Method for selectively plugging highly permeable zones in a subterranean

Abstract

Relatively high permeability zones in a subterranean formation vertically bounded by relatively low permeability zones are selectively plugged by first injecting a solidifiable selective gel solution, preferably a xanthan/chromium gel solution, at a pressure sufficient to cause the gel solution to coat and temporarily plug the injection face of the low permeability zones without any significant amount of the gel penetrating the low permeability zones while allowing the gel solution to flow into the relatively high permeability zones. Reasonably promptly thereafter and before the selective gel solution solidifies in the high permeability zones, a solidifiable non-selective solution is injected into the formation that preferentially enters the relatively high permeability zones and allowed to solidify and plug the relatively high permeability zones. Thereafter, a flushing agent having a gel breaker is injected into the formation that removes the selective gel coating from the face of the relatively low permeability zones thereby restoring permeability of the face of these zones. Thereafter, flooding fluids injected into the formation will preferentially enter the low permeability oil-rich zones to improve sweep efficiency and total oil recovery from the formation.