Method of identifying top of cement in real time when cementing a liner

Abstract

A borehole system and a method of installing a liner in a borehole. A liner is disposed in the borehole. A cement is flowed into an annulus between the liner and a wall of the borehole. An acoustic sensor is disposed within the liner and measures an acoustic impedance of the annulus as the cement is flowing into the annulus. A processor determines a depth of an upper surface of the wet cement from the acoustic impedance and performs an operation based on the depth of the upper surface of the wet cement.

1 . A method of installing a liner in a borehole, comprising:
 flowing a wet cement into an annulus between the liner and a wall of the borehole;   transmitting an ultrasonic pulse from an acoustic sensor on an inner string within the liner, wherein the ultrasonic pulse is transmitted radially outward toward an inner surface of the liner;   receiving a reflection of the ultrasonic pulse from the liner at the acoustic sensor;   determining an acoustic impedance indicative of a type of a fluid in the annulus based on the reflection the ultrasonic pulse as the wet cement is flowing into the annulus;   determining a depth of an upper surface of the wet cement from the acoustic impedance; and   performing an operation based on the depth of the upper surface of the wet cement.   
     
     
         2 . The method of  claim 1 , further comprising measuring the acoustic impedance at a selected depth using the acoustic sensor fixed at the selected depth. 
     
     
         3 . The method of  claim 2 , further comprising securing a liner packoff including the acoustic sensor in the liner at the selected depth. 
     
     
         4 . The method of  claim 1 , further comprising measuring the acoustic impedance at a plurality of depths using a plurality of acoustic sensors, wherein a selected acoustic sensor is located at one of the plurality of depths. 
     
     
         5 . The method of  claim 1 , further comprising measuring the acoustic impedance as the acoustic sensor is moved axially within the borehole. 
     
     
         6 . The method of  claim 1 , further comprising determining the depth of the upper surface by determining the depth at which the acoustic impedance changes from a first value to a second value. 
     
     
         7 . The method of  claim 1 , further comprising measuring a pressure in the annulus using a pressure sensor and calculating a fluid loss from the borehole based on the pressure and the acoustic impedance. 
     
     
         8 . The method of  claim 1 , further comprising measuring a temperature at a location of the acoustic sensor and determining the depth of an upper surface using the acoustic impedance and the temperature. 
     
     
         9 . A borehole system, comprising:
 a liner disposed in a borehole;   a pump for flowing a wet cement into an annulus between the liner and a wall of the borehole;   an acoustic sensor disposed within the liner for transmitting an ultrasonic pulses radially outward toward an inner surface of the liner and receiving a reflection of the ultrasonic pulse from the liner measuring an acoustic impedance of the annulus as the cement is flowing into the annulus; and   a processor configured to:
 determining an acoustic impedance indicative of a type of a fluid in the annulus based on the reflection the ultrasonic pulse; 
 determine a depth of an upper surface of the wet cement from the acoustic impedance; and 
 perform an operation based on the depth of the upper surface of the wet cement. 
   
     
     
         10 . The borehole system of  claim 9 , wherein the acoustic sensor is disposed at a fixed depth in the borehole. 
     
     
         11 . The borehole system of  claim 10 , further comprising a liner packoff secured in the liner at the fixed depth, the liner packoff including the acoustic sensor. 
     
     
         12 . The borehole system of  claim 9 , wherein the acoustic sensor further comprises a plurality of acoustic sensors at a plurality of depths along the borehole. 
     
     
         13 . The borehole system of  claim 9 , an inner string for moving the acoustic sensor axially within the liner. 
     
     
         14 . The borehole system of  claim 9 , wherein the processor is further configured to determine the depth of the upper surface by determining the depth at which the acoustic impedance changes from a first value to a second value. 
     
     
         15 . The borehole system of  claim 9 , further comprising a pressure sensor for measuring a pressure in the annulus, wherein the processor is further configured to calculate a fluid loss from the borehole based on the pressure and the acoustic impedance.