System and Method for Measuring Formation Properties

Abstract

Pressure of a fluid in a geological formation is predicted using measured temperature and pressure changes following the creation of a pressure reduction in a flowline in fluid communication with the fluid in the geological formation.

1 . A method comprising:
 a. creating a pressure reduction in a flowline in a formation tester, the flowline in fluid communication with a fluid having a pressure;   b. measuring temperature change within the flowline as the fluid is drawn into the flowline;   c. normalizing temperature change as measured in the flowline to temperature exterior to the formation tester (δ(ΔT));   d. measuring pressure change in the flowline (δP) as the fluid is drawn into the flowline; and   e. determining whether a curve resulting from the equation δP/δ(ΔT) over a period of time indicates that the pressure reduction reached a flowline pressure that is at or below the pressure of the fluid.   
     
     
         2 . The method of  claim 1 , wherein the step of determining is done at substantially the same time as the measuring steps. 
     
     
         3 . The method of  claim 1 , wherein step e comprises calculating a time integral of the curve. 
     
     
         4 . The method of  claim 3 , wherein the time integral is calculated from the formula 
       
         
           
             
               
                 
                   f 
                    
                   
                     ( 
                     n 
                     ) 
                   
                 
                 = 
                 
                   α 
                   · 
                   
                     
                       ∑ 
                       
                         i 
                         = 
                         
                           v 
                           + 
                           1 
                         
                       
                       n 
                     
                      
                     
                         
                     
                      
                     
                        
                       
                         
                           
                             P 
                             
                               i 
                               - 
                               v 
                             
                           
                           - 
                           
                             P 
                             
                               i 
                               + 
                               v 
                             
                           
                         
                         
                           
                             Δ 
                              
                             
                                 
                             
                              
                             
                               T 
                               
                                 i 
                                 - 
                                 v 
                               
                             
                           
                           - 
                           
                             Δ 
                              
                             
                                 
                             
                              
                             
                               T 
                               
                                 i 
                                 + 
                                 v 
                               
                             
                           
                         
                       
                        
                     
                   
                 
               
               , 
             
           
         
         where P is flowline pressure, ΔT is flowline temperature normalized for temperature exterior to the flowline, i is the index of pressure and temperature measurement starting at i=1, v is a value defining a smoothing window over which individual pressure and temperature measurements are smoothed, n is the number indices i within the selected period of time, and a is an arbitrary scaling factor. 
       
     
     
         5 . The method of  claim 1 , wherein the period of time is less than 2 minutes, from about 30 seconds to about 100 seconds, or about 40 seconds. 
     
     
         6 . The method of  claim 1 , further comprising repeating steps a through e if the curve indicates that the pressure reduction did not reach a flowline pressure that is at or below the pressure of the fluid. 
     
     
         7 . A system comprising:
 a. formation tester having:
 i. a flowline, the flowline in fluid communication with a fluid having a pressure; and 
 ii. one or more sensors, the one or more sensors operable to measure temperature exterior to the formation tester and measure pressure and temperature within the flowline; and 
   b. a processor that:
 i. receives temperature and pressure data from the one or more sensors; and 
 ii. calculates a curve resulting from the equation δP/δ(ΔT), where δP is pressure change in the flowline as the fluid is drawn into the flowline by the creation of a first pressure reduction within the flowline, and where δ(ΔT) is temperature change in the flowline normalized for temperature exterior to the flowline. 
   
     
     
         8 . The system of  claim 7 , wherein the processor further calculates a time integral of the curve. 
     
     
         9 . The system of  claim 8 , wherein the time integral is calculated from the formula 
       
         
           
             
               
                 f 
                  
                 
                   ( 
                   n 
                   ) 
                 
               
               = 
               
                 α 
                 · 
                 
                   
                     ∑ 
                     
                       i 
                       = 
                       
                         v 
                         + 
                         1 
                       
                     
                     n 
                   
                    
                   
                       
                   
                    
                   
                      
                     
                       
                         
                           P 
                           
                             i 
                             - 
                             v 
                           
                         
                         - 
                         
                           P 
                           
                             i 
                             + 
                             v 
                           
                         
                       
                       
                         
                           Δ 
                            
                           
                               
                           
                            
                           
                             T 
                             
                               i 
                               - 
                               v 
                             
                           
                         
                         - 
                         
                           Δ 
                            
                           
                               
                           
                            
                           
                             T 
                             
                               i 
                               + 
                               v 
                             
                           
                         
                       
                     
                      
                   
                 
               
             
           
         
         where P is flowline pressure, ΔT is flowline temperature normalized for temperature exterior to the flowline, i is the index of pressure and temperature measurement starting at i=1, v is a value defining a smoothing window over which individual pressure and temperature measurements are smoothed, n is the number indices i within the selected period of time, and a is an arbitrary scaling factor. 
       
     
     
         10 . The system of  claim 7 , wherein the processor further indicates whether the first pressure reduction reached a flowline pressure that is at or below the pressure of the fluid. 
     
     
         11 . The system of  claim 7 , wherein the processor further initiates creation of a second pressure reduction in the flowline if the calculated curve indicates that the first pressure reduction did not reach a flowline pressure that is at or below the pressure of the fluid.