Inversion of multi-cycle fracture reopening pressures for in-situ stresses

Abstract

Embodiments presented provide for a calculation and quantification of naturally occurring stresses in rock formations using inversion of multi-cycle fracture reopening pressures for in-situ stresses.

What is claimed is: 
     
         1 . A method, comprising,
 defining an interval in a borehole to be tested;   establishing an apparatus in proximity to the interval;   generating a pressure in the interval to be tested to initiate or open a fracture in the interval, the fracture opened by producing tension in the rock;   propagating the fracture in small increments in order to sample the near wellbore stress concentration;   measuring at least one or more fracture reopening pressures under the influence of the near-wellbore stress concentration; and   using the measured at least one fracture reopening pressure in conjunction with or without other data acquired during or after pressurization to perform an analysis to create constrained values of one or more in situ stress components.   
     
     
         2 . The method according to  claim 1 , wherein the other data one or more pressures. 
     
     
         3 . The method according to  claim 1 , wherein the other data is one or more instantaneous shut-in pressures. 
     
     
         4 . The method according to  claim 1 , wherein the other data is one or more closure pressures. 
     
     
         5 . The method according to  claim 1 , wherein the other data is one or more volumes. 
     
     
         6 . The method according to  claim 5 , wherein the one or more volumes are volumes of fluid injected into the fracture. 
     
     
         7 . The method according to  claim 5 , wherein the one or more volumes are estimates of the volume of the open fracture. 
     
     
         8 . The method according to  claim 1 , wherein the fracture is initiated on an intact borehole wall. 
     
     
         9 . The method according to  claim 1 , wherein the fracture existed prior to testing and is opened during the test. 
     
     
         10 . The method according to  claim 1 , wherein the fracture is a predefined type of fracture. 
     
     
         11 . The method according to  claim 10 , wherein the predefined type of fracture is a KGD fracture. 
     
     
         12 . The method according to  claim 1 , further comprising:
 at least one of printing and visually representing one or more in situ stress components.   
     
     
         13 . The method according to  claim 12 , wherein the visually representing in situ stress components is on a computer monitor. 
     
     
         14 . The method according to  claim 1 , wherein the analysis performed uses the formula 
       
         
           
             
               
                 
                   p 
                   reopen 
                 
                 - 
                 
                   p 
                   p 
                 
               
               = 
               
                 
                   ∫ 
                   0 
                   1 
                 
                 
                   
                     K 
                     ⁡ 
                     ( 
                     ξ 
                     ) 
                   
                   ⁢ 
                      
                   
                     ( 
                     
                       
                         
                           σ 
                           
                             θ 
                             ⁢ 
                             θ 
                           
                         
                         ( 
                         ξ 
                         ) 
                       
                       - 
                       
                         p 
                         p 
                       
                     
                     ) 
                   
                   ⁢ 
                      
                   d 
                   ⁢ 
                   ξ 
                 
               
             
           
         
       
     
     
         15 . The method according to  claim 1 , wherein the analysis performed uses the formula 
       
         
           
             
               
                 V 
                 frac 
               
               = 
               
                 
                   
                     4 
                     ⁢ 
                     
                       ( 
                       
                         1 
                         - 
                         v 
                       
                       ) 
                     
                     ⁢ 
                     
                       L 
                       2 
                     
                     ⁢ 
                     h 
                   
                   
                     π 
                     ⁢ 
                     G 
                   
                 
                 ⁢ 
                 
                   
                     ∫ 
                     0 
                     
                          
                       1 
                     
                   
                   
                     
                       ∫ 
                       0 
                       
                            
                         1 
                       
                     
                     
                       Log 
                       ⁢ 
                          
                       
                         ( 
                         
                           
                             2 
                             - 
                             
                               ξ 
                               2 
                             
                             - 
                             
                               s 
                               2 
                             
                             + 
                             
                               2 
                               ⁢ 
                               
                                 
                                   1 
                                   - 
                                   
                                     ξ 
                                     2 
                                   
                                 
                               
                               ⁢ 
                               
                                 
                                   1 
                                   - 
                                   
                                     s 
                                     2 
                                   
                                 
                               
                             
                           
                           
                             
                               ❘ 
                               "\[LeftBracketingBar]" 
                             
                             
                               
                                 ξ 
                                 2 
                               
                               - 
                               
                                 s 
                                 2 
                               
                             
                             
                               ❘ 
                               "\[RightBracketingBar]" 
                             
                           
                         
                         ) 
                       
                       ⁢ 
                          
                       Δ 
                       ⁢ 
                       
                         
                           p 
                           shut 
                         
                         ( 
                         s 
                         ) 
                       
                       ⁢ 
                       dsd 
                       ⁢ 
                       
                         ξ 
                         . 
                       
                     
                   
                 
               
             
           
         
       
     
     
         16 . The method according to  claim 1 , performed in vertical wells, horizontal wells, or wells of any orientation. 
     
     
         17 . The method according to  claim 1 , performed on fractures of any orientation. 
     
     
         18 . The method of  claim 1  wherein the analysis is performed using models that account for plastic yielding or poroelastic effects on fracture re-opening, propagation, or closure. 
     
     
         19 . The method of  claim 1  wherein the constrained in situ stresses may comprise one or more of the following stresses: the minimum horizontal stress, the maximum horizontal stress, the vertical/overburden stress, a tilted principal stress, or a shear stress. 
     
     
         20 . A computer readable non-volatile medium configured to perform code that is executable on a computer, the code comprising a method that enables defining an interval in a borehole to be tested;
 establishing an apparatus in proximity to the test interval;   generating a pressure in the interval to be tested to initiate or open a fracture in the interval, the fracture opened by producing tension in the rock;   propagating the fracture in small increments in order to sample the near wellbore stress concentration,   measuring at least one or more fracture reopening pressures under the influence of the near-wellbore stress concentration; and   using the measured at least one fracture reopening pressure in conjunction with or without other data acquired during or after pressurization to perform an analysis to create constrained values of one or more in situ stress components.