It is well known that increasing the ionic strength of aqueousrnsolutions containing certain categories of anionic surfactantrncan produce interesting behaviors. The molecules of somernsurfactants cluster together forming spherical micelles.rnHowever, a select few surfactants, with particular molecularrnstructure, undergo a remarkable transition from sphericalrnmicelles to larger, anisometric aggregates. The size, flexibilityrnand extent of interaction of these aggregates all have anrninfluence on the rheological properties of such solutions,rnproducing very substantial viscosities at low shear rates.rnConversely, when these surfactant solutions encounter otherrnchemical species, particularly relatively non-polar materials,rnlike alcohols, glycols and hydrocarbons, this affects the shapernand structure of the micelles. As a result, the phase behavior isrnaltered and the solution undergoes a dramatic reduction inrnviscosity.rnProper selection of a surfactant allows its application inrnseveral oil field treatments such as reservoir gravel packing,rnfrac-packing, fracturing, brine thickening, non-damagingrntemporary plugs and also for reservoir flooding and waterrnshut-off.rnThe main advantage of these solutions, compared tornconventional polymer systems, is the potential for reducedrnformation and proppant pack damage. However, there arernmany other advantages. These fluids exhibit unexpectedly lowrnhigh-shear viscosities resulting in low friction pressures, evenrnin small tubular. In addition, due to the very low viscosity ofrnthe broken fluid, faster load recovery of injected fluids isrnpossible. A final benefit offered by these systems isrnoperational simplicity at the well site, since there is no need torn“pre-gel” tanks ahead of the treatment.rnThis paper describes the chemistry involved to develop thesernviscous solutions and their applications in different treatmentsrnin the field.
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