Method and apparatus for applying vibrations during borehole operations

Abstract

A method of conducting borehole operations using a system including an elongate tubular conveyance that is moved through the borehole, the method comprising imposing a torsional vibration at a predetermined frequency on the tubular conveyance as it is moved through the borehole: wherein the predetermined frequency is obtained by determining the frequency-dependent mobility of the system based on the relationship between rotational velocity and torque for the system; and imposing torsional vibrations at a frequency where the relationship is optimised.

1 . A method of conducting borehole operations using a system including an elongate tubular conveyance that is moved through the borehole, the method comprising imposing a torsional vibration at a predetermined frequency on the tubular conveyance as it is moved through the borehole:
 wherein the predetermined frequency is obtained by determining the frequency-dependent mobility of the system based on the relationship between rotational velocity and torque for the system; and imposing torsional vibrations at a frequency where the relationship is optimised.   
     
     
         2 . A method as claimed in  claim 1 , comprising determining the variation in the frequency-dependent amplitude of torque for torsional vibrations in the system, the value of the amplitude being used to determine the predetermined frequency. 
     
     
         3 . A method as claimed in  claim 2 , wherein the predetermined frequency is selected from a frequency range in which the amplitude is at or near a local minimum. 
     
     
         4 . A method as claimed in  claim 1 , wherein the mobility is derived by modelling the system in the borehole taking into account spring, gravitational, inertial, and frictional forces, and hydraulic drag. 
     
     
         5 . A method as claimed in  claim 4 , comprising deriving a static model of the system and modifying it using a dynamic model of the system when the torsional vibrations are applied. 
     
     
         6 . A method as claimed in  claim 5 , wherein non-linear forces are applied to the dynamic model. 
     
     
         7 . A method as claimed in  claim 4 , comprising periodically updating the model to account for changes in the system and/or borehole as the operation progresses. 
     
     
         8 . A method as claimed in  claim 4 , comprising periodically ceasing the borehole operation and varying the operational parameters of the system to provide inputs to the model. 
     
     
         9 . A method as claimed in  claim 1 , wherein the torsional vibration is controlled so as to excite torsional vibrations along a predetermined length of the drill string. 
     
     
         10 . A method as claimed in  claim 8 , wherein the torsional vibration is controlled so as to excite torsional vibrations along substantially its whole length. 
     
     
         11 . A method as claimed in  claim 8 , wherein the predetermined length of the drill string is in a part of the borehole that is deviated from vertical. 
     
     
         12 . A method as claimed in  claim 1 , wherein torsional vibrations are imposed at or near the end of the drill string. 
     
     
         13 . A method as claimed in  claim 1 , wherein torsional vibrations are imposed at locations in the drill string that are determined to be susceptible to frictional contact with the borehole at one or more locations intermediate its ends. 
     
     
         14 . A method as claimed in  claim 1 , comprising a drilling operation using a drilling assembly at the end of the drill string. 
     
     
         15 . A method as claimed in any preceding claim, comprising a drilling operation using a bent sub near a drill bit at the end of the drill string, the method further comprising:
 orienting the bent sub to define a tool face direction; and   controlling the swing amplitude of the torsional vibration so as to control the amount of deviation in drilling trajectory in the tool face direction arising from the bent sub.   
     
     
         16 . A method as claimed in  claim 15 , further comprising controlling swing amplitude to include swing amplitudes comprising partial rotations of the drill string. 
     
     
         17 . A method as claimed in  claim 15 , comprising, prior to orienting the bent sub, applying torsion vibrations at the predetermined frequency to the system to ease any torsion forces in the system. 
     
     
         18 . A method as claimed in  claim 15 , wherein the step of orienting the bent sub comprises applying weight on bit to deviate the tool face direction due to the torque reaction when drilling. 
     
     
         19 . A method as claimed in  claim 17 , comprising periodically repeating the steps of applying vibrations at the predetermined frequency to the system to ease any torsion forces in the system, orienting the bent sub by applying weight on bit to deviate the tool face direction due to the torque reaction when drilling and controlling the swing amplitude of the torsional vibration so as to control the amount of deviation in drilling trajectory in the tool face direction arising from the bent sub. 
     
     
         20 . A method as claimed in  claim 15 , comprising a pipe expansion process including vibrating an unexpanded part of the pipe during the expansion process, an expansion tool, or both. 
     
     
         21 . An apparatus for conducting borehole operations in accordance with the method of any preceding claim, comprising:
 a drill string that can be moved through the borehole during the operation; and   a vibration system engaged with the drill string and operable to impose a torsional vibration on the drill string at the predetermined frequency.   
     
     
         22 . An apparatus as claimed in  claim 21 , further comprising a downhole tool positioned on the drill string so as to be positionable in the borehole at a predetermined position. 
     
     
         23 . An apparatus as claimed in  claim 22 , wherein the downhole tool comprises a drilling assembly including a drilling motor and a drill bit connected to the motor, located at the end of the drill string. 
     
     
         24 . An apparatus as claimed in  claim 21 , wherein the vibration system comprises a vibrator positioned on the drill string so as to be located in the borehole in use. 
     
     
         25 . An apparatus as claimed in  claim 24 , wherein the vibrator comprises an in-line clutch between the drilling assembly and the drill string and operable periodically to release reactive torque during drilling into the drill string. 
     
     
         26 . An apparatus as claimed in  claim 24 , wherein the vibrator comprises a stabiliser that rotates on the drilling motor axis and is configured to engage the borehole wall in use. 
     
     
         27 . An apparatus as claimed in  claim 24 , wherein the vibrator comprises a rotational mass system in the drill string or downhole tool powered by a motor. 
     
     
         28 . An apparatus as claimed in  claim 27 , wherein the mass is mounted on a spring. 
     
     
         29 . An apparatus as claimed in  claim 27 , further comprising a centrifugal clutch to periodically couple the rotating mass to the drill string. 
     
     
         30 . An apparatus as claimed in  claim 24 , wherein the vibrator comprises a motor. 
     
     
         31 . An apparatus as claimed in  claim 30 , wherein the motor is an electric motor. 
     
     
         32 . An apparatus as claimed in  claim 31 , wherein the electric motor is a switched reluctance motor. 
     
     
         33 . An apparatus as claimed in  claim 30 , wherein the motor comprises a number of motor sub-units operable independently or together. 
     
     
         34 . An apparatus as claimed in  claim 21 , further comprising a supply of drilling fluid that can be pumped through the drill string to a fluid-powered motor in a downhole tool, wherein the vibrator comprises a dump valve in the drill string that operates periodically to dump fluid flow to the motor. 
     
     
         35 . An apparatus as claimed in  claim 21 , further comprising a supply of drilling fluid that can be pumped through the drill string to a fluid-powered motor in the downhole tool, wherein the vibrator comprises a pulsed mud pump at the surface. 
     
     
         36 . An apparatus as claimed in  claim 21 , further comprising a system for monitoring the vibration imposed on the drill string and generating a feedback signal therefrom, and using the feedback signal to control the frequency of vibrations provided by the vibrator.