Enhanced Oil Recovery Techniques: State of the Art and Potential

Summary

Since the infancy of petroleum reservoir engineering the oil industry has dreamed of a process which would achieve 100 per cent oil recovery. In fact, at present the average figure for final oil recovery is 32.1 per cent only, including oil from water flooding. The residual oil, remaining unrecovered, represents an enormous potential resource; for the United States reservoirs its volume is evaluated at 300 billion barrels.

When the researchers first began to experiment with the techniques which are the basis of most of the enhanced oil recovery processes being tested today, the goal of achieving complete oil displacement appeared attainable. In fact, this problem appears now much more complicated than it did ten years ago.

Oil recovery processes based on miscible flooding with hydrocarbons or carbon dioxide, micellar/polymer flooding, thermal processes (both in-situ combustion and steam soak/steam drive) have been thoroughly examined on a laboratory scale, evaluated through numerical model simulation and tested both on pilot and fieldwide scale.

The present status of all these processes is critically evaluated, and an up-to-date review is presented of field tests performed throughout the world.

Reservoir heterogeneity proves to be the main factor hindering the achievement of a technical success. This holds particularly for those enhanced recovery processes in which the displacing fluid has an intrinsically high mobility: high pressure gas injection, iin-situ combustion and steam drive.

Investments needed to carry out enhanced recovery processes are of front-end type, while the production of additional oil occurs over long periods of time; this often makes the economics of such processes marginal.

The amount of residual oil in the depleted reservoirs is so huge, and the price of oil is going to be so high, that many enhanced oil recovery processes will become economically viable in the next ten years.

Future developments are discussed, and the research effort made in Italy, to apply enhanced oil recovery techniques to the heavy-oil fractured reservoirs in Sicily and under the Adriatic Sea, is described.