Method for improving injectivity conformance in heterogeneous formations

Abstract

A method for improving injectivity conformance of a hydrocarbon bearing heterogeneous subterranean formation by reducing the variance in water saturation throughout the formation, as a means of improving recovery when steam injection is later applied. A solvent plunger is developed by incremental injections of solvent followed by periods of arrest to permit the solvent to mix with the oil in the areas of relatively high water saturation thereby creating a plunger to uniformly displace the water in the formation to achieve water injectivity conformance along the well.

What is claimed is: 
     
         1 . A method for improving injectivity conformance of a hydrocarbon bearing heterogeneous subterranean formation, the formation having variable water injectivity due to water saturation variance throughout the formation, the method comprising:
 (i) injecting a solvent into the formation, the solvent preferentially displacing into areas of relatively high water saturation;   (ii) arresting injection of the solvent for a sufficient period of time to permit the solvent to mix with the oil in the areas of relatively high water saturation to create a homogenized oil and solvent mix, the homogenized oil and solvent mix having a viscosity that is higher than the viscosity of the solvent;   (iii) resuming injection of the solvent into the formation, the solvent bypassing areas of the formation comprising the homogenized oil and solvent mix such that the solvent preferentially displaces into areas of relatively lesser water saturation than in step (i) to create the homogenized oil and solvent mix; and   (iv) repeating steps (ii) and (iii) until the homogenized oil and solvent mix has uniformly displaced the water in the formation and water injectivity conformance is reached.   
     
     
         2 . The method according to  claim 1 , wherein water injectivity conformance is determined by monitoring the pressure required to inject cycles of solvent injection in step (i) and/or a decline in wellbore or reservoir pressure in step (ii), wherein the change in injection pressure and/or pressure decline indicates the degree of displacement of the water in the formation. 
     
     
         3 . The method according to  claim 1 , wherein the homogenized oil and solvent mix has a viscosity that is higher than the water saturating the formation. 
     
     
         4 . The method according to  claim 1 , wherein the solvent is selected from the group of solvents consisting of xylene, pentane, butane, diesel, naphtha, and various petroleum refinery or upgrader products and combinations thereof. 
     
     
         5 . The method according to  claim 1 , wherein the solvent in step (i) is the same as the solvent in step (iii). 
     
     
         6 . The method according to  claim 1 , wherein the solvent in step (i) is different from the solvent in step (iii). 
     
     
         7 . The method according to  claim 6 , wherein the solvent in step (iii) has a different density than the solvent in step (i). 
     
     
         8 . A method for improving injectivity conformance of a hydrocarbon bearing heterogeneous subterranean formation, the formation having variable water injectivity due to water saturation variance throughout the formation, the method comprising:
 (i) injecting a solvent into the formation, the solvent preferentially displacing into areas of relatively high water saturation;   (ii) arresting injection of the solvent for a sufficient period of time to permit the solvent to mix with the oil in the areas of relatively high water saturation to create a homogenized oil and solvent mix, the homogenized oil and solvent mix having a viscosity that is higher than the viscosity of the solvent;   (iii) monitoring solvent injection pressure, wherein an increase in injection pressure from one injection cycle to a subsequent injection cycle indicates the degree of displacement of the water in the formation;   (iv) resuming injection of the solvent into the formation, the solvent bypassing areas of the formation comprising the homogenized oil and solvent mix such that the solvent preferentially displaces into areas of relatively lesser water saturation than in step (i) to create the homogenized oil and solvent mix; and   (v) repeating steps (ii) to (iv) until the homogenized oil and solvent mix has uniformly displaced the water in the formation and water injectivity conformance is reached.   
     
     
         9 . The method according to  claim 8 , wherein the homogenized oil and solvent mix has a viscosity that is higher than the water saturating the formation. 
     
     
         10 . The method according to  claim 8 , wherein the solvent is selected from the group of solvents consisting of xylene, pentane, butane, diesel, naphtha, and various petroleum refinery or upgrader products and combinations thereof. 
     
     
         11 . The method according to  claim 8 , wherein the solvent in step (i) is the same as the solvent in step (iv). 
     
     
         12 . The method according to  claim 8 , wherein the solvent in step (i) is different from the solvent in step (iv). 
     
     
         13 . The method according to  claim 12 , wherein the solvent in step (iv) has a different density then the solvent in step (i).