Abstract

This document presents the second year results from the project, "Improved Gas Flooding Efficiency," Department of Energy Contract No. DE-FC26-04NT15532. This study focuses on laboratory studies with related analytical and numerical models, as well as work with operators for field tests to enhance our understanding of and capabilities for more efficient enhanced oil recovery (EOR).

Concern over increased greenhouse gas emissions is encouraging increased carbon dioxide (CO₂) injection into geological formations, for EOR as well as for sequestration. The development of CO₂ plumes and their subsequent dissolution into formation brine are essential mechanisms in most sequestration scenarios and are apparent causes for long-term injectivity reduction in EOR WAG (water alternating with gas injection) projects. Chapter 1 reports laboratory tests on sandstone and carbonate core samples to understand end-point and transition saturations in CO₂/brine systems. Gas injection into a brine saturation system to residual brine saturation with respect to gas and brine injection to a residual gas until all gas is produced were performed. The level of CO₂ saturation in the injected brine at reservoir pressure and temperature was varied from zero to over 90% saturation. Sandstone and carbonate rock samples were tested. In most tested cases, once CO₂ saturation was sufficient for a mobile gas, only limited increases in gas saturation occurred. Also, when switched to brine injection, gas saturation generally decreased only by dissolution into the brine; thus gas saturation (retention) and injectivity decreases persisted. This information is being used in CO₂-EOR-WAG projects and for carbon sequestration into geological formations.

Anionic surfactants, good foaming agents, can be used in CO₂ foam flooding to improve high-pressure, high-density CO₂ reservoir sweep efficiency. In Chapter 2, kinetics and equilibrium adsorption were determined by examining adsorption behavior in a system of solid phase sandstone or limestone and of surfactant in 2 wt% brine. Parameters that effect kinetics and equilibrium on surfactant adsorption density for different solid to liquid ratios as well as surfactant concentration, rock type and state, and flow conditions are presented. Three systems