Oil Recovery Method

Abstract

A method for recovering crude oil from a reservoir that is penetrated by at least one injection well includes injecting an aqueous displacement fluid into the reservoir from the injection well. The displacement fluid includes a solution of a zinc salt in an aqueous base fluid. The aqueous base fluid has a total dissolved solids (TDS) concentration in the range of 200 to 250,000 ppmv (parts per million based on the volume of the aqueous base fluid) and a viscosity in the range of 1.00 to 2.00 centipoise (cP) at standard temperature and pressure. The aqueous displacement fluid has a dissolved zinc concentration in the range of 10 to 3,750 ppmv. The aqueous displacement fluid includes dissolved chloride. The molar ratio of dissolved chloride to dissolved zinc in the aqueous displacement fluid is at least 5:1.

What is claimed is: 
     
         1 . A method for recovering crude oil from a reservoir that is penetrated by at least one injection well, the method comprising:
 injecting an aqueous displacement fluid comprising a solution of a zinc salt in an aqueous base fluid into the reservoir from the injection well, wherein the aqueous base fluid has a total dissolved solids (TDS) concentration in the range of 200 to 250,000 ppmv (parts per million based on the volume of the aqueous base fluid) and a viscosity in the range of 1.00 to 2.00 centipoise (cP) at standard temperature and pressure, wherein the aqueous displacement fluid has a dissolved zinc concentration in the range of 10 to 3,750 ppmv, where the aqueous displacement fluid comprises dissolved chloride, and wherein the molar ratio of dissolved chloride to dissolved zinc in the aqueous displacement fluid is at least 5:1.   
     
     
         2 . The method as claimed in  claim 1 , wherein at least 50% by weight of the dissolved solids in the aqueous base fluid are sodium cations and chloride anions (based on the Ionic Strength of the aqueous base fluid). 
     
     
         3 . The method as claimed in  claim 1 , further comprising:
 switching, after injecting the aqueous displacement fluid into the reservoir, the injection well from injection to production; and   recovering oil from the reservoir via the injection well.   
     
     
         4 . The method as claimed in  claim 1 , wherein the aqueous displacement fluid is injected into the reservoir in secondary recovery mode or in a tertiary recovery mode. 
     
     
         5 . The method as claimed in  claim 1 , wherein at least 90% of the dissolved solids in the aqueous base fluid are selected from Group IA metal cations, Group IIA metal cations and halide anions (based on the Ionic Strength of the aqueous base fluid). 
     
     
         6 . The method as claimed in  claim 1 , wherein the aqueous base fluid has a total dissolved solids concentration of at least 1,000 ppmv. 
     
     
         7 . The method as claimed in  claim 1 , wherein the aqueous base fluid has a density in the range of 1.000 to 1.210 g/cm3 at standard temperature and pressure. 
     
     
         8 . The method as claimed in  claim 1 , wherein the aqueous base fluid comprises a water-miscible co-solvent in an amount of less than 5% by volume. 
     
     
         9 . The method as claimed in  claim 1 , wherein a pH of the aqueous displacement fluid is maintained above a value of 3 and below a value of 7 during the injecting. 
     
     
         10 . The method as claimed in  claim 1 , wherein a ratio of an Ionic Strength of the aqueous displacement fluid to a molar concentration of dissolved zinc is at least 5:1 (based on the dissolved solids being in the form of free ions). 
     
     
         11 . The method as claimed in  claim 1 , wherein the aqueous displacement fluid has a concentration of dissolved zinc in the range of 10 to 1000 ppmv. 
     
     
         12 . The method as claimed in  claim 1 , wherein the aqueous displacement fluid is a viscosified aqueous displacement fluid, and wherein the viscosified aqueous displacement fluid is formed by dosing a viscosifying agent and a zinc salt into the aqueous base fluid, wherein the viscosified aqueous displacement fluid has a viscosity at reservoir conditions in the range of 1 to 40 cP. 
     
     
         13 . The method as claimed in  claim 1 , wherein the aqueous displacement fluid is a viscosified aqueous displacement fluid, and wherein the viscosified aqueous displacement fluid is formed by dosing a viscosifying agent into the aqueous displacement fluid, wherein the viscosified aqueous displacement fluid has a viscosity at reservoir conditions in the range of 1 to 40 cP. 
     
     
         14 . The method as claimed in  claim 1 , further comprising:
 injecting an aqueous drive fluid into the reservoir to sweep the aqueous displacement fluid through the reservoir to a production well.   
     
     
         15 . The method as claimed in  claim 14 , wherein the aqueous base fluid has a TDS of at least 20,000 ppmv and the aqueous drive fluid has a density that is less than 0.199 g/cm3 higher than the aqueous base fluid. 
     
     
         16 . A method for recovering crude oil from a reservoir that is penetrated by at least one injection well, the method comprising:
 injecting an aqueous displacement fluid comprising a solution of a zinc salt in an aqueous base fluid into the reservoir from the injection well, wherein the aqueous base fluid has a total dissolved solids (TDS) concentration in the range of 200 to 250,000 ppmv (parts per million based on the volume of the aqueous base fluid) and a viscosity in the range of 1.00 to 2.00 centipoise (cP) at standard temperature and pressure, wherein the aqueous displacement fluid has a dissolved zinc concentration in the range of 10 to 3,750 ppmv, and wherein a ratio of an Ionic Strength of the aqueous displacement fluid to a molar concentration of dissolved zinc is at least 5:1 (based on the dissolved solids being in the form of free ions).   
     
     
         17 . The method of  claim 16 , wherein the aqueous displacement fluid comprises dissolved chloride, and wherein the molar ratio of dissolved chloride to dissolved zinc in the aqueous displacement fluid is at least 5:1. 
     
     
         18 . The method as claimed in  claim 16 , wherein the aqueous base fluid has a total dissolved solids concentration of at least 1,000 ppmv. 
     
     
         19 . The method as claimed in  claim 16 , wherein the aqueous displacement fluid has a concentration of dissolved zinc in the range of 10 to 1000 ppmv. 
     
     
         20 . The method as claimed in  claim 1 , further comprising:
 injecting an aqueous drive fluid into the reservoir to sweep the aqueous displacement fluid through the reservoir to a production well.