Water injection systems and methods

Abstract

There is disclosed a method for enhancing recovery of crude oil from a porous subterranean carbonate formation of which the pore spaces contain crude oil and connate water, the method comprising determining an ionic strength of the connate water; and injecting an aqueous displacement fluid having a lower ionic strength than the connate water into the formation.

1 . A method for enhancing recovery of crude oil from a porous subterranean carbonate formation of which the pore spaces contain crude oil and connate water, the method comprising:
 determining an ionic strength of the connate water; and   injecting an aqueous displacement fluid having a lower ionic strength than the connate water into the formation.   
     
     
         2 . The method of  claim 1 , wherein the aqueous displacement fluid has an Ionic Strength (I) less than about 10% of the Ionic Strength of the connate water. 
     
     
         3 . The method of  claim 1 , wherein the aqueous displacement fluid has an Ionic Strength (I) less than about 0.5% of the Ionic Strength of the connate water. 
     
     
         4 . The method of  claim 1 , wherein the method further comprises:
 determining a total level of multivalent cations (Moles/Volume) of the connate water; and   injecting an aqueous displacement fluid having a lower total level of multivalent cations (Moles/Volume) than the connate water.   
     
     
         5 . The method of  claim 1 , wherein the aqueous displacement fluid comprises at least one additive selected from a surfactant, a foaming agent, a water soluble polymer, and a water soluble solvent having a molar solubility in water of at least 1% and an octanol-water partition coefficient of at least 1 that is selected from the group consisting of an alcohol, an amine, a pyridine, an ether, a carboxylic acid, an aldehyde, a ketone, a phosphate, a quinine, and mixtures thereof. 
     
     
         6 . The method of  claim 1 , wherein the aqueous displacement fluid comprises steam and/or water obtained from an aquifer, river, lake, sea, treated sewage effluent, or ocean. 
     
     
         7 . The method of  claim 1 , wherein the formation is a mineral-bearing carbonate formation. 
     
     
         8 . The method of  claim 1 , wherein the aqueous displacement fluid comprises a viscosifying polymer. 
     
     
         9 . The method of  claim 8 , wherein the aqueous displacement fluid has a viscosity level above 1 mPa·s and comprises at least 200 ppm (mass) of viscosifying polymer. 
     
     
         10 . The method of  claim 8 , wherein the viscosifying polymer comprises a hydrolyzed polyacrylamide. 
     
     
         11 . The method of  claim 1 , wherein the water is treated to provide an aqueous displacement fluid having an ionic strength less than about 5% of the ionic strength of the connate water. 
     
     
         12 . The method of  claim 1 , wherein the water is treated to provide an aqueous displacement fluid having an ionic strength from about 0.1% to about 20% of the ionic strength of the connate water. 
     
     
         13 . The method of  claim 1 , wherein the water is treated to provide an aqueous displacement fluid having a total dissolved solids level from about 0.1% to about 20% of the total dissolved solids level of the connate water.