Testing apparatus and method of deriving young's modulus from tensile stress/strain relationships

Abstract

A method of testing and a tester apparatus to determine the axial stress and strain of cements under the temperature and pressures encountered by cement during use in wellbore environments. Using these stress and strain measurements, the Young's Modulus may be established for a material at the encountered temperature and pressure of the wellbore. By combining static tensile strength testing and elasticity measurements of cements, Young's Modulus values for different cement compositions under stresses that are similar to the conditions occurring in an actual wellbore are possible.

1 . A method of determining a Young's modulus of a cement specimen, the method comprising the steps of: 
 (a) inserting cement into a cement mold inside a pressure vessel;    (b) increasing the pressure and temperature within the vessel;    (c) allowing the specimen to cure to form the cement specimen;    (d) applying a measured axial stress and axial strain tension to the specimen; and    (e) determining a ratio of axial stress to axial strain in the specimen wherein the ratio is the Young's modulus of the spectrum.    
   
   
       2 . The method of  claim 1  which further comprises the steps of measuring the deflection of the specimen during Step (d).  
   
   
       3 . The method of  claim 1  wherein the pressure vessel is at a pressure greater than atmospheric after Step (b).  
   
   
       4 . The method of  claim 1  wherein the pressure vessel is at a temperature from a range of about 32° F. to about 500° F. after Step (b).  
   
   
       5 . The method of  claim 1 , which further comprises the step of using a data acquisition unit to accumulate data during Step (d).  
   
   
       6 . A method of determining a plurality of Young's moduluses for a corresponding plurality of cement specimens, the method which comprises using the Method of  claim 1  to determine the Young's modulus on each corresponding specimen.  
   
   
       7 . The method of  claim 2 , wherein the deflection is measure by at least one precision linear transducer.  
   
   
       8 - 15 . (canceled)  
   
   
       16 . A method of determining Young's modulus in a cement specimen, comprising the steps of: 
 (a) determining axial stress in the specimen;    (b) determining axial strain in the specimen; and    (c) determining the ratio of axial stress to axial strain in the specimen to find the Young's modulus;    wherein Step (a) does not include determining axial stress by compressing the specimen.    
   
   
       17 . The method of  claim 16 , the method which comprises pressurizing the specimen prior to Step (a).  
   
   
       18 . The method of  claim 16 , wherein Step (a) measures a tensional stress.  
   
   
       19 . A method of determining a plurality of Young's moduluses for a corresponding plurality of cement specimens, which comprises using the method of  claim 16  for each specimen, wherein each specimen is contained in a single pressure vessel.