Method for selectively plugging deep subterranean formations with polysulfides

摘要

Improved vertical and/or horizontal sweep efficiency in a deep subterranean oil containing formation having a temperature in excess of 250° F. containing relatively high permeability zones and relatively low permeability zones is obtained by injecting an aqueous polysulfide solution into the formation that preferentially enters the relatively high permeability zones and allowing the aqueous polysulfide solution in the relatively high permeability zones to disproportionate under the temperature conditions within the relatively high permeability zones to form a precipitate of elemental sulfur in situ which plugs the relatively high permeability zones in the formation. Thereafter, improved sweep efficiency is realized in displacing oil from the lesser permeable zones.