Producing a hydrocarbon fluid wherein using a fiber optical distributed acoustic sensing (das) assembly

Abstract

A method of producing a hydrocarbon fluid from a subsurface formation, wherein use is made of a directionally sensitive Distributed Acoustic Sensing (DAS) fiber optical assembly having adjacent lengths of optical fiber (A,B) with different directional acoustic sensitivities, which are used to detect the direction (α) of acoustic signals relative to the lengths of optical fiber (A,B).

That which is claimed is: 
     
         1 - 13 . (canceled) 
     
     
         14 . A method of producing a hydrocarbon fluid from a subsurface formation through a well, wherein use is made of a directionally sensitive Distributed Acoustic Sensing (DAS) fiber optical assembly comprising at least two substantially parallel lengths of adjacent optical fibers with different directional acoustic sensitivities in the well, wherein the at least two lengths of adjacent optical fiber comprise a first length of optical fiber with a first ratio between its axial and radial acoustic sensitivity and the second length of optical fiber with a second ratio between its axial and radial acoustic sensitivity; and
 providing an algorithm for detecting a direction of propagation of an acoustic signal relative to a longitudinal axis of the first and second lengths of optical fiber on the basis of a comparison of differences of radial and axial strain in the first and second lengths of optical fiber resulting from the acoustic signal.   
     
     
         15 . The method of  claim 14 , wherein algorithm comprises the formula's:
   ΔΦ A   DAS   =f (ε axial   outside )+ g (ε radial   outside )
     ΔΦ B   DAS   =h (ε axial   outside )+ k (ε radial   outside )
   
       for determining the axial and radial strains ε axial  and ε radial , respectively, incident at the outside of channels X and Y of the adjacent substantially straight lengths of optical fiber A and B by measuring the signals ΔΦ A   DAS  and ΔΦ B   DAS  of the first and second lengths of optical fiber A and B and wherein the factors f, g, h and k are empirically obtained factors relating to the ratio of sensitivity of the lengths of optical fiber A and B to axial and radial strain ε axial  and ε radial , respectively. 
     
     
         16 . The method of  claim 14 , wherein the first ratio is between 300 and 1000 and the second ratio is between 100 and 300. 
     
     
         17 . The method of  claim 14 , wherein the at least two lengths of adjacent optical fiber comprise a first length of coated fiber having a first coating and a second length of coated fiber having a second coating, wherein the first and second coatings are selected such that the Young's Modulus and Poisson's ratio of the first length of coated fiber is less than the Young's Modulus and Poisson's ratio of the second length of coated fiber. 
     
     
         18 . The method of  claims 14 , wherein the first length of optical fiber has an acrylate coating and the second length of optical fiber has a copper coating. 
     
     
         19 . The method of  claim 14 , wherein the at least two lengths of adjacent optical fiber comprise a first length of optical fiber with a first diameter and a second length of optical fiber with a second diameter. 
     
     
         20 . The method of  claim 14 , wherein the at least two lengths of adjacent optical fiber comprise adjacent sections of a single fiber optic cable having a coating with at least one property that varies along the length of the cable, the at least one property being selected from the group consisting of Poisson's ratio and Young's modulus. 
     
     
         21 . The method of  claim 14 , wherein the adjacent lengths of optical cable with different directional acoustic properties comprise at least one of the following features:
 adjacent lengths of optical cable having a different Young's Modulus;   adjacent lengths of optical cable with different diameters;   adjacent lengths of optical cable comprising fiber layers having a different Young's Modulus;   adjacent lengths of optical cable comprising fiber layers having different inner and/or outer diameters;   adjacent lengths of optical cable comprising annular fiber layers filled with fillings, such as gels having different properties, such as different viscosities and/or Young's Modulus;   adjacent lengths of optical cable surrounded by metal tubes having a different Young's Modulus, different material compositions, and/or thicknesses;   adjacent lengths of optical cable having varying and/or alternating acoustic properties along the length thereof.   
     
     
         22 . The method of  claim 14 , wherein the directionally sensitive DAS fiber optical assembly is used to monitor and/or control features of the subsurface formation. 
     
     
         23 . The method of  claim 22 , wherein the well is a subsurface well in the subsurface formation. 
     
     
         24 . The method of  claim 14 , wherein the directionally sensitive DAS fiber optical assembly is used to monitor and/or control subsurface flux of fluid through the subsurface formation into the well. 
     
     
         25 . The method of  claim 14 , wherein the directionally sensitive DAS fiber optical assembly is used to monitor and/or control fluid flux through the well. 
     
     
         26 . The method of  claim 14 , wherein the well is a subsurface well. 
     
     
         27 . The method according to  claim 14 , wherein the directionally sensitive DAS fiber optical assembly is used to monitor, manage and/or control the flux of the hydrocarbon fluids through the subsurface formation. 
     
     
         28 . The method according to  claim 27 , wherein the well is a subsurface well in the subsurface formation. 
     
     
         29 . The method according to  claim 14 , wherein the directionally sensitive DAS fiber optical assembly is used to monitor, manage and/or control the flux of the hydrocarbon fluids through a hydrocarbon fluid production well assembly. 
     
     
         30 . The method according to  claim 14 , wherein the directionally sensitive DAS fiber optical assembly is used to monitor, manage and/or control the flux of the hydrocarbon fluids through the well.