Systems and methods for determining mechanical properties in subsurface formations

Abstract

A system for monitoring and establishing mechanical properties of a formation may include a strain sensing system and a controller. The strain sensing system may include an elongated fiber, a light emitter, and a detector. The elongated fiber may be or may include a fiber optic cable. Monitoring and establishing mechanical properties of a wellbore may include determining a stress applied to a casing of a length of the wellbore and sensing, with the strain sensing system, a strain that may be resultant from the stress applied to the casing. Based on the stress applied to the casing and the sensed strain, the controller may determine a value related to a mechanical property of the formation extending along the wellbore.

What is claimed is: 
     
         1 . A controller configured to establish an elastic property of a formation extending along an exterior of a casing of a wellbore, the controller comprising:
 a processor;   an input port in communication with the processor; and   memory storing instructions configured to be executed by the processor to cause the processor to:
 determine a value related to a stress applied to the casing of a length of the wellbore when perturbations are applied to the casing of the length of the wellbore; 
 receive, via the input port, values related to a parameter measured by a distributed strain sensing system while the perturbations are applied to the casing of the length of the wellbore; 
 determine a value related to a strain resultant from the stress applied to the casing of the length of the wellbore based on the values related to the parameter measured by the distributed strain sensing system that are received; and 
 determine a value related to the elastic property of the formation extending along the length of the wellbore based on the value related to the stress applied to the casing of the length of the wellbore and the value related to the strain resultant from the stress applied to the casing of the length of the wellbore. 
   
     
     
         2 . The controller of  claim 1 , wherein the memory further comprises instructions configured to be executed by the processor to cause the processor to:
 establish a value related to a force for the perturbations to apply to the casing of the length of the wellbore.   
     
     
         3 . The controller of  claim 2 , wherein the value related to the force is configured to avoid fracturing of the wellbore and avoid fracturing the formation extending along the length of the wellbore. 
     
     
         4 . The controller of  claim 2 , wherein the memory further comprises instructions configured to be executed by the processor to cause the processor to:
 initiate application of the perturbations to the casing of the wellbore, wherein the perturbations are configured to apply the value related to the force to the casing.   
     
     
         5 . The controller of  claim 1 , wherein the memory further comprises instructions configured to be executed by the processor to cause the processor to:
 determine a value related to the elastic property for each layer of a plurality of layers forming the formation extending along the length of the wellbore.   
     
     
         6 . The controller of  claim 1 , wherein the memory further comprises instructions configured to be executed by the processor to cause the processor to:
 repeat at predetermined intervals:
 the determining the value related to the stress applied to the casing of the length of the wellbore; 
 the receiving, via the input port, the values related to the parameter measured by the distributed strain sensing system; 
 the determining the value related to the strain resultant from the stress applied to the casing of the length of the wellbore; and 
 the determining the value related to the elastic property of the formation extending along the length of the wellbore; and 
   maintain a database of the values related to the elastic property of the formation extending along the length of the wellbore that is determined at each of the predetermined intervals.   
     
     
         7 . The controller of  claim 1 , wherein the distributed strain sensing system includes a fiber optic cable extending along the length of the wellbore and the values received from the distributed strain sensing system are related to one or both of an amount of light and a pattern of light received at a light detector of the distributed strain sensing system. 
     
     
         8 . The controller of  claim 1 , wherein the memory further comprises instructions configured to be executed by the processor to cause the processor to:
 initiate application of the perturbations to the casing of the wellbore.   
     
     
         9 . The controller of  claim 1 , wherein the value related to the elastic property of the formation is a value of the elastic property selected from the group consisting of an elastic modulus of the formation, a stiffness of the formation, and compressibility of the formation. 
     
     
         10 . The controller of  claim 1 , wherein the memory further comprises instructions configured to be executed by the processor to cause the processor to establish a formation model of mechanical properties of materials forming the formation extending along the length of the wellbore based on the value related to the stress applied to the casing of the length of the wellbore and the value related to the strain resultant from the stress applied to the casing of the length of the wellbore. 
     
     
         11 . A system for establishing elastic properties, the system comprising:
 a distributed strain sensing system configured to sense a parameter related to strain resultant from a stress applied to a casing of a length of a wellbore, the distributed strain sensing system comprising:
 an elongated fiber configured to extend along the length of the wellbore; and 
 a strain sensing controller configured to provide values of the parameter measured using the elongated fiber, the values of the parameter are related to the strain resultant from the stress applied to the wellbore; 
 a controller in communication with the distributed strain sensing system, the controller is configured to determine an elastic property of a formation extending along an exterior of the casing of the length of the wellbore based on the values of the parameter measured using the elongated fiber. 
   
     
     
         12 . The system of  claim 11 , wherein the controller is configured to:
 receive an input of a value related to the stress applied to the casing of the length of the wellbore; and   determine the elastic property of the formation extending along the exterior of the casing of the length of the wellbore based on the values of the parameter measured using the elongated fiber and the value related to the stress applied to the casing of the length of the wellbore.   
     
     
         13 . The system of  claim 11 , wherein the controller is configured to:
 determine a value related to the stress applied to the casing of the length of the wellbore; and   determine the elastic property of the formation extending along the exterior of the casing of the length of the wellbore based on the values of the parameter measured using the elongated fiber and the value related to the stress applied to the casing of the length of the wellbore.   
     
     
         14 . The system of  claim 11 , wherein the elongated fiber is a fiber optic cable and the values of the parameter are related to one or both of an amount of light and a pattern of light received at a light detector of the distributed strain sensing system. 
     
     
         15 . The system of  claim 11 , wherein the controller is configured to initiate application of perturbations to the casing of the wellbore. 
     
     
         16 . The system of  claim 15 , wherein the perturbations are applied to the casing of the wellbore from within the wellbore. 
     
     
         17 . The system of  claim 15 , wherein the controller is configured to establish a value related to a force for the perturbations to apply to the casing of the wellbore. 
     
     
         18 . A method comprising:
 initiating application of perturbations to a casing of a wellbore, the perturbations causing a force to be applied to the casing;   determining a stress applied to the casing based on the force applied to the casing;   identifying a strain on the casing resulting from the force applied to the the casing; and   establishing a formation model of mechanical properties of materials forming a formation extending along the wellbore based on the stress applied to the casing of the wellbore and the strain resulting from the force applied to the casing.   
     
     
         19 . The method of the  claim 18 , further comprising:
 receiving values measured using a fiber optic cable extending along the wellbore, wherein the values are are related to one or both of an amount of light and a pattern of light received at a light detector of a distributed strain sensing system,   wherein the strain is identified based on the values measured using the fiber optic cable.   
     
     
         20 . The method of  claim 18 , further comprising:
 establishing an initial stiffness model of the formation extending along the wellbore,   wherein establishing the initial stiffness model of the formation comprises updating the initial stiffness model with an empirical stiffness coefficient based on the strain on the casing.