Drilling fluid for casing drilling

Abstract

The present invention provides a method of drilling a hydrocarbon well using a drillstring adapted to provide a continuous or quasi-continuous contact with the wall of the well such that at least of section the well a compacting force is exerted on filter cake deposited thereon; circulating a drilling mud through the borehole during the drilling operation such that a filter cake is deposited on the borehole wall by the drilling mud, the filter cake being compacted by contact with the drillstring, including, before the drilling mud enters the borehole a conditioning additive in the drilling mud, the additive conditioning the filter cake upon the contact with the drillstring to increase the yield strength of the filter cake.

1 . A method of drilling a hydrocarbon well using a drill string adapted to provide a continuous or quasi-continuous contact with the wall of the well such that at least along a section of the well a compacting force is exerted on filter cake deposited thereon 
 circulating a drilling mud through the borehole during the drilling operation such that a filter cake is deposited on the borehole wall by the drilling mud, the filter cake being compacted by contact with the drill string,    the method further comprising:    including, before the drilling mud enters the borehole, a conditioning additive in the drilling mud, the additive conditioning the filter cake upon said contact with the drill string to increase the yield strength of the filter cake.    
   
   
       2 . A method according to  claim 1  wherein the additive is particulate.  
   
   
       3 . A method according to  claim 2  wherein the particles are non-spherical.  
   
   
       4 . A method according to  claim 3  wherein the particles are lamellar.  
   
   
       5 . A method according to  claim 1 , wherein the additive is mica flakes.  
   
   
       6 . A method according to  claim 1 , wherein the additive is rubber particulates.  
   
   
       7 . A method according to  claim 1 , wherein the drilling mud contains at least 5 volume % of the additive.  
   
   
       8 . A method according to  claim 1 , wherein the drilling mud contains up to 20 volume % of the additive.  
   
   
       9 . A method according to  claim 1 , wherein the drill string is assembled from casing tubes.  
   
   
       10 . A method according to  claim 1 , wherein the drill string includes one or more subparts with enlarged diameter to emulate casing drilling.  
   
   
       11 . A method according to  claim 1 , wherein the drill string is adapted to engage a wall of an open uncased borehole with a low angle of attack.  
   
   
       12 . A drilling mud containing at least 5 volume % of mica flakes.  
   
   
       13 . A drilling mud containing at least 5 volume % of rubber particulates.