CO₂ Miscible Flooding--How and Where It Works

Silvia C. Birk

In an oil reservoir, capillary forces cause a substantial oil saturation to remain after waterflooding. Miscible flooding is designed to eliminate the capillary forces and to move the trapped crude oil to the production wells. The most commonly used type of miscible flooding is a dynamic process called multiple contact miscibility, in which the injected fluid and the reservoir crude oil exchange components. An example of a fluid that can develop multiple contact miscibility is carbon dioxide.

Carbon dioxide flooding can be applied in nearly all reservoir environments. Screening criteria for this process include reservoir temperature and pressure, crude oil composition, reservoir size, and proximity of a large source of inexpensive CO₂.

The major problems in CO₂ flooding arise from the low viscosity and low density of the CO₂ and from the reservoir heterogeneity. Techniques have been developed to reduce the effects of the fluid properties. A good reservoir description is essential to minimize the effects of the reservoir character.

AAPG Search and Discovery Article #91037©1987 AAPG Southwest Section, Dallas, Texas, March 22-24, 1987.