Tight Gas Stimulation by In-Situ Nitrogen Generation

Abstract

Provided is a method and composition for the in-situ generation of synthetic sweet spots in tight-gas formations. The composition can include nitrogen generating compounds, which upon activation, react to generate heat and nitrogen gas. The method of using the composition includes injecting the composition into a tight-gas formation such that upon activation, heat and nitrogen gas are generated. Upon the generation of nitrogen gas and heat within the formation, microfractures are produced within the formation and the hydrostatic pressure within the reservoir is reduced to less than the reservoir fluid pressure, such that the rate of production of hydrocarbons from the formation is increased.

That which is claimed is: 
     
         1 . A reaction mixture for the in-situ generation of nitrogen within tight gas wells, the reaction mixture comprising:
 an ammonium containing compound;   a nitrite containing compound; and   a hydrogen releasing activator;   wherein at least one of the ammonium containing compound and the nitrite containing compound are encapsulated with a coating designed to delay the reaction of the ammonium and nitrite containing compounds.   
     
     
         2 . The reaction mixture of  claim 1  wherein the ammonium containing compound is selected from ammonium chloride, ammonium bromide, ammonium nitrate, ammonium sulfate, ammonium carbonate, ammonium nitrite, and ammonium hydroxide. 
     
     
         3 . The reaction mixture of  claim 1  wherein the nitrite containing compound is selected from sodium nitrite, potassium nitrite, and sodium hypochlorite. 
     
     
         4 . The reaction mixture of  claim 1 , wherein the coating encapsulating at least one of the ammonium containing compound and the nitrite containing compound is a polymer selected from guar, chitosan, polyvinyl alcohol, and like compounds. 
     
     
         5 . The reaction mixture of  claim 1 , wherein the coating encapsulating at least one of the ammonium containing compound and the nitrite containing compound is selected from 55-carboxymethyl cellulose, xanthan, and like compounds. 
     
     
         6 . The reaction mixture of  claim 1 , wherein the hydrogen releasing activator is selected from acetic acid and hydrochloric acid. 
     
     
         7 . The reaction mixture of  claim 1 , further comprising a buffer. 
     
     
         8 . A method for stimulating production of gas in a tight-gas formation, the method comprising the steps of:
 injecting into the formation an aqueous solution comprising an ammonium containing compound and a nitrite containing compound, wherein at least one of the ammonium containing compound and the nitrite containing compound are encapsulated with a coating operable to prevent reaction therebetween; and   injecting an activator into the formation an activator, the activator being capable of initiating reaction between the ammonium containing compound and the nitrite containing compound such that the reaction generates heat and nitrogen gas;   wherein upon the generation of nitrogen gas and heat within the formation, microfractures are produced within the formation and the hydrostatic pressure within the reservoir is reduced to less than the reservoir fluid pressure, such that the rate of production of hydrocarbons from the formation is increased.   
     
     
         9 . The method of  claim 8 , further comprising the step of first injecting an aqueous fracturing fluid into the tight gas formation, wherein said aqueous fracturing fluid comprises water and a fracturing polymer gel, wherein the step of injection of the aqueous fracturing fluid is achieved at a sufficient rate and pressure to fracture the formation. 
     
     
         10 . The method of  claim 8 , wherein the ratio of the ammonium containing compound to the nitrite containing compound is between about 1.1:1 and 1:1.1. 
     
     
         11 . The method of  claim 8 , wherein the activator is a weak acid and weak acid salt, said weak acid and weak acid salt being present in a ratio providing an acidic solution pH at which said ammonium and nitrite ion-containing compound react. 
     
     
         12 . The method of  claim 11 , wherein said mixture of weak acid and weak acid salt are present in a concentration providing an aqueous solution of weak acid which is capable of effecting a weak acid reservoir acidization of materials contacted in or around the fracture created within the well. 
     
     
         13 . The method of  claim 11 , wherein said mixture of weak acid and weak acid salt are injected into the formation in a solution having a concentration between about 2-10% by volume. 
     
     
         14 . The method of  claim 8 , wherein the coating encapsulating at least one of the ammonium containing compound and the nitrite containing compound is selected from guar, chitosan, polyvinyl alcohol, and like compounds. 
     
     
         15 . The method of  claim 8 , wherein the coating encapsulating at least one of the ammonium containing compound and the nitrite containing compound is selected from 55-carboxymethyl cellulose, xanthan, and like compounds 
     
     
         16 . The method of  claim 8 , wherein the ammonium containing compound is ammonium chloride. 
     
     
         17 . The method of  claim 8 , wherein the nitrite containing compound is sodium nitrite.