Selective permeability reduction of oil-free zones of subterranean

Abstract

The mobility of fluids in substantially oil-free zones of subterranean formations is controlled by introducing a composition comprising (a) water, (b) a fluid component selected from the group consisting of carbon dioxide, nitrogen, C.sub.1 to C.sub.3 hydrocarbons, and mixtures thereof, and (c) one or more polysaccharide surfactants of the formula RO(R.sup.1 O).sub.x Sacc.sub.z, wherein R is a monovalent organic radical having a carbon number in the range from about 7 to 24; R.sup.1 represents a divalent hydrocarbon radical containing from about 2 to 4 carbon atoms; x is a number having an average value in the range from 0 to about 12; and Sacc.sub.z represents an average number z between about 0.7 and 10 of moieties derived from reducing saccharides containing 5 or 6 carbon atoms. The resulting mixture of components (a), (b), and (c) forms a dispersion, or a 'foam' as that term is commonly used in the art, which is resistant to fluid flow. In certain preferred embodiments, the invention is applied to a formation having both one or more zones of high oil saturation and one or more zones which are substantially free of oil. In such embodiments, the process accomplishes a selective reduction of the permeability of a subsequently injected oil displacement or drive fluid into and through the substantially oil-free zones, without significantly reducing mobility of the drive fluid flow into and through the zones having meaningfully high oil saturation.