The Basic Effects of Steam on a Reservoir
Authors: Holladay C.H. 
Published: December 2007

American Institute of Mining, Metallurgical and Petroleum Engineers Inc.

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The injection of steam into an oil reservoir will increase the production rate and recovery. The thermal properties of steam are such that it is not necessary to inject it at high temperatures and pressures to get the maximum heat transfer rate to the formation. Most steam floods have been in high viscosity reservoirs where viscosity reduction is the main factor in increasing recovery. However, sweep efficiency in low viscosity reservoirs can. also be improved by steam. Cyclic injection projects should be tried only in high-viscosity, high-permeability formations. Projects which failed, due to high injection pressures, might have been successful if the proper chemical treatment, well completion, and injection techniques had been used.

Introduction

It has been shown, both in the laboratory and in the field, that the application of heat to an oil reservoir will increase production rates and total recovery. There are two basic ways to heat up the reservoir. One is to burn fuel in the formation itself, and the other is to generate the heat at the surface and then transport it down the wellbore and into the formation. Steam injection is the most widely used method to get heat generated at the surface into the reservoir. Its attractiveness is due to low initial cost, high heat capacity and commercially available equipment for handling it. It is also, when properly treated, compatible with the reservoir. The technology of steam injection is developing very rapidly, although, in many cases, it is still in the experimental stage. There are many refinements and improvements of the basic technology which are still considered confidential information by many operators. However, in the last year, many of the operators have decided to release much of this information so that the industry as a whole may benefit. This should enable the over-all technology to advance at a much faster rate in the future.

Steam can be used for secondary recovery or stimulation. The secondary recovery, or steam floods, are still in the pilot stages, whereas stimulation, or cyclic injection, projects are being expanded rapidly. Many problems of high injection pressures could be solved by proper chemical treatment, well completion and injection technique.

THERMAL PROPERTIES OF STEAM

Reservoir formations are poor conductors of heat, making it impossible to move Btu's into, the formation at a high rate from a heat source in the wellbore. Down-hole heaters, which have been used for several years with some success, have a maximum heat transfer capacity of about 120,000 Btu's/hour.