Method For Determining The Integrity Of An Oil Well Plug

Abstract

A method for determining the integrity of a plug plugging an oil well includes the following steps: numerically modelling at least one structural characteristic of the plug as the plug solidifies under depth conditions; detection of the formation of a micro-ring fracture and/or of the deterioration of the plug as a function of the at least one structural characteristic of the plug with respect to a criterion for the formation of a micro-ring fracture and/or rupture; when the formation of a micro-ring fracture is detected, numerically modelling at least one structural characteristic of the plug as the plug solidifies under depth conditions on the basis of the dimensional evolution of the micro-ring fracture over the course of time; and, if the micro-ring fracture extends between two critical points of the well and/or if the plug is damaged, detecting a fault with the plug.

1 . A method for determining the integrity of a plug closing an oil well, the method comprising the following steps:
 digitally modeling at least one structural characteristic of the plug, over the course of time, as the plug solidifies under depth conditions;   detecting, over the course of time, the formation of a micro-ring fracture and/or the deterioration of the plug as a function of the at least one structural characteristic of the plug with respect to a micro-ring fracture formation and/or rupture criterion;   when the formation of a micro-ring fracture is detected, digitally modeling at least one structural characteristic of the plug, over the course of time, as the plug solidifies under depth conditions on the basis of the dimensional evolution of the micro-ring fracture over the course of time; and   if the micro-ring fracture extends between two critical points of the well and/or if the plug is damaged, detecting a fault within the plug.   
     
     
         2 . The determining method according to  claim 1 , wherein the step for digitally modeling at least one structural characteristic of the plug, over the course of time, as the plug solidifies under depth conditions is performed based upon:
 properties of the plug;   geometric characteristics of the plug;   properties of the well; and   environmental conditions.   
     
     
         3 . The determining method according to  claim 1 , wherein the step for digitally modeling at least one structural characteristic of the plug, over the course of time, as the plug solidifies under depth conditions takes account of the evolution of the stresses experienced by the plug, the evolution of the deformation of the plug, the evolution of the chemical setting reaction of the plug, the evolution of the temperature at the plug during setting, the evolution of the properties of the plug and the evolution of the pressure of the pores of the plug. 
     
     
         4 . The determining method according to  claim 1 , wherein the method also includes the following additional steps:
 determining the dimensions of the micro-ring fracture; and   determining the quantity of post-expansion agents necessary to increase the volume of the plug in order to fill in the determined dimensions of the micro-ring fracture.   
     
     
         5 . The determining method according to  claim 1 , wherein the tensile damage of the plug is detected. 
     
     
         6 . The determining method according to  claim 1 , wherein the shear damage of the plug is detected, for example according to the Mohr-Coulomb criterion. 
     
     
         7 . The determining method according to  claim 1 , wherein, during the step for digitally modeling at least one structural characteristic of the plug, over the course of time, as the plug solidifies under depth conditions, the method also includes the following steps:
 detecting an end of setting corresponding to an evolution of the degree of solidification per hour of the plug below 2·10 −4 ;   determining a pressure applied above the plug from fluids placed above the plug after detecting an end of setting;   determining a pressure applied below the plug from fluids placed below the plug after detecting an end of setting; and   determining the stresses experienced by the plug, after setting, based upon pressures applied above and below the plug.   
     
     
         8 . The determining method according to  claim 7 , wherein after the step consisting of determining the stresses experienced by the plug, after setting, as a function of the pressures applied above and below the plug, the method also includes the following additional steps:
 simulating the propagation of a chance micro-ring fracture that appears above or below the plug, as a function of the pressures applied above and below the plug;   if the chance micro-ring fracture extends between two critical points, determining a flow rate of the chance micro-ring fracture; and   if the flow rate of the chance micro-ring fracture is above a threshold, detecting a fault with the plug.   
     
     
         9 . The determining method according to  claim 8 , wherein after the step consisting of detecting a fault on the plug by the presence of a chance micro-ring fracture, the method also comprises the following steps:
 determining the dimension of the chance micro-ring fracture; and   determining the quantity of post-expansion agents necessary in order to increase the volume of the plug in order to fill in the determined dimension of the micro-ring fracture.