Abstract:
A method of preventing hydrogen darkening of optic fibre, which includes a step of providing a protective barrier of hydrogen free flowing gas around the optic fibre, such that the flowing gas sweeps away hydrogen.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a method of preventing hydrogen atoms from reacting with and darkening glass optic fibre.  
       BACKGROUND OF THE INVENTION  
       [0002]     Optic fibre is used in oil and gas wells to transmit light waves carrying signals to surface. Hydrogen is invariably present in the hydrocarbon environment of oil and gas wells.  
         [0003]     At temperatures above 170 degrees Celsius, optic fibre is susceptible to attack from hydrogen atoms. The hydrogen atoms penetrate protective coverings and react with the optic fibre.  
         [0004]     This results in a degradation of the signals due to scattering of the light waves. This signal degradation has come to be known as “hydrogen darkening”. Canadian Patent 2,323,042 discloses a method of reducing the time until hydrogen darkening occurs by placing the optic fibre within a tube containing a protective liquid.  
       SUMMARY OF THE INVENTION  
       [0005]     According to the present invention there is provided a method of preventing hydrogen darkening of optic fibre, which includes a step of providing a protective barrier of hydrogen free flowing gas around the optic fibre, such that the flowing gas sweeps away hydrogen atoms. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     These and other features of the invention will become more apparent from the following description in which reference is made to the appended drawings, the drawings are for the purpose of illustration only and are not intended to in any way limit the scope of the invention to the particular embodiment or embodiments shown, wherein:  
         [0007]      FIG. 1  is a first installation illustrating the preferred method of preventing hydrogen darkening of optic fibre in accordance with the teachings of the present invention.  
         [0008]      FIG. 2  is a second installation illustrating the preferred method of preventing hydrogen darkening of optic fibre in accordance with the teachings of the present invention.  
         [0009]      FIG. 3  is a detailed section view of optic fibre used in the first installation illustrated in  FIG. 1  and the second installation illustrated in  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0010]     The preferred method of preventing hydrogen darkening of optic fibre will now be described with reference to  FIG. 1  through  3 .  
         [0011]     Referring to  FIG. 3 , the method provides a protective barrier  12  of substantially hydrogen free flowing gas around the optic fibre  14 , such that the flowing gas sweeps away hydrogen. Referring to  FIG. 1 , a gas supply  16  is provided as the source of flowing gas. A flow rate of between 2 and 50 standard cubic feet per day has been found to be sufficient, depending on the conditions. In addition, the flowing gas may be provided in an intermittent, rather than continuous flow, to conserve gas and energy, in suitable situations. The gas passes through a metering or control valve  18 , and through a pressure gauge  20  that also acts as a bleed off point. This allows the gas pressure to be monitored and controlled. The gas is then passed through another valve  22 , and is an optic fibre  14  is then encased in tubular body  26  at junction  25  that is then strung out through a wellhead  27  and down a well  28 . The details of this can be seen in  FIG. 3 , where an annulus  30  is defined between optic fibre  14  and tubular body  26 , such that the flowing gas passes along annulus  30  to form protective barrier  12 . The information collected downhole is then passed back up, through junction  25 , and into junction box  24 , where the collected information is passed on to a fibre optic SRU (not shown).  
         [0012]     Referring to  FIG. 1 , there may be a turn-around sub  32  that allows tubular body  26  to be brought back to the surface, where the gas is bled off to atmosphere through valve  34 . Alternatively, referring to  FIG. 2 , the gas may be bled off downhole, and allowed to dissipate into the reservoir.  
         [0013]     Examples of suitable flowing gases include air, nitrogen, flourine, helium, argon, oxygen, neon, krypton, xenon, radon, carbon monoxide, carbon dioxide, or a combination of the same. The flowing gas may also contain hydrogen scavenging additives, such as carbon tetrachloride, perfluorohexane, potasssium iodate, or a combination of the same.  
         [0014]     An oil and gas well has been chosen for purposes of illustration, it will be appreciated that the same method can be employed in any hydrocarbon environment. For example, this method may have wide application in oil and gas processing facilities.  
         [0015]     In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements.  
         [0016]     It will be apparent to one skilled in the art that modifications may be made to the illustrated embodiment without departing from the spirit and scope of the invention as hereinafter defined in the Claims.