Method for injecting low salinity water

Abstract

Methods, apparatuses and computer readable instructions for determining the effectiveness of, and for performing, a low salinity waterflood. An ion diffusion distance value is determined based on the rate of diffusion of ions within the rock of a reservoir and the residency time of floodwater within the reservoir. The thickness of the layers of the reservoir are compared to this ion diffusion value to determine the effectiveness of performing a low salinity waterflood and also to enable the effective control of a waterflood and to assist in the determination of locations of wells.

1 - 30 . (canceled) 
     
     
         31 . A computer-implemented method for determining the effectiveness of performing a low salinity waterflood on a hydrocarbon-bearing reservoir, wherein the reservoir comprises relatively permeable layers interbedded with relatively impermeable layers and is penetrated by an injection well and a production well, the low salinity waterflood comprising injecting low salinity water into the hydrocarbon-bearing reservoir from the injection well whereby to pass through the relatively permeable layers of the reservoir from the injection well to the production well, and wherein the relatively impermeable layers have a relatively high concentration of ions compared to that of the relatively permeable layers when the low salinity water is present therein, the method comprising:
 deriving an ion diffusion distance value from: a diffusion coefficient indicative of a rate of diffusion of ions through the relatively permeable layers when the low salinity water is present therein; and a residence time value indicative of the time required for the low salinity water to pass from the injection well to the production well through the reservoir;   comparing the thickness of the relatively permeable layers to the derived ion diffusion distance value; and   using a result of the comparison to generate an output indicative of the effectiveness of performing a low salinity waterflood.   
     
     
         32 . The method of  claim 31 , comprising:
 determining an average thickness of the relatively permeable layers; and   calculating a ratio of the ion diffusion distance value to the average thickness,   whereby to compare the thickness of the relatively permeable layers to the derived ion diffusion distance value.   
     
     
         33 . The method of  claim 32 , wherein an output value based on the calculated ratio is output whereby to generate the output indicative of the effectiveness of performing a low salinity waterflood. 
     
     
         34 . The method of  claim 33 , wherein the output value is calculated from 
       
         
           
             
               1 
               - 
               
                 x 
                 H 
               
             
           
         
       
       where x is the ion diffusion distance value and H is said average thickness. 
     
     
         35 . The method of  claim 31 , wherein the residence time value is calculated from an interwell distance between the injection well and the production well, and a velocity at which the low salinity water passes through the reservoir. 
     
     
         36 . The method of  claim 35 , wherein the ion diffusion distance value is determined from 2A√(D a Lv −1 ) wherein D a  is the apparent diffusion coefficient for ions in the relatively permeable layers, L is the interwell distance between the injection well and production well, v is the velocity of the low salinity water through the reservoir, and A is a constant. 
     
     
         37 . The method of  claim 36 , wherein the predetermined constant A has a value in the range of 0.125-2 and preferably has a value of 0.5. 
     
     
         38 . The method of  claim 35 , wherein the velocity of the low salinity water through the reservoir is indicative of superficial velocity of the low salinity water through the relatively permeable layers. 
     
     
         39 . The method of  claim 31 , wherein the residence time value for the low salinity water in the reservoir is measured using a tracer injected into the reservoir by the injection well. 
     
     
         40 . The method of  claim 31 , comprising using the output indicative of the effectiveness of performing a low salinity waterflood to calculate an estimate for the recovery of hydrocarbons from the reservoir. 
     
     
         41 . The method of  claim 31 , wherein the relatively permeable layers comprise sandstone layers, and the relatively impermeable layers comprise shale layers. 
     
     
         42 . A computer-implemented method of controlling a low salinity waterflood for a hydrocarbon-bearing reservoir, wherein the reservoir comprises relatively permeable layers interbedded with relatively impermeable layers and is penetrated by an injection well and a production well, the low salinity waterflood comprising injecting low salinity water into the hydrocarbon-bearing reservoir from the injection well whereby to pass through the relatively permeable layers of the reservoir from the injection well to the production well, and wherein the relatively impermeable layers have a relatively high concentration of ions compared to that of the relatively permeable layers when the low salinity water is present therein, the method comprising:
 deriving a target velocity based on: a diffusion coefficient indicative of a rate of diffusion of ions through the relatively permeable layers when the low salinity water is present therein; an interwell distance between the injection well and the production well; and a value indicative of a thickness of the relatively permeable layers; and   transmitting the derived target velocity to a control unit of an injection well.   
     
     
         43 . The method of  claim 42 , comprising controlling a velocity at which the low salinity water passes through the relatively permeable layers based on the target velocity. 
     
     
         44 . The method of  claim 43 , comprising controlling the fluid flow through the injection well whereby to control the velocity at which the low salinity water passes through the relatively permeable layers. 
     
     
         45 . The method of  claim 42 , wherein the target velocity is determined from 
       
         
           
             
               16 
                
               
                 
                   
                     D 
                     a 
                   
                    
                   
                     LA 
                     2 
                   
                 
                 
                   
                     
                       H 
                       2 
                     
                      
                     
                       ( 
                       
                         1 
                         - 
                         
                           F 
                           target 
                         
                       
                       ) 
                     
                   
                   2 
                 
               
             
           
         
       
       wherein D a  is the apparent diffusion coefficient for ions in the relatively permeable layers, L is the interwell distance between the injection well and production well, H is a value indicative of an average thickness of the relatively permeable layers, A is a constant and F target  is a predetermined target diffusion degrade factor. 
     
     
         46 . The method of  claim 45 , wherein the constant A has a value in the range of 0.125 to 2 and preferably has a value of 0.5. 
     
     
         47 . The method of any of  claim 42 , wherein predetermined target diffusion degrade factor F target  is a measure of a target effectiveness of the low salinity waterflood. 
     
     
         48 . The method of  claim 47 , wherein the predetermined target diffusion degrade factor F target  has a value between 0.6 and 0.9. 
     
     
         49 . The method of  claim 42 , comprising maintaining an average velocity at which the low salinity water passes through the relatively permeable layers to be at or above the target velocity whereby to control the velocity at which the low salinity water passes through the relatively permeable layers. 
     
     
         50 . The method of  claim 42 , comprising maintaining a minimum velocity at which the low salinity water passes through the relatively permeable layers to be above the target velocity whereby to control the velocity at which the low salinity water passes through the relatively permeable layers. 
     
     
         51 . The method of  claim 42 , wherein the relatively permeable layers comprise sandstone layers, and the relatively impermeable layers comprise shale layers. 
     
     
         52 . A computer-implemented method of determining locations of at least one production well and at least one injection well for a hydrocarbon-bearing reservoir, wherein the reservoir comprises relatively permeable layers interbedded with relatively impermeable layers and is to be penetrated by the at least one injection well and at least one production well, wherein the injection well is arranged to provide a low salinity waterflood comprising injecting low salinity water into the hydrocarbon-bearing reservoir from the injection well whereby to pass through the relatively permeable layers of the reservoir from the injection well to the production well, and wherein the relatively impermeable layers have a relatively high concentration of ions compared to that of the relatively permeable layers when the low salinity water is present therein, the method comprising:
 calculating an interwell distance value based on: a diffusion coefficient indicative of a rate of diffusion of ions through the relatively permeable layers when the low salinity water is present therein; a value indicative of a thickness of the relatively permeable layers; and a velocity at which the low salinity water passes through the reservoir; and   using the interwell distance value to determine the locations of the at least one injection well and the at least one production well such that the interwell distance between the said at least one injection well and at least one production well is less than said interwell distance value.   
     
     
         53 . The method of  claim 52 , wherein the interwell distance value is determined from 
       
         
           
             
               
                 
                   
                     
                       H 
                       2 
                     
                      
                     
                       ( 
                       
                         1 
                         - 
                         
                           F 
                           target 
                         
                       
                       ) 
                     
                   
                   2 
                 
                  
                 v 
               
               
                 16 
                  
                 
                   D 
                   a 
                 
                  
                 
                   A 
                   2 
                 
               
             
           
         
       
       wherein D a  is the apparent diffusion coefficient for ions in the relatively permeable layers, H is a value indicative of an average thickness of the relatively permeable layers, A is a constant, v is a velocity of the low salinity water through the reservoir, and F target  is a predetermined target diffusion degrade factor. 
     
     
         54 . The method of  claim 53 , wherein the constant A has a value in the range of 0.2 to 2 and preferably has a value of 1. 
     
     
         55 . The method of  claim 53 , wherein predetermined target diffusion degrade factor F target  is a measure of a target effectiveness of the low salinity waterflood. 
     
     
         56 . The method of  claim 55 , wherein the predetermined target diffusion degrade factor F target  has a value between 0.6 and 0.9. 
     
     
         57 . The method of  claim 52 , wherein the relatively permeable layers comprise sandstone layers, and the relatively impermeable layers comprise shale layers. 
     
     
         58 . A computer readable storage medium storing computer readable instructions thereon for execution on a computing system to implement a method for determining the effectiveness of performing a low salinity waterflood on a hydrocarbon-bearing reservoir, wherein the reservoir comprises relatively permeable layers interbedded with relatively impermeable layers and is penetrated by an injection well and a production well, the low salinity waterflood comprising injecting low salinity water into the hydrocarbon-bearing reservoir from the injection well whereby to pass through the relatively permeable layers of the reservoir from the injection well to the production well, and wherein the relatively impermeable layers have a relatively high concentration of ions compared to that of the relatively permeable layers when the low salinity water is present therein, the method comprising:
 deriving an ion diffusion distance value from: a diffusion coefficient indicative of a rate of diffusion of ions through the relatively permeable layers when the low salinity water is present therein; and a residence time value indicative of the time required for the low salinity water to pass from the injection well to the production well through the reservoir;   comparing the thickness of the relatively permeable layers to the derived ion diffusion distance value; and   using a result of the comparison to generate an output indicative of the effectiveness of performing a low salinity waterflood.   
     
     
         59 . A computer readable storage medium storing computer readable instructions thereon for execution on a computing system to implement a computer-implemented method of controlling a low salinity waterflood for a hydrocarbon-bearing reservoir, wherein the reservoir comprises relatively permeable layers interbedded with relatively impermeable layers and is penetrated by an injection well and a production well, the low salinity waterflood comprising injecting low salinity water into the hydrocarbon-bearing reservoir from the injection well whereby to pass through the relatively permeable layers of the reservoir from the injection well to the production well, and wherein the relatively impermeable layers have a relatively high concentration of ions compared to that of the relatively permeable layers when the low salinity water is present therein, the method comprising:
 deriving a target velocity based on: a diffusion coefficient indicative of a rate of diffusion of ions through the relatively permeable layers when the low salinity water is present therein; an interwell distance between the injection well and the production well; and a value indicative of a thickness of the relatively permeable layers; and   transmitting the derived target velocity to a control unit of an injection well.   
     
     
         60 . A computer readable storage medium storing computer readable instructions thereon for execution on a computing system to implement a computer-implemented method of determining locations of at least one production well and at least one injection well for a hydrocarbon-bearing reservoir, wherein the reservoir comprises relatively permeable layers interbedded with relatively impermeable layers and is to be penetrated by the at least one injection well and at least one production well, wherein the injection well is arranged to provide a low salinity waterflood comprising injecting low salinity water into the hydrocarbon-bearing reservoir from the injection well whereby to pass through the relatively permeable layers of the reservoir from the injection well to the production well, and wherein the relatively impermeable layers have a relatively high concentration of ions compared to that of the relatively permeable layers when the low salinity water is present therein, the method comprising:
 calculating an interwell distance value based on: a diffusion coefficient indicative of a rate of diffusion of ions through the relatively permeable layers when the low salinity water is present therein; a value indicative of a thickness of the relatively permeable layers; and a velocity at which the low salinity water passes through the reservoir; and   using the interwell distance value to determine the locations of the at least one injection well and the at least one production well such that the interwell distance between the said at least one injection well and at least one production well is less than said interwell distance value.