Enhanced oil recovery by in-situ steam generation

An oil well stimulation method for enhancing oil recovery from one of a formation and a reservoir, the oil well stimulation method comprising:

• designing an aqueous composition to reach a required temperature, the required temperature sufficient to form thermal fractures within hydraulically induced and existing fractures in the formation or reservoir, where reaching the required temperature is a function of concentration of reactants in the aqueous composition;
• injecting, at an injector disposed a distance away from an oil producer, into the formation or reservoir, the aqueous composition, the aqueous composition comprising an ammonium containing compound and a nitrite containing compound;
• injecting, at the injector, into the formation or reservoir, an activator comprising an acidic hydrogen compound including one of a weak acid, a strong acid, and a dilute strong acid, the activator initiating a reaction between the ammonium containing compound and the nitrite containing compound, such that the reaction generates steam in situ and generates nitrogen gas in situ, increasing localized pressure, wherein the activator is consumed by the reaction such that no residual activator remains to cause environmental concerns;
• generating microfractures, including tensile and thermal fractures, within the formation or reservoir creating additional reservoir volume;
• and
• improving oil mobility, in the formation or reservoir, by the steam and nitrogen gas generated in situ, thereby enhancing oil recovery from the formation or reservoir at the oil producer, without requiring a clean-up procedure for any residual acid from unreacted activator after the oil well stimulation method.