Self-controlled directional drilling systems and methods

Abstract

The present invention provides a drilling assembly that includes a mud motor that rotates a drill bit and a set of independently expandable ribs. A stabilizer uphole of the ribs provides stability. A second set of ribs may be disposed on the drilling assembly. Vertical and curved holes are drilled by rotating the drill bit by the mud motor and by independently adjusting the rib forces. The drill string is not rotated. Inclined straight sections and curved sections may be drilled by independent adjustment of the rib forces and by rotating the drill bit with the motor, without rotating the drill string. Inclined sections or curved sections in the vertical plane are drilled by superimposing the drillstring rotation on the mud motor rotation and by setting the rib forces to the same predetermined values. Rib forces are adjusted if the drilling direction differs from the defined inclination. The system is self-adjusting and operates in a closed loop manner. Inclination and navigation sensor data are processed by a downhole controller. The force vectors maybe programmed in the downhole controller. Command signals from a surface controller may be sent to initiate the setting and/or adjustment of the rib forces or the rib force vector.

What is claimed is:  
     
         1 . A drill string for drilling wellbores, comprising: 
 (a) a rotatable tubular member conveyable from a surface location into the wellbore; and    (b) a drilling assembly coupled at a first upper end to the tubular member, said drilling assembly comprising; 
 (i) a drill bit at a second bottom end of the drilling assembly;  
 (ii) a drilling motor uphole of the drill bit for rotating the drill bit;  
 (iii) a first set of ribs containing a plurality of ribs arranged around a section of the drilling assembly, each rib in said first set extending radially outward from the drilling assembly to apply force to the wellbore, upon the application of power thereto;  
 (iv) a power unit supplying power to the ribs; and  
 (v) a controller selectively causing the ribs to apply different forces to the wellbore during drilling of a first section of the wellbore and to apply substantially the same force to each of the ribs in said first set of ribs during drilling of a second section of the wellbore.  
   
     
     
         2 . The drill string according to  claim 1  further comprising a second set of ribs containing a second plurality of ribs axially spaced apart from the first set of ribs and arranged around a section of the drilling assembly, each rib in said second set of ribs extending radially outward from the drilling assembly to apply force to the wellbore inside, upon the application of power thereto.  
     
     
         3 . The drill string according to  claim 1  further comprising a sensor for providing measurements indicative of at least one parameter of interest selected from a group consisting of: 
 (i) inclination of the drilling assembly;  
 (ii) inclination of the borehole; and  
 (iii) position of the ribs relative to borehole high side.  
 
     
     
         4 . The drill string according to  claim 1  further comprising a navigation sensor providing measurements of the direction of the drill bit during the drilling of the wellbore.  
     
     
         5 . A method of drilling a wellbore having a curved section and a straight section, said method comprising: 
 conveying a drilling assembly in said wellbore by a rotatable tubular member, said drilling assembly including a drill bit at an end thereof that is rotatable by a drilling motor carried by the drilling assembly and a first set of ribs, with each rib being independently radially extendable to exert force on the wellbore inside;    drilling the curved section of the wellbore by rotating the drill bit and by applying different force on the wellbore inside by each said rib in said first set of ribs; and    drilling the straight section of the wellbore by rotating the drill bit and by maintaining substantially the same force on each rib in said first set of ribs.    
     
     
         6 . The method of  claim 5  further comprising providing a second set of ribs containing a plurality of independently controllable ribs which are axially spaced apart from said first set of ribs.  
     
     
         7 . The method of  claim 5  wherein rotating the drill bit includes rotating the drill bit by said mud motor and by rotating the tubular member.  
     
     
         8 . The method of  claim 6  further comprising setting the ribs in said second set to exert the same forces on the wellbore during drilling of the straight section.  
     
     
         9 . The method of  claim 5  further comprising measuring inclination of one of (i) drilling assembly or (ii) said wellbore.  
     
     
         10 . The method of  claim 5  further comprising drilling said wellbore along a predetermined well path.  
     
     
         11 . The method of  claim 5  further comprising determining a parameter indicative of direction of drilling of said wellbore.  
     
     
         12 . The method of  claim 11  further comprising altering drilling direction of said wellbore if said parameter is outside a predetermined limit.  
     
     
         13 . The method of  claim 12  wherein altering said drilling direction includes altering force applied by at least one rib in said first set of ribs.