Improvements in or relating to centralisers

Abstract

A centraliser comprises longitudinally spaced collars connected by a plurality of springs, each of the springs comprising two or more bow sections.

1 - 64 . (canceled) 
     
     
         65 . A centraliser comprising longitudinally spaced collars connected by a plurality of springs, each of the springs comprising two or more bow sections. 
     
     
         66 . A centraliser as claimed in  claim 65 , in which each spring comprises a larger, taller outward bow section and a smaller, shorter outward bow section, and an intermediate inward bow section between the outward bows. 
     
     
         67 . A centraliser as claimed in  claim 65 , in which the bow sections have a different height in a resting position. 
     
     
         68 . A centraliser as claimed in  claim 65 , in which each spring has a region of increased width. 
     
     
         69 . A centraliser as claimed in  claim 68 , in which the cross section of the region of increased width is curved. 
     
     
         70 . A centraliser as claimed in  claim 65 , in which the spring contacts the collars at junctions, and in which the junctions are rounded whereby to reduce stress. 
     
     
         71 . A centraliser as claimed in  claim 65 , in which the longitudinal position of the outward bow section peaks on at least two springs is different. 
     
     
         72 . A centraliser as claimed in  claim 71 , in which alternate springs have different peak positions. 
     
     
         73 . A centraliser as claimed in  claim 71 , in which there are two spring section peak positions which are longitudinally offset from each other. 
     
     
         74 . A centraliser as claimed in  claim 65 , in which at least part of the centraliser has surface formations. 
     
     
         75 . A centraliser as claimed in  claim 74 , in which the surface formations are protruding dimples. 
     
     
         76 . A centraliser as claimed in  claim 65 , in which at least part of the centraliser has a low-friction coating. 
     
     
         77 . A centraliser as claimed in  claim 76 , in which the coating is Molybdenum Disulphide or Diamond Like Carbon. 
     
     
         78 . A centraliser as claimed in  claim 65 , in which the centraliser is provided with one or more low-friction pads. 
     
     
         79 . A centraliser as claimed in  claim 65 , in which the centraliser is provided with one or more wear pads. 
     
     
         80 . A centraliser as claimed in  claim 65 , in which each bow has scalloped or wavy or ribbed edges for reducing the stress incurred as the bow flexes in use, whilst at the same time maintaining the overall contact area for skiing across a formation. 
     
     
         81 . A three phase centraliser for preventing a casing from contacting a wellbore wall, the centraliser comprising a plurality of springs, each spring comprising a double outward bow section arrangement and an inward bow section between the outward bow sections, the outward bow arrangement comprising a larger, taller bow section and a smaller, shorter bow section, in which:
 in a first phase, each spring acts as a larger single and weaker bow-spring whilst subject to minimal forces;   in a second phase, as forces are increased, the inward facing bow contacts with the casing and the double outward bow arrangement transforms into a shorter, stiffer bow spring; and   in a third phase, as the height of the two outward bow sections become generally equal, the springs transform into two smaller and stiffer bow-springs.   
     
     
         82 . A casing fitted with one or more centralisers as claimed in  claim 65 . 
     
     
         83 . A well bore having one or more centralisers as claimed in  claim 65 .