Directional drilling

Abstract

A method of controlling the direction of drilling comprising: providing a drill bit comprising mechanical cutting means forming a bit face and a plurality of nozzles for ejecting drilling fluid arranged at different azimuthal positions with respect to the bit face, and an intermediate space between an inlet port of the drill bit and the plurality of nozzles; rotating the drill bit while passing drilling fluid comprising solids through the intermediate space and the plurality of nozzles, so as to deepen the borehole; and modifying solids concentration of drilling fluid portions flowing through the plurality of nozzles while rotating the drill bit, so that the solids concentration, for the drilling fluid portion flowing through each of the nozzles, is relatively increased when the respective nozzle is in a selected first angular sector of the borehole bottom, as compared to a second angular sector.

1 . A method of controlling the direction of drilling a borehole in a subsurface formation, the method comprising
 providing a tubular drill string;   providing a drill bit connected to a lower end of the drill string, the drill bit comprising mechanical cutting means forming a bit face, and comprising a plurality of nozzles for ejecting drilling fluid, which nozzles are arranged at different azimuthal positions with respect to the bit face, and an intermediate space between an inlet port of the drill bit and the plurality of nozzles, each of the nozzles having a nozzle inlet for fluid communication with the intermediate space, from which consecutively one of the nozzle inlets extends during rotation of the drill bit;   rotating the drill bit while passing drilling fluid comprising solids via the drill string through the plurality of nozzles, so as to deepen the borehole; and   modifying solids concentration of drilling fluid portions flowing through the plurality of nozzles while rotating the drill bit, so that the solids concentration, for the drilling fluid portion flowing through each of the nozzles, is relatively increased when the respective nozzle is in a selected first angular sector of the borehole bottom, as compared to the solids concentration of the drilling fluid portion flowing through the respective nozzle when said nozzle is in a selected second angular sector of the borehole bottom.   
     
     
         2 . The method of  claim 1 , wherein the step of modifying solids concentration comprises directing the drilling fluid into a first area of the intermediate space to increase the solids concentration by using an inertia effect, whereas in the intermediate space the drilling fluid is distributed over the various nozzle inlets. 
     
     
         3 . The method according to  claim 1 , wherein simultaneous drilling fluid flow through the nozzles is maintained during rotation. 
     
     
         4 . The method according to  claim 2 , wherein a flow directing means having an outlet member is provided for directing the drilling fluid, and wherein the method further comprises maintaining the outlet member in a geostationary position during at least one rotation of the drill bit. 
     
     
         5 . The method according to  claim 4 , further comprising:
 providing a flow guide in the intermediate space, and   rotating the flow guide together with the drill bit, the flow guide comprising first and second channels each co-operating during time periods of the rotation at an upstream end with the outlet member, depending on the relative rotational position the outlet member and the drill bit, and at a downstream end with the first and second nozzle inlets, respectively.   
     
     
         6 . The method according to  claim 1 ,
 wherein at least a part of the solids in the drilling fluid is magnetic, and   wherein the step of modifying solids concentration comprises applying a rotating magnetic field to divert said part of the solids towards the first angular sector.   
     
     
         7 . A system for directional drilling a borehole, the system comprising:
 a drill string element for passing drilling fluid comprising solids;   a drill bit connected to the drill string element, the drill bit comprising a bit body, mechanical cutting means forming a bit face, an inlet port for receiving the drilling fluid from the drill string element, a plurality of nozzles for ejecting the drilling fluid, which nozzles are arranged at different azimuthal positions with respect to the bit face, and an intermediate space between the inlet port and the plurality of nozzles, each of the nozzles having a nozzle inlet for fluid communication with the intermediate space; and   a diverter for directing at least part of the solids to a first area of the intermediate space, from which first area consecutively one of the nozzle inlets extends during relative rotation of the drill bit with respect to the diverter, as compared with a second area of the intermediate space.   
     
     
         8 . The system of  claim 7 , wherein the diverter is adapted to modify the solids concentration by directing the drilling fluid into the first area of the intermediate space to increase solids concentration by using an inertia effect, whereas in the intermediate space the drilling fluid is distributed over the various nozzle inlets. 
     
     
         9 . The system according to  claim 7 , wherein the diverter comprises:
 a flow directing means at least part of which being provided in the drill string element, the flow directing means comprising the outlet member in rotatable arrangement with respect to the drill bit, the outlet member being arranged to direct the drilling fluid into the first area of the intermediate space; and   a means for controlling relative rotation of the outlet member with respect to the drill bit.   
     
     
         10 . The system according to  claim 9 , wherein the outlet member extends into the intermediate space. 
     
     
         11 . The system according to  claim 9 , further comprising a flow guide provided in the intermediate space in a rotatably locked configuration with the drill bit, the flow guide comprising first and second channels each adapted to co-operate, depending on the relative rotational position the outlet member and the drill bit, at an upstream end with the outlet member, and at a downstream end with the nozzle inlets, respectively. 
     
     
         12 . The system according to  claim 7 ,
 wherein at least a part of the solids in the drilling fluid is magnetic; and   wherein the diverter comprises a magnet for diverting said part of the solids towards the first area of the intermediate space.   
     
     
         13 . The system according to  claim 12 , wherein the magnet is a permanent magnet which is rotatable with respect to the drill bit or an electromagnet with a driver unit capable of producing a rotating magnetic field. 
     
     
         14 . The system according to  claim 7 , wherein the diverter comprises a curved flow path. 
     
     
         15 . The system of  claim 7 , wherein at least part of the diverter is retrievable or replaceable through the drill string element.