigates three types of dispersion in permeable media to obtain realistic estimates of dispersive mixing at the field scale. The dispersivity from single-well tracer tests (SWTT), also known as echo dispersivity, is the dispersivity that is unaffected by fluid flow direction. Layering in permeable media tends to increase the observed dispersivity in well-to-well tracer tests, also known as transmission dispersivity, but leaves the echo dispersivity unaffected. A collection of SWTT data is analyzed to estimate echo dispersivity at the SWTT scale. The estimated echo dispersivities closely match a published trend with length scale in dispersivities obtained from ...
Date: January 28, 2003
Creator: Rossen, William R.; Johns, Russell T. & Pope, Gary A.

Development of More-Efficient Gas Flooding Applicable to Shallow Reservoirs Progress Report

Description: The objective of this research is to widen the applicability of gas flooding to shallow oil reservoirs by reducing the pressure required for miscibility using gas enrichment and increasing sweep efficiency with foam. Task 1 examines the potential for improved oil recovery with enriched gases. Subtask 1.1 examines the effect of dispersion processes on oil recovery and the extent of enrichment needed in the presence of dispersion. Subtask 1.2 develops a fast, efficient method to predict the extent of enrichment needed for crude oils at a given pressure. Task 2 develops improved foam processes to increase sweep efficiency in gas flooding. Subtask 2.1 comprises mechanistic experimental studies of foams with N{sup 2} gas. Subtask 2.2 conducts experiments with CO{sup 2} foam. Subtask 2.3 develops and applies a simulator for foam processes in field application. Regarding Task 1, several key results are described in this report relating to subtask 1.1. In particular, we show how for slimtube experiments, oil recoveries do not increase significantly with enrichments greater than the MME. For field projects, however, the optimum enrichment required to maximize recovery on a pattern scale may be different from the MME. The optimum enrichment is likely the result of greater mixing in reservoirs than in slimtubes. In addition, 2-D effects such as channeling, gravity tonguing, and crossflow can impact the enrichment selected. We also show the interplay between various mixing mechanisms, enrichment level, and numerical dispersion. The mixing mechanisms examined are mechanical dispersion, gravity crossflow, and viscous crossflow. UTCOMP is used to evaluate the effect of these mechanisms on recovery for different grid refinements, reservoir heterogeneities, injection boundary conditions, relative permeabilities, and numerical weighting methods including higher-order methods. For all simulations, the reservoir fluid used is a twelve-component oil displaced by gases enriched above the MME. The results for subtask 1.1 ...
Date: January 28, 2003
Creator: Rossen, William R.; Johns, Russell T. & Pope, Gary A.