Systems and methods for determining the strain experienced by wellhead tubulars

Abstract

A system includes a tubular member ( 60 ) including a radially outer surface ( 60 c ) and a sensor assembly ( 128 ). The sensor assembly includes a strain sensor coupled to the radially outer surface. In addition, the sensor assembly includes a first coating having ( 134 ) a first hardness and a first tensile strength. The first coating encases the strain sensor ( 131,130 ) and at least part ( 64 ) of the outer surface. Further, the sensor assembly includes a second coating ( 136 ) having a second hardness that is greater than the first hardness and a second tensile strength that is greater than the first tensile strength. The second coating encases the first coating and at least another part ( 68 ) of the radially outer surface.

What is claimed is: 
     
         1 . A system, comprising:
 a tubular member including a radially outer surface; and   a sensor assembly comprising:
 a strain sensor coupled to the radially outer surface of the tubular member; 
 a first coating having a first hardness and a first tensile strength, wherein the first coating encases the strain sensor and at least part of the radially outer surface of the tubular member; 
 a second coating having a second hardness that is greater than the first hardness and a second tensile strength that is greater than the first tensile strength, wherein the second coating encases the first coating and at least another part of the radially outer surface of the tubular member. 
   
     
     
         2 . The system of  claim 1 , wherein the strain sensor assembly extends radially outward to a distance from the radially outer surface of the tubular member that is less than about 0.5 inches. 
     
     
         3 . The system of  claim 1 , further comprising:
 an electrical conductor that is coupled to the strain sensor and extends along the radially outer surface of the tubular member, wherein the second coating encases at least a portion of the electrical conductor; and   an electrical connector that is coupled to the electrical conductor and disposed on the radially outer surface of the tubular member.   
     
     
         4 . The system of  claim 1 , wherein the first coating is an electric insulator and is configured to restrict contact of liquid disposed around the tubular member with the strain sensor; and
 wherein the second coating comprises one of at least one of resin, carbon fiber, and rubber.   
     
     
         5 . The system of  claim 1 , further comprising an external gauge ring disposed about the radially outer surface of the tubular member, axially below the sensor assembly;
 wherein the external gauge ring includes a frustoconical lower surface and a radially outer surface; and   wherein the radially outer surface of the external gauge ring is radially outward from the second coating of the sensor assembly.   
     
     
         6 . The system of  claim 1 , further comprising a communication unit in communication with the strain sensor; wherein the communication unit is configured to communicate with a remote surface location via a wireless signal. 
     
     
         7 . The system of  claim 6 , further comprising:
 a temperature sensor coupled to the radially outer surface of the tubular member;   wherein the communication unit is in communication with the temperature sensor.   
     
     
         8 . The system of  claim 1 , further comprising:
 an inner tubular disposed within the tubular member such that an annulus is formed between the inner tubular and the tubular member, wherein the inner tubular has a radially outer surface;   a second strain sensor coupled to the radially outer surface of the inner tubular;   a first transducer coupled to the radially outer surface of the tubular member;   a second transducer coupled to the radially outer surface of the inner tubular;   wherein the second transducer is electrically coupled to the second strain sensor; and   wherein the first transducer is configured to wirelessly communicate with the second transducer across the annulus.   
     
     
         9 . The system of  claim 8 , further comprising:
 a ring member disposed about the radially outer surface of the inner tubular;   wherein the ring member includes an annular recess, wherein the second strain sensor and the second transducer are disposed within the annular recess; and   a power unit disposed within the annular recess and configured to store electrical power and deliver electrical power to the second transducer and the second strain sensor.   
     
     
         10 . A method of measuring strain on a first conductor for use in an oil and gas well, the method comprising:
 (a) measuring a strain on the first conductor with a first strain sensor coupled to a radially outer surface of the first conductor;   (b) protecting the first strain sensor during (a) with an outer coating;   (c) routing data from the first strain sensor to a communication unit after (a);   (d) wirelessly communicating with a remote surface location with the communication unit after (c).   
     
     
         11 . The method of  claim 10 , wherein (a) comprises deforming the first sensor with the strain on the first conductor; and wherein the method further comprises:
 (e) accommodating the deformation in (a) with an inner coating disposed between the outer coating and the first strain sensor; and   (f) resisting contact between liquids disposed about the first conductor and the first strain sensor with the inner coating.   
     
     
         12 . The method of  claim 10 , further comprising:
 (g) forcing the first conductor into a wellbore before (a);   (h) engaging sediment in the wellbore during (g) with an external gauge ring disposed about the first conductor below the first strain sensor; and   (i) forcing the sediment radially away from the radially outer surface of the first conductor during (h).   
     
     
         13 . The method of  claim 10 , further comprising:
 measuring strain on a second conductor disposed within the first conductor with a second strain sensor coupled to a radially outer surface of the second conductor; and   (k) routing data from the second strain sensor across an annulus formed between the first conductor and the second conductor.   
     
     
         14 . The method of  claim 13 , wherein (k) comprises routing data from the second strain sensor across the annulus with a wireless signal. 
     
     
         15 . The method of  claim 14 , wherein the wireless signal comprises an acoustic signal.