injecting into a fractured wellbore a fluid comprising an ammonium-comprising compound through a first tubing and a fluid comprising sodium nitrite through a second tubing,

wherein the fractured wellbore has been fractured with a fracturing fluid comprising an encapsulated breaker; and

reacting the ammonium-comprising compound and the sodium nitrite in an exothermic chemical reaction, wherein the molar ratio of the sodium nitrite to the ammonium-comprising compound ranges from 4:1 to 1:1, the exothermic chemical reaction generating heat to release the encapsulated breaker from encapsulation within 60 minutes.