Centraliser

Abstract

A centraliser comprises two collars that are connected by asymmetric spring bows. The spring bows each comprise two arcs, where the curvature of one arc is inverted with respect to the curvature of the other arc, one being concave and the other convex. The spring bows are in sets that are equidistantly spaced around the circumference of the collars, each set having the same configuration, and the opposite configuration to the spring bows in the other set. Upon insertion into a wellbore, one set of spring bows is therefore compressed before the other set. Upon compression, the deformation of the concave arc leads to mutual deformation of the convex arc, and the spring bows adopt a flatter configuration, enhancing the rotational freedom of the tubular.

1 . A centraliser having a central axis, and having first and second axially spaced collars and first and second sets of resilient devices extending between the collars,
 wherein:
 the resilient devices in each set are spaced around the circumference of the collars, 
 each of the resilient devices comprising a first arc and a second arc, 
 the curvature of the second arc is inverted with respect to the curvature of the first arc, 
 each resilient device is asymmetric along the central axis of the centrailser, 
 the first arc is convex and the second arc is concave, and 
 when each resilient device is radially compressed by the insertion of the centraliser into a well bore, the first and second arcs deform so that the first arc deforms radially inward towards the central axis of the centraliser, and the second arc deforms radially outward, away from the central axis of the centraliser. 
   
     
     
         2 . The centraliser as claimed in  claim 1 , wherein the first and second arcs are inverted with respect to one another in the resting configuration of the resilient device, in the absence of forces urging it into a different configuration. 
     
     
         3 . The centraliser as claimed in  claim 1 , wherein the apex of each resilient device is axially spaced from the apex of each of its immediate neighbouring resilient devices. 
     
     
         4 . The centraliser as claimed in  claim 1 , wherein when each resilient device is radially compressed by the insertion of the centraliser into the well bore, the curvature of the first and second arcs reduces. 
     
     
         5 . The centraliser as claimed in  claim 4 , wherein in the deformed configuration caused by radially inward urging of the apex of each resilient device, the first and second arcs move in radially opposing directions towards one another. 
     
     
         6 . The centraliser as claimed in  claim 1 , wherein:
 the collars have bores which are coaxial with the central axis for receiving a tubular to be centralised, and   in the deformed configuration, the resilient devices are biased radially away from the outer surface of the tubular being centralised.   
     
     
         7 . A centraliser assembly incorporating a tubular, a centraliser having a bore adapted to receive the tubular, the bore having a central axis, and the centraliser having first and second axially spaced collars and first and second sets of resilient devices extending between the collars,
 wherein:
 the resilient devices in each set are spaced around the circumference of the collars, 
 each of the resilient devices comprise a first arc and a second arc, 
 the curvature of the second arc is inverted with respect to the curvature of the first arc, 
 each resilient device is asymmetric along the central axis, 
 the first arc is convex and the second arc is concave 
 when each resilient device is radially compressed by the insertion of the centraliser into a well bore, the first and second arcs deform so that the first arc deforms radially inward towards the central axis, and the second arc deforms radially outward, away from the central axis. 
   
     
     
         8 . The centraliser assembly as claimed in  claim 7 , wherein as the tubular and centraliser are inserted into a wellbore, the first and second arcs deform to reduce the radius of curvature on each of the first and second arcs. 
     
     
         9 . The centraliser assembly as claimed in  claim 7 , wherein in the deformed configuration when the tubular and centraliser are inserted into a wellbore, the first and second arcs do not engage the tubular. 
     
     
         10 . A method of centralising a tubular within a wellbore, the method including
 inserting the tubular into an axial bore of a centraliser, the centraliser having first and second collars that are axially spaced with respect to the bore of the centraliser, and first and second sets of resilient devices extending between the collars,   wherein:
 the resilient devices in each set are spaced around the circumference of the collars, 
 each of the resilient devices comprise a first arc and a second arc, 
 the curvature of the second arc is inverted with respect to the curvature of the first arc, and 
 each resilient device is asymmetric along a central axis of the centraliser, 
   inserting the centraliser and the tubular into the wellbore, and sequentially radially compressing the first and second sets of resilient devices between the tubular and the wellbore at different stages during the insertion of the centraliser into the wellbore,   wherein when each resilient device is radially compressed by the insertion of the centraliser into a well bore, the first and second arcs deform so that the first arc deforms radially inward towards the central axis of the centraliser, and the second arc deforms radially outward, away from the central axis of the centraliser.   
     
     
         11 . The method as claimed in  claim 10 , wherein when each resilient device is radially compressed by the insertion of the centraliser into the wellbore, the curvature of the first and second arcs reduces. 
     
     
         12 . The method as claimed in  claim 10 , wherein in the deformed configuration caused by radial compression of the resilient devices, the first and second arcs move in radially opposing directions towards one another. 
     
     
         13 . The method as claimed in  claim 10 , wherein in the deformed configuration, the resilient devices are biased radially away from the outer surface of the tubular being centralised. 
     
     
         14 . The method as claimed in  claim 10 , wherein in the deformed configuration when the tubular and centraliser are inserted into the wellbore, the first and second arcs do not engage the tubular.