Method of Drilling a Stable Borehole

Abstract

A method of drilling a stable borehole in a formation containing a stress field having a direction of maximal stress, whereby the borehole is drilled with an elongated non-circular cross sectional contour along an axis of elongation and whereby a directional component of the axis of elongation is kept oriented substantially parallel to the direction of maximal stress.

1 . A method of drilling a borehole in a formation containing a stress field having a direction of maximal stress, wherein a portion of the borehole is formed with an elongated non-circular cross section having an axis of elongation and wherein the axis of elongation is substantially parallel to the direction of maximal stress. 
   
   
       2 . The method of  claim 1  wherein each said elongate portion has a longitudinal axis extending in axial direction of the borehole. 
   
   
       3 . (canceled) 
   
   
       4 . (canceled) 
   
   
       5 . The method of  claim 3  wherein the wellbore extends substantially vertically, and wherein said elongate portion extends radially in a direction substantially parallel to the largest horizontal principal stress. 
   
   
       6 . The method of  claim 3  wherein the wellbore extends substantially horizontally, and wherein said elongate portion extends radially in a direction substantially parallel to the vertical principal stress. 
   
   
       7 . The method of  claim 1  wherein during drilling the elongate cross section is made at the same time as progressing the borehole into the formation. 
   
   
       8 . A borehole in a formation containing a stress field having a direction of maximal stress, wherein whereby the borehole has an elongated non-circular cross sectional contour having an axis of elongation, and wherein the axis of elongation is oriented substantially parallel to the direction of maximal stress.