Method for enhanced oil recovery by in situ carbon dioxide generation

Abstract

The method for enhanced oil recovery by in situ carbon dioxide generation utilizes a chelating fluid injected into an oil reservoir through a fluid injection system. The chelating fluid is a low pH solution of a polyamino carboxylic acid chelating agent. The polyamino carboxylic acid chelating agent may have a concentration of about 5 wt %. The polyamino carboxylic acid chelating agent is preferably either an aqueous solution of H 2 Na 2 -ethylenediaminetetraacetic acid (pH 4.5), H 3 -hydroxyethyl ethylenediamine triacetic acid (pH 2.5), or an aqueous solution of H 2 NaHEDTA (pH 4). The injection of the chelating fluid may be preceded by flooding the core with seawater, and is followed by injection of either to seawater, a high pH chelating agent, or low salinity water to ensure maximal extraction of oil from the reservoir. The method is particularly for use in formations where the core of the reservoir has a carbonate rock matrix.

We claim: 
     
         1 . A method for enhanced oil recovery from a carbonate reservoir, comprising the steps of:
 injecting an aqueous solution of a low pH polyamino carboxylic acid chelating agent into the core of the reservoir to generate the production of carbon dioxide in situ; and   subsequently injecting a fluid into the core to complete recovery of oil from the reservoir, the fluid being selected from the group consisting of seawater, a solution of a high pH chelating agent, and a low salinity fluid.   
     
     
         2 . The method for enhanced oil recovery according to  claim 1 , wherein the aqueous solution comprises an aqueous solution of H 2 Na 2 -ethylenediaminetetraacetic acid having a pH of about 4.5. 
     
     
         3 . The method for enhanced oil recovery according to  claim 1 , wherein the aqueous solution comprises an aqueous solution of H 3 -hydroxyethyl ethylenediamine triacetic acid having a pH of about 2.5. 
     
     
         4 . The method for enhanced oil recovery according to  claim 1 , wherein the aqueous solution comprises an aqueous solution of H 2 NaHEDTA having a pH of about 4. 
     
     
         5 . The method for enhanced oil recovery according to  claim 1 , wherein the aqueous solution has a concentration of about 5 wt %. 
     
     
         6 . The method for enhanced oil recovery according to  claim 1 , wherein said step of injecting the aqueous solution further comprises injecting the aqueous solution of a low pH polyamino carboxylic acid chelating agent at a temperature of about 100° C. and at an injection rate of 0.25 mL/min. 
     
     
         7 . The method for enhanced oil recovery according to  claim 1 , further comprising the step of flooding the core of the carbonate reservoir with seawater prior to said step of injecting the aqueous solution of the low pH polyamino carboxylic acid chelating agent into the core.