Apparatus and Method for Steerable Drilling

Abstract

A method for drilling a wellbore comprises extending a rotatable drill string in the wellbore, where the drill string has a bottom hole assembly coupled to a bottom end thereof. A lower section of the bottom hole assembly comprising a steering apparatus is coupled to an upper section of the bottom hole assembly with a controllably adjustable clutch. A steering apparatus toolface angle is detected. The clutch is controllably adjusted to maintain the steering apparatus toolface angle within a predetermined range about a target steering apparatus toolface angle while rotating the upper section with the drill string.

1 . An apparatus for drilling a wellbore comprising:
 a rotatable drill string;   a bottom hole assembly coupled to the drill string, the bottom hole assembly comprising an upper section and a lower section, the lower section comprising a drilling motor, and a steering apparatus having a toolface reference;   a sensor disposed in the bottom hole assembly to provide at least a measure of the toolface angle;   a controllably adjustable clutch coupling the upper section to the lower section; and   a controller in data communication with the sensor and with the controllably adjustable clutch, the controller adjusting the clutch to maintain a steering assembly toolface angle in a predetermined range about a target steering apparatus toolface angle while drilling.   
     
     
         2 . The apparatus of  claim 1  wherein the controller adjusts the clutch to maintain the steering apparatus toolface angle in the predetermined range about the target steering apparatus toolface angle while the upper section rotates with the drill string. 
     
     
         3 . The apparatus of  claim 1  wherein the controllably adjustable clutch comprises:
 a housing coupled to one of the upper section and the lower section; and 
 a shaft rotatably supported by the housing, the shaft coupled to the other of the upper section and the lower section. 
 
     
     
         4 . The apparatus of  claim 3  further comprising a housing clutch plate engaged with the housing and a shaft clutch plate engaged with the shaft wherein an adjustable frictional force between the housing clutch plate and the shaft clutch plate controls the relative rotation between the upper section and the lower section. 
     
     
         5 . The apparatus of  claim 1  wherein the controller comprises a processor in data communications with a memory. 
     
     
         6 . The apparatus of  claim 5 , wherein the processor acts according to programmed instructions stored in the memory to adjust a frictional force between a housing clutch plate and a shaft clutch plate based on a measurement of the toolface to maintain a target bent sub toolface within a predetermined toolface range. 
     
     
         7 . The apparatus of  claim 1  wherein the predetermined range is about ±45° around the target toolface. 
     
     
         8 . The apparatus of  claim 1  wherein the sensor comprises a directional sensor package comprising at least one of: an inclinometer; a magnetometer; and a gyroscope. 
     
     
         9 . The apparatus of  claim 8  further comprising a reference sensor. 
     
     
         10 . The apparatus of  claim 8  wherein the directional sensor package is located in the bent sub. 
     
     
         11 . The apparatus of  claim 8  wherein the directional sensor package is located in the housing. 
     
     
         12 . The apparatus of  claim 8  wherein the directional sensor package is disposed in a measurement while drilling tool disposed in the lower section. 
     
     
         13 . The apparatus of  claim 1  wherein the drill string comprises a wired drill pipe section. 
     
     
         14 . The apparatus of  claim 1  wherein the steering apparatus is chosen from the group consisting of a bent sub and a steerable assembly. 
     
     
         15 . The apparatus of  claim 14  wherein the steerable assembly comprises at least one extendable member to cause the lower section to drill in a predetermined direction. 
     
     
         16 . The apparatus of  claim 14  wherein the steerable assembly comprises a controllably deflectable drilling shaft to cause the lower section to drill in a predetermined direction. 
     
     
         17 . A method for drilling a wellbore comprising:
 extending a rotatable drill string in the wellbore, the drill string having a bottom hole assembly coupled to a bottom end thereof;   coupling a lower section of the bottom hole assembly comprising a steering apparatus to an upper section of the bottom hole assembly with a controllably adjustable clutch;   detecting a steering apparatus toolface angle;   controllably adjusting the clutch to maintain the steering apparatus toolface angle within a predetermined range about a target steering apparatus toolface angle while rotating the upper section with the drill string.   
     
     
         18 . The method of  claim 17  further comprising transmitting the detected steering apparatus toolface angle to a surface control unit. 
     
     
         19 . The method of  claim 18  further comprising downlinking an updated steering apparatus target toolface from the surface to a downhole controller. 
     
     
         20 . The method of  claim 17  further comprising storing a directional model in a downhole memory in data communication with a processor in a downhole controller. 
     
     
         21 . The method of  claim 18  further comprising calculating a new steering apparatus target toolface using the directional model stored in the downhole memory. 
     
     
         22 . The method of  claim 17  wherein detecting a steering apparatus toolface angle comprises disposing a directional sensor package in one of the upper section and the lower section of the bottom hole assembly. 
     
     
         23 . The method of  claim 17  further comprising transmitting a detected steering apparatus toolface to a controller in one of the upper section and the lower section.