Sweep Improvement in CO2 Flooding by Use of Foaming Agents

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Abstract
Summary: This study has two objectives: (1) to screen and select foaming agents for specific CO2 floods and (2) to determine the effectiveness of foam in improving sweep efficiency in CO2 flooding. Foaming agents were evaluated on their ability to produce ample, lasting foam and to have low loss from adsorption on reservoir rock and decomposition at reservoir conditions. Foaming agents that performed well in shaking, blender, long-term stability, and high-pressure stability tests were selected for core-flow experiments. The stability test results demonstrated that foaming agents are reservoir-specific. The extent of the loss depends on the foaming agent, reservoir fluids, reservoir lithology, and reservoir conditions.The core-flow experiments involved the simultaneous injection of CO2 into two waterflooded Berea cores. The cores were arranged in parallel and had different permeabilities. The test temperature and pressure were constant and above the critical conditions for CO2. Three types of core-flow tests, involving injection of CO2 to displace oil, injection of alternate slugs of CO2 and brine, and injection of foaming agents, were conducted. The foaming agents were injected before CO2 injection and after CO2 had displaced oil from the more permeable core.The results show that in-situ foam generation is an effective method for improving CO2 displacement efficiency. Foam was most effective when the foaming agent was injected after CO2 displaced the oil from the more permeable core. The improved sweep efficiency was caused by the tendency of the foam to be generated preferentially in the more permeable core. The foam increased resistance to flow in this core and caused more CO2 to flow through the less permeable core. The second injection method is also more applicable to field implementation.

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