Methods to assess risk of gas breakout in a well and gas breakout risk assessment systems

Abstract

A computer-implemented method to assess risk of gas breakout in a well includes determining a rate of migration of a gas injected into a well containing a section of cement. The method also includes predicting, based on the rate of migration, an amount of time for a breakout to occur, wherein the breakout occurs when the gas penetrates the section of the cement to a location of interest. The method further includes determining an effective diffusivity of the gas when the gas achieves breakout. The method further includes assessing a risk of a gas breakout based on the rate of migration and the effective diffusivity of the gas.

What is claimed is: 
     
         1 . A computer-implemented method to assess risk of gas breakout in a well, comprising:
 determining a rate of migration of a gas injected into a well containing a section of cement;   predicting, based on the rate of migration, an amount of time for a breakout to occur, wherein the breakout occurs when the gas penetrates the section of the cement to a location of interest;   determining an effective diffusivity of the gas when the gas achieves breakout; and   assessing a risk of a gas breakout based on the rate of migration and the effective diffusivity of the gas.   
     
     
         2 . The computer-implemented method of  claim 1 , further comprising:
 determining a depth of penetration of the gas, wherein the depth of penetration of the gas is an extent to which the gas has migrated through the section of cement,   wherein determining the rate of migration comprises determining the rate of migration based on the depth of penetration of the gas.   
     
     
         3 . The computer-implemented method of  claim 2 , wherein determining the depth of penetration of gas comprises determining the depth of penetration of gas as a function of time. 
     
     
         4 . The computer-implemented method of  claim 1 , further comprising:
 determining a rate of migration,   wherein determining the rate of migration comprises determining the rate of migration based on the composition of the cement.   
     
     
         5 . The computer-implemented method of  claim 4 , further comprising assessing one or more variables associated with the composition of cement, the one or more variables comprising one or more of a volume fraction of water to cement slurry, effective quantity of reactive silicates present in the composition of cement, foam quality of foam cement present in the composition of cement, particle size distribution factor of the composition of cement, and an amount of permeability modifier of an additive present in the composition of cement. 
     
     
         6 . The computer-implemented method of  claim 5 , further comprising:
 determining an effective permeability of the gas when the gas achieves breakout based on the effective diffusivity; and   assessing the risk of the gas breakout based on the effective permeability.   
     
     
         7 . The computer-implemented method of  claim 6 , further comprising:
 determining, based on the effective permeability, a flux of the gas when breakout occurs; and   assessing the risk of the gas breakout based on the flux of the gas.   
     
     
         8 . The computer-implemented method of  claim 7 , further comprising determining that breakout has not occurred in response to a determination that the flux of the gas is 0. 
     
     
         9 . The computer-implemented method of  claim 1 , further comprising:
 determining a second rate of migration of the gas injected into a well containing a second section of cement;   predicting, based on the second rate of migration, a second amount of time for a second breakout to occur, wherein the second breakout occurs when the gas reaches a second location of interest;   determining a second effective diffusivity of the gas when the gas achieves breakout; and   assessing a second risk of a second gas breakout based on the second rate of migration and the second effective diffusivity of the gas.   
     
     
         10 . The computer-implemented method of  claim 9 , further comprising:
 determining a second composition of the second cement,   wherein determining the second effective diffusivity of the gas comprises determining the second effective diffusivity of the gas based on the second composition of the second cement.   
     
     
         11 . The computer-implemented method of  claim 9 , further comprising comparing the first risk with the second risk to determine which cement composition provides the lowest risk. 
     
     
         12 . The computer-implemented method of  claim 9 , further comprising:
 determining a third rate of migration of the gas injected into a well containing a third section of cement;   predicting, based on the third rate of migration, a third amount of time for a third breakout to occur, wherein the third breakout occurs when the gas reaches a third location of interest;   determining a third effective diffusivity of the gas when the gas achieves breakout; and   assessing a third risk of a third gas breakout based on the third rate of migration and the third effective diffusivity of the gas; and   comparing the first risk, the second risk, and the third risk to determine which cement composition provides the lowest risk.   
     
     
         13 . The computer-implemented method of  claim 1 , further comprising:
 determining a length of a breakout section through which the gas migrates,   wherein determining the rate of migration comprises determining the rate of migration based on the length of the breakout section.   
     
     
         14 . A gas breakout risk assessment system, comprising:
 a storage medium; and   one or more processors configured to:
 determine a depth of penetration of a gas injected into a well containing a section of cement, wherein the depth of penetration of the gas is an extent to which the gas has migrated through the section of cement; 
 determine a composition of the cement; 
 determine a rate of migration of the based on the depth of penetration and the composition of the cement; 
 predict, based on the rate of migration, an amount of time for a breakout to occur, wherein the breakout occurs when the gas penetrates the section of the cement to a location of interest; 
 determine an effective diffusivity of the gas when the gas achieves breakout; and 
 assess a risk of a gas breakout based on the rate of migration and the effective diffusivity of the gas. 
   
     
     
         15 . The gas breakout risk assessment system of  claim 14 , wherein the one or more processors are further configured to assess one or more variables associated with the composition of cement to determine the composition of the cement, wherein the one or more variables comprise one or more of a volume fraction of water to cement slurry, effective quantity of reactive silicates present in the composition of cement, foam quality of foam cement present in the composition of cement, particle size distribution factor of the composition of cement, and an amount of permeability modifier of an additive present in the composition of cement. 
     
     
         16 . The gas breakout risk assessment system of  claim 14 , wherein the one or more processors are further configured to:
 determine an effective permeability of the gas when the gas achieves breakout based on the effective diffusivity; and   assess the risk of the gas breakout based on the effective permeability.   
     
     
         17 . The gas breakout risk assessment system of  claim 16 , wherein the one or more processors are further configured to:
 determine, based on the effective permeability, a flux of the gas when breakout occurs; and   assess the risk of the gas breakout based on the flux of the gas.   
     
     
         18 . The gas breakout risk assessment system of  claim 16 , wherein the one or more processors are further configured to:
 determine a second rate of migration of the gas injected into a well containing a second section of cement;   predict, based on the second rate of migration, a second amount of time for a second breakout to occur, wherein the second breakout occurs when the gas reaches a second location of interest;   determine a second effective diffusivity of the gas when the gas achieves breakout; and   assess a second risk of a second gas breakout based on the second rate of migration and the second effective diffusivity of the gas.   
     
     
         19 . A non-transitory computer-readable medium comprising instructions, which when executed by a processor, cause the processor to perform operations comprising:
 determining a depth of penetration of a gas injected into a well containing a section of cement, wherein the depth of penetration of the gas is an extent to which the gas has migrated through the section of cement;   determining a composition of the cement;   determining a rate of migration of the based on the depth of penetration and the composition of the cement;   predicting, based on the rate of migration, an amount of time for a breakout to occur, wherein the breakout occurs when the gas penetrates the section of the cement to a location of interest; and   determining an effective diffusivity of the gas when the gas achieves breakout; and   assessing a risk of a gas breakout based on the rate of migration and the effective diffusivity of the gas.   
     
     
         20 . The non-transitory computer-readable medium of  claim 19 , further comprising instructions, which when executed by a processor, cause the processor to perform operations comprising:
 determining a second rate of migration of the gas injected into a well containing a second section of cement;   predicting, based on the second rate of migration, a second amount of time for a second breakout to occur, wherein the second breakout occurs when the gas reaches a second location of interest;   determining a second effective diffusivity of the gas when the gas achieves breakout;   assess a second risk of a second gas breakout based on the second rate of migration and the second effective diffusivity of the gas;   determining a third rate of migration of the gas injected into a well containing a third section of cement;   predicting, based on the third rate of migration, a third amount of time for a third breakout to occur, wherein the third breakout occurs when the gas reaches a third location of interest;   determining a third effective diffusivity of the gas when the gas achieves breakout; and   assessing a third risk of a third gas breakout based on the third rate of migration and the third effective diffusivity of the gas; and   comparing the first risk, the second risk, and the third risk to determine which cement composition provides the lowest risk.