Abstract: A method for generating hydrofluoric acid (HF) in-situ in a subterranean formation (e.g. sandstone formation) by simultaneously injecting an acid generating component having ammonium fluoride and an oxidizing agent and a heat generating component having ammonium and nitrite salts into a wellbore of the formation. The method optionally involves a pre-flush of an acid (e.g. HCl) containing solution prior to the injecting. HF is generated via an endothermic reaction of the ammonium fluoride and the oxidizing agent with the assistance of the heat provided by an exothermic reaction of the ammonium and nitrite salts. The method is effective in enhancing permeability of the formation by at least 30%.

Abstract: A method is described for removing a barite-quartz and a calcite-quartz filter cake from a well bore. The method involves contacting the filter cake with a first composition comprising NH4F, NaBrO3, NH4Cl, and NaNO2. The NH4Cl and NaNO2 react exothermically, and the heat produced drives the endothermic reaction of NH4F and NaBrO3, which produces HF for dissolution of the quartz in the filter cake. Filter cake comprising barite may be further treated with a second composition comprising a converting agent and a chelating agent. Filter cake comprising calcite may be treated with a first composition having an excess of NH4Cl and NaBrO3, which react to produce HCl for calcite dissolution.

Abstract: A method for generating hydrofluoric acid (HF) in-situ in a subterranean formation (e.g. sandstone formation) by simultaneously injecting an acid generating component having ammonium fluoride and an oxidizing agent and a heat generating component having ammonium and nitrite salts into a wellbore of the formation. The method optionally involves a pre-flush of an acid (e.g. HCl) containing solution prior to the injecting. HF is generated via an endothermic reaction of the ammonium fluoride and the oxidizing agent with the assistance of the heat provided by an exothermic reaction of the ammonium and nitrite salts. The method is effective in enhancing permeability of the formation by at least 30%.

Abstract: A method is described for removing a barite-quartz and a calcite-quartz filter cake from a well bore. The method involves contacting the filter cake with a first composition comprising NH4F, NaBrO3, NH4Cl, and NaNO2. The NH4Cl and NaNO2 react exothermically, and the heat produced drives the endothermic reaction of NH4F and NaBrO3, which produces HF for dissolution of the quartz in the filter cake. Filter cake comprising barite may be further treated with a second composition comprising a converting agent and a chelating agent. Filter cake comprising calcite may be treated with a first composition having an excess of NH4Cl and NaBrO3, which react to produce HCl for calcite dissolution.