System for drilling deviated boreholes

Abstract

Improved techniques are provided for drilling a deviated borehole through earth formations utilizing a rotary bit powered by a drill motor, and for obtaining information regarding the borehole or earth formations while drilling. An inclinometer is positioned below the drill motor and within a sealed cavity of a housing fixed to a drill motor sub, and a transmitter within the sealed cavity forwards acoustic or radial wave signals to a receiver provided in a measurement-while-drilling tool. The MWD tool may be provided within a non-magnetic portion of the drill string, and further houses an accelerometer for sensing borehole direction. Both borehole inclination and directional signals are transmitted to the surface by the MWD tool, and the drilling trajectory is altered in response to the signals.

What is claimed is: 
     
       1. A method of drilling a borehole through earth formations with a drill string including a rotary bit at the lower end thereof, and obtaining information regarding a downhole parameter indicative of the borehole or the earth formations, the bit being powered by a drill motor within the drill string and including a power assembly of the drill motor for converting pressurized fluid to rotation of a mandrel interconnected with the bit, a bearing assembly between the power assembly and the bit for guiding the mandrel, and a bearing housing for housing the bearing assembly, the method comprising: sensing the downhole parameter using a sensor fixedly located in the drill string at a location axially below the power assembly;   transmitting signals functionally related to the sensed downhole parameter from a location axially below the power assembly;   receiving the transmitted signals at the surface to determine the downhole parameter; and   altering the drilling trajectory in response to the transmitted signals.   
     
     
       2. The method as defined in claim 1, further comprising: providing a non-magnetic portion of the drill string axially above the drill motor;   further sensing well bore direction at a location axially within the non-magnetic portion of the drill string;   inputting well bore direction signals to a measuring-while-drilling tool positioned within the drill string at a location above the drill motor;   transmitting the well bore direction signals to the surface to determine the direction of the well bore; and   the drilling trajectory is altered in response to the transmitted downhole parameter signals and the transmitted well bore direction signals.   
     
     
       3. The method as defined in claim 2, wherein the measuring-while-drilling tool includes a mud pulse transmitter for transmitting data to the surface. 
     
     
       4. The method as defined in claim 1, further comprising: providing a near bit housing having a sealed cavity rotationally fixed to the bearing housing; and   sensing the downhole parameter utilizing a sensor positioned within the sealed cavity.   
     
     
       5. The method as defined in claim 4, further comprising: providing one or more formation sensors within the sealed cavity to sense at least a selected one of formation characteristics from a group consisting weight on bit, torque, of resistivity, porosity, density, gamma ray count, and temperature.   
     
     
       6. The method as defined in claim 4, further comprising: providing a power supply within the sealed cavity.   
     
     
       7. The method as defined in claim 6, wherein the power supply is driven in response to rotation of the mandrel with respect to the near bit housing. 
     
     
       8. The method as defined in claim 4, further comprising: filling the sealed cavity with a protective material to minimize vibration to components within the sealed cavity.   
     
     
       9. The method as defined in claim 1, wherein the transmitted signals are acoustic signals having a frequency in the range of from 500 to 2,000 Hz. 
     
     
       10. The method as defined in claim 1, wherein the transmitted signals are radio signals having a frequency in the range of from 30 kilo-Hz to 3000 mega-Hz. 
     
     
       11. The method of drilling a deviated borehole through earth formations with a drill string including a rotary bit at the end thereof and obtaining information regarding a downhole parameter indicative of the borehole or the earth formations, the bit being powered by a drill motor within the drill string and including a power assembly for converting pressurized fluid to rotation of a mandrel interconnected with the bit, and a bearing assembly between the power assembly and the bit for guiding the mandrel, the method comprising: monitoring borehole or earth formation characteristics using a sensor fixedly located in the drill string at a location axially below the power assembly;   transmitting signals functionally related to the monitored information from the location axially below the power assembly;   receiving the transmitted signals at the surface to determine the borehole or formation characteristic; and   altering the drilling trajectory in response to the transmitted signals.   
     
     
       12. The method as defined in claim 11, further comprising: providing a near bit housing having a sealed cavity rotationally affixed to the bearing housing; and   sensing the borehole or formation information with a sensor provided within the sealed cavity.   
     
     
       13. The method as defined in claim 11, wherein the transmitted signals are acoustic signals having a frequency in the range of from 500 to 2,000 Hz. 
     
     
       14. The method as defined in claim 11, further comprising: inputting the transmitted signals to a measuring-while-drilling tool positioned within the drill string at a location above the drill motor; and   using a mud pulse transmitter within the measuring-while-drilling tool for transmitting data to the surface.   
     
     
       15. A system for drilling a deviated borehole through earth formations, including a drill string including a drill bit, the bit powered by a drill motor having a power assembly for converting pressurized fluid to rotation of a mandrel interconnected with the bit, a bearing assembly between the power assembly and the bit for guiding the mandrel, and a bearing housing for housing the bearing assembly, the system comprising: a sealed cavity within the drill string at a location below the power assembly;   a sensor within the sealed cavity for sensing a downhole parameter;   a transmitter within the cavity for transmitting signals functionally related to the sensed downhole parameter; and   a receiver spaced axially above the drill motor for receiving the transmitted signals and outputting downhole parameter signals.   
     
     
       16. The system as defined in claim 15, further comprising: a non-magnetic portion of the drill string spaced axially above the drill motor;   a well bore direction sensor spaced within the non-magnetic portion of the drill string for outputting well bore direction signals; and   a second transmitter for transmitting the well bore direction signals to the surface.   
     
     
       17. The system as defined in claim 15, further comprising: an electrical power source within the cavity for powering the sensor and transmitter.   
     
     
       18. The system as defined in claim 17, wherein the electrical power source is an eddy current generator for generating electrical power in response to rotation of the mandrel. 
     
     
       19. The system as defined in claim 15, wherein the transmitter comprises: a voltage to frequency converter for receiving voltage signals from the sensor and generating frequency signals in response thereto.   
     
     
       20. The system as defined in claim 15, further comprising: a downhole computer for storing the transmitted signals.