This paper is based on a speech presented as a Distinguished Lecture during the 1985-1986 season.
Abstract
The addition of compressed gas to a stimulation fluid may be one of the biggest advances in well treating technology in the past two decades. When carefully designed and applied, foams and treatments using gas can result in better stimulations through improved proppant placement, more rapid cleanup, and in some cases, less damage from the treating fluid.
Alas, foam treatments are neither magic nor can they be used as universal stimulations. Obtaining the maximum benefit from a foam or nitrified fluid requires thoughtful design and careful application. This paper provides information on how to get it done.
Introduction
A Little History
The first use of foam as a fracturing fluid was reported as 1968. The first widespread use of foam fracturing followed papers by Blauer, et al., in the early 1970's. From its introduction as a superfluid, foam has rapidly come to be recognized as an excellent fracturing fluid for many reservoirs and a poor choice in a few others. The best attributes of foam as a stimulation fluid were recognized early and have endured the process of reduction of cure-all to reality. They are:Reduction of liquid volumeGood proppant supportExceptional flowback and cleanup.
Other first held beliefs such as low fluid loss and very high viscosity values have given way to well researched fact. These are discussed later.
Following the familiar collapse from superfluid status that is part of the introduction of every new fluid, the best uses of foam were researched and the applications base expanded by improvements in surfactants and hardware. By the mid to late 1970's, foam was entrenched as a treatment for shallow, low pressure gas reservoirs where its low water volume pressure gas reservoirs where its low water volume and rapid cleanup made stimulations possible where previously only marginal successes had been seen. previously only marginal successes had been seen. From this base, advances in foaming agents such as the fluorocarbons have made oil reservoir fracturing practical. Improvements in liquid gelling/ breaking processes, the mechanical sand concentrators, and changes in blender designs have increased sand loadings and helped start foam massive fracturings and foam fracturing with high rate proppant loading.
Foam is an unusual fluid; very few testing techniques applicable to liquid systems were usable in gathering data on foams. The recent advances in test procedures and stimulation foam technology have been due to the persistence of authors such as Harris, Holcomb, Wendorf, Ford, Lord, and others. The technology of foam is just over a decade old, this paper will try to report the advances, the new information, and the problems.
Discussion
Foam Basics
Foams are gas-in-liquid dispersions with many of the same traits as emulsions. The liquid may be water, acid, alcohol, or oil, and the gas is usually either nitrogen or carbon dioxide. A surfactant stabilizes the foam. The type of surfactant depends on the liquid phase; a hydrocarbon surfactant foamer is usually adequate for water or aqueous acid while a fluorocarbon surfactant or a mixture of fluorocarbon and hydrocarbon surfactants are needed for oils and anhydrous alcohols.
